Separator

Abstract

This invention provides a separator suitable for use in the manufacture of optical adhesive sheets that require a high degree of cleanliness. [Solution] The separator of the present invention comprises a base film and a release layer, the base film does not contain fillers, and the ratio of the total projected area of ​​foreign matter on the projection surface in a planar projection according to a predetermined evaluation method is 20% or less.

Description

Technical Field

[0001] The present invention relates to a separator.

Background Art

[0002] A display panel has a laminated structure including a pixel panel, a cover member, and the like. In the manufacturing process of such a display panel, for example, a transparent optical adhesive sheet is used for bonding the elements included in the laminated structure. The optical adhesive sheet is manufactured, for example, in a form in which both sides of the sheet are covered with a separator (release liner). Techniques related to the separator are described, for example, in Patent Document 1 below.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the manufacturing process of an optical adhesive sheet, by irradiating the optical adhesive sheet whose both sides are covered with a separator with light of a predetermined wavelength, the presence or absence of foreign matter inside and on the surface of the sheet is inspected. The higher the required cleanliness of the manufactured optical adhesive sheet, the more detection of smaller foreign matter is required in the foreign matter inspection (that is, more precise inspection is required).

[0005] The present invention provides a separator suitable for use in the manufacture of an optical adhesive sheet that requires a high degree of cleanliness.

Means for Solving the Problems

[0006] The present invention [1] includes a separator in which the ratio of the total projected area of foreign matter on the projection surface in a plan view by the following evaluation method is 20% or less.

[0007] Evaluation method: The following steps 1 to 3 are performed using an apparatus equipped with the following light source and camera device.

[0008] Light source: White LED light source for irradiating the sample for evaluation with inspection light. Camera device: A camera device that is configured to capture the transmitted light and reflected light of the sample used for inspection, and has a resolution of 2.8 μm.

[0009] Step 1: Prepare a separator with a planar size of 50 mm x 50 mm as an evaluation sample, and set the sample in the apparatus so that the inner region (30 mm x 30 mm) surrounded by the outer region of the sample can be imaged by the camera device. Step 2: While irradiating the sample with the inspection light from the white LED light source, the camera device is used to receive the transmitted light and / or reflected light from the sample, and light reception data is acquired over the inner region. Step 3: Using the received light data, the positional information and projected image information of the foreign object on the projection plane of the planar projection of the inner region are derived.

[0010] The present invention [2] includes the separator described in [1] above, wherein the maximum length of the largest foreign object in the planar projection is 30 μm or less.

[0011] The present invention [3] includes the separator described in [1] or [2] above, wherein the number of foreign objects having a maximum length of 20 μm or more and 30 μm or less in the planar projection is 5 or less.

[0012] The present invention [4] includes a separator according to any one of [1] to [3] above, wherein the number of foreign objects having a maximum length of 15 μm or more and 30 μm or less in the planar projection is 10 or less.

[0013] The present invention [5] includes a separator according to any one of the above [1] to [4], wherein the separator has a surface with a surface roughness Ra of 20 nm or less. [Effects of the Invention]

[0014] The separator of the present invention has a total projection area ratio of 20% or less of foreign matter on the projection surface in the planar projection as determined by the evaluation method described above. Such a separator is suitable for performing precise foreign matter inspection to check for the presence or absence of minute foreign matter on an optical adhesive sheet when it is bonded to the sheet. Therefore, this separator is suitable for use in the manufacture of optical adhesive sheets where a high degree of cleanliness is required. [Brief explanation of the drawing]

[0015] [Figure 1] This is a cross-sectional view of one embodiment of the separator of the present invention. [Figure 2] Figure 1 is a cross-sectional view of an optical adhesive sheet (optical adhesive sheet with separator) with separators attached to both sides. [Modes for carrying out the invention]

[0016] As one embodiment of the separator of the present invention, separator 10 has a sheet shape of a predetermined thickness, as shown in Figure 1, and extends in a direction perpendicular to the thickness direction D (surface direction). Separator 10 is, for example, a protective film for an optical adhesive sheet. Figure 2 shows a case in which two separators 10 are used as protective films for an optical adhesive sheet 20. One separator 10 (separator 10A) is placed on one surface of the optical adhesive sheet 20 in the thickness direction D, and the other separator 10 (separator 10B) is placed on the other surface of the optical adhesive sheet 20 in the thickness direction D.

[0017] The optical adhesive sheet 20 is a transparent adhesive sheet disposed at the light-passing portion of an optical article and is used to manufacture the optical article. Examples of the optical article include a display panel. The display panel has a laminated structure including a pixel panel, a cover member, and the like. In the manufacturing process of the display panel, predetermined elements disposed on the image display side of the pixel panel are bonded together with, for example, an optical adhesive sheet. Such display panels include panels of ultra-high-definition displays for VR (Virtual Reality) applications or AR (Augmented Reality) applications and the like.

[0018] In the foreign matter inspection performed during the manufacturing process of the optical adhesive sheet 20, with both surfaces of the optical adhesive sheet 20 protected by the separator 10, inspection light is irradiated onto the optical adhesive sheet 20 through the separator 10 from one surface side of the sheet. As the inspection light, visible light or infrared light is used. The wavelength of the visible light as the inspection light is included, for example, within the range of 400 to 800 nm. As the light source of this visible light, for example, a white LED light source is used. The wavelength of the infrared light as the inspection light is included, for example, within the range of 800 to 1200 nm. As the light source of this infrared light, for example, an infrared lamp is used. Based on the distribution of the visible light transmittance or infrared light transmittance in the irradiation region, the presence, absence, and size of foreign matter inside and on the surface of the optical adhesive sheet 20 are examined. In such an inspection, the distribution of the visible light transmittance or infrared light transmittance also reflects the presence, absence, and size of foreign matter inside and on the surface of the separator 10.

[0019] The separator 10 has a ratio (foreign matter area ratio R) of the total projected area of foreign matter on the projection surface in the plan view projection by the following evaluation method of 20% or less. The foreign matter includes environmental foreign matter, foreign matter as impurities in the raw material, foreign matter resulting from material modification, and air bubbles. Examples of the environmental foreign matter include fiber pieces, skin pieces, metal fine particles, minute oil droplets, and salt fine particles derived from sweat. These foreign matters may also be referred to as defects in the separator or the optical adhesive sheet.

[0020] Evaluation method: Use an evaluation device equipped with the following light source and camera device to perform the following first to third steps.

[0021] Light source: A white LED light source for irradiating inspection light onto a sample for evaluation Camera device: A camera device that is arranged to be able to image the transmitted light and reflected light of the sample of the inspection light and has a resolution of 2.8 μm

[0022] First step: Prepare a separator 10 with a plan view size of 50 mm × 50 mm as a sample for evaluation, and set the sample in the evaluation device in a state where an inner region (30 mm × 30 mm) surrounded by an outer region in the sample can be imaged by the camera device. Second step: While irradiating the inspection light from the white LED light source onto the sample, use the camera device to receive the transmitted light and / or reflected light of the sample, and acquire reception data over the inner region. The transmitted light of the sample is the light that passes through the sample in its thickness direction. The reflected light of the sample is the light reflected by the sample. Third step: Using the reception data, derive the position information and projection image information of foreign matters (each of the foreign matters present in the inner region) on the projection plane of the plan view projection of the inner region.

[0023] Such a separator 10 is suitable for performing a precise foreign matter inspection (defect inspection) to examine the presence or absence of minute foreign matters on such an optically adhesive sheet when it is bonded to the optically adhesive sheet (for example, the optically adhesive sheet 20 shown in FIG. 2). Such a separator 10 is suitable for use in the production of an optically adhesive sheet that requires a high degree of cleanliness. For example, the separator 10 is suitable for use in the production of an optically adhesive sheet that requires much more minute foreign matter (i.e., defect) inspection (i.e., defect management) compared to the conventional case. When the optically adhesive sheet is an adhesive sheet for display panel applications, the separator 10 helps to improve the quality of the display image of a display panel (which has been advancing in high definition in recent years) manufactured using the optically adhesive sheet.

[0024] In the evaluation apparatus described above, the resolution of the camera device is 2.8 μm as described above, but it may be 10 μm or less, preferably 5 μm or less. The camera device may be equipped with a lens (i.e., the camera device may have a configuration in which the light-receiving element receives light through the lens). Furthermore, in the evaluation apparatus described above, the evaluation method consisting of the first to third steps and other evaluation methods can be performed by combining a white LED light source with LED light sources of other colors (examples of LED light sources of other colors include red LED light sources and blue LED light sources). For example, by using an LED light source of another color alone as a light source, or by using two or more LED light sources of multiple colors in combination as a light source, it becomes easier to perform the above-mentioned foreign object inspection depending on the object being inspected.

[0025] In the first step of the evaluation method described above, the sample is set in the evaluation device by, for example, having the outer region of the sample gripped by the chuck mechanism provided in the evaluation device. In the second step, for example, the light-receiving surface of the camera device used is positioned opposite the inner region of the sample, and scanning along the inner region is performed by the camera device. The position information derived in the third step includes, for example, XY coordinate information with the above projection plane as the XY plane, and Z coordinate information with the thickness direction perpendicular to the XY plane as the Z direction. The projection image information derived in the third step is information from which at least the total area of ​​the foreign matter can be derived, and further information from which the size of each foreign matter and the size distribution of the foreign matter can be derived.

[0026] The foreign matter area ratio R is preferably 18% or less, more preferably 15% or less, even more preferably 12% or less, and particularly preferably 10% or less. From the viewpoint of carrying out the above-mentioned precise foreign matter inspection, it is preferable that the foreign matter area ratio R is as close to 0% as possible.

[0027] The separator 10 has a maximum length (maximum foreign matter length L) of the largest foreign matter in the planar projection described above, preferably 30 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, and particularly preferably 8 μm or less. This configuration is suitable for inspecting the optical adhesive sheet for the presence or absence of foreign matter (foreign matter with a maximum length of, for example, about 33 μm) whose maximum length in the planar projection is slightly over 30 μm. From the viewpoint of performing the above-mentioned precision foreign matter inspection, a shorter maximum foreign matter length L is preferable.

[0028] The separator 10 has a number of foreign objects (number of foreign objects in the first range N1) with a maximum length of 20 μm or more and 30 μm or less in the planar projection, preferably 5 or less, more preferably 4 or less, even more preferably 3 or less, especially preferably 2 or less, particularly preferably 1 or less, and most preferably 0. Such a separator 10 is suitable for performing precise foreign object inspection on an optical adhesive sheet when it is bonded to the sheet, and therefore is suitable for use in the manufacture of optical adhesive sheets where a high degree of cleanliness is required.

[0029] The separator 10 has a number of foreign objects (number of foreign objects in the second range N2) with a maximum length of 15 μm or more and 30 μm or less in the planar projection described above, preferably 10 or less, more preferably 7 or less, even more preferably 4 or less, especially preferably 3 or less, even more preferably 2 or less, particularly preferably 1 or less, and extremely preferably 0. Such a separator 10 is suitable for performing precise foreign object inspection on an optical adhesive sheet when it is bonded to the sheet, and therefore is suitable for use in the manufacture of optical adhesive sheets where a high degree of cleanliness is required.

[0030] Methods for controlling foreign matter inside and on the surface of the separator 10 (controlling the presence and size of foreign matter) include, for example, selecting the type of resin material that forms the separator, making the resin material filler-free, adjusting the filtering diameter of the resin material used for film formation, and controlling the air cleanliness in the separator manufacturing line (such as controlling the exhaust removal of airborne particles).

[0031] In this embodiment, the separator 10 includes a base film 11 and a release layer 12. The release layer 12 is located on one side of the base film 11 in the thickness direction D, and preferably on one surface of the base film 11 in the thickness direction D.

[0032] The base film 11 is, for example, a flexible transparent resin film. Examples of resin materials for the base film 11 include polyolefins, polyesters, acrylics, polyamides, polyimides, polyvinyl chlorides, polyvinylidene chlorides, celluloses, modified celluloses, polystyrenes, and polycarbonates. Examples of polyolefins include polyethylene, polypropylene, cycloolefin polymers (COP), poly-1-butene, poly-4-methyl-1-pentene, ethylene-propylene copolymers, ethylene-1-butene copolymers, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-vinyl alcohol copolymers. Examples of polyesters include polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate. Examples of polyamides include polyamide 6, polyamide 6,6, and partially aromatic polyamides. An example of modified cellulose is triacetylcellulose (TAC). These resin materials may be used individually or in combination of two or more types. As the material for the base film 11, a material with a high degree of cleanliness used in optical applications is preferred. From the viewpoint of obtaining a separator 10 with a high degree of cleanliness, polyolefin is preferably used as the material for the base film 11, and COP is more preferably used.

[0033] Furthermore, the resin material preferably contains no fillers or substantially no fillers. A resin material that is substantially free of fillers means that the filler content in the resin material is 0.05% by mass or less. On the other hand, if the resin material contains fillers, the fillers are preferably nanofillers (nanofillers refer to particles with a maximum length of 100 nm or less). These configurations are preferable from the viewpoint of obtaining a highly clean separator 10.

[0034] From the viewpoint of ensuring the strength of the separator 10, the thickness of the base film 11 is preferably 5 μm or more, more preferably 10 μm or more, and more preferably 20 μm or more. Furthermore, from the viewpoint of ensuring appropriate flexibility in the separator 10, the thickness of the base film 11 is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.

[0035] The release layer 12 is a layer that ensures the release of the optical adhesive sheet from the separator surface. Examples of materials for the release layer 12 include silicone resin, long-chain alkyl resin, and fatty acid amide resin. These resins may contain fluorine atoms in their polymer side chains. For example, the silicone resin may be a fluorinated silicone resin containing fluorine atoms in its side chains.

[0036] The separator 10 can be manufactured, for example, as follows. First, a base film 11 is produced by molding a molten resin material into a film. Examples of molding methods include extrusion molding, inflation molding, and calendering. Next, one side of the base film 11 is treated with a release agent to form a release layer 12 (a film of the release agent). The release agent contains, for example, one of the above-mentioned resins as the material for the release layer 12. The separator 10 is preferably manufactured in a clean room. The higher the air cleanliness of the separator 10 manufacturing line (for example, the air cleanliness of the clean room), the less environmental foreign matter and the smaller the size of the environmental foreign matter on the inside and surface of the manufactured separator 10. The air cleanliness of the manufacturing line is preferably Class 3 or lower, more preferably Class 2 or lower, and even more preferably Class 1 according to the ISO 14644-1 standard.

[0037] In this embodiment, the separator 10 is transparent. The haze of the separator 10 is preferably 3% or less, more preferably 2% or less, and even more preferably 1% or less. The haze of the separator 10 can be measured using a haze meter in accordance with JIS K7136 (2000).

[0038] The transmittance of light emitted from the white LED light source in the separator 10 is, for example, 50% or more, preferably 80% or more, and more preferably 90% or more. Such a configuration is preferable from the viewpoint of appropriately performing foreign object inspection using a white LED light source. Furthermore, the infrared transmittance in the separator 10 is, for example, 50% or more, preferably 80% or more, and more preferably 90% or more. Such a configuration is preferable from the viewpoint of appropriately performing foreign object inspection using infrared light.

[0039] The separator 10 preferably has a surface with a surface roughness Ra of 20 nm or less. If the separator 10 has a release layer 12, the surface roughness Ra of the exposed surface of the release layer 12 is preferably 20 nm or less. The surface roughness Ra is more preferably 17 nm or less, even more preferably 15 nm or less, particularly preferably 12 nm or less, even more preferably 10 nm or less, even more preferably 8 nm or less, particularly preferably 6 nm or less, and extremely preferably 5 nm or less. Such a configuration regarding surface roughness is preferable from the viewpoint of suppressing the intrusion of foreign matter onto the separator surface and is useful in the manufacture of optical adhesive sheets using the separator 10, where a high degree of cleanliness is required. The surface roughness Ra is, for example, 0.1 nm or more. The surface roughness Ra is the arithmetic mean roughness of the surface and can be measured by the method described later with respect to the examples.

[0040] The separator 10 preferably has a surface with a surface roughness Rz of 600 nm or less. If the separator 10 has a release layer 12, the surface roughness Rz of the exposed surface of the release layer 12 is preferably 600 nm or less. The surface roughness Rz is more preferably 400 nm or less, even more preferably 300 nm or less, especially preferably 200 nm or less, even more preferably 100 nm or less, even more preferably 80 nm or less, particularly preferably 60 nm or less, and extremely preferably 50 nm or less. Such a configuration regarding surface roughness is preferable from the viewpoint of suppressing the adhesion of foreign matter to the separator surface and is useful in the manufacture of optical adhesive sheets using the separator 10 where a high degree of cleanliness is required. The surface roughness Rz is, for example, 1 nm or more. The surface roughness Rz is the ten-point average roughness of the surface and can be measured by the method described later with respect to the examples.

[0041] The optical adhesive sheet 20 is an optical adhesive sheet having a transparent adhesive layer 21. The adhesive layer 21 is a pressure-sensitive adhesive layer formed from an adhesive composition and is transparent (transmits visible light). The adhesive composition contains a base polymer.

[0042] The base polymer is an adhesive component that provides tackiness in the adhesive layer 21. The base polymer exhibits rubber elasticity at room temperature. Examples of base polymers include acrylic polymers, rubber polymers, polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluoropolymers. From the viewpoint of ensuring good transparency and tackiness in the adhesive layer 21, an acrylic base polymer is preferably used as the base polymer.

[0043] Acrylic-based polymers contain alkyl (meth)acrylate as their main constituent monomer component. "(Meth)acrylic" means acrylic and / or methacrylic.

[0044] (Meth)acrylate alkyl esters include (meth)acrylate alkyl esters in which the alkyl group has 1 to 20 carbon atoms, i.e., (meth)acrylate C 1-20 Alkyl esters are preferably used. Alkyl (meth)acrylate esters may have linear or branched alkyl groups, or cyclic alkyl groups such as alicyclic alkyl groups.

[0045] Examples of alkyl (meth)acrylate esters having linear or branched alkyl groups include methyl (meth)acrylate, ethyl (meth)acrylate, 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 methacrylic acid Examples include isooctyl, 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.

[0046] Examples of alkyl (meth)acrylates having an alicyclic alkyl group include cycloalkyl (meth)acrylates, (meth)acrylates having a bicyclic aliphatic hydrocarbon ring, and (meth)acrylates having three or more aliphatic hydrocarbon rings. Examples of cycloalkyl (meth)acrylates include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, cycloheptyl (meth)acrylate, and cyclooctyl (meth)acrylate. An example of a (meth)acrylate ester having a bicyclic aliphatic hydrocarbon ring is isobornyl (meth)acrylate. Examples of (meth)acrylic acid esters having three or more aliphatic hydrocarbon rings include dicyclopentanyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, tricyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, and 2-ethyl-2-adamantyl (meth)acrylate.

[0047] The amount of alkyl (meth)acrylate per 100 parts by mass of the total monomer components forming the acrylic base polymer is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 75 parts by mass or more. The amount of alkyl (meth)acrylate per 100 parts by mass of the total monomer components forming the acrylic base polymer is preferably 100 parts by mass or less, more preferably 95 parts by mass or less, and even more preferably 92 parts by mass or less.

[0048] Acrylic-based polymers preferably contain polar group-containing monomers in addition to the above-mentioned alkyl (meth)acrylate as monomer components. Examples of polar group-containing monomers include hydroxyl group-containing monomers, carboxyl group-containing monomers, and nitrogen-containing monomers. The inclusion of polar group-containing monomers in the monomer components tends to increase the cohesive strength of the polymer and improve adhesion retention at high temperatures. Furthermore, when introducing a crosslinked structure into an acrylic-based polymer using a crosslinking agent such as an isocyanate crosslinking agent or an epoxy crosslinking agent, hydroxyl groups and carboxyl groups serve as introduction points for the crosslinked structure.

[0049] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate. From the viewpoint of ensuring adhesive strength in the adhesive layer 21 and suppressing clouding of the adhesive layer 21 in a high-humidity environment, 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are preferred as hydroxyl group-containing monomers.

[0050] Examples of monomers containing a carboxyl group include (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid.

[0051] Examples of nitrogen-containing monomers include nitrogen-containing vinyl monomers and cyanoacrylate monomers. Examples of nitrogen-containing vinyl monomers include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth)acryloylmorpholine, N-vinyl carboxylic acid amides, and N-vinylcaprolactam. Examples of cyanoacrylate monomers include acrylonitrile and methacrylonitrile. From the viewpoint of ensuring cohesive force in the adhesive layer 21 and achieving good adhesive strength, N-vinylpyrrolidone is preferably used as the nitrogen-containing monomer.

[0052] From the viewpoint of ensuring good adhesion in the optical adhesive sheet 20 or adhesive layer 21, the amount of polar group-containing monomer per 100 parts by mass of the total monomer components of the acrylic-based polymer is preferably 5 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 10 parts by mass or more. Furthermore, the amount of polar group-containing monomer per 100 parts by mass of the total monomer components of the acrylic-based polymer is preferably 25 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 17 parts by mass or less, and particularly preferably 15 parts by mass or less.

[0053] The monomer components forming the acrylic base polymer preferably include a hydroxyl group-containing monomer as a polar group-containing monomer component. This configuration is suitable for ensuring good adhesion in the adhesive layer 21 and for suppressing clouding of the adhesive layer 21 in high humidity environments. Furthermore, the monomer components forming the acrylic base polymer preferably include a nitrogen-containing monomer as a polar group-containing monomer component. This configuration is suitable for ensuring good adhesion in the adhesive layer 21.

[0054] The amount of hydroxyl group-containing monomer per 100 parts by mass of the total monomer components is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more. The amount of hydroxyl group-containing monomer per 100 parts by mass of the total monomer components is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, and even more preferably 10 parts by mass or less. In particular, it is preferable that the total amount of 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate be within such a range, and more preferably that the amount of 4-hydroxybutyl acrylate be within such a range.

[0055] The amount of nitrogen-containing monomer per 100 parts by mass of the total monomer components of the acrylic-based polymer is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more. The amount of nitrogen-containing monomer per 100 parts by mass of the total monomer components of the acrylic-based polymer is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less. In particular, it is preferable that the amount of N-vinylpyrrolidone be within such a range.

[0056] When the optical adhesive sheet 20 is used to bond a touch panel sensor, it is preferable that the optical adhesive sheet 20 has a low acid content in order to prevent corrosion of the electrodes by acid components. Furthermore, when the optical adhesive sheet 20 is used to bond polarizing plates, it is preferable that the optical adhesive sheet 20 has a low acid content in order to suppress polyene formation of the polyvinyl alcohol-based polarizer by the acid component. Such an acid-free optical adhesive sheet 20 preferably has an organic acid monomer content of 100 ppm or less, more preferably 70 ppm or less, and even more preferably 50 ppm or less, such as (meth)acrylic acid. The organic acid monomer content of the optical adhesive sheet 20 can be determined by immersing the optical adhesive sheet 20 in pure water, heating it at 100°C for 45 minutes, and quantifying the acid monomer extracted into the water using ion chromatography.

[0057] From the viewpoint of reducing the acid monomer content in the optical adhesive sheet 20, it is preferable that the amount of organic acid monomer components such as (meth)acrylic acid in the monomer components constituting the base polymer is small. Therefore, in order to make the optical adhesive sheet 20 acid-free, it is preferable that the base polymer substantially does not contain organic acid monomers (carboxyl group-containing monomers) as monomer components. In an acid-free adhesive sheet, the amount of carboxyl group-containing monomers per 100 parts by mass of the total monomer components of the base polymer is preferably 0.5 parts by mass or less, more preferably 0.1 parts by mass or less, even more preferably 0.05 parts by mass or less, and ideally 0.

[0058] The acrylic-based polymer may contain monomers other than the alkyl (meth)acrylates and polar group-containing monomers mentioned above as monomer components. Examples of other monomer components include vinyl monomers other than those mentioned above, cyanoacrylate monomers other than those mentioned above, glycol-based acrylic ester monomers, and acrylic acid ester monomers other than those mentioned above. Examples of vinyl monomers other than those mentioned above include caprolactone adducts of (meth)acrylic acid, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, vinyl acetate, vinyl propionate, styrene, and α-methylstyrene. Examples of cyanoacrylate monomers other than those mentioned above include acrylonitrile and methacrylonitrile. Examples of epoxy group-containing monomers include glycidyl (meth)acrylate. Examples of glycol-based acrylic ester monomers include polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxyethylene glycol (meth)acrylate, and methoxypolypropylene glycol (meth)acrylate. Examples of acrylic acid ester monomers other than those mentioned above include tetrahydrofurfuryl (meth)acrylate, fluorine (meth)acrylate, and silicone (meth)acrylate.

[0059] For the glass transition temperature (Tg) of a polymer, the theoretical glass transition temperature (Tg) can be obtained based on Fox's equation, as shown below. Fox's equation is a relationship between the glass transition temperature Tg of a polymer and the glass transition temperature Tgi of the homopolymer of the monomers constituting the polymer. In Fox's equation below, Tg represents the glass transition temperature (°C) of the polymer, Wi represents the weight fraction of monomer i constituting the polymer, and Tgi represents the glass transition temperature (°C) of the homopolymer formed from monomer i. For the glass transition temperature of the homopolymer, literature values ​​can be used. For example, "Polymer Handbook" (4th edition, John Wiley & Sons, Inc., 1999) and "New Polymer Library 7: Introduction to Synthetic Resins for Coatings" (by Kyozo Kitaoka, Polymer Publishing Association, 1995) list the glass transition temperatures of various homopolymers. As the Tg of the monomer homopolymer, the peak top temperature of the loss tangent (tanδ) obtained by dynamic viscoelasticity measurement may be used. A specific method for measuring the peak top temperature is described, for example, in Japanese Patent Publication No. 2007-51271.

[0060] Fox's formula 1 / (273+Tg)=Σ[Wi / (273+Tgi)]

[0061] The gel fraction can be determined as the insoluble portion in a solvent such as ethyl acetate. Specifically, the gel fraction is determined as the weight fraction (unit: mass%) of the insoluble components after immersing the adhesive layer sample in ethyl acetate at 23°C for 7 days, relative to the sample before immersion. Generally, the higher the degree of crosslinking of a polymer, the higher the gel fraction of that polymer tends to be. The gel fraction (amount of introduced crosslinking structure) can be adjusted, for example, by selecting the method of introducing the crosslinking structure, selecting the type of crosslinking agent, and the amount of crosslinking agent used.

[0062] Methods for introducing a crosslinked structure into a base polymer include, for example, a method in which a base polymer having a functional group that can react with a crosslinking agent is polymerized, and then the crosslinking agent is added to react the base polymer with the crosslinking agent (first method); and a method in which a branched structure (crosslinked structure) is introduced into the polymer chain by including a polyfunctional compound in the polymerization component of the base polymer (second method). Multiple types of crosslinked structures may be introduced into the base polymer by using a combination of these methods.

[0063] In the first method, a crosslinking agent is added to the polymerized base polymer, and a crosslinked structure is introduced into the base polymer by heating as needed. Examples of crosslinking agents include compounds that react with functional groups (e.g., hydroxyl groups and carboxyl groups) contained in the base polymer. Examples of crosslinking agents include isocyanate crosslinking agents, epoxy crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, carbodiimide crosslinking agents, and metal chelate crosslinking agents.

[0064] In the first method, isocyanate crosslinking agents and epoxy crosslinking agents are preferred as crosslinking agents because they have high reactivity with the functional groups (e.g., hydroxyl groups and carboxyl groups) of the base polymer and facilitate the introduction of a crosslinked structure. These crosslinking agents react with the functional groups (e.g., hydroxyl groups and carboxyl groups) introduced into the base polymer to form a crosslinked structure. In acid-free adhesives where the base polymer does not contain carboxyl groups, it is preferable to use an isocyanate crosslinking agent to form a crosslinked structure by the reaction of the isocyanate crosslinking agent with the hydroxyl groups in the base polymer.

[0065] As isocyanate crosslinking agents, for example, polyisocyanates having two or more isocyanate groups in one molecule are used. Examples of isocyanate crosslinking agents include lower aliphatic polyisocyanates, alicyclic isocyanates, aromatic isocyanates, and isocyanate adducts. Examples of lower aliphatic polyisocyanates include butylene diisocyanate and hexamethylene diisocyanate. Examples of alicyclic isocyanates include cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate. Examples of aromatic isocyanates include 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate. Examples of isocyanate adducts include trimethylolpropane / tolylene diisocyanate trimer adducts (e.g., Tosoh's "Coronate L"), trimethylolpropane / hexamethylene diisocyanate trimer adducts (e.g., Tosoh's "Coronate HL"), trimethylolpropane adducts of xylylene diisocyanate (e.g., Mitsui Chemicals' "Takenate D110N"), and isocyanurate derivatives of hexamethylene diisocyanate (e.g., Tosoh's "Coronate HX").

[0066] In the second method described above, the monomer components constituting the acrylic base polymer and the entire amount of the polyfunctional compound for introducing the crosslinking structure may be reacted (polymerized) at once, or polymerized in multiple steps. In the multi-step polymerization method, for example, first, the monofunctional monomers constituting the base polymer are polymerized (prepolymerization) to prepare a partially polymerized product (prepolymer composition). Next, a polyfunctional compound such as a polyfunctional (meth)acrylate is added to the prepolymer composition to polymerize the prepolymer composition and the polyfunctional monomer (main polymerization). The prepolymer composition is a partially polymerized product containing polymers with a low degree of polymerization and unreacted monomers.

[0067] By prepolymerizing the components of the acrylic-based polymer, branching points (crosslinking points) by the polyfunctional compound can be uniformly introduced into the base polymer. Alternatively, a mixture of a low molecular weight polymer or partially polymerized product and an unpolymerized monomer component (adhesive composition) can be applied to a substrate, and then the main polymerization can be carried out on the substrate to form an optical adhesive sheet 20. Since low polymerization compositions such as prepolymer compositions have low viscosity and excellent coatability, the method of applying an adhesive composition, which is a mixture of a prepolymer composition and a polyfunctional compound, to a substrate and then carrying out the main polymerization is preferred from the viewpoint of productivity and uniformity of thickness of the optical adhesive sheet 20.

[0068] Examples of polyfunctional compounds used to introduce crosslinked structures include compounds containing two or more polymerizable functional groups (ethylenically unsaturated groups) having unsaturated double bonds in one molecule. As polyfunctional compounds, polyfunctional (meth)acrylates are preferred because they readily copolymerize with monomer components of acrylic-based polymers. When introducing branched (crosslinked) structures by active energy ray polymerization (photopolymerization), polyfunctional acrylates are preferred.

[0069] Examples of polyfunctional (meth)acrylates include polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, bisphenol A ethylene oxide modified di(meth)acrylate, bisphenol A propylene oxide modified di(meth)acrylate, alkanediol di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, ethoxylated isocyanuric acid tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol Examples include di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropanetetra(meth)acrylate, ethoxylated pentaerythritoltetra(meth)acrylate, pentaerythritoltetra(meth)acrylate, dipentaerythritol poly(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, glycerin di(meth)acrylate, epoxy(meth)acrylate, butadiene(meth)acrylate, and isoprene(meth)acrylate.

[0070] From the viewpoint of appropriately adjusting the viscoelasticity (e.g., storage modulus G' and loss tangent tanδ) by introducing a crosslinked structure in an acrylic-based polymer, the molecular weight of the polyfunctional compound, such as a polyfunctional (meth)acrylate, is preferably 1500 or less, more preferably 1000 or less. The functional group equivalent (g / eq) of the polyfunctional compound is preferably 50 or more, more preferably 70 or more, and even more preferably 80. The functional group equivalent is preferably 500, more preferably 300 or less, and even more preferably 200.

[0071] Polymerization methods for acrylic-based polymers include, for example, solution polymerization, active energy ray polymerization, bulk polymerization, and emulsion polymerization. Solution polymerization and active energy ray polymerization (e.g., UV polymerization) are preferred in terms of transparency, water resistance, and cost of the adhesive. Examples of solvents for solution polymerization include ethyl acetate and toluene.

[0072] When preparing acrylic-based polymers, polymerization initiators may be used depending on the type of polymerization reaction. Examples of polymerization initiators include photopolymerization initiators and thermal polymerization initiators. Examples of photopolymerization initiators include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators. Examples of thermal polymerization initiators include azo-based initiators, peroxide-based initiators, and redox-based initiators combining peroxides and reducing agents (for example, combinations of persulfate and sodium bisulfite, and combinations of peroxide and sodium ascorbate).

[0073] In polymerization, chain transfer agents and polymerization inhibitors (polymerization retarders) may be used, for example, from the viewpoint of molecular weight adjustment. Examples of chain transfer agents include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and α-methylstyrene dimers.

[0074] The molecular weight of the base polymer can be adjusted by controlling the type and amount of polymerization initiator. For example, in radical polymerization, a larger amount of polymerization initiator leads to a higher radical concentration in the reaction system, resulting in a higher density of reaction initiator sites and a tendency for a smaller polymer molecular weight. Conversely, a smaller amount of polymerization initiator leads to a lower density of reaction initiator sites, allowing the polymer chain to elongate more easily and resulting in a tendency for a larger polymer molecular weight.

[0075] To achieve high adhesive strength in the adhesive layer 21, it is preferable that the acrylic base polymer has a high gel fraction with a low crosslinking point density. To increase the gel fraction (the ratio of polymer chains in which crosslinking structures are introduced) with a low crosslinking density, the molecular weight (polymer chain length) of the base polymer should be increased. To increase the molecular weight of the base polymer, it is preferable to reduce the amount of polymerization initiator used when polymerizing the base polymer.

[0076] The amount of polymerization initiator used during base polymer polymerization is appropriately set according to, for example, the type of polymerization reaction, the monomer composition, the type of polymerization initiator, and the target molecular weight. From the viewpoint of increasing the molecular weight of the base polymer and increasing the gel fraction with a small amount of crosslinking agent, the amount of polymerization initiator used is preferably 0.001 parts by mass or more, more preferably 0.003 parts by mass or more, and even more preferably 0.005 parts by mass or more, per 100 parts by mass of the total monomer components constituting the base polymer. The same amount is preferably 0.4 parts by mass or less, more preferably 0.1 parts by mass or less, and even more preferably 0.05 parts by mass or less.

[0077] When introducing a crosslinked structure using an isocyanate crosslinking agent, it is preferable to polymerize the base polymer by solution polymerization, then add the crosslinking agent to the polymerization solution, and heat the solution as needed to introduce the crosslinked structure into the base polymer. When introducing a crosslinked structure using a polyfunctional compound such as a polyfunctional (meth)acrylate, it is preferable to polymerize the base polymer or prepare a prepolymer composition by solution polymerization or active energy ray polymerization, add the polyfunctional compound to the polymerization solution, and introduce the crosslinked structure by the polyfunctional compound by further active energy ray polymerization.

[0078] A prepolymer composition can be prepared, for example, by partially polymerizing (prepolymerizing) a composition (prepolymer-forming composition) obtained by mixing monomer components constituting an acrylic-based polymer with a polymerization initiator. The monomer components in the prepolymer-forming composition are preferably monofunctional monomer components from among the monomer components constituting the acrylic-based polymer. These monofunctional monomer components are, for example, the alkyl (meth)acrylates and polar group-containing monomers mentioned above. In addition to monofunctional monomers, the prepolymer-forming composition may also contain polyfunctional monomers. For example, a portion of the polyfunctional monomer may be included in the prepolymer-forming composition, and the remainder of the polyfunctional monomer component may be added after prepolymerization for main polymerization.

[0079] The polymerization rate of the prepolymer is not particularly limited, but from the viewpoint of achieving a viscosity suitable for coating onto a substrate, it is preferably 3% by mass or more, more preferably 5% by mass or more, and also preferably 50% by mass or more, more preferably 40% by mass or less. The polymerization rate of the prepolymer can be adjusted by selecting the type and amount of photopolymerization initiator, as well as by adjusting the irradiation intensity and irradiation time of active energy rays such as UV light.

[0080] The adhesive sheet may contain an oligomer in addition to the acrylic-based polymer. The weight-average molecular weight of the acrylic oligomer is, for example, 1000 or more, and also, for example, 30000 or less. The acrylic oligomer contains an alkyl (meth)acrylate as its main constituent monomer component.

[0081] From the viewpoint of improving the adhesive strength of the adhesive sheet, the glass transition temperature of the acrylic oligomer is preferably 60°C or higher, more preferably 80°C or higher, even more preferably 100°C or higher, and particularly preferably 110°C or higher. By using a low-Tg acrylic base polymer with a crosslinked structure in combination with a high-Tg acrylic oligomer, the adhesive strength in the adhesive layer 21 tends to improve, and in particular, the adhesive retention strength at high temperatures tends to improve. The glass transition temperature of the acrylic oligomer is preferably 200°C or lower, more preferably 180°C or lower, and even more preferably 160°C or lower. The glass transition temperature of the acrylic oligomer is calculated using the Fox formula described above.

[0082] Acrylic oligomers with a glass transition temperature of 60°C or higher preferably contain, as constituent monomer components, alkyl (meth)acrylates having linear or branched alkyl groups, and / or alkyl (meth)acrylates having alicyclic alkyl groups. Specific examples of these are as described above as constituent monomers of acrylic-based polymers.

[0083] In acrylic oligomers, methyl methacrylate is preferred as the alkyl (meth)acrylate ester having a linear or branched alkyl group due to its high glass transition temperature and excellent compatibility with the base polymer. Examples of alkyl (meth)acrylate esters having an alicyclic alkyl group include dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate. Preferably, the acrylic oligomer contains, as constituent monomer components, one or more selected from the group consisting of dicyclopentanyl acrylate, dicyclopentanyl methacrylate, cyclohexyl acrylate, and cyclohexyl methacrylate, and methyl methacrylate.

[0084] The amount of alkyl (meth)acrylate having a linear or branched alkyl group relative to the total amount of monomer components constituting the acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and also preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. Furthermore, the amount of alkyl (meth)acrylate having an alicyclic alkyl group relative to the total amount of monomer components constituting the acrylic oligomer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and also preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0085] The weight-average molecular weight of the acrylic oligomer is preferably 1000 or more, more preferably 1500 or more, and even more preferably 2000. Alternatively, the weight-average molecular weight may be 30000 or less, more preferably 10000 or less, and even more preferably 8000 or less. Acrylic oligomers having molecular weights within this range are suitable for achieving good adhesion and adhesion retention in the adhesive layer 21.

[0086] Acrylic oligomers are obtained by polymerizing the above monomer components using various polymerization methods. Various polymerization initiators may be used in the polymerization of acrylic oligomers. Furthermore, chain transfer agents may be used in the polymerization reaction from the viewpoint of adjusting the molecular weight.

[0087] From the viewpoint of sufficiently increasing the adhesive strength of the adhesive layer 21, the amount of acrylic oligomer in the adhesive layer 21 relative to 100 parts by mass of the base polymer 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. The amount of acrylic oligomer in the adhesive layer 21 may be 1.3 parts by mass or more, 1.5 parts by mass or more, 1.8 parts by mass or more, 2 parts by mass or more, 2.3 parts by mass or more, or 2.5 parts by mass or more, relative to 100 parts by mass of the base polymer. The greater the amount of high-Tg acrylic oligomer added, the more the adhesive strength of the adhesive layer 21 tends to improve.

[0088] If the amount of acrylic oligomer added to the adhesive layer 21 is excessively large, the haze of the adhesive layer 21 tends to increase and transparency decreases due to a decrease in compatibility. Since high transparency is required for optical adhesive sheets that are positioned on the viewing side of the image display panel, the amount of acrylic oligomer in the optical adhesive sheet 20 (adhesive layer 21) is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, even more preferably 6 parts by mass or less, and particularly preferably 5 parts by mass or less, per 100 parts by mass of the base polymer.

[0089] An adhesive composition for forming an adhesive layer 21 is prepared by mixing an acrylic oligomer, a crosslinking agent and / or a polyfunctional compound for introducing a crosslinked structure, and other additives as needed, into an acrylic-based polymer (or prepolymer composition). The adhesive composition may optionally contain the remainder of the monomer components constituting the acrylic-based polymer. Thickening additives may be used for purposes such as viscosity adjustment.

[0090] When the adhesive composition contains a prepolymer composition and a polyfunctional compound, it is preferable to add a photopolymerization initiator and a chain transfer agent for the main polymerization to the adhesive composition. After prepolymerization, a polymerization initiator for the main polymerization may be added to the prepolymer composition. If the polymerization initiator from the prepolymerization remains in the prepolymer composition without being deactivated, the addition of a polymerization initiator for the main polymerization may be omitted. The adhesive composition may also contain a chain transfer agent.

[0091] The adhesive composition preferably contains 50% by mass or more of acrylic-based polymer (or prepolymer composition) relative to the total amount of nonvolatile matter, more preferably 70% by mass, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0092] The amount of crosslinking agent and / or polyfunctional compound in the adhesive composition is adjusted so that the gel fraction falls within the above range. As described above, in order to obtain an adhesive layer 21 with a small storage modulus G' and excellent adhesive strength, it is preferable to increase the molecular weight of the acrylic base polymer and increase the gel fraction with a small crosslinking point density. For example, when introducing a crosslinked structure with an isocyanate crosslinking agent, the amount of crosslinking agent is preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, and even more preferably 0.02 parts by mass per 100 parts by mass of the acrylic base polymer. The amount of crosslinking agent is preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, and even more preferably 0.1 parts by mass or less. When introducing a crosslinked structure with a polyfunctional (meth)acrylate, the amount of polyfunctional (meth)acrylate is preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, and even more preferably 0.02 parts by mass or more per 100 parts by mass of the acrylic base polymer (prepolymer). The amount of polyfunctional (meth)acrylate is preferably 0.3 parts by mass or less, more preferably 0.2 parts by mass or less, and even more preferably 0.1 parts by mass or less.

[0093] From the viewpoint of adjusting the adhesive strength of the adhesive layer 21, a silane coupling agent may be added to the adhesive composition. When a silane coupling agent is added to the adhesive composition, the amount of silane coupling agent added is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 2.0 parts by mass or less, per 100 parts by mass of the base polymer.

[0094] The adhesive composition may contain other components besides those listed above. Examples of other components include tackifiers, plasticizers, softeners, degradation inhibitors, fillers, colorants, UV absorbers, antioxidants, surfactants, and antistatic agents.

[0095] The optical adhesive sheet 20 can be manufactured, for example, by applying the above-mentioned adhesive composition onto the separator 10 to form a coating film, and then drying the coating film.

[0096] 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. The drying temperature of the coating film is, for example, 50°C to 200°C. The drying time is, for example, 5 seconds to 20 minutes.

[0097] When the adhesive composition contains a crosslinking agent, the crosslinking reaction proceeds simultaneously with the drying process described above, or through subsequent aging. The aging conditions are appropriately set depending on the type of crosslinking agent. The aging temperature is, for example, 20°C to 160°C. The aging time is, for example, 1 minute to 7 days.

[0098] Furthermore, it is preferable to laminate another separator 10 on top of the adhesive layer 21 on the separator 10 before or after aging.

[0099] When the adhesive composition is a photopolymerizable composition containing a prepolymer composition and a polyfunctional compound, etc., the adhesive composition is applied in layers onto the separator 10, and then photocuring is performed by irradiating it with active light. When performing photocuring, it is preferable to attach a cover sheet to the surface of the applied layer and irradiate it with active light while the adhesive composition is sandwiched between the two sheets to prevent polymerization inhibition by oxygen.

[0100] The active light is selected depending on the type of monomer component, polymerizable component (e.g., polyfunctional (meth)acrylate), and photopolymerization initiator. Generally, ultraviolet and / or short-wavelength visible light are used. The integrated light intensity of the irradiation is, for example, 100 to 5000 mJ / cm². 2 To that extent, a light source capable of emitting light in the wavelength range to which the photopolymerization initiator contained in the adhesive composition is sensitive is used as the light source for light irradiation. Examples of light sources include LED light sources, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, and xenon lamps.

[0101] In this manner, an optical adhesive sheet 20 (adhesive sheet X with separator) can be manufactured with both sides covered by the separator 10.

[0102] From the viewpoint of ensuring sufficient adhesion to the adherend, the thickness of the adhesive layer 21 is preferably 5 μm or more, more preferably 10 μm or more. From the viewpoint of the handling properties of the optical adhesive sheet 20, the thickness of the adhesive layer 21 is preferably 300 μm or less, more preferably 200 μm or less.

[0103] The haze of the adhesive layer 21 is preferably 3% or less, more preferably 2% or less. The haze of the adhesive layer 21 can be measured using a haze meter in accordance with JIS K7136 (2000). Examples of haze meters include the "NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. and the "HM-150" manufactured by Murakami Color Technology Laboratory Co., Ltd.

[0104] The transmittance of light emitted from the white LED light source in the adhesive layer 21 is, for example, 50% or more, preferably 80% or more, and more preferably 90% or more. Such a configuration is preferred from the viewpoint of appropriately performing foreign object inspection using a white LED light source. Furthermore, the infrared transmittance in the adhesive layer 21 is, for example, 50% or more, preferably 80% or more, and more preferably 90% or more. Such a configuration is preferred from the viewpoint of appropriately performing foreign object inspection using infrared light.

[0105] In the adhesive sheet X with separators, two separators 10 protect the optical adhesive sheet 20 (adhesive layer 21). Specifically, the separators 10 suppress or prevent scratches and dents from occurring on the optical adhesive sheet 20, for example, during transport. In addition, the separators 10 suppress or prevent environmental foreign matter from adhering to the optical adhesive sheet 20 (therefore, the transfer of environmental foreign matter from the optical adhesive sheet 20 to its adherend is suppressed or prevented). [Examples]

[0106] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Furthermore, the specific numerical values ​​such as the amounts (content), physical properties, and parameters described below can be substituted with the upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or "greater than") of the corresponding amounts (content), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0107] [Example 1] In a cleanroom, the separator of Example 1 was prepared by forming a silicone-based release layer on one side of a cycloolefin polymer (COP) film (product name "Zeonor Film ZF16", thickness 50 μm, manufactured by Nippon Zeon) as the base film. The air cleanliness of the cleanroom was Class 3 according to the ISO 14644-1 standard. In forming the silicone-based release layer, a release agent solution was first prepared by diluting a mixture of 30 parts by mass of addition-type silicone composition (product name "LTC761", manufactured by Toray Dow Corning), 0.9 parts by mass of silicone dispersion (product name "BY 24-850", manufactured by Toray Dow Corning), and 2 parts by mass of platinum catalyst for silicone curing (product name "SRX 212", manufactured by Toray Dow Corning) with a mixed solvent of toluene and hexane (volume ratio of toluene to hexane is 1:1). Next, this solution was applied to one side of a 50 μm thick COP film and heated and dried in a hot air dryer at 130°C for 1 minute. This produced the separator of Example 1. The separator of Example 1 comprises a COP film as a base film and a silicone release layer on one side thereof.

[0108] [Example 2] The separator of Example 2 was prepared in the same manner as the separator of Example 1, except that a filler-free polyethylene terephthalate (PET) film (product name "38-U41", thickness 38 μm, manufactured by Toray) was used as the base film instead of the COP film.

[0109] [Comparative Example 1] Comparative Example 1 was prepared in the same manner as the separator in Example 1, except that a biaxially oriented polyester film (product name "Lumirror XD500P", 75 μm thick, filler-containing PET film, manufactured by Toray Advanced Materials Korea) was used as the base film instead of the COP film.

[0110] [Comparative Example 2] The separator for Comparative Example 2 was prepared in the same manner as the separator for Example 1, except that a biaxially oriented polypropylene film (product name "Trefan #30-2500H", thickness 75 μm, filler-containing film, manufactured by Toray) was used as the base film instead of the COP film.

[0111] [Comparative Example 3] The separator for Comparative Example 3 was prepared in the same manner as the separator for Example 1, except that a biaxially oriented polyester film (product name "Diafoil T100C50", 50 μm thick, filler-containing PET film, manufactured by Mitsubishi Chemical Corporation) was used as the base film instead of the COP film.

[0112] <Measurement of foreign matter in separators> For each separator in Examples 1 and 2 and Comparative Examples 1 to 3, the amount and size of foreign matter were investigated. Specifically, the foreign matter area ratio R obtained by the evaluation method described below, the maximum foreign matter length L, the number of foreign matter particles in the first range N1, and the number of foreign matter particles in the second range N2 were investigated.

[0113] [Evaluation Method] The following steps 1 to 3 were performed using an evaluation apparatus equipped with the following light source and camera device.

[0114] Light source: White LED light source for irradiating the sample for evaluation with inspection light. Camera device: A camera device that is configured to capture both the transmitted and reflected light of the sample for inspection, and has a resolution of 2.8 μm.

[0115] <Step 1> First, a separator with a planar size of 50 mm x 50 mm was prepared as an evaluation sample. Next, the sample was set in the evaluation device in a state where the inner region (30 mm x 30 mm) surrounded by the outer region of the sample could be imaged by the camera device. In this step, the sample was set in the evaluation device by gripping the outer region of the sample with the chuck mechanism provided by the evaluation device.

[0116] <Step 2> While irradiating a sample set in the evaluation device with inspection light from a white LED light source, a camera device received both transmitted and reflected light from the sample across the entire inner region. This allowed for the acquisition of received light data across the entire inner region.

[0117] <Step 3> Using the received light data, positional information and projected image information of foreign objects (each foreign object present in the inner region) on the projection plane of the planar projection of the inner region were derived. The positional information derived in the third step includes XY coordinate information with the above projection plane as the XY plane, and Z coordinate information with the thickness direction perpendicular to the XY plane as the Z direction. The projected image information derived in the third step is information from which the total area of ​​the foreign objects, the size of each foreign object, and the size distribution of the foreign objects can be derived.

[0118] The foreign matter area ratio R is the ratio of the total projected area of ​​foreign matter on the projection surface of the planar projection using the evaluation method described above. A foreign matter area ratio R of 10% or less was evaluated as "excellent," a ratio exceeding 10% but 20% or less was evaluated as "good," and a ratio exceeding 20% ​​was evaluated as "poor." The evaluation results are shown in Table 1.

[0119] The maximum foreign matter length L is the maximum length of the largest foreign matter in the planar projection. For the maximum foreign matter length L, a value of 15 μm or less was evaluated as "excellent," a value exceeding 15 μm and 30 μm or less was evaluated as "good," a value exceeding 30 μm and 50 μm or less was evaluated as "acceptable," and a value exceeding 50 μm was evaluated as "poor." The evaluation results are shown in Table 1.

[0120] The number N1 is the number of foreign objects whose maximum length in the planar projection is 20 μm or more and 30 μm or less. The number N2 is the number of foreign objects whose maximum length in the planar projection is 15 μm or more and 30 μm or less. These are shown in Table 1. In each of the separators in Comparative Examples 1 to 3, N1 exceeded 20 and N2 exceeded 100.

[0121] <Surface roughness> The surface roughness of each separator in Examples 1 and 2 and Comparative Examples 1 to 3 was investigated. Specifically, first, the surface roughness Ra (arithmetic mean roughness) of the exposed surface of the release layer of the separator was determined from a 0.7 mm × 0.52 mm observation image using a scanning white light interferometer (product name "NewView7300", manufactured by Zygo). In addition, the surface roughness Rz (ten-point mean roughness) of the exposed surface of the release layer of the separator was determined from the same 0.7 mm × 0.52 mm observation image using the same scanning white light interferometer. The respective surface roughness Ra and Rz (nm) are shown in Table 1.

[0122] [Table 1] [Explanation of Symbols]

[0123] 10 Separators 11. Base film 12 Release layer 20 Optical adhesive sheets 21 Adhesive layer X Optical adhesive sheet with separator

Claims

1. It comprises a base film and a release layer, The aforementioned base film does not contain fillers. A separator in which the total area of ​​foreign objects on the projection surface of a planar view projection, according to the evaluation method described below, is 20% or less. Evaluation method: The following steps 1 to 3 are performed using an apparatus equipped with the following light source and camera device. Light source: White LED light source for irradiating the evaluation sample with inspection light. Camera device: A camera device that is configured to capture the transmitted light and reflected light of the sample used for inspection, and has a resolution of 2.8 μm. Step 1: A separator with a planar size of 50 mm x 50 mm is prepared as an evaluation sample, and the sample is set in the apparatus in a state where the inner region (30 mm x 30 mm) surrounded by the outer region of the sample can be imaged by the camera device. Step 2: While irradiating the sample with the inspection light from the white LED light source, the camera device is used to receive the transmitted light and / or reflected light from the sample. Light reception data is acquired over the aforementioned inner region. Step 3: Using the received light data, positional information and projected image information of the foreign object on the projection plane of the planar projection of the inner region are derived.

2. The separator according to claim 1, wherein the maximum length of the largest foreign object in the planar projection is 30 μm or less.

3. The separator according to claim 1 or 2, wherein the number of foreign objects with a maximum length of 20 μm or more and 30 μm or less in the planar projection is 5 or less.

4. The separator according to any one of claims 1 to 3, wherein the number of foreign objects with a maximum length of 15 μm or more and 30 μm or less in the planar projection is 10 or less.

5. The separator according to any one of claims 1 to 4, wherein the separator has a surface with a surface roughness Ra of 20 nm or less.

Images