JP7365772B2 - Adhesive sheets, optical laminates, and image display devices - Google Patents

Description

The present invention relates to an adhesive sheet. The present invention also relates to an optical laminate in which an adhesive sheet is laminated on an optical film, and an image display device in which members are bonded together via the adhesive sheet.

BACKGROUND ART Liquid crystal display devices and organic EL display devices are widely used as various image display devices such as mobile devices such as mobile phones, smartphones, and tablet terminals, in-vehicle devices such as car navigation devices, personal computer monitors, and televisions. A cover window made of a transparent resin plate or a glass plate is sometimes provided on the surface of the image display device for the purpose of preventing damage to the image display panel due to impact from the outer surface and improving visibility. In recent years, image display devices having a touch panel disposed on the viewing side surface have become widespread.

Adhesive sheets are used for bonding constituent members of image display devices, touch panels, etc., bonding image display panels and touch panels together, fixing cover windows to the surface of image display devices, and the like. Adhesive sheets placed on the viewing side of image display devices are required to not only be transparent and colorless at room temperature, but also not to become cloudy when exposed to high temperature and high humidity environments (cloud resistance). There is. Patent Document 1 describes that clouding resistance can be improved by increasing the moisture content (water absorption) of the pressure-sensitive adhesive sheet.

International Publication No. 2011/111576

In recent years, the moisture permeability of constituent members of image display devices has been reduced. In particular, organic EL display devices are being installed mainly in mobile devices, and the trend toward lower moisture permeability of structural members is accelerating from the viewpoint of preventing deterioration of organic EL elements due to moisture. For example, a polyethylene terephthalate (PET) film is widely used as a base material for a transparent electrode sensor film of a touch panel, but it is increasingly being replaced with a low moisture permeable film such as a cyclic polyolefin film.

Optical components (for example, touch panels) in which a low-moisture-permeable material is bonded using a highly water-absorbent adhesive sheet are likely to become cloudy when subjected to a sudden environmental change from a high-temperature, high-humidity environment to a room-temperature environment. In view of this problem, an object of the present invention is to provide a pressure-sensitive adhesive sheet that has excellent clouding resistance even when bonded to a low moisture permeable member.

As a result of studies, the inventors of the present invention found that a pressure-sensitive adhesive sheet with a low moisture content (water absorption rate) and high moisture permeability has excellent clouding resistance, leading to the present invention.

The pressure-sensitive adhesive sheet of the present invention is a layered adhesive composition containing a base polymer. The adhesive sheet has a thickness of D, a moisture content of X% after standing for 72 hours in an environment of a temperature of 85°C and a relative humidity of 85%, and a moisture permeability of Y when measured under test conditions of a temperature of 65°C and a relative humidity of 90%. It is. The thickness D of the adhesive sheet is, for example, about 10 to 100 μm. The adhesive force of the adhesive sheet to glass is preferably 1 N/20 mm or more.

The moisture content X is preferably 0.4 or less, and the YD is preferably 5×10 ⁻² g/m·24 h or more. The moisture permeability Y may be 2000 g/m ² ·24 h or more.

The product YD (g/m·24h) of moisture content X (%), moisture permeability Y, and thickness D preferably satisfies the following formula (A).
log(YD)-2.1X≧-1.2...(A)

It is preferable that the moisture content X (%) and the moisture permeability Y (g/m ² ·24h) satisfy the following formula (B).
log(Y)-2.1X≧3.4...(B)

The adhesive sheet is made of, for example, an acrylic adhesive composition. The acrylic adhesive preferably contains 50% by weight or more of an acrylic base polymer. In the acrylic base polymer, the amount of the hydroxy group-containing monomer may be 5 parts by weight or less based on 100 parts by weight of the total amount of the constituent monomer components. Further, the total amount of the hydroxy group-containing monomer, carboxyl group-containing monomer, and nitrogen-containing monomer may be 10 parts by weight or less based on 100 parts by weight of the total amount of the constituent monomer components.

In a pressure-sensitive adhesive sheet used for bonding touch panels, etc., it is preferable that the base polymer of the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet does not substantially contain an organic acid monomer as a constituent monomer component.

Furthermore, the present invention relates to an optical laminate in which a plurality of optical members are bonded together via the above adhesive sheet. Examples of optical members that can be bonded together using adhesive sheets include optical films such as polarizing plates, transparent conductive films for touch panels, and image display device forming members such as cover windows.

The pressure-sensitive adhesive sheet of the present invention has excellent clouding resistance even when bonded to a low moisture permeable member. Therefore, in an image display device in which optical members are bonded together via the adhesive sheet of the present invention, visibility is unlikely to deteriorate due to clouding even when the environment such as temperature or humidity changes rapidly.

FIG. 2 is a schematic cross-sectional view showing one form of a pressure-sensitive adhesive sheet to which a release film is attached. FIG. 2 is a cross-sectional view showing an example of a stacked structure of an image display device including a touch panel.

FIG. 1 is a schematic cross-sectional view showing a configuration example of a pressure-sensitive adhesive sheet. In the pressure-sensitive adhesive sheet 80 with a release film shown in FIG. 1, release films 81 and 82 are releasably attached to both surfaces of the pressure-sensitive adhesive sheet 20.

The adhesive sheet 20 is a sheet of adhesive formed. The thickness D of the adhesive sheet 20 is, for example, about 10 to 200 μm. From the viewpoint of making the image display device thinner, the adhesive sheet used for bonding optical films together, bonding transparent electrodes of a touch panel, and bonding an optical film and a touch panel should have a thickness D of 100 μm or less. The thickness is preferably 70 μm or less, more preferably 50 μm or less. The thickness D of the adhesive sheet may be 40 μm or less or 30 μm or less.

It is preferable that the adhesive sheet 20 has high transparency. The haze of the adhesive sheet is preferably 1% or less, and the total light transmittance is preferably 90% or more. Haze and total light transmittance are measured using a haze meter according to JIS K7136.

The adhesive sheet 20 preferably has a moisture content X of 0.4% or less after being allowed to stand for 72 hours in an environment with a temperature of 85° C. and a relative humidity of 85%. Moisture percentage Calculated from the mass of

It is preferable that the pressure-sensitive adhesive sheet 20 has a product YD of moisture permeability Y and thickness D of 5×10 ⁻² g/m·24 h or more. Moisture permeability is the weight of water vapor that permeates a sample with an area of 1 m ² in 24 hours under a predetermined environment, and is measured according to the JIS Z0208 moisture permeability test (cup method). Note that while the test conditions in JIS Z0208 are a temperature of 25°C or 40°C and a relative humidity of 90%, in this specification, the test conditions are consistent with the evaluation of cloudiness resistance in a higher temperature test environment. For this purpose, the moisture permeability Y under test conditions of a temperature of 65° C. and a relative humidity of 90% is used.

Moisture permeability Y and thickness D are in an inversely proportional relationship, and in sheet-like materials made of the same material, the product YD of moisture permeability and thickness is approximately constant. YD is an index representing the ease with which moisture moves (diffuses) in the material, and the larger YD is, the faster the moisture moves within the pressure-sensitive adhesive sheet 20, and the easier the moisture is released.

Since the moisture content X and the product YD of moisture permeability Y and thickness D of the adhesive sheet are within the above ranges, even when the adhesive sheet is bonded to a low moisture permeable material, it will not be susceptible to sudden environmental changes (especially changes in temperature and humidity). clouding of the laminate due to the change) tends to be suppressed. Therefore, it is possible to prevent a decrease in visibility in an image display device in which members are bonded together using an adhesive sheet.

The reason why cloudiness is suppressed by having a small moisture content One example is that the retention of is suppressed.

When a laminate in which an optical member such as a low moisture permeable film is bonded to the main surface of an adhesive sheet is exposed to a high temperature and high humidity environment for a long time, the adhesive sheet absorbs moisture and the moisture content increases. After that, when the laminate is moved to a room temperature environment, the temperature and humidity drop rapidly, and it is thought that one of the reasons for the cloudiness is that the moisture absorbed by the adhesive sheet in the high temperature and high humidity environment becomes supersaturated. It will be done.

If a low moisture permeability material is attached to the main surface of the adhesive sheet, the movement of moisture will be blocked by the low moisture permeability material, so it is almost impossible to expect moisture to dissipate from the main surface of the adhesive sheet. Moisture tends to accumulate at the bonding interface between the material and the low moisture permeable material. When the product YD of the moisture permeability Y and the thickness D of the adhesive sheet is large, the movement speed of moisture within the adhesive sheet is high, so the speed of moisture dissipation from the side surfaces (end faces) of the adhesive sheet is high, and the moisture inside the adhesive sheet is Also, it is thought that cloudiness is less likely to occur because water retention at the interface between the adhesive sheet and the low moisture permeable member is suppressed.

However, the area of the end surface of the pressure-sensitive adhesive sheet is smaller than the area of the main surface, and the amount of water dissipated from the end surface is limited. Even if the product YD of moisture permeability Y and thickness D is large, if the moisture content It will take longer. On the other hand, when the moisture content be.

Therefore, in addition to the large YD of the adhesive sheet, the small moisture content X suppresses the retention of moisture in the laminate with the low moisture permeability member, which contributes to the improvement of the white clouding resistance. it is conceivable that.

From the viewpoint of increasing cloudiness resistance, the moisture content X of the adhesive sheet 20 is preferably 0.4% or less, more preferably 0.3% or less. The moisture content X may be 0.25% or less or 0.2% or less. Further, the product YD of moisture permeability Y and thickness D of the adhesive sheet 20 is preferably 5×10 ⁻² g/m·24 h or more, more preferably 7×10 ⁻² g/m·24 h or more, and 8×10 −2 g/m·24 h ^or more. More preferably, it is ² g/m/24 hours or more. YD may be 0.1 g/m·24 h or more, 0.12 g/m·24 h or more, or 0.15 g/m·24 h or more.

From the viewpoint of keeping the thickness D of the adhesive sheet in the above-mentioned range and YD within the above-mentioned range, the moisture permeability Y of the adhesive sheet 20 is preferably 2000 g/m ² ·24 h or more, and 3000 g/m ²・24 hours or more is more preferable, and 4000 g/m ²・24 hours or more is even more preferable. The moisture permeability Y of the adhesive sheet 20 may be 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.

The upper limit of the moisture permeability Y of the adhesive sheet 20 is not particularly limited, but is generally 200000 g/m ² ·24 h or less. The upper limit of YD is also not particularly limited, but is generally 10 g/m·24 h or less.

As mentioned above, the larger the product YD of the moisture permeability Y and the thickness D of the adhesive sheet 20, the faster the movement of moisture inside the adhesive sheet. Moisture tends to dissipate out of the system from the end face in a short period of time. Therefore, even when the moisture content X of the pressure-sensitive adhesive sheet is high, cloudiness is suppressed, and even when cloudiness occurs, it is easy to eliminate the cloudiness in a short time. In particular, it is preferable that the product YD (g/m·24h) of moisture content X (%), moisture permeability Y, and thickness D of the adhesive sheet satisfy the following formula (A).
log(YD)-2.1X≧-1.2...(A)

On the left side of equation (A), log(YD) is related to the movement speed of moisture within the adhesive sheet, and 2.1X is related to the moisture content in the adhesive sheet exposed to high temperature and high humidity conditions for a long time. related to quantity. Since the smaller X is, the lower the amount of water is, supersaturated water is dissipated out of the system in a short time, and the supersaturated state is eliminated. Furthermore, the larger the log(YD), the greater the amount of water dissipated out of the system per unit time, so that the supersaturated state of water can be eliminated in a short time. Therefore, the larger the number on the left side of formula (A), the faster the cloudiness tends to be resolved.

From the same viewpoint, it is preferable that the moisture content X (%) and moisture permeability Y (g/m ² ·24h) of the pressure-sensitive adhesive sheet satisfy the following formula (B).
log(Y)-2.1X≧3.4...(B)

In formula (B) as well, the larger the number on the left side, the faster the supersaturated state of water tends to be resolved.

[Composition of adhesive]
(Composition of base polymer)
Examples of the adhesive constituting the adhesive sheet 20 include acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate/vinyl chloride copolymer, modified polyolefin, epoxy type, fluorine type, natural rubber, synthetic rubber, etc. A polymer having a rubber-based polymer or the like as a base polymer can be appropriately selected and used. In particular, acrylic adhesives containing acrylic polymers as the base polymer have excellent optical transparency, exhibit adhesive properties such as appropriate wettability, cohesiveness, and adhesiveness, and can achieve high moisture permeability. agents are preferably used.

The content of the acrylic base polymer in the acrylic adhesive is preferably 50% by weight or more, more preferably 60% by weight or more. The acrylic polymer as the base polymer contains (meth)acrylic acid alkyl ester as a main constituent monomer component. In addition, in this specification, "(meth)acrylic" means acrylic and/or methacryl. When the base polymer is a copolymer, the arrangement of the constituent monomers may be random or block.

As the (meth)acrylic acid alkyl ester, a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms is preferably used. The (meth)acrylic acid alkyl ester may have a branched alkyl group or a cyclic alkyl group.

Specific examples of (meth)acrylic acid alkyl esters having a chain alkyl group include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, and (meth)acrylate. s-butyl acrylate, t-butyl (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, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate , undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridodecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, (meth) Examples include cetyl acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

Specific examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, cyclooctyl (meth)acrylate, etc. (meth)acrylic acid cycloalkyl ester; (meth)acrylic acid ester having a bicyclic aliphatic hydrocarbon ring such as isobornyl (meth)acrylate; dicyclopentanyl (meth)acrylate, dicyclopentanyloxy Tricycles such as ethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, etc. Examples include (meth)acrylic esters having the above aliphatic hydrocarbon rings.

The amount of the (meth)acrylic acid alkyl ester relative to the total amount of monomer components constituting the acrylic polymer is preferably 40% by weight or more, more preferably 50% by weight or more, and even more preferably 60% by weight or more.

The acrylic polymer may contain a monomer component having a crosslinkable functional group as a copolymerization component. Examples of the monomer having a crosslinkable functional group include a hydroxy group-containing monomer and a carboxyl group-containing monomer.

Hydroxy group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and (meth)acrylate. Examples include 8-hydroxyoctyl acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)-methyl (meth)acrylate.

When the content of the hydroxy group-containing monomer unit in the acrylic polymer is high, the moisture content X becomes large due to the high water absorption of the pressure-sensitive adhesive sheet, which may result in insufficient clouding resistance. Therefore, the amount of the hydroxy group-containing monomer relative to 100 parts by weight of the monomer components constituting the acrylic polymer is preferably 5 parts by weight or less, more preferably 4 parts by weight or less. The amount of hydroxy group-containing monomer may be up to 3 parts by weight, up to 2 parts by weight, or up to 1.5 parts by weight.

On the other hand, from the viewpoint of increasing the moisture permeability Y of the pressure-sensitive adhesive sheet, the acrylic polymer preferably contains a small amount of hydroxy group-containing monomer unit. Furthermore, in order to introduce a crosslinked structure using an isocyanate crosslinking agent or the like into the acrylic polymer, it is preferable that the acrylic monomer contains a hydroxy group-containing monomer unit. The amount of the hydroxy group-containing monomer relative to 100 parts by weight of the monomer components constituting the acrylic polymer is preferably 0.1 part by weight or more, more preferably 0.3 part by weight or more, and even more preferably 0.5 part by weight or more. .

Examples of carboxy group-containing monomers include acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. .

When an adhesive sheet is used to adhere sensor electrodes of a touch panel, the adhesive sheet is preferably an acid-free adhesive sheet with a low acid content in order to prevent corrosion of the electrodes due to acid components. The content of organic acid monomers such as (meth)acrylic acid in the acid-free adhesive sheet is preferably 100 ppm or less, more preferably 70 ppm or less, and even more preferably 50 ppm or less. The organic acid monomer content of the adhesive sheet is determined by immersing the adhesive sheet in pure water, heating it at 100° C. for 45 minutes, and quantifying the acid monomer extracted into the water using ion chromatography.

In order to reduce the acid monomer content in the adhesive sheet, it is preferable that the amount of organic acid monomer components such as (meth)acrylic acid in the monomer components constituting the base polymer is small. Therefore, in order to make the pressure-sensitive adhesive sheet acid-free, it is preferable that the base polymer does not substantially contain an organic acid monomer (carboxy group-containing monomer) as a monomer component. In the acid-free pressure-sensitive adhesive sheet, the amount of the carboxy group-containing monomer relative to the total 100 parts by weight of the monomer components of the base polymer is preferably 0.5 parts by weight or less, more preferably 0.1 parts by weight or less, and 0.05 parts by weight or less. is more preferable, and ideally it is 0.

If the adhesive sheet does not come into contact with the sensor electrodes of the touch panel, the adhesive sheet does not need to be acid-free. However, if the content of carboxy group-containing monomer units in the acrylic polymer is large, the water absorption of the pressure-sensitive adhesive sheet tends to increase. The amount is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, even more preferably 5 parts by weight or less.

The acrylic polymer may contain a nitrogen-containing monomer as a constituent monomer component. Examples of nitrogen-containing monomers include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, and N-vinyl. Examples include carboxylic acid amides, N-vinylcaprolactam, and the like. Among them, N-vinylpyrrolidone and (meth)acryloylmorpholine are preferably used.

If the content of the nitrogen-containing monomer unit in the acrylic polymer is large, the water absorption of the pressure-sensitive adhesive sheet tends to be high. It is preferably 12 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 8 parts by weight or less.

As mentioned above, when the amount of hydroxy groups, carboxy groups, nitrogen atoms, etc. contained in the base polymer is large, the polarity of the base polymer is large, and the moisture content X of the pressure-sensitive adhesive sheet tends to be high. From the viewpoint of reducing the moisture content X of the pressure-sensitive adhesive sheet and increasing its white turbidity resistance, the total amount of the hydroxy group-containing monomer, carboxyl group-containing monomer, and nitrogen-containing monomer is 10 parts by weight based on the total amount of monomer components constituting the acrylic polymer. It is preferably at most 8 parts by weight, more preferably at most 7 parts by weight, even more preferably at most 7 parts by weight. The amount of these polar group-containing monomer components may be 5 parts by weight or less, 4 parts by weight or less, or 3 parts by weight or less.

On the other hand, if the base polymer does not contain any polar group-containing monomer units, the cohesive force may be insufficient and the adhesive force to the adherend may be insufficient. Moreover, when the base polymer contains a small amount of polar group-containing monomer unit, the moisture permeability Y of the pressure-sensitive adhesive sheet tends to be increased, and the clouding resistance tends to be improved. Therefore, the total amount of the hydroxy group-containing monomer, carboxyl group-containing monomer, and nitrogen-containing monomer relative to 100 parts by weight of the total amount of the constituent monomer components of the acrylic polymer is preferably 0.1 part by weight or more, more preferably 0.3 part by weight or more. , more preferably 0.5 parts by weight or more.

Even when the amount of a polar group-containing monomer component such as a hydroxy group-containing monomer is large, the moisture content X of the pressure-sensitive adhesive sheet can be reduced by selecting other monomer components constituting the base polymer. For example, by using a highly hydrophobic monomer such as a (meth)acrylic acid alkyl ester having an alicyclic alkyl group as a constituent monomer component of the base polymer, the moisture content of the pressure-sensitive adhesive sheet tends to be reduced. In particular, when the amount of the hydroxy group-containing monomer is more than 5 parts by weight based on a total of 100 parts by weight of the monomer components constituting the base polymer, the monomer component is an alkyl (meth)acrylate having a polycyclic alicyclic alkyl group. Preference is given to using esters.

The acrylic polymer contains, as monomer components other than those mentioned above, an acid anhydride group-containing monomer, a caprolactone adduct of (meth)acrylic acid, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, vinyl acetate, vinyl propionate, styrene, α - Vinyl monomers such as methylstyrene; cyano group-containing monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing monomers such as glycidyl (meth)acrylate; polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate Glycol-based acrylic ester monomers such as , methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate; tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, silicone (meth)acrylate, and (meth)acrylate. It may also contain a (meth)acrylic acid ester monomer such as 2-methoxyethyl acrylate.

(Crosslinked structure of base polymer)
A crosslinked structure may be introduced into the base polymer. By introducing a crosslinked structure into the base polymer, the gel fraction of the adhesive increases, and the adhesiveness and hardness of the adhesive can be adjusted to an appropriate range. From the viewpoint of imparting appropriate adhesive properties to the adhesive, the gel fraction of the adhesive is preferably 40 to 85%, more preferably 50 to 80%.

Gel fraction can be determined as the insoluble content in a solvent such as ethyl acetate, and specifically, the insoluble content after immersing the adhesive layer in ethyl acetate at 23°C for 7 days relative to the sample before immersion. It is determined as a weight fraction (unit: weight %). Generally, the gel fraction of a polymer is equal to the degree of crosslinking, and the more crosslinked parts in the polymer, the higher the gel fraction. The gel fraction (amount of the crosslinked structure introduced) can be adjusted to a desired range by the method of introducing the crosslinked structure, the type and amount of the crosslinking agent, etc.

The method for introducing a crosslinked structure into a base polymer is as follows: (1) After polymerizing a base polymer having a functional group (hydroxy group, carboxy group, etc.) that can react with a crosslinking agent, add a crosslinking agent and crosslink with the base polymer. and (2) a method of introducing a branched structure (crosslinked structure) into the polymer chain by including a polyfunctional compound in the polymerization components of the base polymer. These may be used in combination to introduce multiple types of crosslinked structures into the base polymer.

In the above method (1) of reacting a base polymer with a crosslinking agent, a crosslinking structure is introduced into the base polymer by adding a crosslinking agent to the base polymer after polymerization and heating as necessary. Examples of the crosslinking agent include compounds that react with functional groups such as hydroxy groups and carboxy groups contained in the base polymer. Specific examples of the crosslinking agent include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, metal chelate crosslinking agents, and the like.

Among these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred because they have high reactivity with the hydroxyl group or carboxy group of the base polymer and can easily introduce a crosslinked structure. These crosslinking agents react with functional groups such as hydroxy groups and carboxy groups introduced into the base polymer to form a crosslinked structure. In an acid-free adhesive in which the base polymer does not contain a carboxyl group, it is preferable to use an isocyanate-based crosslinking agent to form a crosslinked structure by reacting the hydroxyl group in the base polymer with the isocyanate crosslinking agent.

As the isocyanate crosslinking agent, polyisocyanate having two or more isocyanate groups in one molecule is used. Examples of the isocyanate-based crosslinking agent include lower aliphatic polyisocyanates such as butylene diisocyanate and hexamethylene diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; 2,4-tolylene diisocyanate; Aromatic isocyanates such as isocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate; trimethylolpropane/tolylene diisocyanate trimer adduct (for example, "Coronate L" manufactured by Tosoh), trimethylolpropane/hexamethylene Diisocyanate trimer adducts (e.g. "Coronate HL" manufactured by Tosoh), trimethylolpropane adducts of xylylene diisocyanate (e.g. "Takenate D110N" manufactured by Mitsui Chemicals), isocyanurates of hexamethylene diisocyanate (e.g. Tosoh) Examples include isocyanate adducts such as "Coronate HX").

In the method of (2) above, in which a polyfunctional monomer is included in the polymerization components of the base polymer, the entire amount of the monomer components constituting the base polymer and the polyfunctional compound for introducing the crosslinked structure may be reacted at once, or in multiple steps. Polymerization may be carried out using As a multi-step polymerization method, monofunctional monomers constituting the base polymer are polymerized (prepolymerized) to prepare a partially polymerized product (prepolymer composition), and a polyfunctional (meth) monomer is added to the prepolymer composition. A preferred method is to add a polyfunctional compound such as acrylate and polymerize the prepolymer composition and the polyfunctional monomer (main polymerization). The prepolymer composition is a partially polymerized product containing a polymer with a low degree of polymerization and unreacted monomers.

By prepolymerizing the constituent components of the base polymer, branching points (crosslinking points) caused by the polyfunctional compound can be uniformly introduced into the base polymer. Alternatively, after applying a mixture (adhesive composition) of a low molecular weight polymer or partially polymerized product and unpolymerized monomer components onto a base material, main polymerization is performed on the base material to form an adhesive sheet. You can also do it. Since low-polymerization compositions such as prepolymer compositions have low viscosity and excellent coating properties, a method in which main polymerization is performed on a substrate after applying an adhesive composition, which is a mixture of a prepolymer composition and a polyfunctional compound, has been proposed. Accordingly, the productivity of the adhesive sheet can be improved and the thickness of the adhesive sheet can be made uniform.

Examples of the polyfunctional compound used for introducing the crosslinked structure include compounds containing two or more polymerizable functional groups (ethylenic unsaturated groups) having an unsaturated double bond in one molecule. As the polyfunctional compound, polyfunctional (meth)acrylate is preferred because it can be easily copolymerized with the monomer components constituting the acrylic polymer. When introducing a branched (crosslinked) structure by active energy ray polymerization (photopolymerization), polyfunctional acrylates are preferred.

Examples of polyfunctional (meth)acrylates include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, bisphenol A ethylene oxide-modified di(meth)acrylate, and bisphenol A propylene oxide. Modified di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol di( meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, ethoxylated pentaerythrtetra(meth)acrylate, pentaerythol tetra(meth)acrylate, dipentaerythol poly(meth)acrylate Acrylate, dipentaerythol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, epoxy(meth)acrylate, butadiene(meth)acrylate, isoprene(meth)acrylate, and the like.

(Preparation of base polymer)
The base polymer can be prepared by known polymerization methods such as solution polymerization, UV polymerization, bulk polymerization, and emulsion polymerization. From the viewpoint of adhesive transparency, water resistance, cost, etc., solution polymerization method or active energy ray polymerization method (for example, UV polymerization) is preferable. Ethyl acetate, toluene, etc. are generally used as a solvent for solution polymerization.

When preparing the base polymer, a polymerization initiator such as a photopolymerization initiator or a thermal polymerization initiator may be used depending on the type of polymerization reaction. The photopolymerization initiator is not particularly limited as long as it initiates photopolymerization, and examples include benzoin ether photopolymerization initiators, acetophenone photopolymerization initiators, α-ketol photopolymerization initiators, and aromatic sulfonyl photopolymerization initiators. Chloride photoinitiator, photoactive oxime photoinitiator, benzoin photoinitiator, benzyl photoinitiator, benzophenone photoinitiator, ketal photoinitiator, thioxanthone photoinitiator , an acylphosphine oxide photopolymerization initiator, and the like can be used. Examples of thermal polymerization initiators include azo initiators, peroxide initiators, redox initiators that are a combination of peroxide and reducing agent (for example, a combination of persulfate and sodium bisulfite, peroxide combinations of sodium ascorbate and sodium ascorbate, etc.) can be used.

During polymerization, a chain transfer agent, a polymerization inhibitor (polymerization retardant), etc. may be used for the purpose of controlling the molecular weight. Examples of chain transfer agents include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol; Examples include α-methylstyrene dimer.

When introducing a crosslinked structure using an isocyanate-based crosslinking agent or the like, it is preferable to add the crosslinking agent after polymerizing the base polymer by solution polymerization, heat as necessary, and introduce the crosslinked structure into the base polymer. When introducing a crosslinked structure using a polyfunctional compound such as a polyfunctional (meth)acrylate, the base polymer is polymerized or a prepolymer composition is prepared by solution polymerization or active energy ray polymerization, and after the polyfunctional compound is added. It is preferable to introduce a crosslinked structure using a polyfunctional compound by active energy ray polymerization.

The prepolymer composition is prepared, for example, by partially polymerizing (prepolymerizing) a composition (referred to as a "prepolymer-forming composition") in which monomer components constituting the acrylic base polymer and a polymerization initiator are mixed. can. The monomer in the prepolymer-forming composition is preferably a monofunctional monomer. The composition for forming a prepolymer may contain a polyfunctional monomer in addition to a monofunctional monomer. For example, a part of the polyfunctional monomer may be contained in the composition for forming a prepolymer, and after preliminary polymerization, the remaining part of the polyfunctional monomer component may be added to perform main polymerization.

The polymerization rate of the prepolymer is not particularly limited, but from the viewpoint of achieving a viscosity suitable for coating onto a substrate, it is preferably 3 to 50% by weight, more preferably 5 to 40% by weight. The polymerization rate of the prepolymer can be adjusted within a desired range by adjusting the type and amount of photopolymerization initiator used, the irradiation intensity and irradiation time of active light such as UV light, and the like.

(Adhesive composition)
A pressure-sensitive adhesive composition is prepared by mixing a base polymer (or prepolymer composition) with a crosslinking agent and/or a polyfunctional compound for introducing a degree of crosslinked structure, other additives, and the like. The remainder of the monomer components constituting the base polymer may be added to the pressure-sensitive adhesive composition, if necessary.

The adhesive composition may contain an oligomer in addition to the base polymer. In addition to acrylic base polymers, acrylic adhesives include silicone polymers, polyesters, polyurethanes, polyamides, polyvinyl ethers, vinyl acetate/vinyl chloride copolymers, modified polyolefins, epoxy systems, fluorine systems, natural rubber, synthetic rubber, etc. It may also contain polymers such as rubber-based polymers.

When the adhesive composition contains a prepolymer composition, a polyfunctional compound, etc., the adhesive composition preferably contains a photopolymerization initiator for main polymerization. After prepolymerization, a polymerization initiator for main polymerization may be added to the prepolymer composition. If the polymerization initiator used in the preliminary polymerization remains in the prepolymer composition without being deactivated, the addition of the polymerization initiator for the main polymerization may be omitted. The adhesive composition may contain a chain transfer agent.

A silane coupling agent may be added to the adhesive composition for the purpose of adjusting adhesive strength. When a silane coupling agent is added to the adhesive composition, the amount added is usually about 0.01 to 5.0 parts by weight, and 0.03 to 2.0 parts by weight, based on 100 parts by weight of the base polymer. Preferably, it is about parts by weight.

In addition to the above-mentioned components, the adhesive composition may include tackifiers, plasticizers, softeners, anti-deterioration agents, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, antistatic agents, etc. It may contain additives.

[Formation of adhesive sheet]
A pressure-sensitive adhesive sheet is formed on the base material by applying the pressure-sensitive adhesive composition onto the base material, and performing main polymerization by drying and removing the solvent and/or irradiating actinic rays as necessary. Any suitable base material can be used as the base material for forming the pressure-sensitive adhesive sheet. The base material may be a release film (separator) having a release layer on the surface in contact with the pressure-sensitive adhesive sheet.

Films made of various resin materials are used as the film base material of the release film. Examples of resin materials include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth)acrylic resins, Examples include polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl alcohol resin, polyarylate resin, polyphenylene sulfide resin, and the like. Among these, polyester resins such as polyethylene terephthalate are particularly preferred. The thickness of the film base material is preferably 10 to 200 μm, more preferably 25 to 150 μm. Examples of the material for the mold release layer include silicone mold release agents, fluorine mold release agents, long chain alkyl mold release agents, fatty acid amide mold release agents, and the like. The thickness of the release layer is generally about 10 to 2000 nm.

Methods for applying the adhesive composition onto the substrate include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, and curtain coating. Various methods such as , lip coat, die coater, etc. are used.

When the base polymer of the adhesive composition is a solution polymerized polymer, it is preferable to dry the solvent after application. As the drying method, an appropriate method may be adopted depending on the purpose. The heat drying temperature is preferably 40°C to 200°C, more preferably 50°C to 180°C, particularly preferably 70°C to 170°C. As the drying time, an appropriate time can be adopted as needed. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, particularly preferably 10 seconds to 10 minutes.

When the adhesive composition contains a crosslinking agent, a crosslinking reaction may be performed after applying the adhesive composition onto the substrate. During crosslinking, heating may be performed if necessary. The temperature of the crosslinking reaction is usually in the range of 20°C to 160°C, and the time of the crosslinking reaction is about 1 minute to 7 days. After applying the adhesive composition, heating for drying the solvent may also serve as heating for crosslinking. After drying the solvent, it is preferable to attach a cover sheet to protect the surface of the pressure-sensitive adhesive sheet. As the cover sheet, it is preferable to use a release film having a release layer on the surface in contact with the pressure-sensitive adhesive sheet, similar to the base film.

When the adhesive composition is a photopolymerizable composition containing a prepolymer composition, a polyfunctional compound, etc., the adhesive composition is coated in a layer on the base material and then exposed to actinic rays. Curing takes place. When performing photocuring, a cover sheet is attached to the surface of the coating layer, and active light is irradiated with the adhesive composition sandwiched between the two sheets to prevent polymerization inhibition due to oxygen. preferable.

The active light may be selected depending on the type of polymerizable components such as monomers and polyfunctional (meth)acrylates, the type of photopolymerization initiator, etc., and in general, ultraviolet rays and/or short wavelength visible light are used. It will be done. The cumulative amount of irradiation light is preferably about 100 to 5000 mJ/cm ² . The light source for light irradiation is not particularly limited as long as it can irradiate light in the wavelength range to which the photopolymerization initiator contained in the adhesive composition is sensitive, and includes LED light sources, high-pressure mercury lamps, and ultra-high-pressure mercury lamps. Lamps, metal halide lamps, xenon lamps, etc. are preferably used.

[Optical laminate and image display device]
The adhesive sheet 20 can be used for bonding various transparent members and opaque members. The type of adherend is not particularly limited, and examples thereof include various resin materials, glass, metals, and the like. The pressure-sensitive adhesive sheet of the present invention has high transparency and excellent resistance to clouding, and is therefore suitably used for bonding constituent members of an image display device.

It is preferable that the pressure-sensitive adhesive sheet used for bonding the constituent members of the image display device exhibits high adhesiveness to the adherend. The adhesive force of the adhesive sheet to glass is preferably 1 N/20 mm or more. The adhesive strength is the test force obtained by laminating a 20 mm wide adhesive sheet to a glass plate and performing a 180° peel test at a peeling rate of 300 mm/min.

FIG. 2 is a cross-sectional view showing a stacked structure of an image display device 100 that includes a touch panel 5 on the image display panel 1 and a cover window 7 on the viewing side surface.

A polarizing plate 13 is generally provided on the viewing side surface of the image display panel 1. For example, in a liquid crystal display device, a polarizing plate provided on the viewing side of a liquid crystal panel adjusts transmittance according to the polarization state of light transmitted through a liquid crystal cell. In an organic EL display device, by providing a circularly polarizing plate on the viewing side of the organic EL panel, it is possible to improve the visibility of the display by blocking external light reflected by the metal electrodes of the organic EL panel from being emitted to the viewing side.

As a polarizing plate, a polarizer having an appropriate transparent protective film laminated on one or both sides, if necessary, is generally used. The polarizer is not particularly limited, and various types can be used. As a polarizer, for example, a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, a partially saponified ethylene/vinyl acetate copolymer film, or a dichroic film such as iodine or a dichroic dye is used. Examples include polyene-based oriented films such as those obtained by adsorbing a sexual substance and uniaxially stretched, polyvinyl alcohol dehydrated products, and polyvinyl chloride dehydrochlorinated products.

The transparent protective film used as a protective film for polarizers is made of cellulose resin, cyclic polyolefin resin, acrylic resin, phenylmaleimide resin, polycarbonate resin, etc., which have transparency, mechanical strength, thermal stability, and moisture barrier properties. Those having excellent properties and optical isotropy are preferably used. Note that when transparent protective films are provided on both sides of the polarizer, protective films made of the same polymer material may be used on the front and back sides, or protective films made of different polymer materials or the like may be used on the front and back sides.

An optical film may be laminated on one or both surfaces of the polarizing plate via a suitable adhesive layer or pressure-sensitive adhesive layer, if necessary. As such films, those used for forming image display devices such as retardation plates, viewing angle expansion films, viewing angle limiting (prevention of prying eyes) films, and brightness enhancement films are used, and the types thereof are not particularly limited. . For example, in a liquid crystal display device, an image display panel (liquid crystal panel) and a polarizing plate are used to appropriately convert the polarization state of light emitted from a liquid crystal cell to the viewing side to improve viewing angle characteristics. An optical compensation film may be used in between.

As mentioned above, in an organic EL display device, by providing a circularly polarizing plate with a 1/4 wavelength plate arranged on the surface of the polarizer on the organic EL panel side, external light reflected by the metal electrode is emitted toward the viewing side. can be shielded. By arranging a quarter wavelength plate on the viewing side of the polarizer and making the emitted light circularly polarized, it is possible to make an appropriate image display visible even to a viewer wearing polarized sunglasses. These optical films (optically anisotropic films) may be laminated on the polarizer without intervening other films. In this case, the optical film also functions as a protective film for the polarizer.

As the touch panel 5, any type of touch panel such as a resistive type, a capacitive type, an optical type, an ultrasonic type, etc. is used. As shown in FIG. 2, when the cover window 7 is arranged on the viewing side surface, a capacitive touch panel is preferable.

In the form shown in FIG. 2, two transparent conductive films 30 and 40 are bonded together with an adhesive sheet 25 interposed therebetween. The transparent conductive films 30 and 40 act as sensor electrodes in the touch panel, and include transparent electrodes 32 and 42 on transparent film substrates 31 and 41.

As the resin material for the transparent film substrates 31 and 32, polyester such as polyethylene terephthalate and polyethylene naphthalate, polycarbonate, cyclic polyolefin, polyolefin, (meth)acrylic resin, cellulose resin, etc. are used. When a high moisture barrier property is required for the image display device, it is preferable to use a low moisture permeable film such as a cyclic polyolefin.

The conductive materials constituting the transparent electrodes 32 and 42 include metals such as platinum, gold, silver, and copper; metal oxides such as tin oxide, indium oxide, cadmium oxide, and zinc oxide; indium tin oxide (ITO), and indium oxide. Examples include composite oxides such as zinc (IZO), fluorine-doped indium oxide (FTO), antimony-doped tin oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide. Among them, indium tin oxide (ITO) is preferred.

Although FIG. 2 shows a configuration in which the touch panel 5 is disposed between the image display panel 1 and the cover window 7, the touch panel may be provided within the image display panel. For example, a touch panel may be arranged between the image display cell 11 and the polarizing plate 13.

As the cover window 7, a transparent plate having appropriate mechanical strength and thickness is used. As such a transparent plate, for example, a transparent resin plate such as acrylic resin or polycarbonate resin, or a glass plate is used. A colored layer 72 formed by decorative printing may be provided on the surface of the transparent plate 71 in the shape of a frame.

The pressure-sensitive adhesive sheet of the present invention can be used for bonding these optical members together. For example, the adhesive sheet of the present invention may be used as the adhesive sheet 25 for bonding the transparent conductive films 30 and 40 of the touch panel 5 together. The pressure-sensitive adhesive sheet of the present invention can exhibit excellent clouding resistance even when bonded to a film material provided with a low moisture permeability layer such as an ITO thin film. In addition, in FIG. 2, the transparent electrodes 32 and 42 of the two transparent conductive films 30 and 40 are arranged so as to face each other, but the transparent electrodes and the transparent film substrate are bonded together via an adhesive sheet. Good too.

The adhesive sheet of the present invention may be used as the adhesive sheet 23 for bonding the polarizing plate 13 and the touch panel 5 together. Furthermore, the adhesive sheet of the present invention may be used to bond the touch panel 5 and the cover window 7 together. In addition, in an image display device that does not have a touch panel or in an image display device that has a touch panel built into the image display panel, it is necessary to bond the polarizing plate 13 disposed on the surface of the image display panel 1 and the cover window 7. , the adhesive sheet of the present invention may be used. The adhesive sheet of the present invention may be used as the adhesive sheet 21 for bonding the image display cell 11 and the polarizing plate 13 together.

In either form, by using the pressure-sensitive adhesive sheet of the present invention, even when there is a sudden environmental change from a high temperature and high humidity environment to a room temperature environment, clouding is difficult to occur, and even if cloudiness occurs, it becomes cloudy in a short period of time. is resolved. Therefore, the image display device using the adhesive sheet of the present invention can maintain high visibility even when environmental changes occur.

The present invention will be further explained below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Example 1]
<Polymerization of base polymer>
In a reaction vessel equipped with a thermometer, a stirrer, a cooler, and a nitrogen gas introduction tube, as monomer components, butyl acrylate (BA): 99 parts by weight, and 4-hydroxybutyl acrylate (4HBA): 1 part by weight, and 0.1 part by weight of azoisobutyronitrile (AIBN) as a thermal polymerization initiator was added together with ethyl acetate, and nitrogen gas was introduced while stirring gently at room temperature to perform nitrogen substitution. Thereafter, the temperature was raised to 60° C. and a polymerization reaction was carried out for 7 hours to prepare an acrylic base polymer solution having a weight average molecular weight of 1.6 million.

<Preparation of adhesive composition>
To the acrylic base polymer solution obtained above, 0.1 weight of trimethylolpropane adduct of xylylene diisocyanate ("Takenate D110N" manufactured by Mitsui Chemicals) was added as an isocyanate crosslinking agent to 100 parts by weight of the base polymer. and 0.1 part by weight of 3-glycidoxypropyltrimethoxysilane (KBM-403, manufactured by Shin-Etsu Chemical) as a silane coupling agent to prepare an adhesive composition.

<Preparation of adhesive sheet>
The adhesive composition was applied to the release-treated side of a release film (a polyethylene terephthalate (PET) film with a silicone release layer on one side) so that the thickness after drying was 12 μm, and the adhesive composition was heated at 100°C for 30 minutes. After removing the solvent by heating for a minute, another release film was laminated onto the coating layer. This laminate was aged in an atmosphere at 25° C. for 3 days to promote crosslinking, and a pressure-sensitive adhesive sheet having release films temporarily attached on both sides was obtained.

[Example 2, 3]
A pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, except that the thickness of the pressure-sensitive adhesive composition was changed to 25 μm (Example 2) or 50 μm (Example 3).

[Example 4]
<Polymerization of prepolymer>
In a reaction vessel equipped with a thermometer, a stirrer, a cooler, and a nitrogen gas introduction tube, 97 parts by weight of BA, 1 part by weight of 4HBA, 2 parts by weight of N-vinylpyrrolidone (NVP), and light were placed as monomer components. After adding 0.05 parts by weight of each of BASF's "Irgacure 184" and "Irgacure 651" as polymerization initiators, nitrogen gas was flowed and nitrogen substitution was performed for about 1 hour while stirring. Thereafter, under a nitrogen atmosphere, polymerization was performed by irradiating UVA at 5 mW/cm ² to prepare a prepolymer composition. The polymerization time was adjusted so that the polymerization rate of the prepolymer was about 10%.

<Preparation of adhesive composition>
0.3 parts by weight of 1,6-hexanediol diacrylate ("NK Ester A-HD-N" manufactured by Shin Nakamura Industrial Chemical Co., Ltd.) as a polyfunctional monomer to the prepolymer composition (the total amount is 100 parts by weight), A photopolymerizable adhesive composition was prepared by adding 0.1 part by weight of "KBM-403" as a silane coupling agent and 0.3 part by weight of "Irgacure 651" as a photopolymerization initiator.

<Preparation of adhesive sheet>
A pressure-sensitive adhesive composition was applied onto the release film to a thickness of 25 μm, and another release film was bonded onto the coated layer. Thereafter, 5 mW/cm ² of UVA (integrated light amount 3000 mJ/cm ² ) was irradiated onto one of the release films to advance polymerization, thereby obtaining a pressure-sensitive adhesive sheet with release films temporarily attached to both sides.

[Examples 5 to 10 and Comparative Examples 1 to 4]
The monomer composition charged during prepolymer polymerization, the amount of photopolymerization initiator added, the type and amount of added components to the prepolymer composition, and the thickness of the adhesive sheet were changed as shown in Table 1, and Example 4 and A pressure-sensitive adhesive sheet was produced in the same manner.

[Comparative example 5]
<Preparation of adhesive composition>
100 parts by weight of polyisobutylene with a weight average molecular weight of approximately 750,000 ("OPPANOL B80" manufactured by BASF) as a base polymer, and 30 parts by weight of hydrogenated terpene phenol resin ("YS Polyster TH130" manufactured by Yasuhara Chemical) as a tackifier. A pressure-sensitive adhesive composition was prepared by dissolving in toluene so that the solid content concentration was 20% by weight.

<Preparation of adhesive sheet>
A pressure-sensitive adhesive composition is applied onto the release film to a thickness of 25 μm after drying, heated at 130° C. for 2 minutes to remove the solvent, and then another release film is laminated onto the coated layer. A pressure-sensitive adhesive sheet with a release film temporarily attached to both sides was obtained.

[Comparative example 6]
A pressure-sensitive adhesive sheet was produced in the same manner as in Comparative Example 5, except that the thickness of the pressure-sensitive adhesive composition was changed to 50 μm.

[Comparative Example 7]
As a base polymer, 100 parts by weight of polystyrene-poly(ethylene/propylene)-polystyrene block copolymer ("Septon 2063" manufactured by Kuraray, styrene content: 13% by weight), and as a tackifier, "YS Polyster" was used as a base polymer. TH130'': 40 parts by weight, styrene oligomer (manufactured by Eastman Chemical, ``Picolastic A5''): 60 parts by weight, and low molecular weight polybutene (JXTG Energy, Ltd., ``Nisseki Polybutene HV-300''): 10 parts by weight, solid A pressure-sensitive adhesive composition was prepared by dissolving it in toluene to a concentration of 34% by weight.

<Preparation of adhesive sheet>
A pressure-sensitive adhesive composition is applied onto the release film to a thickness of 25 μm after drying, heated at 60°C for 3 minutes, then heated at 130°C for 4 minutes to remove the solvent, and then another release layer is applied on the coated layer. The mold films were pasted together to obtain a pressure-sensitive adhesive sheet with release films temporarily attached to both sides.

[Comparative example 8]
A pressure-sensitive adhesive sheet was produced in the same manner as in Comparative Example 7 except that the thickness of the pressure-sensitive adhesive composition was changed to 50 μm.

[evaluation]
<Moisture percentage>
An adhesive sheet with a release film temporarily attached on both sides was cut into a size of 4 cm x 5 cm (area: 20 cm ² ), the release film on one side was peeled off, and the sheet was pasted on a pre-weighed aluminum foil. Combined. The release film on the other side of the pressure-sensitive adhesive sheet was peeled off, and the pressure-sensitive adhesive sheet was placed in a constant temperature and humidity bath at a temperature of 85° C. and a relative humidity of 85%, and was taken out after 72 hours. After weighing a test piece made of a laminated adhesive sheet and aluminum, Karl Fischer coulometric titration was performed using a moisture meter (Mitsubishi Chemical Analytech Model CA-200) equipped with a heating vaporizer (Mitsubishi Chemical Analytech Model VA-200). The moisture content was measured by the method under the following conditions.
Anolyte: Aquamicron AKX (manufactured by Mitsubishi Chemical)
Catholyte: Aquamicron CXU (manufactured by Mitsubishi Chemical)
Heating vaporization temperature: 150℃

<Moisture permeability>
The pressure-sensitive adhesive sheet, on which release films were temporarily attached on both sides, was left standing in an atmosphere of 23° C. and 55% humidity for 3 days to adjust its condition. After peeling off the release film on one side of the adhesive sheet and pasting it on a triacetyl cellulose film with a thickness of 25 μm, the release film on the other side was peeled off and subjected to a moisture permeability test (cup method) according to JIS Z0208. Accordingly, the water vapor permeability T ₀ of a laminate of a triacetyl cellulose film and an adhesive sheet was measured in an atmosphere at a temperature of 65° C. and a relative humidity of 90%. The moisture permeability T ₂ of the triacetyl cellulose film (single substance) was measured under the same conditions, and the moisture permeability T ₁ calculated based on the following relational expression (1) from T ₀ and T ₂ was calculated based on the pressure sensitive adhesive sheet (single substance). The water vapor permeability Y was set as
1/T ₀ = 1/T ₁ +1/T ₂ (1)

<White clouding resistance>
Two transparent conductive films each having an indium tin oxide (ITO) thin film provided on one side of a norbornene resin film (Nippon Zeon's "Zeonor Film") were placed through an adhesive sheet so that the ITO thin film-formed surfaces faced each other. Pasted together. A glass plate was bonded to one surface of this laminate using the same adhesive sheet to produce a touch panel for evaluation.

The evaluation touch panel was placed in a constant temperature and humidity chamber at a temperature of 65° C. and a relative humidity of 90%, and after 500 hours, it was taken out and left to stand in an environment of a temperature of 25° C. and a relative humidity of 50%. Thirty minutes and 8 hours after being removed from the constant temperature and humidity chamber, the touch panel for evaluation was visually observed to confirm the presence or absence of cloudiness, and the resistance to cloudiness was evaluated according to the following criteria.
〇: No cloudiness was observed after 30 minutes △: White cloudiness was observed after 30 minutes, but no cloudiness was observed after 8 hours ×: Cloudiness was not observed after 30 minutes or 8 hours was observed

[Evaluation results]
Table 1 shows the base polymer composition of each adhesive sheet, the thickness of the adhesive sheet, and the evaluation results. In addition, in Table 1, each component is described by the following abbreviations.

<Monofunctional monomer>
BA: Butyl acrylate 2EHA: 2-ethylhexyl acrylate ISTA: Isostearyl acrylate 4HBA: 4-hydroxybutyl acrylate HEA: Hydroxyethyl acrylate NVP: N-vinylpyrrolidone IBXA: Isobornyl acrylate <polyfunctional monomer>
HDDA: 1,6-hexanediol diacrylate <polymerization initiator>
AIBN: Azoisobutyronitrile (thermal radical polymerization initiator)
IRG184: Irgacure 184 (photoradical polymerization initiator)
IRG651: Irgacure 651 (photoradical polymerization initiator)
<Rubber polymer>
Septon: Septon 2063 (block copolymer)
OPPANO: OPPANOL N80 (polyisobutylene)
<Crosslinking agent>
Takenate: Takenate D110N (isocyanate crosslinking agent)
<Tackifier>
YS Polyster: YS Polyster TH130 (hydrogenated terpene phenol resin)
Picolastic: Picolastic A5 (styrene oligomer)
Polybutene: Nisseki Polybutene HV-300 (polybutene with number average molecular weight 1400)

In Comparative Examples 5 to 8, in which adhesive sheets were formed using rubber-based adhesives, the moisture permeability Y was low and the white clouding resistance was poor. Comparative Examples 1 to 4, in which adhesive sheets were formed using acrylic adhesives with high moisture content, also had poor clouding resistance.

In Examples 1 to 10, in which the moisture content X was small and the moisture permeability Y (product YD of moisture permeability Y and thickness D) was large, the cloudiness disappeared within 8 hours after being taken out from a high temperature and high humidity environment to a room temperature environment. Ta. Particularly, in Examples 1 to 7 in which log(YD)-2.1X was -1.2 or more, the cloudiness disappeared within 3 hours, demonstrating excellent resistance to cloudiness.

20, 21, 23, 25, 27 Adhesive sheet 81, 82 Release film 80 Adhesive sheet with release film 1 Image display panel 13 Polarizing plate 5 Touch panel 30, 40 Transparent conductive film 31, 41 Transparent film substrate 32, 42 Transparent electrode 7 Cover window 100 Image display device

Claims (11)

A pressure-sensitive adhesive sheet made of a pressure-sensitive adhesive composition containing 50% by weight or more of an acrylic base polymer,
The thickness is D; the moisture content after standing for 72 hours in an environment of a temperature of 85°C and a relative humidity of 85% is X%; the moisture permeability measured under test conditions of a temperature of 65°C and a relative humidity of 90% is Y;
X is 0.4 or less, YD is 8×10 ⁻² g/m・24h or more,
The acrylic base polymer is
The amount of the hydroxy group-containing monomer is 0.1 to 5 parts by weight based on 100 parts by weight of the total amount of the constituent monomer components,
The constituent monomer components include a polyfunctional (meth)acrylate, and a crosslinked structure is introduced into the polymer chain by the polyfunctional (meth)acrylate.
Adhesive sheets (excluding those in which the hydroxy groups of the acrylic base polymer are crosslinked with an isocyanate curing agent having two or more isocyanate groups in one molecule). The adhesive sheet according to claim 1, wherein the moisture permeability Y is 2000 g/m ² ·24 h or more. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the moisture content X (%), the product YD (g/m·24h) of the moisture permeability Y and thickness D satisfy the following relationship.
log(YD)-2.1X≧-1.2 The adhesive sheet according to any one of claims 1 to 3, wherein the moisture content X (%) and the moisture permeability Y (g/m ² · 24h) satisfy the following relational expression.
log(Y)-2.1X≧3.4 Any one of claims 1 to 4, wherein the acrylic base polymer has a total amount of a hydroxy group-containing monomer, a carboxyl group-containing monomer, and a nitrogen-containing monomer of 10 parts by weight or less based on 100 parts by weight of the total amount of constituent monomer components. Adhesive sheet as described in section . The pressure-sensitive adhesive sheet according to any one of claims 1 to 5 , wherein the base polymer of the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive sheet does not substantially contain an organic acid monomer as a constituent monomer component. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6 , having a thickness D of 10 to 100 μm. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7 , having an adhesive force to glass of 1 N/20 mm or more. A pressure-sensitive adhesive sheet according to any one of claims 1 to 8 ; a first optical member bonded to the first main surface of the pressure-sensitive adhesive sheet; and a second optical member bonded to the second main surface of the pressure-sensitive adhesive sheet. An optical laminate including an optical member. The optical laminate according to claim 9 , wherein the first optical member and the second optical member are each selected from the group consisting of a polarizing plate, a transparent conductive film, and a cover window. An image display device, wherein at least two constituent members are bonded together via the adhesive sheet according to any one of claims 1 to 8 .

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