Adhesive sheet

Abstract

Provided is an adhesive sheet which has excellent reliability under a high-temperature and high-humidity environment and with which polyene formation in a polarizing film is unlikely to occur.　An adhesive sheet 1 is an optical adhesive sheet. The adhesive sheet 1 has a thickness of 150 µm or more, a saturated water content X1 of 2.0 mass% or less at a temperature of 23 °C and a relative humidity of 50%, and a moisture permeability Y1, in terms of a thickness of 50 µm, of 200 g / m2·24 h or more at a temperature of 40 °C and a relative humidity of 92%. In the adhesive sheet 1, it is preferable that a relationship between a saturated water content X2 and the saturated water content X1 at a temperature of 85 °C and a relative humidity of 85% satisfies 0.5≤X2-X1≤2.

Description

Adhesive sheet

[0001] This invention relates to an adhesive sheet.

[0002] In recent years, image display devices such as liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs), as well as touch panels that incorporate touch sensors into these image display devices, have become widely used in various fields. Such image display devices and touch panels have a structure in which various optical components such as polarizing films, phase difference films, optical compensation films, touch sensor films, and cover films are laminated onto an image display panel. Adhesive sheets having an adhesive layer are used to bond these optical components together. For example, optical adhesive sheets are used to bond various optical components in image display devices (see, for example, Patent Documents 1 to 3).

[0003] For example, polarizing films are typically used in image display panels mounted on image display devices. Polarizing films can typically be used as optical laminates combined with functional layers.

[0004] Japanese Patent Publication No. 2003-238915, Japanese Patent Publication No. 2003-342542, Japanese Patent Publication No. 2004-231723

[0005] In high-temperature, high-humidity environments, optical components such as polarizing films repeatedly expand and contract, causing the adhesive sheets attached to them to peel off easily, resulting in poor reliability. Furthermore, under high-temperature, high-humidity conditions, polarizing films often experience discoloration due to polyene formation (a phenomenon in which numerous double bonds are formed within the polyvinyl alcohol molecules of the polarizer through dehydration condensation reactions).

[0006] The present invention aims to solve these problems, and its objective is to provide an adhesive sheet that is highly reliable in high-temperature and high-humidity environments and less prone to polyene formation of the polarizing film.

[0007] The present invention has a thickness of 150 μm or more, a saturated water content X1 of 2.0 mass% or less at a temperature of 23°C and a relative humidity of 50%, and a moisture permeability Y1 of 200 g / m² (calculated for 50 μm) at a temperature of 40°C and a relative humidity of 92%.２ - Provide an optical adhesive sheet with a shelf life of 24 hours or more.

[0008] The above adhesive sheet preferably satisfies the following equation (1) regarding the relationship between the saturated moisture content X2 and the saturated moisture content X1 at a temperature of 85°C and a relative humidity of 85%: 0 ≤ X2 - X1 ≤ 2 (1)

[0009] The above adhesive sheet preferably satisfies the following equation (2) regarding the relationship between the moisture permeability Y2 and the moisture permeability Y1 at a temperature of 85°C and a relative humidity of 85% (calculated as 50 μm): 1.5 ≤ Y2 / Y1 ≤ 10 (2)

[0010] The elastic modulus of the above adhesive sheet at a temperature of 85°C is 0.5 × 10⁻⁶. ４ ~20.0 x 10 ４ Pa is preferred.

[0011] The above adhesive sheet preferably has an adhesive surface that has an adhesive strength of 0.5 to 20.0 N / 20 mm after being stored at a temperature of 85°C and a relative humidity of 85% for two hours or more.

[0012] The above adhesive sheet is preferably used for bonding optical components for automotive applications.

[0013] Furthermore, the present invention provides an image display device equipped with the above-mentioned adhesive sheet.

[0014] The image display device preferably comprises a cover member, the adhesive sheet, the polarizing film, and the display module in this order.

[0015] In the above image display device, it is preferable that the adhesive sheet is bonded to the cover member and the polarizing film.

[0016] The adhesive sheet of the present invention offers excellent reliability in high-temperature and high-humidity environments, and is less prone to polyene formation of the polarizing film.

[0017] This is a schematic diagram (cross-sectional view) showing one embodiment of the adhesive sheet of the present invention. This is a schematic diagram (cross-sectional view) showing one embodiment of the optical laminate of the present invention.

[0018] [Adhesive Sheet] An embodiment of the adhesive sheet of the present invention will be described with reference to Figure 1. Figure 1 is a schematic cross-sectional view showing an embodiment of the adhesive sheet of the present invention. The adhesive sheet 1 shown in Figure 1 is formed from a single layer of adhesive and does not have a base material (base layer), and is a so-called "base material-less type" adhesive sheet (hereinafter sometimes referred to as a "base material-less double-sided adhesive sheet"). A release liner 2 and a release liner 3 are provided on both adhesive surfaces of the adhesive sheet 1, respectively. Note that the above-mentioned "base material (base layer)" does not include the release liner that is peeled off when the adhesive sheet is used (applied).

[0019] The thickness of the adhesive sheet of the present invention is 150 μm or more, preferably 180 μm or more, more preferably 200 μm or more, and even more preferably 220 μm or more. When the thickness is 150 μm or more, the thickness is sufficiently thick, allowing stress generated by the expansion and contraction of the adherend to be relieved within the adhesive sheet, suppressing peeling from the adherend in high temperature and high humidity environments, and providing excellent reliability in high temperature and high humidity environments. In addition, cracking of the optical component to which the adhesive sheet is bonded is less likely to occur in high temperature and high humidity environments. The above thickness is not particularly limited, but from the viewpoint of miniaturization, it may be, for example, 1000 μm or less, 800 μm or less, 700 μm or less, 600 μm or less, 500 μm or less, or 400 μm or less.

[0020] The saturated water content X1 of the adhesive sheet of the present invention at a temperature of 23°C and a relative humidity of 50% (23°C 50% RH) is 2.0% by mass or less, preferably 1.6% by mass or less, more preferably 1.2% by mass or less, and may be 1.0% by mass or less, 0.8% by mass or less, or 0.6% by mass or less. When the saturated water content X1 is 2.0% by mass or less, the saturated water content of the adhesive sheet at room temperature is sufficiently low, and the amount of moisture that can be retained is small, so the effect of moisture on the polarizing film can be reduced, and the polyene formation of the polarizing film can be suppressed. The saturated water content X1 is preferable as it is lower, but may be 0.001% by mass or more, 0.01% by mass or more, 0.03% by mass or more, 0.06% by mass or more, or 0.08% by mass or more.

[0021] The above-mentioned saturation moisture content X1 can be calculated by collecting the gas generated from the adhesive sheet after heating the adhesive sheet to 150°C and measuring the moisture content after leaving the adhesive sheet at 23°C and 50% RH for 24 hours or more. The above-mentioned saturation moisture content X1 can be adjusted by adjusting the type of base polymer, crosslinking degree, monomer composition, blending ratio, etc. that constitute the adhesive sheet.

[0022] The moisture permeability Y1 in terms of 50 μm of the adhesive sheet of the present invention at a temperature of 40°C and a relative humidity of 92% (40°C 92% RH) is 200 g / m ２ · 24 h or more, preferably 300 g / m ２ · 24 h or more, 400 g / m ２ · 24 h or more, 500 g / m ２ · 24 h or more, 700 g / m ２ · 24 h or more, 800 g / m ２ · 24 h or more, or 1000 g / m ２ · It may be 24 h or more. When the moisture permeability Y1 is 200 g / m ２ · When it is 24 h or more, the moisture permeability in a high-temperature and high-humidity environment is sufficiently high, and it is difficult for moisture to be retained in the adhesive sheet in a high-temperature and high-humidity environment. Therefore, the influence of moisture on the polarizing film can be reduced, and the polyene formation of the polarizing film can be suppressed. The higher the moisture permeability Y1, the more preferable it is, but 10000 g / m ２ · 24 h or less, 8000 g / m ２ · 24 h or less, 6000 g / m ２ · 24 h or less, or 5000 g / m ２ · It may be 24 h or less.

[0023] The above-mentioned moisture permeability Y1 is measured by leaving the adhesive sheet in an environment of 40°C 92% RH for 24 hours in accordance with the moisture permeability test (cup method) of JIS Z0208, and the obtained moisture permeability is converted into the moisture permeability in terms of 50 μm by the following formula and calculated. The above-mentioned moisture permeability Y1 can be adjusted by adjusting the type of base polymer, crosslinking degree, monomer composition, blending ratio, etc. that constitute the adhesive sheet. Formula: Moisture permeability Y1 = (Obtained moisture permeability [g / m ２ · 24 h] × (50 [μm] / Thickness of the measured adhesive sheet [μm])

[0024] For the adhesive sheet of the present invention, the saturated water content X2 at a temperature of 85°C and a relative humidity of 85% (85°C 85% RH) is preferably 8.0% by mass or less, more preferably 6.0% by mass or less, and still more preferably 4.0% by mass or less. When the saturated water content X2 is 8.0% by mass or less, since the amount of water that can be kept at a sufficiently low saturated water content under high temperature and high humidity environment of the adhesive sheet is small, the influence of water on the polarizing film can be reduced, and the polyene formation of the polarizing film under high temperature and high humidity environment can be more suppressed. The saturated water content X2 is preferably as low as possible, but may be 0.001% by mass or more, 0.01% by mass or more, 0.03% by mass or more, 0.06% by mass or more, or 0.08% by mass or more.

[0025] The saturated water content X2 can be calculated by leaving the adhesive sheet in an environment of 85°C 85% RH for 24 hours or more and then heating it to 150°C to collect the gas generated from the adhesive sheet and measuring the amount of water. The saturated water content X2 can be adjusted by adjusting the type of base polymer, crosslinking degree, monomer composition, blending ratio, etc. that constitute the adhesive sheet.

[0026] The water vapor permeability Y2 of the adhesive sheet of the present invention at a temperature of 85°C and a relative humidity of 85% (85°C 85% RH) is preferably 1500 g / m ２ ·24 h or more, more preferably 2000 g / m ２ ·24 h or more, still more preferably 3000 g / m ２ ·24 h or more, and 5000 g / m ２ ·24 h or more, 6000 g / m ２ ·24 h or more, or 7000 g / m ２ ·24 h or more may be acceptable. When the water vapor permeability Y2 is 1500 g / m ２ ·24 h or more, the water vapor permeability under high temperature and high humidity environment is sufficiently high, and it is difficult for water to be retained in the adhesive sheet under high temperature and high humidity environment. Therefore, the influence of water on the polarizing film can be reduced, and the polyene formation of the polarizing film can be more suppressed. The water vapor permeability Y2 is preferably as high as possible, but 55000 g / m ２ ·24 h or less, 50000 g / m２ ・ 24 hours or less, 40,000 g / m ２ ・ 24 hours or less, or 30,000 g / m ２ ・ It may be 24 hours or less.

[0027] The above moisture permeability Y2 can be measured by leaving the adhesive sheet standing in an environment of 85°C and 85% RH for 24 hours in accordance with the moisture permeability test (cup method) of JIS Z0208, and the obtained moisture permeability can be converted into the moisture permeability in terms of 50 μm by the following formula. The above moisture permeability Y2 can be adjusted by adjusting the type of base polymer, crosslinking degree, monomer composition, blending ratio, etc. constituting the adhesive sheet. Formula: Moisture permeability Y2 = (Obtained moisture permeability [g / m ２ ・ 24 h] × (50 [μm] / Thickness of the measured adhesive sheet [μm])

[0028] It is preferable that the relationship between the above saturated water content X2 and the above saturated water content X1 satisfies the following formula (1). When the following formula (1) is satisfied, it is difficult to absorb moisture even when the environment changes from a normal temperature environment to a high temperature and high humidity environment state, and polyene formation is less likely to occur. X2 - X1 is preferably 0.1 or more, and may be 0.3 or more, 0.5 or more, 0.6 or more, or 0.7 or more. Also, X2 - X1 is preferably 1.9 or less, more preferably 1.8 or less. 0 ≤ X2 - X1 ≤ 2 (1)

[0029] It is preferable that the relationship between the above moisture permeability Y2 and the above moisture permeability Y1 satisfies the following formula (2). When the following formula (2) is satisfied, moisture easily escapes from the adhesive sheet even when the environment changes from a normal environment to a high temperature and high humidity environment, and polyene formation is less likely to occur. Y2 / Y1 is preferably 2.0 or more, more preferably 2.4 or more, and further preferably 2.7 or more. Also, Y2 / Y1 is preferably 9.7 or less, more preferably 9.3 or less. 1.5 ≤ Y2 / Y1 ≤ 10 (2)

[0030] The elastic modulus (storage elastic modulus) at a temperature of 85°C of the adhesive sheet of the present invention is 0.5×10 ４ ~20.0×10 ４ Pa is preferable, more preferably 0.7×10 ４ ~14.0×10 ４ Pa, and further preferably 0.8×10４ ~11.5 x 10 ４ The elastic modulus is Pa. When the above modulus is within the above range, the adhesive sheet exhibits excellent stress relaxation properties and superior reliability in high-temperature, high-humidity environments.

[0031] The above-mentioned modulus of elasticity can be adjusted by adjusting the type and degree of crosslinking of the base polymer constituting the adhesive sheet, the monomer composition, the molecular weight of the base polymer, and the type and proportion of additives such as crosslinking agents.

[0032] The adhesive sheet of the present invention preferably has an adhesive surface with an adhesive strength of 0.5 N / 20 mm or more after being stored at a temperature of 85°C and a relative humidity of 85% (85°C 85% RH) for two hours or more. More preferably, the adhesive strength is 1.0 N / 20 mm or more, and even more preferably 2.0 N / 20 mm or more. When the adhesive strength is 0.5 N / 20 mm or more, peeling from the adherend is less likely to occur in high temperature and high humidity environments, resulting in superior reliability. While a higher adhesive strength is preferable, it may be, for example, 20.0 N / 20 mm or less, 19.0 N / 20 mm or less, or 18.0 N / 20 mm or less. Furthermore, the adhesive strength of both adhesive surfaces of the adhesive sheet of the present invention may be within the above range.

[0033] The adhesive strength of the above adhesive sheet is measured by storing the adhesive sheet at 85°C and 85% RH for more than two hours, then attaching it to a glass plate and peeling it off under conditions of 23°C and 50% RH, with a peel angle of 180° and a tensile speed (peeling speed) of 300 mm / min. The above adhesive strength can be adjusted, for example, by adjusting the type of base polymer constituting the adhesive sheet, the degree of crosslinking, the monomer composition, and the blending ratio.

[0034] The base polymer included in the adhesive sheet of the present invention is not particularly limited, but examples include acrylic polymers, rubber polymers, silicone polymers, polyester polymers, urethane polymers, polyamide polymers, epoxy polymers, vinyl alkyl ether polymers, and fluorine polymers. The above base polymer may be one or more types.

[0035] The content of the base polymer in the above adhesive sheet is not particularly limited, but is preferably 75% by mass or more (for example, 75 to 99.9% by mass) and more preferably 85% by mass or more (for example, 85 to 99.9% by mass) based on the total amount of the adhesive sheet (100% by mass).

[0036] The above-mentioned base polymer preferably contains a low-polarity monomer as a monomer component constituting the base polymer. The low-polarity monomer is a monomer with lower polarity than the high-polarity monomer described later, and examples include aliphatic vinyl monomers (olefins) such as ethylene, propylene, butylene, isobutylene (2-methylpropene), butadiene, and isoprene; vinyl monomers consisting only of hydrocarbons such as aromatic vinyl monomers such as styrene; and alkyl (meth)acrylates described later. The low-polarity monomer may be used alone or two or more.

[0037] The proportion of low-polarity monomers in the above-mentioned base polymer is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more, based on the total amount (100% by mass) of the monomer components constituting the above-mentioned base polymer. The above proportion is, for example, 99% by mass or less or 96% by mass or less.

[0038] In this specification, the term "monomer component" refers to a compound having only one polymerizable functional group, and does not include compounds having two or more polymerizable functional groups, such as polyfunctional compounds described later.

[0039] The above-mentioned base polymer may contain a highly polar monomer as a monomer component constituting the base polymer. The highly polar monomer is a monomer that has higher polarity than the above-mentioned low-polarity monomer, and examples include monomers having polar groups (such as hydroxyl groups, sulfonic acid groups, phosphoric acid groups, acetate groups, carboxyl groups, acid anhydride groups, epoxy groups, alkoxy groups, amino groups, cyano groups (nitrile groups), nitrogen atom-containing groups such as nitrogen atom-containing rings, etc.) (e.g., the polar group-containing monomers described later); and monomers having a carbon-halogen bond in the molecule. The highly polar monomer may be used by one type or by two or more types.

[0040] The proportion of highly polar monomers in the above base polymer is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, based on the total amount (100% by mass) of monomer components constituting the base polymer, and may be substantially absent. When the proportion of highly polar monomers is 40% by mass or less, the saturated water content X1 and X2 can be easily reduced.

[0041] In this specification, "substantially absent" means not actively incorporating the target ingredient unless it is unavoidably present.

[0042] The above-mentioned base polymer is preferably one of the following: (i) it contains low-polarity monomers and high-polarity monomers as monomers constituting the base polymer, and (ii) the mass per mol of the monomer composition constituting the base polymer is 300 [g / mol] or less.

[0043] When (i) above is satisfied, the proportion of high-polarity monomers in the base polymer is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, based on the total amount (100% by mass) of monomer components constituting the base polymer. It is presumed that including low-polarity monomers and high-polarity monomers allows for an appropriate amount of moisture attracted by the polarity, making it easier to adjust the saturated water content X1, X2 and moisture permeability Y1, Y2 to an appropriate range.

[0044] In (ii) above, the "mass per mol of monomer composition" is calculated by multiplying the mass per mol of each monomer component in the monomer composition constituting the base polymer by the molar ratio of that monomer component to the total moles of all monomer components, and then summing the resulting values ​​[g / mol]. Low-polarity monomers also have a small degree of polarity, and it is presumed that this small polarity attracts moisture to an appropriate degree. Therefore, when (ii) above is satisfied, the number of monomer molecules (moles) contained in the monomer composition per unit mass increases, so an appropriate polarity can be obtained as a base polymer, and it is easy to adjust the saturated water content X1, X2 and moisture permeability Y1, Y2 to an appropriate range.

[0045] As the base polymer, acrylic polymers are preferred from the viewpoint of transparency, weather resistance, adhesive reliability, and ease of functional design of adhesive sheets due to the wide variety of monomers available. In other words, the adhesive sheet of the present invention is preferably an acrylic adhesive sheet containing an acrylic polymer as the base polymer.

[0046] The above-mentioned acrylic polymer is a polymer that contains an acrylic monomer (a monomer having a (meth)acryloyl group in its molecule) as a monomer component constituting the polymer. That is, the above-mentioned acrylic polymer contains constituent units derived from an acrylic monomer. Note that only one type of acrylic polymer may be used, or two or more types may be used. Furthermore, the above-mentioned acrylic polymer may contain only one type of acrylic monomer as a monomer component, or it may contain two or more types.

[0047] The above acrylic polymer is preferably a polymer composed (formed) with (meth)acrylate alkyl ester as an essential monomer component. That is, the above acrylic polymer preferably contains (meth)acrylate alkyl ester as a constituent unit. In this specification, "(meth)acrylic" means "acrylic" and / or "methacrylic" (either one or both of "acrylic" and "methacrylic"), and the same applies to other terms.

[0048] The above acrylic monomer preferably contains an alkyl (meth)acrylate. The alkyl (meth)acrylate is preferably an alkyl (meth)acrylate having 1 to 20 carbon atoms in the alkyl group. The alkyl (meth)acrylate may have a linear or branched alkyl group, or a cyclic alkyl group such as an alicyclic alkyl group. One or more of the alkyl (meth)acrylate may be used.

[0049] Examples of alkyl (meth)acrylate esters having linear or branched alkyl groups include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, (meth)acrylate Examples include isononyl acrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate (i.e., lauryl methacrylate), isotridecyl methacrylate, tetradecyl methacrylate, isotetradecyl methacrylate, pentadecyl methacrylate, cetyl methacrylate, heptadecyl methacrylate, stearyl methacrylate, isostearyl methacrylate, and nonadecyl methacrylate.

[0050] Examples of alkyl (meth)acrylates having an alicyclic alkyl group include cycloalkyl (meth)acrylates, alkyl (meth)acrylates having a bicyclic aliphatic hydrocarbon ring, and alkyl (meth)acrylates having three or more aliphatic hydrocarbon rings. Examples of cycloalkyl (meth)acrylates include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. Examples of alkyl (meth)acrylates having a bicyclic aliphatic hydrocarbon ring include isobornyl (meth)acrylate. Examples of alkyl (meth)acrylates having three or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0051] The (meth)acrylate alkyl ester is preferably an alkyl acrylate having an alkyl group having 3 to 15 carbon atoms, more preferably an alkyl acrylate having an alkyl group having 4 to 10 carbon atoms, and even more preferably an alkyl acrylate having an alkyl group having 4 to 16 carbon atoms (sometimes referred to as "alkyl acrylate (A)") from the viewpoint of easily adjusting the polarity of the acrylic polymer. The alkyl acrylate (A) is preferably at least one selected from the group consisting of n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), n-octyl acrylate (NOAA), isostearyl acrylate (iSTA), lauryl acrylate (LA), cyclohexyl acrylate (CHA), isononyl acrylate (INAA), and isodecyl acrylate (IDAA).

[0052] From the viewpoint of appropriately exhibiting basic properties such as tackiness in the adhesive sheet, the proportion of alkyl (meth)acrylate is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more, based on the total amount (100% by mass) of the monomer components constituting the base polymer. The above proportion is, for example, 99% by mass or less or 96% by mass or less.

[0053] From the viewpoint of increasing the moisture permeability Y1 and Y2 of the adhesive sheet, the proportion of alkyl acrylate (A) is preferably 55% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more, based on the total amount (100% by mass) of the alkyl (meth)acrylate. The above proportion may be 100% by mass, or 99% by mass or less, or 96% by mass or less.

[0054] The above monomer component may include copolymerizable monomers that can copolymerize with alkyl (meth)acrylate esters. Examples of the above copolymerizable monomers include monomers having polar groups (polar group-containing monomers). Examples of the above polar group-containing monomers include monomers containing hydroxyl groups, monomers containing carboxyl groups, and monomers having nitrogen atom-containing rings. The above polar group-containing monomers are useful for modifying acrylic polymers, such as introducing crosslinking points into acrylic polymers and ensuring the cohesive strength of acrylic polymers. One type of the above copolymerizable monomer may be used, or two or more types may be used.

[0055] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate. The hydroxyl group-containing monomer is preferably at least one selected from the group consisting of 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA).

[0056] The proportion of hydroxyl group-containing monomers may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, relative to the total amount (100% by mass) of monomer components constituting the base polymer, from the viewpoint of introducing a crosslinked structure into the acrylic polymer and ensuring cohesive force in the adhesive sheet. From the viewpoint of adjusting the polarity of the acrylic polymer (related to the compatibility between various additive components in the adhesive sheet and the acrylic polymer), the above proportion is preferably 40% by mass or less, more preferably 30% by mass or less, and may be 20% by mass or less, or may not be substantially contained at all.

[0057] Examples of monomers containing a carboxyl group include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0058] The proportion of carboxyl group-containing monomers may be 0.1% by mass or more, or 0.3% by mass or more, relative to the total amount (100% by mass) of monomer components constituting the base polymer, from the viewpoint of introducing a crosslinked structure into the acrylic polymer, ensuring cohesive force in the adhesive sheet, and ensuring the adhesive strength of the adhesive sheet. From the viewpoint of avoiding the risk of corrosion of the adherend by acid, the above proportion is preferably 3% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less, and may be substantially absent.

[0059] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholindione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, and N-vinylisothiazole.

[0060] The proportion of monomers having nitrogen atom-containing rings is, for example, 0.5% by mass or more, and may be 1% by mass or more, or 1.5% by mass or more, based on the total amount (100% by mass) of monomeric components constituting the base polymer. The above proportion is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, and may be substantially absent.

[0061] The above monomer component may also contain other copolymerizable monomers. Examples of these other copolymerizable monomers include acid anhydride monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds. One or more of these other copolymerizable monomers may be used.

[0062] The proportion of the above-mentioned other copolymerizable monomers may be, for example, 0.05% by mass or more, or 0.5% by mass or more, based on the total amount (100% by mass) of the monomer components constituting the base polymer. The above proportion may also be, for example, 20% by mass or less, 10% by mass or less, 5% by mass or less, or 2% by mass or less, and may be substantially absent.

[0063] The above adhesive sheet may contain structural components derived from a crosslinking agent. By using the above crosslinking agent, the base polymer will have a crosslinked structure. Examples of the above crosslinking agent include compounds that are reactive with polar groups (such as hydroxyl groups and carboxyl groups) in the above polar group-containing monomer. Examples of such crosslinking agents include isocyanate crosslinking agents, peroxide crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents. Only one crosslinking agent may be used, or two or more may be used.

[0064] From the viewpoint of ensuring the cohesive force of the adhesive sheet, the content of the structural component derived from the above-mentioned crosslinking agent (compound having reactivity with the above-mentioned polar group) is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.05 parts by mass or more, and also preferably 3 parts by mass or less, more preferably 1 part by mass or less, and even more preferably 0.5 parts by mass or less, per 100 parts by mass of the total amount of monomer components (or total amount of base polymer).

[0065] Furthermore, examples of the crosslinking agent include polyfunctional compounds having multiple groups that can react with polymerizable functional groups in the monomer component. Examples of the polyfunctional compound include polyfunctional monomers and polyfunctional oligomers containing two or more ethylenically unsaturated double bonds in one molecule. Examples of polyfunctional monomers include polyfunctional (meth)acrylates.

[0066] Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and polyfunctional (meth)acrylates with four or more functions.

[0067] Examples of difunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, ethoxylated bisphenol A diacrylate (BPAEODE), and neopentyl glycol di(meth)acrylate.

[0068] Examples of trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris(acryloyloxyethyl) isocyanurate.

[0069] Examples of polyfunctional (meth)acrylates with four or more functions include ditrimethylolpropanetetra(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0070] Examples of polyfunctional oligomers include urethane (meth)acrylate oligomers, polyester (meth)acrylate oligomers, polyether (meth)acrylate oligomers, polyol (meth)acrylate oligomers, epoxy (meth)acrylate oligomers, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate.

[0071] Preferably, the polyfunctional compound used is at least one selected from the group consisting of trimethylolpropane triacrylate (TMPTA) and dipentaerythritol hexaacrylate (DPHA).

[0072] From the viewpoint of ensuring the cohesive force of the adhesive sheet, the content of the structural component derived from the above polyfunctional compound is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, and even more preferably 0.05 parts by mass or more, per 100 parts by mass of the total amount of monomer components. From the viewpoint of ensuring the flexible deformability of the adhesive sheet, the content is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less.

[0073] The adhesive sheet of the present invention may contain a silane coupling agent. The content of the silane coupling agent is preferably 0.1 parts by mass or more, and more preferably 0.2 parts by mass or more, based on 100 parts by mass of the total amount of the base polymer. The content is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less.

[0074] The adhesive sheet of the present invention may contain other components besides those described above, as long as they do not impair the effects of the present invention. Examples of these other components include polymerization initiators, chain transfer agents, curing agents, curing catalysts, crosslinking accelerators, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.), antioxidants, fillers (metal powders, organic fillers, inorganic fillers, etc.), colorants (pigments, dyes, etc.), antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, rust inhibitors, granular materials, foil-like materials, flame retardants, and ion trapping agents. Each of these other components may be used individually or in combination of two or more.

[0075] The adhesive sheet of the present invention is preferably transparent. The haze of the adhesive sheet of the present invention (according to JIS K7136) is not particularly limited, but is preferably 1.2% or less, more preferably 1.1% or less, even more preferably 1.0% or less, even more preferably 0.9% or less, and particularly preferably 0.8% or less. When the haze is, for example, 1.2% or less, excellent transparency and excellent appearance are easily obtained. The above haze can be measured, for example, by setting the thickness of the adhesive sheet to 25 μm, leaving it at normal conditions (23°C, 50% RH) for at least 24 hours, and then laminating it onto a glass slide (for example, total light transmittance 91.8%, haze 0.4%) as a sample, and measuring it using a haze meter (product name "HM-150", manufactured by Murakami Color Technology Research Institute Co., Ltd.).

[0076] The adhesive sheet of the present invention may take any form, for example, an emulsion type, a solvent type (solution type), an active energy ray curing type, a hot melt type, etc. Among these, an active energy ray curing type adhesive sheet is preferred from the viewpoint of excellent productivity and environmental adaptability.

[0077] Examples of the active energy rays mentioned above include ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, as well as ultraviolet rays, with ultraviolet rays being particularly preferred. In other words, the active energy ray curing adhesive sheet is preferably an ultraviolet-curing adhesive sheet.

[0078] The above-mentioned adhesive sheet can be manufactured, for example, by applying an adhesive composition for forming an adhesive sheet onto a release liner and drying and curing the resulting adhesive composition layer, or by applying the above-mentioned adhesive composition onto a release liner and curing the resulting adhesive composition layer by irradiating it with active energy rays. Furthermore, if necessary, it may be further heated and dried.

[0079] A known coating method may be used for applying (coating) the above adhesive composition. For example, coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, spray coaters, comma coaters, and direct coaters may be used.

[0080] Examples of the above-mentioned adhesive compositions include adhesive compositions containing the above-mentioned base polymer, compositions containing monomer components that form the above-mentioned base polymer when an adhesive sheet is formed (sometimes referred to as "monomer compositions"), and compositions containing a partial polymer thereof.

[0081] Examples of the above monomer compositions include compositions composed of a single monomer component and compositions composed of two or more monomer components (monomer mixtures). Furthermore, the above "partially polymerized product" may also be referred to as a "prepolymer" or "syrup," and means a composition in which one or more monomer components of the above monomer composition are partially polymerized.

[0082] The above adhesive composition may contain polymerization initiators such as photopolymerization initiators. The above base polymer can be formed, for example, by photopolymerizing the above polymerizable components. The above photopolymerization initiator may be used alone or two or more types.

[0083] Examples of the above-mentioned photopolymerization initiators include radical photopolymerization initiators, cationic photopolymerization initiators, and anionic photopolymerization initiators.

[0084] Examples of the radical photopolymerization initiators mentioned above include acylphosphine oxide photopolymerization initiators, benzoin ether photopolymerization initiators, acetophenone photopolymerization initiators, α-ketol photopolymerization initiators, aromatic sulfonyl chloride photopolymerization initiators, photoactive oxime photopolymerization initiators, benzoin photopolymerization initiators, benzyl photopolymerization initiators, benzophenone photopolymerization initiators, ketal photopolymerization initiators, and thioxanthone photopolymerization initiators.

[0085] Examples of acylphosphine oxide photopolymerization initiators include bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-2,4-di-n-butoxyphenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide. Examples of benzoin ether photopolymerization initiators include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, and 2,2-dimethoxy-1,2-diphenylethane-1-one. Examples of acetophenone photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of photoactive oxime photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of benzoin photopolymerization initiators include benzoin. Examples of benzyl photopolymerization initiators include benzyl. Examples of benzophenone photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, and polyvinylbenzophenone. Examples of ketal photopolymerization initiators include benzyldimethylketal. Examples of thioxanthone photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

[0086] The amount of the above-mentioned photopolymerization initiator used (or the total amount of multiple photopolymerization initiators if multiple photopolymerization initiators are used) is, for example, 0.01 parts by mass or more, preferably 0.03 parts by mass or more, more preferably 0.05 parts by mass or more, and also, for example, 1 part by mass or less, preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and even more preferably 0.2 parts by mass or less, based on 100 parts by mass of the total amount of monomer components.

[0087] The above adhesive composition is preferably solvent-free. That is, it is preferable that the adhesive composition does not contain or substantially contains organic solvents. With a solvent-free adhesive composition, there is no need to remove the solvent from the coating film of the composition during the process of manufacturing an adhesive sheet from the composition. Therefore, adhesive sheets formed from a solvent-free adhesive composition are suitable for reducing environmental impact.

[0088] The above-mentioned organic solvent is not particularly limited as long as it is an organic compound used as a solvent, but examples include hydrocarbon solvents such as cyclohexane, hexane, and heptane; aromatic solvents such as toluene and xylene; ester solvents such as ethyl acetate and methyl acetate; ketone solvents such as acetone and methyl ethyl ketone; and alcohol solvents such as methanol, ethanol, butanol, and isopropyl alcohol. The above-mentioned organic solvent may also be a mixed solvent containing two or more organic solvents.

[0089] The content of organic solvents in the above adhesive composition is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.2% by mass or less, based on the total amount (100% by mass) of the adhesive composition, and it is particularly preferable that it is substantially absent.

[0090] Alternatively, after curing a monomer mixture or a partially polymer thereof by active energy ray irradiation to form an adhesive sheet, a solution containing an additive may be applied to the adhesive sheet, allowing the additive to penetrate from one side of the adhesive sheet in the thickness direction. This allows the adhesive sheet to be imparted with the desired properties by the additive. Furthermore, the transparency of the adhesive sheet is maintained as the additive penetrates in solution form. Subsequently, the adhesive sheet is dried by heating or other means. This process returns the adhesive sheet to a state close to that before application. That is, since the adhesive sheet has been cured once, its physical properties such as adhesive strength and elastic modulus are restored to a state close to that before the above solution was applied. Because the adhesive sheet is cured before the additive is added, once the composition, curing conditions, and physical properties of the adhesive composition are determined, there is no need to redesign the composition by adding an additive, and the thickness of the adhesive sheet can be easily changed. Furthermore, the desired properties imparted to the adhesive sheet can be controlled by changing the subsequent coating conditions of the additive solution. In this way, the control of the physical properties of the adhesive sheet and the control of the desired properties by the additive can be separated, so there is no need to redesign the adhesive sheet from scratch when changing the thickness of the adhesive sheet or the amount of additive added, which is efficient.

[0091] The above additives can be used without particular limitations, and those used in the field of adhesives can be used. Examples include polymerization initiators, crosslinking agents, ultraviolet absorbers, rust inhibitors, antistatic agents, crosslinking accelerators, silane coupling agents, tackifying resins, anti-aging agents, colorants such as dyes, antioxidants, chain transfer agents, plasticizers, softeners, and surfactants. From the viewpoint of easily exhibiting the desired effects of the present invention, polymerization initiators, crosslinking agents, ultraviolet absorbers, rust inhibitors, and antistatic agents are preferred.

[0092] In high-temperature, high-humidity environments such as the inside of a car in summer, optical components such as polarizing films repeatedly expand and contract, causing the adhesive sheet bonded to the optical component to peel off easily and resulting in poor reliability. Increasing the thickness of the adhesive sheet can alleviate the stress generated in the sheet, making it less likely for the adhesive sheet to peel off or the bonded object to crack. However, the thicker the adhesive sheet, the greater the amount of moisture it tends to hold. A high moisture content in the adhesive sheet promotes the polyene conversion of the polarizing film. In contrast, the adhesive sheet of the present invention, when bonded to an optical component, offers excellent reliability in high-temperature, high-humidity environments, is less prone to peeling of the adhesive sheet or cracking of the bonded object, and is less likely to cause polyene conversion of the polarizing film.

[0093] [Release Liner] The adhesive surface of the adhesive sheet of the present invention may be provided with a release liner until use. The release liner protects the adhesive surface that comes into contact with the adhesive sheet until use, and is peeled off when the adhesive sheet is used. If the adhesive sheet is a double-sided adhesive sheet, each adhesive surface may be protected by two release liners, or it may be protected by a single release liner with both sides being release surfaces, in a roll-like manner. The release liner is used as a protective material for the adhesive sheet and is peeled off when it is attached to the object. The release liner also plays a role as a support for the adhesive sheet. Note that the release liner is not necessarily required.

[0094] Examples of substrates for the above-mentioned release liner include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, and fluororesin film. Crosslinked films of these are also acceptable. Furthermore, laminated films of these may also be used.

[0095] It is preferable that the release surface of the above-mentioned release liner (particularly the surface in contact with the adhesive surface) is subjected to a release treatment. Examples of release agents used in the release treatment include alkyd, silicone, fluorine, unsaturated polyester, polyolefin, and wax-based release agents.

[0096] The thickness of the release liner is not particularly limited, but is, for example, about 20 to 150 μm.

[0097] [Applications] The adhesive sheet of the present invention is used in optical applications, specifically for bonding to optical components. More specifically, it is used, for example, for bonding optical components (for bonding optical components) and for manufacturing products using the above-mentioned optical components (optical products). Using the adhesive sheet of the present invention in optical applications provides superior reliability.

[0098] The adhesive sheet of the present invention is used, for example, in optical components of electrical and electronic equipment to attach (mount) various members or parts to predetermined locations (e.g., housing, front panel, window portion, etc.). "Electrical and electronic equipment" refers to equipment that falls under at least one of either electrical equipment or electronic equipment. Examples of such electrical and electronic equipment include image display devices such as liquid crystal displays, organic / inorganic electroluminescent displays, and plasma displays, as well as portable electronic devices. Examples of such image display devices include image display devices in portable electronic devices, in-vehicle displays, and digital signage (electronic billboards). The image display device may be in a rigid or flexible form (structure), or it may be a foldable or rollable form (structure).

[0099] Examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (e.g., wristwear-type devices worn on the wrist like watches, modular devices attached to a part of the body with clips or straps, eyewear-type devices including glasses (monocular and binocular types, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. as accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game consoles, electronic dictionaries, electronic organizers, e-books, in-car information systems, portable radios, portable televisions, portable printers, portable scanners, and portable modems. In this specification, "portable" means not merely being able to carry something, but having a level of portability that allows an individual (a typical adult) to carry it relatively easily.

[0100] In particular, the adhesive sheet of the present invention is preferable to be used laminated to an optical component including a polarizing film, and is especially preferable to be used laminated to a polarizing film, from the viewpoint of having excellent reliability in high temperature and high humidity environments and being less likely to cause polyene formation of the polarizing film.

[0101] The above-mentioned image display device preferably comprises a cover member, the adhesive sheet of the present invention, a polarizing film, and a display module in this order. Specifically, the adhesive sheet of the present invention is preferably used for bonding the cover member and the polarizing film in the image display device, and is particularly preferably used for bonding the cover member and the polarizing film in an image display device comprising a cover member, the adhesive sheet of the present invention, a polarizing film, and a display module in this order.

[0102] Furthermore, the adhesive sheet of the present invention is preferably used in automotive optical products. Specifically, it is preferably used for bonding optical components used in automotive optical products (optical component bonding applications).

[0103] [Optical Laminate] By providing the adhesive sheet of the present invention between a cover member and a polarizing film, an optical laminate (optical laminate of the present invention) is obtained, comprising a cover member, the adhesive sheet of the present invention, a polarizing film, and a display module in this order. An example of the optical laminate of the present invention is the image display device described above.

[0104] The cover member described above is provided on the surface of the optical laminate and protects the internal components of the optical laminate. Examples of the cover member include cover glass and plastic covers. The cover member may be bonded to a layer constituting the optical laminate, such as a polarizing film, via an adhesive sheet.

[0105] Examples of the above-mentioned display modules include various optical components used in image display devices, such as liquid crystal panels, OLED panels, micro-LED panels, display units and image reflection mirrors for head-up displays, display units and lenses for VR goggles, and image projection screens for AR glasses.

[0106] Figure 2 shows one embodiment of the optical laminate of the present invention. The image display device 4, which is an optical laminate shown in Figure 2, comprises, in this order, a display module 5, a polarizing film 6 provided on the display module 5, an adhesive sheet 1 of the present invention, and a cover member 7 provided on the surface of the image display device 4. The polarizing film 6 and the cover member 7 are bonded together by the adhesive sheet 1 of the present invention.

[0107] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit it.

[0108] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. Note that all amounts (parts by mass) refer to the amount of each component described.

[0109] Example 1 (Preparation of Prepolymer Composition) A monomer composition consisting of 100 parts by mass of n-octyl acrylic acid (NOAA) was mixed with 0.05 parts by mass of a photopolymerization initiator (trade name "Omnirad 184", manufactured by IGM Resins B.V.) and 0.05 parts by mass of another photopolymerization initiator (trade name "Omnirad 651", manufactured by IGM Resins B.V.). The mixture was then irradiated with ultraviolet light until the viscosity (BH viscometer No. 5 rotor, 10 rpm, measurement temperature 30°C) reached approximately 20 Pa·s, thereby obtaining a prepolymer composition in which a portion of the monomer components had polymerized.

[0110] (Preparation of adhesive composition) An adhesive composition was prepared by mixing 100 parts by mass of the above prepolymer composition with 0.03 parts by mass of trimethylolpropane triacrylate (TMPTA) as a crosslinking agent and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.).

[0111] (Preparation of Adhesive Sheet) The above adhesive composition was applied to a polyethylene terephthalate (PET) release liner (heavy-duty release liner, product name "MRF75", manufactured by Mitsubishi Chemical Corporation) to a final thickness (thickness of the adhesive sheet) of 250 μm, forming a coating layer (adhesive composition layer). Next, a PET release liner (light-duty release liner, product name "MRE75", manufactured by Mitsubishi Chemical Corporation) was placed on the coating layer to cover the coating layer and block oxygen. A laminate of MRF75 / coating layer (adhesive composition layer) / MRE75 was then obtained. Next, a black light (manufactured by Toshiba Corporation) was used to illuminate this laminate from the top surface (MRE75 side) at an illuminance of 5 mW / cm². ２ The material was irradiated with ultraviolet light for 300 seconds. Further drying was performed in a 90°C dryer for 2 minutes to volatilize any remaining monomers. This resulted in a substrate-less double-sided adhesive sheet consisting of only a single adhesive layer, with both adhesive surfaces protected by a release liner.

[0112] Examples 2-13 and Comparative Examples 1-3: Prepolymer compositions, adhesive compositions, and substrate-less double-sided adhesive sheets were prepared in the same manner as in Example 1, except that the types and amounts of monomer components and crosslinking agents in the monomer composition, and the thickness of the adhesive sheet were changed as shown in Table 1. In Table 1, "BA" represents n-butyl acrylate, "2EHA" represents 2-ethylhexyl acrylate, "INAA" represents isononyl acrylate, "IDAA" represents isodecyl acrylate, "iSTA" represents isostearyl acrylate, "LA" represents lauryl acrylate, "CHA" represents cyclohexyl acrylate, "HEA" represents 2-hydroxyethyl acrylate, "4HBA" represents 4-hydroxybutyl acrylate, "NVP" represents N-vinyl-2-pyrrolidone, and "DPHA" represents dipentaerythritol hexaacrylate. The unit of the numerical values ​​for each component in Table 1 is "parts by mass".

[0113] [Evaluation] The following measurements or evaluations were performed on the substrate-less double-sided adhesive sheets of the examples and comparative examples. The evaluation results are shown in Table 1.

[0114] (1) Saturated water content (X1, X2) The substrate-less double-sided adhesive sheets of the examples and comparative examples were cut to a size of 10 mm x 50 mm and left to stand for 24 hours or more in an environment of 23°C 50% RH or 85°C 85% RH. After weighing each sample, it was placed in a heating vaporizer (product name "VA-200", manufactured by Nitto Seiko Analytech Co., Ltd.), and the gas generated at 150°C was introduced into a titration cell. The water content was measured using a coulometric titration type moisture meter (product name "CA-200", manufactured by Nitto Seiko Analytech Co., Ltd.). The value obtained by dividing the water content by the initial weight was defined as the saturated water content.

[0115] (2) Water Permeability (Y1, Y2) Measurement samples were prepared by cutting the substrate-less double-sided adhesive sheets of the examples and comparative examples into 10 cmΦ circles and peeling off the release liner. The samples were then left to stand for 24 hours in an environment of 40°C 92% RH or 85°C 85% RH in accordance with the water permeability test (cup method) of JIS Z0208, and the water permeability was measured. The water permeability obtained from the measurement was then converted to water permeability on a 50 μm basis using the following formula. Formula: Water permeability on a 50 μm basis = (Obtained water permeability [g / m²]) ２ • 24h × (50 [μm] / Thickness of the measured adhesive sheet [μm])

[0116] (3) Storage modulus For the substrate-less double-sided adhesive sheets of the examples and comparative examples, the required number of measurement samples were prepared. Specifically, first, multiple pieces of the substrate-less double-sided adhesive sheet cut from the substrate-less double-sided adhesive sheet were bonded together to prepare a sample sheet with a thickness of approximately 2 mm. Next, this sheet was punched out to obtain cylindrical pellets (7.9 mm in diameter) which were to be used as measurement samples. Then, using a viscoelasticity measuring device (product name "ARES-G2", manufactured by TA Instruments), the measurement samples were fixed to a parallel plate jig with a diameter of 7.9 mm, and viscoelasticity measurements were performed in a predetermined temperature range under the conditions of a frequency of 1 Hz and a measurement load of 0.98 N to obtain the storage modulus.

[0117] (4) Adhesion Strength The substrate-less double-sided adhesive sheets of the examples and comparative examples were stored in an environment of 85°C and 85% RH for more than 2 hours. After that, the light release liner was peeled off, and a PET film (product name "Lumirror S10", manufactured by Toray Industries, Inc., thickness 25 μm) was bonded to the exposed surface of the exposed adhesive sheet to obtain a laminate. Next, a test piece (width 20 mm x length 150 mm) was cut out from this laminate, the heavy release liner was peeled off, and it was bonded to a glass plate (manufactured by Matsunami Glass Co., Ltd.). In this bonding, the test piece was pressed against the glass plate by running a 2 kg roller back and forth once in an environment of 25°C. After the bonding described above, the test piece was left to stand at 23°C for 2 minutes, and the stress when peeling the test piece from the glass plate was measured as the adhesive strength using a tensile testing machine (manufactured by Instron). In the above measurements, the measurement environment was set to 23°C and 50% RH, the peel angle of the test specimen relative to the glass plate was set to 180°, and the tensile speed (peel speed) of the test specimen was set to 300 mm / min.

[0118] (5) Peeling evaluation A sample was prepared by laminating a first glass plate measuring 50 mm x 100 mm x 0.7 mm thick, a polarizing film (product name "HDZQ", manufactured by Nitto Denko Corporation), the substrate-less double-sided adhesive sheet obtained in the examples and comparative examples, and the second glass plate in this order, and leaving it standing in a 95°C environment for 1000 hours. After that, the sample was taken out to a room temperature environment and the presence or absence of peeling on both adhesive surfaces of the substrate-less double-sided adhesive sheet was visually checked. If peeling was confirmed on at least one side, it was evaluated as "yes".

[0119] (6) Polyene formation evaluation The samples that underwent the peeling evaluation described above were visually inspected for discoloration of the polarizing film due to polyene formation.

[0120]

[0121] As shown in Table 1, the substrate-less double-sided adhesive sheets of the examples did not peel off or polyene formation of the polarizing film even when attached to a polarizing film and left in a high-temperature, high-humidity environment for a long period of time. On the other hand, when the moisture permeability Y1 was low (Comparative Example 1) and when the saturated water content X1 was high (Comparative Example 2), polyene formation was observed when attached to a polarizing film and left in a high-temperature, high-humidity environment for a long period of time. Furthermore, when the adhesive sheet was thin (Comparative Example 3), peeling from the polarizing film was observed when attached to a polarizing film and left in a high-temperature, high-humidity environment for a long period of time, and it was evaluated as having poor reliability.

[0122] The following describes variations of the invention related to this disclosure. [Note 1] The thickness is 150 μm or more, the saturated water content X1 at a temperature of 23°C and a relative humidity of 50% is 2.0 mass% or less, and the moisture permeability Y1 calculated for 50 μm at a temperature of 40°C and a relative humidity of 92% is 200 g / m ２ - An optical adhesive sheet with a shelf life of 24 hours or more. [Note 2] The relationship between the saturated water content X2 and the saturated water content X1 at a temperature of 85°C and a relative humidity of 85% satisfies the following formula (1) for the adhesive sheet described in Note 1. 0 ≤ X2 - X1 ≤ 2 (1) [Note 3] The relationship between the moisture permeability Y2 and the moisture permeability Y1 at a temperature of 85°C and a relative humidity of 85% (calculated at 50 μm) satisfies the following formula (2) for the adhesive sheet described in Note 1 or 2. 1.5 ≤ Y2 / Y1 ≤ 10 (2) [Note 4] The modulus of elasticity at a temperature of 85°C is 0.5 × 10 ４ ~20.0 x 10 ４An adhesive sheet according to any one of Appendix 1 to 3, wherein the adhesive strength is Pa. [Appendix 5] An adhesive sheet according to any one of Appendix 1 to 4, having an adhesive surface with an adhesive strength of 0.5 to 20.0 N / 20 mm after being stored at a temperature of 85°C and a relative humidity of 85% for two hours or more. [Appendix 6] An adhesive sheet according to any one of Appendix 1 to 5, used for bonding automotive optical components. [Appendix 7] An image display device comprising an adhesive sheet according to any one of Appendix 1 to 6. [Appendix 8] An image display device according to Appendix 7, comprising a cover member, the adhesive sheet, a polarizing film, and a display module in this order. [Appendix 9] An image display device according to Appendix 8, wherein the adhesive sheet is bonded to the cover member and the polarizing film.

[0123] 1. Adhesive sheet 2, 3. Release liner 4. Image display device 5. Display module 6. Polarizing film 7. Cover component

Claims

1. The thickness is 150 μm or more, the saturated water content X1 at a temperature of 23°C and a relative humidity of 50% is 2.0 mass% or less, and the moisture permeability Y1 (calculated for 50 μm) at a temperature of 40°C and a relative humidity of 92% is 200 g / m². ２ Optical adhesive sheet with a shelf life of 24 hours or more.

2. The adhesive sheet according to claim 1, wherein the relationship between the saturated water content X2 and the saturated water content X1 at a temperature of 85°C and a relative humidity of 85% satisfies the following formula (1): 0 ≤ X2 - X1 ≤ 2 (1) 3. The adhesive sheet according to claim 1 or 2, wherein the relationship between the moisture permeability Y2 and the moisture permeability Y1 at a temperature of 85°C and a relative humidity of 85% (calculated as 50 μm) satisfies the following formula (2): 1.5 ≤ Y2 / Y1 ≤ 10 (2) 4. The modulus of elasticity at a temperature of 85°C is 0.5 × 10⁻⁶. ４ ~20.0 x 10 ４ The adhesive sheet according to claim 1 or 2, wherein the material is Pa.

5. The adhesive sheet according to claim 1 or 2, having an adhesive surface having an adhesive strength of 0.5 to 20.0 N / 20 mm after being stored at a temperature of 85°C and a relative humidity of 85% for two hours or more.

6. The adhesive sheet according to claim 1 or 2, used for bonding optical components for automotive applications.

7. An image display device comprising the adhesive sheet according to claim 1 or 2.

8. The image display device according to claim 7, comprising a cover member, the adhesive sheet, a polarizing film, and a display module in this order.

9. The image display device according to claim 8, wherein the adhesive sheet is bonded to the cover member and the polarizing film.

Images