TWI819120B - Adhesive sheet for backlight attachment and backlight unit - Google Patents

Abstract

[Problem] Provide an adhesive sheet for backlight attachment, which can be attached to a backlight provided with a plurality of light emitters on a substrate to encapsulate the light emitters without gaps, and provide a backlight unit with such an adhesive sheet for backlight attachment It is attached to the backlight. [Solution] It is an adhesive sheet 1 with an adhesive layer 11 attached to the substrate 21 and provided with a plurality of luminous bodies 22 to encapsulate the backlight 20. The storage modulus of the adhesive layer 11 at 50°C is 0.001. MPa or more and 0.15MPa or less, the gel fraction of the adhesive constituting the adhesive layer 11 is 10% or more and 75% or less, and the thickness of the adhesive layer 11 is 110 μm or more. The adhesive sheet 1 for backlight attachment.

Description

Adhesive sheet and backlight unit for backlight attachment

The present invention relates to an adhesive sheet for attaching a backlight to a display device having a display portion composed of a liquid crystal panel, various optical members, etc., and a backlight that illuminates the display portion, and to an adhesive sheet for attaching the backlight to such a backlight. Backlight unit with adhesive layer.

In recent years, liquid crystal display devices are often used as displays in electronic devices such as mobile phones, smart phones, tablet computers, and game consoles. Since a display portion composed of a liquid crystal panel or the like does not emit light itself, the display device is configured with a display portion and a backlight that illuminates the display portion.

There are two types of backlight light source arrangements in a display device: a side-light type in which the light source is arranged on the side of the light guide plate, and a direct type in which the light source is arranged directly behind the display unit. From the perspective of screen brightness and contrast, direct-type backlights have become mainstream. In a direct-type backlight, a large number of light-emitting bodies, typically light-emitting diodes (LEDs), are provided on a substrate in order to obtain the amount of light and make the light uniform.

Here, the display device usually adheres and fixes the display part and the backlight via an adhesive sheet. Such adhesive sheets are disclosed in Patent Documents 1 and 2, for example. Such an adhesive sheet has a planar frame-like shape, and the display portion and the backlight are bonded to each other at the edges. Therefore, a gap is formed inside the frame-shaped adhesive sheet, and an air layer exists. [Previous Patent Document] [Patent Document]

[Patent Document 1] Japanese Patent No. 5192682 [Patent Document 2] Japanese Patent Application Publication No. 2007-059386

[Problem to be solved by the invention]

However, once an air layer exists inside the display device as described above, the difference in refractive index between the air layer and its adjacent layer causes an increase in light reflection loss, thereby degrading the image quality of the display device.

In order to solve the above problem, it is considered to attach an adhesive sheet to the entire surface of the backlight. However, as mentioned above, a large number of LEDs are provided on the substrate of the backlight. It is known that there is no adhesive sheet that can be attached to the entire surface of such a backlight without gaps. For example, some of the adhesive sheets disclosed in Patent Documents 1 and 2 have specified performance when used as a frame-shaped portion, but they do not have sufficient performance to be directly attached to many LEDs without gaps.

On the other hand, it is also considered to not use an adhesive sheet, but to coat the entire surface of the backlight with an adhesive to form an adhesive layer, but there is a problem of poor productivity.

In view of the above actual situation, the present invention is to provide an adhesive sheet for backlight attachment, which is attached to a backlight provided with a plurality of luminous bodies on a substrate to encapsulate the luminous bodies without gaps, and such an adhesive sheet for backlight attachment. The purpose is to attach a backlight unit to the backlight unit. [Technical means to solve problems]

In order to achieve the above objects, first, the present invention provides an adhesive sheet for backlight attachment, which is an adhesive sheet with an adhesive layer. The adhesive layer is attached to a backlight provided with a plurality of luminous bodies on a substrate to encapsulate the luminous material. The body is characterized in that the storage modulus of the adhesive layer at 50°C is between 0.001 MPa and 0.15 MPa, the gel fraction of the adhesive constituting the adhesive layer is between 10% and 75%, and the above-mentioned adhesive The thickness of the agent layer is 110 μm or more (Invention 1).

According to the above invention (Invention 1), the adhesive layer has the above physical properties, and a backlight with a plurality of luminous bodies is provided on the substrate, and the adhesive layer can be attached without gaps to encapsulate the luminous bodies.

In the above invention (Invention 1), it is preferable that the storage modulus of the adhesive layer at 23°C is 0.01 MPa or more and 0.20 MPa or less (Invention 2).

In the above inventions (Inventions 1 and 2), the adhesive is preferably an acrylic adhesive (Invention 3).

In the above invention (Inventions 1 to 3), it is preferable to have two release sheets, and the adhesive layer that is in contact with the release surfaces of the two release sheets and sandwiched between the release sheets (Invention 4).

Secondly, the present invention provides a backlight unit, which is a backlight unit having a plurality of luminous bodies on one or more substrates, and an adhesive layer attached to the backlight to encapsulate the luminous bodies. It is characterized in that the adhesive layer is the adhesive layer (Invention 5) of the above-mentioned adhesive sheet for backlight attachment (Inventions 1 to 4).

In the above invention (Invention 5), it is preferable that the light-emitting body is a light-emitting diode (Invention 6). [Effects of the invention]

The adhesive sheet for backlight attachment according to the present invention can be attached to a backlight provided with a plurality of luminous bodies on a substrate to encapsulate the luminous bodies without gaps. In addition, in the backlight unit of the present invention, the plurality of light emitters on the substrate are encapsulated with an adhesive layer attached to the backlight in a gap-free manner, so that degradation of the image quality of the resulting display can be suppressed.

[For carrying out the invention]

The embodiments of the present invention will be described below. [Adhesive sheet for backlight attachment] An adhesive sheet for attaching a backlight (sometimes referred to as an "adhesive sheet" in this specification) according to an embodiment of the present invention has an adhesive layer attached to a backlight with a plurality of luminous bodies on a substrate to encapsulate the backlight. The luminous body is preferably formed by laminating a release sheet on one or both sides of the adhesive layer.

The specific structure of an example of an adhesive sheet for attaching a backlight according to this embodiment is shown in Figure 1 . As shown in Figure 1, the adhesive sheet (adhesive sheet) 1 for backlight attachment is composed of two peeling sheets 12a and 12b and is sandwiched between the two peeling sheets 12a and 12b and is in contact with the peeling surfaces of the two peeling sheets 12a and 12b. The adhesive layer 11 is formed between the release sheets 12a and 12b. In addition, the release surface of the release sheet in this specification refers to the surface of the release sheet that has releasability, and also includes the surface that has been subjected to release treatment and the surface that has not been subjected to release treatment but shows releasability.

1. Each component 1-1. Adhesive layer The adhesive layer 11 of the adhesive sheet 1 of this embodiment has a storage modulus at 50°C of 0.001 MPa or more and 0.15 MPa or less, and the gel fraction of the adhesive constituting the adhesive layer 11 is 10% or more. Below 75%, thickness is above 110μm.

The adhesive layer 11 has the above physical properties. The adhesive sheet 1 of this embodiment allows the adhesive layer 11 to be attached to a backlight provided with a plurality of luminous bodies on a substrate to encapsulate the luminous bodies without gaps. Thereby, there is no air layer or gap between the display part and the backlight of a display device, etc., so it is possible to prevent deterioration in image quality due to light reflection loss.

Specifically, the storage modulus of the adhesive layer 11 at 50°C is 0.15 MPa or less, and the gel fraction of the adhesive constituting the adhesive layer 11 is 75% or less, so the adhesive layer 11 exhibits excellent flexibility. And stress relaxation, it is easy to bury the luminous body, and the luminous body can be packaged without gaps.

On the other hand, a plurality of luminous bodies provided in the backlight may generate heat due to light emission. When a plurality of luminous bodies are provided, the adhesive layer 11 may be exposed to high temperature conditions (durability conditions). The storage modulus of the adhesive layer 11 at 50°C is more than 0.001 MPa, and the above-mentioned gel fraction is more than 10%, so the void-free encapsulation of the adhesive layer 11 can be easily maintained even under the above-mentioned durable conditions.

From the viewpoint of embedding properties of the luminous body, the storage modulus of the adhesive layer 11 at 50° C. is preferably 0.13 MPa or less, particularly preferably 0.09 MPa or less, and more preferably 0.05 MPa or less. In addition, from the viewpoint of encapsulation of the light-emitting body under durable conditions, the storage modulus is preferably 0.01 MPa or more, particularly preferably 0.02 MPa or more, and more preferably 0.03 MPa or more.

From the viewpoint of embedding the luminous body, the gel fraction of the adhesive constituting the adhesive layer 11 is preferably 70% or less, particularly 64% or less, and even more preferably 57% or less. In addition, from the viewpoint of encapsulation of the light emitter under durable conditions, the gel fraction is preferably 20% or more, more preferably 30% or more, particularly preferably 40% or more, and more preferably 50% or more.

On the other hand, the storage modulus of the adhesive layer 11 at 23°C is preferably 0.20 MPa or less, more preferably 0.18 MPa or less, particularly preferably 0.15 MPa or less, and particularly preferably 0.11 MPa or less, from the viewpoint of embedding properties of the luminous body. In addition, from the viewpoint of encapsulation of the light-emitting body under durable conditions, the storage modulus is preferably 0.01 MPa or more, particularly preferably 0.02 MPa or more, and more preferably 0.04 MPa or more.

The storage modulus in this manual is a value measured by a torsional shear test at a measurement frequency of 1 Hz in accordance with JIS K7244-6. In addition, the method for measuring the gel fraction of the adhesive in this manual is as shown in the test example described below.

Since the adhesive layer 11 has the above-mentioned storage modulus and gel fraction, and has a thickness of 110 μm or more, it can encapsulate the luminous body according to the type of the luminous body. From the perspective of luminous body packaging, the thickness of the adhesive layer 11 is preferably 130 μm or more, particularly preferably 160 μm or more, and more preferably 200 μm or more. On the other hand, from the viewpoint of thinning the obtained display, the thickness of the adhesive layer 11 is preferably 1000 μm or less, particularly preferably 800 μm or less, and more preferably 500 μm or less.

In addition, the ratio of the thickness of the adhesive layer 11 to the thickness of the luminous body (thickness of the adhesive layer/thickness of the luminous body) is preferably 1.1 or more, more preferably 1.4 or more, and 2.0 or more from the perspective of reliably encapsulating the luminous body. Very good, 2.2 or above is better. On the other hand, the thickness ratio described above is preferably 10 or less, more preferably 8 or less, particularly preferably 5 or less, and more preferably 2.9 or less, from the viewpoint of thinning the obtained display.

The type of adhesive constituting the adhesive layer 11 of the adhesive sheet 1 in this embodiment is not particularly limited as long as it satisfies the aforementioned physical property values. For example, it can be an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, or a rubber adhesive. Adhesives, silicone adhesives, etc. In addition, the adhesive may be any one of emulsion type, solvent type or solvent-free type, and may be any one of cross-linked type or non-cross-linked type. Among these, an acrylic adhesive that easily satisfies the aforementioned physical property values is preferred.

In addition, the acrylic adhesive may be active energy ray curable or active energy ray non-curable, but an active energy ray non-curable acrylic adhesive that does not require a photopolymerization initiator is preferred. The active energy ray non-hardening acrylic adhesive is particularly preferably a cross-linking type, and even more preferably a thermal cross-linking type.

The above-mentioned adhesive is cross-linked with an adhesive composition (hereinafter referred to as "adhesive composition P") containing a (meth)acrylate polymer (A) and a cross-linking agent (B). Whichever is better. In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same goes for other similar terms. In addition, "polymer" also includes the concept of "copolymer".

(1) Ingredients of adhesive composition (1-1) (Meth)acrylate polymer (A) In this embodiment, the (meth)acrylate polymer (A) uses a reactive group-containing monomer having a reactive group in the molecule that reacts with the cross-linking agent (B) as the monomer constituting the polymer. Unit is better. The reactive group derived from the reactive group-containing monomer reacts with the cross-linking agent (B) to form a cross-linked structure (three-dimensional network structure), and it is easy to obtain an adhesive with the aforementioned gel fraction and storage modulus.

Preferred examples of the reactive group-containing monomer include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomer), monomers having a carboxyl group in the molecule (carboxyl group-containing monomer), and monomers having an amine group in the molecule (hydroxyl group-containing monomer). Amine monomer), etc. Among these, hydroxyl-containing monomers are particularly preferred from the viewpoint of maintaining a low storage modulus.

Hydroxyl-containing monomers, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, Hydroxyalkyl (meth)acrylate, such as 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and the like. Among them, from the viewpoint of the reactivity of the hydroxyl group in the obtained (meth)acrylate polymer (A) with the cross-linking agent (B) and the copolymerizability with other monomers, a hydroxyl group having a carbon number of 1 to 4 Alkyl hydroxyalkyl (meth)acrylates are preferred. Specific examples include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and the like, and particularly 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate. These can be used individually or in combination of 2 or more types.

Ethylenically unsaturated carboxylic acid containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, citraconic acid, etc. acid. Among them, acrylic acid is preferred from the viewpoint of the reactivity between the carboxyl group in the obtained (meth)acrylate polymer (A) and the cross-linking agent (B) and the copolymerizability with other monomers. These can be used individually or in combination of 2 or more types.

Amino group-containing monomers, such as aminoethyl (meth)acrylate, n-butylaminoethyl (meth)acrylate, etc. These can be used individually or in combination of 2 or more types.

The (meth)acrylate polymer (A) preferably contains a lower limit value of 3 mass % or more of a reactive group-containing monomer as the monomer unit constituting the polymer, and particularly preferably 10 mass % or more. , preferably more than 15% by mass. The (meth)acrylate polymer (A) preferably contains an upper limit of 35% by mass or less of a reactive group-containing monomer as the monomer unit constituting the polymer, and preferably contains 30% by mass or less, In particular, the content is preferably 25% by mass or less. When the (meth)acrylate polymer (A) contains the above-mentioned amount of reactive group-containing monomers as monomer units, the aforementioned storage modulus and gel fraction can be easily obtained.

Furthermore, it is preferable that the (meth)acrylate polymer (A) does not contain a carboxyl group-containing monomer as a monomer unit constituting the polymer. Since the carboxyl group is an acid component, by not containing a carboxyl group-containing monomer, defects caused by acid can be suppressed in the objects to which the adhesive is attached, such as the encapsulating resin of the light emitter, the metal wiring of the substrate, the metal reflective film on the substrate, etc. Where possible, defects (deterioration, corrosion, etc.) caused by acid can also be suppressed. However, it is allowed to contain a predetermined amount of carboxyl group-containing monomer to an extent that does not cause such disadvantages. Specifically, the (meth)acrylate polymer (A) is allowed to contain 0.1 mass % or less of carboxyl group-containing monomers as monomer units, preferably 0.01 mass % or less, and more preferably 0.001 mass % or less. quantity.

The (meth)acrylate polymer (A) preferably contains an alkyl (meth)acrylate as a monomer unit constituting the polymer. As a result, good adhesion can be expressed. The alkyl group may be linear or branched.

The alkyl (meth)acrylate is preferably an alkyl (meth)acrylate having a carbon number of 1 to 20 in the alkyl group from the viewpoint of adhesiveness. Alkyl (meth)acrylate with an alkyl group having 1 to 20 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-(meth)acrylate Butyl ester, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, etc. Among them, from the viewpoint of further improving the adhesion, (meth)acrylate having an alkyl group having 1 to 8 carbon atoms is preferred, and methyl (meth)acrylate, n-butyl (meth)acrylate, or (meth)acrylate is preferred. 2-ethylhexyl methacrylate is particularly preferred. Moreover, these may be used individually or in combination of 2 or more types.

The (meth)acrylate polymer (A) preferably contains 30% by mass or more of alkyl (meth)acrylate as a monomer unit constituting the polymer, preferably 40% by mass or more, and preferably 50% by mass. % or more is particularly preferred, and 55 mass% or more is even more preferred. When the lower limit of the alkyl (meth)acrylate content is the above, the (meth)acrylate polymer (A) can exhibit appropriate adhesiveness. Moreover, the (meth)acrylate polymer (A) preferably contains 97% by mass or less of alkyl (meth)acrylate as a monomer unit constituting the polymer, preferably 90% by mass or less, and contains A content of 80% by mass or less is particularly preferred, and a content of 70% by mass or less is even more preferred. When the upper limit of the alkyl (meth)acrylate content is the above, an appropriate amount of other monomer components such as a reactive functional group-containing monomer may be introduced into the (meth)acrylate polymer (A). , it is easy to adjust the aforementioned gel fraction and storage modulus.

The (meth)acrylate polymer (A) preferably contains a monomer having an alicyclic structure in the molecule (alicyclic structure-containing monomer) as a monomer unit constituting the polymer. Due to the large volume of the alicyclic structural monomer, it is present in the polymer, which presumably increases the distance between the polymers and makes the resulting adhesive more flexible. On the other hand, monomers containing alicyclic structures themselves can provide a certain degree of hardness to the polymer. Therefore, since the (meth)acrylate polymer (A) has an alicyclic structural monomer as a constituent monomer unit, the gel fraction and storage modulus of the resulting adhesive, especially when stored at 50°C The module can be easily adjusted within the aforementioned range.

The carbocyclic ring of the alicyclic structure containing the alicyclic structural monomer may be a saturated structure or may have a part of unsaturated bonds. The alicyclic structure may be a monocyclic alicyclic structure or a polycyclic alicyclic structure such as bicyclic or tricyclic. As mentioned above, from the viewpoint of adjusting the physical property values of the obtained adhesive, the alicyclic structure is preferably a polycyclic alicyclic structure (polycyclic structure). Furthermore, considering the compatibility between the (meth)acrylate polymer (A) and other components, the above-mentioned polycyclic structure is particularly preferably bicyclic to tetracyclic. In addition, as mentioned above, from the viewpoint of adjusting the physical property values of the obtained adhesive, the number of carbon atoms in the alicyclic structure (meaning the total number of carbon atoms in the part forming the ring), and when a plurality of rings exist independently, represents the total number of carbon atoms. number), usually 5 or more is better, and 7 or more is especially good. On the other hand, the upper limit of the number of carbon atoms in the alicyclic structure is not particularly limited. From the viewpoint of compatibility as described above, 15 or less is preferred, and 10 or less is particularly preferred.

Specific examples of the above-mentioned alicyclic structure-containing monomers include cyclohexyl (meth)acrylate, dicyclopentyl (meth)acrylate, adamantyl (meth)acrylate, isocamphenyl (meth)acrylate, (methyl) Dicyclopentenyl acrylate, dicyclopentenyloxyethyl (meth)acrylate, etc. Among them, dicyclopentenyl (meth)acrylate (alicyclic carbon dioxide) exhibits better embedding properties of the luminous substance. Number: 10), adamantane (meth)acrylate (number of carbon atoms in the alicyclic structure: 10), or isocamphenyl (meth)acrylate (number of carbon atoms in the alicyclic structure: 7), especially (methyl)acrylate Base) isocamphenyl acrylate is preferred. These can be used individually or in combination of 2 or more types.

When the (meth)acrylate polymer (A) contains an alicyclic structure-containing monomer as a monomer unit constituting the polymer, it is preferable to contain the alicyclic structure-containing monomer in an amount of 1 mass % or more, especially It is preferable that it contains 5 mass % or more, and it is more preferable that it contains 9 mass % or more. In addition, the (meth)acrylate polymer (A) preferably contains 30% by mass or less of alicyclic structure-containing monomers as the monomer units constituting the polymer, and particularly preferably contains 25% by mass or less. More preferably, it contains 25% by mass or less. The content is preferably 20% by mass or less. When the content of the alicyclic structural monomer is within the above range, the obtained adhesive can be easily adjusted to have the above physical property values.

It is also preferable that the (meth)acrylate polymer (A) contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer. Because nitrogen atom-containing monomers exist as structural units in the polymer, they can provide the polarity specified by the adhesive, and can also have excellent affinity for adherends with a certain degree of polarity such as glass. The above-mentioned nitrogen atom-containing monomer has appropriate rigidity in the (meth)acrylate polymer (A), increases the gel fraction, and increases the storage modulus at 50° C. of the resulting adhesive to a specified level. Monomers with nitrogen-containing heterocycles are preferred. From the viewpoint of increasing the degree of freedom of the portion derived from the nitrogen atom-containing monomer in the high-dimensional structure of the adhesive, the nitrogen atom-containing monomer is preferably used to form (meth)acrylate polymerization Those that do not contain a reactive unsaturated double bond group other than one polymerizable group used for polymerization of substance (A). In addition, the nitrogen atom-containing monomer described here excludes the aforementioned reactive functional group-containing monomer.

Monomers with nitrogen-containing heterocycles, such as N-(meth)acrylylmorpholine, N-vinyl-2-pyrrolidinone, N-(meth)acrylylpyrrolidinone, N-(methyl) N-(meth)acrylylpiperidine, N-(meth)acrylylpyrrolidine, N-(meth)acrylyl azinecyclopropane, (meth)acrylate azethylenecyclopropyl ethyl ester, 2-vinylpyridine , 4-vinylpyridine, 2-vinylpyridine , 1-vinylimidazole, N-vinylcarbazole, N-vinylphthaloimide, etc., among which N-(meth)acrylylmorpholine, which exhibits better adhesion, is preferred, especially N -Acrylomorpholine is preferred. These can be used individually or in combination of 2 or more types.

When the (meth)acrylate polymer (A) contains a nitrogen atom-containing monomer as a monomer unit constituting the polymer, the nitrogen atom-containing monomer is preferably contained in an amount of 1% by mass or more, and in particular, the nitrogen atom-containing monomer is preferably contained in an amount of 2% by mass or more. It is preferable that it contains 3 mass % or more, and it is more preferable that it contains 3 mass % or more. In addition, the (meth)acrylate polymer (A) preferably contains 20% by mass or less of nitrogen atom-containing monomers as the monomer units constituting the polymer, particularly preferably 15% by mass or less, and more preferably The content is preferably 10% by mass or less. If the content of the nitrogen atom-containing monomer is within the above range, it is easy to adjust the storage modulus at 50°C and the gel fraction of the resulting adhesive to be within the above range.

The (meth)acrylate polymer (A) may also contain other monomers as monomer units constituting the polymer if necessary. In order not to hinder the aforementioned effects of the reactive functional group-containing monomer, other monomers are preferably monomers that do not contain reactive functional groups. Examples of such monomers include alkoxyalkyl (meth)acrylate such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, ethyl acetate, and styrene. These can be used individually or in combination of 2 or more types.

The (meth)acrylate polymer (A) is preferably a linear polymer. Since it is a linear polymer, entanglement of molecular chains easily occurs, and it is easy to obtain an adhesive having the aforementioned gel fraction.

In addition, the (meth)acrylate polymer (A) is preferably a solution polymer obtained by a solution polymerization method. Since it is a solution polymer, it is easy to obtain a high molecular weight polymer, and it is expected that the cohesion force will be improved, so it is easy to obtain an adhesive with better encapsulation properties of light emitters under durable conditions. In addition, the amount of residual monomers in the adhesive is reduced and the adhesive has excellent light resistance.

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

The lower limit of the weight average molecular weight of the (meth)acrylate polymer (A) is preferably 200,000 or more, particularly 300,000 or more, and even more preferably 400,000 or more. When the lower limit of the weight average molecular weight of the (meth)acrylate polymer (A) is the above, it is easy to satisfy the aforementioned lower limits of the gel fraction and storage modulus.

The upper limit of the weight average molecular weight of the (meth)acrylate polymer (A) is preferably 2 million or less, more preferably 1.5 million or less, and particularly preferably 1 million or less. When the upper limit of the weight average molecular weight of the (meth)acrylate polymer (A) is the above or lower, the upper limit of the storage modulus described above is easily satisfied. In addition, the weight average molecular weight in this specification is the value converted with the standard polystyrene measured by the gel permeation chromatography (GPC) method.

Moreover, in the adhesive composition P, the (meth)acrylate polymer (A) may be used individually by 1 type, and may be used in combination of 2 or more types.

(1-2) Cross-linking agent (B) The cross-linking agent (B) can cross-link the (meth)acrylate polymer (A) by heating the adhesive composition P to form a three-dimensional network structure. Therefore, the cohesive force of the obtained adhesive is improved, and the gel fraction and storage modulus of the obtained adhesive are easily adjusted to the above ranges.

The above-mentioned cross-linking agent (B) can be one that reacts with the reactive group of the (meth)acrylate polymer (A), such as isocyanate cross-linking agent, epoxy cross-linking agent, amine cross-linking agent, Melamine cross-linking agents, azine-cyclopropane cross-linking agents, hydrazine cross-linking agents, aldehyde cross-linking agents, tetrazoline cross-linking agents, metal alkoxide cross-linking agents, metal chelating agent cross-linking agents agents, metal salt cross-linking agents, ammonium salt cross-linking agents, etc. Among the above, when the reactive group of the (meth)acrylate polymer (A) is a hydroxyl group, it is preferable to use an isocyanate cross-linking agent that has excellent reactivity with the hydroxyl group. When the reactive group of (A) is a carboxyl group, it is appropriate to use an epoxy cross-linking agent that has excellent reactivity with carboxyl groups. Moreover, the cross-linking agent (B) may be used individually by 1 type, and may be used in combination of 2 or more types.

The isocyanate cross-linking agent contains at least a polyisocyanate compound. Polyisocyanate compounds include aromatic polyisocyanates such as toluene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, and isophorone diisocyanate. Alicyclic polyisocyanates such as isocyanate, hydrogenated diphenylmethane diisocyanate, etc., and their biuret (biuret) body, tripolyisocyanate body, and for example, ethylene glycol, propylene glycol, neopentyl glycol, triglyceride Adducts of reactants of small-molecule active hydrogen-containing compounds such as hydroxymethylpropane and castor oil. Among them, trimethylolpropane-modified aromatic polyisocyanate, especially trimethylolpropane-modified toluene diisocyanate and trimethylolpropane-modified xylene diisocyanate are used from the viewpoint of reactivity with hydroxyl groups. good.

Epoxy resin cross-linking agents such as 1,3-bis(N,N-diepoxypropylaminomethyl)cyclohexane, N,N,N',N'-tetraepoxypropyl-m- Xylenediamine, ethylene glycol diepoxypropyl ether, 1,6-hexanediol diepoxypropyl ether, trimethylolpropane diepoxypropyl ether, diepoxypropylaniline, bicyclic Oxypropylamine etc. Among them, 1,3-bis(N,N-diepoxypropylaminomethyl)cyclohexane is preferred from the viewpoint of reactivity with carboxyl groups.

The content of the cross-linking agent (B) in the adhesive composition P is preferably 0.01 parts by mass or more, particularly preferably 0.05 parts by mass or more, and 0.1 parts by mass relative to 100 parts by mass of the (meth)acrylate polymer (A). More than one portion is better. In addition, the content is preferably 10 parts by mass or less, particularly preferably 5 parts by mass or less, and more preferably 0.4 parts by mass or less. When the content of the cross-linking agent (B) is within the above range, it is easier to satisfy the above gel fraction and storage modulus.

(1-3) Various additives In the adhesive composition P, various commonly used additives may be added to the acrylic adhesive as needed, such as silane coupling agent, ultraviolet absorber, antistatic agent, tackifier, antioxidant, light stabilizer, softener, refractive index Adjusters, anti-rust agents, etc. In addition, the polymerization solvent and the diluting solvent mentioned later are not included in the additives constituting the adhesive composition P.

Among the above, the adhesive composition P preferably contains a silane coupling agent. Therefore, the adhesion to optical elements such as the backlight (light emitter, substrate, reflective film) and diffusion elements of the adherend is improved, and the encapsulation of the light emitter under durable conditions is even better.

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

Such silane coupling agents include polymerizable unsaturated group-containing silicon compounds such as ethylenetrimethoxysilane, ethylenetriethoxysilane, methacryloxypropyltrimethoxysilane, and 3-epoxypropyl Silicon compounds with epoxy structures such as propyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-mercaptopropane Thiol group-containing silicon compounds such as triethoxysilane, 3-mercaptopropyldimethoxymethylsilane, 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3 -Aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane and other amino group-containing silicon compounds, 3-chloropropyltrimethoxysilane silane, 3-isocyanatepropyltriethoxysilane, or at least one of these and methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane Condensates of silicon compounds containing alkyl groups, etc. These may be used individually by 1 type, and may be used in combination of 2 or more types.

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 based on 100 parts by mass of the (meth)acrylate polymer (A). good. In addition, the content is preferably 1 part by mass or less, particularly preferably 0.5 part by mass or less, and more preferably 0.3 part by mass or less.

(2) Preparation of adhesive composition The adhesive composition P can be produced by producing the (meth)acrylate polymer (A), mixing the obtained (meth)acrylate polymer (A) and the cross-linking agent (B), and adding additives if necessary. .

The (meth)acrylate polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by a general radical polymerization method. The (meth)acrylate polymer (A) is preferably polymerized by a solution polymerization method using a polymerization initiator if necessary. Examples of the polymerization solution include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, etc., and two or more types may be used in combination.

Examples of polymerization initiators include azo compounds, organic peroxides, and the like, and two or more types may be used in combination. Azo compounds such as 2,2'-Azobisisobutyronitrile, 2,2'-Azobis(2-methylbutyronitrile), 1,1'-Azobis(cyclohexane 1-carbonitrile) , 2,2'-Azobis(2,4-dimethylvaleronitrile), 2,2'-Azobis(2,4-dimethyl-4-methoxyvaleronitrile), 2,2 '-Azobis(2-methylpropionic acid)dimethyl ester, 4,4'-Azobis(4-cyanovaleric acid), 2,2'-Azobis(2-hydroxymethylpropionitrile) , 2,2'-azobis[2-(2-imidazolin-2-yl)propane], etc.

Organic peroxides such as benzoyl peroxide, tertiary butyl peroxybenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, bis(2-ethyl) Oxyethyl) peroxydicarbonate, tertiary butyl neodecanoate peroxide, tertiary butyl peroxytrimethylacetate, peroxide (3,5,5-trimethylhexanoic acid), dipropylene peroxide Diethyl peroxide, diethyl peroxide, etc.

In addition, in the above-mentioned polymerization step, by blending a chain transfer agent such as 2-mercaptoethanol, the weight average molecular weight of the resulting polymer can be adjusted.

If the (meth)acrylate polymer (A) is obtained, add the cross-linking agent (B) to the solution of the (meth)acrylate polymer (A), and if necessary, add the diluting solvent and additives, and mix thoroughly. A solvent-diluted adhesive composition P (coating solution) was obtained. Furthermore, if any of the above components is used in solid form, or if it precipitates when mixed with other components in an undiluted state, the component can be separately dissolved or diluted in a diluting solvent before being mixed with other components.

Examples of the diluting solvent include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane, aromatic hydrocarbons such as toluene and xylene, methylene chloride, and ethylene chloride. Halogenated hydrocarbons, alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol, acetone, methyl ethyl ketone, 2-pentanone, isophorone, cyclohexanone, etc. Ketones, esters such as ethyl acetate and butyl acetate, cellosolve solvents such as ethylcellulose, etc.

The concentration and viscosity of the coating solution produced in this way can be within the range that can be coated, and are not particularly limited, and can be appropriately selected depending on the situation. For example, the concentration of the adhesive composition P is diluted to 10 to 60% by mass. In addition, when obtaining the coating solution, the addition of a diluting solvent or the like is not a necessary condition. If the adhesive composition P has a coating viscosity, etc., the diluting solvent does not need to 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 the diluent solvent.

(3) Formation of adhesive layer The adhesive layer 11 of this embodiment is preferably composed of an adhesive that crosslinks the adhesive composition P (the coating layer). Cross-linking of the adhesive composition P can usually be carried out via heat treatment. In addition, this heat treatment may also serve as a drying treatment when the coating layer of the adhesive composition P applied to a desired object evaporates the diluting solvent or the like.

The heating temperature for the heat treatment is preferably 50 to 150°C, especially 70 to 120°C. The heating time is preferably 10 seconds to 10 minutes, especially 50 seconds to 2 minutes.

After heat treatment, you can also set a curing time of about 1 to 2 weeks at normal temperature (for example, 23°C, 50%RH) if necessary. When the aging time is necessary, the adhesive is formed after the aging time has elapsed. When the aging time is not required, the adhesive is formed after the heat treatment is completed.

Through the above-mentioned heat treatment (and aging), the (meth)acrylate polymer (A) is fully cross-linked through the cross-linking agent (B). The adhesive obtained in this way easily satisfies the above physical property values.

(4) Physical properties of adhesive The amount of monomers contained in the adhesive in this embodiment is mainly the residual amount of monomers used for copolymerization of the (meth)acrylate polymer (A), and is preferably 10% by mass or less, especially 1% by mass. % or less is preferred, and less than 0.1 mass% is preferred. Therefore, the obtained adhesive layer 11 has excellent light resistance and can suppress discoloration even if it is used for a long time in contact with a plurality of light-emitting bodies.

The lower limit of the monomer content of the adhesive in this embodiment is preferably 0% by mass, usually 0.001% by mass or more, and particularly preferably 0.005% by mass or more.

1-2. Peel-off sheet The peeling sheets 12a and 12b protect the adhesive layer 11 until the adhesive sheet 1 is used, and are peeled off when the adhesive sheet 1 (adhesive layer 11) is used. In the adhesive sheet 1 of this embodiment, one or both of the release sheets 12a and 12b are not necessary.

As the release sheets 12a and 12b, for example, polyethylene film, polypropylene film, polybutylene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film can be used. Diester film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene ethyl acetate film, ionomer resin film, ethylene·(meth)acrylic acid copolymer film, ethylene •(Meth)acrylate copolymer film, polystyrene film, polycarbonate film, polyimide film, fluororesin film, etc. Such cross-linked films may also be used. Furthermore, it may also be a laminated film.

It is preferable to perform a peeling process on the peeling surface of the said peeling sheet 12a, 12b (particularly the surface which contacts the adhesive layer 11). Strippers used for stripping treatments, such as alkyd, polysiloxane, fluorine, unsaturated polyester, polyolefin, and wax strippers. Among the release sheets 12a and 12b, it is preferable that one of the release sheets is a heavy release type release sheet with a large release force, and the other release sheet is a light release type release sheet with a small release force.

The thickness of the release sheets 12a and 12b is not particularly limited, but is usually about 20 to 150 μm.

2. Physical properties (1) Total light transmittance The total light transmittance (value measured according to JIS K7361-1:1997) of the adhesive layer 11 of the adhesive sheet 1 of this embodiment is preferably 90% or more, especially 93% or more. More preferably, it is 93% or more. Better than 95%. When the total light transmittance is above, the transparency is high, making it suitable for backlight attachment.

In addition, the total light transmittance of the adhesive layer 11 after the adhesive sheet 1 of this embodiment is placed under the conditions of 50°C and 50% RH for 500 hours is preferably 90% or more, especially 93% or more. It is better, and more than 95% is better. When the total light transmittance is as above, even under heat-resistant conditions where the heating state of the luminous body in contact with the adhesive layer 11 lasts for a long time, the transparency is still high, making it more suitable for backlight attachment.

Furthermore, for the adhesive sheet 1 of this embodiment, the total light transmittance of the adhesive layer 11 after irradiating ultraviolet rays for 500 hours at an illumination intensity of 500 mW/m ² is preferably 90% or more, especially 93% or more. , preferably above 95%. When the total light transmittance is as above, even under the condition that the light-emitting state in contact with the adhesive layer 11 lasts for a long time, it can still be said to have excellent light resistance, making it more suitable for backlight attachment.

(2) Haze value

The haze value of the adhesive layer 11 of the adhesive sheet 1 in this embodiment is preferably 30% or less, more preferably 20% or less, especially 10% or less, and even more preferably 1% or less. Since the haze value of the adhesive layer 11 is as described above, it has excellent light transmittance and is suitable for backlight attachment. In addition, the above-mentioned haze value is a characteristic value that also includes the thickness of the adhesive layer. Regardless of the thickness of the adhesive layer, those that satisfy the above-mentioned haze value are preferred.

Even if the thickness of the adhesive layer 11 in this embodiment is thicker than 250 μm, it is easy to satisfy the above haze value. The adhesive sheet 1 of this embodiment can achieve the low haze value as mentioned above by using the above-mentioned adhesive composition P.

In addition, the haze value of the adhesive layer 11 after the adhesive sheet 1 of this embodiment is placed under the conditions of 50°C and 50% RH for 500 hours is preferably 30% or less, preferably 20% or less, especially It is better to be below 10%, and even better to be below 1%. When the haze value is as above, even under heat-resistant conditions where the heat generation state of the luminous body in contact with the adhesive layer 11 lasts for a long time, the transparency is still high, making it more suitable for backlight attachment.

Furthermore, for the adhesive sheet 1 of this embodiment, the haze value of the adhesive layer 11 after irradiation with ultraviolet rays at an illumination intensity of 500 mW/m ² for 500 hours is preferably 30% or less, preferably 20% or less, especially 10 It is better to be below %, and even better to be below 1%. When the haze value is as above, even if the light-emitting state in contact with the adhesive layer 11 lasts for a long time, the light resistance can be said to be excellent, making it more suitable for backlight attachment.

In addition, under any conditions, the lower limit of the haze value of the adhesive layer 11 of the adhesive sheet 1 of this embodiment is not particularly limited, but it is preferably 0% or more, and more preferably 0.1% or more. Here, the haze value in this manual is the value measured in accordance with JIS K7136:2000.

(3)Color

According to the chromaticity a* specified in the CIE1976L*a*b* color system, the adhesive layer 11 of this embodiment is preferably -5.0~5.0, especially -3.0~3.0, and more preferably -2.0~2.0 Better. In addition, the adhesive layer 11 of this embodiment has a chromaticity b* specified in the CIE1976L*a*b* color system, which is preferably -5.0~5.0, especially -3.0~3.0, and more preferably -2.0~ 2.0 is better. When the chromaticity a* and chromaticity b* are within the above range, the adhesive layer 11 is nearly colorless and transparent, making it suitable for backlight attachment.

In addition, the chromaticity a* of the adhesive layer 11 after the adhesive sheet 1 of this embodiment is placed under the conditions of 50°C and 50% RH for 500 hours is preferably -5.0 to 5.0, especially -3.0 to 3.0. is better, and -2.0~2.0 is even better. In addition, the color b* is preferably -5.0~5.0, especially -3.0~3.0, and even more preferably -2.0~2.0. When the chromaticity a* and chromaticity b* are within the above range, even under heat-resistant conditions where the heating state of the luminous body in contact with the adhesive layer 11 lasts for a long time, the adhesive layer 11 remains close to colorless and transparent, making it more suitable for For backlight attachment users.

Furthermore, for the adhesive sheet 1 of this embodiment, the chromaticity a* of the adhesive layer 11 after irradiation with ultraviolet rays for 500 hours at an illumination intensity of 500 mW/m ² is preferably -5.0 to 5.0, and particularly -3.0 to 3.0. Better, -2.0~2.0 is better. In addition, the color b* is preferably -5.0~5.0, especially -3.0~3.0, and even more preferably -2.0~2.0. When the chromaticity a* and chromaticity b* are within the above range, even if the luminescent state of the luminous body in contact with the adhesive layer 11 lasts for a long time, the adhesive layer 11 is still close to colorless and transparent, which can be said to have excellent light resistance. Becoming more suitable as a backlight attachment user.

In addition, the measurement method of chromaticity a* and chromaticity b* in this specification is as described in the test example mentioned later.

(4) Adhesion The lower limit of the adhesion force of the adhesive sheet 1 of this embodiment to soda-lime glass at 23°C is preferably above 10N/25mm, preferably above 13N/25mm, especially preferably above 15N/25mm, and more preferably 26N/ 25mm or above is preferred. When the lower limit of the adhesion force is the above, the light-emitting device has better encapsulation properties. In addition, the upper limit of the adhesive force of the adhesive sheet 1 of this embodiment to soda-lime glass at 23°C is preferably 100N/25mm or less, more preferably 80N/25mm or less, and particularly preferably 50N/25mm or less. The upper limit of the adhesive force is the above, and good reworkability can be obtained.

Here, the adhesive force at 23°C in this manual basically refers to the adhesive force measured according to the 180-degree tear-off method of JIS Z0237:2009. The measurement sample is 25 mm wide and 100 mm long. The measurement sample is attached After applying pressure to the adherend at 0.5MPa at 50°C for 20 minutes, place it at normal pressure, 23°C, and 50%RH for 24 hours, and measure at a peeling speed of 300mm/min.

The lower limit of the adhesive force of the adhesive sheet 1 of this embodiment to soda-lime glass at 50°C is preferably 2N/25mm or more, especially 4N/25mm or more, and even more preferably 6N/25mm or more. When the lower limit value of the adhesive force is the above, the encapsulation property of the light emitter under heat-resistant conditions becomes better. In addition, the upper limit of the adhesive force of the adhesive sheet 1 of this embodiment to soda-lime glass at 50°C is not particularly limited, but is preferably 100N/25mm or less, more preferably 80N/25mm or less, and particularly preferably 50N/25mm or less. .

The measurement method of adhesive force at 50℃ in this manual basically refers to the adhesive force measured according to the 180-degree tear-off method of JIS Z0237:2009. The measurement sample is 25mm wide and 100mm long. The measurement sample is pasted Attach to the adherend, pressurize it at 0.5MPa at 50°C for 20 minutes, then place it under normal pressure, 50°C, and 50% RH for 6 hours, and measure at a peeling speed of 300mm/min.

3. Manufacturing of adhesive sheets One example of manufacturing the adhesive sheet 1 is to apply a coating solution of the above-mentioned adhesive composition P on the release surface of one of the release sheets 12a (or 12b), and perform heat treatment to thermally crosslink the adhesive composition P. After forming the coating layer, the coating layer is overlapped with the peeling surface of the other peeling sheet 12b (or 12a). When curing time is necessary, the above-mentioned coating layer is directly formed into the adhesive layer 11 after the curing time is passed. When curing time is not required, the above-mentioned coating layer is directly formed. In this way, the above-mentioned adhesive sheet 1 is obtained. The conditions for heat treatment and aging are as described above.

Another manufacturing example of the adhesive sheet 1 is to apply the above-mentioned coating solution of the adhesive composition P on the peeling surface of one of the peeling sheets 12a, and perform heat treatment to thermally cross-link the adhesive composition P to form a coating. cloth layer to obtain a peeling sheet 12a with a coating layer. On the peeling surface of the other peeling sheet 12b, apply the coating solution of the above-mentioned adhesive composition P, and perform heat treatment to thermally cross-link the adhesive composition P to form a coating layer, thereby obtaining a coating layer. The peeling piece 12b. Thereafter, the peeling sheet 12a with the coating layer and the peeling sheet 12b with the coating layer are bonded together so that the two coating layers are in contact with each other. Here, a plurality of release sheets with coating layers may be produced, and only a desired number of the coating layers may be bonded. When curing time is required, the curing time is allowed to pass. When curing time is not required, the laminated coating layer is directly formed into the adhesive layer 11 . In this way, the above-mentioned adhesive sheet 1 is obtained. According to this manufacturing example, stable manufacturing is possible even when the adhesive layer 11 is thick.

As a method of applying the coating solution of the adhesive composition P, for example, rod coating, blade coating, roll coating, plate coating, nozzle coating, gravure coating, etc. can be used.

[Backlight unit] A backlight unit according to an embodiment of the present invention is shown in Figure 2 . As shown in Figure 2, the backlight unit 2 of this embodiment has a backlight 20 with a plurality of luminous bodies 22 provided on one or more substrates 21, and is attached to the backlight 20 to encapsulate the luminous bodies. 22 composed of adhesive layer 11.

The adhesive layer 11 of the backlight unit 2 is the adhesive layer 11 of the adhesive sheet 1 for attaching the backlight. The plurality of luminous bodies 22 are sealed through the adhesive layer 11 without gaps. Through this, the resulting display has no air layer and gaps inside, which can prevent the degradation of image quality caused by light reflection loss.

The substrate 21 is not particularly limited, and one generally used for backlights can be used. This substrate 21 is usually a printed circuit board (PCB substrate; Printed Circuit Board).

The substrate 21 may be integrally formed with a plurality of luminous bodies 22 in an integrated manner, or may be formed separately, such as by mounting one luminous body 22 on one substrate 21 . When formed separately, each substrate 21 is usually fixed to a frame, a support, a frame, or the like. In this embodiment, as shown in FIG. 2 , it is preferable that the plurality of luminous bodies 22 are integrally formed on the substrate 21 in an integrated manner.

A reflective layer may be formed on the surface of the substrate 21 on the adhesive layer 11 side, or a reflective element may be provided. Therefore, the brightness caused by the backlight 20 can be effectively increased. The materials of the reflective layer and the reflective element can be made of publicly known materials.

Types of the light emitter 22 include, for example, light emitting diodes (LEDs), laser diodes (LD), organic electroluminescent elements, inorganic electroluminescent elements, and the like. Among them, from the viewpoint of the encapsulation properties of the adhesive layer 11 , LEDs are preferred, and sub-millimeter light-emitting diodes (Mini LEDs) or micro-light emitting diodes (Micro LEDs) are particularly preferred.

The thickness of the luminous body 22 is preferably 10 μm or more, more preferably 30 μm or more, particularly preferably 50 μm or more, and more preferably 80 μm or more. In addition, the thickness of the luminous body 22 is preferably 300 μm or less, particularly preferably 150 μm or less, and further preferably 100 μm or less. With the adhesive layer 11 of this embodiment, even if the thickness of the luminous body 22 is within the above range, it is easy to seal the luminous body 22 without gaps.

In addition, the gap width between adjacent luminous bodies 22 is preferably 0.01 mm or more, particularly 0.1 mm or more, and more preferably 0.5 mm or more. In addition, the above-mentioned gap width is preferably 100 mm or less, more preferably 10 mm or less, particularly preferably 4 mm or less, and more preferably 2 mm or less. If the adhesive layer 11 of this embodiment is used, even if the gap width between the adjacent luminous bodies 22 is within the above range, it is easy to seal the luminous bodies 22 without gaps.

The shape of the luminous body 22 is not particularly limited, and is usually rectangular parallelepiped, hemispherical, or the like. The size of the luminous body 22 is not particularly limited. However, from the perspective of packaging properties of the luminous body, one side or diameter in plan view is preferably 0.01~100mm, preferably 0.1~10mm, especially 0.2~5mm, and more preferably 0.5~2mm. Better.

Here, a display using the backlight unit 2 of this embodiment will be described. The type of display is not particularly limited as long as it uses a backlight unit, but a liquid crystal display device is mainly exemplified.

A liquid crystal display device according to an example of this embodiment is shown in FIG. 3 . As shown in FIG. 3 , the liquid crystal display device 3 of this embodiment has the above-mentioned backlight unit 2 , a diffusion element 31 stacked on the adhesive layer 11 of the backlight unit 2 , and a diffusion element 31 stacked on the opposite side of the backlight unit 2 . It is composed of a liquid crystal panel 32 on the side. Here, the backlight 20 of the liquid crystal display device 3 corresponds to a direct type backlight.

The diffusion element 31 is an element that diffuses the light irradiated from the backlight unit 2. This diffusion element 31 can effectively suppress the occurrence of uneven brightness. The diffusion element 31 can be a well-known one, such as a diffusion plate and a diffusion film, and a combination thereof can be used. The liquid crystal panel 32 may be a publicly known one.

In addition, desired optical elements may be provided between the adhesive layer 11 and the diffusion element 31 , between the diffusion element 31 and the liquid crystal panel 32 , or on the surface of the liquid crystal panel 32 opposite to the diffusion element 31 . Such optical elements include, for example, brightness improvement films, contrast improvement films, viewing angle compensation films, transparent conductive films, liquid crystal polymer films, semi-transflective films, anti-scattering films, and the like.

In manufacturing the liquid crystal display device 3 of this embodiment, for example, one peeling sheet 12 a of the adhesive sheet 1 is peeled off, and the exposed adhesive layer 11 of the adhesive sheet 1 is bonded to the surface of the backlight 20 on the side where the luminous body 22 is present. .

Thereafter, the other release sheet 12 b is peeled off from the adhesive layer 11 of the adhesive sheet 1 , and the exposed adhesive layer 11 of the adhesive sheet 1 and the diffusion element 31 are bonded together. Thereafter, the diffusion element 31 and the liquid crystal panel 32 are bonded using a desired adhesive sheet. In other examples, the order of laminating the backlight 20 and the diffusion element 31 can also be changed.

In the above-mentioned liquid crystal display device 3, the plurality of light emitters 22 of the backlight unit 2 are sealed without gaps due to the adhesive layer 11. Therefore, deterioration in image quality caused by light reflection loss can be prevented. In addition, even if the liquid crystal display device 3 is left under durable conditions, such as 85° C., 85% RH, and 72 hours, the occurrence of floating, peeling, etc. at the interface between the adhesive layer 11 and the luminous body 22 can be suppressed. , the encapsulation of the luminous body 22 by the adhesive layer 11 can be well maintained.

The embodiments described above are described to facilitate understanding of the present invention and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design changes or equivalents that fall within the technical field of the present invention.

For example, either or both of the release sheets 12a and 12b of the adhesive sheet 1 may be omitted, or a desired optical element may be laminated instead of the release sheets 12a and/or 12b. [Example]

The present invention will be further explained in detail below through examples and the like, but the scope of the present invention is not limited to these examples and the like.

[Example 1] 1. Production of (meth)acrylate polymer 60 parts by mass of 2-ethylhexyl acrylate, 10 parts by mass of isocamphenyl acrylate, 10 parts by mass of N-acrylylmorpholine, and 20 parts by mass of 2-hydroxyethyl acrylate were copolymerized by a solution polymerization method , to prepare (meth)acrylate polymer (A). The molecular weight of this (meth)acrylate polymer (A) was measured by the method described below, and was a weight average molecular weight (Mw) of 500,000.

2. Preparation of adhesive composition Mix 100 parts by mass of the (meth)acrylate polymer (A) obtained in the above step 1 (solid content conversion value, the same below) and trimethylolpropane-modified toluene diisocyanate (B) as the cross-linking agent (B). TOYOCHEM, product name "BHS8515") 0.15 parts by mass, and 0.2 parts by mass of 3-epoxypropylpropyltrimethoxysilane as a silane coupling agent, stir thoroughly, and dilute with methyl ethyl ketone to obtain a coating of an adhesive composition cloth solution.

Table 1 shows each preparation (solid content conversion value) of the adhesive composition when the (meth)acrylate polymer (A) is 100 parts by mass (solid content conversion value). In addition, detailed information such as codes listed in Table 1 is as follows. [(Meth)acrylate polymer (A)] 2EHA: 2-ethylhexyl acrylate IBXA: Isobornyl acrylate ACMO: N-Acrylylmorpholine HEA: 2-hydroxyethyl acrylate BA: n-butyl acrylate AA: Acrylic MA: Methyl acrylate EA: Ethyl acrylate [Crosslinking agent (B)] TDI: Trimethylolpropane modified toluene diisocyanate (manufactured by TOYOCHEM, product name "BHS8515") XDI: Trimethylolpropane modified xylylene diisocyanate (manufactured by Soken Chemical Co., Ltd., product name "TD-75") Epoxy resin: 1,3-bis(N,N-diepoxypropylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name "TETRAD-C") A1 chelating agent: aluminum triacetyl acetonate (manufactured by Soken Chemical Co., Ltd., product name "M-5A")

3. Manufacturing of adhesive sheets The coating solution of the adhesive composition obtained in the above step 2 is applied to a heavy-peel release sheet with a polyethylene terephthalate side that is peeled off with a polysiloxane release agent using a knife coating method ( Lintech Corporation, product name "SP-PET752150") was heat-treated at 90°C for 1 minute to form a coating layer (thickness: about 50 μm), and a heavy-peel release sheet with a coating layer was produced.

On the other hand, apply the coating solution of the adhesive composition obtained in the above step 2 on one side of the polyethylene terephthalate using a knife coating method and perform a light peeling treatment with a polysiloxane release agent. After peeling the surface of the type release sheet (manufactured by Lintech, product name "SP-PET381130"), heat treatment at 90°C for 1 minute to form a coating layer (thickness: about 50 μm), and produce a lightly peelable type with a coating layer Peel off the piece. Make 4 pieces of this coated light peel-off type peel-off sheet.

The surface of the heavy release type release sheet with a coating layer obtained above is on the coating layer side, and the surface on the side of the coating layer of the first light release type release sheet with a coating layer obtained above is bonded together, A first laminated body consisting of a coating layer with a total thickness of approximately 100 μm was obtained between a heavy-peel-type release sheet and a light-peel-type release sheet.

Next, the light release type release sheet was peeled off from the first laminated body to expose the exposed surface of the coating layer, and the surface on the coating layer side of the second light release type release sheet with the coating layer was bonded to obtain a heavy-duty product. A second laminated body composed of a coating layer with a total thickness of approximately 150 μm sandwiched between a release-type release sheet and a light-release release sheet.

Next, the lightly peelable release sheet was peeled off from the second laminated body to expose the exposed surface of the coating layer, and the surface on the coating layer side of the third lightly peelable release sheet with a coating layer was bonded to obtain a heavy-weighted product. A third laminated body composed of a coating layer with a total thickness of about 200 μm sandwiched between a peel-off release sheet and a light release release sheet.

Next, the light release type release sheet was peeled off from the third laminated body to expose the exposed surface of the coating layer, and the surface on the coating layer side of the fourth light release type release sheet with the coating layer was bonded to obtain a heavy-duty product. A fourth laminate composed of a coating layer with a total thickness of approximately 250 μm sandwiched between a release-type release sheet and a light-release release sheet.

The above-mentioned fourth laminated body was aged for 7 days under conditions of 23° C. and 50% RH to prepare an adhesive sheet having a structure of a heavy-peel type release sheet/adhesive layer (thickness: 250 μm)/light-peel type release sheet.

In addition, the thickness of the above-mentioned adhesive layer is a value measured using a constant pressure thickness measuring device (manufactured by TECLOCK, product name "PG-02") in accordance with JIS K7130.

[Examples 2 to 6, Comparative Examples 1 to 3] The types and proportions of the monomers constituting the (meth)acrylate polymer (A), the weight average molecular weight (Mw) of the (meth)acrylate polymer (A), the type and compounding amount of the cross-linking agent (B) The adhesive sheet was produced in the same manner as in Example 1 except that the amount of the silane coupling agent and the thickness of the adhesive layer were changed as shown in Table 1. Furthermore, in Example 3 and Comparative Example 2, the thickness of the adhesive layer was changed by changing the number of laminations of the coating layers formed on the light release type release sheet.

Here, the above-mentioned weight average molecular weight (Mw) is a weight average molecular weight in terms of polystyrene measured using the gel permeation chromatography (GPC) method under the following conditions (GPC measurement). >Measurement conditions> •Measuring device: Made by TOSOH, HLC-8320 •GPC column (through the following order): Made by TOSOH Co., Ltd. TSK gel superH-H TSK gel superHM-H TSK gel superH2000 •Measurement solvent: tetrahydrofuran •Measuring temperature: 40℃

[Test Example 1] (Measurement of gel fraction) Cut the adhesive sheet obtained in the Examples and Comparative Examples into a size of 80 mm × 80 mm, wrap the adhesive layer in a polyester mesh (mesh size 200), weigh the mass on a precision balance, and subtract the weight of the mesh. Mass alone, calculate the mass of adhesive only. At this time, it is recorded as mass M1.

Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23° C.) for 24 hours. Then take out the adhesive, air-dry it for 24 hours at a temperature of 23°C and a relative humidity of 50%, and then dry it in an oven at 80°C for 12 hours. After drying, its mass is weighed on a precision balance, and the mass of the adhesive alone is calculated by subtracting the mass of the mesh alone. At this time, it is recorded as mass M2. The gel fraction (%) is expressed as (M2/M1)×100. The results are shown in Table 2.

[Test Example 2] (Measurement of storage modulus) The release sheets were peeled off from the adhesive sheets obtained in Examples and Comparative Examples, and a plurality of adhesive layers were laminated so as to have a thickness of 3 mm. A cylinder with a diameter of 8 mm (height 3 mm) was punched out from the obtained laminate of the adhesive layer, and this was used as a sample.

For the above sample, a viscoelasticity measuring device (manufactured by Physica, product name "MCR300") was used to measure the storage modulus (MPa) at 23°C and 50°C under the following conditions using a torsional shear test in accordance with JIS K7244-6. The results are shown in Table 2. Measurement frequency: 1Hz Measuring temperature: 23℃, 50℃

[Test Example 3] (Measurement of adhesive force) From the adhesive sheets obtained in Examples and Comparative Examples, the light release type release sheet was peeled off, and the exposed adhesive layer and polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "PET") with an easy-adhesion layer A4300", thickness: 100μm), the easy-adhesive layer was bonded to obtain a laminate of release sheet/adhesive layer/PET film. The obtained laminated body was cut into a width of 25 mm and a length of 100 mm, and this was used as a sample.

The heavy-peel release sheet was peeled off from the above sample in an environment of 23°C and 50% RH, and the exposed adhesive layer was attached to soda-lime glass (manufactured by Nippon Sheet Glass Co., Ltd.), and then sterilized in a sterilization kettle manufactured by Kurihara Seisakusho Co., Ltd. Pressurize at 0.5MPa and 50℃ for 20 minutes. After that, leave it at 23°C, 50%RH for 24 hours, or 50°C, 50%RH for 6 hours.

Thereafter, in the same environment as the above conditions (23°C･50%RH/50°C･50%RH), a tensile testing machine (manufactured by ORIENTEC, product name "Tensilon") was used to test at a peeling speed of 300mm/min, Under the condition that the peeling angle is 180 degrees, the adhesion force (N/25mm) is measured at 23°C and 50°C. Conditions other than those stated here are measured in accordance with JIS Z0237:2009. The results are shown in Table 2.

[Test example 4] (Evaluation of embeddability) An adhesive sheet (manufactured by Lintech, product name "MO-T015C") sandwiched between two release sheets with an acrylic adhesive layer (thickness 25 μm) was prepared, and one release sheet was peeled off. The exposed adhesive layer was bonded to an easily adhesive layer of a PET film (manufactured by Toyobo Co., Ltd., product name "PET A4300", thickness: 75 μm) having an easily adhesive layer to obtain a laminate of release sheet/adhesive layer/PET film. . The obtained laminate was cut into a width of 1 mm and a length of 70 mm to use as an adhesive tape, and a plurality of the adhesive tapes were produced.

Peel off the other peeling piece from the above-mentioned adhesive tape, and attach the plurality of adhesive tapes with the adhesive layer exposed to a 70mm × 70mm soda-lime glass ( Manufactured by Nippon Sheet Glass Co., Ltd.), use these as adherends.

On the other hand, the light-peelable release sheet was peeled off from the adhesive sheets obtained in Examples and Comparative Examples, and the exposed adhesive layer and PET film having an easy-adhesive layer (manufactured by Toyobo Co., Ltd., product name "PET A4300", thickness: 50 μm) easy-adhesive layer is bonded to obtain a laminate of release sheet/adhesive layer/PET film. After that, this laminated body is cut into a size of 70mm×70mm.

In an environment of 23°C and 50% RH, the heavy-peel release sheet was peeled off from the above-mentioned laminate to expose the adhesive layer. Next, a laminator (manufactured by FUJIPLA, product name "LPD3214") was used to cover each adhesive tape with an adhesive layer and the laminate was laminated on the adhered volume, and these were used as samples for evaluation.

The obtained evaluation sample was treated in a sterilizing kettle under conditions of 50°C and 0.5MPa for 30 minutes, and then left for 24 hours at room temperature, 23°C, and 50% RH. First, the state of the interface between the adherend and the adhesive layer is visually observed in this state, and the embedding properties (before durability) are evaluated based on the following criteria. The results are shown in Table 2. ◎: No floating or peeling ○: No floating or peeling, but bubbles occur ×: Floating and peeling occur

Thereafter, the above-mentioned sample for evaluation was stored under humid heat conditions of 85° C. and 85% RH for 72 hours (durability test), and then the embedding properties were evaluated in the same manner as above (after durability). The results are shown in Table 2.

[Test Example 5] (Measurement of total light transmittance) From the adhesive sheets obtained in Examples and Comparative Examples, the light release type release sheets were peeled off, and the exposed adhesive layer was bonded to the glass, and these were used as measurement samples. For background measurement using glass, the heavy-peel release sheet was peeled off from the above-mentioned measurement sample to expose the adhesive surface, and a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd.) was used in accordance with JIS K7361-1:1997 at 23°C. , product name "NDH-5000") to measure the total light transmittance (before durability; %). The results are shown in Table 3.

Thereafter, the above-mentioned measurement sample was stored under high temperature conditions of 50° C. and 50% RH for 500 hours (heat resistance test), and then the total light transmittance (after heat resistance test; %) was measured in the same manner as above. The results are shown in Table 3.

On the other hand, the above-mentioned measurement sample was put into a light resistance testing machine (manufactured by SUGA Test Machine Co., Ltd., product name "UV FADE METER U48", light source: carbon arc lamp), and ultraviolet rays were irradiated from the heavy-peel type release sheet side (illuminance: 500mW/m ² ) 500 hours. After that, the total light transmittance (after light resistance test; %) is measured as above. The results are shown in Table 3.

[Test Example 6] (Measurement of haze value) From the adhesive sheets obtained in Examples and Comparative Examples, the light release type release sheets were peeled off, and the exposed adhesive layer was bonded to the glass, and these were used as measurement samples. For background measurement using glass, peel off the heavy-peel release sheet from the above-mentioned measurement sample to expose the adhesive surface, and use a haze meter (manufactured by Nippon Denshoku Industry Co., Ltd., in accordance with JIS K7136:2000) at 23°C. Named "NDH-5000") to measure the haze value (before durability: %). The results are shown in Table 3.

Thereafter, the above-mentioned measurement sample was stored under high temperature conditions of 50° C. and 50% RH for 500 hours (heat resistance test), and then the haze value was measured as above (after heat resistance test; %). The results are shown in Table 3.

On the other hand, the above-mentioned measurement sample was put into a light resistance testing machine (manufactured by SUGA Test Machine Co., Ltd., product name "UV FADE METER U48", light source: carbon arc lamp), and ultraviolet rays were irradiated from the heavy-peel type release sheet side (illuminance: 500mW/m ² ) 500 hours. After that, measure the haze value as above (after light resistance test; %). The results are shown in Table 3.

[Test Example 7] (Measurement of L*a*b*) The adhesive layers of the adhesive sheets obtained in Examples and Comparative Examples were measured according to the CIE1976 L*a*b* color system using a simultaneous photometry spectrophotometer (manufactured by Nippon Denshoku Industry Co., Ltd., product name "SQ2000"). Chroma a* and chroma b* (before durability). The results are shown in Table 3.

Thereafter, the above-mentioned adhesive sheet was stored under high temperature conditions of 50° C. and 50% RH for 500 hours (heat resistance test), and then the chroma a* and chroma b* were measured as above (after the heat resistance test). The results are shown in Table 3.

On the other hand, the above-mentioned adhesive sheet was put into a light resistance testing machine (manufactured by SUGA Test Machine Co., Ltd., product name "UV FADE METER U48", light source: carbon arc lamp), and ultraviolet rays were irradiated from the side of the heavy-peel type release sheet (illuminance: 500 mW/m ² ) 500 hours. After that, measure the chromaticity a* and chromaticity b* as above (after the light fastness test). The results are shown in Table 3.

[Test Example 8] (Measurement of residual monomer amount) 0.02 g of adhesive was separated from each of the adhesive sheets obtained in Examples and Comparative Examples, and the adhesive was put into a small glass bottle with a capacity of 22 mL, and maintained at 120° C. for 30 minutes. Thereafter, a headspace sampler (manufactured by PerkinElmer, product name "Turbomatrix 40") was used to introduce the gas phase components in the small glass bottle into a gas chromatography column (manufactured by Hewlett-Packard, product name "Turbomatrix 40"). 6890"), perform component analysis. In addition, HP-5 manufactured by Hewlett-Packard Co., Ltd. was used as the separation column. The results confirmed that in any example of the adhesive, the amount of residual monomer was less than 0.1% by mass.

[Table 1] (Meth)acrylate polymer (A) Cross-linking agent (B) Silane coupling agent Adhesive layer thickness (μm) composition Mw Kind parts by mass parts by mass Example 1 2EHA/IBXA/ACMO/HEA =60/10/10/20 500,000 TDI 0.15 0.2 250 Example 2 0.15 - 250 Example 3 0.15 0.2 150 Example 4 XDI 0.15 0.2 250 Example 5 BA/AA=90/10 400,000 Epoxy resin 0.05 0.2 250 Example 6 BA/MA/HEA=60/20/20 800,000 TDI 0.25 0.2 250 Comparative example 1 2EHA/IBXA/ACMO/HEA =60/10/10/20 500,000 TDI 3 0.2 250 Comparative example 2 0.15 0.2 100 Comparative example 3 BA/EA/AA=75/20/5 1 million AI chelating agent 0.7 - 250

[Table 2] Gel fraction (%) Storage modulus (MPa) Adhesion (N/25mm) embedded assessment 23℃ 50℃ 23℃ 50℃ Tape interval: 5mm Tape interval: 3mm Tape interval: 1mm long ago After a long time long ago After a long time long ago After a long time Example 1 55 0.07 0.03 33 9 ◎ ◎ ◎ ◎ ◎ ◎ Example 2 55 0.07 0.03 32 8 ◎ ◎ ◎ ◎ ◎ ◎ Example 3 55 0.07 0.03 28 10 ◎ ◎ ◎ ◎ ◎ 〇 Example 4 55 0.07 0.03 34 8 ◎ ◎ ◎ ◎ ◎ ◎ Example 5 58 0.16 0.07 43 33 ◎ 〇 ◎ 〇 ◎ 〇 Example 6 68 0.13 0.07 30 15 ◎ ◎ ◎ 〇 〇 〇 Comparative example 1 95 0.21 0.14 8 1 × × × × × × Comparative example 2 55 0.07 0.03 25 11 × × × × × × Comparative example 3 80 0.16 0.12 twenty three 35 × × × × × ×

[table 3] Total light transmittance (%) Haze value(%) a* b* long ago After heat resistance test After light fastness test long ago After heat resistance test After light fastness test long ago After heat resistance test After light fastness test long ago After heat resistance test After light fastness test Example 1 99≦ 99≦ 99≦ 0.5 0.4 0.5 -0.3 -0.3 -0.3 0.2 0.3 0.4 Example 2 99≦ 99≦ 99≦ 0.4 0.5 0.5 -0.3 -0.3 -0.3 0.2 0.3 0.4 Example 3 99≦ 99≦ 99≦ 0.4 0.4 0.5 -0.3 -0.3 -0.3 0.3 0.3 0.4 Example 4 99≦ 99≦ 99≦ 0.4 0.5 0.5 -0.3 -0.3 -0.2 0.2 0.3 0.3 Example 5 99≦ 99≦ 99≦ 0.5 0.5 0.5 -0.3 -0.3 -0.3 0.3 0.2 0.3 Example 6 99≦ 99≦ 99≦ 0.5 0.4 0.4 -0.3 -0.2 -0.2 0.3 0.4 0.5 Comparative example 1 99≦ 99≦ 99≦ 0.5 0.6 0.6 -0.3 -0.3 -0.3 0.3 0.5 0.7 Comparative example 2 99≦ 99≦ 99≦ 0.4 0.4 0.5 -0.3 -0.2 -0.3 0.3 0.3 0.4 Comparative example 3 99≦ 99≦ 99≦ 0.5 0.5 0.5 -0.4 -0.3 -0.3 0.5 0.5 0.5

As can be seen from Table 2, the adhesive sheet obtained in the Example has excellent embedability before and after the durability test. As can be seen from Table 3, the adhesive sheet obtained in the Example has a high degree of colorless transparency before the durability test, after the heat resistance test, and after the light resistance test. [Industrial Availability]

The adhesive sheet for backlight attachment and the backlight unit of the present invention can be suitably used in, for example, a liquid crystal display device using a direct-type backlight.

1: Adhesive sheet for backlight attachment 11: Adhesive layer 12a,12b: Peel-off sheet 2:Backlight unit 20:Backlight 21:Substrate 22: Luminous body 3: Liquid crystal display device 31: Diffusion element 32:LCD panel

Figure 1 is a cross-sectional view of an adhesive sheet for attaching a backlight according to an embodiment of the present invention. Figure 2 is a cross-sectional view of a backlight unit according to an embodiment of the present invention. Figure 3 is a cross-sectional view of a liquid crystal display device according to an embodiment of the present invention.

1: Adhesive sheet for backlight attachment

11: Adhesive layer

12a,12b: Peel-off sheet

Claims (2)

A backlight unit, which is a backlight unit having a plurality of luminous bodies on one or more substrates, and an adhesive layer attached to the backlight to encapsulate the luminous bodies, characterized in that the adhesive layer The adhesive layer is composed of a single layer. The storage modulus of the adhesive layer at 50°C is above 0.001MPa and below 0.15MPa. The storage modulus of the adhesive layer at 23°C is above 0.01MPa and below 0.07MPa, which constitutes the adhesive layer. The gel fraction of the adhesive in the agent layer is 10% or more and 75% or less. The adhesive is an active energy ray non-hardening acrylic adhesive, and the thickness of the adhesive layer is 110 μm or more. The backlight unit of claim 1, wherein the light-emitting body is a light-emitting diode.

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