JP2024050395A - Optical Adhesive Sheet - Google Patents

Abstract

[Problem] To provide an optical adhesive sheet suitable for reducing environmental load and for use in display panels. [Solution] The adhesive sheet 10 of the present invention is an optical adhesive sheet that contains a base polymer as a photopolymer and has photocurability. The adhesive sheet 10 has a gel fraction of 75% by mass or more after curing by photocuring treatment under conditions of an accumulated light irradiation amount of 3000 mJ/cm2. The adhesive sheet 10 has an adhesive strength of 2.5 N/10 mm or more in a peel test in which the adhesive sheet 10 is peeled from the alkali glass plate under conditions of 85°C, a peel angle of 180°, and a tensile speed of 300 mm/min after a photocuring treatment under conditions of an accumulated light irradiation amount of 3000 mJ/cm2 for the adhesive sheet 10, subsequent lamination of the adhesive sheet 10 to an alkali glass plate prepared by a float method, and subsequent heating and pressurizing treatment of the adhesive sheet 10 on the alkali glass plate under conditions of 50°C, 0.5 MPa, and 15 minutes. [Selected Figure] Figure 1

Description

The present invention relates to an optical adhesive sheet.

A display panel has a laminated structure including elements such as a pixel panel, a polarizing film, and a cover glass. In the manufacturing process of the display panel, for example, a transparent adhesive sheet (optical adhesive sheet) is used to bond the elements included in the laminated structure. Adhesive sheets for use in display panels are described, for example, in Patent Document 1 below.

JP 2012-62345 A

The optical adhesive sheet of Patent Document 1 is manufactured as follows. First, a reaction solution containing a monomer component for forming an acrylic-based polymer, a thermal polymerization initiator, and a solvent is prepared, and then an acrylic-based polymer is formed by solution polymerization in the reaction solution. Next, a solvent is added to the reaction solution to prepare a polymer solution in which the polymer concentration is adjusted. Next, a thermal crosslinking agent is added to the polymer solution to prepare a pressure-sensitive adhesive composition (solvent-based pressure-sensitive adhesive composition). Next, the pressure-sensitive adhesive composition is applied to a substrate to form a coating film. Next, the coating film on the substrate is dried by heating to form a pressure-sensitive adhesive layer (drying process). Next, a crosslinking reaction of the base polymer by the thermal crosslinking agent is promoted in the pressure-sensitive adhesive layer by an aging treatment. In this manner, an optical adhesive sheet is formed on a substrate. Thus, Patent Document 1 describes an optical adhesive sheet formed from a solvent-based pressure-sensitive adhesive composition.

However, in the drying process, a relatively large amount of the solvent in the coating film evaporates outside the coating film. Optical adhesive sheets that include such a process in their manufacturing process are not preferred from the perspective of reducing the environmental impact.

On the other hand, the laminated structure of the display panel includes elements having surface steps. For example, a decorative or light-shielding printed layer is provided on the edge of the pixel panel side surface of the cover glass, and there is a step (printed step) between the cover glass surface and the printed layer surface. For example, a predetermined resin layer is provided along a part of the peripheral edge of the polarizing film on the pixel panel on the polarizing film side surface of the pixel panel, and there is a step (resin step) between the surface of the polarizing film edge and the surface of the resin layer. Such a pixel panel with polarizing film and the above-mentioned cover glass are bonded via an optical adhesive sheet during the manufacturing process of the display panel. Therefore, the optical adhesive sheet for display panel use is required to be soft enough to follow the printed step (step followability). Insufficient step followability of the optical adhesive sheet causes air bubbles to form along the step when the optical adhesive sheet is attached to the stepped surface of an adherend having a surface step (for example, a cover glass having a printed step and a pixel panel with a polarizing film having a resin step), which is undesirable.

In addition, the laminated structure of a display panel contains elements with high surface smoothness, such as cover glass and polarizing film. Therefore, optical adhesive sheets for use in display panels are also required to have high adhesive properties.

The present invention provides an optical adhesive sheet that is suitable for reducing the environmental impact and for use in display panels.

The present invention [1] is an optical adhesive sheet that contains a base polymer as a photopolymer and has photocurability, and has a gel fraction of 75% by mass or more after curing by photocuring treatment under conditions of an accumulated light irradiation amount of 3000 mJ/ ^cm2 , and has an adhesive strength of 2.5 N/10 mm or more in a peel test in which the optical adhesive sheet is peeled from the alkali glass plate under conditions of 85°C, a peel angle of 180°, and a tensile speed of 300 mm/min after photocuring treatment under the above conditions for the optical adhesive sheet, subsequent lamination of the optical adhesive sheet to an alkali glass plate prepared by a float method, and subsequent heating and pressurizing treatment of the optical adhesive sheet on the alkali glass plate under conditions of 50°C, 0.5 MPa, and 15 minutes.

The present invention [2] includes the optical adhesive sheet described in [1] above, which further contains a photopolymerizable multifunctional compound and a photopolymerization initiator.

The present invention [3] includes the optical adhesive sheet described in [1] or [2] above, in which the weight average molecular weight of the base polymer is 800,000 or more.

The present invention [4] includes an optical adhesive sheet according to any one of [1] to [3] above, in which the optical adhesive sheet after curing by photocuring treatment under conditions of an accumulated light irradiation amount of 3000 mJ/ ^cm2 has a residual stress of 65 N/ ^m2 or less 5 minutes after being stretched to 6 times its length under conditions of 23°C and a tensile speed of 200 mm/min.

The present invention [5] includes an optical adhesive sheet according to any one of [1] to [4] above, which is subjected to a photocuring treatment of the optical adhesive sheet under conditions of an accumulated light irradiation amount of 3000 mJ/ ^cm2 , followed by bonding of the optical adhesive sheet to an alkali glass plate prepared by a float method, and then a heating and pressurizing treatment of the optical adhesive sheet on the alkali glass plate under conditions of 50°C, 0.5 MPa and 15 minutes, and then a constant load peel test in which the optical adhesive sheet is peeled from the alkali glass plate under conditions of 23°C, a peel angle of 90° and a tensile load of 2.5 N/10 mm, and the peel speed is 35 μm/sec or less.

As described above, the optical adhesive sheet of the present invention has a base polymer that is a photopolymer. Such an adhesive sheet is suitable for production from a solventless adhesive composition. Furthermore, in the process of producing an adhesive sheet from the composition, the solventless adhesive composition does not require a drying step for volatilizing and removing the solvent from the coating film of the composition, and is therefore suitable for reducing the environmental load.

As described above, the optical adhesive sheet of the present invention has photocurability. Such an optical adhesive sheet can be attached to the stepped surface of an adherend in a soft state before photocuring. The optical adhesive sheet can be photocured after attachment to the adherend to make it highly elastic. Such an optical adhesive sheet is suitable for achieving good step-following properties when attached to an adherend having a stepped surface. Therefore, the optical adhesive sheet of the present invention is suitable for use in bonding elements including elements having surface steps (such as cover glass) in the manufacturing process of a display panel.

In addition, as described above, the optical adhesive sheet of the present invention has an adhesive strength of 2.5 N/10 mm or more at high temperature (85°C) to an alkaline glass plate produced by the float method after photocuring under specified conditions. Although an adhesive is difficult to adhere to an alkaline glass plate produced by the float method due to its high surface smoothness, the optical adhesive sheet of the present invention has excellent adhesiveness to the same glass plate. Such an optical adhesive sheet is suitable for bonding adherends with high surface smoothness, such as cover glass and polarizing films in display panels. Therefore, the optical adhesive sheet of the present invention is suitable for display panel applications.

In addition, as described above, the optical adhesive sheet of the present invention has a gel fraction of 75% by mass or more after photocuring under specified conditions. The optical adhesive sheet with such a high gel fraction is unlikely to peel off from an adherend to which it is attached before the adhesive sheet is cured (high elasticity) or from an adherend to which it is attached after the adhesive sheet is cured (high elasticity). The optical adhesive sheet capable of such a high gel fraction is suitable for ensuring good bonding reliability between the first and second adherends by bonding to a first adherend having a surface step (bonding the adhesive sheet in a soft state before photocuring), photocuring the adhesive sheet, and bonding the first adherend and the second adherend via the adhesive sheet. Therefore, the optical adhesive sheet of the present invention is suitable for display panel applications.

1 is a schematic cross-sectional view of one embodiment of an optical adhesive sheet of the present invention. An example of a method for producing the optical adhesive sheet shown in Fig. 1 is shown. Fig. 2A shows a process for forming a coating film of the adhesive composition, Fig. 2B shows a process for forming a base adhesive sheet, Fig. 2C shows a process for peeling a light release liner, Fig. 2D shows a process for supplying a post-added component to the base adhesive sheet, and Fig. 2E shows a process for bonding a light release liner to a sheet. An example of a method of using the optical adhesive sheet shown in Fig. 1 is shown. Fig. 3A shows a step of bonding the optical adhesive sheet to a first adherend (lamination step), Fig. 3B shows a step of photocuring the optical adhesive sheet on the first adherend (photocuring step), and Fig. 3C shows a step of bonding the first adherend and a second adherend via the optical adhesive sheet on the first adherend (bonding step). 1 shows the positional relationship between the glass plate and the pressure-sensitive adhesive sheet in the laminate used for evaluating the step-conforming ability (before photocuring) for the Examples and Comparative Examples.

As shown in FIG. 1, an adhesive sheet 10 according to one embodiment of the present invention has a sheet shape with a predetermined thickness and extends in a direction (surface direction) perpendicular to the thickness direction H. The adhesive sheet 10 has an adhesive surface 11 and an adhesive surface 12 opposite to the adhesive surface 11. FIG. 1 exemplarily shows a state in which release liners 21 and 22 are attached to the adhesive surfaces 11 and 12 of the adhesive sheet 10. The release liner 21 is disposed on the adhesive surface 11. The release liner 22 is disposed on the adhesive surface 12. The adhesive sheet 10 is an optical adhesive sheet disposed at a light passing portion in a display panel. Examples of the display panel include a liquid crystal panel and an organic EL panel. The display panel has a laminated structure including elements such as a pixel panel, a polarizing film, a touch panel, and a cover glass. The adhesive sheet 10 is used, for example, in the manufacturing process of the display panel to bond elements included in the laminated structure.

The adhesive sheet 10 is a sheet-shaped pressure-sensitive adhesive. The adhesive sheet 10 contains a base polymer as a photopolymer, and in this embodiment, further contains a photopolymerizable multifunctional compound and a photopolymerization initiator, and has photocurability. Photocurability refers to the property of becoming highly elastic when irradiated with active energy rays such as ultraviolet rays. The adhesive sheet 10 has a gel fraction of 75% by mass or more after curing by photocuring treatment under conditions of an accumulated irradiation light amount of 3000 mJ/cm ² , and has an adhesive strength F of 2.5 N/10 mm or more in the following peel test. The method for measuring the gel fraction is as described below in relation to the examples. The adhesive strength F is the adhesive strength of the adhesive sheet 10, which is attached to an alkaline glass plate after photocuring, to the glass plate. The strength of the adhesive strength of the adhesive sheet to an alkaline glass plate is, for example, an indicator of the strength of the adhesive strength of the adhesive sheet to a polarizing film.

In the peel test, the adhesive sheet 10 is subjected to a photocuring treatment under conditions of an accumulated light amount of 3000 mJ/ ^cm2 , and then the adhesive sheet 10 is attached to an alkali glass plate prepared by a float method, and then the adhesive sheet 10 on the alkali glass plate is subjected to a heating and pressurizing treatment under conditions of 50°C, 0.5 MPa, and 15 minutes, and then the adhesive sheet 10 is peeled off from the alkali glass plate under conditions of 85°C, a peel angle of 180°, and a pulling speed of 300 mm/min to measure the adhesive force F. More specifically, the peel test is as described below in relation to the examples.

As described above, the base polymer of the adhesive sheet 10 is a photopolymer. Such an adhesive sheet 10 is suitable for production from a solventless adhesive composition. Furthermore, in the process of producing an adhesive sheet from the composition, the solventless adhesive composition does not require a drying step for volatilizing and removing the solvent from the coating film of the composition, and is therefore suitable for reducing the environmental load.

As described above, the adhesive sheet 10 is photocurable. Such an adhesive sheet 10 can be attached to the stepped surface of an adherend in a soft state before photocuring. The adhesive sheet 10 can be photocured after attachment to the adherend to make it highly elastic. Such an adhesive sheet 10 is suitable for achieving good step conformability when attached to an adherend having a stepped surface. Therefore, the adhesive sheet 10 is suitable for use in bonding elements including elements having surface steps (such as cover glass) during the manufacturing process of a display panel.

In addition, as described above, the adhesive sheet 10 has an adhesive strength F of 2.5 N/10 mm or more at high temperature (85°C) to an alkaline glass plate produced by the float method after photocuring under specified conditions. Although an alkaline glass plate produced by the float method has a high surface smoothness to which an adhesive does not easily adhere, the adhesive sheet 10 has excellent adhesive properties to the same glass plate. Such an adhesive sheet 10 is suitable for bonding adherends with high surface smoothness, such as glass substrates and polarizing films in display panels. Therefore, the adhesive sheet 10 is suitable for use in display panels.

In addition, as described above, the adhesive sheet 10 has a gel fraction of 75% by mass or more after photocuring under the specified conditions. The adhesive sheet 10 with such a high gel fraction is unlikely to peel off from an adherend to which it is attached before the adhesive sheet 10 is cured (high elasticity), or from an adherend to which it is attached after the adhesive sheet 10 is cured (high elasticity). The adhesive sheet 10 capable of such a high gel fraction is suitable for ensuring good bonding reliability between the first and second adherends by bonding to a first adherend having a surface step (bonding in a soft state before the adhesive sheet 10 is photocured), photocuring the adhesive sheet 10, and bonding between the first adherend and the second adherend via the cured adhesive sheet 10. Therefore, the adhesive sheet 10 is suitable for display panel applications.

As described above, the adhesive sheet 10 is suitable for reducing the environmental impact and is also suitable for use in display panels.

From the viewpoint of good adhesion to an adherend with high surface smoothness, the adhesive strength F is preferably 2.7 N/10 mm or more, more preferably 2.9 N/10 mm or more, and even more preferably 3.1 N/10 mm or more. The adhesive strength F is, for example, 4 N/10 mm or less, 7 N/10 mm or less, or 10 N/10 mm or less. Methods for adjusting the adhesive strength F include, for example, selecting the type of base polymer in the adhesive sheet 10, adjusting the molecular weight, and adjusting the blending amount. The selection of the type of base polymer includes adjusting the composition of the monomer that forms the base polymer. Methods for adjusting the adhesive strength F also include selecting the type of components other than the base polymer in the adhesive sheet 10, and adjusting the blending amount of the components. The components include a photopolymerizable multifunctional compound, a photopolymerization initiator, a silane coupling agent, and an oligomer.

In the adhesive sheet 10, the weight average molecular weight (Mw) of the base polymer is preferably 800,000 or more, more preferably 850,000 or more, and even more preferably 900,000 or more, from the viewpoint of ensuring the reliability of the bonding between the adherends by the adhesive sheet 10. The weight average molecular weight of the base polymer is preferably 1,500,000 or less, more preferably 1,200,000 or less, and even more preferably 1,000,000 or less, from the viewpoint of ensuring the reliability of the bonding between the adherends by the adhesive sheet 10. The weight average molecular weight is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

The above-mentioned gel fraction after photocuring of the adhesive sheet 10 is preferably 76% or more, more preferably 77% or more, and even more preferably 78% or more, from the viewpoint of ensuring the flexibility of the adhesive sheet 10 after curing. The gel fraction after photocuring of the adhesive sheet 10 is preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less, from the viewpoint of ensuring the flexibility of the adhesive sheet 10 after curing. Examples of methods for adjusting the gel fraction after photocuring of the adhesive sheet 10 include, for example, selecting the type of base polymer in the adhesive sheet 10, adjusting the molecular weight, and adjusting the amount of the base polymer. Examples of methods for adjusting the gel fraction after photocuring include selecting the type of photopolymerizable polyfunctional compound in the adhesive sheet 10, adjusting the molecular weight, and adjusting the amount of the base polymer. The method for measuring the gel fraction is as described below in the examples.

The gel fraction of the adhesive sheet 10 (before photocuring) is preferably 20% or more, more preferably 25% or more, even more preferably 30% or more, from the viewpoint of ensuring the handleability of the adhesive sheet 10, and is preferably 65% or less, more preferably 60% or less, even more preferably 55% or less. Methods for adjusting the gel fraction of the adhesive sheet 10 before photocuring include, for example, selecting the type of base polymer in the adhesive sheet 10, adjusting the molecular weight, and adjusting the amount of the base polymer.

The adhesive sheet 10 has a residual stress S of preferably 65 N/m 2 or less, more preferably 55 N/m ² or less, even more preferably 50 N/m ² or less, and even more preferably 40 N/m ² or less after 5 minutes from elongation to 6 times the length under conditions of 23 ° C. and a tensile speed of 200 mm / ^{min after curing by photocuring treatment under conditions of an accumulated light irradiation amount of 3000 mJ / cm 2. The} residual stress S is preferably 10 N / m ² or more, more preferably 20 N / m ² or more, and even more preferably 30 N / m ² or more. These configurations regarding the residual stress S are preferable for ensuring the step followability of the adhesive sheet 10 after photocuring. Examples of methods for adjusting the residual stress S include adjustment of the monomer composition of the base polymer in the adhesive sheet 10, adjustment of the molecular weight, adjustment of the blending amount, and adjustment of the degree of crosslinking. The method for measuring the residual stress S is specifically as described below in the examples.

The pressure-sensitive adhesive sheet 10 has a peel speed in the constant-load peel test described below of preferably 35 μm/sec or less, more preferably 30 μm/sec or less, and preferably 25 μm/sec or less. The peel speed is, for example, 0.1 μm/sec or more, 0.5 μm/sec or more, or 1 μm/sec or more.
Such a configuration regarding the peel speed is preferable for ensuring the bonding reliability of the adhesive sheet 10 to an adherend when the photocured adhesive sheet 10 is attached to the surface steps of an adherend with an uneven surface.

In the constant load peel test, the adhesive sheet 10 is subjected to a photocuring treatment under the condition of an accumulated light amount of 3000 mJ/cm ² irradiated thereto, and then the adhesive sheet 10 is attached to an alkali glass plate prepared by a float method, and then the adhesive sheet 10 on the alkali glass plate is subjected to a heating and pressurizing treatment under the conditions of 50°C, 0.5 MPa and 15 minutes, and then the optical adhesive sheet is peeled off from the alkali glass plate under the conditions of 23°C, a peel angle of 90° and a tensile load of 2.5 N/10 mm to measure the peeling speed. More specifically, the constant load peel test is as described later in the examples. Examples of the method for adjusting the peeling speed include, for example, the selection of the type of the first photopolymerizable multifunctional compound described later in the adhesive sheet 10, the adjustment of the molecular weight, and the adjustment of the blending amount. Examples of the method for adjusting the peeling speed include the adjustment of the monomer composition of the base polymer in the adhesive sheet 10, the adjustment of the molecular weight, the adjustment of the blending amount, and the adjustment of the degree of crosslinking.

The adhesive sheet 10 has a transmittance R1 of 85% or more at a wavelength of 420 nm, and a transmittance R2 of 15% or less at a wavelength of 380 nm. Such a configuration is preferable for the adhesive sheet 10 to ensure the transparency required for display panel applications while ensuring the protective function of the display panel by blocking ultraviolet rays. From the viewpoint of transparency, the transmittance R1 is preferably 87% or more, more preferably 89% or more, and even more preferably 90% or more. The transmittance R1 is, for example, 99% or less. From the viewpoint of protective function, the transmittance R2 is preferably 14% or less, more preferably 13% or less, more preferably 12% or less, more preferably 11% or less, more preferably 10% or less, more preferably 9% or less, more preferably 8% or less, more preferably 7% or less, more preferably 6% or less, and more preferably 5% or less. The transmittance R2 is, for example, 0.1% or more. The method for measuring the light transmittance at a wavelength of 380 nm and the light transmittance at a wavelength of 420 nm is specifically as described below in the examples.

The adhesive sheet 10 contains a base polymer (photopolymerized product), a photopolymerizable multifunctional compound (first photopolymerizable multifunctional compound), and a photopolymerization initiator, and has photocurability. The adhesive sheet 10 may contain a monofunctional monomer in addition to the photopolymerizable multifunctional compound as a polymerizable component. A photopolymerized product is a polymer produced by photopolymerization. Photopolymerization is a polymerization method in which a polymerization reaction of a polymerizable component is promoted by irradiation with active energy rays such as ultraviolet light.

The base polymer is a polymerized product obtained by photopolymerization of a polymerizable component including a monofunctional monomer and a photopolymerizable multifunctional compound (a second photopolymerizable multifunctional compound). The base polymer is, for example, a polymerized product obtained by photopolymerization of a partial polymerized product obtained by photopolymerization of a monofunctional monomer (a mixture of a polymerized product of a monofunctional monomer and an unreacted monofunctional monomer) and a second photopolymerizable multifunctional compound. The monofunctional monomer may be used alone or in combination of two or more kinds. The second photopolymerizable multifunctional compound may be used alone or in combination of two or more kinds.

Such a base polymer includes a photopolymerization polymer (first photopolymerization polymer) having a photocrosslinking structure. The photocrosslinking structure is a structure in which a linear structure of units derived from a monofunctional monomer is crosslinked by units derived from a second photopolymerizable polyfunctional compound. The base polymer may include a photopolymerization polymer (second photopolymerization polymer) that does not have such a photocrosslinking structure. The second photopolymerization polymer is a polymer of a monofunctional monomer. The base polymer is preferably an acrylic polymer. The acrylic polymer is a copolymer of polymerizable components containing 50% or more by mass of (meth)acrylic acid ester. "(Meth)acrylic" means acrylic and/or methacrylic.

As the monofunctional monomer, preferably, a monofunctional (meth)acrylic acid ester is used. As the monofunctional (meth)acrylic acid ester, preferably, a (meth)acrylic acid alkyl ester is used, more preferably, a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms is used. The (meth)acrylic acid alkyl ester may have a linear or branched alkyl group, or may have a cyclic alkyl group such as an alicyclic alkyl group.

Examples of linear or branched (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)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, and isooctyl (meth)acrylate. Examples of acrylates include ethyl, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, cetyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, and nonadecyl (meth)acrylate.

Examples of (meth)acrylic acid alkyl esters having an alicyclic alkyl group include (meth)acrylic acid cycloalkyl esters, (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring. Examples of (meth)acrylic acid cycloalkyl esters include (meth)acrylic acid cyclopentyl, (meth)acrylic acid cyclohexyl, (meth)acrylic acid cycloheptyl, and (meth)acrylic acid cyclooctyl. Examples of (meth)acrylic acid esters having a bicyclic aliphatic hydrocarbon ring include (meth)acrylic acid isobornyl. Examples of (meth)acrylic acid esters having a tricyclic or higher aliphatic hydrocarbon ring 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.

As the (meth)acrylic acid alkyl ester, preferably, an acrylic acid alkyl ester having an alkyl group having 3 to 15 carbon atoms is used, and more preferably, at least one selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, and dodecyl acrylate is used.

The proportion of monofunctional monomers in the polymerizable components forming the base polymer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, from the viewpoint of adequately expressing basic properties such as adhesiveness in the adhesive sheet 10. The proportion is, for example, 99% by mass or less.

The polymerizable component may contain, as a monofunctional monomer, a copolymerizable monomer that is copolymerizable with the monofunctional (meth)acrylic acid ester. Examples of the copolymerizable monomer include polar group-containing monomers. Examples of the polar group-containing monomer include hydroxy group-containing monomers, carboxy group-containing monomers, and monomers having a nitrogen atom-containing ring. The polar group-containing monomer is useful for modifying the acrylic polymer, such as ensuring the cohesive force of the acrylic polymer.

Examples of hydroxy 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. As the hydroxy group-containing monomer, at least one selected from the group consisting of 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate is preferably used.

The proportion of the hydroxyl group-containing monomer in the polymerizable component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of ensuring the cohesive strength of the adhesive sheet 10. From the viewpoint of adjusting the polarity of the acrylic polymer (related to the compatibility of the various additive components in the adhesive sheet 10 with the acrylic polymer), the proportion is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

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

The proportion of the carboxyl group-containing monomer in the polymerizable component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoints of ensuring the cohesive strength of the adhesive sheet 10 and ensuring the adhesive strength of the adhesive sheet 10 to the adherend. The proportion is preferably 20% by mass or less, more preferably 10% by mass or less, from the viewpoints of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend by acid.

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-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and acryloylmorpholine. The monomer having a nitrogen atom-containing ring is preferably at least one selected from the group consisting of N-vinyl-2-pyrrolidone and acryloylmorpholine.

The proportion of the monomer having a nitrogen atom-containing ring in the polymerizable component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of ensuring the cohesive strength of the pressure-sensitive adhesive sheet and the adhesive strength of the pressure-sensitive adhesive sheet to the adherend. The proportion is preferably 30% by mass or less, more preferably 20% by mass or less, from the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (related to the compatibility of various additive components in the pressure-sensitive adhesive sheet with the acrylic polymer).

Examples of the second photopolymerizable multifunctional compound include multifunctional monomers and multifunctional oligomers, and preferably multifunctional oligomers are used.

An example of a polyfunctional monomer is a polyfunctional (meth)acrylate that contains two or more ethylenically unsaturated double bonds in one molecule. As a polyfunctional monomer, a polyfunctional (meth)acrylate is preferred from the viewpoint of ease of introducing a crosslinked structure by photopolymerization (active energy ray polymerization).

Examples of polyfunctional (meth)acrylates include difunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional or higher polyfunctional (meth)acrylates.

Examples of bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol dimethacrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, stearic acid modified pentaerythritol di(meth)acrylate, dicyclopentenyl diacrylate, di(meth)acryloyl isocyanurate, and ethoxylated bisphenol A diacrylate (BPAEODE).

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

Examples of tetrafunctional or higher polyfunctional (meth)acrylates include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, alkyl-modified dipentaerythritol pentaacrylate, and dipentaerythritol hexa(meth)acrylate.

The molecular weight of the polyfunctional monomer is preferably 5,000 or less, more preferably 3,000 or less, even more preferably 2,000 or less, particularly preferably 1,000 or less, and preferably 200 or more. Such a configuration is preferable from the viewpoint of appropriately adjusting the viscoelasticity (e.g., shear storage modulus and loss tangent) of the base polymer.

Examples of polyfunctional oligomers include urethane acrylate oligomers (oligomers having a urethane backbone and two or more acryloyl groups), epoxy acrylate oligomers (oligomers having an epoxy backbone and two or more acryloyl groups), and silicone acrylate oligomers (oligomers having a siloxane backbone and two or more acryloyl groups). As the polyfunctional oligomer, urethane acrylate oligomers are preferably used. Examples of commercially available urethane acrylate oligomers include Art Resin UN-333, UN-350, UN-353, UN-5500, and UN-5590 manufactured by Negami Chemical Industries Co., Ltd.

The weight average molecular weight (Mw) of the polyfunctional oligomer is preferably 20,000 or less, more preferably 15,000 or less, and preferably 5,000 or more. Such a configuration is preferable from the viewpoint of appropriately adjusting the viscoelasticity (e.g., shear storage modulus and loss tangent) of the base polymer. The weight average molecular weight is measured by gel permeation chromatography (GPC) and calculated in terms of polystyrene.

The proportion of the second photopolymerizable multifunctional compound in the polymerizable component is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more. Such a configuration is preferable for maintaining the sheet shape of the adhesive sheet 10 before photocuring, and therefore is preferable for ensuring the handleability of the adhesive sheet 10. The proportion of the second photopolymerizable multifunctional compound in the polymerizable component is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less. Such a configuration is preferable for ensuring a high degree of softness in the adhesive sheet 10 before photocuring, and achieving good step-following properties.

The polymerizable component may contain other copolymerizable monomers. Examples of other copolymerizable monomers include acid anhydride monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds. These other copolymerizable monomers may be used alone or in combination of two or more.

The first photopolymerizable multifunctional compound may be, for example, a multifunctional monomer or a multifunctional oligomer, and preferably a multifunctional monomer is used. The multifunctional monomer may be, for example, the multifunctional monomer described above for the second photopolymerizable multifunctional compound. The multifunctional oligomer may be, for example, the multifunctional oligomer described above for the second photopolymerizable multifunctional compound. The first photopolymerizable multifunctional compound may be used alone or in combination of two or more kinds. As the first photopolymerizable multifunctional compound, preferably, at least one selected from the group consisting of ethoxylated bisphenol A diacrylate (BPAEODE), trimethylolpropane triacrylate (TMPTA), and dipentaerythritol hexaacrylate (DPHA) is used.

The content of the first photopolymerizable polyfunctional compound in the adhesive sheet 10 is preferably 2.5 parts by mass or more, more preferably 3 parts by mass or more, even more preferably 3.5 parts by mass or more, and preferably 8 parts by mass or less, more preferably 7 parts by mass or less, even more preferably 6 parts by mass or less, per 100 parts by mass of the base polymer. Such a configuration is suitable for ensuring good bonding reliability in the adhesive sheet 10 after photocuring.

Examples of photopolymerization initiators include radical photopolymerization initiators, cationic photopolymerization initiators, and anionic photopolymerization initiators.

Examples of radical photopolymerization initiators 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.

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-diphenylethan-1-one. Examples of acetophenone-based photopolymerization initiators include 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexyl phenyl ketone, 4-phenoxydichloroacetophenone, and 4-(t-butyl)dichloroacetophenone. Examples of α-ketol-based photopolymerization initiators include 2-methyl-2-hydroxypropiophenone and 1-[4-(2-hydroxyethyl)phenyl]-2-methylpropan-1-one. Examples of aromatic sulfonyl chloride-based photopolymerization initiators include 2-naphthalenesulfonyl chloride. Examples of photoactive oxime-based photopolymerization initiators include 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)-oxime. Examples of benzoin-based photopolymerization initiators include benzoin. Examples of benzyl-based photopolymerization initiators include benzyl. Examples of benzophenone-based photopolymerization initiators include benzophenone, benzoylbenzoic acid, 3,3'-dimethyl-4-methoxybenzophenone, and polyvinylbenzophenone. Examples of ketal-based photopolymerization initiators include benzyl dimethyl ketal. Examples of thioxanthone-based photopolymerization initiators include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-diisopropylthioxanthone, and dodecylthioxanthone.

Examples of cationic photopolymerization initiators (photoacid generators) include onium compounds that generate acid when irradiated with ultraviolet light. The onium compounds are provided in the form of onium salts of onium cations and anions. Examples of onium cations _include sulfonium and iodonium. Examples of anions include ^Cl- , ^{Br- , I-} , _{ZnCl3- , HSO3-} ^, _{BF4- , PF6-} ^, _AsF6- ^, _SbF6- ^, _CH3SO3- ^, _CF3SO3- ^, _C4F9HSO3- ^, ( _C6F5 ⁾ _4B- ^, _{and ( C4H9 ) 4B-} ^. Commercially available cationic photopolymerization initiators include, for example, CPI-100, CPI-100P, CPI-101A, CPI-200K, CPI-210S, IK-1, IK-2, CPI-310B, and CPI-410S manufactured by San-Apro Co., Ltd. Commercially available cationic photopolymerization initiators include, for example, SP-056, SP-066, SP-130, SP-140, SP-150, SP-170, SP-171, and SP-172 manufactured by ADEKA Corporation.

Examples of anionic photopolymerization initiators (photobase generators) include α-aminoacetophenone compounds, oxime ester compounds, and compounds having a biguanide-type cation. Examples of biguanide-type cations include alkylbiguanidium, cycloalkylbiguaninium, and cycloalkyl-alkylbiguaninium. Examples of anions that pair with biguanide-type cations include borate-type anions. Commercially available anionic photopolymerization initiators include Fujifilm's WPBG-018 (9-anthramethyl N,N'-diethylcarbamate), WPBG-027 ((E)-1-[3-(2-hydroxyphenyl)-2-propenoyl]piperidine), WPBG-082 (guanidium 2-(3-benzoylphenyl)propionate), WPBG-140 (1-(anthraquinone-2-yl)ethylimidazole carboxylate), and WPBG -266 (1,2-diisopropyl-3-[bis(dimethylamino)methylene]guanidinium 2-(3-benzoylphenyl)propionate), WPBG-300 (1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidinium n-butyltriphenylborate), and WPBG-345 (1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidinium tetrakis(3-fluorophenyl)borate).

The content of the photopolymerization initiator in the adhesive sheet 10 is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.03 parts by mass or more, even more preferably 0.05 parts by mass or more, even more preferably 0.07 parts by mass or more, especially more preferably 0.1 parts by mass or more, and particularly preferably 0.2 parts by mass or more, per 100 parts by mass of the base polymer. Such a configuration is preferable for forming a crosslinked network with sufficient crosslink density in the adhesive sheet 10 by the photopolymerization reaction when the adhesive sheet 10 is irradiated with light, and significantly changing the viscoelasticity of the adhesive sheet 10. The content of the photopolymerization initiator in the adhesive sheet 10 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, per 100 parts by mass of the base polymer. Such a configuration is preferable for suppressing the excessive generation of the polymerization initiator when the adhesive sheet 10 is irradiated with light, and for forming a long-distance and continuous crosslinked network by the photopolymerization reaction.

The adhesive sheet 10 may contain other components. Examples of the other components include oligomers, ultraviolet absorbers, antioxidants, silane coupling agents, rust inhibitors, rework improvers, isocyanate crosslinkers, and metal deactivators.

When the base polymer is an acrylic polymer, the oligomer is preferably an acrylic oligomer. The acrylic oligomer is a copolymer of monomer components containing 50% or more by mass of (meth)acrylic acid ester, and has a weight average molecular weight of, for example, 1,000 or more and 30,000 or less.

The acrylic oligomer is preferably a polymer of monomer components including an alkyl (meth)acrylate ester having a chain alkyl group (chain alkyl (meth)acrylate) and an alkyl (meth)acrylate ester having an alicyclic alkyl group (alicyclic alkyl (meth)acrylate). Specific examples of these alkyl (meth)acrylate esters include the alkyl (meth)acrylate esters described above as polymerizable components of the acrylic polymer.

As the linear alkyl (meth)acrylate, methyl methacrylate is preferred because it has a high glass transition temperature and excellent compatibility with the base polymer. As the alicyclic alkyl (meth)acrylate, dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate are preferred. In other words, the acrylic oligomer is preferably a polymer of monomer components containing methyl methacrylate and one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate.

The proportion of alicyclic alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. The proportion is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The proportion of chain alkyl (meth)acrylate in the monomer component of the acrylic oligomer is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The proportion is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more.

The acrylic oligomer is obtained by polymerizing the monomer components of the acrylic oligomer. Examples of the polymerization method include solution polymerization, bulk polymerization, and emulsion polymerization. The acrylic oligomer is preferably formed by solution polymerization. Examples of the solvent in solution polymerization include toluene and ethyl acetate. In the polymerization of the acrylic oligomer, a thermal polymerization initiator may be used, and a chain transfer agent may be used for the purpose of adjusting the molecular weight. In this embodiment, after the formation of the acrylic oligomer, low molecular weight components and the solvent are volatilized and removed from the reaction system such as the reaction solution by heating. Examples of the low molecular weight components include unreacted monomers, chain transfer agents, thermal polymerization initiators, and decomposition products (residues) thereof.

Examples of thermal polymerization initiators include azo polymerization initiators and peroxide polymerization initiators. Examples of azo polymerization initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid)dimethyl, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis(2-methylpropionamidine)disulfate, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine)dihydrochloride. Examples of peroxide polymerization initiators include dibenzoyl peroxide, t-butyl permaleate, and lauroyl peroxide.

Chain transfer agents include α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and α-methylstyrene dimer.

The weight average molecular weight of the oligomer is preferably 1000 or more, more preferably 1500 or more, and even more preferably 2000 or more. The weight average molecular weight is preferably 30000 or less, more preferably 10000 or less, and even more preferably 8000 or less. Such a molecular weight range of the oligomer is preferable for ensuring the adhesive strength of the pressure-sensitive adhesive sheet 10.

The content of the oligomer in the adhesive sheet 10 is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of the base polymer in order to sufficiently increase the adhesive strength of the adhesive sheet 10. From the viewpoint of ensuring the transparency of the adhesive sheet 10, the content of the oligomer in the adhesive sheet 10 is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, even more preferably 5 parts by mass or less, even more preferably 4 parts by mass or less, and particularly preferably 3 parts by mass or less, per 100 parts by mass of the base polymer.

Examples of ultraviolet absorbers include triazine-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers. As ultraviolet absorbers, triazine-based ultraviolet absorbers and benzotriazole-based ultraviolet absorbers are preferred because they have high absorption of ultraviolet rays in the wavelength range of 320 to 370 nm and have excellent compatibility with acrylic polymers. The ultraviolet absorbers may be used alone or in combination of two or more types.

Commercially available triazine-based UV absorbers include, for example, bisethylhexyloxyphenol methoxyphenyl triazine (product name "Tinosorb S", manufactured by BASF), reaction product of 2-(4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl)-5-hydroxyphenyl with [(alkyloxy)methyl]oxirane (product name "TINUVIN 400", manufactured by BASF), reaction product of 2-(2,4-dihydroxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine with (2-ethylhexyl)-glycidic acid ester (product name "TINUVIN 405", manufactured by BASF), (2,4-bis[2-hydroxy-4-butoxyphenyl]-6-(2,4-dibutoxyphenyl)-1,3,5-triazine (product name "TINUVIN 460" manufactured by BASF), 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[(hexyl)oxy]-phenol (trade name "TINUVIN 577" manufactured by BASF), 2-(2-hydroxy-4-[1-octyloxycarbonylethoxy]phenyl)-4,6-bis(4-phenylphenyl)-1,3,5-triazine (trade name "TINUVIN 479" manufactured by BASF), and 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethylhexanoyloxy)ethoxy]-phenol ("ADK STAB LA-46" manufactured by ADEKA).

Commercially available benzotriazole-based UV absorbers include, for example, 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol (product name "TINUVIN 928", manufactured by BASF), 2-(2-hydroxy-5-tert-butylphenyl)-2H-benzotriazole (product name "TINUVIN PS", manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-bis(1-methyl-1-phenylethyl)phenol (product name "TINUVIN 900", manufactured by BASF), 2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methylphenol (product name "TINUVIN 571", manufactured by BASF), and 2-(2H-benzotriazol-2-yl)-p-cresol (product name "TINUVIN P”, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4-6-bis(1-methyl-1-phenylethyl)phenol (product name “TINUVIN 234”, manufactured by BASF), 2-[5-chloro(2H)-benzotriazol-2-yl]-4-methyl-6-(tert-butyl)phenol (product name “TINUVIN 326”, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (product name “TINUVIN 328”, manufactured by BASF), 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (product name “TINUVIN 329" manufactured by BASF), and 2-[2-hydroxy-3-(3,4,5,6-tetrahydrophthalimido-methyl)-5-methylphenyl]benzotriazole (trade name "Sumisorb 250" manufactured by Sumitomo Chemical).

In the adhesive sheet 10, the specific absorbance (first specific absorbance) of the photopolymerization initiator at a wavelength of 405 nm is preferably 10 or more, more preferably 15 or more, and the specific absorbance (second specific absorbance) of the ultraviolet absorber at a wavelength of 405 nm is preferably 5 or less, more preferably 3 or less. This configuration is preferable from the viewpoint of compatibility between the ultraviolet cut function for device protection and photocurability in the adhesive sheet 10. Among the above photopolymerization initiators, for example, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and 2,4,6-trimethylbenzoyldiphenylphosphine oxide have a first specific absorbance of 15 or more. Among the above ultraviolet absorbers, for example, bisethylhexyloxyphenol methoxyphenyl triazine and 2-(2H-benzotriazol-2-yl)-6-(1-methyl-1-phenylethyl)-4-(1,1,3,3-tetramethylbutyl)phenol have a second specific absorbance of 3 or less.

The content of the UV absorber in the adhesive sheet 10 is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 3 parts by mass or less, more preferably 2 parts by mass or less, per 100 parts by mass of the base polymer. Such a configuration is preferable from the viewpoint of achieving both the UV-cutting function for device protection and photocurability in the adhesive sheet 10.

Examples of antioxidants include phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, and amine-based antioxidants. The antioxidants may be used alone or in combination of two or more types.

As the antioxidant, a phenol-based antioxidant is preferably used, and more preferably a hindered phenol-based antioxidant is used. Examples of hindered phenol-based antioxidants include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (product name "Irganox 1010", manufactured by BASF) and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (product name "Irganox 1076", manufactured by BASF).

The content of the antioxidant in the adhesive sheet 10 is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 3 parts by mass or less, more preferably 2 parts by mass or less, per 100 parts by mass of the base polymer. This configuration is preferable from the viewpoint of achieving both suppression of oxidative deterioration of the adhesive sheet 10 and photocurability.

Examples of the silane coupling agent include silane coupling agents containing an epoxy group. Examples of the silane coupling agent containing an epoxy group include 3-glycidoxydialkyldialkoxysilane and 3-glycidoxyalkyltrialkoxysilane. Examples of the 3-glycidoxydialkyldialkoxysilane include 3-glycidoxypropylmethyldimethoxysilane and 3-glycidoxypropylmethyldiethoxysilane. Examples of the 3-glycidoxyalkyltrialkoxysilane include 3-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane. As the silane coupling agent, preferably, 3-glycidoxyalkyltrialkoxysilane is used, and more preferably, 3-glycidoxypropyltrimethoxysilane is used. The silane coupling agent may be used alone or in combination of two or more types. The content of the silane coupling agent in the adhesive sheet 10 is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less, per 100 parts by mass of the base polymer.

The adhesive sheet 10 is substantially free of any residue of the thermal polymerization initiator. The residue of the thermal polymerization initiator includes decomposition products of the thermal polymerization initiator. The proportion of the residue of the thermal polymerization initiator in the adhesive sheet 10 is preferably 0.005% by mass or less, more preferably 0.001% by mass or less, and particularly preferably 0.

From the viewpoint of ensuring sufficient adhesion to the adherend, the thickness of the adhesive sheet 10 is preferably 10 μm or more, more preferably 15 μm or more. From the viewpoint of the handleability and laser processability of the adhesive sheet 10, the thickness of the adhesive sheet 10 is preferably 500 μm or less, more preferably 400 μm or less, more preferably 300 μm or less, more preferably 250 μm or less, more preferably 200 μm or less, more preferably 150 μm or less, more preferably 135 μm or less, more preferably 100 μm or less, more preferably 75 μm or less, more preferably 50 μm or less.

The total light transmittance of the adhesive sheet 10 is preferably 90% or more, more preferably 92% or more. Such a configuration is preferable for ensuring the transparency required of the adhesive sheet 10 for use in a display panel. The total light transmittance of the adhesive sheet 10 is, for example, 100% or less. The total light transmittance can be measured in accordance with JIS K 7375 (2008).

The adhesive sheet 10 can be manufactured, for example, as follows.

First, a prepolymer composition is prepared (prepolymer composition preparation step). Specifically, first, a mixture (liquid) containing the above-mentioned monofunctional monomer for forming the base polymer and a photopolymerization initiator is prepared. This mixture does not contain a solvent. Next, the mixture is irradiated with ultraviolet light to photopolymerize a portion of the monofunctional monomer in the mixture to obtain a prepolymer composition (solvent-free prepolymer composition). Examples of light sources for ultraviolet light irradiation include ultraviolet LED lights, black lights, high-pressure mercury lamps, and metal halide lamps. In addition, in ultraviolet light irradiation, a wavelength cut filter for cutting a portion of the wavelength region of the light emitted from the light source may be used as necessary. In ultraviolet light irradiation, the illuminance is, for example, 5 to 200 mW/cm ² m, and the cumulative irradiation light amount is, for example, 100 to 5000 mJ/cm ^2. It is preferable to continue ultraviolet light irradiation until the viscosity of the composition becomes about 15 to 25 Pa·s. This viscosity is a value measured by a B-type viscometer under the conditions of a rotor No. 5, a rotor rotation speed of 10 rpm, and a temperature of 30°C. The prepolymer composition contains a photopolymerized product of a monofunctional monomer (the second photopolymerized polymer) and a monofunctional monomer that has not undergone a polymerization reaction (a residual monomer). The prepolymer composition does not contain a solvent.

Next, a second photopolymerizable multifunctional compound, a photopolymerization initiator, and other components as necessary are added to the prepolymer composition to prepare a pressure-sensitive adhesive composition (pressure-sensitive adhesive composition preparation process). Examples of other components include an antioxidant and a silane coupling agent. The pressure-sensitive adhesive composition does not contain a solvent, and is therefore a solvent-free pressure-sensitive adhesive composition.

Next, as shown in FIG. 2A, a coating film 10A is formed between the release liners 21 and 22' (coating film forming process). Specifically, a pressure-sensitive adhesive composition is applied onto the release liner 21 to form the coating film 10A, and then the release liner 22' is bonded onto the coating film 10A on the release liner 21.

The release liners 21 and 22' are, for example, flexible plastic films. Examples of such plastic films include polyester films such as polyethylene terephthalate films, polyethylene films, and polypropylene films. The thickness of the release liners is, for example, 3 μm or more and, for example, 200 μm or less. The surface of the release liners is preferably subjected to a release treatment.

Methods for applying the adhesive composition include, for example, roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and die coating.

Next, as shown in FIG. 2B, the coating film 10A between the release liners 21 and 22' is irradiated with ultraviolet light to photocure it, forming a base adhesive sheet 10B (base adhesive sheet formation process). When irradiated with ultraviolet light, a photopolymerization reaction proceeds in the coating film in a system containing the above-mentioned residual monomer and the second photopolymerizable multifunctional compound, forming a first photopolymerized polymer having a photocrosslinked structure.

Next, as shown in FIG. 2C, the release liner 22' is peeled off from the base adhesive sheet 10B (peeling process).

Next, as shown in FIG. 2D, the post-added component is supplied to the base adhesive sheet 10B (post-added component supplying step). For example, a post-added component solution (not shown) containing the post-added component and a solvent is applied to the exposed surface of the base adhesive sheet 10B. The post-added component contains a first photopolymerizable multifunctional compound and a photopolymerization initiator, and may contain additives such as an ultraviolet absorber and an antioxidant. Next, the post-added component is allowed to penetrate into the base adhesive sheet 10B from the surface of the base adhesive sheet 10B, and the solvent is evaporated by heating as necessary. Before this step, the base polymer has already formed a crosslinked structure to form the base adhesive sheet 10B. Therefore, the orange peel surface is not easily formed (not substantially formed) on the base adhesive sheet 10B due to the evaporation of the solvent in this step. In addition, the photocurable adhesive sheet 10 is formed by the base adhesive sheet 10B and the post-added component. The amount of the first photopolymerizable multifunctional compound added in this step is preferably 2.5 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 3.5 parts by mass or more per 100 parts by mass of the total of the above-mentioned prepolymer composition and the second photopolymerizable multifunctional compound, and is preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less. Such a configuration is suitable for ensuring good bonding reliability in the adhesive sheet 10 after photocuring.

Next, as shown in FIG. 2E, the release liner 22 is attached to the adhesive sheet 10 (attachment process). Examples of the release liner 22 include the plastic films described above with respect to the release liners 21 and 22'.

In this manner, an adhesive sheet 10 can be manufactured in which the adhesive surface is covered and protected by release liners 21 and 22. The adhesive sheet 10 formed from a solvent-free adhesive composition is suitable for reducing the environmental load. Furthermore, the release liners 21 and 22 are peeled off from the adhesive sheet 10 as necessary when using the adhesive sheet 10.

Figures 3A to 3C show an example of a method of using the adhesive sheet 10. The method of using the adhesive sheet 10 is a method of bonding adherends together using the adhesive sheet 10. This method includes a lamination step (Figure 3A), a light curing step (Figure 3B), and a bonding step (Figure 3C).

First, in the lamination process, as shown in FIG. 3A, the adhesive sheet 10 is laminated to the cover glass 31 (first adherend). The cover glass 31 has a first surface 31a and a second surface 31b opposite to the first surface 31a. A decorative or light-shielding printed layer 32 is formed on the edge of the first surface 31a. The printed layer 32 is provided, for example, around the entire edge of the cover glass 31. The cover glass 31 has a step (printed step) between the first surface 31a and the surface of the printed layer 32. That is, the cover glass 31 is a stepped adherend having a step on its surface. In this process, specifically, the adhesive sheet 10 before photocuring is laminated to an area including the printed layer 32 on the surface 31a of the cover glass 31. FIG. 3A exemplarily shows a case where the adhesive sheet 10 before photocuring is laminated to the entire surface 31a of the cover glass 31.

Next, in the photocuring step, as shown in FIG. 3B, the adhesive sheet 10 on the cover glass 31 is photocured by ultraviolet irradiation. By the ultraviolet irradiation, the photopolymerization reaction of the first photopolymerizable multifunctional compound proceeds in the adhesive sheet 10, and a photopolymerization product of the first photopolymerizable multifunctional compound is formed. Since the photopolymerization reaction proceeds around the base polymer (the first photopolymerization polymer having a photocrosslinking structure, the second photopolymerization polymer), the photopolymerization product of the first photopolymerizable multifunctional compound is formed while forming an interpenetrating polymer network structure (IPN) with the base polymer. This makes the adhesive sheet 10 highly elastic. Examples of light sources for ultraviolet irradiation include ultraviolet LED lights, black lights, high-pressure mercury lamps, and metal halide lamps. In addition, in the ultraviolet irradiation, a wavelength cut filter for cutting a part of the wavelength region of the light emitted from the light source may be used. In the ultraviolet irradiation, the irradiation cumulative light amount is, for example, 50 to 10,000 mJ/cm ² .

Next, in the bonding process, as shown in FIG. 3C, the cover glass 31 and the member 33 are bonded via the photocured adhesive sheet 10 on the cover glass 31. The member 33 is, for example, a pixel panel for a display panel, a polarizing film, or a touch panel. The member 33 may have the above-mentioned resin step on the surface on the adhesive sheet 10 side (one side in the thickness direction H). This results in a bonded body W (cover glass 31/adhesive sheet 10/member 33).

As described above, the adhesive sheet 10 has photocuring properties. In the lamination process (FIG. 3A), such an adhesive sheet 10 can be attached to the stepped surface of the adherend (surface 31a of the cover glass 31) in a soft state before photocuring. Therefore, the adhesive sheet 10 is suitable for achieving good step-following properties.

As described above, the adhesive sheet 10 has an adhesive strength F of 2.5 N/10 mm or more at high temperature (85°C) to an alkaline glass plate produced by the float method after photocuring under specified conditions. Such an adhesive sheet 10 is suitable for bonding adherends with high surface smoothness, such as glass substrates and polarizing films in display panels. Therefore, the adhesive sheet 10 is suitable for display panel applications.

As described above, the adhesive sheet 10 has a gel fraction of 75% by mass or more after photocuring under the specified conditions. The adhesive sheet 10 with such a high gel fraction is unlikely to peel off from an adherend to which it is attached before the adhesive sheet 10 is cured, and from an adherend to which it is attached after the adhesive sheet 10 is cured. The adhesive sheet 10 capable of such a high gel fraction is suitable for ensuring good bonding reliability between the first and second adherends by bonding to a cover glass 31 (first adherend) having a surface step (FIG. 3A), photocuring the adhesive sheet 10 (FIG. 3B), and bonding between the cover glass 31 and a member 33 (second adherend) via the cured adhesive sheet 10. Therefore, the adhesive sheet 10 is suitable for display panel applications.

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples. Furthermore, the specific numerical values of the compounding amounts (contents), physical property values, parameters, etc. described below can be replaced with the upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or more than") of the corresponding compounding amounts (contents), physical property values, parameters, etc. described in the above-mentioned "Form for carrying out the invention."

Preparation of Acrylic Oligomer
First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, a mixture containing 60 parts by mass of dicyclopentanyl methacrylate (DCPMA), 40 parts by mass of methyl methacrylate (MMA), 3.5 parts by mass of α-thioglycerol as a chain transfer agent, and 100 parts by mass of toluene as a polymerization solvent was stirred under a nitrogen atmosphere at 70°C for 1 hour. Next, 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added to the mixture to prepare a reaction solution, which was reacted under a nitrogen atmosphere at 70°C for 2 hours and then at 80°C for 2 hours (polymerization reaction). Next, the reaction solution was heated at 130°C to volatilize and remove toluene, the chain transfer agent, and unreacted monomers. As a result, an acrylic oligomer (solid state) was obtained. The weight average molecular weight of this acrylic oligomer was 5100.

Preparation of Prepolymer Composition
In a flask, 71 parts by mass of n-butyl acrylate (BA), 13 parts by mass of N-vinyl-2-pyrrolidone (NVP), 13 parts by mass of 4-hydroxybutyl acrylate (4HBA), and 3 parts by mass of acryloylmorpholine (ACMO) were added to a monomer mixture, and 0.031 parts by mass of a first photopolymerization initiator (product name "Omnirad 184", 1-hydroxycyclohexyl phenyl ketone, manufactured by BASF) and 0.031 parts by mass of a second photopolymerization initiator (product name "Omnirad 651", 2,2-dimethoxy-1,2-diphenylethane-1-one, manufactured by BASF) were then added. The mixture was then irradiated with ultraviolet light under a nitrogen atmosphere to polymerize a portion of the monomer components in the mixture to obtain a prepolymer composition. The ultraviolet light irradiation was continued until the viscosity of the composition reached about 20 Pa·s. This viscosity is a value measured using a Brookfield viscometer with a rotor No. 5 at a rotor rotation speed of 10 rpm at a temperature of 30° C. The obtained prepolymer composition contains a photopolymerized product (photopolymerized polymer P1a) and a monomer component that has not undergone a polymerization reaction (residual monomer).

Preparation of Pressure-Sensitive Adhesive Composition
Next, 100 parts by mass of the prepolymer composition, 3 parts by mass of the acrylic oligomer, 0.6 parts by mass of a urethane acrylate oligomer (product name "UN-350", manufactured by Negami Chemical Industrial Co., Ltd.) as a second photopolymerizable polyfunctional compound, 0.4 parts by mass of a third photopolymerization initiator (product name "Omnirad 819", bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, manufactured by BASF), 0.5 parts by mass of an antioxidant (product name "Irganox 1010", manufactured by BASF), 0.2 parts by mass of a rust inhibitor (product name "BT-120", manufactured by Johoku Chemical Industry Co., Ltd.), and 0.3 parts by mass of a silane coupling agent (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) were mixed to obtain a pressure-sensitive adhesive composition.

<Preparation of base adhesive sheet>
Next, a pressure-sensitive adhesive composition was applied onto the release-treated surface of a first release liner (product name "Diafoil MRF", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side to form a coating film. Next, a release-treated surface of a second release liner (product name "Diafoil MRE", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side was attached onto the coating film on the first release liner. Next, ultraviolet light was irradiated from the second release liner side to photo-cure the coating film to form a pressure-sensitive adhesive layer with a thickness of 100 μm (ultraviolet light irradiation step). In the ultraviolet light irradiation, a black light (wavelength 320 nm to 400 nm, manufactured by Toshiba) was used as a light source, the illuminance was set to 6.5 mW/cm ² , and the cumulative irradiation light amount was set to 1500 mJ/cm ² . In the ultraviolet irradiation step, a photopolymerization reaction proceeds in the coating film in a system containing the above-mentioned residual monomer and the second photopolymerizable multifunctional compound (urethane acrylate oligomer), forming a photopolymerized polymer P1b having a photocrosslinking structure. In addition, since the photopolymerization reaction proceeds around the photopolymerized polymer P1a, the photopolymerized polymer P1b is formed around the photopolymerized polymer P1a. The adhesive layer formed in this step contains such photopolymerized polymer P1a and photopolymerized polymer P1b as the base polymer P1. In this manner, a base adhesive sheet with double-sided release liners (first release liner/base adhesive sheet (thickness 100 μm)/second release liner) was produced.

Example 1
Preparation of Post-Added Component Solutions
First, 4.0 parts by mass of a polyfunctional acrylate monomer (trade name "Viscoat #295", trimethylolpropane triacrylate (TMPTA), manufactured by Osaka Organic Chemical Industry Co., Ltd.) as a first photopolymerizable polyfunctional compound, 0.3 parts by mass of a third photopolymerization initiator (trade name "Omnirad 819", manufactured by BASF), 7.0 parts by mass of an ultraviolet absorber (trade name "Tinosorb S", manufactured by BASF), and 88.7 parts by mass of ethyl acetate as a solvent were mixed to prepare a post-added component solution (everything other than the solvent in the solution is a post-added component). The amounts of the post-added component solution are shown in Table 1. The units of the amounts shown in Table 1 are relative "parts by mass".

<Preparation of photocurable optical adhesive sheet>
Next, after peeling off the second release liner from the base adhesive sheet with double-sided release liner, the post-added component solution was applied to the exposed surface of the base adhesive sheet to a thickness of 20 μm (coating process). For the coating, a bar coater RDS No. 10 manufactured by R.D. SPECIALTIES was used. Next, a drying process was performed for 60 seconds in a dryer at 110° C. The coating process and drying process allowed the post-added components (multifunctional acrylate monomer, third photopolymerization initiator, ultraviolet absorber) to permeate the base adhesive sheet, and also vaporized the solvent. The base adhesive sheet was changed into a photocurable adhesive sheet due to the permeation of the post-added components. In this example, 4 parts by mass of the first photopolymerizable multifunctional compound (TMPTA in Example 1) per 100 parts by mass of the total of the above-mentioned prepolymer composition and the above-mentioned second photopolymerizable multifunctional compound (i.e., 100 parts by mass of the base polymer) was added to the base adhesive sheet (the parts by mass of the first photopolymerizable multifunctional compound per 100 parts by mass of the base polymer are shown in Table 2). Next, the release-treated surface of a third release liner (product name "Diafoil MRE", thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) having a release-treated surface on one side was attached to the adhesive sheet on the first release liner.

In this manner, the optical adhesive sheet with double-sided release liner of Example 1 (first release liner/photocurable optical adhesive sheet (thickness 100 μm)/third release liner) was produced.

[Examples 2 to 8]
Except for changing the composition of the post-addition component solution to the composition shown in Table 1, the double-sided release lined PSA sheets of Examples 2 to 8 were prepared in the same manner as the double-sided release lined PSA sheet of Example 1. In Examples 3 to 5, in addition to TMPTA, ethoxylated bisphenol A diacrylate (BPAEODE) (product name "ABE-300", manufactured by Shin-Nakamura Chemical Co., Ltd.) was used as the first photopolymerizable multifunctional compound in preparing the post-addition component solution. In Examples 6 to 8, in addition to TMPTA, polypropylene glycol #400 diacrylate (product name "APG-400", manufactured by Shin-Nakamura Chemical Co., Ltd.) was used as the first photopolymerizable multifunctional compound in preparing the post-addition component solution.

Comparative Examples 1 to 6
Each of the pressure-sensitive adhesive sheets with double-sided release liners of Comparative Examples 1 to 6 was prepared in the same manner as the pressure-sensitive adhesive sheet with double-sided release liners of Example 1, except for the following. The composition of the post-added component solution was changed to the composition shown in Table 1. In the ultraviolet irradiation step for preparing the base pressure-sensitive adhesive sheet, ultraviolet irradiation (first irradiation) was performed using a black light, followed by ultraviolet irradiation (second irradiation) using an ultraviolet LED light (wavelength 365 nm, manufactured by Quark Technology). In the second irradiation, the illuminance was set to 90 mW/ ^cm2 , and the accumulated irradiation light amount was set to 1800 mJ/ ^cm2 . By such an ultraviolet irradiation step, a base polymer P2 having a weight average molecular weight (Mw) smaller than that of the above-mentioned base polymer P1 was formed.

Weight Average Molecular Weight
The weight average molecular weight (Mw) of each of the base polymers P1 and P2 was determined. Specifically, the Mw of the base polymer was measured by gel permeation chromatography (GPC) under the following measurement conditions and determined in terms of polystyrene. In the measurement, a GPC measuring device (name: "Alliance", manufactured by Waters) was used. The sample solution was prepared as follows. First, a tetrahydrofuran (THF) solution (containing 10 mM phosphoric acid) with a sample concentration of 0.15% by mass was prepared using the base polymer as a sample, and the THF solution was left for 20 hours. Next, the THF solution was filtered through a membrane filter with an average pore size of 0.45 μm, and the filtrate was obtained as a sample solution for molecular weight measurement.

[GPC measurement conditions]
Columns: G7000H _XL (upstream) and GMH _XL and GMH _XL (downstream), each manufactured by Tosoh Column temperature: 40°C
Eluent: tetrahydrofuran solution containing phosphoric acid (phosphoric acid concentration 10 mM)
Flow rate: 0.8 mL/min Sample injection volume: 100 μL
Standard sample: polystyrene (PS)
Detector: Differential refractometer (RI)

<Gel Fraction>
The gel fraction after photocuring was measured for each of the optical pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 6. Specifically, the gel fraction was measured as follows.

First, the optical adhesive sheet between the release liners was irradiated with ultraviolet light through the release liners. In the ultraviolet irradiation, a metal halide lamp was used as a light source, the illuminance was set to 300 mW/cm ² , and the cumulative amount of irradiation was set to 3000 mJ/cm ^2. Next, about 1 g of an adhesive sample was taken from the optical adhesive sheet. Next, the mass (W ₁ ) of the adhesive sample was measured. Next, the adhesive sample was immersed in 40 g of ethyl acetate in a container for 7 days. Next, all components insoluble in ethyl acetate (insoluble parts) were collected. Next, the insoluble parts were dried at 130° C. for 2 hours (removal of ethyl acetate). Next, the mass (W ₂ ) of the insoluble parts was measured. Then, the gel fraction of the optical adhesive sheet after photocuring was calculated based on the following formula. The values are shown in Tables 2 and 3.

Gel fraction (mass%)=( _W2 / _W1 )×100

<Transmittance>
The transmittance of each of the optical adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 6 was measured as follows. First, a sample for measuring the transmittance was prepared. Specifically, after peeling off one release liner from the optical adhesive sheet, the exposed surface of the optical adhesive sheet was attached to alkali-free glass (manufactured by Matsunami Glass Co., Ltd.), and the release liner was peeled off from the optical adhesive sheet on the glass. This resulted in a sample for measurement. Next, a spectrophotometer (name "U4100", manufactured by Hitachi High-Technologies Corporation) was used to measure the transmittance of the optical adhesive sheet in the sample. In addition, in this measurement, the measurement results obtained by measuring only the alkali-free glass under the same conditions were used as the baseline. The transmittance at a wavelength of 380 nm and the transmittance at a wavelength of 420 nm measured for the optical adhesive sheet are shown in Table 1.

<Adhesive force>
For each of the optical pressure-sensitive adhesive sheets in Examples 1 to 8 and Comparative Examples 1 to 6, the adhesive strength was measured by the following peel test.

First, a test piece was prepared for each optical adhesive sheet. In preparing the test piece, first, the third release liner was peeled off from the optical adhesive sheet, and a PET film (thickness 50 μm) was attached to the exposed surface of the optical adhesive sheet exposed thereby to obtain a laminated film (first release liner / optical adhesive sheet / PET film). Next, a test piece (width 10 mm x length 100 mm) was cut out from the laminated film. Next, ultraviolet light was irradiated from the first release liner side to the optical adhesive sheet in the test piece (photocuring treatment). In the ultraviolet irradiation, a metal halide lamp was used as a light source, the illuminance was set to 300 mW / cm ² , and the cumulative irradiation light amount was set to 3000 mJ / cm ² . Next, in an environment of 23°C and 50% relative humidity, the first release liner was peeled off from the optical adhesive sheet of the test piece, and the exposed surface of the optical adhesive sheet was attached to the air side of an alkali glass plate (blue plate glass, manufactured by Matsunami Glass Industry Co., Ltd.) produced by the float method to obtain a first laminate (alkali glass plate/optical adhesive sheet/PET film). The air side is the exposed surface (opposite to the surface in contact with the molten metal) of the alkali glass plate when the alkali glass plate flows over the molten metal in the manufacturing process of the alkali glass plate. In the lamination, the test piece was pressed against the alkali glass plate by a 2 kg roller going back and forth once (the same applies to the lamination described below). Next, the first laminate was autoclaved (heated and pressurized). In the autoclaving, the temperature was 50°C, the pressure was 0.5 MPa, and the treatment time was 15 minutes. Next, the first laminate was left to stand for 30 minutes in an environment of 23°C and 50% relative humidity.

After this, a tensile test was carried out to peel the test piece from the alkali glass plate under conditions of 85°C, 50% relative humidity, a peel angle of 180°, and a tensile speed of 300 mm/min, and the peel strength was measured. A tensile tester (trade name "Tension and Compression Tester TCM-1kNB", manufactured by Minebea Co., Ltd.) was used for this measurement. The measured peel strength is shown in Tables 2 and 3 as the adhesive strength F (N/10 mm) after photocuring against an alkali glass plate prepared by the float method.

Residual stress
The residual stress when stretched (distorted) was examined for each of the optical pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 6. Specifically, the results are as follows.

First, a sheet piece (first release liner/optical adhesive sheet/third release liner) with a width of 10 mm and a length of 60 mm was cut out from the optical adhesive sheet with double-sided release liners. Next, the first and third release liners were peeled off from the optical adhesive sheet of the sheet piece to obtain a test piece (optical adhesive sheet piece). Next, the test piece was pulled in the length direction using a tensile tester (product name "Autograph AGS-J", manufactured by Shimadzu Corporation), and the residual stress generated in the test piece was measured at a strain value of 600% (6 times the length). In this test, the initial chuck distance was 100 mm, and the temperature condition was 23°C. In this test, while measuring the stress generated in the test piece, the test piece was stretched to 6 times the length (chuck distance 600 mm) at a tensile speed of 200 mm/min, and then the length was maintained. The value of the residual stress S after 5 minutes had elapsed since the test piece was stretched to 6 times the length is shown in Tables 2 and 3.

<Constant load peel test>
For each of the optical pressure-sensitive adhesive sheets in Examples 1 to 8 and Comparative Examples 1 to 6, the peel speed was measured in the following constant load peel test.

First, a test piece was prepared for each optical adhesive sheet. In preparing the test piece, first, the third release liner was peeled off from the optical adhesive sheet, and a PET film (thickness 50 μm) was attached to the exposed surface of the optical adhesive sheet exposed thereby to obtain a laminated film (first release liner / optical adhesive sheet / PET film). Next, a test piece (width 10 mm x length 100 mm) was cut out from the laminated film. Next, ultraviolet light was irradiated from the first release liner side to the optical adhesive sheet in the test piece (photocuring treatment). In the ultraviolet irradiation, a metal halide lamp was used as a light source, the illuminance was set to 300 mW / cm ² , and the cumulative irradiation light amount was set to 3000 mJ / cm ² . Next, in an environment of 23°C and 50% relative humidity, the first release liner was peeled off from the optical adhesive sheet of the test piece, and the exposed surface of the optical adhesive sheet was attached to the air side of an alkaline glass plate (blue plate glass, manufactured by Matsunami Glass Industry Co., Ltd.) prepared by the float method to obtain a second laminate (alkaline glass plate/optical adhesive sheet/PET film). Next, the second laminate was autoclaved (heated and pressurized). In the autoclaving, the temperature was 50°C, the pressure was 0.5 MPa, and the treatment time was 15 minutes. Next, the second laminate was left to stand for 30 minutes in an environment of 23°C and 50% relative humidity.

After this, a tensile test was carried out to peel the test piece from the alkali glass plate under the conditions of 23°C, 50% relative humidity, a peel angle of 90°, and a tensile load of 2.5 N/10 mm (constant), and the peel speed was measured. A tensile tester (name "Tension and Compression Tester TCM-1kNB", manufactured by Minebea Co., Ltd.) was used for this measurement. The measured peel speeds (μm/sec) are shown in Tables 2 and 3.

(Step-following ability before photo-curing)
The step-following ability of each of the optical adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 6 before photocuring was examined as follows.

First, a sample sheet (length 75 mm x width 45 mm) was cut out from the optical adhesive sheet with double-sided release liners. Next, the third release liner was peeled off from the optical adhesive sheet in the sample sheet, and the exposed surface of the optical adhesive sheet was bonded to the center of a PET film (length 100 mm x width 50 mm, thickness 125 μm). In the bonding, a roll laminator was used, the pressure between the rolls was 0.2 MPa, and the feed speed was 100 mm/min (the same applies to the bonding described below). Next, the first release liner was peeled off from the optical adhesive sheet on the PET film, and the exposed surface of the optical adhesive sheet was bonded to a glass plate (length 100 mm x width 50 mm, thickness 500 μm) with a printed layer by vacuum pressure bonding (surface pressure 0.3 MPa, pressure 100 Pa) to obtain a first bonded body. Figure 4 shows the positional relationship between the glass plate 41 and the optical adhesive sheet 42 in this first bonded body. On one surface of the thickness direction of the glass plate 41, a printed layer 43 (45 μm thick, black ink layer) is formed around the entire edge of the glass plate 41. The printed layer 43 is formed in a range of 15 mm inward from each end of the glass plate 41 in the length direction L1, and in a range of 5 mm inward from each end of the glass plate 41 in the width direction L2 (the printed layer is represented by hatching in FIG. 4). The optical adhesive sheet 42 is attached to the center of one surface of the thickness direction of the glass plate 41 and is in contact with the printed layer 43 around the entire edge of the sheet. In other words, the printed layer 43 on the glass plate 41 is sandwiched between the glass plate 41 and the optical adhesive sheet 42 in a range of 2.5 mm outward from the inner end of the layer.

Next, the first bonded body was autoclaved for 30 minutes at 50°C and 0.5 MPa. After this, the vicinity of the inner edge of the printed layer in the first bonded body was observed. Specifically, the inside of the inner edge of the printed layer (the area where the optical adhesive sheet should be in close contact with the glass plate) was observed from the PET film side of the first bonded body using a digital microscope at a magnification of 20. Then, with regard to the step-following ability of the optical adhesive sheet, if no air bubbles were observed within the observed range, it was evaluated as "excellent," and if air bubbles were observed, it was evaluated as "poor." The results are shown in Tables 2 and 3.

(Step-following ability after photocuring)
The step-following ability of each of the optical adhesive sheets of Examples 1 to 8 and Comparative Examples 1 to 6 after photocuring was examined as follows.

First, a sample sheet of a predetermined size was cut out from the optical adhesive sheet with double-sided release liner. Next, the third release liner was peeled off from the optical adhesive sheet in the sample sheet, and the exposed surface of the optical adhesive sheet was attached to a glass plate. The optical adhesive sheet on the glass plate was irradiated with ultraviolet light from the first release liner side to photocure the optical adhesive sheet. In the ultraviolet irradiation, a metal halide lamp was used as a light source, the illuminance was set to 300 mW/ ^cm2 , and the cumulative irradiation light amount was set to 3000 mJ/ ^cm2 .

After laminating a specified polarizing film to one side of a PET film (75 μm thick), a polyimide (PI) tape (50 μm thick) having an adhesive layer on one side was laminated to a partial area of the polarizing film on the PET film. This resulted in a PET film with a polarizing film on which a surface step (simulated resin step) was formed by the PI tape.

Next, the first release liner was peeled off from the optical adhesive sheet on the glass plate, and the optical adhesive sheet was then attached to the polarizing film side of the polarizing film-attached PET film to obtain a second bonded structure. Specifically, the optical adhesive sheet and the polarizing film-attached PET film were attached together in such a way that the ends of the PI tape and the optical adhesive sheet overlapped by 180 μm. A vacuum bonding device was used for this bonding. The bonding pressure was 0.1 MPa. After this bonding, the second bonded structure was autoclaved for 5 minutes under heating and pressurizing conditions of 40°C and 0.4 MPa.

Next, the edge of the PI tape in the second bonded body was observed with an optical microscope to confirm that no air bubbles had occurred. Next, the second bonded body was subjected to a 100-hour high-temperature humidity test. In this test, the heating temperature was 85°C and the relative humidity was 85%. After the high-temperature humidity test, the edge of the PI tape in the second bonded body was observed with an optical microscope. Then, regarding the step-following ability of the optical adhesive sheet after photocuring, if no air bubbles were found within the observed range, it was rated as "excellent," and if air bubbles were found, it was rated as "poor." The results are shown in Tables 2 and 3.

10 Optically adhesive sheet (optically adhesive sheet)
H: thickness direction 21, 22: release liner 31: cover glass 32: printing layer 33: member

Claims (5)

An optical adhesive sheet comprising a base polymer as a photopolymer and having photocurability,
After curing by photocuring treatment under conditions of an accumulated light irradiation amount of 3000 mJ/ ^cm2 , the composition has a gel fraction of 75% by mass or more;
The optical adhesive sheet is subjected to a photocuring treatment under the above conditions, then bonded to an alkaline glass plate prepared by a float method, and then heated and pressurized to the optical adhesive sheet on the alkaline glass plate at 50°C, 0.5 MPa and 15 minutes. In a peel test in which the optical adhesive sheet is peeled from the alkaline glass plate at 85°C, a peel angle of 180° and a tensile speed of 300 mm/min, the optical adhesive sheet has an adhesive strength of 2.5 N/10 mm or more. The optical adhesive sheet according to claim 1, further comprising a photopolymerizable multifunctional compound and a photopolymerization initiator. The optical adhesive sheet according to claim 1, wherein the weight average molecular weight of the base polymer is 800,000 or more. The optical adhesive sheet according to claim 1, wherein the optical adhesive sheet after curing by photocuring treatment under conditions of an accumulated light irradiation amount of 3000 mJ/ ^cm2 is stretched to 6 times its length under conditions of 23°C and a tensile speed of 200 mm/min, and 5 minutes later, the residual stress of the optical adhesive sheet is 65 N/ ^m2 or less. The optical adhesive sheet is subjected to a photocuring treatment under conditions of an accumulated light irradiation amount of 3000 mJ/cm ² , followed by bonding of the optical adhesive sheet to an alkali glass plate prepared by a float method, and then subjected to a heating and pressurizing treatment of the optical adhesive sheet on the alkali glass plate under conditions of 50 ° C., 0.5 MPa and 15 minutes. In a constant load peel test in which the optical adhesive sheet is peeled from the alkali glass plate under conditions of 23 ° C., a peel angle of 90 ° and a tensile load of 2.5 N / 10 mm, the peel speed is 35 μm / sec or less. The optical adhesive sheet according to any one of claims 1 to 4.

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