阅读说明：本技术 粘着片、背光源单元及显示装置 (Adhesive sheet, backlight unit, and display device ) 是由 福岛裕贵 高桥洋一 小鲭翔 于 2020-08-14 设计创作，主要内容包括：本发明提供一种表现出高雾度值且颜色不均抑制性优异的粘着片、背光源单元及显示装置。所述粘着片为具有粘着剂层(11)的粘着片(1),其中,构成粘着剂层(11)的粘着剂含有光扩散微粒,粘着剂层(11)对波长380nm的光线的雾度值、对波长580nm的光线的雾度值及对波长780nm的光线的雾度值的平均值为70％以上、100％以下,粘着剂层(11)对波长380nm的光线的雾度值、对波长580nm的光线的雾度值及对波长780nm的光线的雾度值的标准偏差为7.50以下,粘着剂层(11)的总透光率为70％以上。(The invention provides an adhesive sheet, a backlight unit and a display device, wherein the adhesive sheet has a high haze value and excellent color unevenness inhibition. The adhesive sheet (1) is provided with an adhesive layer (11), wherein the adhesive constituting the adhesive layer (11) contains light diffusion particles, the average value of the haze value of the adhesive layer (11) to light with a wavelength of 380nm, the haze value to light with a wavelength of 580nm and the haze value to light with a wavelength of 780nm is 70% or more and 100% or less, the standard deviation of the haze value of the adhesive layer (11) to light with a wavelength of 380nm, the haze value to light with a wavelength of 580nm and the haze value to light with a wavelength of 780nm is 7.50 or less, and the total light transmittance of the adhesive layer (11) is 70% or more.)

1. An adhesive sheet having an adhesive layer, characterized in that,

the adhesive constituting the adhesive layer contains light diffusing particles,

the average value of the haze value of the adhesive layer to light with the wavelength of 380nm, the haze value to light with the wavelength of 580nm and the haze value to light with the wavelength of 780nm is more than 70% and less than 100%,

the standard deviation of the haze value of the adhesive layer to light with a wavelength of 380nm, the haze value to light with a wavelength of 580nm and the haze value to light with a wavelength of 780nm is less than 7.50,

the total light transmittance of the adhesive layer is 70% or more.

2. The adhesive sheet according to claim 1, wherein the adhesive layer has a combined image clarity of 0.125mm, 0.25mm, 0.5mm, 1.0mm and 2.0mm combs of 0.1 to 400 inclusive.

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

4. The adhesive sheet according to claim 1, wherein a storage modulus G' of the adhesive constituting the adhesive layer at 23 ℃ is 0.001MPa or more and 10MPa or less.

5. The adhesive sheet according to claim 1, wherein the adhesive sheet has an adhesive force to soda lime glass of 0.1N/25mm or more.

6. The adhesive sheet according to claim 1, wherein the adhesive is an acrylic adhesive.

7. The adhesive sheet according to claim 1,

the adhesive sheet is provided with two sheets of release sheets,

the adhesive layer is sandwiched between the two release sheets so as to be in contact with the release surfaces of the two release sheets.

8. The adhesive sheet according to claim 1, which is used for attaching two hard bodies.

9. A backlight unit comprising a backlight having a plurality of light-emitting bodies and an adhesive layer laminated on the backlight, characterized in that,

the adhesive layer is the adhesive sheet according to any one of claims 1 to 8.

10. The backlight unit according to claim 9, wherein the light emitter is a light emitting diode.

11. A display device is characterized by comprising:

the backlight unit as claimed in claim 9, and

and a display portion laminated on the adhesive layer of the backlight unit.

Technical Field

The present invention relates to an adhesive sheet having a light-diffusing adhesive layer, and a backlight unit and a display device using the adhesive sheet.

Background

In recent years, liquid crystal display devices are widely used as display devices (displays) in electronic devices such as mobile phones, smartphones, tablet terminals, and game machines. Since a display portion formed of a liquid crystal panel or the like does not emit light by itself, a display device using the display portion includes a backlight (backlight) for illuminating the display portion.

Conventionally, the light sources of the backlight in the display device described above are generally arranged in a side-in type in which the light sources are arranged on the side of the light guide plate. On the other hand, in recent years, direct-type backlights in which a light source is disposed directly below a display unit have been studied from the viewpoint of the brightness and contrast of a screen. In a direct type backlight, in order to obtain a light amount and to make the light amount uniform between, for example, a center of a screen and an edge of the screen when a display device is manufactured, a plurality of light emitters, typically, Light Emitting Diodes (LEDs) are disposed on a substrate.

However, when a plurality of light-emitting bodies are used as a light source of a direct type backlight, the light-emitting bodies are desirably sealed with a resin or the like because the light-emitting bodies have low water resistance. In addition, when a display device is manufactured using a backlight having a plurality of light-emitting bodies as a light source, luminance unevenness occurs in an obtained image due to an existing region and an absent region of the light-emitting bodies.

Patent document 1 proposes providing an adhesive layer containing light scattering particles on the light-emitting body of the backlight.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5590582

Disclosure of Invention

Technical problem to be solved by the invention

However, in patent document 1, it is necessary to provide an adhesive layer by directly coating an adhesive on the backlight. In addition, when a conventional adhesive is used, light from a light source or diffused light thereof may be accidentally colored, resulting in color unevenness.

In view of the above circumstances, an object of the present invention is to provide an adhesive sheet, a backlight unit, and a display device that exhibit a high haze value and are excellent in color unevenness suppression.

Means for solving the problems

In order to achieve the above object, the first aspect of the present invention provides an adhesive sheet comprising an adhesive layer, wherein the adhesive constituting the adhesive layer contains light diffusing fine particles, the average value of the haze value of the adhesive layer with respect to a light beam having a wavelength of 380nm, the haze value of the adhesive layer with respect to a light beam having a wavelength of 580nm, and the haze value of the adhesive layer with respect to a light beam having a wavelength of 780nm is 70% or more and 100% or less, the standard deviation of the haze value of the adhesive layer with respect to a light beam having a wavelength of 380nm, the haze value of the adhesive layer with respect to a light beam having a wavelength of 580nm, and the haze value of the adhesive layer with respect to a light beam having a wavelength of 780nm is 7.50 or less, and the total light transmittance of the adhesive.

In the above invention (invention 1), a high haze value is exhibited, and the light from the light source and the diffused light thereof can be suppressed from being colored unexpectedly, and the occurrence of color unevenness can be suppressed. Further, the image and the video visibility when used in a display device are also excellent.

In the invention (invention 1), the adhesive layer preferably has a total image clarity of 0.125mm, 0.25mm, 0.5mm, 1.0mm and 2.0mm combs (optical ) of 0.2 to 400.

In the above inventions (inventions 1 and 2), the adhesive agent layer preferably has a thickness of 10 μm to 500 μm (invention 3).

In the above inventions (inventions 1 to 3), it is preferable that the storage modulus G' of the adhesive constituting the adhesive agent layer at 23 ℃ is 0.001MPa or more and 10MPa or less (invention 4).

In the above inventions (inventions 1 to 4), the adhesive sheet preferably has an adhesive force to soda-lime glass of 0.1N/25mm or more (invention 5).

In the above inventions (inventions 1 to 5), the adhesive is preferably an acrylic adhesive (invention 6).

In the above inventions (inventions 1 to 6), it is preferable that: the adhesive sheet comprises two release sheets, and the adhesive layer is sandwiched between the release sheets so as to be in contact with release surfaces of the two release sheets (invention 7).

The adhesive sheet of the above inventions (inventions 1 to 7) is preferably used for bonding two hard bodies (invention 8).

The second aspect of the present invention provides a backlight unit comprising a backlight having a plurality of light-emitting bodies and an adhesive layer laminated on the backlight, wherein the adhesive layer is the adhesive layer of the adhesive sheet (aspects 1 to 8) (aspect 9).

In the above invention (invention 9), the light-emitting body is preferably a light-emitting diode (invention 10).

The present invention provides a display device comprising the backlight unit (inventions 9 and 10) and a display unit (invention 11) laminated on the adhesive layer of the backlight unit.

Effects of the invention

The adhesive sheet, the backlight unit and the display device of the present invention exhibit a high haze value and are excellent in color unevenness suppression.

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 a backlight unit according to an embodiment of the present invention.

Fig. 3 is a sectional view of a display device according to an embodiment of the present invention.

Description of the reference numerals

1: an adhesive sheet; 11: an adhesive layer; 12a, 12 b: a release sheet; 2: a backlight unit; 20: a backlight source; 21: a substrate; 22: a light emitter; 3: a display device; 30: 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 has an adhesive layer. 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 of one embodiment is composed of two release sheets 12a and 12b and an adhesive layer 11, and the 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 one of a surface subjected to a release treatment and a surface showing releasability even if the release treatment is not performed.

1. Each component

1-1. adhesive layer

The adhesive constituting the adhesive layer 11 contains light diffusing fine particles. The adhesive layer 11 has the following physical properties. That is, the average value of the haze value for a light ray having a wavelength of 380nm, the haze value for a light ray having a wavelength of 580nm, and the haze value for a light ray having a wavelength of 780nm is 70% or more and 100% or less, the standard deviation of the haze value for a light ray having a wavelength of 380nm, the haze value for a light ray having a wavelength of 580nm, and the haze value for a light ray having a wavelength of 780nm is 7.50 or less, and the total light transmittance is 70% or more. The haze value and the total light transmittance for each light ray were measured according to JIS K7375: 2008.

When the average value of the haze values is 70% or more, unevenness in brightness is easily suppressed, but color unevenness is easily generated. However, by setting the standard deviation of the haze value to 7.50 or less, it is possible to suppress color unevenness, and it is possible to suppress light from the light source and diffused light thereof from being accidentally colored. Further, by setting the total light transmittance to 70% or more, the visibility of an image and a video (the visibility of a display device) when used in a display device is excellent.

From the viewpoint of the suppression of uneven brightness, the average value of the haze values is preferably 80% or more, preferably 86% or more, particularly preferably 88% or more, and more preferably 90% or more. The average value of the haze value is 100% or less, but from the viewpoint of achieving a high total light transmittance, it is preferably 98% or less, particularly preferably 95% or less, and further preferably less than 94%.

In addition, from the viewpoint of color unevenness suppression, the standard deviation needs to be 7.50 or less, preferably 5.00 or less, particularly preferably 2.50 or less, and further preferably 1.50 or less. On the other hand, the lower limit of the standard deviation is most preferably 0 from the viewpoint of color unevenness suppression, and is preferably 0.01 or more, particularly preferably 0.10 or more, and further preferably 0.50 or more from the viewpoint of easy adjustment of the value of the standard deviation.

From the viewpoint of visibility of the display device, the total light transmittance needs to be 70% or more, preferably 80% or more, particularly preferably 90% or more, and further preferably 99% or more. In addition, from the viewpoint of visibility of the display device, the upper limit value of the total light transmittance is most preferably 100%.

The total value of the image clarity of the optical combs of 0.125mm, 0.25mm, 0.5mm, 1.0mm, and 2.0mm, measured according to JIS K7374:2007, of the adhesive layer 11 of the present embodiment is preferably 400 or less, more preferably 300 or less, particularly preferably 200 or less, and further preferably 180 or less. Conventionally, when a display device is manufactured using a backlight having a plurality of light-emitting bodies as a light source, luminance unevenness may occur in a displayed image due to an existing region and an absent region of the light-emitting bodies. However, by making the total value of the image sharpness smaller as described above, an excellent effect of suppressing the luminance unevenness can be obtained.

The total value of the image sharpness is preferably 0.1 or more, more preferably 1 or more, particularly preferably 10 or more, and further preferably 30 or more. This improves the visibility of the image and the map of the display.

Here, the image clarity is obtained by measuring the amount of parallel light rays transmitted through the test object by an optical comb having a transmission portion and a light shielding portion. The smaller the width (comb width) of the transmission portion and the light shielding portion of the optical comb, the higher the image definition is displayed. Image clarity according to JIS K7374:2007 by the transmission method. The specific measurement method is shown in the test examples described later.

The storage modulus G' at 23 ℃ of the adhesive constituting the adhesive layer 11 of the present embodiment is preferably 0.001MPa or more, more preferably 0.01MPa or more, particularly preferably 0.03MPa or more, and further preferably 0.05MPa or more. The storage modulus G' is preferably 10MPa or less, more preferably 1MPa or less, particularly preferably 0.20MPa or less, and further preferably 0.09MPa or less. By setting the storage modulus G' within the above range, excellent embedding properties of the irregularities can be obtained, and not only in the initial stage but also under high-temperature and high-humidity conditions (for example, 85 ℃, 85% RH, 72 hours), the state in which the irregularities generated by the light-emitting body and the like are sufficiently embedded by the adhesive agent layer can be maintained, and the occurrence of floating, peeling, and the like at the interface between the irregularities and the adhesive agent layer can be suppressed. The method for measuring the storage modulus G' in the present specification is as shown in test examples described later.

From the viewpoint of reducing the standard deviation of the haze value and lowering the image clarity, the average particle diameter of the light diffusing fine particles contained in the adhesive constituting the adhesive layer 11 by the centrifugal sedimentation light transmission method is preferably 0.5 μm or more, more preferably 1 μm or more, particularly preferably 2 μm or more, and further preferably 4 μm or more.

In addition, from the viewpoint of increasing the average value of the haze value by a small amount of the light diffusing fine particles added, the average particle diameter of the light diffusing fine particles is preferably 50 μm or less, more preferably 30 μm or less, particularly preferably 17 μm or less, and further preferably 13 μm or less.

The average particle diameter obtained by the centrifugal sedimentation light transmission method is a value obtained by measuring a substance obtained by sufficiently stirring 1.2g of light-diffusing fine particles and 98.8g of isopropyl alcohol as a measurement sample by using a centrifugal automatic particle size distribution measuring apparatus (HORIBA, manufactured by ltd., product name "CAPA-700").

The adhesive constituting the adhesive layer 11 is formed of light-diffusing fine particles and a matrix (matrix) other than the light-diffusing fine particles.

In the present embodiment, the absolute value of the difference (refractive index difference) between the refractive index of the matrix of the adhesive and the refractive index of the light diffusing particles is preferably 0.001 or more, more preferably 0.010 or more, particularly preferably 0.020 or more, further preferably 0.030 or more, and most preferably 0.040 or more, from the viewpoint of increasing the average value of the haze values and suppressing the standard deviation of the haze values to be low. In addition, from the viewpoint of increasing the total light transmittance and reducing the image clarity, the absolute value of the refractive index difference is preferably 0.5 or less, more preferably 0.2 or less, particularly preferably 0.15 or less, and further preferably 0.10 or less.

Here, the method of measuring the refractive index of the matrix is described in the test examples described below. The refractive index of the light diffusing fine particles can be determined by method B of JIS K7142: 2008.

The refractive index of the matrix of the adhesive is preferably 1.10 or more, more preferably 1.20 or more, particularly preferably 1.30 or more, further preferably 1.40 or more, and most preferably 1.45 or more. The refractive index of the matrix of the adhesive is preferably 2.00 or less, more preferably 1.80 or less, particularly preferably 1.60 or less, and further preferably 1.50 or less. By making the refractive index of the matrix of the adhesive within the above range, the absolute value of the refractive index difference easily falls within the above range.

The refractive index of the light diffusing fine particles is preferably 1.10 or more, more preferably 1.20 or more, particularly preferably 1.30 or more, and further preferably 1.40 or more. The refractive index of the light diffusing fine particles is preferably 2.00 or less, more preferably 1.80 or less, particularly preferably 1.60 or less, and further preferably 1.58 or less. Thus, the absolute value of the difference in refractive index is liable to fall within the above range

From the viewpoint of reducing the standard deviation of the haze value and easily obtaining an adhesive having high haze and low image clarity, the content of the light diffusing fine particles in the adhesive is preferably 0.1 mass% or more, more preferably 1 mass% or more, particularly preferably 3 mass% or more, and further preferably 5 mass% or more. In addition, from the viewpoint of suppressing the storage modulus G' of the adhesive to be low, the content of the light diffusing fine particles in the adhesive is preferably 40% by mass or less, more preferably 30% by mass or less, particularly preferably 20% by mass or less, further preferably 10% by mass or less, and most preferably 8% by mass or less.

The type of the adhesive constituting the adhesive layer 11 of the adhesive sheet 1 of the present embodiment is not particularly limited as long as the adhesive satisfies the above-described physical properties and does not inhibit the effect of the light diffusing fine particles. For example, the pressure sensitive adhesive may be any of an acrylic pressure sensitive adhesive, a polyester pressure sensitive adhesive, a polyurethane pressure sensitive adhesive, a rubber pressure sensitive adhesive, a silicone pressure sensitive adhesive, and the like. 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 acrylic pressure-sensitive adhesive, and more preferably a thermally crosslinked acrylic pressure-sensitive adhesive.

The adhesive of the present embodiment may be curable by actinic energy rays or by actinic energy rays, and the description will be given below mainly on adhesives curable by actinic energy rays.

Specifically, the pressure-sensitive adhesive of the present embodiment is preferably obtained by crosslinking a pressure-sensitive adhesive composition (hereinafter, may be referred to as "pressure-sensitive adhesive composition P") containing a (meth) acrylate polymer (a), a crosslinking agent (B), and light-diffusing fine particles (C). The adhesive obtained by crosslinking the adhesive composition P is likely to satisfy the above physical properties. In the present specification, the term (meth) acrylic acid means acrylic acid and methacrylic acid. Other similar terms are also the same. Further, the term "copolymer" is also included in the term "polymer".

(1) Components of the adhesive composition P

(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 reactive 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 the like. 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 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 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate is particularly preferably mentioned. These 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 may be used alone or in combination of two or more.

The lower limit of the content of the reactive group-containing monomer in the (meth) acrylate polymer (a) is preferably 1% by mass or more, particularly preferably 6% by mass or more, further preferably 12% by mass or more, and most preferably 17% by mass or more. In addition, the (meth) acrylate polymer (a) preferably contains 40% by mass or less, particularly preferably 35% by mass or less, further preferably 30% by mass or less, and most preferably 25% by mass or less of the reactive functional group-containing monomer as a monomer unit constituting the polymer, in terms of the above-mentioned limit. 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 the above-mentioned physical properties such as storage modulus G' can be easily satisfied. In addition, the dispersibility of the light-diffusing fine particles (C) 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, since the carboxyl group-containing monomer is not contained, even when a substance causing a problem due to an acid, for example, a transparent conductive film such as tin-doped indium oxide (ITO) or a metal film is present in an object to which the adhesive is to be attached, the problem (corrosion, change in resistance value, or the like) caused by the 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 problems do not occur. Specifically, the carboxyl group-containing monomer is allowed to be contained as a monomer unit 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.

The (meth) acrylate polymer (a) preferably contains an alkyl (meth) acrylate as a monomer unit constituting the polymer. This can exhibit good adhesion. 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 them, from the viewpoint of further improving the adhesiveness and easily satisfying the above physical properties, an alkyl (meth) acrylate having an alkyl group having 4 to 8 carbon atoms 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 may be used alone or in combination of two or more.

The (meth) acrylate polymer (a) preferably contains 30% by mass or more, more preferably 40% by mass or more, particularly preferably 50% by mass or more, and further preferably 55% by mass or more of an alkyl (meth) acrylate as a monomer unit constituting the polymer. 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 and the storage modulus G' can be made low. On the other hand, the (meth) acrylic acid ester polymer (a) preferably contains 85 mass% or less, more preferably 80 mass% or less, particularly preferably 75 mass% or less, and further preferably 70 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, an appropriate amount of other monomer components such as a reactive functional group-containing monomer can be introduced into the (meth) acrylate polymer (a).

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. 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 increases the distance between the polymers, and thereby the above-mentioned physical properties, particularly the storage modulus G', are easily satisfied.

The alicyclic carbon ring in the alicyclic structure-containing monomer may be saturated or partially unsaturated. 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. From the viewpoint of making the distance between the obtained (meth) acrylate polymers (a) appropriate and reducing the storage modulus G', the alicyclic structure is preferably a polycyclic alicyclic structure (polycyclic structure). Further, the above polycyclic structure is particularly preferably a bicyclic ring to a tetracyclic ring in view of compatibility of the (meth) acrylate polymer (a) with other components. From the same viewpoint as above, the number of carbon atoms of the alicyclic structure (which means the number of all carbon atoms of the portion forming a ring, and when a plurality of rings are present independently, the number of the total carbon atoms thereof) 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 concavo-convex embedding property is preferable, isobornyl (meth) acrylate is particularly preferable, and isobornyl acrylate is more preferable. These 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 easily satisfying the storage modulus G'. From the same viewpoint as above, the content of the alicyclic structure-containing monomer is preferably 40% by mass or less, particularly preferably 30% by mass or less, and further preferably 20% 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 constituent unit in a polymer, a predetermined polarity can be imparted to an adhesive, and the adhesive is excellent in affinity even for an adherend having a certain polarity such as glass. From the viewpoint of imparting suitable 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 portion derived from the nitrogen atom-containing monomer in the high dimensional structure of the adhesive agent to be constituted, 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 adhesion is preferable, and N-acryloylmorpholine is particularly preferable. These 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 0.1% by mass or more, more preferably 1% by mass or more, particularly preferably 3% by mass or more, and further preferably 8% by mass or more. The (meth) acrylate polymer (a) preferably contains 30% by mass or less, particularly preferably 20% by mass or less, and further preferably 14% 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 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 having excellent uneven embedding properties under high-temperature and high-humidity conditions can be easily obtained.

Further, the (meth) acrylate polymer (a) is preferably a solution polymer obtained by a solution polymerization method. Since a high molecular weight polymer can be easily obtained by using a solution polymer, and an improvement in cohesive force can be expected, an adhesive having excellent uneven embedding properties 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 10 ten thousand or more, more preferably 25 ten thousand or more, and particularly preferably 40 ten thousand or more. The weight average molecular weight of the (meth) acrylate polymer (a) is preferably 300 ten thousand or less, particularly preferably 200 ten thousand or less, and more preferably 100 ten thousand or less. When the weight average molecular weight of the (meth) acrylate polymer (a) is within the above range, the storage modulus G' and the adhesive force of the obtained adhesive are easily suitable. Here, 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 any agent that can react with the reactive group of the (meth) acrylate polymer (a). Examples of the crosslinking agent (B) 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. The crosslinking agent (B) may be used alone or in combination of two or more.

When the reactive group of the (meth) acrylate polymer (a) is a hydroxyl group, an isocyanate-based crosslinking agent having high reactivity with the hydroxyl group is preferably used. When the reactive group of the (meth) acrylate polymer (a) is a carboxyl group, an epoxy crosslinking agent having high reactivity with the carboxyl group is preferably used.

The isocyanate-based crosslinking agent contains at least a polyisocyanate (polyisocynate) 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; and biuret or isocyanurate of these compounds, and further includes adducts with reactants of 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 is 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 0.001 parts by mass or more, particularly preferably 0.01 parts by mass or more, and more preferably 0.1 parts by mass or more, relative to 100 parts by mass of the (meth) acrylate polymer (a). The content of the crosslinking agent (B) is preferably 10 parts by mass or less, particularly preferably 1 part by mass or less, and more preferably 0.5 part by mass or less, based on 100 parts by mass of the (meth) acrylate polymer (a). When the content of the crosslinking agent (B) is in the above range, the storage modulus G', the adhesive force, and the like of the obtained adhesive are easily optimized.

(1-3) light diffusing particles (C)

The light-diffusing fine particles (C) may exhibit a predetermined light-diffusing property, and the obtained adhesive layer 11 may satisfy the above physical properties.

Examples of the light-diffusing fine particles (C) include inorganic light-diffusing fine particles such as silica, calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay, talc, and titanium dioxide; organic light-diffusing fine particles such as acrylic resins, polystyrene resins, polyethylene resins, epoxy resins, copolymers thereof, and mixtures thereof; light diffusing particles made of a silicon-containing compound having an intermediate structure between inorganic and organic Materials such as silicone resin (for example, TOSPEARL series manufactured by Momentive Performance Materials Japan), composite light diffusing particles made of an organic resin and a silicone resin, and the like. Among them, light-diffusing particles made of a polymethyl methacrylate-polystyrene copolymer, light-diffusing particles made of a silicone resin, or composite light-diffusing particles of a polystyrene resin and a silicone resin are preferable. Thus, the obtained adhesive layer 11 easily satisfies the above physical properties. The light-diffusing fine particles (C) may be used singly or in combination of two or more.

The shape of the light diffusion particles (C) is preferably spherical light diffusion particles having uniform light diffusion, but the shape is not limited thereto. The average particle diameter of the light diffusing fine particles (C) is as described above.

The content of the light-diffusing fine particles (C) in the adhesive composition P is the same as the content of the light-diffusing fine particles in the adhesive.

(1-4) 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 modifiers, and the like can be added to the adhesive composition P as needed. In addition, a polymerization solvent or a dilution solvent described later is not included in the additive constituting the adhesive composition P.

The adhesive composition P preferably contains the silane coupling agent among the above. This improves the adhesion to the adherend, and also improves the uneven embedding property under high-temperature and high-humidity conditions, regardless of whether the adherend is a plastic member or a glass member.

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 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; isocyanatopropyltriethoxysilane; 1, 6-bis (trimethoxysilyl) hexane; or condensates of at least one of these silane coupling agents with an alkyl group-containing silicon compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, or the like. These 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 P

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 light-diffusing fine particles (C) are mixed, and additives and the like are added as needed.

The (meth) acrylate polymer (a) can be prepared by polymerizing a mixture of monomers constituting the polymer by a general 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), 2 ' -azobis (methyl 2-methylpropionate), 4 ' -azobis (4-cyanovaleric acid), 2 ' -azobis (2-hydroxymethylpropionitrile), and 2,2 ' -azobis [2- (2-imidazolin-2-yl) propane ].

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 light-diffusing fine particles (C), and, if necessary, a diluting solvent, additives, and the like are added to a solution of the (meth) acrylate polymer (a) and sufficiently mixed, thereby obtaining a solvent-diluted adhesive composition P (coating solution). In the case where a solid substance is used for 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.

The diluting solvent is not particularly limited as long as the state of dissolution or dispersion of the adhesive composition P can be maintained, and for example, the same solvent as the polymerization solvent is preferably used.

The concentration and viscosity of the coating solution prepared in the above manner are not particularly limited as long as they are within a range enabling coating, and may be appropriately selected according to circumstances. 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, it is not essential to add a diluting solvent, and the diluting solvent may not be added if the adhesive composition P has a coatable viscosity or the like. 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 adhesive layer 11 of the present embodiment is preferably composed of an adhesive obtained by crosslinking (the 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 applied to 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.

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

The (meth) acrylate polymer (a) is crosslinked by the crosslinking agent (B) by the heat treatment (and curing) to obtain an adhesive.

(4) Constitution of adhesive layer

The adhesive agent layer 11 of the present embodiment may be formed of a single layer or may be formed by stacking a plurality of layers. In the adhesive layer 11 of the present embodiment, an adhesive layer (transparent adhesive layer) containing no light diffusion particles may be laminated on one surface or both surfaces of an adhesive layer (light diffusion adhesive layer) containing light diffusion particles.

When the transparent adhesive layer is present as described above, the transparent adhesive layer is preferably bonded so as to be positioned on a surface in contact with an adherend having irregularities. This can suppress the light diffusing adhesive layer from being compressed or deformed due to unevenness of the adherend, and can provide an optical laminate (display) having more excellent color unevenness suppression properties and luminance unevenness suppression properties.

1-2. Release sheet

The release sheets 12a and 12b protect the adhesive layer 11 until the adhesive sheet 1 is used, and are released when the adhesive sheet 1 (adhesive layer 11) is used. In the adhesive sheet 1 of the present embodiment, one or both of the release sheets 12a and 12b are not necessarily required.

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. Further, a crosslinked film of the above-described film may also be used. Further, a laminated film of the above-described films may be used.

The release surfaces (particularly, the surfaces in contact with the adhesive agent layer 11) of the release sheets 12a and 12b 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. Of the release sheets 12a and 12b, one release sheet is preferably a heavy release type release sheet having a large release force, and the other release sheet is preferably a light release type release sheet having 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) Thickness of adhesive layer

The thickness (value measured according to JIS K7130) of the adhesive layer 11 in the adhesive sheet 1 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, in terms of the lower limit. This makes it possible to embed the unevenness of the backlight with the adhesive layer 11, and to obtain a desired light diffusibility. The thickness of the adhesive layer 11 is preferably 500 μm or less, more preferably 300 μm or less, particularly preferably 200 μm or less, and further preferably 150 μm or less, as defined above. This makes it easy to obtain a desired light diffusibility and also makes processability good.

(2) Adhesive force

The adhesive sheet 1 of the present embodiment has an adhesive force to soda-lime glass of preferably 0.1N/25mm or more, more preferably 1N/25mm or more, particularly preferably 10N/25mm or more, and further preferably 20N/25mm or more, as the lower limit value. When the lower limit of the adhesive force is as described above, the embedding property of the unevenness under high temperature and high humidity conditions is further excellent. In addition, the adhesive force of the adhesive sheet 1 of the present embodiment to soda lime glass is preferably 70N/25mm or less, more preferably 50N/25mm or less, and particularly preferably 40N/25mm or less, in an upper limit value. When the upper limit of the adhesive force of the adhesive sheet is as described above, good reworkability can be obtained, and when a bonding failure occurs, an expensive display member component can be reused.

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

3. Production of adhesive sheet

The case of using the adhesive composition P will be described as one example of the production of the adhesive sheet 1. After a coating solution of the adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), and heat treatment is performed to thermally crosslink the adhesive composition P to form a coating layer, the release surface of the other release sheet 12b (or 12a) is laminated on the coating layer. When the curing period is required, the coating layer becomes the adhesive layer 11 by providing the curing period, and when the curing period is not required, the coating layer directly becomes the adhesive layer 11. Thus, the adhesive sheet 1 was obtained. The conditions for the heat treatment and aging are as described above.

As another production example of the adhesive sheet 1, a coating solution of the adhesive composition P 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. The coating solution of the adhesive composition P is applied to the release surface of the other release sheet 12b, and heat treatment is 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. When the curing period is required, the stacked coating layers become the adhesive layer 11 by providing the curing period, and when the curing period is not required, the stacked coating layers directly become the adhesive layer 11. Thus, the adhesive sheet 1 was obtained. According to this production example, even when the adhesive layer 11 is thick, stable production can be performed.

Examples of the method for applying the coating liquid of the adhesive composition P include bar coating, blade coating, roll coating, blade coating, die coating, and gravure coating.

4. Use of adhesive sheet

The adhesive sheet 1 of the present embodiment can be suitably used for bonding two hard bodies. The adhesive sheet 1 of the present embodiment can favorably bond two hard bodies together, although it is more difficult to bond the hard bodies to each other than to bond the films to each other or bond the films to the hard bodies, and the yield in bonding is likely to decrease.

In the present specification, a hard body refers to a member whose structure can be bent at an angle of less than 90 ° without irreversible deformation. The angle is preferably less than 60 °, more preferably less than 45 °, particularly preferably less than 10 °, and particularly preferably less than 5 °. The bendable angle (bending angle) is an angle that is raised from a horizontal surface when a rigid body is placed on the horizontal surface, one end portion is fixed, and the opposite end portion is raised. The hard body may be formed of a single layer or one member, or may be formed of a plurality of layers or a plurality of members. In the latter case, the hard body is an object formed of a plurality of layers or members which is used as one object and satisfies the bending angle as a whole when the object is bonded to the adhesive layer, and even if a part of the layers or members of the object do not satisfy the bending angle, the object can be referred to as a hard body.

Specifically, as described later, the adhesive sheet 1 of the present embodiment can be suitably used for bonding a backlight to a display portion such as a liquid crystal panel or other hard optical member. The backlight and the display unit are generally formed of a rigid body. However, the present invention is not limited to this, and can also be used to attach display body constituent members that are required hard bodies to each other.

[ backlight Unit ]

A backlight unit according to one embodiment of the present invention includes a backlight having a plurality of light-emitting bodies, and an adhesive layer laminated on the backlight. Since the backlight unit includes a plurality of light-emitting bodies, the surface on the adhesive layer side often has irregularities.

Fig. 2 shows a specific configuration of an example of the backlight unit according to the present embodiment. As shown in fig. 2, the backlight unit 2 of one embodiment includes a backlight 20 and an adhesive layer 11 laminated on the backlight 20.

1. Constituent elements

(1) Back light source

The backlight 20 includes one or more substrates 21 and a plurality of light-emitting bodies 22 provided on the substrates 21. The backlight 20 has irregularities caused by the plurality of light-emitting bodies 22.

The substrate 21 is not particularly limited, and a substrate generally used for a backlight can be used. The substrate 21 is typically a Printed Circuit Board (PCB substrate).

The substrate 21 may be integrally formed to mount a plurality of light emitters 22 collectively, or may be formed separately from each other to mount one light emitter 22 on one substrate 21. When formed separately, each substrate 21 is generally fixed to a frame, a support, a case, or the like. In the present embodiment, as shown in fig. 2, the substrate 21 is preferably formed integrally so as to mount a plurality of light emitters 22 collectively.

The substrate 21 may have a reflective layer formed on the surface thereof on the adhesive layer 11 side, or may have a reflective member provided thereon. This can effectively improve the luminance of the backlight 20. The material of the reflective layer or the reflective member can be a known material.

Examples of the type of the light-emitting body 22 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 the sealing property by the 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 22 is preferably 5 μm or more, more preferably 50 μm or more, particularly preferably 100 μm or more, and further preferably 200 μm or more. The thickness of the light-emitting body 22 is preferably 1000 μm or less, particularly preferably 500 μm or less, and further preferably 250 μm or less.

The width of the gap between the adjacent light emitters 22 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 22 is not particularly limited, and is usually a rectangular parallelepiped, a hemisphere, or the like. The size of the light-emitting body 22 is not particularly limited, and from the viewpoint of sealing property of the light-emitting body, the side or 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.

(2) Adhesive layer

The adhesive layer 11 of the present embodiment is preferably the adhesive layer 11 of the adhesive sheet 1 described above. The adhesive layer 11 of the present embodiment is preferably composed of an adhesive obtained by crosslinking the adhesive composition P.

The adhesive layer 11 of the present embodiment embeds irregularities caused by the light-emitting bodies 22. That is, the plurality of light emitters 22 can be sealed with the adhesive layer 11 without any void. This improves water resistance, and protects the light emitting body 22 (particularly, LED) from moisture. Further, the adhesive layer 11 diffuses light irradiated from the backlight 20. Further, by having the above-described physical properties, the light from the light source and the diffused light thereof are suppressed from being accidentally colored, that is, the occurrence of color unevenness is effectively suppressed.

The adhesive layer 11 may be laminated in direct contact with the backlight 20, or may be indirectly laminated via another layer or member.

2. Manufacture of backlight unit

In order to manufacture the backlight unit 2 of the present embodiment, for example, one release sheet 12a of the adhesive sheet 1 is peeled off, and the adhesive layer exposed on the adhesive sheet 1 is bonded to the surface of the backlight 20 on the side where the light-emitting bodies 22 are present.

Next, at a desired timing, the other release sheet 12b is peeled from the adhesive layer 11 of the adhesive sheet 1. The peeling of the release sheet 12b is preferably performed at the time of manufacturing the display device 3 described later, and until then, the adhesive layer 11 is preferably protected by the release sheet 12 b.

3. Other constitution

A sealing material may be provided between the backlight 20 and the adhesive layer 11. In this case, irregularities are often formed on the surface of the sealing material opposite to the backlight 20, and the irregularities can be absorbed by the adhesive layer 11.

Further, another adhesive layer may be laminated between the backlight 20 and the adhesive layer 11. Even in such a case, the influence of the other adhesive layer on the uneven embedding can be alleviated by the adhesive layer 11.

Further, two or more layers of the sealing material and the adhesive layer may be stacked between the backlight 20 and the adhesive layer 11.

[ display device ]

A display device according to an embodiment of the present invention includes the backlight unit according to the above-described embodiment, and a display portion stacked on the adhesive layer of the backlight unit. The display portion may be laminated in direct contact with the adhesive layer, or may be indirectly laminated via another layer or member.

Fig. 3 shows a display device as an example of this embodiment mode.

As shown in fig. 3, the display device 3 of the present embodiment includes the backlight unit 2 described above and the display section 30 laminated on the adhesive layer 11 of the backlight unit 2. The backlight 20 in the display device 3 corresponds to a direct type backlight.

Examples of the type of the display device 3 include a Liquid Crystal Display (LCD), a Light Emitting Diode (LED) display, an organic electroluminescence (organic EL) display, and electronic paper. The display device 3 may be a touch panel. Among the above, a liquid crystal display (liquid crystal display device) having a high necessity of a backlight is preferable.

The display unit 30 is, for example, a liquid crystal panel, but is not limited thereto, and may be, for example, a part of a constituent member of the liquid crystal panel or an optical member (for example, a light diffusion plate, an ultraviolet absorption filter, or the like) used together for adding or enhancing a function of the liquid crystal panel. The display unit 30 can be a known display unit.

In order to manufacture the display device 3 of the present embodiment, the adhesive layer 11 exposed from the backlight unit 2 is bonded to the display portion 30. When the release sheet 12b is laminated on the adhesive layer 11, the release sheet 12b is peeled to expose the adhesive layer 11, and then the adhesive layer 11 is bonded to the display portion 30.

In manufacturing the display device 3 of the present embodiment, the adhesive layer 11 may be first attached to the display portion 30, and then the adhesive layer 11 may be attached to the backlight 20.

Here, a desired optical member may be provided between the adhesive agent layer 11 and the display portion 30, or on the surface of the display portion 30 opposite to the adhesive agent 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, a scattering preventing film, and a light diffusing plate.

The embodiments described above are described for the convenience of understanding the present invention, and are not described for the purpose of 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 of the release sheets 12a and 12b of the adhesive sheet 1 may be omitted.

Examples

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

[ example 1]

Preparation of (meth) acrylate polymers

The (meth) acrylic ester polymer (a) was prepared by copolymerizing 30 parts by mass of 2-ethylhexyl acrylate, 30 parts by mass of N-butyl acrylate, 10 parts by mass of isobornyl acrylate, 10 parts by mass of N-acryloylmorpholine, and 20 parts by mass of 2-hydroxyethyl acrylate. The molecular weight of the (meth) acrylate polymer (a) was measured by the method described below, and as a result, the weight average molecular weight (Mw) was 50 ten thousand.

2. Preparation of adhesive composition

100 parts by mass (in terms of solid content; the same applies hereinafter) of the (meth) acrylate polymer (A) obtained in step 1 above, 0.2 parts by mass of trimethylolpropane-modified toluene diisocyanate (TOYOCHEM CO., LTD., product name "BHS 8515") as a crosslinking agent (B), 7.5 parts by mass of light-diffusing particles (C) formed of a silicone resin (a silicon-containing compound having an inorganic and organic intermediate structure) (C1; manufactured by Momentive Performance Materials Japan, product name "TOSPEARL 145" having an average particle diameter of 4.5 μm and a refractive index of 1.43) as a light-diffusing particles (C), and 0.13 parts by mass of 3-glycidyl ether oxypropyltrimethoxysilane (Si1) as a silane coupling agent were mixed and sufficiently stirred, and diluted with methyl ethyl ketone to obtain a coating solution of an 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

BA: acrylic acid n-butyl ester

IBXA: acrylic acid isobornyl ester

ACMO: n-acryloyl morpholine

HEA: 2-Hydroxyethyl acrylate

AA: acrylic acid

4 HBA: acrylic acid 4-hydroxybutyl ester

EA: acrylic acid ethyl ester

[ crosslinking agent (B) ]

B1: trimethylolpropane-modified toluene diisocyanate (TOYOCHEM CO., LTD., product name "BHS 8515")

B2: trimethylolpropane-modified xylylene diisocyanate (manufactured by Soken Chemical & Engineering Co., Ltd., product name "TD-75")

B3: 1, 3-bis (N, N-diglycidylaminomethyl) cyclohexane

B4: aluminum triacetylacetonate

[ light-diffusing particles (C) ]

C1: light-diffusing particles formed of a silicone resin (silicon-containing compound having an intermediate structure of inorganic and organic structures) (manufactured by Momentive Performance Materials Japan, product name "TOSPEARL 145", average particle diameter: 4.5 μm, refractive index: 1.43)

C2: light-diffusing particles formed of a silicone resin (silicon-containing compound having an intermediate structure of inorganic and organic structures) (manufactured by Momentive Performance Materials Japan, product name "TOSPEARL 1100", average particle diameter: 11 μm, refractive index: 1.43)

C3: polymethyl methacrylate-polystyrene copolymer particles in the form of a regular sphere (Sekisui Kasei Co., manufactured by Ltd., product name "XX-13 LA", average particle diameter: 4 μm, refractive index: 1.565)

C4: light-diffusing fine particles formed of a silicone resin and a polystyrene resin (manufactured by Nippon Shokubai Co., Ltd., product name "SOLIOSTATER RA-Y50X", average particle diameter: 5 μm, refractive index: 1.57)

C5: light-diffusing particles formed of a silicone resin (silicon-containing compound having an intermediate structure of inorganic and organic structures) (manufactured by Momentive Performance Materials Japan, product name "TOSPEARL 120", average particle diameter: 2 μm, refractive index: 1.43)

C6: light-diffusing particles formed of a melamine resin and a benzoguanamine resin (manufactured by Nippon Shokubai Co., Ltd., product name "EPASTAR M-30", average particle diameter: 3 μ M, refractive index: 1.66)

[ silane coupling agent ]

Si 1: 3-glycidyloxypropyltrimethoxysilane

Si 2: a-50(Soken Chemical & Engineering Co., Ltd.)

3. Production of adhesive sheet

The obtained coating solution of the adhesive composition was applied to the release-treated surface of a heavy release type release sheet (product name "SP-PET 752150", manufactured by linec CORPORATION) having one surface of a polyethylene terephthalate film subjected to a release treatment using a silicone-based release agent, using a blade coater, and then heat-treated at 90 ℃ for 1 minute to form a coating layer.

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

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

Examples 2 to 10 and comparative example 1

An adhesive sheet was produced in the same manner as in example 1, except that the kind and ratio of each monomer constituting the (meth) acrylate polymer (a), the weight average molecular weight (Mw) of the (meth) acrylate polymer (a), the kind and blending amount of the crosslinking agent (B), the kind and blending amount of the light diffusing particles (C), the kind and blending amount of the silane coupling agent, and the thickness of the adhesive layer were changed as shown in table 1. In example 7, an adhesive layer having a thickness of 100 μm was prepared by laminating 2 adhesive layers having a thickness of 50 μm.

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

[ test example 1] (measurement of refractive index)

Adhesive compositions were prepared in the same manner as in each of the examples and comparative examples, except that the light diffusing fine particles were not blended. Then, using the adhesive composition, an adhesive sheet was produced in the same manner as in each of the examples and comparative examples. The refractive index of the adhesive layer of the obtained adhesive sheet was measured according to JIS K0062-1992 using an Abbe refractometer (ATAGO CO., manufactured by LTD., product name "Abbe refractometer DR-M2", Na light source, wavelength: 589 nm). The measurement result corresponds to the refractive index of the matrix of the adhesive. The results are shown in Table 1.

In addition, the difference between the measured refractive index of the matrix of the adhesive and the refractive index of the light diffusing fine particles used in each of the examples and comparative examples was calculated as an absolute value. The results are shown in Table 2.

[ test example 2] (measurement of haze value)

The adhesive layers of the adhesive sheets produced in examples and comparative examples were bonded to glass, and the bonded sheets were used as measurement samples. The haze value (%) of light at every 5nm wavelength from 380nm to 780nm was measured using a haze meter (NIPPON DENSHOKU INDUSTRIES Co., LTD., product name "NDH 7000") according to JIS K7375:2008 on the basis of background measurement (background measurement) using glass. The haze values (%) of light beams having wavelengths of 380nm, 580nm and 780nm are shown in Table 2. In addition, the average value and standard deviation of the haze values of light rays having wavelengths of 380nm, 580nm and 780nm were calculated. The results are shown in Table 2.

[ test example 3] (measurement of Total light transmittance)

The adhesive layers of the adhesive sheets produced in examples and comparative examples were bonded to glass, and the bonded sheets were used as measurement samples. The total light transmittance (%) was measured using a haze meter (NIPPON DENSHOKU indtrastries co., ltd., product name "NDH 5000") in accordance with JIS K7375:2008, on the basis of the background measurement using glass. The results are shown in Table 2.

[ test example 4] (measurement of image clarity)

The adhesive layer of the adhesive sheet produced in the examples and comparative examples was measured for image clarity (%) of 5 types of combs (comb widths: 0.125mm, 0.25mm, 0.5mm, 1.0mm, and 2.0mm) by a transmission method according to JIS K7374:2007 using an image formation tester (image sensing gauge) (manufactured by Suga Test Instruments co., ltd., product name "ICM-10P"), and the total value thereof was calculated. The results are shown in Table 2.

[ test example 5] (measurement of storage modulus)

The release sheet was peeled from the adhesive sheets produced in the examples and comparative examples, and the adhesive layers were laminated so as to have a thickness of 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.

For the above sample, the storage modulus (G') (MPa) at 23 ℃ was measured under the following conditions by a torsional shear method (ね was manufactured by リせ one-end-to-end method) using a viscoelasticity measuring apparatus (product name "MCR 300" manufactured by Physica Co., Ltd.) according to JIS K7244-6. The results are shown in Table 2.

Measuring frequency: 1Hz

Measuring temperature: 23 deg.C

[ test example 6] (measurement of adhesive force)

The light release sheet was peeled from the adhesive sheets produced in examples and comparative examples, and the exposed adhesive layer was bonded to an easy adhesive layer of a polyethylene terephthalate (PET) film (TOYOBO co., ltd., product name "PET a 4300" with a thickness of 100 μm) having an easy adhesive layer, to obtain a laminate of a heavy release sheet/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 was peeled from the laminate under an atmosphere of 23 ℃ and 50% RH, and the exposed adhesive layer was attached to soda-lime Glass (manufactured by Nippon Sheet Glass co., ltd.), followed by pressurization at 0.5MPa and 50 ℃ for 20 minutes using an autoclave manufactured by kurihia sesisakusho co., ltd. Then, the sample was left at 23 ℃ and 50% RH for 24 hours. Then, the adhesion (before UV; mN/25mm) was measured using a tensile tester (ORIENTEC Co., Ltd., product name "TENSILON") under conditions of a peeling speed of 300 mm/min and a peeling angle of 180 degrees. The conditions not described herein were measured according to JIS Z0237: 2009. The results are shown in Table 2.

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

The light-release Sheet was peeled from the adhesive Sheet produced in each of the examples and comparative examples, and the exposed adhesive layer was bonded to a soda-lime Glass plate (manufactured by Nippon Sheet Glass co., ltd., thickness: 0.7mm) to obtain a laminate composed of the heavy-release Sheet/the adhesive layer/the soda-lime Glass plate.

The three-wavelength fluorescent lamp (distance from the fluorescent lamp: 200cm) was covered with the laminate, and the color of the fluorescent lamp and the light diffused to the periphery thereof, which were observed through the laminate, were observed. Then, the color unevenness suppression performance was evaluated according to the following criteria. The results are shown in Table 2.

Pah … shows no color unevenness even when the shielding angle is changed, and is white as a whole.

Good … shows that the fluorescent lamp portion is slightly colored (red, etc.) depending on the shielding angle, but the entire color is white at an angle where coloring is not observed.

Δ …, although the fluorescent lamp portion was observed to be slightly colored (red, etc.), the light diffused to the surroundings of the fluorescent lamp was white, regardless of the shielding angle.

X … the fluorescent lamp portion was clearly colored (red, etc.) regardless of the shielding angle, and it was observed that the light diffused to the surroundings of the fluorescent lamp was also colored.

[ test example 8] (evaluation of luminance unevenness suppression)

An LED point light source of a square type of 5mm × 5mm (total beam 20 lumens (lumen)) was manufactured using enoto co., ltd. (product name "5050D/G PKG"), an LED manufactured by GeneLite inc. (product name "B3838 ECI 1"), a gold wire manufactured by precious metal company in japan (product name "GLF ═ 30"), Shin-Etsu Chemical co., a sealing resin manufactured by ltd. (product name "KJR-9022"), and a die bond manufactured by Shin-Etsu Chemical co., ltd. (product name "KER 3000-M2"). Next, 4 LED point light sources obtained were fixed on a black resin substrate at intervals of 5mm so as to be arranged in a square shape, thereby obtaining a pseudo backlight.

A pseudo-display device having a backlight unit was obtained by placing the laminate produced in test example 7 on the pseudo-backlight so that the heavy-peel release sheet side was in contact with the pseudo-backlight. The LED point light source was turned on, the outer shape of the point light source was visually confirmed from a position 30cm directly above the pseudo display device, and the luminance unevenness suppression performance was evaluated based on the following criteria. The results are shown in Table 2.

Circa … is completely unable to identify a point source.

Good … can recognize a point light source if gazed at, but to a degree that is hardly noticeable.

X … can clearly identify a point light source.

[ test example 9] (evaluation of concave-convex embedding Property)

An ultraviolet curable ink (TEIKOKU PRINTING INKS mfg. co., ltd., product name "POS-911 semi") was screen-printed in a frame shape (outer shape: 90mm long by 50mm wide by 5mm wide) on the surface of a Glass plate (NSG Precision Cells, inc., product name "CORNING Glass EAGLE XG", 90mm long by 50mm wide by 0.5mm thick). Then, ultraviolet rays (80W/cm) were irradiated²2 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 (height of step:any one of 15 μm, 20 μm, 25 μm, and 50 μm).

The light release type release sheet was peeled from the adhesive sheets produced in examples and comparative examples, and the exposed adhesive layer was bonded to an easy adhesion layer of a polyethylene terephthalate film (TOYOBO CO., LTD., product name "PET A4300" with a thickness of 100 μm) having an easy adhesion layer. Subsequently, the heavy-release type release sheet is peeled off to expose the adhesive layer. Then, the laminate was laminated on each step-difference glass plate using a laminator (laminator) (product name "LPD 3214" manufactured by fujiapla inc.) so that the adhesive agent layer covered the entire frame-shaped printing surface, and the laminate was used as an evaluation sample.

The obtained evaluation sample was autoclaved at 50 ℃ and 0.5MPa for 30 minutes and then left to stand at room temperature, 23 ℃ and 50% RH for 24 hours. Subsequently, the molded article was stored under high temperature and high humidity conditions of 85 ℃ and 85% RH for 72 hours (durability test), and then the surface roughness embedding property was evaluated. The unevenness embedding property was judged by whether or not the printing step difference (unevenness) was completely embedded in the adhesive layer, and a case where air bubbles, floating, peeling, and the like were observed at the interface between the printing step difference and the adhesive layer was judged as a case where the printing step difference (unevenness) was not embedded in the adhesive layer. Here, the unevenness embedding property was calculated in the form of a step following ratio (%) shown by the following formula, and evaluated by the following criteria. The results are shown in Table 2.

The step following ratio (%) { (height of step (μm) which is free from bubbles, floating, peeling, and the like and maintains an embedded state after the durability test))/(thickness (μm) of the adhesive layer) } × 100

< evaluation Standard of concave-convex embedding Property >

Circleincis … step following rate of 40% or more

Good … has a step following ratio of less than 40% and not less than 30%

The following rate of the x … step difference is less than 30%

[ Table 1]

As is clear from table 2, the adhesive sheets produced in the examples were excellent in color unevenness suppression. Further, the adhesive sheets produced in examples 1 to 8 and 10 were also excellent in the unevenness in brightness suppression. Further, the adhesive sheets produced in examples 1 to 9 were also excellent in the embedding property of unevenness.

Industrial applicability

The adhesive sheet and the backlight unit of the present invention are suitable for display devices, particularly liquid crystal display devices, etc., which require color unevenness suppression.