JP2023055632A - Foldable optical adhesive sheet - Google Patents

Abstract

An object of the present invention is to provide a foldable optical pressure-sensitive adhesive sheet that has foldability while being excellent in workability and processability. A foldable optical adhesive sheet 1 has a shape extending in a first direction orthogonal to a thickness direction. The foldable optical adhesive sheet 1 has one edge 11 and the other edge 12 in a second direction perpendicular to the thickness direction and the first direction. The foldable optical pressure-sensitive adhesive sheet 1 includes a soft portion 2 and two hard portions 3 arranged adjacent to both sides of the soft portion 2 in the first direction and harder than the soft portion 2 . The soft portion 2 is arranged continuously in the second direction from one end edge 11 to the other end edge 12 . [Selection diagram] Fig. 1

Description

TECHNICAL FIELD The present invention relates to a foldable optical pressure-sensitive adhesive sheet.

Optical devices that can be repeatedly folded (foldable) are known. An optical device includes a plurality of optical members in order in the thickness direction. Optical members include, for example, pixel panels, touch panels, polarizing plates and cover films. Optical members adjacent in the thickness direction are adhered (bonded) using an optical adhesive sheet. The optical pressure-sensitive adhesive sheet is sometimes called a "foldable optical pressure-sensitive adhesive sheet" because the optical device is foldable.

For example, a foldable optical pressure-sensitive adhesive sheet that is uniform in the surface direction and flexible has been proposed (see, for example, Patent Document 1 below).

JP 2018-111754 A

A foldable optical pressure-sensitive adhesive sheet is required to have excellent workability. The workability is a property of being able to lift only one foldable optical pressure-sensitive adhesive sheet from a laminate obtained by laminating a plurality of foldable optical pressure-sensitive adhesive sheets in the thickness direction.

In addition, the foldable optical pressure-sensitive adhesive sheet is required to have excellent workability. Processability is a property that allows the foldable optical pressure-sensitive adhesive sheet to be reliably processed into a desired size and/or shape. Processing includes cutting. Workability is also a property that the cut surface is smooth.

The present invention provides a foldable optical pressure-sensitive adhesive sheet that is excellent in workability and processability and has foldability.

The present invention (1) has a shape extending in a first direction orthogonal to the thickness direction, has one edge and the other edge in a second direction orthogonal to the thickness direction and the first direction, and has a soft portion and two hard portions arranged adjacent to both sides of the soft portion in the first direction and harder than the soft portion, the soft portion extending in the second direction from the one edge to the other edge. It includes a foldable optical adhesive sheet arranged continuously.

Since this foldable optical pressure-sensitive adhesive sheet has two hard portions, it is excellent in workability and workability.

This foldable optical pressure-sensitive adhesive sheet has a soft portion. Therefore, the foldable optical pressure-sensitive adhesive sheet can be bent along the soft portion. As a result, the foldable optical pressure-sensitive adhesive sheet has foldability.

The present invention (2) includes the foldable optical pressure-sensitive adhesive sheet according to (1), wherein the soft portion has a substantially linear shape from the one end edge to the other end edge.

The present invention (3) is for foldable according to (1) or (2), wherein the length of the soft portion in the first direction is shorter than the length of each of the two hard portions in the first direction. Includes optical adhesive sheet.

According to the present invention (4), the foldable optical system according to any one of (1) to (3), wherein the fluctuation rate of the total light transmittance of the soft portion obtained by the following formula is 5% or less. Includes adhesive sheet.

Variation rate (%) of total light transmittance of the soft portion =|T1−T0|/T0×100
T1: total light transmittance of the soft portion after the following bending test T0: total light transmittance of the soft portion before the following bending test Bending test: centering on the soft portion, the two hard portions The foldable optical pressure-sensitive adhesive sheets are bent 1,000 times so as to approach each other.

The present invention (5) comprises a boundary region including a boundary between the soft portion and the hard portion, and in the boundary region, the material of the soft portion progresses in the first direction from the soft portion toward the hard portion. The optical pressure-sensitive adhesive sheet for foldable according to any one of (1) to (4), in which the concentration of is gradually decreased.

The foldable optical pressure-sensitive adhesive sheet of the present invention has foldability while being excellent in workability and workability.

1A and 1B show an embodiment of the foldable optical pressure-sensitive adhesive sheet of the present invention. FIG. 1A is a plan view. FIG. 1B is a cross-sectional view. FIG. 2 is a cross-sectional view of a coater used in the first method. FIG. 3 shows a step of arranging two kinds of pressure-sensitive adhesive compositions in a lump in the first method. FIG. 4 shows the step of exposing the adhesive composition to active energy rays through a photomask in the second method. FIG. 5 shows a state in which the foldable optical pressure-sensitive adhesive sheet is bent at the soft portion. FIG. 6 is a plan view of a foldable optical pressure-sensitive adhesive sheet of a modified example. FIG. 7 is a cross-sectional view of a foldable optical pressure-sensitive adhesive sheet of a modification. 8 is a graph showing the peel force in the peel test of the foldable optical pressure-sensitive adhesive sheet of Example 1. FIG. 9 shows the IR spectrum of the foldable optical pressure-sensitive adhesive sheet of Example 1. FIG. Figures 10A-10C illustrate workability testing. FIG. 10A is a cross-sectional view of the sample. FIG. 10B shows a mode in which only one release sheet-attached pressure-sensitive adhesive sheet is lifted. FIG. 10C shows a mode in which a plurality of pressure-sensitive adhesive sheets with release sheets are lifted. Figures 11A to 11C illustrate workability testing. FIG. 11A is a plan view of cutting a pressure-sensitive adhesive sheet with a release sheet to prepare a sample. FIG. 11B is an embodiment in which the cut portion of the sample contains a defect. FIG. 11C shows an aspect in which the cut portion of the sample includes protrusion.

1. One Embodiment of Foldable Optical Adhesive Sheet One embodiment of the foldable optical adhesive sheet of the present invention will be described with reference to FIGS. 1A and 1B.

As shown in FIGS. 1A and 1B, the foldable optical adhesive sheet 1 has a shape extending in the first direction. The first direction is orthogonal to the thickness direction. The foldable optical adhesive sheet 1 has, for example, the same thickness in the first direction. In addition, the foldable optical adhesive sheet 1 has one edge 11 and the other edge 12 in the second direction. The second direction is orthogonal to the thickness direction and the first direction. In this embodiment, the foldable optical adhesive sheet 1 has a substantially rectangular shape in plan view. In this embodiment, one edge 11 is spaced apart from the other edge 12 in the second direction.

A foldable optical adhesive sheet 1 includes a soft portion 2 and two hard portions 3 . In the foldable optical pressure-sensitive adhesive sheet 1, one hard portion 3, a soft portion 2, and another hard portion 3 are arranged in order in the first direction. In addition, in FIGS. 1A and 1B, the boundary 40 between the soft portion 2 and the hard portion 3 is drawn with a solid line, but the boundary 40 does not have to be visually observed in practice.

1.1 Soft part 2
The soft portion 2 is continuously arranged in the second direction from one edge 11 to the other edge 12 of the foldable optical adhesive sheet 1 . In this embodiment, the soft portion 2 is arranged substantially in the middle in the first direction. Moreover, preferably, the soft portion 2 has a substantially linear shape extending from one edge 11 to the other edge 12 of the foldable optical adhesive sheet 1 .

1.1.1 Size of Soft Part 2 The size of the soft part 2 is not limited. The length L1 of the soft portion 2 in the first direction is, for example, 30 mm or less, preferably 20 mm or less, more preferably 15 mm or less, and is, for example, 2 mm or more. The thickness of the soft portion 2 is, for example, 1 μm or more, preferably 10 μm or more, and is, for example, 1,000 μm or less, preferably 100 μm or less.

1.1.2 Storage shear modulus G' of the soft portion 2
The storage shear modulus G′ of the soft portion 2 at 25° C. is, for example, less than 150 kPa, preferably 140 kPa or less, more preferably 130 kPa or less, still more preferably 125 kPa or less, and for example, 1 kPa or more, preferably is 10 kPa or more. The storage shear modulus G′ of the soft part 2 at 25° C. is measured in a temperature range of −50° C. to 150° C., a heating rate of 5° C./min, a frequency of 1 Hz, and a shear mode (torsion mode). obtained by dynamic viscoelasticity measurement.

If the storage shear elastic modulus G′ of the soft portion 2 is equal to or less than the above upper limit, the soft portion 2 can be reliably made softer than the two hard portions 3 .

1.1.3 Breaking elongation of the soft part 2 The breaking elongation of the soft part 2 at 25°C is, for example, 800% or more, preferably 1,000% or more, more preferably 1,500% or more, and still more preferably , 1,750% or more and, for example, 10,000% or less. The breaking elongation of the soft portion 2 is obtained from the stress-strain curve. The stress-strain curve is obtained by pulling the foldable optical pressure-sensitive adhesive sheet 1 at a speed of 300 mm/min.

If the elongation at break of the soft portion 2 is equal to or higher than the above-described lower limit, the soft portion 2 can be reliably made softer than the two hard portions 3 .

1.1.4 Maximum stress of soft portion 2 The maximum stress of the soft portion 2 at 25°C is not limited. The maximum stress of the soft portion 2 at 25° C. is, for example, 100 kPa or more, preferably 500 kPa or more, more preferably 1,000 kPa or more, and for example, 10,000 kPa or less, preferably 5,000 kPa or less, More preferably, it is 2,000 kPa or less. The maximum stress of the soft portion 2 is obtained from the stress-strain curve. The stress-strain curve is obtained by pulling the foldable optical pressure-sensitive adhesive sheet 1 at a speed of 300 mm/min.

1.1.5 Variation rate of total light transmittance of soft portion 2 The variation rate of the total light transmittance of the soft portion 2 obtained by the following formula is, for example, 5% or less, preferably 4% or less, more preferably , 3% or less, more preferably 2% or less, particularly preferably 1% or less, and most preferably 0.1% or less. The lower limit of the fluctuation rate of the total light transmittance of the soft portion 2 is not limited. The lower limit of the fluctuation rate of the total light transmittance of the soft portion 2 is, for example, 0.0%.

Variation rate (%) of total light transmittance of soft portion 2 =|T1−T0|/T0×100
T1: total light transmittance of the soft portion 2 after the following bending test T0: total light transmittance of the soft portion 2 before the following bending test

Bending test: As shown in FIG. 5, the foldable optical pressure-sensitive adhesive sheet is bent 1,000 times so that the two hard portions 3 (described later) come closer to each other with the soft portion 2 as the center. Details of the flex test are described in later examples.

The total light transmittance of the soft portion 2 is measured based on JIS K 7375 (2008).

If the fluctuation rate is equal to or less than the upper limit, the optical properties of the soft portion 2 after repeated bending are excellent.

The total light transmittance of the soft portion 2 before the bending test is, for example, 60% or more, preferably 80% or more, more preferably 85% or more, and for example, 100% or less. If the total light transmittance of the soft portion 2 is equal to or higher than the above lower limit, the optical properties of the soft portion 2 are excellent.

1.1.6 Haze of Soft Part 2 The haze of the soft part 2 is 3% or less, preferably 2% or less, more preferably 1% or less, and is, for example, 0% or more. The haze of the soft portion 2 is measured using a haze meter based on JIS K7136 (2000). If the haze of the soft portion 2 is equal to or less than the upper limit described above, the optical properties of the soft portion 2 are excellent.

The soft portion 2 contains a base polymer. Details of the base polymer will be described later.

1.2 Hard part 3
Two hard portions 3 are arranged adjacent to both sides of the soft portion 2 in the first direction. In this embodiment, each of the two rigid portions 3 is continuously arranged in the second direction from one edge 11 to the other edge 12 of the foldable optical adhesive sheet 1 . In this embodiment, each of the two rigid portions 3 has a substantially rectangular shape in plan view.

1.2.1 Size of each of rigid portions 3 The size of each of the two rigid portions 3 is not limited. The length L2 of each of the two hard portions 3 in the first direction is longer than the length L1 of the soft portion 2 in the first direction, for example. In other words, the length L1 of the soft portion 2 in the first direction is shorter than the length L2 of each of the two hard portions 3 in the first direction. When the length L1 of the soft portion 2 in the first direction is shorter than the length L2 of each of the two hard portions 3 in the first direction, workability and workability are sufficiently ensured, and foldability is improved. can be secured.

The ratio (L1/L2) of the length L1 of the soft portion 2 to the length L2 of the hard portion 3 is, for example, 0.75 or less, preferably 0.5 or less, more preferably 0.25 or less, Moreover, it is 0.001 or more, for example.

The value obtained by subtracting the length L1 of the soft portion 2 from the length L2 of the hard portion 3 (L2-L1) is, for example, 10 mm or more, preferably 30 mm or more, more preferably 50 mm or more. 298 mm or less.

Specifically, the length L2 of the hard portion 3 is, for example, 40 mm or more and, for example, 300 mm or less.

1.2.2 Hardness of Hard Part 3 Each of the two hard parts 3 is harder than the soft part 2 .

In this embodiment, the storage shear modulus G' of each of the two hard portions 3 at 25°C is higher than the storage shear modulus G' of the soft portion 2 at 25°C, for example. When the storage shear modulus G′ at 25° C. of each of the two hard portions 3 is higher than the storage shear modulus G′ of the soft portion 2 at 25° C., the foldable optical pressure-sensitive adhesive sheet 1 has poor workability and It has foldability while being excellent in workability. The storage shear modulus G′ of the hard part 3 at 25° C. is measured in a temperature range of −50° C. to 150° C., a heating rate of 5° C./min, a frequency of 1 Hz, and a shear mode (torsion mode). obtained by dynamic viscoelasticity measurement.

Specifically, the storage shear elastic modulus G′ at 25° C. of each of the two hard portions 3 is, for example, 150 kPa or more, preferably 175 kPa or more, more preferably 200 kPa or more. 000 kPa or less.

The ratio of the storage shear modulus G' at 25°C of the soft portion 2 to the storage shear modulus G' at 25°C of each of the two hard portions 3 (the storage shear modulus G' of the soft portion 2/the ratio of the storage shear modulus G' of the hard portion 3 The storage shear modulus G′) is, for example, 0.9 or less, preferably 0.8 or less, more preferably 0.7 or less, and for example, 0.01 or more, preferably 0.03. That's it.

If the above ratio is equal to or less than the above upper limit, the soft portion 2 can be made sufficiently softer than the hard portion 3, and therefore the foldable optical pressure-sensitive adhesive sheet 1 is excellent in foldability. If the above ratio is equal to or higher than the above lower limit, it is possible to suppress the soft portion 2 from becoming excessively soft, and it is possible to suppress the hard portion 3 from becoming excessively hard, and therefore workability and workability are excellent.

The elongation at break of each of the two hard portions 3 at 25°C is smaller than the elongation at break of the soft portion 2 at 25°C. When the breaking elongation at 25° C. of each of the two hard portions 3 is smaller than the breaking elongation of the soft portion 2 at 25° C., the foldable optical pressure-sensitive adhesive sheet 1 is excellent in workability and workability and is foldable. have sex.

Specifically, the breaking elongation at 25° C. of each of the two hard portions 3 is, for example, 750% or less, preferably 700% or less, more preferably 650% or less, and, for example, 150% or more. , preferably 200% or more.

The ratio of the breaking elongation at 25°C of the soft portion 2 to the breaking elongation at 25°C of each of the two hard portions 3 (breaking elongation of the soft portion 2/breaking elongation of the hard portion 3) is, for example, 1.2 or more, It is preferably 1.5 or more, more preferably 2.0 or more, still more preferably 2.5 or more, and is, for example, 100 or less, preferably 10 or less.

If the above ratio is equal to or higher than the above lower limit, the soft portion 2 can be made sufficiently softer than the hard portion 3, and therefore the foldable optical pressure-sensitive adhesive sheet 1 is excellent in foldability. If the above ratio is equal to or less than the above upper limit, it is possible to prevent the soft portion 2 from becoming excessively soft, and it is possible to prevent the hard portion 3 from becoming excessively hard, and therefore workability and workability are excellent.

The elongation at break of each of the two hard portions 3 is obtained in the same manner as that of the soft portion 2 .

1.2.3 Maximum stress of hard part 3 The maximum stress at 25° C. of each of the two hard parts 3 is not limited. The maximum stress of the hard portion 3 at 25° C. is, for example, 250 kPa or more, preferably 500 kPa or more, more preferably 700 kPa or more, and for example, 1,500 kPa or less, preferably 1,000 kPa or less, more preferably. is 900 kPa or less. The maximum stress for each of the two hard parts 3 is determined in the same way as for the soft part 2 .

1.2.4 Thickness, Total Light Transmittance and Haze of Hard Part 3 The thickness, total light transmittance and haze of each of the two hard parts 3 are the same as those of the soft part 2 described above.

The hard portion 3 contains a base polymer.

1.3 Base Polymer, etc. Next, the base polymer commonly contained in the soft portion 2 and the hard portion 3 will be described, and the components that differ between the soft portion 2 and the hard portion 3 will be described.

The base polymer is an adhesive component that makes the foldable optical adhesive sheet 1 exhibit adhesiveness. Examples of the base polymer include base polymers described in JP-A-2018-111754, preferably acrylic polymers.

1.3.1 Acrylic polymer Acrylic polymer is a polymer of monomer components containing 50% by mass or more of (meth)acrylic acid alkyl ester. "(Meth)acrylic acid" means acrylic acid and/or methacrylic acid. That is, the monomer component contains (meth)acrylic acid alkyl ester as a main component. In other words, the (meth)acrylic acid alkyl ester is the main component of the monomer component.

A (meth)acrylic acid alkyl ester is a monofunctional monomer since it has one functional group. Examples of (meth)acrylic acid alkyl esters include (meth)acrylic acid alkyl esters in which the alkyl group has from 1 to 20 carbon atoms. Examples of the (meth)acrylic acid alkyl esters described above include (meth)acrylic acid alkyl esters described in JP-A-2018-111754.

The (meth)acrylic acid alkyl ester for polymerizing the base polymer contained in the soft portion 2 preferably includes a (meth)acrylic acid alkyl ester having 3 to 20 carbon atoms, and more preferably a (meth)acrylic acid alkyl ester having 3 to 20 carbon atoms. 7 or more and 15 or less (meth)acrylic acid alkyl esters are mentioned. Specific examples include butyl (meth)acrylate (BA/BMA), 2-ethylhexyl (meth)acrylate (2EHA/2EHMA), and lauryl (meth)acrylate (LA/LMA). The (meth)acrylic acid alkyl ester described above may be referred to as the first (meth)acrylic acid alkyl ester.

The (meth)acrylic acid alkyl ester for polymerizing the base polymer contained in the hard portion 3 preferably includes a (meth)acrylic acid alkyl ester having 6 to 20 carbon atoms, and more preferably a (meth)acrylic acid alkyl ester having 6 to 20 carbon atoms. Examples thereof include (meth)acrylic acid alkyl esters having 7 to 18 carbon atoms, and more preferably, (meth)acrylic acid alkyl esters having 8 to 15 carbon atoms. Specific examples include 2-ethylhexyl (meth)acrylate (2EHA/2EHMA). The (meth)acrylic acid alkyl ester described above may be referred to as a second (meth)acrylic acid alkyl ester.

The proportion of the (meth)acrylic acid alkyl ester in the monomer component is, for example, 50% by mass or more, preferably 55% by mass or more, more preferably 60% by mass or more, and is, for example, 99% by mass or less.

1.3.2 Copolymerizable Monomer The monomer component may contain a copolymerizable monomer copolymerizable with the (meth)acrylic acid alkyl ester. Examples of copolymerizable monomers include polar group-containing monomers.

Polar group-containing monomers include polar group-containing monomers described in JP-A-2018-111754, preferably nitrogen atom-containing ring-containing monomers and hydroxy group-containing monomers. Nitrogen atom-containing ring-containing monomers include, for example, N-vinyl-2-pyrrolidone (NVP). Examples of hydroxy group-containing monomers include 4-hydroxybutyl (meth)acrylate (HBA/HBMA).

The ratio of the polar group-containing monomer in the monomer component is, for example, 0.1% by mass or more, preferably 0.3% by mass or more, and is, for example, 30% by mass or less, preferably 20% by mass or less. .

1.4 Boundary area 4
In this embodiment, as shown in FIGS. 1A and 1B, the foldable optical pressure-sensitive adhesive sheet 1 further includes a boundary region 4 indicated by a dashed line. The boundary region 4 includes a boundary 40 indicated by a solid line between the soft portion 2 and the hard portion 3 in plan view. The boundary region 4 is arranged continuously in the second direction from one edge 11 to the other edge 12 of the foldable optical adhesive sheet 1 . Specifically, the boundary region 4 includes a first boundary region 4A including a boundary 40 between the soft portion 2 and the hard portion 3 arranged on one side in the first direction, the soft portion 2, and the first boundary region 4A. and a second boundary region 4B including a boundary 40 with the hard portion 3 arranged on the other side in one direction.

In each of the two boundary regions 4 , the concentration of the material in the soft portion 2 gradually decreases in the first direction from the soft portion 2 to the hard portion 3 . For example, when the soft portion 2 contains the first (meth)acrylic acid alkyl ester polymer and the hard portion 3 contains the second (meth)acrylic acid alkyl ester polymer, in the boundary region 4, the second The polymer concentration of the (meth)acrylic acid alkyl ester of 1 gradually decreases in the first direction from the soft portion 2 to the hard portion 3 . That is, the boundary region 4 has a gradient of the polymer concentration of the first (meth)acrylic acid alkyl ester described above.

Therefore, the boundary area 4 is the area from the point where the gradient of concentration starts to the point where the gradient ends.

In the present embodiment, the length L1 of the soft portion 2 in the first direction is between the midpoint of the first boundary region 4A in the first direction and the midpoint of the second boundary region 4B in the first direction. can be defined as distance. The starting points of the length L2 of the two hard portions 3 in the first direction are respectively the midpoint of the first boundary region 4A and the midpoint of the second boundary region 4B in the first direction. can do.

Further, in the present embodiment, the physical properties of the soft portion 2 and the hard portion 3 (storage shear elastic modulus G′, elongation at break, maximum stress, total light transmittance, change in total light transmittance) are (for example, the central portion in the first direction).

1.5 Method for Producing Foldable Optical Adhesive Sheet 1 Next, a method for producing the foldable optical adhesive sheet 1 will be described. A manufacturing method is not limited. The manufacturing method includes, for example, the first method to the third method.

1.5.1 First Method In the first method, two types of adhesive compositions are applied to the surface of the release sheet 5 at the same time.

Examples of the release sheet 5 include a plastic sheet. Specifically, the release sheet 5 includes a plastic sheet described in JP-A-2018-111754. In this embodiment, the release sheet 5 has a substantially rectangular shape in plan view.

The two types of adhesive compositions are the first adhesive composition and the second adhesive composition.

The first adhesive composition is the material for the soft portion 2 described above. The first pressure-sensitive adhesive composition contains a first (meth)acrylic acid alkyl ester polymer (containing BA as a main component).

The second adhesive composition is the material for the hard portion 3 described above. The second adhesive composition contains a second (meth)acrylic acid alkyl ester polymer (containing 2EHA as a main component).

In addition to the base polymer, the first and second pressure-sensitive adhesive compositions can further contain at least one component selected from the group consisting of oligomers, cross-linking agents, and silane coupling agents. Examples of oligomers include acrylic oligomers described in JP-A-2021-055076. The cross-linking agent includes cross-linking agents described in JP-A-2018-111754, preferably isocyanate cross-linking agents and peroxide cross-linking agents. Examples of the silane coupling agent include silane coupling agents described in JP-A-2018-111754, and preferably epoxy silane coupling agents. The blending amount of each component described above is, for example, 0.01 parts by mass or more and, for example, 1 part by mass or less with respect to 100 parts by mass of the base polymer.

In addition to the components described above, additives can be added to the pressure-sensitive adhesive composition in an appropriate proportion. Additives include, for example, tackifiers, antidegradants, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents.

A coating method is not limited. Examples of coating methods include 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. mentioned.

In the coating described above, for example, as shown in FIG. 2, a coater 6 having a partition 61 is used.

The coater 6 has a discharge port 62 . The outlet 62 extends in the first direction.

Two partitions 61 are arranged in the coater 6 . The two partitions 61 are spaced apart from each other in the first direction. The two partitions 61 partition the ejection port 62 into three regions.

The three regions include a central region 71 and two side regions 72 . A central region 71 corresponds to the soft portion 2 . The two side regions 72 correspond to the two rigid portions 3 .

The coater 6 can simultaneously eject the first adhesive composition from the central region 71 and the second adhesive composition from the both side regions 72 .

Next, the coater 6 is relatively moved in the second direction (see FIG. 1A) with respect to the release sheet 5 while simultaneously discharging the first pressure-sensitive adhesive composition and the second pressure-sensitive adhesive composition from the coater 6 . Thereby, a coating film composed of the first and second pressure-sensitive adhesive compositions is formed.

After that, the coating films (first and second adhesive compositions) are dried. The drying temperature is, for example, 50°C to 200°C. The drying time is, for example, 5 seconds to 20 minutes.

As a result, the foldable optical adhesive sheet 1 having the soft portion 2 and the two hard portions 3 on the surface of the release sheet 5 is manufactured.

As another coating method, as shown in FIG. 3, one lump 51 made of the first pressure-sensitive adhesive composition and the second pressure-sensitive adhesive composition are placed on one end of the surface of the release sheet 5 in the second direction. Two masses 52 of objects are arranged with a relatively large thickness. After that, a method of moving the bar 9 from one end toward the other end in the first direction is also available. The bar 9 extends along the first direction. This also produces the foldable optical pressure-sensitive adhesive sheet 1 having the soft portion 2 and two hard portions 3 .

In the boundary region 4 of the foldable optical pressure-sensitive adhesive sheet 1 produced by the first method, the polymer of the first (meth)acrylic acid alkyl ester in the first pressure-sensitive adhesive composition is the polymer of the second pressure-sensitive adhesive composition. with the polymer of the second (meth)acrylic acid alkyl ester in (mutual migration). Therefore, in the boundary region 4 , the concentration of the first (meth)acrylic acid alkyl ester polymer gradually decreases in the first direction from the soft portion 2 toward the hard portion 3 .

1.5.2 Second Method The second method comprises a first step and a second step. A 1st process and a 2nd process are implemented in order.

1.5.2.1 First Step In the first step, first, the pressure-sensitive adhesive composition is applied to the surface of the release sheet 5 . Thereby, a coating film made of the pressure-sensitive adhesive composition is formed. The coating is homogeneous over the first direction.

1.5.2.2 Second step In the second step, the modifying agent is blended by coating (added later) to part of the coating film. For example, modifiers include, for example, polyfunctional monomers and plasticizers.

1.5.2.3 Polyfunctional monomer The polyfunctional monomer is blended in both the first pressure-sensitive adhesive composition and the second pressure-sensitive adhesive composition, and the proportion of the polyfunctional monomer in the first pressure-sensitive adhesive composition is It is lower than the mixing ratio of the polyfunctional monomer to the second pressure-sensitive adhesive composition. As a result, more cross-linked structures are introduced into the hard portion 3 than the soft portion 2 , making the hard portion 3 harder than the soft portion 2 . Therefore, the polyfunctional monomer is blended (post-added) in the coating film (adhesive composition) for forming the hard portion 3 .

Polyfunctional monomers include, for example, polyfunctional (meth)acrylates. A polyfunctional (meth)acrylate contains, for example, two or more ethylenically unsaturated double bonds in one molecule. Polyfunctional (meth)acrylates include bifunctional (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 (also known as hexamethylenediol di(meth)acrylate), 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, neopentyl glycol di(meth)acrylate, and di(meth)acryloyl Isocyanurate can be mentioned.

Trifunctional (meth)acrylates include, for example, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and tris((meth)acryloyloxyethyl)isocyanurate.

Tetrafunctional or higher polyfunctional (meth)acrylates include, for example, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, and dipentaerythritol hexa( meth)acrylates.

The amount of the polyfunctional monomer blended in the first pressure-sensitive adhesive composition (soft part 2) is, for example, 0.2 parts by mass or less, preferably 0.1 parts by mass, with respect to 100 parts by mass of the base polymer. Below, it is more preferably 0.05 parts by mass or less, and for example, it is 0 parts by mass or more, preferably 0.005 parts by mass or more. The amount of the polyfunctional monomer blended in the second PSA composition (hard portion 3) is, for example, more than 0.2 parts by mass, preferably 0.25 parts by mass, with respect to 100 parts by mass of the base polymer. or more, and for example, 2 parts by mass or less, preferably 1 part by mass or less. The ratio of the amount of the polyfunctional monomer blended in the second pressure-sensitive adhesive composition to the amount of the polyfunctional monomer blended in the first pressure-sensitive adhesive composition is, for example, 2 or more, preferably 5 or more. Yes, and for example, 100 or less, preferably 50 or less.

1.5.2.4 Plasticizer A plasticizer is a component that makes the soft portion 2 softer than the hard portion 3 . Therefore, the plasticizer is blended (post-added) in the coating film (adhesive composition) for forming the soft portion 2 . Plasticizers include, for example, phthalates and adipates. Phthalates include, for example, dioctyl phthalate and dioctyl tin laurate. Adipate esters include, for example, dioctyl adipate and diisononyl adipate. The ratio of the plasticizer is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, and for example, 30 parts by mass or less, preferably 20 parts by mass, with respect to 100 parts by mass of the monomer component. It is below the department.

For example, the coater 6 shown in FIG. 2 is used in the coating of the second step. The modifier described above is overcoated onto the coating film described above. Overcoating allows the modifier to enter the interior of the coating.

Specifically, if the modifier is a polyfunctional monomer, the polyfunctional monomer is discharged from both side regions 72 . If the modifier is a plasticizer, the plasticizer is expelled from central region 71 . If the modifier is a multifunctional monomer and a plasticizer, the multifunctional monomer is expelled from both side regions 72 and the plasticizer is expelled from the central region 71 .

In a second step, the polyfunctional monomer is then reacted if the modifier comprises a polyfunctional monomer. Reaction methods include, for example, heating and ultraviolet irradiation. Thereby, the hard portion 3 contains a crosslinked structure.

As a result, the foldable optical pressure-sensitive adhesive sheet 1 having the soft portion 2 and two hard portions 3 is manufactured.

1.5.2.5 Concentration of Materials in Soft Section 2, Hard Section 3 and Border Region 4 In the second method, when the modifier is a polyfunctional monomer, the adhesive composition corresponding to hard section 3 The product contains polyfunctional monomers in addition to (meth)acrylic acid alkyl esters (monofunctional monomers). On the other hand, the pressure-sensitive adhesive composition corresponding to the soft portion 2 does not contain a polyfunctional monomer, but contains a (meth)acrylic acid alkyl ester (monofunctional monomer). Therefore, the concentration of the monofunctional monomer polymer in the soft portion 2 is higher than the concentration of the monofunctional monomer polymer in the hard portion 3 .

In the boundary region 4 of the foldable optical pressure-sensitive adhesive sheet 1 produced by the second method in which the modifier is a polyfunctional monomer, the concentration of the (meth)acrylic acid alkyl ester polymer of the first pressure-sensitive adhesive composition is , gradually decreases in the first direction from the soft portion 2 to the hard portion 3 . Also, in the boundary region 4 , the concentration of the crosslinked structure gradually increases in the first direction from the soft portion 2 toward the hard portion 3 .

In the boundary region 4 of the foldable optical pressure-sensitive adhesive sheet 1 manufactured by the second method in which the modifier is a plasticizer, in the boundary region 4, the concentration of the plasticizer increases from the soft portion 2 toward the hard portion 3. It gradually decreases in one direction.

1.5.3 Third Method The third method comprises a third step and a fourth step. A 3rd process and a 4th process are implemented in order.

1.5.3.1 Third Step In the third step, the surface of the release sheet 5 is coated with the adhesive composition. The applied adhesive composition is homogeneous over the first direction. The coating film (adhesive composition) has a component and/or molecular structure that can react with active energy rays. Active energy rays include, for example, ultraviolet rays. Examples of the above-described components include the above-described polyfunctional monomers. The proportion of polyfunctional monomer is not limited.

1.5.3.2 Fourth Step As shown in FIG. 4 , in the fourth step, the coating film (adhesive composition) is irradiated (exposed) with an active energy ray through a photomask 10 .

The photomask 10 has a light shielding portion 101 and two light transmitting portions 102 . The light shielding part 101 has the same pattern as the soft part 2 . The translucent part 102 has the same pattern as the two rigid parts 3 .

The active energy rays that have passed through the two translucent portions 102 act on the above-described components in the coating film (adhesive composition), and the above-described components react to harden the hard portion 3 .

On the other hand, active energy rays do not pass through the light shielding portion 101 . Therefore, the soft portion 2 corresponding to the light shielding portion 101 does not harden and remains soft.

As a result, the foldable optical pressure-sensitive adhesive sheet 1 having the soft portion 2 and two hard portions 3 is manufactured.

1.5 Applications This foldable optical pressure-sensitive adhesive sheet 1 is used for bonding optical members. Examples of optical members include pixel panels, touch panels, polarizing plates and cover films.

Before and/or after the bonding described above, the foldable optical pressure-sensitive adhesive sheet 1 is processed into a predetermined shape and/or size.

The foldable optical pressure-sensitive adhesive sheet 1 and the optical member are provided in an optical device. This optical device can be repeatedly bent and used. At that time, as shown in FIG. 5, the foldable optical pressure-sensitive adhesive sheet 1 is folded along the soft portion 2 so that the two hard portions 3 come closer to each other.

2. Effect of foldable optical pressure-sensitive adhesive sheet 1 Since this foldable optical pressure-sensitive adhesive sheet 1 has two rigid portions 3, it is excellent in workability and workability.

In addition, the foldable optical pressure-sensitive adhesive sheet 1 has a soft portion 2 . Therefore, the foldable optical adhesive sheet 1 can be bent along the soft portion 2 . As a result, the foldable optical pressure-sensitive adhesive sheet 1 has foldability.

Since the soft portion 2 has a substantially linear shape from one edge 11 to the other edge 12 of the foldable optical adhesive sheet 1 , the foldable optical adhesive sheet 1 can be easily and reliably bent along the soft portion 2 . .

Since the fluctuation rate of the total light transmittance of the soft portion 2 is 5% or less, the optical properties of the soft portion 2 are excellent.

If the length L1 of the soft portion 2 in the first direction is shorter than the length L2 of each of the two hard portions 3 in the first direction, the foldable optical pressure-sensitive adhesive sheet 1 sufficiently secures workability and processability. The foldability can be ensured while doing so.

3. Modifications In each modification below, the same reference numerals are given to the same members and steps as in the above-described embodiment, and detailed description thereof will be omitted. Moreover, each modification can have the same effects as the one embodiment, unless otherwise specified. Furthermore, one embodiment and modifications can be combined as appropriate.

In the modified example, in the boundary region 4 of the foldable optical adhesive sheet 1, the concentration of the material of the soft portion 2 changes discontinuously. Note that a boundary 40 is clearly formed. Specifically, the material of the soft portion 2 does not exist on one side in the first direction from the boundary 40 between the soft portion 2 and the hard portion 3 arranged on one side in the first direction. The material of the hard portion 3 does not exist on the other side of the boundary 40 in the first direction.

As the method for producing the optical pressure-sensitive adhesive sheet 1 for foldables, the second method and the third method are preferable, and the third method is more preferable. Since the above-described method can suppress the migration that tends to occur in the first method, it is possible to suppress the concentration of the material of the soft portion 2 from gradually decreasing toward the hard portion 3 .

When contrasting the one embodiment with the modification, one embodiment is preferred. In one embodiment, interfacial separation at the boundary 40 due to the concentration gradient described above can be suppressed. Interfacial delamination is separation of the hard portion 3 from the soft portion 2 and separation of the soft portion 2 from the hard portion 3 when stress is applied to the boundary 40 when the foldable optical pressure-sensitive adhesive sheet 1 is bent. including doing

As shown in FIG. 6 , one edge 11 in the second direction of the foldable optical adhesive sheet 1 has a first concave portion 13 . The first recessed portion 13 is recessed toward the other side in the second direction. A bottom portion of the first recess 13 forms one edge 11 of the soft portion 2 .

The other edge 12 in the second direction of the foldable optical adhesive sheet 1 has a second concave portion 14 . The second recessed portion 14 is recessed toward one side in the second direction. The bottom of the second recess 14 forms the other edge 12 of the soft portion 2 .

In the case of the foldable optical pressure-sensitive adhesive sheet 1 shown in FIG. 6, the soft portion 2 has the first concave portion 13 and the second concave portion 14, so that the one end edge 11 and the other end edge 12 of the soft portion 2 in the first direction It is possible to further suppress deterioration in workability due to contact with other members. That is, the foldable optical pressure-sensitive adhesive sheet 1 shown in FIG. 6 is even more excellent in workability.

As shown in FIG. 7 , the foldable optical adhesive sheet 1 may have a plurality (two or more) of soft portions 2 . The foldable optical pressure-sensitive adhesive sheet 1 may have three or more soft portions 2 .
The soft portions 2 and the hard portions 3 are alternately arranged in the first direction. Hard portions 3 are arranged on both ends of the foldable optical pressure-sensitive adhesive sheet 1 in the first direction. Therefore, if the number of soft portions 2 is n (positive number of 2 or more), the number of hard portions 3 is n+1 (positive number of 2 or more).

According to this modification, the foldable optical adhesive sheet 1 can be wound around a roll. When the foldable optical pressure-sensitive adhesive sheet 1 is wound around a roll, the foldable optical pressure-sensitive adhesive sheet 1 is wound so that both ends in the first direction are close to each other.

Although not shown, the soft portion 2 may have a curved shape. Curved shapes include curved shapes.

The hardness of the two hard parts 3 may be different. For example, one hard portion 3 is harder than the other hard portion 3 . Even in this case, hard portion 3 is harder than soft portion 2 . That is, the soft portion 2, the other hard portion 3, and the one hard portion 3 are harder in this order.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. The invention is not limited to the examples. In addition, the specific numerical values such as the compounding amount (content), physical property values, parameters, etc. described below are the corresponding compounding amounts ( content), physical property values, parameters, etc., upper limits (values defined as “more than” or “less than”) or lower limits (values defined as “less than” or “greater than”).

<Preparation of base polymer>
Preparation example 1
Butyl acrylate (BA) 80 parts by mass, 4-hydroxybutyl acrylate (4HBA) 10 parts by mass, cyclohexyl acrylate (CHA) 10 parts by mass, 2,2-dimethoxy-1,2-diphenyl-1-one (trade name “Irgacure 651" manufactured by Ciba Japan Co., Ltd.) and 0.05 parts by mass of 1-hydroxy-cyclohexyl-phenyl-ketone (trade name "Irgacure 184" manufactured by Ciba Japan Co., Ltd.) were charged into a four-necked flask. A partially polymerized product (monomer syrup) having a polymerization rate of 10% was obtained by partially photopolymerizing the polymer by exposing it to ultraviolet rays in a nitrogen atmosphere.

Preparation example 2
2-ethylhexyl acrylate (2EHA) 62 parts by mass, lauryl acrylate (LA) 30 parts by mass, 4-hydroxybutyl acrylate (4HBA) 5 parts by mass, N-vinyl-2-pyrrolidone (NVP) 3 parts by mass, 2,2- 0.05 parts by weight of dimethoxy-1,2-diphenyl-1-one (trade name “Irgacure 651” manufactured by Ciba Japan) and 1-hydroxy-cyclohexyl-phenyl-ketone (trade name “Irgacure 184” Ciba Japan) Co., Ltd.) was put into a four-necked flask and partially photopolymerized by exposing it to ultraviolet rays in a nitrogen atmosphere to obtain a partial polymer (monomer syrup) with a polymerization rate of 8%. .

Preparation example 3
2-ethylhexyl acrylate (2EHA) 75 parts by mass, 4-hydroxybutyl acrylate (4HBA) 5 parts by mass, N-vinyl-2-pyrrolidone (NVP) 20 parts by mass, 2,2-dimethoxy-1,2-diphenyl-1 -On (trade name “Irgacure 651” manufactured by Ciba Japan) 0.05 parts by weight and 1-hydroxy-cyclohexyl-phenyl-ketone (trade name “Irgacure 184” manufactured by Ciba Japan) 0.05 parts by weight The mixture was placed in a four-necked flask and partially photopolymerized by exposure to ultraviolet rays in a nitrogen atmosphere to obtain a partially polymerized product (monomer syrup) having a polymerization rate of 12%.

The respective formulations of Preparation Examples 1 to 3 are transcribed in Table 1.

<Preparation of acrylic oligomer>
Preparation example 4
95 parts by mass of cyclohexyl methacrylate (CHMA), 5 parts by mass of acrylic acid (AA), and α-methyl as a chain transfer agent were mixed in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube. A mixture containing 10 parts by mass of styrene dimer and 120 parts by mass of toluene as a solvent was stirred at room temperature for 1 hour under a nitrogen atmosphere. After that, 10 parts by mass of 2,2′-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator is added to the mixture to prepare a reaction solution, which is reacted at 85° C. for 5 hours under a nitrogen atmosphere. (formation of acrylic oligomers). As a result, an oligomer solution containing an acrylic oligomer (solid concentration: 50% by mass) was obtained. The acrylic oligomer had a weight average molecular weight of 4,000. Moreover, the glass transition temperature (Tg) of the acrylic oligomer was 84°C.

<Preparation of first adhesive composition>
Preparation example 5
To 100 parts by mass of the polymer solution of Preparation Example 1, 0.01 part by mass of dipentaerythritol hexaacrylate was added and mixed to prepare a first adhesive composition.

<Preparation of second adhesive composition>
Preparation example 6
To 100 parts by mass of the polymer solution of Preparation Example 2, 0.1 part by mass of hexamethylenediol diacrylate was added and mixed to prepare a first adhesive composition.

Preparation Example 7
To 100 parts by mass of the polymer solution of Preparation Example 3, 0.3 parts by mass of hexamethylenediol diacrylate was added and mixed to prepare a second adhesive composition.

<Production of foldable optical adhesive sheet 1>

Example 1
A mass 51 composed of the first pressure-sensitive adhesive composition of Preparation Example 5 and a mass 52 composed of the second pressure-sensitive adhesive composition of Preparation Example 7 were arranged at one end of the release sheet 5 in the second direction. A mass 51 of 100 parts by volume was placed in the center of the release sheet 5 in the first direction, and two masses 52 of 250 parts by volume were placed on each end of the release sheet 5 in the first direction.

Thereafter, the first pressure-sensitive adhesive composition and the second pressure-sensitive adhesive composition were spread in the first direction by moving the bar 9 from one end toward the other end in the first direction.

Thus, the soft portion 2 containing a monomer component polymer containing n-butyl acrylate (BA) as a main component and a monomer component polymer containing 2-ethylhexyl acrylate (2EHA) as a main component are contained. A foldable optical pressure-sensitive adhesive sheet 1 having two rigid portions 3 was produced.

The length L1 of the soft portion 2 in the first direction was 10 mm. The length L2 of each of the two soft portions 3 in the first direction was 100 mm.

Example 2
A foldable optical pressure-sensitive adhesive sheet 1 was produced in the same manner as in Example 1. However, instead of the first pressure-sensitive adhesive composition of Preparation Example 5, the first pressure-sensitive adhesive composition of Preparation Example 6 was used.

Comparative example 1
A mass 51 of the first pressure-sensitive adhesive composition of Preparation Example 5 was placed in the center of the release sheet 5 in the first direction.

After that, the first pressure-sensitive adhesive composition was spread in the first direction by moving the bar 9 from one end to the other end in the first direction.

As a result, foldable optical adhesive sheet 1 containing the first adhesive composition of Preparation Example 5 was produced.

Comparative example 2
In the same manner as in Comparative Example 1, a foldable optical adhesive sheet 1 was produced. However, instead of the first pressure-sensitive adhesive composition of Preparation Example 5, the first pressure-sensitive adhesive composition of Preparation Example 6 was used.

Comparative example 3
In the same manner as in Comparative Example 1, a foldable optical adhesive sheet 1 was produced. However, instead of the first adhesive composition of Preparation Example 5, the second adhesive composition of Preparation Example 7 was used.

None of Comparative Examples 1 to 3 described above had both the soft portion 2 and the hard portion 3 .

The respective formulations of Examples 1 to 2 and Comparative Examples 1 to 3 are transcribed in Tables 1 and 3.

<Physical properties>
The following physical properties of the foldable optical pressure-sensitive adhesive sheets 1 of Examples 1 and 2 and Comparative Examples 1 and 3 were measured. Table 3 shows the results. Table 2 shows the physical properties of the pressure-sensitive adhesive composition, which is the material of the soft portion 2 and the hard portion 3 .

1. Storage shear elastic modulus G′ at 25° C. of the soft portion 2 and the hard portion 3
A sample sheet having a thickness of 50 μm was prepared from each of the first adhesive composition of Preparation Example 5, the first adhesive composition of Preparation Example 6, and the second adhesive composition of Preparation Example 7. A sample sheet of 30 mm wide by 80 mm long was then cut and rolled into a cylinder with a cross-sectional area of 40 mm ² . This was pulled at 300 mm/min by a universal tensile tester (Autograph AG-X manufactured by Shimadzu Corporation) to measure stress-strain. A stress-strain curve was obtained, and the maximum stress and elongation at break were determined.

2. Flexibility, total light transmittance, and variation thereof of the soft portion 2 A transparent polyimide film having a thickness of 75 μm was laminated to each of one side and the other side of the foldable optical adhesive sheet 1 in the thickness direction, and a strip of 100 mm × 20 mm was formed. A sample was prepared by cutting it out. Note that this sample has a soft portion 2 and a hard portion 3 . The sample was set in a no-load U-shaped stretch tester (“small tabletop durability tester DLMD111LHA” and “U-shaped stretch test jig” manufactured by Yuasa System Co., Ltd.), and a bending test was performed under the following conditions.

Environmental conditions: 25°C, 55% RH,
test speed: 60 rpm,
Bending radius: 3 mm,
Bending times: 1,000 times

Flexibility of the soft portion 2 was evaluated according to the following criteria.

A case where there was no peeling between the transparent polyimide film and the foldable optical pressure-sensitive adhesive sheet 1 was evaluated as ◯.
The case where peeling occurred between the transparent polyimide film and the foldable optical pressure-sensitive adhesive sheet 1 was evaluated as x.

The total light transmittance of the soft portion 2 before and after bending was obtained based on JIS K 7375 (2008).

3. Tensile Force and IR Measurement of Boundary Region 4 (1) Tensile Force A PET film having a thickness of 50 μm was adhered to one surface of the foldable optical adhesive sheet 1, and a sample of 25 mm width×100 mm was cut out along the first direction. After bonding the sample to the alkali glass, the sample was autoclaved under the conditions of 50° C., 0.5 MPa, and 15 minutes to sufficiently adhere the sample and the alkali glass. Thereafter, using a universal tensile tester (Autograph AG-X manufactured by Shimadzu Corporation), a peel test was performed along the first direction at a peel angle of 180 degrees and a peel speed of 30 mm/min to measure the tensile force. A graph of the peel force in the peel test of Example 1 is shown in FIG.

As can be seen from FIG. 8, the peeling force in the boundary region 4 gradually increases from the soft portion 2 toward the hard portion 3 .

(2) IR measurement Four points (P1, P2, P3, P4) (see white circles in FIG. 1A) in the boundary region 4 of the foldable optical pressure-sensitive adhesive sheet 1 and in the vicinity thereof were measured using the following apparatus and under the following conditions. was measured. Each of the four IR spectra are shown in FIG.

The IR measurement was performed by the ATR method (total reflection measurement method) (Ge crystal) using an FT-IR spectrophotometer manufactured by Thermo Fisher Scientific.

The soft portion 2 contains a polymer of monomer components having BA as a main component. The hard portion 3 contains a polymer of monomer components containing 2HEA as a main component.

Point P4 is located in hard portion 3 other than boundary region 4 . At point P4, two peaks were observed at 2850 cm ⁻¹ to 2900 cm ⁻¹ that are prominent in 2-ethylhexyl acrylate (2EHA). A point P1 is located on the soft portion 2 other than the boundary region 4 . At point P1, the above two peaks were not observed. Also, it can be seen that the second peak (right side) becomes smaller from point P3 toward point P2.

From the above, it can be seen that the concentration of the polymer of the monomer component containing 2-ethylhexyl acrylate (2EHA) as the main component decreases from the hard portion 3 toward the soft portion 2 in the boundary region 4 .

<Evaluation>
The following items were evaluated for each of the foldable optical pressure-sensitive adhesive sheets 1 of Examples 1 and 2 and Comparative Examples 1 and 3. Table 3 shows the results.

1. Workability A release-sheet-attached pressure-sensitive adhesive sheet 7 comprising a foldable optical pressure-sensitive adhesive sheet 1 and two release sheets 5 sandwiching the optical pressure-sensitive adhesive sheet 1 in the thickness direction was prepared. That is, one pressure-sensitive adhesive sheet 7 with a release sheet includes one release sheet 5, one foldable optical pressure-sensitive adhesive sheet 1, and one release sheet 5 facing one side (upper side) in the thickness direction. Prepare in order. Next, the pressure-sensitive adhesive sheet 7 with a release sheet was cut into a size of 5 cm×10 cm, and 10 cut pressure-sensitive adhesive sheets 7 with a release sheet were laminated to prepare a sample 20 as shown in FIG. 10A. In sample 20, the release sheet 5 placed below the foldable optical pressure-sensitive adhesive sheet 1 in the pressure-sensitive adhesive sheet 7 with a release sheet positioned at the top, and the pressure-sensitive adhesive sheet 7 with a release sheet positioned second from the top The release sheet 5 arranged on the upper side of the foldable optical adhesive sheet 1 is in contact.

Subsequently, the sample 20 was stored in a 50° C. environment for 100 hours. After storage, the topmost adhesive sheet 7 with a release sheet of sample 20 was removed. A lifting test was carried out using 31B tape (manufactured by Nitto Denko), and workability was evaluated according to the following criteria.

◯: As shown in FIG. 10B, only one release sheet-attached pressure-sensitive adhesive sheet 7 positioned at the top was lifted. That is, only the single adhesive sheet 7 with release sheet was lifted from the sample 20 .
x: As shown in FIG. 10C, in addition to the uppermost pressure-sensitive adhesive sheet 7 with a release sheet, the second and subsequent pressure-sensitive adhesive sheets 7 from the top were lifted together. In other words, only one adhesive sheet 7 with a release sheet could not be lifted from the sample 20 .

2. Processability An adhesive sheet 7 with a release sheet was prepared, which includes an optical adhesive sheet 1 for foldable and two release sheets 2 sandwiching the optical adhesive sheet 1 in the thickness direction. As indicated by the solid line in FIG. 11A, the adhesive sheet 7 with a release sheet had a length in the first direction of 30 cm and a length in the second direction of 20 cm. Next, as indicated by the thick lines in FIG. 11A , the pressure-sensitive adhesive sheet 7 with a release sheet was cut to have a length of 10 cm in the first direction and a length of 7 cm in the second direction to prepare sample 15 . A cutter was used for cutting. The sample 15 has one soft portion 2 and two hard portions 3 .
The cut portion 30 formed on the other edge of the sample 15 in the first direction was observed under a microscope to evaluate workability according to the following criteria.

◯: The cut portion 30 was smooth with neither defect X (see FIG. 11B) nor protrusion Y (see FIG. 11C) observed.
x: Defect X (see FIG. 11B) and/or protrusion Y (see FIG. 11C) was observed in the cut portion 30 .

1 Optical adhesive sheet for foldable 2 Soft part 3 Hard part 4 Boundary region 40 Boundary 11 One edge 12 Other edge L1 Length of soft part in first direction L2 Length of each of two hard parts in first direction

Claims (9)

Having a shape extending in a first direction orthogonal to the thickness direction, having one edge and the other edge in a second direction orthogonal to the thickness direction and the first direction,
a soft portion, and two hard portions arranged adjacent to both sides of the soft portion in the first direction and harder than the soft portion;
The optical pressure-sensitive adhesive sheet for foldables, wherein the soft portion is continuously arranged in the second direction from the one end edge to the other end edge. 2. The foldable optical pressure-sensitive adhesive sheet according to claim 1, wherein said soft portion has a substantially linear shape from said one end edge to said other end edge. 3. The foldable optical pressure-sensitive adhesive sheet according to claim 1, wherein the length of the soft portion in the first direction is shorter than the length of each of the two hard portions in the first direction. 3. The foldable optical pressure-sensitive adhesive sheet according to claim 1, wherein the fluctuation rate of the total light transmittance of the soft portion obtained by the following formula is 5% or less.
Variation rate (%) of total light transmittance of the soft portion =|T1−T0|/T0×100
T1: total light transmittance of the soft portion after the following bending test T0: total light transmittance of the soft portion before the following bending test Bending test: centering on the soft portion, the two hard portions The foldable optical pressure-sensitive adhesive sheets are bent 1,000 times so as to approach each other. 4. The foldable optical pressure-sensitive adhesive sheet according to claim 3, wherein the fluctuation rate of the total light transmittance of the soft portion obtained by the following formula is 5% or less.
Variation rate (%) of total light transmittance of the soft portion =|T1−T0|/T0×100
T1: total light transmittance of the soft portion after the following bending test T0: total light transmittance of the soft portion before the following bending test Bending test: centering on the soft portion, the two hard portions The foldable optical pressure-sensitive adhesive sheets are bent 1,000 times so as to approach each other. A boundary region including a boundary between the soft portion and the hard portion,
3. The foldable optical pressure-sensitive adhesive sheet according to claim 1, wherein in said boundary region, the concentration of the material of said soft portion gradually decreases in said first direction from said soft portion to said hard portion. A boundary region including a boundary between the soft portion and the hard portion,
4. The foldable optical pressure-sensitive adhesive sheet according to claim 3, wherein, in said boundary region, the concentration of the material of said soft portion gradually decreases in said first direction from said soft portion to said hard portion. A boundary region including a boundary between the soft portion and the hard portion,
5. The foldable optical pressure-sensitive adhesive sheet according to claim 4, wherein in said boundary region, the concentration of the material of said soft portion gradually decreases in said first direction from said soft portion to said hard portion. A boundary region including a boundary between the soft portion and the hard portion,
6. The foldable optical pressure-sensitive adhesive sheet according to claim 5, wherein in said boundary region, the concentration of the material of said soft portion gradually decreases in said first direction from said soft portion to said hard portion.

Images