CN112442325A

CN112442325A - Adhesive sheet and optical laminate

Info

Publication number: CN112442325A
Application number: CN202010876312.4A
Authority: CN
Inventors: 福岛裕贵; 小鲭翔; 高桥洋一
Original assignee: Lintec Corp
Current assignee: Lintec Corp
Priority date: 2019-09-05
Filing date: 2020-08-25
Publication date: 2021-03-05
Also published as: JP2021038365A; JP7340997B2; TW202111053A; KR20210029081A

Abstract

The invention provides an adhesive sheet and an optical laminate, which have excellent light diffusion uniformity and excellent step following performance. The adhesive sheet (1) has a composite adhesive layer (11), wherein the composite adhesive layer (11) comprises a light diffusion adhesive layer (111) containing light diffusion particles and a transparent adhesive layer (112) not containing the light diffusion particles, and at least one of the light diffusion adhesive layer (111) and the transparent adhesive layer (112) is composed of an active energy ray-curable adhesive.

Description

Adhesive sheet and optical laminate

Technical Field

The present invention relates to an adhesive sheet having light diffusion properties and an optical laminate obtained using the adhesive sheet.

Background

In recent years, various mobile electronic devices such as smartphones and tablet terminals include a display using a display module including a liquid crystal element, a light emitting diode (LED element), an organic electroluminescence (organic EL) element, and the like, and the display is often a touch panel.

In the display described above, for example, an adhesive may be used to bond the display module to a protective panel for protecting the display module, or to bond the display module to a backlight system for illuminating the display module.

Here, when the protective panel and the display module are bonded to each other with an adhesive, a frame-shaped printed layer may be present as a step difference on the display module side of the protective panel. In this case, if the adhesive layer does not follow the step, the adhesive layer floats up in the vicinity of the step, and reflection loss of light is generated. Therefore, the adhesive agent layer is required to have step following properties. In addition, the step following property may be required for other parts of the display.

In order to solve the above-mentioned problems, patent document 1 discloses that the shear storage modulus (G') at 25 ℃ and 1Hz is 1.0X 10⁵Pa or less and a gel fraction of 40% or more. The adhesive layer reduces the storage modulus at room temperature, thereby improving the step following property.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2010-97070

Disclosure of Invention

Technical problem to be solved by the invention

On the other hand, in a display using a backlight system, there is a problem that brightness unevenness (luminance unevenness) may occur due to a light source of the backlight. To solve this problem, a light diffusion plate is provided.

Here, from the viewpoint of reducing the number of components of the display and reducing the thickness and cost, or from the viewpoint of enhancing the light diffusion performance, it is conceivable to use an adhesive layer having a light diffusion property in place of the light diffusion plate or in combination with the light diffusion plate. The light-diffusing adhesive layer can be obtained by adding light-diffusing fine particles to the adhesive layer to increase the haze value. However, the higher the haze value of such a light-diffusing adhesive layer, the higher the storage modulus becomes, and at the same time, the adhesive force decreases. Therefore, the light-diffusing adhesive layer may have a problem of a decrease in step following property. Further, there may be a problem that the uniformity of light diffusion is lowered due to a step difference.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an adhesive sheet and an optical laminate which are excellent in uniformity of light diffusion and excellent in step following property.

Means for solving the problems

In order to achieve the above object, the first aspect of the present invention provides an adhesive sheet comprising a composite adhesive layer comprising a light-diffusing adhesive layer containing light-diffusing fine particles and a transparent adhesive layer containing no light-diffusing fine particles, wherein at least one of the light-diffusing adhesive layer and the transparent adhesive layer is composed of an active energy ray-curable adhesive (invention 1).

The pressure-sensitive adhesive sheet of the invention (invention 1) can be attached to an adherend having a step by bringing the transparent pressure-sensitive adhesive layer containing no light diffusion fine particles into contact with the adherend and attaching the transparent pressure-sensitive adhesive layer to the adherend. This can suppress the light diffusion adhesive layer from being compressed or deformed due to the step difference of the adherend, and can maintain the uniformity of light diffusion in the light diffusion adhesive layer and the composite adhesive layer. Further, since the transparent adhesive layer can maintain flexibility because the elastic modulus is lower than that of the light diffusing adhesive layer, the composite adhesive layer is likely to follow the level difference of the adherend by bringing the transparent adhesive layer into contact with the adherend having the level difference and attaching the adherend. Therefore, the step following property in the initial stage is excellent, and the step following property under high temperature and high humidity conditions after the active energy ray curing is excellent.

In the invention (invention 1), the haze value of the composite adhesive layer is preferably 40% or more and 99% or less (invention 2).

In the above inventions (inventions 1 to 2), the composite adhesive layer preferably has a storage modulus G1 of 0.001MPa to 0.2MPa at 23 ℃ (invention 3).

In the above inventions (inventions 1 to 3), it is preferable that the composite adhesive layer has a storage modulus G2 of 0.08MPa to 10MPa at 23 ℃ after irradiation with an active energy ray (invention 4).

In the above-described inventions (inventions 1 to 4), it is preferable that the storage modulus change rate Δ G' as a ratio of the storage modulus G2 at 23 ℃ to the storage modulus G1 at 23 ℃ of the composite adhesive layer after irradiation with an active energy ray is 1.1 or more and 100 or less (invention 5).

In the above inventions (inventions 1 to 5), the adhesive force of the transparent adhesive layer side of the adhesive sheet to soda-lime glass is preferably 20N/25mm or more and 80N/25mm or less (invention 6).

In the above inventions (inventions 1 to 6), it is preferable that the adhesive sheet has an adhesive force to soda-lime glass of 20N/25mm or more and 80N/25mm or less on the transparent adhesive layer side after irradiation with active energy rays (invention 7).

In the above inventions (inventions 1 to 7), the adhesive force of the light diffusing adhesive layer side in the adhesive sheet to soda lime glass is preferably 1N/25mm or more and 60N/25mm or less (invention 8).

In the above-mentioned inventions (inventions 1 to 8), it is preferable that the adhesive sheet has an adhesive force to soda-lime glass of 10N/25mm or more and 60N/25mm or less on the light-diffusing adhesive layer side after irradiation with active energy rays (invention 9).

In the above inventions (inventions 1 to 9), the thickness of the composite adhesive layer is preferably 20 μm or more and 1000 μm or less (invention 10).

In the above inventions (inventions 1 to 10), the thickness of the light diffusing adhesive layer is preferably 10 μm or more and 500 μm or less (invention 11).

In the above inventions (inventions 1 to 11), the thickness of the transparent adhesive agent layer is preferably 10 μm or more and 500 μm or less (invention 12).

In the above inventions (inventions 1 to 12), it is preferable that the adhesive sheet includes two release sheets, and the composite adhesive layer is sandwiched between the release sheets so as to be in contact with release surfaces of the two release sheets (invention 13).

Secondly, the present invention provides an optical laminate comprising one optical member, another optical member, and a cured composite adhesive layer which bonds the one optical member and the another optical member to each other, wherein the cured composite adhesive layer is a layer obtained by curing the composite adhesive layer of the pressure-sensitive adhesive sheet (inventions 1 to 13) with an active energy ray (invention 14).

In the above invention (invention 14), it is preferable that at least one of the one optical member and the other optical member has an unevenness on a surface on a side to be bonded with the cured composite adhesive layer, and the transparent adhesive layer of the cured composite adhesive layer is in contact with the unevenness (invention 15).

Effects of the invention

The adhesive sheet of the present invention has sufficiently uniform light diffusion properties and is excellent in step following properties. The optical laminate of the present invention is excellent in step following property and luminance unevenness suppression property.

Drawings

Fig. 1 is a sectional view of an adhesive sheet according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view of an optical stack according to an embodiment of the present invention.

Figure 3 is a cross-sectional view of an optical stack according to another embodiment of the present invention.

FIG. 4 is a sectional view of an adhesive sheet according to another embodiment of the present invention.

Description of the reference numerals

1. 1A: an adhesive sheet; 11: a composite adhesive layer; 111: a light diffusing adhesive layer; 112: a transparent adhesive layer; 12a, 12 b: a release sheet; 2A, 2B: an optical laminate; 11': a cured composite adhesive layer; 21: a first optical member; 22: a second optical member; 23: printing layer; 30: a backlight source; 31: a substrate; 32: a light emitter; 40: a display unit.

Detailed Description

Hereinafter, embodiments of the present invention will be described.

[ adhesive sheet ]

The adhesive sheet according to one embodiment of the present invention includes a composite adhesive layer including a light diffusion adhesive layer containing light diffusion particles and a transparent adhesive layer containing no light diffusion particles. At least one of the light diffusing adhesive layer and the transparent adhesive layer is made of an active energy ray curable adhesive. In the present specification, the "active energy ray-curable adhesive" refers to an adhesive which is cured by irradiation with an active energy ray. Therefore, the "active energy ray-curable adhesive" does not include an adhesive which has been cured by the previous irradiation with an active energy ray to such an extent that the curing cannot be further performed.

In the composite adhesive layer, the transparent adhesive layer may be present in two or more layers. In this case, at least one transparent adhesive layer is preferably located on a surface that is in contact with an adherend, particularly an adherend having a step (unevenness). In addition, the light diffusing adhesive layer may be present in two or more layers, but at least one outermost layer in the composite adhesive layer is a transparent adhesive layer. In addition, from the viewpoint of controlling the haze value of the composite adhesive layer, it is preferable that the light diffusing adhesive layer is one layer.

When the light diffusion adhesive layer containing the light diffusion fine particles is brought into contact with and follows a step (unevenness) of an adherend, the light diffusion adhesive layer is compressed or deformed by the step of the adherend. This causes the light diffusion adhesive layer to have uneven density of light diffusion fine particles, and the uniformity of light diffusion is impaired. The pressure-sensitive adhesive sheet of the present embodiment can attach a transparent pressure-sensitive adhesive layer containing no light diffusion fine particles to an adherend having a level difference by bringing the layer into contact with the adherend. This can suppress the light diffusion adhesive layer from being compressed or deformed due to the step difference of the adherend, and can maintain the uniformity of light diffusion in the light diffusion adhesive layer and the composite adhesive layer. An optical laminate (display) having excellent brightness unevenness suppression can be obtained from a composite adhesive layer (a cured composite adhesive layer) having uniform light diffusion properties.

Further, since the light diffusing adhesive layer containing the light diffusing fine particles tends to have a low flexibility because of a high elastic modulus, the followability to an adherend having a step (unevenness) tends to be low. The pressure-sensitive adhesive sheet of the present embodiment can attach a transparent pressure-sensitive adhesive layer containing no light diffusion fine particles to an adherend having a level difference by bringing the layer into contact with the adherend. Thus, the composite adhesive layer can easily follow the step difference, and can suppress the generation of bubbles, floating, and the like in the vicinity of the step difference. Then, after a member (e.g., a glass plate) having the level difference is bonded to another member (e.g., a glass plate) by the composite adhesive layer, the composite adhesive layer is cured by irradiation with an active energy ray to obtain a cured composite adhesive layer. In this way, a laminate in which 2 members were bonded to each other by the cured composite adhesive layer was obtained. The laminate can suppress the generation of bubbles, floating, peeling, and the like in the vicinity of a step even when left to stand under high-temperature and high-humidity conditions, for example, 85 ℃ and 85% RH for 72 hours. That is, the adhesive sheet of the present embodiment is excellent in initial step following property and step following property under high-temperature and high-humidity conditions.

Further, since the light diffusion adhesive layer containing light diffusion fine particles is liable to have a reduced adhesive force, when it is attached to a member (for example, a plastic plate) which outgases at a high temperature or with time, foaming such as bubbling, floating, peeling, and the like is liable to occur. The adhesive sheet of the present embodiment can attach a transparent adhesive layer having a high adhesive strength and containing no light diffusion fine particles to a member which is to be degassed by contacting the member. In the adhesive sheet of the present embodiment, either one of the transparent adhesive layer and the light diffusing adhesive layer is preferably composed of an active energy ray-curable adhesive, and further, it is more preferable that the entire composite adhesive layer is made active energy ray-curable. In this case, the composite adhesive layer is attached to an adherend, and then cured by irradiation with an active energy ray to obtain a cured composite adhesive layer, whereby the cured composite adhesive layer is excellent in blister resistance. For example, a member (for example, a plastic plate) which is to be degassed by the composite adhesive layer is bonded to another member (for example, a glass plate), and then the composite adhesive layer is cured by irradiation with an active energy ray to obtain a cured composite adhesive layer. In this way, a laminate in which two members are bonded to each other with the cured composite adhesive layer can be obtained. This laminate can suppress the occurrence of blisters such as bubbles, floating, and peeling at the interface between the composite adhesive layer and the adherend (particularly, plastic plate) after curing, even when left to stand under high-temperature and high-humidity conditions, for example, 85 ℃ and 85% RH for 72 hours.

Here, when a thick adhesive layer is formed using a solvent-based material, a plurality of adhesive layers are generally stacked to form a thick adhesive layer. When a plurality of light-diffusing adhesive layers are laminated to obtain an adhesive layer having a desired haze value, particularly a high-haze-value adhesive layer, if the haze value of each light-diffusing adhesive layer deviates from the target haze value, the deviation from the target haze value increases when the plurality of light-diffusing adhesive layers are laminated, and a adhesive layer having a desired haze value cannot be obtained. Therefore, there is a problem that the manufacturing yield is easily lowered. In contrast, by using the light diffusion adhesive layer and the transparent adhesive layer as in the adhesive sheet of the present embodiment, the cumulative thickness of the transparent adhesive layer can be utilized while reducing the number of layers (preferably, making one layer) of the light diffusion adhesive layer. This makes it easy to obtain a stable adhesive layer (composite adhesive layer) having a desired haze value, and improves product stability.

The haze value (value measured according to JIS K7136: 2000) of the composite adhesive layer in the adhesive sheet of the present embodiment is preferably 40% or more, more preferably 50% or more, particularly preferably 60% or more, and further preferably 80% or more. This makes it easy to obtain good light diffusion properties and good luminance unevenness prevention properties. On the other hand, from the viewpoint of visibility of the optical laminate (display), the haze value of the composite adhesive layer is preferably 99% or less, more preferably 98% or less, particularly preferably 97% or less, and further preferably 96% or less. In addition, the haze value of the composite adhesive layer hardly changes before and after the irradiation with the active energy ray.

The lower limit of the total light transmittance (measured according to JIS K7361-1: 1997) of the composite adhesive layer in the adhesive sheet of the present embodiment is preferably 70% or more, particularly preferably 90% or more, and more preferably 99% or more. When the total light transmittance of the composite adhesive layer is set to the above value, the visibility of the optical laminate (display) becomes good. On the other hand, the upper limit of the total light transmittance of the composite adhesive layer is not particularly limited, but is usually 100% or less. In addition, the total light transmittance of the composite adhesive layer hardly changes before and after irradiation with active energy rays.

From the viewpoint of step difference following properties under high-temperature and high-humidity conditions, the storage modulus G1 at 23 ℃ of the composite adhesive layer of the adhesive sheet of the present embodiment is preferably 0.001MPa or more, more preferably 0.01MPa or more, particularly preferably 0.02MPa or more, and further preferably 0.04MPa or more. The storage modulus G1 is preferably 0.2MPa or less, more preferably 0.1MPa or less, particularly preferably 0.09MPa or less, and further preferably 0.08MPa or less. This makes the initial step following property more excellent. The storage modulus in this specification is a value measured by a torsional shear method (ね manufactured by りせ one turn at one turn) at a measurement frequency of 1Hz in accordance with JIS K7244-6. Specifically, the following test examples are shown.

The composite adhesive layer of the adhesive sheet of the present embodiment has a storage modulus G2 at 23 ℃ after irradiation with active energy rays of preferably 0.08MPa or more, more preferably 0.09MPa or more, particularly preferably 0.10MPa or more, and further preferably 0.11MPa or more. This makes the step following property under high-temperature and high-humidity conditions more excellent. The storage modulus G2 is preferably 10MPa or less, more preferably 5MPa or less, particularly preferably 1MPa or less, and further preferably 0.2MPa or less. This exhibits good adhesive force, and the adhesiveness to an adherend becomes further excellent. The phrase "after irradiation with an active energy ray" means after irradiation with an active energy ray at an irradiation dose equivalent to the irradiation dose of an active energy ray when an active energy ray-curable adhesive layer (composite adhesive layer) is incorporated into a product. In the present specification, the irradiation dose of the active energy ray shown in test example 1 is taken as a reference, but the present invention is not limited thereto.

The storage modulus change rate Δ G' which is the ratio of the storage modulus G2 to the storage modulus G1 (storage modulus G2/storage modulus G1) is preferably 1.1 or more, more preferably 1.2 or more, particularly preferably 1.4 or more, and further preferably 1.8 or more. The storage modulus change rate Δ G' is preferably 100 or less, more preferably 10 or less, particularly preferably 5 or less, and further preferably 2.5 or less. When the storage modulus change rate Δ G' is in the above range, the initial level difference following property and the level difference following property under high-temperature and high-humidity conditions can be further improved.

The light-diffusing adhesive layer of the present embodiment has a storage modulus GD1 at 23 ℃ of preferably 0.001MPa or more, more preferably 0.01MPa or more, particularly preferably 0.02MPa or more, and further preferably 0.04MPa or more, from the viewpoint of stably retaining the light-diffusing fine particles in the light-diffusing adhesive layer. The storage modulus GD1 is preferably 0.2MPa or less, more preferably 0.16MPa or less, particularly preferably 0.12MPa or less, and further preferably 0.09MPa or less. This ensures good adhesion to the transparent adhesive layer.

When the light diffusing adhesive layer is formed of an active energy ray-curable adhesive, the storage modulus GD2 at 23 ℃ after irradiation with an active energy ray in the light diffusing adhesive layer is preferably 0.08MPa or more, more preferably 0.10MPa or more, particularly preferably 0.12MPa or more, and further preferably 0.15MPa or more, from the viewpoint of blister resistance. The storage modulus GD2 is preferably 10MPa or less, more preferably 5MPa or less, particularly preferably 1MPa or less, and further preferably 0.3MPa or less. This exhibits good adhesive force, and the adhesiveness to an adherend becomes further excellent.

The storage modulus change rate Δ GD, which is the ratio of the storage modulus GD2 to the storage modulus GD1 (storage modulus GD 2/storage modulus GD1), is preferably 1.1 or more, more preferably 1.4 or more, particularly preferably 1.8 or more, and further preferably 2.1 or more. The storage modulus change rate Δ GD is preferably 100 or less, more preferably 10 or less, particularly preferably 5 or less, and further preferably 3 or less. By setting the storage modulus change rate Δ GD within the above range, the balance between the maintenance of the adhesive force after curing and the blistering resistance can be favorably achieved.

From the viewpoint of step following property under high-temperature and high-humidity conditions, the storage modulus GT1 at 23 ℃ of the transparent adhesive layer of the present embodiment is preferably 0.001MPa or more, more preferably 0.01MPa or more, particularly preferably 0.02MPa or more, and further preferably 0.04MPa or more. The storage modulus GT1 is preferably 0.2MPa or less, more preferably 0.1MPa or less, particularly preferably 0.09MPa or less, and further preferably 0.08MPa or less. This makes the initial step following property more excellent.

When the transparent adhesive layer is formed of an active energy ray-curable adhesive, the storage modulus GT2 at 23 ℃ after irradiation with an active energy ray of the transparent adhesive layer is preferably 0.08MPa or more, more preferably 0.09MPa or more, particularly preferably 0.10MPa or more, and further preferably 0.11MPa or more. This makes the step following property under high-temperature and high-humidity conditions more excellent. The storage modulus GT2 is preferably 10MPa or less, more preferably 5MPa or less, particularly preferably 1MPa or less, and further preferably 0.2MPa or less. This exhibits good adhesive force, and the adhesiveness to an adherend becomes further excellent.

The storage modulus change rate Δ GT, which is the ratio of the storage modulus GT2 to the storage modulus GT1 (storage modulus GT 2/storage modulus GT1), is preferably 1.1 or more, more preferably 1.2 or more, particularly preferably 1.6 or more, and still more preferably 1.8 or more. The storage modulus change rate Δ GT is preferably 100 or less, more preferably 10 or less, particularly preferably 5 or less, further preferably 3 or less, and further preferably 2.5 or less. When the storage modulus change rate Δ GT is within the above range, the initial level difference following property and the level difference following property under high-temperature and high-humidity conditions can be further improved.

From the viewpoint of step difference following properties under high-temperature and high-humidity conditions, the gel fraction of the composite adhesive layer of the adhesive sheet of the present embodiment is preferably 20% or more, more preferably 30% or more, particularly preferably 40% or more, and further preferably 50% or more. The gel fraction is preferably 80% or less, more preferably 70% or less, particularly preferably 65% or less, and further preferably 60% or less. This makes the initial step following property more excellent. The method for measuring the gel fraction of the adhesive in the present specification is shown in the test examples described below.

The gel fraction of the composite adhesive layer of the adhesive sheet of the present embodiment after irradiation with active energy rays is preferably 40% or more, more preferably 50% or more, particularly preferably 60% or more, and further preferably 65% or more. This makes the step following property under high-temperature and high-humidity conditions more excellent. The gel fraction is preferably 99% or less, more preferably 89% or less, particularly preferably 80% or less, and further preferably 75% or less. This exhibits good adhesive force, and the adhesiveness to an adherend becomes further excellent.

The light diffusing adhesive layer of the present embodiment preferably has a gel fraction of 30% or more, more preferably 40% or more, particularly preferably 50% or more, and even more preferably 55% or more, from the viewpoint of effectively exhibiting the luminance unevenness suppression, such as maintaining the dispersed state of the light diffusing fine particles. The gel fraction is preferably 90% or less, more preferably 80% or less, particularly preferably 70% or less, and further preferably 65% or less. This ensures good adhesion to the transparent adhesive layer.

When the light diffusing adhesive layer is composed of an active energy ray-curable adhesive, the gel fraction of the light diffusing adhesive layer after irradiation with active energy rays is preferably 40% or more, more preferably 50% or more, particularly preferably 60% or more, and further preferably 65% or more, from the viewpoint of blister resistance. The gel fraction is preferably 99% or less, more preferably 90% or less, particularly preferably 85% or less, and further preferably 80% or less. This exhibits good adhesive force, and the adhesiveness to an adherend becomes further excellent.

From the viewpoint of step difference following properties under high-temperature and high-humidity conditions, the gel fraction of the transparent adhesive agent layer of the present embodiment is preferably 20% or more, more preferably 30% or more, particularly preferably 40% or more, and further preferably 50% or more. The gel fraction is preferably 80% or less, more preferably 70% or less, particularly preferably 60% or less, and further preferably 55% or less. This makes the initial step following property more excellent.

When the transparent adhesive layer is composed of an active energy ray-curable adhesive, the gel fraction of the transparent adhesive layer after irradiation with active energy rays is preferably 40% or more, more preferably 50% or more, particularly preferably 60% or more, and further preferably 65% or more. This makes the step following property under high-temperature and high-humidity conditions more excellent. The gel fraction is preferably 98% or less, more preferably 87% or less, particularly preferably 75% or less, and still more preferably 70% or less. This exhibits good adhesive force, and the adhesiveness to an adherend becomes further excellent.

From the viewpoint of step difference followability and handling property under high-temperature and high-humidity conditions, the adhesive force of the transparent adhesive layer side in the adhesive sheet of the present embodiment to soda-lime glass is preferably 20N/25mm or more, more preferably 30N/25mm or more, particularly preferably 35N/25mm or more, and further preferably 40N/25mm or more. The above-mentioned adhesive force is preferably 80N/25mm or less, more preferably 70N/25mm or less, particularly preferably 60N/25mm or less, and still more preferably 50N/25mm or less. This makes it possible to obtain excellent reworkability and reuse the adherend even when a bonding error occurs.

The adhesive sheet of the present embodiment has an adhesive force to soda-lime glass of preferably 20N/25mm or more, more preferably 30N/25mm or more, particularly preferably 40N/25mm or more, and further preferably 45N/25mm or more on the transparent adhesive layer side after irradiation with active energy rays. This makes the step following property under high-temperature and high-humidity conditions more excellent. The above-mentioned adhesive force is preferably 80N/25mm or less, more preferably 70N/25mm or less, particularly preferably 60N/25mm or less, and still more preferably 50N/25mm or less. This can provide good reworkability.

From the viewpoint of handling properties, the adhesive force of the light diffusing adhesive layer side in the adhesive sheet of the present embodiment to soda lime glass is preferably 1N/25mm or more, more preferably 4N/25mm or more, particularly preferably 8N/25mm or more, and further preferably 13N/25mm or more. The above-mentioned adhesive force is preferably 60N/25mm or less, more preferably 50N/25mm or less, particularly preferably 40N/25mm or less, and still more preferably 35N/25mm or less. This makes it possible to obtain excellent reworkability and reuse the adherend even when a bonding error occurs.

The adhesive sheet of the present embodiment has an adhesive force to soda-lime glass of preferably 10N/25mm or more, more preferably 15N/25mm or more, particularly preferably 20N/25mm or more, and further preferably 25N/25mm or more on the light-diffusing adhesive layer side after irradiation with active energy rays. This makes the blister resistance more excellent. The above-mentioned adhesive force is preferably 60N/25mm or less, more preferably 50N/25mm or less, particularly preferably 45N/25mm or less, and still more preferably 40N/25mm or less. This can provide good reworkability.

Here, the adhesive force in the present specification means an adhesive force measured by a 180 degree peel method substantially in accordance with JIS Z0237:2009, wherein a measurement sample is made 25mm wide and 100mm long, and the measurement sample is attached to an adherend, pressurized at 0.5MPa and 50 ℃ for 20 minutes, left under normal pressure, 23 ℃ and 50% RH for 24 hours, and then measured at a peel speed of 300 mm/minute.

The thickness of the composite adhesive layer in the adhesive sheet of the present embodiment is preferably 20 μm or more, more preferably 40 μm or more, particularly preferably 60 μm or more, and further preferably 80 μm or more. This enables the level difference (unevenness) of the adherend to be filled well, and the level difference following property is further improved. The thickness of the composite adhesive layer is preferably 1000 μm or less, more preferably 800 μm or less, particularly preferably 400 μm or less, and further preferably 200 μm or less. This improves workability, and prevents appearance defects due to squeeze marks and the like.

The thickness of the light diffusing adhesive layer of the present embodiment is preferably 10 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, and further preferably 40 μm or more. Thus, a desired light diffusivity or haze value is easily obtained, and also a desired adhesion is easily obtained. The thickness of the light diffusing adhesive layer is preferably 500 μm or less, more preferably 400 μm or less, particularly preferably 200 μm or less, and further preferably 100 μm or less. Thus, desired light diffusibility or haze value is easily obtained, and workability is also improved.

In the pressure-sensitive adhesive sheet of the present embodiment, the thickness of the transparent pressure-sensitive adhesive layer on the surface in contact with the level difference (unevenness) of the adherend is preferably larger than the height of the level difference of the adherend. Thus, the step of the adherend can be absorbed by the transparent adhesive layer, and the light diffusion adhesive layer can be more effectively prevented from being compressed or deformed by the step. Therefore, the light diffusion uniformity of the light diffusion adhesive layer (composite adhesive layer) becomes higher.

Specifically, the thickness of the transparent adhesive layer of the present embodiment is preferably 10 μm or more, more preferably 20 μm or more, particularly preferably 30 μm or more, and further preferably 40 μm or more. This makes the composite adhesive layer more excellent in uniformity of light diffusion, step following properties under high-temperature and high-humidity conditions, and blister resistance. On the other hand, the thickness of the transparent adhesive layer is preferably 500 μm or less, more preferably 400 μm or less, particularly preferably 200 μm or less, and further preferably 100 μm or less. This improves workability and prevents appearance defects such as dents. In addition, when a plurality of transparent adhesive layers are present as shown in fig. 4 described later, the thickness is the thickness of one transparent adhesive layer.

Preferably, the composite adhesive layer is an adhesive layer for bonding one optical member to another optical member. The optical member will be described later. In an optical laminate (display) obtained using the composite adhesive layer of the adhesive sheet of the present embodiment, the optical laminate (display) is suppressed from being uneven in brightness by making the light diffusion property of the composite adhesive layer uniform. However, the adhesive sheet of the present embodiment is not limited to the use in an optical laminate or a display.

Fig. 1 shows a specific structure of an example of the adhesive sheet of the present embodiment.

As shown in fig. 1, the adhesive sheet 1 is composed of two

release sheets

12a and 12b and a composite adhesive layer 11, and the composite adhesive layer 11 is sandwiched between the two

release sheets

12a and 12b so as to be in contact with the release surfaces of the two

release sheets

12a and 12 b. The release surface of the release sheet in the present specification means a surface having releasability in the release sheet, and includes any of a surface subjected to a release treatment and a surface showing releasability even if the release treatment is not performed.

The composite adhesive layer 11 of the present embodiment is a laminate of one light diffusing adhesive layer 111 and one transparent adhesive layer 112. However, the present invention is not limited thereto. The transparent adhesive layer 112 is preferably located on a surface of the composite adhesive layer 11 that is in contact with a step of an adherend.

1. Each component

1-1. Compound adhesive layer

The light diffusion adhesive layer 111 is preferably made of an adhesive containing light diffusion fine particles. On the other hand, the transparent adhesive layer 112 is preferably made of an adhesive containing no light diffusion fine particles. The phrase "containing no light diffusion fine particles" means "containing almost no light diffusion fine particles", and includes a case where the light diffusion fine particles are contained in an amount not to impair the effects of the present embodiment, in addition to the case where the light diffusion fine particles are not contained at all. The amount of the light diffusion fine particles is preferably 0.1% by mass or less, particularly preferably 0.01% by mass or less, more preferably 0.001% by mass or less, and most preferably 0% by mass.

The type of adhesive constituting the light diffusion adhesive layer 111 and the transparent adhesive layer 112 of the adhesive sheet 1 of the present embodiment is not particularly limited as long as at least one of the light diffusion adhesive layer 111 and the transparent adhesive layer 112 is composed of an active energy ray-curable adhesive. For example, any one of an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, a rubber adhesive, and a silicone adhesive may be used. The adhesive may be any of emulsion type, solvent type, and non-solvent type, and may be any of crosslinking type and non-crosslinking type. Among them, acrylic adhesives having excellent adhesive properties, optical characteristics, and the like are preferable. The acrylic pressure-sensitive adhesive is preferably a crosslinked type, and more preferably a thermally crosslinked type.

The adhesive constituting the light diffusion adhesive layer 111 and the adhesive constituting the transparent adhesive layer 112 may be the same type as each other or different types from each other, but both of them are preferably active energy ray-curable adhesives, and particularly preferably both of them are active energy ray-curable acrylic adhesives. This can exhibit excellent blister resistance. In this case, the compositions other than the light diffusion fine particles may be the same or different. In addition, the monomer composition of the main polymer may be the same or different. In addition, as the adhesive constituting the light diffusion adhesive layer 111 and the adhesive constituting the transparent adhesive layer 112, one may be an acrylic adhesive curable by active energy rays, and the other may be an acrylic adhesive not curable by active energy rays.

Hereinafter, a case will be described in which the adhesive constituting the light diffusion adhesive layer 111 and the adhesive constituting the transparent adhesive layer 112 are both active energy ray-curable acrylic adhesives, but the present invention is not limited thereto.

From the viewpoint of further enhancing the cohesive force between the polymers, the adhesive constituting the light diffusion adhesive layer 111 and the adhesive constituting the transparent adhesive layer 112 are preferably obtained by crosslinking an adhesive composition containing a (meth) acrylate polymer (a), a crosslinking agent (B), and an active energy ray-curable component (C) (hereinafter sometimes referred to as "adhesive composition P"). In the case of the light diffusing adhesive layer 111, the adhesive composition P further contains light diffusing fine particles (D). In the case of the adhesive composition P having the above composition, the storage modulus, gel fraction, haze value, adhesive force, and the like described above can be easily satisfied.

The adhesive obtained from the adhesive composition P can exhibit excellent optical characteristics, adhesive force, step following property, and the like. In the present specification, (meth) acrylic acid refers to both acrylic acid and methacrylic acid. Other similar terms are also the same. Further, the concept of "copolymer" is also included in "polymer".

(1) Components of adhesive compositions

(1-1) (meth) acrylate ester Polymer (A)

The (meth) acrylate polymer (a) of the present embodiment preferably contains a reactive group-containing monomer having a reactive group that reacts with the crosslinking agent (B) in the molecule as a monomer unit constituting the polymer. By reacting the reactive group derived from the reactive group-containing monomer with the crosslinking agent (B), a crosslinked structure (three-dimensional network structure) can be formed, and an adhesive having a desired cohesive force can be obtained.

Examples of the reactive group-containing monomer include a monomer having a hydroxyl group in the molecule (hydroxyl group-containing monomer), a monomer having a carboxyl group in the molecule (carboxyl group-containing monomer), and a monomer having an amino group in the molecule (amino group-containing monomer). Among these, a hydroxyl group-containing monomer or a carboxyl group-containing monomer having excellent reactivity with the crosslinking agent (B) is preferable.

Examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate. Among them, hydroxyalkyl (meth) acrylates having a hydroxyalkyl group having 1 to 4 carbon atoms are preferable from the viewpoint of reactivity of the hydroxyl group in the obtained (meth) acrylate polymer (a) with the crosslinking agent (B) and copolymerizability with other monomers. Specifically, for example, 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and the like are preferably mentioned, and particularly, 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate is preferably mentioned. These hydroxyl group-containing monomers may be used alone or in combination of two or more.

Examples of the carboxyl group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferable because of reactivity of the carboxyl group in the obtained (meth) acrylate polymer (a) with the crosslinking agent (B) and copolymerizability with other monomers. These carboxyl group-containing monomers may be used alone or in combination of two or more.

Examples of the amino group-containing monomer include aminoethyl (meth) acrylate, n-butylaminoethyl (meth) acrylate, and the like. These amino group-containing monomers may be used alone or in combination of two or more. In addition, a nitrogen atom-containing monomer described later is excluded from the amino group-containing monomer.

In the (meth) acrylate polymer (a), the reactive group-containing monomer is contained in an amount of preferably 5% by mass or more, particularly preferably 10% by mass or more, and further preferably 15% by mass or more, based on the lower limit of the monomer unit constituting the polymer. In addition, the reactive group-containing monomer is contained in the (meth) acrylate polymer (a) in an amount of preferably 40% by mass or less, particularly preferably 30% by mass or less, and further preferably 25% by mass or less, based on the upper limit of the monomer unit constituting the polymer. When the (meth) acrylate polymer (a) contains the reactive group-containing monomer as a monomer unit in the above-mentioned amount, a favorable crosslinked structure can be formed in the obtained adhesive, and a desired gel fraction and storage modulus can be easily obtained. Further, when the light diffusion fine particles (D) are contained, the dispersibility of the light diffusion fine particles (D) in the obtained adhesive tends to be good.

Further, the (meth) acrylate polymer (a) preferably does not contain a carboxyl group-containing monomer as a monomer unit constituting the polymer. Since the carboxyl group is an acid component, the carboxyl group-containing monomer is not contained, and therefore, even when a substance which causes a problem due to an acid, for example, a transparent conductive film such as tin-doped indium oxide (ITO), a metal film, or the like is present on the attachment target of the adhesive, the above problem (corrosion, change in resistance value, or the like) due to an acid can be suppressed. However, it is also permissible to contain a predetermined amount of the carboxyl group-containing monomer to such an extent that the above-described disadvantages do not occur. Specifically, the carboxyl group-containing monomer is allowed to be contained in the (meth) acrylate polymer (a) in an amount of 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less as a monomer unit.

The (meth) acrylate polymer (a) preferably contains an alkyl (meth) acrylate as a monomer unit constituting the polymer. Thus, good tackiness can be exhibited, and at the same time, the storage modulus of the resulting adhesive can be induced to be low. The alkyl group may be linear or branched.

From the viewpoint of adhesiveness, the alkyl (meth) acrylate is preferably an alkyl (meth) acrylate having an alkyl group with 1 to 20 carbon atoms. Examples of the alkyl (meth) acrylate having an alkyl group with 1 to 20 carbon atoms include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate, tetradecyl (meth) acrylate, hexadecyl (meth) acrylate, and octadecyl (meth) acrylate. Among these, from the viewpoint of further improving the adhesiveness or from the viewpoint of inducing the storage modulus to be low, an alkyl (meth) acrylate in which the number of carbon atoms of the alkyl group is 4 to 8 is preferable, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, or isooctyl (meth) acrylate is particularly preferable, and n-butyl acrylate, 2-ethylhexyl acrylate, or isooctyl acrylate is further preferable. These alkyl (meth) acrylates may be used alone or in combination of two or more.

In the (meth) acrylate polymer (a), the monomer unit constituting the polymer is preferably 45% by mass or more, particularly preferably 55% by mass or more, and further preferably 65% by mass or more of an alkyl (meth) acrylate. When the lower limit of the content of the alkyl (meth) acrylate is as described above, the (meth) acrylate polymer (a) can exhibit appropriate tackiness. In addition, when the light diffusion fine particles (D) are contained, the dispersibility of the light diffusion fine particles (D) in the adhesive tends to be good, and the desired adhesive property of the (meth) acrylate polymer (a) can be suppressed from being impaired. On the other hand, the (meth) acrylate polymer (a) preferably contains 99% by mass or less, more preferably 95% by mass or less, particularly preferably 90% by mass or less, and further preferably 75% by mass or less of an alkyl (meth) acrylate as a monomer unit constituting the polymer. When the upper limit of the content of the alkyl (meth) acrylate is as described above, other monomer components such as a reactive functional group-containing monomer can be introduced into the (meth) acrylate polymer (a) in an appropriate amount.

The (meth) acrylate polymer (a) preferably further contains a monomer having an alicyclic structure in the molecule (alicyclic structure-containing monomer) as a monomer unit constituting the polymer. The alicyclic structure-containing monomer raises the glass transition temperature of the polymer, and increases the storage modulus of the resulting adhesive. Further, since the alicyclic structure-containing monomer has a large volume, it is presumed that the presence of the alicyclic structure-containing monomer in the polymer enlarges the interval between the polymers, reduces the viscosity of the coating liquid, and facilitates the thickening of the adhesive layer.

The alicyclic carbon ring in the alicyclic structure-containing monomer may be a saturated structure or may have an unsaturated bond in part. The alicyclic structure may be a monocyclic alicyclic structure, or may be a polycyclic alicyclic structure such as a bicyclic structure or a tricyclic structure. The alicyclic structure is preferably a polycyclic alicyclic structure (polycyclic structure) in view of adjusting the storage modulus of the resulting adhesive to a high level and thickening the adhesive layer. Further, the polycyclic structure is particularly preferably a bicyclic ring to tetracyclic ring in view of compatibility of the (meth) acrylate polymer (a) with other components. In addition, as described above, from the viewpoint of improving the storage modulus or making the film thicker, the number of carbon atoms of the alicyclic structure (the total number of carbon atoms of the portion indicating a ring, and the total number of carbon atoms when a plurality of rings are independently present) is preferably 5 or more, and particularly preferably 7 or more. On the other hand, the upper limit of the number of carbon atoms of the alicyclic structure is not particularly limited, but from the same viewpoint as above, it is preferably 15 or less, and particularly preferably 10 or less.

Specific examples of the alicyclic structure-containing monomer include cyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, adamantyl (meth) acrylate, isobornyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, etc., and among them, dicyclopentanyl (meth) acrylate (carbon number of alicyclic structure: 10), adamantyl (meth) acrylate (carbon number of alicyclic structure: 10), or isobornyl (meth) acrylate (carbon number of alicyclic structure: 7) which exhibits more excellent step following property is preferable, isobornyl (meth) acrylate is particularly preferable, and isobornyl acrylate is more preferable. These alicyclic structure-containing monomers may be used alone or in combination of two or more.

When the (meth) acrylate polymer (a) contains an alicyclic structure-containing monomer as a monomer unit constituting the polymer, the alicyclic structure-containing monomer is preferably contained in an amount of 1 mass% or more, particularly preferably 5 mass% or more, and further preferably 10 mass% or more, from the viewpoint of adjusting the storage modulus of the resulting adhesive to a preferable range. From the same viewpoint as above, the content of the alicyclic structure-containing monomer is preferably 25% by mass or less, particularly preferably 20% by mass or less, and further preferably 15% by mass or less.

The (meth) acrylic acid ester polymer (A) preferably further contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer. By having a monomer containing a nitrogen atom as a structural unit in a polymer, a predetermined polarity can be imparted to an adhesive, and the adhesive has excellent affinity even for an adherend having a certain polarity such as glass. From the viewpoint of imparting appropriate rigidity to the (meth) acrylate polymer (a), the nitrogen atom-containing monomer is preferably a monomer having a nitrogen-containing heterocycle. In addition, from the viewpoint of enhancing the degree of freedom of the moiety derived from the nitrogen atom-containing monomer in the high-dimensional structure of the adhesive agent, it is preferable that the nitrogen atom-containing monomer does not contain a reactive unsaturated double bond group other than one polymerizable group used in the polymerization for forming the (meth) acrylate polymer (a).

Examples of the monomer having a nitrogen-containing heterocycle include N- (meth) acryloylmorpholine, N-vinyl-2-pyrrolidone, N- (meth) acryloylpyrrolidone, N- (meth) acryloylpiperidine, N- (meth) acryloylpyrrolidine, N- (meth) acryloylaziridine, aziridinylethyl (meth) acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinylpyrazine, 1-vinylimidazole, N-vinylcarbazole, N-vinylphthalimide, and the like, and among them, N- (meth) acryloylmorpholine which exhibits more excellent adhesive force is preferable, and N-acryloylmorpholine is particularly preferable. These nitrogen-containing heterocyclic monomers may be used alone or in combination of two or more.

When the (meth) acrylate polymer (a) contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer, the content of the nitrogen atom-containing monomer is preferably 1% by mass or more, particularly preferably 2% by mass or more, and more preferably 4% by mass or more. The (meth) acrylate polymer (a) preferably contains 24% by mass or less, particularly preferably 16% by mass or less, and further preferably 8% by mass or less of the nitrogen atom-containing monomer as a monomer unit constituting the polymer. When the content of the nitrogen atom-containing monomer is within the above range, the resulting adhesive can sufficiently exhibit excellent adhesion to glass.

The (meth) acrylate polymer (a) may also contain other monomers as monomer units constituting the polymer, as required. In order not to inhibit the above-mentioned action of the reactive functional group-containing monomer, as the other monomer, a monomer not containing a reactive functional group is preferable. Examples of the monomer include alkoxyalkyl (meth) acrylates such as methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate, vinyl acetate, and styrene. These other monomers may be used alone or in combination of two or more.

The (meth) acrylate polymer (a) is preferably a linear polymer. Since entanglement of molecular chains is easily caused by the linear polymer and improvement of cohesive force can be expected, an adhesive excellent in step following property and blister resistance under high-temperature and high-humidity conditions can be easily obtained.

The (meth) acrylate polymer (a) is preferably a solution polymer obtained by a solution polymerization method. Since a solution polymer is used, a polymer having a high molecular weight can be easily obtained and an improvement in cohesive force can be expected, an adhesive having excellent step following properties and blister resistance under high-temperature and high-humidity conditions can be easily obtained.

The polymerization form of the (meth) acrylate polymer (a) may be a random copolymer or a block copolymer.

The weight average molecular weight of the (meth) acrylate polymer (a) is preferably 20 ten thousand or more, more preferably 30 ten thousand or more, and particularly preferably 40 ten thousand or more. This can improve the storage modulus and gel fraction of the obtained adhesive, and can further improve the step difference following property under high temperature and high humidity conditions. Further, the weight average molecular weight is more preferably 50 ten thousand or more. Thus, a high storage modulus can be obtained to the extent that sufficient cohesive force can be exerted even in an adhesive containing the light diffusing fine particles (D). Further, the light diffusion fine particles (D) tend to have good dispersibility in the adhesive.

The upper limit of the weight average molecular weight of the (meth) acrylate polymer (a) is preferably 150 ten thousand or less, more preferably 120 ten thousand or less, particularly preferably 100 ten thousand or less, and further preferably 80 ten thousand or less. When the upper limit value of the weight average molecular weight of the (meth) acrylate polymer (a) is set to the above value, the storage modulus of the obtained adhesive is likely to have an appropriate value, and the initial step following property is more excellent. The weight average molecular weight in the present specification is a value in terms of standard polystyrene measured by a Gel Permeation Chromatography (GPC) method.

In the adhesive composition P, one kind of the (meth) acrylate polymer (a) may be used alone, or two or more kinds may be used in combination.

(1-2) crosslinking agent (B)

The crosslinking agent (B) may be a substance that reacts with the reactive group of the (meth) acrylate polymer (a), and examples thereof include isocyanate crosslinking agents, epoxy crosslinking agents, amine crosslinking agents, melamine crosslinking agents, aziridine crosslinking agents, hydrazine crosslinking agents, aldehyde crosslinking agents, oxazoline crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, and ammonium salt crosslinking agents. Among the above, an isocyanate-based crosslinking agent having excellent reactivity with a hydroxyl group and a carboxyl group, or an epoxy-based crosslinking agent having excellent reactivity with a carboxyl group is preferably used. The crosslinking agent (B) may be used alone or in combination of two or more.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of the polyisocyanate compound include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate, biuret and isocyanurate products thereof, and adducts thereof with low-molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane and castor oil. Among them, trimethylolpropane-modified aromatic polyisocyanates are preferable from the viewpoint of reactivity with hydroxyl groups, and trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate are particularly preferable.

Examples of the epoxy-based crosslinking agent include 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N, N ', N' -tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1, 6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, and diglycidylamine. Among them, 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane is preferable from the viewpoint of reactivity with a carboxyl group.

The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.01 part by mass or more, particularly preferably 0.05 part by mass or more, and more preferably 0.1 part by mass or more, relative to 100 parts by mass of the (meth) acrylate polymer (a). The content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, particularly preferably 1 part by mass or less, further preferably 0.4 parts by mass or less, and most preferably 0.2 parts by mass or less. When the content of the crosslinking agent (B) is within the above range, the storage modulus, gel fraction, adhesive force and the like of the obtained adhesive are easily suitable.

(1-3) active energy ray-curable component (C)

It is presumed that in an adhesive obtained by curing an adhesive active energy ray formed by crosslinking an adhesive composition P containing an active energy ray-curable component (C), the active energy ray-curable components (C) are polymerized with each other, and the polymerized active energy ray-curable component (C) is entangled in a crosslinked structure (three-dimensional network structure) of the (meth) acrylate polymer (a). The adhesive having such a high-dimensional structure can improve the storage modulus and gel fraction to some extent, and is particularly excellent in step following properties under high-temperature and high-humidity conditions.

The active energy ray-curable component (C) is not particularly limited as long as it can be cured by irradiation with an active energy ray to obtain the above-described effects, and may be any of a monomer, an oligomer, or a polymer, or a mixture thereof. Among them, polyfunctional acrylate monomers having more excellent blister resistance are preferably used.

Examples of the polyfunctional acrylate monomer include 1, 4-butanediol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, neopentyl glycol adipate di (meth) acrylate, neopentyl glycol hydroxypivalate di (meth) acrylate, dicyclopentyl di (meth) acrylate, bifunctional types such as tricyclodecane dimethanol (meth) acrylate, caprolactone-modified dicyclopentenyl di (meth) acrylate, ethylene oxide-modified phosphoric acid di (meth) acrylate, di (acryloyloxyethyl) isocyanurate, allylated cyclohexyl di (meth) acrylate, ethoxylated bisphenol a diacrylate, and 9, 9-bis [4- (2-acryloyloxyethoxy) phenyl ] fluorene; trifunctional types such as trimethylolpropane tri (meth) acrylate, dipentaerythritol tri (meth) acrylate, propionic acid-modified dipentaerythritol tri (meth) acrylate, pentaerythritol tri (meth) acrylate, propylene oxide-modified trimethylolpropane tri (meth) acrylate, tris (acryloyloxyethyl) isocyanurate, and e-caprolactone-modified tris- (2- (meth) acryloyloxyethyl) isocyanurate; tetrafunctional types such as diglycerin tetra (meth) acrylate and pentaerythritol tetra (meth) acrylate; pentafunctional types such as propionic acid-modified dipentaerythritol penta (meth) acrylate; and hexa-functional types such as dipentaerythritol hexa (meth) acrylate and caprolactone-modified dipentaerythritol hexa (meth) acrylate. These polyfunctional acrylate monomers may be used alone or in combination of two or more. In addition, from the viewpoint of compatibility with the (meth) acrylate polymer (a), as the polyfunctional acrylate monomer, a polyfunctional acrylate monomer having a molecular weight of less than 1000 is preferable.

From the viewpoint of making the storage modulus of the adhesive after irradiation with active energy rays and the storage modulus change rate Δ G' before and after curing appropriate values and further making the step following property under high temperature and high humidity conditions more excellent, the lower limit of the content of the active energy ray-curable component (C) in the adhesive composition P is preferably 1 part by mass or more, particularly preferably 3 parts by mass or more, and further preferably 4 parts by mass or more, per 100 parts by mass of the (meth) acrylate polymer (a). On the other hand, the upper limit of the content is preferably 20 parts by mass or less, particularly preferably 12 parts by mass or less, and further preferably 8 parts by mass or less, from the viewpoint of the adhesive force of the adhesive after irradiation with an active energy ray.

(1-4) light diffusing particles (D)

The light diffusion fine particles (D) may be those which can satisfy the above physical properties of the light diffusion adhesive layer 111 and the composite adhesive layer 11.

Examples of the light diffusing fine particles (D) include inorganic fine particles such as silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay, talc, and titanium dioxide; organic light-transmitting fine particles such as acrylic resin, polystyrene resin, polyethylene resin, and epoxy resin; and fine particles made of a silicon-containing compound having a structure between inorganic and organic Materials, such as silicone resin (for example, Tospearl series manufactured by Momentive Performance Materials Japan inc.). Among these, fine particles made of silicone resin are preferable. Thus, the adhesive sheet easily satisfies the above-described haze value and image clarity. The light diffusion fine particles (D) may be used alone or in combination of two or more.

The shape of the light diffusion fine particles (D) is preferably spherical fine particles having uniform light diffusion. The lower limit of the average particle diameter of the light diffusing fine particles (D) by the centrifugal sedimentation light transmission method is preferably 1.0 μm or more, particularly preferably 2.0 μm or more, and more preferably 3.0 μm or more. When the lower limit of the average particle diameter is as described above, the desired haze can be easily expressed. On the other hand, the upper limit of the average particle size is preferably 10 μm or less, particularly preferably 8 μm or less, and more preferably 6 μm or less. When the upper limit value of the average particle diameter is as described above, it is easy to prevent the haze value from becoming too high, and a highly accurate display image can be displayed favorably.

The average particle size by the centrifugal sedimentation method was measured using a centrifugal automatic particle size distribution measuring apparatus (HORIBA, ltd., CAPA-700) as a measurement sample, which was a sample obtained by sufficiently stirring 1.2g of fine particles and 98.8g of isopropyl alcohol.

The content of the light diffusion fine particles (D) in the adhesive composition P may be an amount that can satisfy the above physical properties. Specifically, the content of the light diffusion fine particles (D) is preferably 1 mass% or more, more preferably 3 mass% or more, particularly preferably 6 mass% or more, and further preferably 8 mass% or more. The content of the light diffusion fine particles (D) is preferably 50 mass% or less, more preferably 40 mass% or less, particularly preferably 30 mass% or less, and further preferably 25 mass% or less. When the content of the light diffusion fine particles (D) is within the above range, the haze value, the storage modulus, and the adhesive force described above are easily satisfied.

(1-5) photopolymerization initiator (E)

When ultraviolet rays are used as the active energy rays for curing the adhesive composition P, the adhesive composition P preferably further contains a photopolymerization initiator (E). By containing the photopolymerization initiator (E) in this manner, the active energy ray-curable component (C) can be efficiently polymerized, and the polymerization curing time and the irradiation dose of active energy rays can be reduced.

Examples of the photopolymerization initiator (E) include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone, 2-dimethoxy-2-phenylacetophenone, 2-diethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, 2-methyl-1- [4- (methylthio) phenyl ] -2-morpholino-1-propanone, 4- (2-hydroxyethoxy) phenyl-2- (hydroxy-2-propyl) ketone, benzophenone, p-phenylbenzophenone, and mixtures thereof, 4, 4' -diethylaminobenzophenone, dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2, 4-dimethylthioxanthone, 2, 4-diethylthioxanthone, benzildimethylketal, acetophenone dimethylketal, p-dimethylaminobenzoate, oligo [ 2-hydroxy-2-methyl-1 [4- (1-methylvinyl) phenyl ] propanone ], 2,4, 6-trimethylbenzoyl-diphenyl-phosphine oxide, bis (2,4, 6-trimethylbenzoyl) -phenylphosphine oxide and the like. These photopolymerization initiators may be used alone or in combination of two or more.

Among the above, preferred is a phosphine oxide-based photopolymerization initiator which is easily cleaved and easily and reliably cures an adhesive even when irradiated with ultraviolet light through a plastic plate containing an ultraviolet absorber. Specifically, 2,4, 6-trimethylbenzoyl-diphenyl-phosphine oxide, bis (2,4, 6-trimethylbenzoyl) -phenylphosphine oxide, and the like are preferable.

The lower limit of the content of the photopolymerization initiator (E) in the adhesive composition P is preferably 0.1 part by mass or more, particularly preferably 1 part by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of the active energy ray-curable component (C). The upper limit is preferably 30 parts by mass or less, particularly preferably 20 parts by mass or less, and further preferably 12 parts by mass or less.

(1-6) various additives

Various additives generally used in acrylic adhesives, for example, silane coupling agents, rust inhibitors, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, refractive index adjusters, and the like can be added to the adhesive composition P as needed. The polymerization solvent and the diluting solvent described below are not included in the additives constituting the adhesive composition P.

Among the above, the adhesive composition P preferably contains a silane coupling agent. Thus, the adhesion to the adherend is improved regardless of whether the adherend is a plastic plate or a glass member, and the step following property and blister resistance under high-temperature and high-humidity conditions are further improved.

The silane coupling agent is preferably an organosilicon compound having at least 1 alkoxysilyl group in the molecule, which has good compatibility with the (meth) acrylate polymer (a) and light transmittance.

Examples of the silane coupling agent include silicon compounds containing a polymerizable unsaturated group such as vinyltrimethoxysilane, vinyltriethoxysilane, and methacryloxypropyltrimethoxysilane; silicon compounds having an epoxy structure such as 3-glycidoxypropyltrimethoxysilane and 2- (3, 4-epoxycyclohexyl) ethyltrimethoxysilane; mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyldimethoxymethylsilane, etc.; amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane and N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane; 3-chloropropyltrimethoxysilane, 3-isocyanopropyltriethoxysilane, or a condensate of at least one of these with an alkyl group-containing silicon compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, or ethyltrimethoxysilane. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent in the adhesive composition P is preferably 0.01 part by mass or more, particularly preferably 0.05 part by mass or more, and more preferably 0.1 part by mass or more, relative to 100 parts by mass of the (meth) acrylate polymer (a). The content is preferably 1.2 parts by mass or less, particularly preferably 0.8 parts by mass or less, and further preferably 0.4 parts by mass or less.

(2) Preparation of adhesive composition

The adhesive composition P can be prepared by: the (meth) acrylate polymer (a) is prepared, and the obtained (meth) acrylate polymer (a), the crosslinking agent (B), and the active energy ray-curable component (C) are mixed, and a photopolymerization initiator (E), additives, and the like are added as needed. In the case of the light diffusing adhesive layer 111, light diffusing fine particles (D) may be further blended.

The (meth) acrylate polymer (a) can be prepared by polymerizing a mixture of monomers constituting the polymer by a conventional radical polymerization method. The polymerization of the (meth) acrylate polymer (a) is preferably carried out by a solution polymerization method using a polymerization initiator as needed. However, the present invention is not limited thereto, and polymerization may be carried out without a solvent. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone, and two or more of them may be used simultaneously.

Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more of them may be used simultaneously. Examples of the azo compound include 2,2 ' -azobisisobutyronitrile, 2 ' -azobis (2-methylbutyronitrile), 1 ' -azobis (cyclohexane-1-carbonitrile), 2 ' -azobis (2, 4-dimethylvaleronitrile), 2 ' -azobis (2, 4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2 '-azobis (2-methylpropionate), 4' -azobis (4-cyanovaleric acid), 2 '-azobis (2-hydroxymethylpropionitrile), 2' -azobis [2- (2-imidazolin-2-yl) propane ], and the like.

Examples of the organic peroxide include benzoyl peroxide, tert-butyl peroxybenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di (2-ethoxyethyl) peroxydicarbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, 3,5, 5-trimethylhexanoyl peroxide, dipropionyl peroxide, and diacetyl peroxide.

In the polymerization step, a chain transfer agent such as 2-mercaptoethanol is added to adjust the weight average molecular weight of the obtained polymer.

After the (meth) acrylate polymer (a) is obtained, the crosslinking agent (B), the active energy ray-curable component (C), and if necessary, a diluting solvent, the light diffusing fine particles (D), the photopolymerization initiator (E), additives, and the like are added to a solution of the (meth) acrylate polymer (a) and sufficiently mixed, thereby obtaining the adhesive composition P (coating solution) diluted with the solvent. In the case where a solid substance is used as any of the above-mentioned components or in the case where the solid substance is precipitated when the solid substance is mixed with another component in an undiluted state, the component may be dissolved or diluted in a diluting solvent in advance and then mixed with another component.

Examples of the diluting solvent include aliphatic hydrocarbons such as hexane, heptane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as dichloromethane and vinyl chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosolve solvents such as ethyl cellosolve.

The concentration and viscosity of the coating solution prepared in this manner are not particularly limited as long as they are within a range in which coating can be performed, and can be appropriately selected according to the situation. For example, the adhesive composition P is diluted so that the concentration thereof is 10 to 60 mass%. In addition, when obtaining the coating solution, the addition of a diluting solvent or the like is not an essential condition, and if the adhesive composition P has a viscosity capable of being coated or the like, the diluting solvent may not be added. In this case, the adhesive composition P is a coating solution in which the polymerization solvent of the (meth) acrylate polymer (a) is directly used as a dilution solvent.

(3) Formation of adhesive layer

The light diffusion adhesive layer 111 and the transparent adhesive layer 112 of the present embodiment are preferably each composed of an adhesive obtained by crosslinking (a coating layer of) the adhesive composition P. The crosslinking of the adhesive composition P can generally be carried out by heat treatment. Further, the drying treatment when evaporating the diluting solvent or the like from the coating layer of the adhesive composition P coated on the desired object may be used as the heating treatment.

The heating temperature of the heating treatment is preferably 50 to 150 ℃, and particularly preferably 70 to 120 ℃. The heating time is preferably 10 seconds to 10 minutes, and particularly preferably 50 seconds to 2 minutes.

After the heat treatment, if necessary, a curing period of about 1 to 2 weeks may be provided at normal temperature (e.g., 23 ℃ C., 50% RH). When the curing period is required, an adhesive is formed after the curing period, and when the curing period is not required, an adhesive is formed directly after the heating treatment is completed.

By the above-mentioned heat treatment (and curing), the (meth) acrylate polymer (a) is sufficiently crosslinked via the crosslinking agent (B).

The composite adhesive layer 11 of the present embodiment can be obtained by laminating the light diffusion adhesive layer 111 and the transparent adhesive layer 112. The timing of the lamination may be before or after the curing of each adhesive layer. However, in order to further improve the adhesion between the light diffusion adhesive layer 111 and the transparent adhesive layer 112, it is preferable to laminate the adhesive layers before curing.

1-2. Release sheet

The

release sheets

12a, 12b protect the composite adhesive layer 11 until the time of using the adhesive sheet 1, and are released when using the adhesive sheet 1 (composite adhesive layer 11). In the adhesive sheet 1 of the present embodiment, one or both of the

release sheets

12a and 12b are not essential.

Examples of the

release sheets

12a and 12b include a polyethylene film, a polypropylene film, a polybutylene film, a polybutadiene film, a polymethylpentene film, a polyvinyl chloride film, a vinyl chloride copolymer film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polybutylene terephthalate film, a polyurethane film, an ethylene-vinyl acetate film, an ionomer resin film, an ethylene- (meth) acrylic acid copolymer film, an ethylene- (meth) acrylate copolymer film, a polystyrene film, a polycarbonate film, a polyimide film, and a fluororesin film. In addition, crosslinked films of these films may also be used. Further, a laminated film of these films may be used.

The release surfaces of the

release sheets

12a and 12b (particularly, the surfaces in contact with the composite adhesive layer 11) are preferably subjected to a release treatment. Examples of the release agent used for the release treatment include alkyd based, silicone based, fluorine based, unsaturated polyester based, polyolefin based, and wax based release agents.

The thickness of the

release sheets

12a and 12b is not particularly limited, but is usually about 20 to 150 μm.

2. Production of adhesive sheet

As one production example of the adhesive sheet 1, a coating solution of the adhesive composition P for forming the transparent adhesive layer 112 is applied to the release surface of one release sheet 12a, and heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer, thereby obtaining a release sheet 12a with a coating layer. Further, a coating solution of the adhesive composition P for forming the light diffusion adhesive layer 111 was applied to the release surface of the other release sheet 12b, and heat treatment was performed to thermally crosslink the adhesive composition P to form a coating layer, thereby obtaining a release sheet 12b with a coating layer. Then, the coated release sheet 12a and the coated release sheet 12b are bonded to each other so that the two coated layers are in contact with each other. Here, a plurality of release sheets with coating layers may be produced, and the coating layers may be laminated in a desired number of layers in a desired lamination order. When the curing period is required, the laminated coating layer becomes the composite adhesive layer 11 by providing the curing period, and when the curing period is not required, the laminated coating layer directly becomes the composite adhesive layer 11. Thus, the adhesive sheet 1 having the composite adhesive layer 11 was obtained, and the composite adhesive layer 11 was a laminate of the light diffusion adhesive layer 111 and the transparent adhesive layer 112. The conditions for heat treatment and aging are as described above.

In addition, the coating layer for forming the transparent adhesive layer 112 and the coating layer for forming the light diffusion adhesive layer 111 may be sandwiched by two release sheets, respectively, and when the coating layer for forming the transparent adhesive layer 112 and the coating layer for forming the light diffusion adhesive layer 111 are laminated, one release sheet may be released, respectively.

As a method for applying the coating solution of the adhesive composition P, for example, a bar coating method, a blade coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method, or the like can be used.

[ optical layered body ]

An optical laminate according to one embodiment of the present invention includes one optical member, another optical member, and a cured composite adhesive layer that bonds the one optical member and the another optical member to each other. The cured composite adhesive layer is a layer obtained by irradiating the composite adhesive layer of the adhesive sheet of the above embodiment with an active energy ray and curing the layer.

In this case, it is preferable that the transparent adhesive layer of the cured composite adhesive layer is in contact with the step.

The optical laminate of the present embodiment may be the display itself or may be a member constituting a part of the display. The present invention is not limited to this, and can be applied to members for optical use other than display bodies.

Examples of the display include a Liquid Crystal Display (LCD) display, a Light Emitting Diode (LED) display, an organic electroluminescence (organic EL) display, and electronic paper. The display body can also be a touch panel.

Fig. 2 shows a specific structure of an optical stack according to an embodiment of the present invention. As shown in fig. 2, the optical laminate 2A of the present embodiment includes a first optical member 21 (one optical member), a second optical member 22 (the other optical member), and a cured composite adhesive layer 11' located therebetween, which bonds the first optical member 21 and the second optical member 22 to each other.

One of the first optical member 21 and the second optical member 22 may have a step on the surface on the side where the cured composite adhesive layer 11' is bonded. In the embodiment shown in fig. 2, the first optical member 21 has a step difference by the printed layer 23 on the surface on the composite adhesive layer 11 side.

The cured composite adhesive layer 11' in the display 2A is a layer obtained by curing the composite adhesive layer 11 of the adhesive sheet 1 with an active energy ray. The cured composite adhesive layer 11' of the present embodiment is a laminate of one light-diffusing adhesive layer 111 and one transparent adhesive layer 112, and the transparent adhesive layer 112 is located on the side in contact with the step difference formed by the printed layer 23.

The first optical member 21 is preferably a protective panel made of a laminate including a glass plate, a plastic plate, and the like, in addition to the glass plate, the plastic plate, and the like. In this case, the printed layer 23 is usually formed in a frame shape on the composite adhesive layer 11 side of the first optical member 21.

The glass plate is not particularly limited, and examples thereof include chemically strengthened glass, alkali-free glass, quartz glass, soda-lime glass, barium-strontium-containing glass, aluminosilicate glass, lead glass, borosilicate glass, and barium borosilicate glass. The thickness of the glass plate is not particularly limited, but is usually 0.1 to 5mm, preferably 0.2 to 2 mm.

The plastic plate is not particularly limited, and examples thereof include acrylic plates and polycarbonate plates. The thickness of the plastic sheet is not particularly limited, but is usually 0.2 to 5mm, preferably 0.4 to 3 mm.

Further, various functional layers (a transparent conductive film, a metal layer, a silica layer, a hard coat layer, an antiglare layer, etc.) may be provided on one surface or both surfaces of the glass plate or the plastic plate, and an optical member may be laminated. In addition, the transparent conductive film and the metal layer may also be patterned.

The second optical member 22 is preferably an optical member to be attached to the first optical member 21, a display module (for example, a Liquid Crystal (LCD) module, a Light Emitting Diode (LED) module, an organic electroluminescence (organic EL) module, or the like), an optical member that is a part of the display module, or a laminate including the display module.

Examples of the optical member include an anti-scattering film, a polarizing plate (polarizing film), a polarizer, a retardation plate (retardation film), a viewing angle compensation film, a brightness enhancement film, a contrast enhancement film, a liquid crystal polymer film, a diffusion film, a semi-transmissive reflective film, and a transparent conductive film. Examples of the anti-scattering film include a hard coat film in which a hard coat layer is formed on one surface of a base film.

The material constituting the printed layer 23 is not particularly limited, and a known material for printing can be used. The lower limit of the thickness of the printed layer 23, that is, the height of the step is preferably 3 μm or more, more preferably 5 μm or more, particularly preferably 7 μm or more, and most preferably 10 μm or more. By setting the lower limit value to the above value, it is possible to sufficiently ensure concealment of the electric wiring lines and the like from the observer side. The upper limit is preferably 50 μm or less, more preferably 35 μm or less, particularly preferably 25 μm or less, and further preferably 20 μm or less. By setting the upper limit value to the above value, it is possible to prevent the step following property of the composite adhesive layer 11' to the printed layer 23 from being deteriorated after curing, and to maintain the uniformity of light diffusion well.

In order to manufacture the display 2A, one release sheet 12A of the adhesive sheet 1 is peeled off, and the transparent adhesive layer 112 exposed from the adhesive sheet 1 is bonded to the surface of the first optical member 21 on the side where the printed layer 23 is present.

Then, the other release sheet 12b is peeled off from the composite adhesive layer 11 of the adhesive sheet 1, and the light diffusion adhesive layer 111 exposed from the adhesive sheet 1 is bonded to the second optical member 22. In addition, as another example, the order of attaching the first optical member 21 and the second optical member 22 may be changed.

Next, the composite adhesive layer 11 is irradiated with an active energy ray to prepare a cured composite adhesive layer 11'. The composite adhesive layer 11 is usually irradiated with an energy ray through either the first optical member 21 or the second optical member 22, and preferably irradiated with an energy ray through the first optical member 21 as a protective panel.

The active energy ray is an active energy ray having an energy quantum in an electromagnetic wave or a charged particle beam, and specifically, an ultraviolet ray, an electron beam, or the like can be mentioned. Among the active energy rays, ultraviolet rays which are easy to handle are preferable.

The ultraviolet irradiation can be performed using a high-pressure mercury lamp, fusion H lamp (fusion H lamp), xenon lamp, or the like, and the amount of ultraviolet irradiation is preferably 50 to 1000mW/cm in illuminance meter²About, more preferably 100 to 500mW/cm²Left and right. In addition, the light quantity is preferably 50 to 10000mJ/cm²More preferably 200 to 7000mJ/cm²Particularly preferably 500 to 3000mJ/cm². On the other hand, the irradiation of the electron beam can be performed by using an electron beam accelerator or the like, and the irradiation amount of the electron beam is preferably about 10 to 1000 krad.

As shown in fig. 3, a display 2B according to another embodiment includes a backlight 30, a cured composite adhesive layer 11 'laminated on the backlight 30, and a display portion 40 laminated on the cured composite adhesive layer 11'. The backlight 30 in the display 2B belongs to the first optical member, and the display unit 40 belongs to the second optical member.

The backlight 30 includes 1 or 2 or more substrates 31 and a plurality of light emitters 32 provided on the substrates 31. The backlight 30 has irregularities formed by a plurality of light emitters 32.

The cured composite adhesive layer 11' in the display 2B is a layer obtained by curing the composite adhesive layer 11 of the adhesive sheet 1 with an active energy ray. The cured composite adhesive layer 11' of the present embodiment is a laminate of one light-diffusing adhesive layer 111 and one transparent adhesive layer 112, and the transparent adhesive layer 112 is located on the side in contact with the irregularities of the light-emitting bodies 32. The plurality of light emitters 32 are sealed by the transparent adhesive layer 112 without any gap. This can protect the light emitter 32 from moisture.

The substrate 31 is not particularly limited, and a substrate generally used in a backlight can be used. The substrate 31 is typically a Printed Circuit Board (PCB substrate).

The substrate 31 may be formed by integrating a plurality of light-emitting bodies 32 in a lump, or may be formed by separating one light-emitting body 32 from another so that one light-emitting body 32 is mounted on one substrate 31. When formed separately, each substrate 31 is generally fixed to a frame, a support, a housing, or the like. In the present embodiment, as shown in fig. 3, the substrate 31 is preferably formed integrally so as to mount a plurality of light emitters 32 in a lump.

A reflective layer may be formed on the surface of the substrate 31 on the composite adhesive layer 11 side, or a reflective member may be provided. This can effectively improve the luminance of the backlight 30. The material of the reflective layer or the reflective member can be a known material.

Examples of the type of the light emitter 32 include a Light Emitting Diode (LED), a Laser Diode (LD), an organic electroluminescence light emitting element, and an inorganic electroluminescence light emitting element. Among them, from the viewpoint of sealing property by the cured composite adhesive layer 11', an LED is preferable, and a mini LED or a micro LED is particularly preferable.

The thickness of the light-emitting body 32 is preferably 10 μm or more, more preferably 30 μm or more, particularly preferably 50 μm or more, and further preferably 80 μm or more. The thickness of the light-emitting body 32 is preferably 300 μm or less, particularly preferably 150 μm or less, and further preferably 100 μm or less.

The width of the gap between the adjacent light emitters 32 is preferably 0.01mm or more, particularly preferably 0.1mm or more, and more preferably 0.5mm or more. The width of the gap is preferably 100mm or less, more preferably 10mm or less, particularly preferably 4mm or less, and further preferably 2mm or less.

The shape of the light emitter 32 is not particularly limited, and is usually a rectangular parallelepiped, a hemispherical shape, or the like. The size of the light emitter 32 is not particularly limited, and from the viewpoint of light emitter sealing property, the one side or the diameter in a plan view is preferably 0.01 to 100mm, more preferably 0.1 to 10mm, particularly preferably 0.2 to 5mm, and further preferably 0.5 to 2 mm.

The light diffusion adhesive layer 111 of the present embodiment diffuses light emitted from the backlight 30, and can effectively suppress the occurrence of luminance unevenness.

The display unit 40 is, for example, a liquid crystal panel, but is not limited thereto, and may be, for example, a part of a constituent member of a liquid crystal panel or an optical member (for example, a light diffusion plate, an ultraviolet absorption filter, or the like) used together to increase or enhance the function of a liquid crystal panel. The display unit 40 can be a known display unit.

Further, a sealing material may be provided between the backlight 30 and the cured composite adhesive layer 11'. In this case, irregularities are often formed on the surface of the sealing material opposite to the backlight 30, and these irregularities can be absorbed by the transparent adhesive layer 112 of the cured composite adhesive layer 11'.

In addition, a desired optical member may be provided between the cured composite adhesive layer 11 'and the display portion 40, or on the surface of the display portion 40 opposite to the cured composite adhesive layer 11'. Examples of the optical member include a luminance improving film, a contrast improving film, a viewing angle compensating film, a transparent conductive film, a liquid crystal polymer film, a semi-transmissive reflective film, and a scattering preventing film.

In order to manufacture the display 2B of the present embodiment, for example, one release sheet 12a of the adhesive sheet 1 is peeled off, and the transparent adhesive layer 112 exposed on the adhesive sheet 1 is bonded to the surface of the backlight 30 on the side where the light-emitting bodies 32 are present.

Next, the other release sheet 12b is peeled off from the composite adhesive layer 11 of the adhesive sheet 1, and the light diffusion adhesive layer 111 exposed from the adhesive sheet 1 is bonded to the display portion 40. Next, the composite adhesive layer 11 is irradiated with an active energy ray to prepare a cured composite adhesive layer 11'. Alternatively, the composite adhesive layer 11 is irradiated with an active energy ray between the bonded display portions 40 to prepare a cured composite adhesive layer 11', and then bonded to the display portion 40 (the release sheet 12 b). The irradiation conditions of the active energy ray and the like are the same as those of the display 2A.

As another example, the order of attaching the backlight 30 and the display unit 40 may be changed.

The embodiments described above are described for easy understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiments also covers all design changes and equivalents that fall within the technical scope of the present invention.

For example, either one or both of the

release sheets

12a and 12b in the adhesive sheet 1 may be omitted, or a desired optical member may be laminated instead of the release sheet 12a and/or 12 b.

Further, as shown in the adhesive sheet 1A shown in fig. 4, the composite adhesive layer 11 may be formed by laminating a transparent adhesive layer 112, a light diffusion adhesive layer 111, and a transparent adhesive layer 112 in this order. The adhesive sheet 1A is effective when both the first optical member and the second optical member have a step (unevenness) on the composite adhesive layer 11 side. For example, the adhesive sheet 1A is effective when the first optical member and the second optical member are both liquid crystal panels.

For example, any of the

release sheets

12a and 12b in the adhesive sheet 1 may be omitted.

Examples

The present invention will be described in more detail with reference to examples, but the scope of the present invention is not limited to these examples.

[ production example 1] (production of light diffusing adhesive sheet)

Preparation of (meth) acrylate polymers

The (meth) acrylate polymer (a) was prepared by copolymerizing 65 parts by mass of 2-ethylhexyl acrylate, 15 parts by mass of isobornyl acrylate, 5 parts by mass of N-acryloylmorpholine, and 15 parts by mass of 2-hydroxyethyl acrylate by a solution polymerization method. The molecular weight of the (meth) acrylate polymer (a) was measured by the following method, and the weight average molecular weight (Mw) was 50 ten thousand.

2. Preparation of adhesive composition

100 parts by mass of the (meth) acrylate polymer (A) (solid content equivalent; the same applies hereinafter) obtained in the above step 1, 0.20 part by mass of trimethylolpropane-modified tolylene diisocyanate (TOYO KAGAKU, manufactured by INC., product name "BHS 8515") as a crosslinking agent (B), 5.2 parts by mass of epsilon-caprolactone-modified tris- (2-acryloyloxyethyl) isocyanurate (SHIIN-NAKAMURA CHEMICAL CO., LTD., product name "NK ester A-9300-1 CL") as an active energy ray-curable component (C), 5.0 parts by mass of fine particles (manufactured by Momentive Performance Materials Inc.) composed of a silicone resin (a silicon-containing compound having a structure between inorganic and organic substances) as light-diffusing fine particles (D), 5.0 parts by mass of photo-polymerization initiator (E), 5.145 "Tospe, average particle diameter: 4.5 μm), 0.5 part by mass of 4, 6-trimethylbenzoyl-diphenyl-phosphine oxide and 0.2 part by mass of 3-glycidyloxypropyltrimethoxysilane as a silane coupling agent were mixed, sufficiently stirred, and diluted with methyl ethyl ketone to obtain a coating solution of the adhesive composition.

Table 1 shows the respective compounding ratios (solid content equivalent) of the adhesive compositions when the (meth) acrylate polymer (a) is 100 parts by mass (solid content equivalent). The abbreviations and the like shown in table 1 are as follows.

[ (meth) acrylic ester Polymer (A) ]

2 EHA: 2-ethylhexyl acrylate

IBXA: acrylic acid isobornyl ester

ACMO: n-acryloyl morpholine

HEA: 2-Hydroxyethyl acrylate

BA: acrylic acid n-butyl ester

AA: acrylic acid

[ crosslinking agent (B) ]

TDI compounds: trimethylolpropane-modified tolylene diisocyanate (TOYO KAGAKU, manufactured by INC., product name "BHS 8515")

XDI: trimethylolpropane-modified xylylene diisocyanate (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75")

Epoxy resin: 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane (MITSUBISHI GAS CHEMICAL COMPANY, manufactured by INC., product name "TETRAD-C")

[ light diffusing particles (D) ]

D1: microparticles having an average particle diameter of 4.5 μm and composed of a silicone resin (a silicon-containing compound having a structure between inorganic and organic) (manufactured by Momentive Performance Materials Japan Inc., product name "Tospearl 145", refractive index: 1.43)

D2: microparticles having an average particle diameter of 2.0 μm and composed of a silicone resin (a silicon-containing compound having a structure between inorganic and organic) (manufactured by Momentive Performance Materials Japan Inc., product name "Tospearl 120", refractive index: 1.43)

D3: spherical polymethyl methacrylate-polystyrene copolymer fine particles having an average particle diameter of 4.0. mu.m (manufactured by Sekisui Kasei Co., Ltd., product name "XX-30 LA", refractive index: 1.56)

3. Production of light-diffusing adhesive sheet

The coating solution of the adhesive composition obtained in the above step 2 was coated on the release-treated surface of a heavy release type release sheet (manufactured by Lintec Corporation, product name "SP-PET 752150") which had been subjected to a release treatment on one surface of a polyethylene terephthalate film using a silicone-based release agent, using a blade coater, and then heat-treated at 90 ℃ for 1 minute, thereby forming a coating layer (thickness: 50 μm).

Next, the coating layer on the heavy-release type release sheet obtained in the above was bonded to a light-release type release sheet (product name "SP-PET 381031" manufactured by linetec Corporation) obtained by peeling one surface of a polyethylene terephthalate film with a silicone-based release agent so that the peeled surface of the light-release type release sheet was in contact with the coating layer, to thereby produce a light-diffusing adhesive sheet having a structure of a coating layer (thickness: 50 μm)/light-release type release sheet of the heavy-release type release sheet/light-diffusing adhesive layer (a).

The thickness of the light-diffusing adhesive layer is a value measured by using a constant pressure thickness measuring instrument (TECLOCK co., ltd., product name "PG-02") in accordance with JIS K7130 (the same applies hereinafter).

[ production examples 2 to 7, 9 to 10] (production of light diffusion adhesive sheet)

The light diffusion adhesive layer (B) (production example 2), the light diffusion adhesive layer (C) (production example 3), the light diffusion adhesive layer (D) (production example 4), the light diffusion adhesive layer (E) (production example 5), the light diffusion adhesive layer (f) (production example 6), the light diffusion adhesive layer (g) (production example 7), and the light diffusion adhesive layer (i) (production example 9) were produced in the same manner as in production example 1 except that the kinds and proportions of the monomers constituting the (meth) acrylate polymer (a), the weight average molecular weight (Mw) of the (meth) acrylate polymer (a), the blending amount of the crosslinking agent (B), the blending amount of the active energy ray-curable component (C), the kinds and blending amounts of the light diffusion microparticles (D), the photopolymerization initiator (E), and the silane coupling agent were changed to those shown in table 1, And a light-diffusing adhesive sheet comprising the light-diffusing adhesive layer (j) (production example 10). In the light diffusion adhesive sheet having the light diffusion adhesive layer (j) (production example 10), the light diffusion adhesive layer was cured by irradiating active energy rays (ultraviolet rays) through a light-release type release sheet under the same conditions as in test example 1 described below.

[ production example 8] (production of transparent adhesive sheet)

A transparent adhesive sheet having a transparent adhesive layer (h) (production example 8) was produced in the same manner as production example 1, except that the kinds and proportions of the monomers constituting the (meth) acrylate polymer (a), the weight average molecular weight (Mw) of the (meth) acrylate polymer (a), the blending amount of the crosslinking agent (B), the blending amount of the active energy ray-curable component (C), the blending amount of the light diffusion fine particles (D) (not blended), the blending amount of the photopolymerization initiator (E), and the blending amount of the silane coupling agent were changed to those shown in table 1. The transparent adhesive sheet having the transparent adhesive layer (h) used in example 9 was previously irradiated with active energy rays (ultraviolet rays) through a light-release type release sheet under the same conditions as those in test example 1 described below, and the transparent adhesive layer was cured.

The weight average molecular weight (Mw) is a polystyrene-equivalent weight average molecular weight measured by Gel Permeation Chromatography (GPC) under the following conditions (GPC measurement).

< measurement Condition >

GPC measurement apparatus: HLC-8020 manufactured by TOSOH CORPORATION

GPC column (passage in the following order): TOSOH CORPORATION, Inc

TSK guard column HXL-H

TSK gel GMHXL(×2)

TSK gel G2000HXL

Determination of the solvent: tetrahydrofuran (THF)

Measurement temperature: 40 deg.C

[ example 1]

The light release type release sheet was peeled from the light diffusion adhesive sheet prepared in production example 1 to expose the coating layer of the light diffusion adhesive layer (a). Further, the light release type release sheet was peeled from the transparent adhesive sheet prepared in production example 8 to expose the coating layer of the transparent adhesive layer (g). The coating layer of the transparent adhesive layer (g) was laminated on the coating layer of the light-diffusing adhesive layer (a), and then cured at 23 ℃ and 50% RH for 7 days. In this way, an adhesive sheet (light diffusion adhesive layer + transparent adhesive layer — composite adhesive layer) was produced which was composed of a heavy-release type release sheet/light diffusion adhesive layer (a) (50 μm)/transparent adhesive layer (g) (50 μm)/heavy-release type release sheet.

Examples 2 to 9 and comparative examples 1 to 3

An adhesive sheet was produced in the same manner as in example 1, except that the kinds of the light diffusing adhesive layer and the transparent adhesive layer were changed to those shown in table 2. For convenience, table 2 also shows the transparent adhesive layer in the column of the light-diffusing adhesive layer in comparative example 1, and the light-diffusing adhesive layers in the columns of the transparent adhesive layers in comparative examples 2 and 3.

[ test example 1] (measurement of gel fraction)

The adhesive sheet (after aging) produced in each production example and the adhesive sheets obtained in examples and comparative examples were cut into 80mm × 80mm, the adhesive layer was wrapped in a polyester mesh (mesh size 200), the mass thereof was weighed with a precision balance, and the mass of the mesh alone was subtracted, thereby calculating the mass of the adhesive itself. The mass at this time was designated as M1.

Subsequently, the adhesive wrapped in the polyester net was immersed in ethyl acetate at room temperature (23 ℃ C.) for 24 hours. The adhesive was then removed, air-dried at a temperature of 23 ℃ and a relative humidity of 50% for 24 hours, and further dried in an oven at 80 ℃ for 12 hours. After drying, the mass of the adhesive itself was calculated by weighing it with a precision balance and subtracting the mass of the web alone. The mass at this time was designated as M2. Gel fraction (%) was expressed as (M2/M1). times.100. This led to the gel fraction (before UV) of the adhesive. The results are shown in Table 2.

On the other hand, the adhesive layers of the adhesive sheets (after curing) produced in the respective production examples and the adhesive sheets (except for production example 10 and comparative example 3) obtained in examples and comparative examples were irradiated with active energy rays (ultraviolet rays; UV) through a light-release type release sheet under the following conditions to cure the adhesive layers, thereby producing cured adhesive layers. The gel fraction (after UV) of the adhesive of the cured adhesive layer was derived in the same manner as described above. The results are shown in Table 2.

< active energy ray irradiation Condition >

Using high-pressure mercury lamps

Illuminance of 200mW/cm²Light quantity 1000mJ/cm²

UV illuminance-photometer Using "UVPF-A1" manufactured by EYE GRAPHICS Co., Ltd "

[ test example 2] (measurement of storage modulus)

The adhesive sheets prepared in the respective production examples (after curing) and the adhesive sheets obtained in the examples and comparative examples were peeled off from each other, and the adhesive layers were laminated so that the thickness thereof became 800 μm. A cylindrical body (height: 800 μm) having a diameter of 8mm was punched out of the laminate of the obtained adhesive layer, and this was used as a sample.

The storage modulus at 23 ℃ of the above sample (GD1, GT1, G1) (before UV; MPa) was measured by the torsional shear method using a viscoelasticity measuring apparatus (product name "MCR 300" manufactured by Physica corporation) in accordance with JIS K7244-6 under the following conditions. The results are shown in Table 2.

Measuring frequency: 1Hz

Measuring temperature: 23 deg.C

In addition, the same sample as described above (except for production example 10 and comparative example 3) was irradiated with active energy rays (ultraviolet rays; UV) under the same conditions as in test example 1, and the adhesive was cured, thereby obtaining a sample irradiated with active energy rays. The storage modulus at 23 ℃ of the obtained sample after irradiation with active energy rays (GD2, GT2, G2) (after UV; MPa) was measured in the same manner as the sample before irradiation with active energy rays. The results are shown in Table 2.

Further, storage modulus change rates (Δ GD, Δ GT, Δ G') were calculated as ratios (GD2/GD1, GT2/GT1, G2/G1) of storage moduli after irradiation with active energy rays (GD2, GT2, G2) to storage moduli before irradiation with active energy rays (GD1, GT1, G1). The results are shown in Table 2.

[ test example 3] (measurement of haze value)

The composite adhesive layers of the adhesive sheets produced in examples and comparative examples were bonded to glass, and used as samples for measurement. The haze value (%) of the above-mentioned sample for measurement was measured using a haze meter (product name "SH-7000" manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136:2000, on the basis of background measurement (background measurement) using glass. The results are shown in Table 2.

[ test example 4] (measurement of Total light transmittance)

The composite adhesive layers of the adhesive sheets produced in examples and comparative examples were bonded to glass, and used as samples for measurement. The total light transmittance (%) was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "SH-7000" by Ltd.) according to K7361-1:1997 for the above-mentioned measurement sample, on the basis of the background measurement using glass. The results are shown in Table 2.

[ test example 5] (measurement of adhesive force)

The heavy release sheet on the light diffusion adhesive layer side was peeled from the adhesive sheets obtained in examples and comparative examples, and the exposed light diffusion adhesive layer was bonded to an easy adhesive layer of a polyethylene terephthalate (PET) film (TOYOBO co., ltd., product name "PET a 4300", thickness: 100 μm) having an easy adhesive layer, to obtain a laminate of the heavy release sheet/composite adhesive layer/PET film. The obtained laminate was cut into a width of 25mm and a length of 100 mm.

The heavy-release type release Sheet on the transparent adhesive agent layer side was peeled from the laminate in an atmosphere of 23 ℃ and 50% RH, the exposed transparent adhesive agent layer was attached to soda-lime Glass (manufactured by Nippon Sheet Glass co., Ltd), and then pressurized at 0.5MPa and 50 ℃ for 20 minutes using an autoclave manufactured by shiitake. Then, the sample was left at 23 ℃ and 50% RH for 24 hours. Further, the adhesive force was measured using a tensile tester (product name "TENSILON" manufactured by ORIENTEC CORPORATION) under the conditions of a peeling speed of 300 mm/min and a peeling angle of 180 degrees (before the transparent adhesive layer-UV; N/25 mm). The conditions not described herein were measured according to JIS Z0237: 2009.

Next, the sample was irradiated with an active energy ray through a PET film under the same conditions as in test example 1, and the composite adhesive layer was cured to obtain a cured composite adhesive layer. The adhesive force of the cured composite adhesive layer (transparent adhesive layer-after UV; N/25mm) was measured in the same manner as described above. The results are shown in Table 2.

Further, the adhesive force before UV (before light diffusing adhesive layer-UV; N/25mm) on the light diffusing adhesive layer side and the adhesive force after UV (after light diffusing adhesive layer-UV; N/25mm) on the light diffusing adhesive layer side were measured in the same manner as described above. The results are shown in Table 2.

[ test example 5] (evaluation of step tracking Property)

An ultraviolet curable ink (Teikoku Printing Inks Mfg. Co., manufactured by Ltd., product name "POS-911 ink") was screen-printed in a frame shape (outer shape: 90mm in length: 50mm in width, 5mm in width) on the surface of a glass plate (manufactured by NSG Precision Cells, Inc., product name "burning glass eagle XG", 90mm in length X50 mm in width X0.5 mm in thickness). Then, ultraviolet rays (80W/cm) were irradiated²2 metal halogen lamps, a lamp height of 15cm, a belt speed of 10 to 15 m/min), and curing the printed ultraviolet curable ink to produce a printed ultraviolet curable ink having a step difference (height of step difference: 5 μm, 10 μm, 15 μm and 20 μm).

The heavy-release type release Sheet on the light diffusion adhesive layer side was peeled from the adhesive sheets obtained in examples and comparative examples, and the exposed light diffusion adhesive layer was bonded to a soda-lime Glass plate (manufactured by Nippon Sheet Glass co., Ltd, thickness: 0.7 mm). Then, the heavy-release type release sheet on the side of the transparent adhesive layer is peeled off to expose the transparent adhesive layer. Then, the laminate was laminated on glass plates having different steps so that the entire frame-shaped printing surface was covered with the composite adhesive layer using a laminator (product name "LPD 3214" manufactured by fujiapla inc.). Then, the plate was autoclaved at 50 ℃ and 0.5MPa for 30 minutes and left to stand at normal pressure, 23 ℃ and 50% RH for 24 hours.

Next, the composite adhesive layer was cured by irradiating the above soda-lime glass plate with an active energy ray under the same conditions as in test example 1 to prepare a cured composite adhesive layer (except for comparative example 3). Then, the process is carried out. The resultant was stored under wet heat conditions of 85 ℃ and 85% RH for 72 hours (durability test). Then, the level difference following property was evaluated based on the following criteria. The results are shown in Table 2.

Very good: the air bubble-free air.

O: the step height was all followed before the durability test, but after the durability test, the step height of 15 μm or more was foamed, floated, or peeled off.

X: bubbles or floating occurred before the endurance test.

[ test example 6] (evaluation of blister resistance)

The heavy-release type release sheet on the transparent adhesive layer side was peeled from the adhesive sheets obtained in examples and comparative examples, and the exposed transparent adhesive layer was bonded to a PC board side of a plastic board (MITSUBISHI GAS CHEMICAL COMPANY, inc., product name "yupulon sheet MR 58U", thickness: 0.7mm, containing an ultraviolet absorber) in which a PMMA layer was laminated on the PC board, to obtain a plastic board with a composite adhesive layer.

The heavy-release type release Sheet on the light diffusion adhesive layer side was peeled from the plastic plate with the composite adhesive layer obtained in the above, and the plastic plate was attached to a soda-lime Glass plate (manufactured by Nippon Sheet Glass co., Ltd, thickness: 0.7mm) having a size of 70mm × 150mm via the exposed light diffusion adhesive layer. Then, the mixture was autoclaved at 50 ℃ and 0.5MPa for 30 minutes and left at normal pressure, 23 ℃ and 50% RH for 24 hours.

Next, the composite adhesive layer was irradiated with active energy rays through a soda-lime glass plate under the same conditions as in test example 1, and the composite adhesive layer was cured to obtain a cured composite adhesive layer (except for comparative example 3). In this manner, a laminate (70 mm. times.150 mm) in which a plastic plate and a glass plate were bonded by the cured composite adhesive layer was obtained.

The laminate was stored at 85 ℃ under 85% RH high temperature and high humidity for 72 hours. The state of the interface between the cured composite adhesive layer and the adherend (plastic plate, glass plate) was visually confirmed, and the blister resistance was evaluated by the following criteria. The results are shown in Table 2.

No bubbles, floating and peeling.

Fine bubbles were generated.

The whole generates bubbles or floats and peels off.

[ test example 7] (evaluation of luminance unevenness suppression)

As the surface light source, a liquid crystal display device of a flat panel terminal (product name "iPad (registered trademark)", manufactured by Apple inc., resolution: 264ppi) was prepared. The surface of the liquid crystal display device was covered with a stainless steel mesh to obtain a simulated point light source. The conditions of the liquid crystal display device and the details of the stainless steel mesh are as follows.

< liquid crystal display device >

Representation color (display color): white colour

Brightness setting: maximum of

Number of pixels: 980 x 980

< stainless steel net >

Stainless steel type: SUS316

Knitting method: plain weave

Wire diameter: 50 μm

Pore diameter: 204 μm

Open porosity: 64.5 percent

Mesh number: 100(/25.4mm)

On the other hand, the surface of the adhesive Sheet obtained in examples and comparative examples on the light-diffusing adhesive layer side was bonded to a soda-lime Glass plate (manufactured by Nippon Sheet Glass co., Ltd, thickness: 0.7mm), and the obtained laminate was used as a sample.

The sample was placed on a pseudo point light source so that the transparent adhesive layer side of the sample was in contact with the pseudo point light source, and whether or not the wire was visible was visually checked from a position 30cm directly above the sample, and sensory evaluation was performed. Based on the results, the luminance unevenness suppressing performance was evaluated by the following criteria. The results are shown in Table 2.

The wire is hidden and the brightness is distributed uniformly.

The wire was observed in the gaze, but the brightness distribution was almost uniform.

The wire was observed to be conspicuously elongated and the luminance distribution was not uniform.

As is clear from table 2, the adhesive sheets produced in the examples were excellent in the step following property and also excellent in the luminance unevenness suppressing property. In addition, the adhesive sheets produced in examples 1 to 8 were also excellent in blister resistance.

Industrial applicability

The adhesive sheet and the optical laminate of the present invention are suitably used for members or devices requiring uniform light diffusion and durability, and are particularly suitably used for liquid crystal displays and the like.

Claims

1. An adhesive sheet comprising a composite adhesive layer, wherein the composite adhesive layer comprises a light-diffusing adhesive layer containing light-diffusing particles and a transparent adhesive layer containing no light-diffusing particles,

at least one of the light diffusing adhesive layer and the transparent adhesive layer is composed of an active energy ray-curable adhesive.

2. The adhesive sheet according to claim 1, wherein the haze value of the composite adhesive layer is 40% or more and 99% or less.

3. The adhesive sheet according to claim 1, wherein the storage modulus G1 at 23 ℃ of the composite adhesive layer is 0.001MPa or more and 0.2MPa or less.

4. The adhesive sheet according to claim 1, wherein the composite adhesive layer has a storage modulus G2 at 23 ℃ of 0.08MPa or more and 10MPa or less after irradiation with an active energy ray.

5. The adhesive sheet according to claim 1, wherein a storage modulus change rate Δ G' which is a ratio of a storage modulus G2 at 23 ℃ to a storage modulus G1 at 23 ℃ of the composite adhesive layer after irradiation with an active energy ray is 1.1 or more and 100 or less.

6. The adhesive sheet according to claim 1, wherein the adhesive force of the transparent adhesive layer side of the adhesive sheet to soda lime glass is 20N/25mm or more and 80N/25mm or less.

7. The adhesive sheet according to claim 1, wherein the adhesive force of the transparent adhesive layer side of the adhesive sheet to soda-lime glass after irradiation with active energy rays is 20N/25mm or more and 80N/25mm or less.

8. The adhesive sheet according to claim 1, wherein the adhesive force of the light diffusing adhesive layer side of the adhesive sheet to soda lime glass is 1N/25mm or more and 60N/25mm or less.

9. The adhesive sheet according to claim 1, wherein the adhesive force of the light-diffusing adhesive layer side of the adhesive sheet to soda-lime glass after irradiation with active energy rays is 10N/25mm or more and 60N/25mm or less.

10. The adhesive sheet according to claim 1, wherein the thickness of the composite adhesive layer is 20 μm or more and 1000 μm or less.

11. The adhesive sheet according to claim 1, wherein the thickness of the light diffusing adhesive layer is 10 μm or more and 500 μm or less.

12. The adhesive sheet according to claim 1, wherein the thickness of the transparent adhesive layer is 10 μm or more and 500 μm or less.

13. The adhesive sheet according to claim 1, which comprises two release sheets, wherein the composite adhesive layer is sandwiched between the release sheets so as to be in contact with release surfaces of the two release sheets.

14. An optical laminate comprising one optical member, another optical member, and a cured composite adhesive layer obtained by bonding the one optical member and the another optical member to each other, wherein the cured composite adhesive layer is a layer obtained by curing the composite adhesive layer of the adhesive sheet according to any one of claims 1 to 13 with an active energy ray.

15. The optical laminate according to claim 14, wherein at least one of the one optical member and the other optical member has an unevenness on a surface on a side to be bonded with the cured composite adhesive layer, and wherein the transparent adhesive layer of the cured composite adhesive layer is in contact with the unevenness.