Particles for optical bonding, adhesive, and display device

Abstract

Provided are optical bonding particles capable of accurately controlling a gap and improving legibility.　The optical bonding particles according to the present invention are provided with silicone particles, and coating particles or a coating layer disposed on the surface of the silicone particles, wherein the absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coating particles or coating layer is 0.03 or less.

Description

Technical Field

[0001] The present invention relates to particles for optical bonding using silicone particles. The present invention also relates to an adhesive and a display device using the above-described particles for optical bonding.

Background Art

[0002] Various adhesives are used to bond two adherends. Further, in order to make the thickness of the adhesive layer formed by the adhesive uniform and control the interval (gap) between the two adherends, a gap material (spacer) may be blended in the adhesive.

[0003] A conventional liquid crystal display device includes a liquid crystal panel in which a liquid crystal layer is enclosed between substrates, a pair of polarizing plates sandwiching the liquid crystal panel, an image display unit composed of a backlight unit, and a transparent protective material. In a conventional liquid crystal display device, since there is a gap between the image display unit and the transparent protective material, interface reflection may occur due to the difference in refractive index between the transparent protective material and air, and the visibility of the image may be reduced.

[0004] On the other hand, a technique (optical bonding) is known in which a light-transmitting material (for example, an adhesive or the like) having a refractive index equivalent to that of the transparent protective material is filled in the gap between the image display unit and the transparent protective material, thereby reducing the reflection loss occurring at the interface of the transparent protective material and improving the visibility.

[0005] In recent years, optical bonding has been increasingly used in various fields. For example, in display devices such as in-vehicle displays, the use of optical bonding is being considered to improve visibility. Specifically, a material used for optical bonding (an optical bonding material, such as a light-transmissive material like an adhesive) is applied onto an image display element, a transparent protective material is disposed on the surface opposite to the image display element side of the optical bonding material, and curing of the optical bonding material is being considered, etc. An adhesive layer that bonds the image display element and the transparent protective material is formed by the cured product of the optical bonding material.

[0006] In the optical bonding material used for a display device (such as an in-vehicle display etc.), it may be difficult to uniformly apply it onto the image display element. Also, since the viscosity of the optical bonding material is low, until the curing of the optical bonding material is completed, for example, due to the weight of the transparent protective material etc., the optical bonding material may flow on the image display element, and it may not be possible to sufficiently ensure the thickness (gap) of the cured product (adhesive layer) of the optical bonding material on the image display element. For this reason, the use of a gap material in the optical bonding material is being considered. As the above gap material, coated silicone particles etc. may be used.

[0007] Patent Document 1 below discloses silicone fine particles having 100 parts by mass of silicone elastomer spherical fine particles with a volume average particle diameter of 0.1 μm to 100 μm and 0.5 parts by mass to 25 parts by mass of polyorganosilsesquioxane that coats the surface thereof. The above polyorganosilsesquioxane is granular and has a size of 60 nm or less.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] When using conventional coated silicone particles or the like as described in Patent Document 1 as a gap material for an optical bonding material, since the particle diameter of the coated particles is small (the thickness of the coating layer is thin), it may not be possible to sufficiently reduce the refractive index difference between the optical bonding material and the gap material. Further, when the particle diameter of the coated particles is small, it becomes difficult to uniformly coat the surface of the silicone particles, and there may be variations in the refractive index difference between the optical bonding material and the gap material. As a result, it may be difficult to sufficiently improve the visibility with conventional coated silicone particles.

[0010] In addition, when a display device (for example, an in-vehicle display or the like) is repeatedly exposed to temperature changes from low temperature to high temperature, stress may be generated between members (for example, an image display element, a transparent protective material, etc.) due to differences in the linear expansion coefficients of the members. When the thickness (gap) of the cured product (adhesive layer) of the optical bonding material cannot be sufficiently ensured, the stress generated between the members cannot be sufficiently relaxed, and cracks or peeling may occur in the cured product (adhesive layer) of the optical bonding material or the like. In order to relax the stress generated between the members, it is required to sufficiently ensure the thickness (gap) of the cured product (adhesive layer) of the optical bonding material.

[0011] An object of the present invention is to provide optical bonding particles that can improve visibility and can control the gap with high precision. Another object of the present invention is to provide an adhesive and a display device using the above optical bonding particles.

Means for Solving the Problems

[0012] According to a broad aspect of the present invention, there are provided particles for optical bonding, comprising silicone particles and coating particles or a coating layer disposed on the surface of the silicone particles, wherein the absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coating particles or the refractive index of the coating layer is 0.03 or less.

[0013] In a specific aspect of the particles for optical bonding according to the present invention, the material of the coating particles or the material of the coating layer is silica or silicone resin.

[0014] In a specific aspect of the particles for optical bonding according to the present invention, the particle diameter of the coating particles or the thickness of the coating layer is 30 nm or more and 500 nm or less.

[0015] In a specific aspect of the particles for optical bonding according to the present invention, the area of the portion where the coating particles or the coating layer is present in 100% of the total surface area of the silicone particles is 80% or more.

[0016] In a specific aspect of the particles for optical bonding according to the present invention, the refractive index of the particles for optical bonding is 1.40 or more and 1.43 or less.

[0017] In a specific aspect of the particles for optical bonding according to the present invention, the particle diameter of the particles for optical bonding is 30 μm or more and 500 μm or less.

[0018] In a specific aspect of the particles for optical bonding according to the present invention, the silicone particles include a plurality of inorganic oxide particles, and at least a part of the inorganic oxide particles is present inside the silicone particles.

[0019] According to a broad aspect of the present invention, there is provided an adhesive comprising the above-described particles for optical bonding and a curable component.

[0020] In a specific aspect of the adhesive according to the present invention, the absolute value of the difference between the refractive index of the cured product obtained by curing the curable component under the conditions of 23°C and 1 hour and the refractive index of the silicone particles is 0.05 or less.

[0021] In a specific aspect of the adhesive according to the present invention, the absolute value of the difference between the refractive index of the cured product obtained by curing the curable component under the conditions of 23°C and 1 hour and the refractive index of the coated particles or the refractive index of the coating layer is 0.03 or less.

[0022] In a specific aspect of the adhesive according to the present invention, the ratio of the transmittance of the cured product of the adhesive at a wavelength of 650 nm, cured under the conditions of 23°C and 1 hour, to the transmittance of the cured product of the curable component at a wavelength of 650 nm, cured under the conditions of 23°C and 1 hour, is 0.94 or more.

[0023] According to a broad aspect of the present invention, there is provided a display device including a first member, an image display element as a second member, and an adhesive layer bonding the first member and the second member, wherein the adhesive layer is a cured product of an adhesive containing the above-described optical bonding particles and a curable component.

[0024] In a specific aspect of the display device according to the present invention, the first member is a transparent protective material.

Advantages of the Invention

[0025] The optical bonding particles according to the present invention include silicone particles and coated particles or a coating layer disposed on the surface of the silicone particles. In the optical bonding particles according to the present invention, the absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coated particles or the refractive index of the coating layer is 0.03 or less. Since the above configuration is provided in the optical bonding particles according to the present invention, visibility can be improved and the gap can be controlled with high precision.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0027] Hereinafter, the details of the present invention will be described.

[0028] (Optical Bonding Particles) The optical bonding particles according to the present invention include silicone particles and coating particles or a coating layer disposed on the surface of the silicone particles. In the optical bonding particles according to the present invention, the absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coating particles or the refractive index of the coating layer is 0.03 or less.

[0029] In the optical bonding particles according to the present invention, since the above configuration is provided, visibility can be improved and the gap can be controlled with high precision.

[0030] In recent years, the use of optical bonding has been promoted in various fields. For example, in display devices such as in-vehicle displays, the use of optical bonding is being considered to improve visibility. Specifically, a material used for optical bonding (an optical bonding material, for example, a light-transmitting material such as an adhesive) is applied onto an image display element, a transparent protective material is disposed on the surface opposite to the image display element side of the optical bonding material, and curing the optical bonding material and the like are being considered. An adhesive layer that bonds the image display element and the transparent protective material is formed by the cured product of the optical bonding material.

[0031] In the optical bonding material used for a display device (for example, an in-vehicle display or the like), it may be difficult to uniformly apply it onto the image display element. Further, the viscosity of the optical bonding material is low, and until the curing of the optical bonding material is completed, for example, due to the weight of the transparent protective material or the like, the optical bonding material flows on the image display element, and it may not be possible to sufficiently secure the thickness (gap) of the cured product (adhesive layer) of the optical bonding material on the image display element. For this reason, the use of a gap material in the optical bonding material is being considered. As the above gap material, coated silicone particles or the like may be used.

[0032] When using conventional coated silicone particles or the like as the gap material of the optical bonding material, since the particle diameter of the coated particles in the coated silicone particles is small (the thickness of the coating layer is thin), it may not be possible to sufficiently reduce the refractive index difference between the optical bonding material and the gap material. Further, when the particle diameter of the coated particles in the coated silicone particles is small, it becomes difficult to uniformly coat the surface of the silicone particles, and variations may occur in the refractive index difference between the optical bonding material and the gap material. As a result, it may be difficult to sufficiently improve the visibility with conventional coated silicone particles. Since the optical bonding particles according to the present invention have the above configuration, even when a gap material (optical bonding particles) is included in the optical bonding material, the visibility can be improved.

[0033] Further, when a display device (for example, an in-vehicle display or the like) is repeatedly exposed to temperature changes from low temperature to high temperature, stress may be generated between members (for example, an image display element, a transparent protective material, etc.) due to differences in the linear expansion coefficients of the members. When the thickness (gap) of the cured product (adhesive layer) of the optical bonding material cannot be sufficiently ensured, the stress generated between the members cannot be sufficiently relaxed, and cracks or peeling may occur in the cured product (adhesive layer) of the optical bonding material. In order to relax the stress generated between the members, it is required to sufficiently ensure the thickness (gap) of the cured product (adhesive layer) of the optical bonding material. By using the optical bonding particles according to the present invention, the thickness (gap) of the adhesive layer can be controlled with high precision, and the thickness (gap) of the adhesive layer can be sufficiently ensured.

[0034] FIG. 1 is a cross-sectional view showing the optical bonding particles according to the first embodiment of the present invention.

[0035] The optical bonding particle 1 shown in FIG. 1 includes a silicone particle 2 and a coating particle 3 disposed on the surface of the silicone particle 2. The coating particle 3 is in contact with the surface of the silicone particle 2 and covers the surface of the silicone particle 2. The optical bonding particle 1 is a coated particle in which the surface of the silicone particle 2 is covered by the coating particle 3. The coating particle may completely cover the surface of the silicone particle, or may not completely cover the surface of the silicone particle. The silicone particle may have a portion not covered by the coating particle. The coating particle may be in contact with other coating particles or may overlap with other coating particles. In the optical bonding particle, a plurality of the coating particles may overlap to form a laminated structure.

[0036] FIG. 2 is a cross-sectional view showing the optical bonding particle according to the second embodiment of the present invention.

[0037] The optical bonding particle 11 shown in FIG. 2 includes a silicone particle 2 and a coating layer 4 disposed on the surface of the silicone particle 2. The coating layer 4 is in contact with the surface of the silicone particle 2 and covers the surface of the silicone particle 2. The optical bonding particle 11 is a coated particle in which the surface of the silicone particle 2 is covered by the coating layer 4. The coating layer may completely cover the surface of the silicone particle, or may not completely cover the surface of the silicone particle. The silicone particle may have a portion not covered by the coating layer. The coating layer may have a single-layer structure or a laminated structure of two or more layers. When the coating layer has a laminated structure of two or more layers, the materials of each layer may be the same or different.

[0038] FIG. 3 is a cross-sectional view showing the optical bonding particle according to the third embodiment of the present invention.

[0039] The optical bonding particle 1A shown in Fig. 3 includes silicone particles 2 and coating particles 3 disposed on the surface of the silicone particles 2. The silicone particles 2 include a plurality of inorganic oxide particles 5. The coating particles 3 are in contact with the surface of the silicone particles 2 and cover the surface of the silicone particles 2. The optical bonding particle 1A is a coated particle in which the surface of the silicone particles 2 is covered by the coating particles 3. The coating particles may completely cover the surface of the silicone particles, or may not completely cover the surface of the silicone particles. The silicone particles may have a portion not covered by the coating particles. The coating particles may be in contact with other coating particles or may overlap with other coating particles. In the optical bonding particle, a plurality of the coating particles may overlap to form a laminated structure. In the optical bonding particle 1A, at least a part of the inorganic oxide particles 5 exists inside the silicone particles 2. In the optical bonding particle 1A, a part of the inorganic oxide particles 5 exists outside the silicone particles 2. In the optical bonding particle, all of the inorganic oxide particles may exist inside the silicone particles. The inorganic oxide particles may be in contact with other inorganic oxide particles or may overlap with other inorganic oxide particles.

[0040] Fig. 4 is a cross-sectional view showing the optical bonding particle according to the fourth embodiment of the present invention.

[0041] The optical bonding particles 11A shown in Fig. 4 include silicone particles 2 and a coating layer 4 disposed on the surface of the silicone particles 2. The silicone particles 2 include a plurality of inorganic oxide particles 5. The coating layer 4 is in contact with the surface of the silicone particles 2 and covers the surface of the silicone particles 2. The optical bonding particles 11A are coated particles in which the surface of the silicone particles 2 is covered by the coating layer 4. The coating layer may completely cover the surface of the silicone particles, or may not completely cover the surface of the silicone particles. The silicone particles may have a portion not covered by the coating layer. The coating layer may have a single-layer structure or a laminated structure of two or more layers. When the coating layer has a laminated structure of two or more layers, the materials of each layer may be the same or different. In the optical bonding particles 11A, at least a part of the inorganic oxide particles 5 is present inside the silicone particles 2. In the optical bonding particles 11A, a part of the inorganic oxide particles 5 is present outside the silicone particles 2. In the optical bonding particles, all of the inorganic oxide particles may be present inside the silicone particles. The inorganic oxide particles may be in contact with other inorganic oxide particles or may overlap with other inorganic oxide particles.

[0042] From the viewpoint of further improving visibility, the refractive index of the optical bonding particles is preferably 1.40 or more, more preferably 1.41 or more, preferably 1.43 or less, and more preferably 1.42 or less.

[0043] The refractive index can be measured by methods such as the minimum deviation angle method, the critical angle method, and the V-block method. The refractive index of a micro sample such as particles for optical bonding is preferably measured by a method conforming to JIS K7142:2014 Plastics - Methods for determining refractive index - Method B. When the particles for optical bonding are contained in an adhesive together with a curable component, the curable component can be dissolved with a solvent such as toluene, the particles for optical bonding can be recovered, washed, dried, and then the refractive index can be measured. Also, the refractive index of silicone particles, the refractive index of coated particles, and the refractive index of a coating layer can be measured by the following method. Immerse the particles for optical bonding in acetone to swell the silicone particles and peel off the coated particles or coating layer disposed on the surface of the silicone particles. Recover the peeled coated particles or coating layer, wash and dry them, and measure the refractive index of the coated particles or coating layer. Wash and dry the silicone particles from which the coated particles or coating layer disposed on the surface have been removed, and measure the refractive index of the silicone particles.

[0044] The particle diameter of the above-mentioned particles for optical bonding is preferably 30 μm or more, more preferably 100 μm or more, preferably 500 μm or less, and more preferably 200 μm or less. When the particle diameter of the above-mentioned particles for optical bonding is equal to or greater than the above lower limit and equal to or less than the above upper limit, they can be more suitably used for optical bonding applications, and the particles for optical bonding can be more suitably used to obtain an adhesive for optical bonding.

[0045] When the particle diameter of the above-mentioned particles for optical bonding means the diameter in the case where the above-mentioned particles for optical bonding are spherical, and when the above-mentioned particles for optical bonding are in a shape other than spherical, it means the diameter when assuming a true sphere equivalent to its volume. The particle diameter of the above-mentioned particles for optical bonding is preferably the average particle diameter, and more preferably the number average particle diameter. The particle diameter of the above-mentioned particles for optical bonding can be measured by any particle size distribution measuring device. For example, it can be measured using a particle size distribution measuring device based on principles such as laser light scattering, change in electrical resistance value, and image analysis after imaging. More specifically, as a method for measuring the particle diameter of the above-mentioned particles for optical bonding, a method of measuring the particle diameters of about 100,000 particles for optical bonding using a particle size distribution measuring device (Multisizer4 manufactured by Beckman Coulter) and calculating the average particle diameter can be mentioned.

[0046] The coefficient of variation (CV value) of the particle diameter of the above-mentioned particles for optical bonding is preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less. When the CV value is below the above upper limit, the gap can be controlled with higher precision, and the particles for optical bonding can be more suitably used for optical bonding applications.

[0047] The above CV value is represented by the following formula.

[0048] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of the particle diameter of the particles for optical bonding Dn: Average value of the particle diameter of the particles for optical bonding

[0049] The above-mentioned particles for optical bonding are preferably used to obtain an adhesive. The above-mentioned particles for optical bonding are preferably used in an adhesive for bonding two members. The above-mentioned particles for optical bonding are preferably used as a spacer. The above-mentioned particles for optical bonding are preferably used as a spacer in the above-mentioned adhesive. Examples of the method of using the above-mentioned particles for optical bonding include a spacer for gap control, a spacer for stress relaxation, and the like. The above-mentioned spacer for gap control can be used for gap control of a stacked chip for ensuring a standoff height and flatness, and for gap control of an optical component for ensuring smoothness of a glass surface and thickness of an adhesive layer. The above-mentioned spacer for stress relaxation can be used for stress relaxation of a sensor chip or the like, stress relaxation of an adhesive structure such as a pressure sensor, and stress relaxation of an adhesive layer bonding two adherends. The above-mentioned particles for optical bonding can be used in a pressure sensor, a die bonding material, a conductive adhesive, an optical bonding material, and the like. The above-mentioned particles for optical bonding are preferably used to obtain an optical bonding adhesive.

[0050] Hereinafter, other details of the particles for optical bonding will be described. In this specification, “(meth)acrylate” means one or both of “acrylate” and “methacrylate”, and “(meth)acrylic” means one or both of “acrylic” and “methacrylic”.

[0051] (Silicone particles) The material of the above-mentioned silicone particles is preferably a silicone resin. The above-mentioned silicone particles preferably contain a silicone resin. The above-mentioned silicone particles are preferably silicone spacers.

[0052] From the viewpoint of further improving visibility, it is preferable that the silicone particles include a plurality of inorganic oxide particles. In the silicone particles, it is preferable that at least a part of the inorganic oxide particles is present inside the silicone particles. In the silicone particles, a part of the inorganic oxide particles may be present outside the silicone particles, or all of the inorganic oxide particles may be present inside the silicone particles. The volume of the portion of any one of the inorganic oxide particles present inside the silicone particles is preferably 10% or more, more preferably 30% or more, still more preferably 50% or more, out of 100% of the volume of the inorganic oxide particle. The volume of the portion of any one of the inorganic oxide particles present inside the silicone particles is preferably 100% or less, and may be less than 100%, out of 100% of the volume of the inorganic oxide particle. From the viewpoint of improving the dispersibility of the silicone particles, it is preferable that the silicone particles are silicone particles in which inorganic oxide particles having a part of the inorganic oxide particles present inside the silicone particles and inorganic oxide particles having all of the inorganic oxide particles present inside the silicone particles are mixed.

[0053] Examples of the material of the inorganic oxide particles include silica, silicone resin, fluororesin, alumina, barium titanate, zirconia, silicate glass, borosilicate glass, lead glass, soda lime glass, and aluminosilicate glass.

[0054] The material of the inorganic oxide particles preferably contains silica, silicone resin, or fluororesin, more preferably contains silica or silicone resin, still more preferably contains silica, and particularly preferably is silica. When the material of the inorganic oxide particles satisfies the above preferred embodiments, the visibility can be further improved, and the gap can be controlled with higher precision.

[0055] The above silicone particles preferably do not contain a platinum catalyst or contain a platinum catalyst at 100 ppm or less. When using a platinum catalyst, the lower the content of the platinum catalyst, the better. When the content of the platinum catalyst is high, the reliability tends to decrease. The content of the platinum catalyst is more preferably 80 ppm or less, even more preferably 60 ppm or less, still more preferably 50 ppm or less, even still more preferably 40 ppm or less, particularly preferably 30 ppm or less, also particularly preferably 20 ppm or less, and most preferably 10 ppm or less.

[0056] Generally, silicone particles are often obtained by polymerizing monomers using a platinum catalyst. In such silicone particles, even if washed, the platinum catalyst is contained inside and the content of the platinum catalyst exceeds 100 ppm. In contrast, in silicone particles obtained without using a platinum catalyst, the platinum catalyst is generally not contained.

[0057] The material of the above silicone particles is preferably an organopolysiloxane, and more preferably a silane alkoxide. Only one kind of organopolysiloxane and silane alkoxide may be used respectively, or two or more kinds may be used in combination.

[0058] From the viewpoint of further improving visibility and from the viewpoint of more precisely controlling the gap, the above silane alkoxide preferably contains silane alkoxide A represented by the following formula (1A) or silane alkoxide B represented by the following formula (1B). The above silane alkoxide may contain silane alkoxide A represented by the following formula (1A) or may contain silane alkoxide B represented by the following formula (1B).

[0059] Si(R1) n (OR2) 4-n ···(1A)

[0060] In the above formula (1A), R1 represents a hydrogen atom, a phenyl group, or an alkyl group having 1 to 30 carbon atoms, R2 represents an alkyl group having 1 to 6 carbon atoms, and n represents an integer of 0 to 2. When n is 2, the plurality of R1s may be the same or different. The plurality of R2s may be the same or different.

[0061] When the above R1 in the above formula (1A) is an alkyl group having 1 to 30 carbon atoms, specific examples of R1 include a methyl group, an ethyl group, a propyl group, an isopropyl group, an isobutyl group, an n-hexyl group, a cyclohexyl group, an n-octyl group, and an n-decyl group. The number of carbon atoms of this alkyl group is preferably 10 or less, more preferably 6 or less. The alkyl group includes a cycloalkyl group.

[0062] Specific examples of the above R2 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and an isobutyl group.

[0063] Specific examples of the above silane alkoxide A include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, isopropyltrimethoxysilane, isobutyltrimethoxysilane, cyclohexyltrimethoxysilane, n-hexyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diisopropyldimethoxysilane, and diphenyldimethoxysilane. Silane alkoxides other than these may also be used.

[0064] Si(R1) n (OR2) 4-n ···(1B)

[0065] In the above formula (1B), R1 represents a hydrogen atom, a phenyl group, an alkyl group having 1 to 30 carbon atoms, or an organic group having 1 to 30 carbon atoms with a polymerizable double bond, R2 represents an alkyl group having 1 to 6 carbon atoms, and n represents an integer of 0 to 2. When n is 2, the plurality of R1s may be the same or different. The plurality of R2s may be the same or different. However, at least one R1 is an organic group having 1 to 30 carbon atoms with a polymerizable double bond. At least one R1 is preferably a vinyl group, a styryl group or a (meth)acryloxy group, more preferably a vinyl group or a (meth)acryloxy group, and even more preferably a (meth)acryloxy group.

[0066] When the above R1 in the above formula (1B) is an alkyl group having 1 to 30 carbon atoms, specific examples of R1 include a methyl group, an ethyl group, a propyl group, an isopropyl group, an isobutyl group, an n-hexyl group, a cyclohexyl group, an n-octyl group, and an n-decyl group. The number of carbon atoms of this alkyl group is preferably 10 or less, more preferably 6 or less. The alkyl group includes a cycloalkyl group.

[0067] Examples of the above polymerizable double bond include a carbon-carbon double bond. When the above R1 is an organic group having 1 to 30 carbon atoms with a polymerizable double bond, specific examples of R1 include a vinyl group, a styryl group, an allyl group, an isopropenyl group, and a 3-(meth)acryloxyalkyl group. Examples of the above styryl group include a p-styryl group, an o-styryl group, and an m-styryl group. Examples of the above (meth)acryloxyalkyl group include a (meth)acryloxymethyl group, a (meth)acryloxyethyl group, and a (meth)acryloxypropyl group. The number of carbon atoms of the organic group having 1 to 30 carbon atoms with a polymerizable double bond is preferably 2 or more, preferably 30 or less, and more preferably 10 or less. The term "(meth)acryloxy" indicates acryloxy and methacryloxy.

[0068] Specific examples of the above R2 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and an isobutyl group.

[0069] From the viewpoint of further improving visibility and from the viewpoint of more precisely controlling the gap, it is preferable that the above silane alkoxide contains dialkoxysilane.

[0070] In the hydrolysis condensate of the above silane alkoxide, the monoalkoxysilane is 0% by weight (unused) or more and 20% by weight or less, the dialkoxysilane is 70% by weight or more and 99.9% by weight or less, and the total of the trialkoxysilane and the tetraalkoxysilane is preferably 0.1% by weight or more and 30% by weight or less, based on 100% by weight of the silane alkoxide. In the hydrolysis condensate of the above silane alkoxide, the monoalkoxysilane is 0% by weight (unused) or more and 15% by weight or less, the dialkoxysilane is 75% by weight or more and 99% by weight or less, and the total of the trialkoxysilane and the tetraalkoxysilane is preferably 1% by weight or more and 25% by weight or less. By the hydrolysis condensate of the above silane alkoxide satisfying the above preferred embodiment, it is possible to further improve visibility and to obtain a gap material capable of more precisely controlling the gap.

[0071] From the viewpoint of more easily adjusting the particle size, it is preferable that the above silane alkoxide contains a silane alkoxide having a polymerizable functional group, and it is more preferable that it contains a silane alkoxide having a polymerizable double bond. Examples of the silane alkoxide having a polymerizable double bond include vinyltrimethoxysilane, vinyltriethoxysilane, dimethoxymethylvinylsilane, dimethoxyethylvinylsilane, diethoxymethylvinylsilane, diethoxyethylvinylsilane, ethylmethyldivinylsilane, methylvinyldimethoxysilane, ethylvinyldimethoxysilane, methylvinyldiethoxysilane, ethylvinyldiethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane. Further, cyclic siloxanes may be used, or modified (reactive) silicone oils or the like may be used. Examples of the cyclic siloxane include decamethylcyclopentasiloxane. Examples of the modified silicone oil include monofunctional modified silicone oil, bifunctional silicone oil, and side-chain type silicone oil.

[0072] As a specific method for producing the above silicone particles, after preliminarily condensing the above silane alkoxide to obtain an oligomer, a polymerization reaction is carried out by a suspension polymerization method, a dispersion polymerization method, a miniemulsion polymerization method, an emulsion polymerization method, or the like to produce silicone particles.

[0073] From the viewpoint of further improving the visibility, the refractive index of the above silicone particles is preferably 1.39 or more, more preferably 1.40 or more, preferably 1.44 or less, and more preferably 1.43 or less.

[0074] The refractive index of the above silicone particles can be measured by a method conforming to JIS K7142:2014 Plastics - Method for determining refractive index, Method B.

[0075] The particle size of the silicone particles is preferably 30 μm or more, more preferably 50 μm or more, and even more preferably more than 100 μm. The particle size of the silicone particles is preferably 500 μm or less, more preferably 200 μm or less. When the particle size of the silicone particles satisfies the above lower limit and upper limit, the silicone particles can be more suitably used for optical bonding applications, and the silicone particles can be more suitably used to obtain particles for optical bonding.

[0076] The particle size of the silicone particles means the diameter when the silicone particles are spherical, and when the silicone particles are in a shape other than spherical, it means the diameter when assuming a true sphere equivalent to its volume. The particle size of the silicone particles is preferably the average particle size, and more preferably the number average particle size. The particle size of the silicone particles can be measured by any particle size distribution measuring device. For example, it can be measured using a particle size distribution measuring device based on the principles such as laser light scattering, change in electrical resistance value, and image analysis after imaging. More specifically, as a method for measuring the particle size of the silicone particles, a method of measuring the particle sizes of about 100,000 silicone particles using a particle size distribution measuring device ("Multisizer4" manufactured by Beckman Coulter) and calculating the average particle size can be mentioned.

[0077] The coefficient of variation (CV value) of the particle size of the silicone particles is preferably 10% or less, more preferably 7% or less, and even more preferably 5% or less. When the CV value is below the above upper limit, the gap can be controlled with higher precision, and the silicone particles can be more suitably used to obtain particles for optical bonding.

[0078] The CV value is represented by the following formula.

[0079] CV value (%) = (ρ / Dn) × 100 ρ: Standard deviation of the particle size of the silicone particles Dn: Average value of the particle size of the silicone particles

[0080] (Coated particles or coating layer) The material of the coated particles or the coating layer is not particularly limited. The material of the coated particles or the coating layer may be an organic material or an inorganic material.

[0081] Examples of the organic material include polyolefin resins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyisobutylene, and polybutadiene; acrylic resins such as polymethyl methacrylate and polymethyl acrylate; polycarbonate, polyamide, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, phenol resin, melamine resin, benzoguanamine resin, urea resin, epoxy resin, unsaturated polyester resin, saturated polyester resin, polyethylene terephthalate, polysulfone, polyphenylene oxide, polyacetal, polyimide, polyamideimide, polyetheretherketone, polyethersulfone, divinylbenzene polymer, and divinylbenzene copolymer. Examples of the divinylbenzene copolymer include divinylbenzene-styrene copolymer and divinylbenzene-(meth)acrylate copolymer. Since the coated particles or the coating layer can be easily produced, the material of the coated particles or the coating layer is preferably a polymer obtained by polymerizing one or more polymerizable monomers having an ethylenically unsaturated group.

[0082] When the coated particles or the coating layer is obtained by polymerizing a polymerizable monomer having an ethylenically unsaturated group, examples of the polymerizable monomer having an ethylenically unsaturated group include non-crosslinkable monomers and crosslinkable monomers.

[0083] As the above non-crosslinkable monomer, as vinyl compounds, styrene monomers such as styrene, α-methylstyrene, chlorostyrene; vinyl ether compounds such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether; vinyl ester compounds such as vinyl acetate, vinyl butyrate, vinyl laurate, vinyl stearate; halogen-containing monomers such as vinyl chloride, vinyl fluoride; as (meth)acrylic compounds, alkyl (meth)acrylate compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate; oxygen atom-containing (meth)acrylate compounds such as 2-hydroxyethyl (meth)acrylate, glycerol (meth)acrylate, polyoxyethylene (meth)acrylate, glycidyl (meth)acrylate; nitrile-containing monomers such as (meth)acrylonitrile; halogen-containing (meth)acrylate compounds such as trifluoromethyl (meth)acrylate, pentafluoroethyl (meth)acrylate, (perfluorobutyl)ethyl (meth)acrylate, perfluorobutyl-hydroxypropyl (meth)acrylate, (perfluorohexyl)ethyl (meth)acrylate, octafluoropentyl (meth)acrylate, perfluorooctylethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate; as α-olefin compounds, olefin compounds such as diisobutylene, isobutylene, linearene, ethylene, propylene; as conjugated diene compounds, isoprene, butadiene, etc. may be mentioned.

[0084] As the crosslinkable monomer, as vinyl compounds, vinyl monomers such as divinylbenzene, 1,4-divinyloxybutane, divinyl sulfone; as (meth)acrylic compounds, tetramethylolmethane tetra(meth)acrylate, polytetramethylene glycol diacrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol tri(meth)acrylate, glycerol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate and other polyfunctional (meth)acrylate compounds; as allyl compounds, triallyl (iso)cyanurate, triallyl trimellitate, diallyl phthalate, diallyl acrylamide, diallyl ether; as silane compounds, tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, isopropyltrimethoxysilane, isobutyltrimethoxysilane, cyclohexyltrimethoxysilane, n-hexyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diisopropyldimethoxysilane, trimethoxysilylstyrene, γ-(meth)acryloxypropyltrimethoxysilane, 1,3-divinyltetramethyldisiloxane, methylphenyldimethoxysilane, diphenyldimethoxysilane and other silane alkoxide compounds;Polymerizable double bond-containing silane alkoxides such as vinyltrimethoxysilane, vinyltriethoxysilane, dimethoxymethylvinylsilane, dimethoxyethylvinylsilane, diethoxymethylvinylsilane, diethoxyethylvinylsilane, ethylmethyldivinylsilane, methylvinyldimethoxysilane, ethylvinyldimethoxysilane, methylvinyldiethoxysilane, ethylvinyldiethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane; cyclic siloxanes such as decamethylcyclopentasiloxane; modified (reactive) silicone oils such as monofunctional modified silicone oil, bifunctional silicone oil, and side-chain type silicone oil; carboxyl group-containing monomers such as (meth)acrylic acid, maleic acid, and maleic anhydride, etc.

[0085] The above-mentioned coated particles or the above-mentioned coating layer can be obtained by polymerizing the polymerizable monomer having the above-mentioned ethylenically unsaturated group. The above polymerization method is not particularly limited, and known methods such as radical polymerization, ionic polymerization, polycondensation (condensation polymerization, polycondensation), addition condensation, living polymerization, and living radical polymerization can be mentioned. Further, as another polymerization method, suspension polymerization in the presence of a radical polymerization initiator can be mentioned.

[0086] Examples of the above-mentioned inorganic materials include silica, alumina, barium titanate, zirconia, carbon black, silicate glass, borosilicate glass, lead glass, soda-lime glass, and aluminosilicate glass.

[0087] The material of the above-mentioned coated particles or the above-mentioned coating layer preferably contains silica, silicone resin, or fluororesin, and more preferably contains silica or silicone resin. When the material of the above-mentioned coated particles or the above-mentioned coating layer satisfies the above-mentioned preferred embodiment, the visibility can be further improved, and the gap can be controlled with higher precision.

[0088] From the viewpoint of further improving the visibility, the refractive index of the coating particles and the refractive index of the coating layer are preferably 1.39 or more, more preferably 1.395 or more, preferably 1.42 or less, and more preferably 1.415 or less.

[0089] The refractive index of the coating particles and the refractive index of the coating layer can be measured by a method conforming to JIS K 7142:2014 Plastics - Method for determining refractive index - Method B. When the size of the coating particles or the thickness of the coating layer is smaller than the wavelength of light and a clear image cannot be observed with an optical microscope, the phenomenon that a turbid region is not observed with an optical microscope in an immersion liquid having the same refractive index as the sample and a turbid region is observed with an optical microscope in an immersion liquid having a refractive index different from that of the sample is utilized. That is, the refractive index of the immersion liquid in which no turbid region is observed is taken as the refractive index of the coating particles or the refractive index of the coating layer.

[0090] The absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coating particles or the refractive index of the coating layer is preferably 0.025 or less, more preferably 0.020 or less. The lower limit of the absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coating particles or the refractive index of the coating layer is not particularly limited. The absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coating particles or the refractive index of the coating layer may be 0 or more. When the absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coating particles or the refractive index of the coating layer is within the above lower limit and the above upper limit, the visibility can be further improved.

[0091] As a method for controlling the absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coating particles or the refractive index of the coating layer within the above preferred range, a method using a silane compound having a radical polymerizable functional group containing fluorine in the side chain as the material of the coating particles or the material of the coating layer can be mentioned.

[0092] Of the total surface area of 100% of the silicone particles, the area of the portion having the coated particles or the coating layer (coating rate) is preferably 80% or more, more preferably 85% or more. The upper limit of the coating rate is not particularly limited. The coating rate may be 99% or less. When the coating rate is at least the lower limit, the visibility can be further improved, and the gap can be controlled with higher precision.

[0093] Of the total surface area of 100% of the silicone particles, the area of the portion having the coated particles or the coating layer (coating rate) is determined by observing the silicone particles with an electron microscope or an optical microscope and calculating the percentage of the surface area of the portion having the coated particles or the coating layer with respect to the projected area of the silicone particles.

[0094] In the particles for optical bonding, the particle diameter of the coated particles or the thickness of the coating layer is preferably 30 nm or more, more preferably more than 60 nm, still more preferably 80 nm or more, and particularly preferably 100 nm or more. In the particles for optical bonding, the particle diameter of the coated particles or the thickness of the coating layer is preferably 500 nm or less, more preferably 200 nm or less. When the particle diameter of the coated particles or the thickness of the coating layer satisfies the lower limit and the upper limit, the visibility can be further improved, and the gap can be controlled with higher precision.

[0095] When the above optical bonding particles include the above coating particles, the particle diameter of the above coating particles means the diameter when the above coating particles are spherical, and when the above coating particles have a shape other than spherical, it preferably means the diameter when assuming a sphere equivalent to its volume. The particle diameter of the above coating particles is preferably the average particle diameter, and more preferably the number average particle diameter. The particle diameter of the above coating particles can be determined by observing 50 arbitrary coating particles with an electron microscope or an optical microscope and calculating the average value, or by performing laser diffraction particle size distribution measurement. In the observation with an electron microscope or an optical microscope, the particle diameter of each coating particle is determined as the particle diameter equivalent to a circle. In the observation with an electron microscope or an optical microscope, the average particle diameter in terms of the circle equivalent diameter of 50 arbitrary coating particles is almost equal to the average particle diameter in terms of the sphere equivalent diameter. In the laser diffraction particle size distribution measurement, the particle diameter of each coating particle is determined as the particle diameter in terms of the sphere equivalent diameter. The particle diameter of the above coating particles is preferably calculated by laser diffraction particle size distribution measurement.

[0096] When the above optical bonding particles include the above coating layer, the thickness of the above coating layer can be measured, for example, by observing the cross section of the above optical bonding particles using a transmission electron microscope (TEM). Regarding the thickness of the above coating layer, it is preferable to calculate the average value of 5 thicknesses of arbitrary coating layers as the thickness of the coating layer of one optical bonding particle, and more preferably to calculate the average value of the thickness of the entire coating layer as the thickness of the coating layer of one optical bonding particle. In the case of a plurality of optical bonding particles, the thickness of the above coating layer is preferably determined by calculating the average value of 10 arbitrary optical bonding particles.

[0097] In the above-mentioned particles for optical bonding, the ratio of the particle diameter of the coated particles or the thickness of the coating layer to the particle diameter of the silicone particles (particle diameter of the coated particles or thickness of the coating layer / particle diameter of the silicone particles) is preferably 0.0003 or more, more preferably 0.001 or more, preferably 0.02 or less, and more preferably 0.01 or less. When the above ratio (particle diameter of the coated particles or thickness of the coating layer / particle diameter of the silicone particles) is equal to or greater than the above lower limit and equal to or less than the above upper limit, the visibility can be further improved, and the gap can be controlled with higher precision.

[0098] The method of disposing the coated particles or the coating layer on the surface of the silicone particles is not particularly limited. Examples of the method of disposing the coated particles or the coating layer include a method of introducing a graft chain by chemical bonding, a mechanochemical method of applying mechanical energy to fix it on the surface, and a heteroaggregation method using the potential difference on the surface. From the viewpoint of more easily disposing the coated particles or the coating layer on the surface of the silicone particles, the method of disposing the coated particles or the coating layer is preferably a heteroaggregation method using the potential difference on the surface.

[0099] (Adhesive) The adhesive according to the present invention contains the above-mentioned particles for optical bonding and a curable component. The above-mentioned particles for optical bonding are preferably dispersed in the curable component. The curable component preferably has fluidity. The adhesive or the curable component is preferably in the form of a paste. The paste form includes a liquid state.

[0100] The adhesive may be a one-component type in which the main agent and the curing agent are premixed, or a two-component type in which the main agent and the curing agent are separated. The adhesive may be a condensation curing type or an addition curing type. The adhesive may be cured using a catalyst such as platinum, or may be cured by moisture or the like. From the viewpoint of more effectively reducing the residual stress in the cured product of the adhesive, the adhesive preferably cures at room temperature.

[0101] The above-mentioned adhesive can bond, for example, two adherends. The above-mentioned adhesive is preferably used to form an adhesive layer for bonding two adherends. Further, the above-mentioned adhesive is preferably used to relieve the stress of the above-mentioned adhesive layer, and preferably cures at 25°C.

[0102] The above-mentioned adhesive may or may not contain conductive particles. The above-mentioned adhesive may or may not be used for conductive connection. The above-mentioned adhesive may or may not be used for anisotropic conductive connection. The above-mentioned adhesive may not be a conductive material, nor an anisotropic conductive material. The above-mentioned adhesive may or may not be used in a liquid crystal display element. The above-mentioned adhesive is preferably used for optical bonding applications. In a display device, the above-mentioned adhesive is preferably used to fill the gap between an image display element and a transparent protective material, reduce the reflection loss occurring at the interface of the transparent protective material, and improve visibility.

[0103] From the viewpoint of further improving visibility, the refractive index of the cured product obtained by curing the above-mentioned curable component under the conditions of 23°C and 1 hour is preferably 1.40 or more, more preferably 1.41 or more, preferably 1.43 or less, and more preferably 1.42 or less.

[0104] The refractive index of the above-mentioned cured product can be measured as follows.

[0105] The curable component is cured under the conditions of 23°C and 1 hour to produce a film with a thickness of about 1 μm. For the obtained film, the refractive index is measured with an Abbe refractometer (such as "ER-7MW" manufactured by ERMA).

[0106] From the viewpoint of further improving visibility, the absolute value of the difference between the refractive index of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour and the refractive index of the silicone particles is preferably 0.05 or less, more preferably 0.03 or less. The absolute value of the difference between the refractive index of the cured product and the refractive index of the silicone particles may be 0 or more.

[0107] From the viewpoint of further improving visibility, the absolute value of the difference between the refractive index of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour and the refractive index of the coated particles or the refractive index of the coating layer is preferably 0.03 or less, more preferably 0.02 or less. The absolute value of the difference between the refractive index of the cured product and the refractive index of the coated particles or the refractive index of the coating layer may be 0 or more.

[0108] The ratio of the transmittance at a wavelength of 650 nm of the cured product obtained by curing the adhesive under the conditions of 23°C for 1 hour to the transmittance at a wavelength of 650 nm of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour is preferably 0.92 or more, more preferably 0.94 or more, and even more preferably 0.95 or more. The upper limit of the ratio (transmittance at a wavelength of 650 nm of the cured product obtained by curing the adhesive under the conditions of 23°C for 1 hour / transmittance at a wavelength of 650 nm of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour) is not particularly limited. The ratio (transmittance at a wavelength of 650 nm of the cured product obtained by curing the adhesive under the conditions of 23°C for 1 hour / transmittance at a wavelength of 650 nm of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour) may be 0.9999 or less. When the ratio (transmittance at a wavelength of 650 nm of the cured product obtained by curing the adhesive under the conditions of 23°C for 1 hour / transmittance at a wavelength of 650 nm of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour) is equal to or higher than the above lower limit, visibility can be further improved.

[0109] The transmittance of the cured product obtained by curing the above curable component under the conditions of 23°C for 1 hour at a wavelength of 650 nm is preferably 92% or more, more preferably 95% or more, and even more preferably 98% or more. The upper limit of the transmittance of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour at a wavelength of 650 nm is not particularly limited. The transmittance of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour at a wavelength of 650 nm may be 99.9% or less. When the transmittance of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour at a wavelength of 650 nm is not less than the above lower limit, the visibility can be further improved.

[0110] The transmittance of the cured product obtained by curing the adhesive under the conditions of 23°C for 1 hour at a wavelength of 650 nm can be measured as follows.

[0111] The adhesive is applied to a thickness of 0.1 mm, and a cured product is obtained by curing it under the conditions of 23°C for 1 hour. Using the obtained cured product, the transmittance at a wavelength of 650 nm is measured at 25°C. The above transmittance can be measured using, for example, a spectrophotometer (double-beam spectrophotometer "U-2910" manufactured by Hitachi High-Technologies Corporation), etc. An integrating sphere can be used for the detector.

[0112] Also, the transmittance of the cured product obtained by curing the curable component under the conditions of 23°C for 1 hour at a wavelength of 650 nm can be measured as follows.

[0113] The curable component is applied to a thickness of 0.1 mm, and a cured product is obtained by curing it under the conditions of 23°C for 1 hour. Using the obtained cured product, the transmittance at a wavelength of 650 nm is measured at 25°C. The above transmittance can be measured using, for example, a spectrophotometer (double-beam spectrophotometer "U-2910" manufactured by Hitachi High-Technologies Corporation), etc. An integrating sphere can be used for the detector.

[0114] As a method for controlling the absolute value of the difference between the refractive index of the cured product obtained by curing the above curable component under the conditions of 23°C for 1 hour and the refractive index of the above silicone particles, and the absolute value of the difference between the refractive index of the cured product obtained by curing the above curable component under the conditions of 23°C for 1 hour and the refractive index of the above coated particles or the refractive index of the above coating layer within the above preferable range, the following methods and the like can be mentioned. A method of adding a low refractive index filler (such as silica or fluororesin) to the curable component. A method of reducing the difference in refractive index at the interface between the curable component and the coated particles or the coating layer.

[0115] The above curable component is not particularly limited. Examples of the above curable component include a thermosetting component, a photocurable component, and a room temperature curable component. When a thermosetting component or a photocurable component is used as the above curable component, residual stress may occur in the cured product of the above adhesive (the cured product of the above curable component). Since the residual stress in the cured product of the above adhesive (the cured product of the above curable component) may affect reliability and the like, it is necessary to reduce the residual stress as much as possible. As a method for reducing the residual stress in the cured product of the above adhesive (the cured product of the above curable component), using a room temperature curable component as the above curable component and the like can be mentioned. The above curable component is preferably a room temperature curable component. The room temperature is, for example, 25°C.

[0116] From the viewpoint of further improving visibility, more effectively suppressing the generation of residual stress, and more effectively enhancing heat resistance, the above curable component preferably contains an acrylic resin or a silicone resin, and more preferably contains a silicone resin.

[0117] The above acrylic resin may be a polymer of a (meth)acrylic compound. When the above acrylic resin is obtained by polymerizing a (meth)acrylic compound, examples of the above (meth)acrylic compound include the above-mentioned non-crosslinkable (meth)acrylic compounds and the above-mentioned crosslinkable (meth)acrylic compounds. The above acrylic resin is preferably a room temperature curable resin.

[0118] The above (meth)acrylic compound can be polymerized by a known method to obtain the above acrylic resin. Examples of this method include suspension polymerization in the presence of a radical polymerization initiator.

[0119] Examples of the above acrylic resin include polymethyl methacrylate and polymethyl acrylate. From the viewpoints of further improving visibility, more effectively suppressing the generation of residual stress, and more effectively enhancing heat resistance, the above acrylic resin is preferably polymethyl methacrylate.

[0120] The above silicone resin may be an organopolysiloxane compound. The above organopolysiloxane compound may have a hydroxyl group at the terminal or a vinyl group at the terminal. The above silicone resin may be a polypropylene oxide having a methyldimethoxysilyl group. The above silicone resin is preferably a room-temperature curable resin.

[0121] The material of the above silicone resin may be the material of the above silicone particles described above. The above silicone resin can be obtained by polymerizing the material of the above silicone particles described above by a known method. Examples of this method include a method of performing a polymerization reaction using a silane compound to form a siloxane bond.

[0122] Examples of the above silicone resin include organopolysiloxane and polyorganosilsesquioxane. From the viewpoints of further improving visibility, more effectively suppressing the generation of residual stress, and more effectively enhancing heat resistance, the above silicone resin is preferably organopolysiloxane.

[0123] In addition to the above curable component and the above optical bonding particles, the above adhesive may contain a vinyl resin, a thermoplastic resin, a curable resin, a thermoplastic block copolymer, an elastomer, a solvent, etc. Only one of these components may be used, or two or more of them may be used in combination.

[0124] Examples of the vinyl resin include vinyl acetate resin, acrylic resin, and styrene resin. Examples of the thermoplastic resin include polyolefin resin, ethylene-vinyl acetate copolymer, and polyamide resin. Examples of the curable resin include epoxy resin, urethane resin, polyimide resin, and unsaturated polyester resin. The curable resin may be a room temperature curable resin, a heat curable resin, a photo curable resin, or a moisture curable resin. The curable resin may be used in combination with a curing agent. Examples of the thermoplastic block copolymer include styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated product of styrene-butadiene-styrene block copolymer, and hydrogenated product of styrene-isoprene-styrene block copolymer. Examples of the elastomer include styrene-butadiene copolymer rubber and acrylonitrile-styrene block copolymer rubber.

[0125] Examples of the solvent include water and organic solvents. Organic solvents are preferred because they can be easily removed. Examples of the organic solvent include alcohol compounds such as ethanol, ketone compounds such as acetone, methyl ethyl ketone, and cyclohexanone, aromatic hydrocarbon compounds such as toluene, xylene, and tetramethylbenzene, glycol ether compounds such as cellosolve, methyl cellosolve, butyl cellosolve, carbitol, methyl carbitol, butyl carbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol diethyl ether, and tripropylene glycol monomethyl ether, ester compounds such as ethyl acetate, butyl acetate, butyl lactate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and propylene carbonate, aliphatic hydrocarbon compounds such as octane and decane, and petroleum solvents such as petroleum ether and naphtha.

[0126] In addition to the above curable component and the above optical bonding particles, the above adhesive may contain various additives such as, for example, fillers, extenders, softeners, plasticizers, polymerization catalysts, curing catalysts, colorants, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, lubricants, antistatic agents, and flame retardants.

[0127] As a method for dispersing the above optical bonding particles in the above curable component, a conventionally known dispersion method can be used and is not particularly limited. Examples of the method for dispersing the above optical bonding particles in the above curable component include the following methods. After adding the above optical bonding particles to the above curable component, kneading and dispersing with a planetary mixer or the like. A method in which the above optical bonding particles are uniformly dispersed in water or an organic solvent using a homogenizer or the like, then added to the above curable component, and kneaded and dispersed with a planetary mixer or the like. A method in which the above curable component is diluted with water or an organic solvent or the like, then the above optical bonding particles are added, and kneaded and dispersed with a planetary mixer or the like.

[0128] In 100% by weight of the above adhesive, the content of the above optical bonding particles is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, preferably 80% by weight or less, more preferably 60% by weight or less, still more preferably 40% by weight or less, particularly preferably 20% by weight or less, and most preferably 10% by weight or less. When the content of the above optical bonding particles is equal to or more than the above lower limit and equal to or less than the above upper limit, the visibility can be further improved, and the gap can be controlled with higher precision. When the content of the above optical bonding particles is equal to or more than the above lower limit and equal to or less than the above upper limit, the above optical bonding particles can more effectively exhibit the function as a spacer.

[0129] In 100% by weight of the above adhesive, the content of the above curable component is preferably 10% by weight or more, more preferably 30% by weight or more, still more preferably 50% by weight or more, particularly preferably 70% by weight or more, and preferably 99.99% by weight or less, more preferably 99.9% by weight or less. When the content of the above curable component is equal to or higher than the above lower limit and equal to or lower than the above upper limit, the adhesive layer can be formed even better using the above adhesive, and the optical bonding particles can more effectively exhibit their function as a spacer.

[0130] (Display device) The display device according to the present invention includes a first member, an image display element as a second member, and an adhesive layer that adheres the first member and the second member. In the display device according to the present invention, the adhesive layer is a cured product of an adhesive containing the above-described optical bonding particles and a curable component. The adhesive layer is preferably formed by a curing agent of the above adhesive.

[0131] FIG. 5 is a cross-sectional view showing an example of a display device using optical bonding particles according to the first embodiment of the present invention.

[0132] The display device 21 shown in FIG. 5 includes a first member 22, an image display element as a second member 23, and an adhesive layer 24 that adheres the first member 22 and the second member 23. The adhesive layer 24 is a cured product of an adhesive containing optical bonding particles 1 and a curable component. Instead of the optical bonding particles 1, optical bonding particles 11 may be used.

[0133] Optical bonding particles 1 are present between the first member 22 and the second member 23, and a constant interval (gap) is maintained between the first member 22 and the second member 23. The thickness of the adhesive layer 24 is kept constant by the optical bonding particles 1, and the thickness of the adhesive layer 24 is ensured.

[0134] The thickness of the above-mentioned adhesive layer is preferably 30 μm or more, more preferably 50 μm or more, preferably 500 μm or less, and more preferably 200 μm or less. When the thickness of the above-mentioned adhesive layer is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the stress generated between the members can be more effectively relaxed, and the occurrence of cracks in the adhesive layer and the peeling of the adhesive layer can be more effectively prevented.

[0135] The manufacturing method of the above-mentioned display device is not particularly limited. As an example of the manufacturing method of the display device, a method of disposing the above-mentioned adhesive between the above-mentioned first member and the above-mentioned second member to obtain a laminate and then curing the above-mentioned adhesive can be mentioned.

[0136] The above-mentioned first member is preferably a transparent protective material. Examples of the material of the above-mentioned transparent protective material include glass and plastic. The above-mentioned transparent protective material is preferably a light-transmissive material. The above-mentioned transparent protective material is preferably a material that protects the surface of the above-mentioned image display element.

[0137] Examples of the above-mentioned display device include a liquid crystal display device and an in-vehicle display.

[0138] Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited only to the following Examples.

[0139] (Particles for Optical Bonding 1) A mixture of 30 parts by weight of both-end acrylic silicone oil (Shin-Etsu Chemical Co., Ltd.'s "X-22-2445") and 3.3 parts by weight of vinyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd.'s "KBM-1003") was prepared. A solution A was prepared by dissolving 0.5 part by weight of 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate (polymerization initiator, NOF Corporation's "Perocta O") in this mixture. Also, 0.8 part by weight of a 40% by weight aqueous solution of triethanolamine lauryl sulfate (emulsifier) and 80 parts by weight of a 5% by weight aqueous solution of polyvinyl alcohol (degree of polymerization: about 2000, saponification degree: 86.5 mol% - 89 mol%, Nippon Synthetic Chemical Industry Co., Ltd.'s "Gosenol GH-20") were mixed with 150 parts by weight of ion-exchanged water to prepare an aqueous solution B. After putting the above solution A into a separable flask installed in a warm bath, the above aqueous solution B was added. Then, it was confirmed that the particle size reached a predetermined value. Then, the temperature was raised to 90 °C and polymerization was carried out for 9 hours. After washing the total amount of the particles after polymerization with water by centrifugation and performing a classification operation, they were freeze-dried to obtain silicone particles A. In the obtained silicone particles A, the particle size was 101 μm and the CV value of the particle size was 10%.

[0140] Next, as the coated particles, silica particles A (Shin-Etsu Chemical Co., Ltd.'s "QSG-100") were prepared. The particle size of the prepared silica particles A was 110 nm.

[0141] 7.0 parts by weight of the obtained silicone particles A and 88.5 parts by weight of distilled water were put into a 500 ml separable flask installed in a warm bath, and while irradiating with ultrasonic waves, 0.2 part by weight of silica particles A previously dispersed in 4.0 parts by weight of methanol was gently dropped. Then, it was stirred at room temperature for 6 hours to coat the surface of the silicone particles with silica particles. The total amount of the treated particles was washed with water by centrifugation to obtain optical bonding particles 1.

[0142] (Optical bonding particles 2) 30 parts by weight of both-end acrylic silicone oil (“X-22-2445” manufactured by Shin-Etsu Chemical Co., Ltd.) was used to prepare a solution C in which 0.5 part by weight of 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate (polymerization initiator, “Peroct O” manufactured by NOF Corporation) was dissolved. Also, 0.8 part by weight of a 40% by weight aqueous solution of triethanolamine lauryl sulfate (emulsifier) and 80 parts by weight of a 5% by weight aqueous solution of polyvinyl alcohol (degree of polymerization: about 2000, saponification degree: 86.5 mol% - 89 mol%, “Gosenol GH-20” manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) were mixed with 150 parts by weight of ion-exchanged water to prepare an aqueous solution B. The solution C was placed in a separable flask installed in a warm bath, and then the aqueous solution B was added. After that, it was confirmed that the particle size reached a predetermined value. Then, the temperature was raised to 90 °C and polymerization was carried out for 9 hours. After washing the total amount of the polymerized particles with water by centrifugation and performing a classification operation, they were freeze-dried to obtain silicone particles B. In the obtained silicone particles B, the particle size was 102 μm and the CV value of the particle size was 11%.

[0143] Next, as the coated particles, silica particles A (“QSG-100” manufactured by Shin-Etsu Chemical Co., Ltd.) were prepared. The particle size of the prepared silica particles A was 110 nm.

[0144] 7.0 parts by weight of the obtained silicone particles B and 88.5 parts by weight of distilled water were placed in a 500 ml separable flask installed in a warm bath, and while irradiating with ultrasonic waves, 0.2 part by weight of silica particles A previously dispersed in 4.0 parts by weight of methanol was gently dropped. Then, it was stirred at room temperature for 6 hours to coat the surface of the silicone particles with silica particles. The total amount of the treated particles was washed with water by centrifugation to obtain particles 2 for optical bonding.

[0145] (Particles 3 for optical bonding) Silicone particles B obtained during the production of the above optical bonding particles 2 were prepared. Using the prepared silicone particles B, optical bonding particles 3 were obtained in the same manner as the production of the above optical bonding particles 2, except that silica particles B ("QSG-30" manufactured by Shin-Etsu Chemical Co., Ltd.) were used instead of silica particles A as the coating particles.

[0146] (Optical bonding particles 4) Silicone particles A obtained during the production of the above optical bonding particles 1 were prepared. 7 parts by weight of the prepared silicone particles A, 85 parts by weight of distilled water, 7 parts by weight of methanol, and 0.2 parts by weight of 28% aqueous ammonia were placed in a 500 ml separable flask installed in a warm bath, and the temperature was raised to 80 °C with stirring and reacted for 1 hour to promote the hydrolysis of the silanol groups introduced on the surface to form a silica coating layer. The obtained particles were washed with water by centrifugation to obtain optical bonding particles 4.

[0147] (Optical bonding particles 5) Silicone particles B obtained during the production of the above optical bonding particles 2 were prepared. Using the prepared silicone particles B, optical bonding particles 5 were obtained in the same manner as the production of the above optical bonding particles 2, except that silica particles C ("Sea Hostar KE-P50" manufactured by Nippon Shokubai Co., Ltd.) were used instead of silica particles A as the coating particles.

[0148] (Optical bonding particles 6) A mixture of 30 parts by weight of both-end acrylic silicone oil ("X-22-2445" manufactured by Shin-Etsu Chemical Co., Ltd.) and 3.3 parts by weight of vinyltrimethoxysilane ("KBM-1003" manufactured by Shin-Etsu Chemical Co., Ltd.) was prepared. To this mixture, 0.5 part by weight of 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate (polymerization initiator, "Peroct O" manufactured by NOF Corporation) and 5 parts by weight of silica particles A ("QSG-100" manufactured by Shin-Etsu Chemical Co., Ltd., particle diameter 110 nm) were dispersed to obtain a dispersion D. Also, 0.8 part by weight of a 40% by weight aqueous solution of triethanolamine lauryl sulfate (emulsifier) and 80 parts by weight of a 5% by weight aqueous solution of polyvinyl alcohol (degree of polymerization: about 2000, saponification degree: 86.5 mol% to 89 mol%, "Gosenol GH-20" manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) were mixed with 150 parts by weight of ion-exchanged water to prepare an aqueous solution B. The dispersion D was placed in a separable flask installed in a warm bath, and then the aqueous solution B was added. Thereafter, it was confirmed that the particle size had reached a predetermined value. Thereafter, the temperature was raised to 90 °C and polymerization was carried out for 9 hours. After washing the total amount of the polymerized particles with water by centrifugation and performing a classification operation, they were freeze-dried to obtain silicone particles C. In the obtained silicone particles C, the particle size was 80 μm and the CV value of the particle size was 10%.

[0149] Silicone particles C and, as coated particles, silica particles D ("QSG-100" manufactured by Shin-Etsu Chemical Co., Ltd., particle diameter 110 nm) were prepared. A dispersion E was prepared by dispersing 0.2 part by weight of silica particles D in 4.0 parts by weight of methanol.

[0150] 7.0 parts by weight of silicone particles C and 88.5 parts by weight of distilled water were placed in a 500 ml separable flask installed in a warm bath, and while irradiating with ultrasonic waves, the dispersion E was gently dropped. Thereafter, it was stirred at room temperature for 6 hours to coat the surface of the silicone particles C with silica particles D. The total amount of the treated particles was washed with water by centrifugation to obtain particles 6 for optical bonding.

[0151] (Particles 7 for optical bonding) Silicone particles C were prepared. 7 parts by weight of silicone particles C, 85 parts by weight of distilled water, 7 parts by weight of methanol, and 0.2 parts by weight of 28% aqueous ammonia were placed in a 500 ml separable flask installed in a warm bath, and the temperature was raised to 80 °C with stirring and reacted for 1 hour to promote the hydrolysis of the silanol groups introduced on the surface to form a silica coating layer. The obtained particles were washed with water by centrifugation to obtain optical bonding particles 7.

[0152] (Optical bonding particles A) Silicone particles B obtained in the preparation of the above optical bonding particles 2 were prepared. 7.0 parts by weight of silicone particles B, 0.6 parts by weight of hexadecyltrimethylammonium bromide, 240 parts by weight of distilled water, and 120 parts by weight of methanol were placed in a 500 ml separable flask installed in a warm bath. After stirring at 40 °C for 1 hour, 2.1 parts by weight of divinylbenzene and 0.35 parts by weight of styrene were added, and the temperature was raised to 75 °C and stirred for 0.5 hour. Then, 0.28 parts by weight of 2,2'-azobis(isobutyric acid) dimethyl was added and stirred and reacted for 8 hours. The total amount of the polymerized particles was washed with water by centrifugation to obtain optical bonding particles A.

[0153] (Optical bonding particles B) Silicone particles B obtained in the preparation of the above optical bonding particles 2 were prepared. 7.0 parts by weight of silicone particles B, 0.6 parts by weight of hexadecyltrimethylammonium bromide, 240 parts by weight of distilled water, and 120 parts by weight of methanol were placed in a 500 ml separable flask installed in a warm bath. After stirring at 40 °C for 1 hour, 0.2 parts by weight of polytetramethylene glycol dimethacrylate and 2.2 parts by weight of methyl methacrylate were added, and the temperature was raised to 75 °C and stirred for 0.5 hour. Then, 0.28 parts by weight of 2,2'-azobis(isobutyric acid) dimethyl was added and stirred and reacted for 8 hours. The total amount of the polymerized particles was washed with water by centrifugation to obtain optical bonding particles B.

[0154] (Example 1) (Preparation of Adhesive) To silicone adhesive (“LUMISIL 102” manufactured by Asahi Kasei Wacker Silicone), optical bonding particles 1 were added so that the content in the resulting adhesive would be 2% by weight, and the mixture was stirred with a planetary stirrer and uniformly dispersed to prepare an adhesive.

[0155] (Fabrication of Display Device) The obtained adhesive was filled into a syringe, and using a dispenser, the adhesive was applied onto the image display element so that the thickness would be 120 μm to form an adhesive layer. Then, a transparent protective material was laminated on the formed adhesive layer to obtain a laminate. The adhesive layer of the obtained laminate was cured under the conditions of 23°C for 1 hour to bond the image display element and the transparent protective material, thereby obtaining a display device.

[0156] (Example 2) A display device was obtained in the same manner as in Example 1, except that optical bonding particles 2 were used instead of optical bonding particles 1 during the preparation of the adhesive.

[0157] (Example 3) A display device was obtained in the same manner as in Example 1, except that optical bonding particles 3 were used instead of optical bonding particles 1 during the preparation of the adhesive.

[0158] (Example 4) A display device was obtained in the same manner as in Example 1, except that optical bonding particles 4 were used instead of optical bonding particles 1 during the preparation of the adhesive.

[0159] (Example 5) A display device was obtained in the same manner as in Example 1, except that optical bonding particles 5 were used instead of optical bonding particles 1 during the preparation of the adhesive.

[0160] (Example 6) A display device was obtained in the same manner as in Example 1, except that optical bonding particles 6 were used instead of optical bonding particles 1 when preparing the adhesive.

[0161] (Example 7) A display device was obtained in the same manner as in Example 1, except that optical bonding particles 7 were used instead of optical bonding particles 1 when preparing the adhesive.

[0162] (Comparative Example 1) A display device was obtained in the same manner as in Example 1, except that optical bonding particles A were used instead of optical bonding particles 1 when preparing the adhesive.

[0163] (Comparative Example 2) A display device was obtained in the same manner as in Example 1, except that optical bonding particles B were used instead of optical bonding particles 1 when preparing the adhesive.

[0164] (Evaluation) (1) Particle diameter of silicone particles and particle diameter of optical bonding particles Regarding the obtained silicone particles and optical bonding particles, the particle diameters of about 100,000 optical bonding particles or silicone particles were measured using a particle size distribution measuring device ("Multisizer4" manufactured by Beckman Coulter), and the average value was calculated.

[0165] (2) Particle diameter of coated particles and thickness of coating layer When the obtained particles for optical bonding include coated particles, the particle diameter of the coated particles was measured by observing the cross-section of the particles for optical bonding using a transmission electron microscope (TEM) ("JEM2100" manufactured by JEOL Ltd.). The particle diameter of the coated particles was calculated as the average value of the particle diameters of any 10 coated particles as the particle diameter of the coated particles of one particle for optical bonding, and for any 10 particles for optical bonding, these average values were calculated and obtained.

[0166] When the obtained particles for optical bonding include a coating layer, the thickness of the coating layer was measured by observing the cross-section of the particles for optical bonding using a transmission electron microscope (TEM) ("JEM2100" manufactured by JEOL Ltd.). The thickness of the coating layer was calculated as the average value of the thicknesses at 5 locations of any coating layer as the thickness of the coating layer of one particle for optical bonding, and for any 10 particles for optical bonding, these average values were calculated and obtained.

[0167] Also, from the obtained results, the ratio of the particle diameter of the coated particles or the thickness of the coating layer to the particle diameter of the silicone particles was calculated.

[0168] (3) Refractive index For the obtained silicone particles, coated particles, and particles for optical bonding, the refractive index (R1) of the silicone particles, the refractive index (R2) of the coated particles, and the refractive index (R3) of the particles for optical bonding were measured by a method conforming to JIS K7142:2014 Plastics - Method for determining refractive index - Method B. The refractive index (R2) of the coating layer was measured by the above-described method after synthesis and drying in the absence of silicone particles. From the obtained results, the absolute value of the difference between the refractive index (R1) of the silicone particles and the refractive index (R2) of the coated particles or the refractive index (R2) of the coating layer was calculated.

[0169] Also, a silicone adhesive (LUMISIL 102 manufactured by Asahi Kasei Wacker Silicone Co., Ltd.), which is a curable component of the adhesive, was prepared. For the prepared curable component, the refractive index (R4) of the cured product obtained by curing the curable component under the conditions of 23°C and 1 hour was measured by the method described above. From the obtained results, the absolute value of the difference between the refractive index (R4) of the cured product obtained by curing the curable component under the conditions of 23°C and 1 hour and the refractive index (R1) of the silicone particles, and the absolute value of the difference between the refractive index (R4) of the cured product obtained by curing the curable component under the conditions of 23°C and 1 hour and the refractive index (R2) of the coated particles or the refractive index (R2) of the coating layer were calculated.

[0170] (4) Transmittance For the obtained adhesive, the transmittance (T1) at a wavelength of 650 nm of the cured product obtained by curing the adhesive under the conditions of 23°C and 1 hour was measured by the method described above. Also, a silicone adhesive (LUMISIL 102 manufactured by Asahi Kasei Wacker Silicone Co., Ltd.), which is a curable component of the adhesive, was prepared. For the prepared curable component, the transmittance (T2) at a wavelength of 650 nm of the cured product obtained by curing the curable component under the conditions of 23°C and 1 hour was measured by the method described above. From the obtained results, the ratio (T1 / T2) of the transmittance (T1) at a wavelength of 650 nm of the cured product obtained by curing the adhesive under the conditions of 23°C and 1 hour to the transmittance (T2) at a wavelength of 650 nm of the cured product obtained by curing the curable component under the conditions of 23°C and 1 hour was calculated.

[0171] (5) Coating rate For the obtained optical bonding particles, the area (coating rate) of the part with coated particles or a coating layer in 100% of the total surface area of the silicone particles was measured. The above coating rate was measured as follows.

[0172] Method for measuring coating rate: Observation was performed with an electron microscope, and the projected area S1 per one optical bonding particle obtained and the circular converted area S2 of the uncoated part were calculated using image analysis software, and the coating rate was obtained by the following formula.

[0173] Coating rate (%) = (S1 - S2) / S1 × 100

[0174] (6) Gap controllability For the 10 obtained display devices, the thickness of the adhesive layer was measured using a stereomicroscope (“SMZ-10” manufactured by Nikon Corporation), and the average thickness of the adhesive layer in the 10 display devices was calculated. The gap controllability was determined according to the following criteria.

[0175] [Criteria for judging gap controllability] ○○: The average thickness of the adhesive layer is 108 μm or more and 132 μm or less ○: The average thickness of the adhesive layer is 96 μm or more and less than 108 μm, or exceeds 132 μm and is 150 μm or less ×: The average thickness of the adhesive layer is less than 96 μm or exceeds 150 μm

[0176] (7) Visibility For the obtained display devices, it was visually evaluated whether reflection in outdoor light occurred. The visibility was determined according to the following criteria.

[0177] [Criteria for judging visibility] ○○: Almost no reflection in outdoor light occurs ○: Reflection in outdoor light occurs slightly to the extent that there is no problem in actual use ×: Reflection in outdoor light occurs

[0178] (8) Stress relaxation characteristics Using the obtained display device, a thermal shock tester of the liquid bath type (“TSB-51” manufactured by ESPEC Corporation) was used, and after holding at -40°C for 5 minutes, the temperature was raised to 150°C, and after holding at 150°C for 5 minutes, a thermal cycle test was carried out with the process of cooling to -40°C as one cycle. After 500 cycles, the display device was taken out.

[0179] The display device was observed with a stereomicroscope (“SMZ-10” manufactured by Nikon Corporation). It was observed whether cracks occurred in the adhesive layer or whether peeling of the adhesive layer occurred. The stress relaxation characteristics were determined according to the following criteria.

[0180] [Criterion for Stress Relaxation Characteristics] ○○: No crack has occurred in the adhesive layer and no peeling of the adhesive layer has occurred. ○: To such an extent that there is no problem in actual use, slight cracks have occurred in the adhesive layer or slight peeling of the adhesive layer has occurred. ×: Cracks have occurred in the adhesive layer or peeling of the adhesive layer has occurred.

[0181] The results are shown in Tables 1 and 2 below.

[0182] [Table 1]

[0183] [Table 2] [Explanation of Reference Signs]

[0184] 1, 1A, 11, 11A... Particles for optical bonding 2... Silicon particles 3... Coated particles 4... Coating layer 5... Inorganic oxide particles 21... Display device 22... First member 23... Second member (image display element) 24... Adhesive layer

Claims

1. Comprising silicone particles and coating particles or a coating layer disposed on the surface of the silicone particles, Optical bonding particles, wherein the absolute value of the difference between the refractive index of the silicone particles and the refractive index of the coating particles or the refractive index of the coating layer is 0.03 or less.

2. The optical bonding particles according to claim 1, wherein the material of the coating particles or the material of the coating layer is silica or silicone resin.

3. The optical bonding particles according to claim 1 or 2, wherein the area of the portion with the coating particles or the coating layer in 100% of the total surface area of the silicone particles is 80% or more.

4. The optical bonding particles according to any one of claims 1 to 3, wherein the refractive index of the optical bonding particles is 1.40 or more and 1.43 or less.

5. The silicone particles comprise a plurality of inorganic oxide particles, The optical bonding particles according to any one of claims 1 to 4, wherein at least a part of the inorganic oxide particles is present inside the silicone particles.

6. An adhesive comprising the optical bonding particles according to any one of claims 1 to 5 and a curable component.

7. The adhesive according to claim 6, wherein the absolute value of the difference between the refractive index of the cured product obtained by curing the curable component under the conditions of 23 °C for 1 hour and the refractive index of the silicone particles is 0.05 or less.

8. The adhesive according to claim 6 or 7, wherein the absolute value of the difference between the refractive index of the cured product obtained by curing the curable component under the conditions of 23 °C for 1 hour and the refractive index of the coating particles or the refractive index of the coating layer is 0.03 or less.

9. The adhesive according to any one of claims 6 to 8, wherein the ratio of the transmittance at a wavelength of 650 nm of the cured product obtained by curing the adhesive under the conditions of 23 °C for 1 hour to the transmittance at a wavelength of 650 nm of the cured product obtained by curing the curable component under the conditions of 23 °C for 1 hour is 0.94 or more.

10. A first member, An image display element as a second member, And an adhesive layer bonding the first member and the second member, A display device, wherein the adhesive layer is a cured product of an adhesive comprising the optical bonding particles according to any one of claims 1 to 5 and a curable component.

11. The display device according to claim 10, wherein the first member is a transparent protective material.

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