Optical thin film with adhesive layer and image display device including the optical thin film with adhesive layer

Abstract

This invention provides an optical film with an adhesive layer that significantly suppresses adhesive deficiency in irregularly shaped processing sections and exhibits excellent transparency. The optical film with an adhesive layer according to an embodiment of this invention comprises an optical film and an adhesive layer located on one side of the optical film, and has an irregular shape other than a rectangle. The adhesive composition constituting the adhesive layer includes a (meth)acrylate-based polymer and an isocyanate-based crosslinking agent. The (meth)acrylate-based polymer includes aromatic (meth)acrylates as monomer components. The adhesive contains 2 to 20 parts by weight of the isocyanate-based crosslinking agent per 100 parts by weight of the (meth)acrylate-based polymer.

Description

[Technical Field]

[0001] The present invention relates to an optical thin film with an adhesive layer and an image display device comprising the optical thin film with the adhesive layer. [Previous Technology]

[0002] Optical films are widely used in image display devices such as mobile phones and laptops to achieve image display and / or improve the performance of the image display. An optical film is defined as an optical film with an adhesive layer, which can be bonded to an image display unit. In recent years, there has been a desire to process optical films into shapes other than rectangles (irregular shape processing: for example, forming notches and / or through holes). However, irregularly shaped portions of optical films with adhesive layers are prone to adhesive loss (the phenomenon of missing adhesive at the end of the adhesive layer). To address this, adhesives that can suppress adhesive loss in irregularly shaped portions have been examined; however, the high haze of these adhesives results in insufficient transparency of the resulting optical film with an adhesive layer. Previous Artwork Patent Documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2017-090896 [Summary of the Invention]

[0004] Problem to be solved by the invention The present invention is made to solve the above-mentioned prior art problems. Its main objective is to provide an optical film with an adhesive layer that can significantly suppress adhesive deficiency in irregularly shaped processing parts and has excellent transparency.

[0005] Means for Solving the Problem The optical film with an adhesive layer according to the present invention has an optical film and an adhesive layer located on one side of the optical film, and has an irregular shape other than a rectangle. The adhesive composition constituting the adhesive layer includes a (meth)acrylate-based polymer and an isocyanate-based crosslinking agent. The (meth)acrylate-based polymer includes an aromatic (meth)acrylate as a monomer component. The adhesive contains 2 to 20 parts by weight of the isocyanate-based crosslinking agent relative to 100 parts by weight of the (meth)acrylate-based polymer. In one embodiment, the isocyanate-based crosslinking agent is a toluene diisocyanate-based crosslinking agent. In another embodiment, the (meth)acrylate-based polymer contains 10 to 30 parts by weight of the aromatic (meth)acrylate relative to 100 parts by weight of the total monomer components. In one embodiment, the (meth)acrylic acid-based polymer further comprises at least one monomer component selected from carboxyl-containing monomers, hydroxyl-containing monomers, amide-containing monomers, nitrile-containing monomers, and multifunctional monomers. In one embodiment, the (meth)acrylic acid-based polymer comprises 0.1 to 1 part by weight of the aforementioned hydroxyl-containing monomer relative to 100 parts by weight of the total monomer component. In one embodiment, the (meth)acrylic acid-based polymer comprises 2 to 8 parts by weight of the aforementioned carboxyl-containing monomer relative to 100 parts by weight of the total monomer component. In one embodiment, the (meth)acrylic acid-based polymer has a weight average molecular weight of 2 million to 3 million. In one embodiment, the optical film comprises a polarizing element. In one embodiment, the optical film further comprises a phase retardation layer. According to another aspect of the present invention, an image display device is provided. The image display device comprises the aforementioned optical film with an adhesive layer.

[0006] Effects of the Invention According to an embodiment of the present invention, for an optical film having an adhesive layer with an irregular shape (irregular processing portion) other than a rectangle, by incorporating an adhesive composition constituting the adhesive layer containing an aromatic (meth) acrylate and a predetermined amount of isocyanate-based crosslinking agent, an optical film with an adhesive layer that can significantly suppress adhesive deficiency in the irregular processing portion and has excellent transparency can be achieved.

Implementation Method

[0008] The following description refers to specific embodiments of the present invention with reference to the drawings, but the present invention is not limited to these embodiments. In addition, the drawings are shown schematically for ease of viewing, and the proportions such as length, width, and thickness, as well as the angles in the drawings, are different from the actual figures.

[0009] A. Overview of the Optical Film with Adhesive Layer The optical film with adhesive layer according to an embodiment of the present invention comprises an optical film and an adhesive layer located on one side of the optical film. In an embodiment of the present invention, the optical film with adhesive layer has an irregular shape other than a rectangle. In this specification, "having an irregular shape other than a rectangle" means that the top view shape of the optical film with adhesive layer has a shape other than a rectangle (including rectangles and cases where corners are cut off). Irregular shape refers to an irregularly shaped processing section. Therefore, "an optical film with an adhesive layer having an irregular shape other than a rectangle" (hereinafter referred to as "irregularly shaped optical film") includes not only cases where the entire irregularly shaped optical film (i.e., the outer edge used to define the top view shape of the film) has a shape other than a rectangle, but also cases where an irregularly shaped processing section is formed in the portion that recedes inward from the outer edge of the rectangular optical film. In such irregularly shaped processing sections, adhesive loss is prone to occur, but according to an embodiment of the present invention, such adhesive loss can be significantly suppressed. As shown in Figures 1 and 2, irregularly shaped (machined) parts can include through holes and machined parts that appear as concave portions when viewed from above. Representative examples of concave portions include shapes resembling a boat, V-shaped notches, and U-shaped notches. Another example of an irregularly shaped (machined) part is shown in Figures 3 and 4, which corresponds to the shape of a car dashboard. This shape has an outer edge that forms an arc along the direction of rotation of the instrument needle, and includes a portion where the outer edge forms a V-shape (including the arc) that convexes inward in the direction of the surface. Of course, the shape of irregularly shaped (machined) parts is not limited to the examples shown in the figures. For example, the shape of a through hole can be any suitable shape (e.g., ellipse, triangle, square, pentagon, hexagon, octagon) depending on the purpose, in addition to the approximately circular shape shown in the figures. Furthermore, the through hole can be located in any suitable position depending on the purpose. The through-hole can be located approximately at the center of the long side of the rectangular optical film, as shown in Figure 2; it can be located at a predetermined position at the end of the long side, or at a corner of the optical film; although not shown, it can be located at the end of the short side of the rectangular optical film; and it can also be located at the center of the irregularly shaped optical film, as shown in Figure 3 or Figure 4. The shapes of the diagrams can be appropriately combined depending on the purpose. For example, a through-hole can be formed at any position on the irregularly shaped optical film of Figure 1; a V-shaped notch and / or a U-shaped notch can also be formed at any appropriate position on the outer edge of the irregularly shaped optical film of Figure 3 or Figure 4. This type of irregularly shaped optical film is suitable for use in image display devices such as automotive dashboards, smartphones, tablet PCs, or smartwatches.

[0010] In an embodiment of the present invention, the adhesive composition constituting the adhesive layer (hereinafter referred to simply as adhesive) comprises a (meth)acrylate-based base polymer and an isocyanate-based crosslinking agent. The (meth)acrylate-based base polymer comprises an aromatic (meth)acrylate. The adhesive comprises 2 to 20 parts by weight of an isocyanate-based crosslinking agent per 100 parts by weight of the (meth)acrylate-based base polymer. As described above, by incorporating an aromatic (meth)acrylate and a predetermined amount of isocyanate-based crosslinking agent into the adhesive constituting the adhesive layer, insufficient adhesive application in the irregularly shaped processing section can be significantly suppressed, and the haze of the resulting adhesive layer can be reduced, resulting in an optical film with excellent transparency of the adhesive layer. Furthermore, details of the composition of the adhesive layer will be described later in section C.

[0011] The amount of adhesive missing in the adhesive layer of the optical film with the adhesive layer attached (especially the adhesive layer of the irregularly shaped processing section) should preferably be 55µm or less, more preferably 52µm or less, and even more preferably 50µm or less. The smaller the amount of adhesive missing, the better, and its lower limit can be, for example, 5µm. According to the embodiment of the present invention, the amount of adhesive missing in the irregularly shaped processing section can be made very small as described above. In this specification, "amount of adhesive missing" refers to the maximum value of the adhesive layer missing in the direction from the outer edge of the optical film (including the outer edge of the through hole) toward the inner side of the surface.

[0012] B. Optical Thin Films Optical thin films can be single-layer films or laminates. Specific examples of single-layer optical thin films include window films, polarizing elements, and phase retardation films. Specific examples of laminated optical thin films include polarizing plates (representatively, a laminate of a polarizing element and a protective film), conductive films for touch panels, surface-treated films, and laminates formed by appropriately stacking such single-layer optical thin films and / or laminated optical thin films for various purposes (e.g., circular polarizing plates for anti-reflection applications, polarizing plates with conductive layers for touch panels). Below, polarizing plates and circular polarizing plates will be briefly described as representative examples of optical thin films.

[0013] B-1. Polarizing plate The polarizing plate has a polarizing element and a protective layer disposed on one or both sides of the polarizing element.

[0014] B-1-1. Polarizing element A polarizing element is represented as being constructed of a resin film containing a dichroic substance. Regarding the resin film, any suitable resin film suitable for use as a polarizing element may be used. A representative resin film is a polyvinyl alcohol-based resin (hereinafter referred to as "PVA-based resin") film. The resin film may be a single-layer resin film or a laminate of two or more layers.

[0015] A specific example of a polarizing element composed of a single-layer resin film may be a PVA-based resin film that has undergone iodine dyeing and stretching treatment (represented by uniaxial stretching). The aforementioned iodine dyeing can be performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The stretching ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching can be performed after dyeing or during dyeing. Alternatively, stretching can be performed before dyeing. The PVA-based resin film can be subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment, etc., as needed. For example, immersing the PVA-based resin film in water for washing before dyeing not only removes dirt or anti-adhesive agents from the surface of the PVA-based film but also causes the PVA-based resin film to swell, thereby preventing uneven dyeing.

[0016] Specific examples of polarizing elements obtained using a laminate include a laminate consisting of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a polarizing element obtained using a resin substrate and a laminate coated with a PVA-based resin layer formed on the resin substrate. A polarizing element obtained using a resin substrate and a laminate coated with a PVA-based resin layer formed on the resin substrate can be manufactured, for example, by the following steps: coating a PVA-based resin solution onto a resin substrate and drying it to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer; and extending and dyeing the laminate to form a polarizing element from the PVA-based resin layer. In this embodiment, extending typically includes immersing the laminate in an aqueous boric acid solution and extending it. Furthermore, if necessary, extending may further include air-stretching the laminate at a high temperature (e.g., above 95°C) before extending it in the aqueous boric acid solution. The resulting resin substrate / polarizer laminate can be used directly (i.e., the resin substrate can be used as a protective layer for the polarizer), or the resin substrate can be peeled off from the resin substrate / polarizer laminate and used as any suitable protective layer for the purpose on the peeled area layer. Detailed descriptions of the manufacturing method of the polarizer are available, for example, in Japanese Patent Application Publication No. 2012-73580 and Japanese Patent No. 6470455. The entire contents of these publications are incorporated herein by reference.

[0017] The thickness of the polarizing element should preferably be less than 25µm, more preferably 1µm to 12µm, even more preferably 3µm to 12µm, and especially preferably 3µm to 8µm. If the thickness of the polarizing element is within the above range, curling during heating can be well suppressed, and good appearance durability during heating can be obtained.

[0018] The polarizing element should preferably exhibit absorption dichroism at any wavelength between 380nm and 780nm. The transmittance of a single element should preferably be between 43.0% and 46.0%, more preferably between 44.5% and 46.0%. The polarization degree of the polarizing element is preferably above 97.0%, more preferably above 99.0%, and even more preferably above 99.9%.

[0019] B-1-2. Protective Layer The protective layer is formed of any suitable thin film that can be used as a protective layer for a polarizing element. Specific examples of materials that are the main components of the thin film include cellulose resins such as cellulose triacetate (TAC), or transparent resins such as polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyether ether, polyether ether, polystyrene, polynorbornene, polyolefin, (meth)acrylic acid, and acetate. Also, thermosetting or UV-curing resins such as (meth)acrylic acid, carbamate, (meth)acrylate carbamate, epoxy, and polysiloxane are also possible. Other examples include glassy polymers such as silicate polymers. Furthermore, polymer films described in Japanese Patent Application Publication No. 2001-343529 (WO01 / 37007) may also be used. As a material for this film, for example, a resin composition can be used containing a thermoplastic resin having substituted or unsubstituted amide groups on the side chains and a thermoplastic resin having substituted or unsubstituted phenyl and nitrile groups on the side chains. Examples include resin compositions comprising an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer. The polymer film can be, for example, an extruded product of the aforementioned resin composition.

[0020] The protective layer (outer protective layer) located on the opposite side of the adhesive layer may also be subjected to surface treatments such as hard coating, anti-reflective treatment, anti-sticking treatment, and anti-glare treatment as needed.

[0021] In one embodiment, the protective layer (inner protective layer) on the adhesive layer side is preferably optically isotropic. In this specification, "optically isotropic" means that the in-plane phase difference Re(550) is 0 nm to 10 nm, and the phase difference Rth(550) in the thickness direction is -10 nm to +10 nm. In another embodiment, the inner protective layer may also be a phase difference film, a brightness enhancement film, a diffusion film, etc.

[0022] The thickness of the protective layer can be any suitable thickness. The thickness of the protective layer is preferably 5µm to 200µm, 15µm to 45µm is more preferred, and 20µm to 40µm is even better. Furthermore, when a surface treatment is applied, the thickness of the protective layer includes the thickness of the surface treatment layer.

[0023] B-2. Circular Polarizing Plate A circular polarizing plate typically includes a polarizing element and a phase retardation layer. In practical use, the polarizing element can be incorporated into the circular polarizing plate in the form of a polarizing plate with protective layers on one or both sides. The phase retardation layer is typically disposed between the polarizing plate and the adhesive layer. The polarizing element and polarizing plate are as described in section B-1 above.

[0024] The phase difference layer can be a single layer or have a stacked structure.

[0025] When the phase retardation layer is composed of a single layer, it can function as λ / 4. In this case, the in-plane phase difference Re(550) of the phase retardation layer is preferably 100nm~190nm, more preferably 110nm~170nm, and even more preferably 130nm~160nm. The angle formed by the slow axis of the phase retardation layer and the absorption axis of the polarizer is preferably 40°~50°, more preferably 42°~48°, and even more preferably about 45°. The phase retardation layer can exhibit the inverse wavelength dispersion characteristic where the phase difference value increases with the wavelength of the measurement light, the normal wavelength dispersion characteristic where the phase difference value decreases with the wavelength of the measurement light, and the flat wavelength dispersion characteristic where the phase difference value hardly changes with the wavelength of the measurement light. In one embodiment, the phase retardation layer exhibits the inverse wavelength dispersion characteristic. In this case, the Re(450) / Re(550) of the phase retardation layer is preferably 0.8 or more and less than 1, and more preferably 0.8 or more and less than 0.95.

[0026] When the phase difference layer has a stacked structure, it means that it has a two-layer structure of a first phase difference layer and a second phase difference layer. In this case, either the first phase difference layer or the second phase difference layer can function as a λ / 2 plate, while the other can function as a λ / 4 plate. For example, when the first phase retardation layer functions as a λ / 2 plate and the second phase retardation layer functions as a λ / 4 plate, the Re(550) of the first phase retardation layer is preferably 200nm~300nm, more preferably 230nm~290nm, and even more preferably 250nm~280nm. The angle formed by its slow axis and the absorption axis of the polarizer is preferably 10°~20°, 12°~18° is preferred, and about 15° is even better. The Re(550) of the second phase retardation layer 22 is preferably 100nm~190nm, more preferably 110nm~170nm, and even more preferably 130nm~160nm. The angle formed by its slow axis and the absorption axis of the polarizer is preferably 70°~80°, 72°~78° is preferred, and about 75° is even better.

[0027] The retardation layer can be made of any suitable material as long as it meets the characteristics described above. For example, the retardation layer can be a resin film (represented by an extended film) or a liquid crystal compound orientation-cured layer (liquid crystal orientation-cured layer). Representative examples of resins constituting the resin film include polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyaryl ester resins, cyclic olefin resins, cellulose resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, and acrylic resins. These resins can be used alone or in combination (e.g., blending, copolymerization). When the retardation layer is made of a resin film exhibiting inverse dispersion wavelength characteristics, polycarbonate resins or polyester carbonate resins (hereinafter referred to only as polycarbonate resins) are suitable. Detailed descriptions of polycarbonate resins suitable for use in retardation layers and methods for forming retardation layers are provided, for example, in Japanese Patent Application Publications Nos. 2014-10291, 2014-26266, 2015-212816, 2015-212817, and 2015-212818; specific examples of liquid crystal compounds and detailed descriptions of methods for forming orientation-cured layers are provided, for example, in Japanese Patent Application Publication No. 2006-163343. This specification incorporates the descriptions in these publications by way of reference.

[0028] C. Adhesive Layer C-1. Characteristics of the Adhesive Layer The haze of the adhesive layer is preferably 2.0% or less, more preferably 1.8% or less, more preferably 1.5% or less, especially preferably 1.2% or less, and particularly preferably 1.0% or less. The lower the haze, the better, and its lower limit can be, for example, 0.05%. According to an embodiment of the present invention, the haze of the adhesive layer can be reduced to such a low level as described above (resulting in the realization of an optical film with excellent transparency of the adhesive layer), and at the same time, as described above, the lack of adhesive in irregularly shaped processing parts can be suppressed. In addition, the haze can be determined by JIS K 7136.

[0029] The creep value of the adhesive layer at 85°C is preferably below 500µm, more preferably 5µm to 500µm. In one embodiment, the creep value is preferably 200µm to 450µm, more preferably 220µm to 420µm. In another embodiment, the creep value is preferably 5µm to 300µm, more preferably 5µm to 200µm, even more preferably 10µm to 100µm, particularly preferably 15µm to 70µm, and especially preferably 20µm to 50µm. If the creep value is within the above range, insufficient adhesive in irregularly shaped processing parts can be significantly suppressed, and peeling under high temperature and high humidity environments can be significantly suppressed. We hypothesize that even with relatively large latent values ​​(e.g., above 200 µm), insufficient adhesive can be suppressed by controlling the composition of the adhesive constituting the adhesive layer (e.g., type of base polymer (polarity, Tg, flexibility), molecular weight) and crosslinking structure (e.g., type of crosslinking agent, distance between crosslinking points (molecular weight between crosslinking points), crosslinking density, and uncrosslinked components (sol content)). Furthermore, the latent value can be determined, for example, by attaching a test specimen cut from an optical film with an adhesive layer to a support plate with a 10 mm × 10 mm bonding surface. The support plate with the test specimen attached is fixed, and a load of 500 gf is applied vertically below this state. The offset from the support plate is measured after 1 second and 3600 seconds of the applied load, and these offsets are denoted as Cr1 and Cr3600, respectively. ΔCr is obtained from Cr1 and Cr3600 using the following formula and used as the latent value: ΔCr = Cr3600 - Cr1

[0030] The storage modulus of elasticity of the adhesive layer at 85°C is preferably 1.0 × 10⁴ Pa or higher, more preferably 2.0 × 10⁴ Pa or higher, more preferably 5.0 × 10⁴ Pa or higher, and especially preferably 1.0 × 10⁵ Pa or higher. If the storage modulus of elasticity is within this range, the desired creep value can be easily achieved. On the other hand, the storage modulus of elasticity is, for example, 3.0 × 10⁶ Pa or lower. If the upper limit of the storage modulus of elasticity is within this range, peeling of the adhesive layer under high temperature and high humidity conditions can be significantly suppressed.

[0031] The gel fraction of the adhesive layer is preferably 55% to 95%. In one embodiment, the gel fraction is preferably 60% to 93%, more preferably 80% to 91%. In this case, the weight average molecular weight Mw of the high molecular weight component derived from the base polymer in the uncrosslinked component (sol portion) of the adhesive composition is, for example, 50,000 to 1,000,000, preferably 50,000 to 500,000, more preferably 100,000 to 400,000. Furthermore, the gel fraction can be obtained by immersing the crosslinked adhesive in a predetermined solvent (e.g., ethyl acetate) for 6 days and then drying it, using (dry weight after immersion / dry weight before immersion) × 100. The weight average molecular weight Mw of the high molecular weight component derived from the base polymer in the uncrosslinked component (sol portion) of the base polymer and the adhesive composition can be determined using a gel permeation chromatography (GPC) and obtained from a value calculated using polystyrene.

[0032] The swelling degree of the adhesive layer should preferably be 35 times or less, more preferably 10 to 30 times, more preferably 11 to 28 times, and especially preferably 12 to 20 times. If the swelling degree is within the above range, the lack of adhesive in the irregularly shaped processing part can be significantly suppressed. In addition, the swelling degree can be obtained by immersing the cross-linked adhesive in a predetermined solvent (e.g., ethyl acetate) for 6 days and using (weight after immersion / dry weight after immersion).

[0033] The storage elastic modulus, gel fraction, and swelling degree of the adhesive layer can be controlled by adjusting the composition of the adhesive constituting the adhesive layer (e.g., the type of base polymer (polarity, Tg, softness), molecular weight), and crosslinking structure (e.g., the type of crosslinking agent, the distance between crosslinking points (molecular weight between crosslinking points), and the crosslinking density). More specifically, the type and combination of monomer components of the base polymer, the polymerization conditions of the base polymer, and the type and amount of crosslinking agent can be appropriately set.

[0034] The thickness of the adhesive layer is preferably 2µm to 55µm, more preferably 2µm to 30µm, even more preferably 2µm to 20µm, and especially preferably 5µm to 15µm. If the thickness of the adhesive layer is within the above range, the lack of adhesive in the irregularly shaped processing part can be significantly suppressed by the synergistic effect of the adhesive being made into the predetermined structure.

[0035] The adhesive layer is typically formed from an adhesive composition containing a (meth)acrylate polymer, a carbamate polymer, a polysiloxane polymer, or a rubber polymer as a base polymer. When a (meth)acrylate polymer is used as the base polymer, the adhesive layer is formed from an adhesive composition containing, for example, a (meth)acrylate polymer (A) as the base polymer. The (meth)acrylate polymer (A) contains an alkyl (meth)acrylate as a main component. In this invention, there are cases where the (meth)acrylate polymer used as the base polymer is referred to as a (meth)acrylate base polymer.

[0036] C-2. (Meth)acrylate polymer (A) As described above, the (meth)acrylate polymer (A) contains alkyl (meth)acrylate as a main component. From the viewpoint of improving the adhesion of the adhesive layer, the alkyl (meth)acrylate should preferably be 50 parts by weight or more relative to 100 parts by weight of the total monomer components forming the (meth)acrylate polymer (A), while the remaining monomers other than the alkyl (meth)acrylate can be arbitrarily set. Furthermore, (meth)acrylate refers to acrylate and / or methacrylate.

[0037] The alkyl methacrylate constituting the main skeleton of the (meth)acrylic polymer (A) may be linear or branched, with 1 to 18 carbon atoms. Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, cyclohexyl, heptyl, 2-ethylhexyl, isooctyl, nonyl, decyl, isodecyl, dodecyl, isomycinyl, lauryl, tridecanyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, etc. Alkyl methacrylates may be used alone or in combination. The average number of carbon atoms in the alkyl group is preferably 3 to 10.

[0038] In this embodiment of the invention, the (meth)acrylic polymer (A) includes an aromatic hydrocarbon monomer (a1) as a monomer component. The aromatic hydrocarbon monomer (a1) is a compound whose structure contains an aromatic hydrocarbon group and polymerizable unsaturated double bonds such as (meth)acrylic acid group and vinyl group. Specific examples of the aromatic hydrocarbon monomer (a1) include aromatic (meth)acrylates such as phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, and benzyl (meth)acrylate. Aromatic (meth)acrylates can be used alone or in combination. By using the aromatic hydrocarbon monomer (a1) as a monomer component, an adhesive layer with appropriate suppression of glue defects and low haze can be formed. More specifically, as described later, by using a predetermined amount or more of an isocyanate-based crosslinking agent, glue defects can be significantly suppressed. On the other hand, if a large amount of isocyanate-based crosslinking agent is used, the haze of the resulting adhesive layer may increase due to its refractive index, dispersibility, etc. By using aromatic hydrocarbon monomers (a1) as monomer components, the refractive index difference with isocyanate-based crosslinking agents can be reduced, and the dispersibility of isocyanate-based crosslinking agents in the adhesive composition can be improved. As a result, an adhesive layer (ultimately an optical film with an adhesive layer attached) can be achieved that balances the suppression of adhesive defects and transparency (low haze).

[0039] Relative to 100 parts by weight of the total monomer composition forming the (meth)acrylic polymer (A), the content of aromatic hydrocarbon monomer (a1) is preferably 10 parts by weight to 50 parts by weight, 10 parts by weight to 30 parts by weight is more preferred, and 11 parts by weight to 25 parts by weight is even more preferred. When the content is too low, the haze of the resulting adhesive layer will increase.

[0040] The (meth)acrylic polymer (A) may contain comonomers such as carboxyl-containing monomers (a2) and hydroxyl-containing monomers (a3), in addition to alkyl (meth)acrylates and aromatic hydrocarbon monomers (a1). Comonomers may be used alone or in combination. When the adhesive composition contains a crosslinking agent (described later), the comonomer becomes a reaction site with the crosslinking agent. Carboxyl-containing and hydroxyl-containing monomers exhibit good reactivity with intermolecular crosslinking agents, making them suitable for improving the cohesiveness and heat resistance of the resulting adhesive layer. From the viewpoint of balancing durability and reworkability, carboxyl-containing monomers are preferred, while from the viewpoint of improving reworkability, hydroxyl-containing monomers are preferred.

[0041] A carboxyl-containing monomer (a2) is a compound whose structure contains a carboxyl group and polymerizable unsaturated double bonds such as (meth)acrylic acid, (meth)acrylate, carboxyethyl methacrylate, (meth)acrylate, isoconic acid, maleic acid, fumaric acid, crotonic acid, etc. Among these, acrylic acid is preferable from the viewpoint of improving copolymerization, price, and adhesive properties of the adhesive layer.

[0042] When using a carboxyl-containing monomer (a2) as a monomer component, the content of the carboxyl-containing monomer (a2) should preferably be 0.01 parts by weight to 10 parts by weight, more preferably 2 parts by weight to 8 parts by weight, relative to 100 parts by weight of the total monomer component forming the (meth)acrylic polymer (A).

[0043] The hydroxyl-containing monomer (a3) ​​is a compound whose structure contains a hydroxyl group and polymerizable unsaturated double bonds such as (meth)acrylic acid, vinyl group, etc. Examples of hydroxyl-containing monomers include hydroxyalkyl esters of (meth)acrylate such as 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl methacrylate, 8-hydroxyoctyl methacrylate, 10-hydroxydecyl methacrylate, and 12-hydroxylaurate methacrylate; and (4-hydroxymethylcyclohexyl)-methacrylate. From the viewpoint of improving the durability of the adhesive layer, 2-hydroxyethyl methacrylate and 4-hydroxybutyl methacrylate are preferred, with 4-hydroxybutyl methacrylate being more desirable.

[0044] When using a hydroxyl-containing monomer (a3) ​​as a monomer component, the content of the hydroxyl-containing monomer (a3) ​​is preferably 0.01 parts by weight to 10 parts by weight, more preferably 0.05 parts by weight to 1 part by weight, relative to 100 parts by weight of the total monomer component forming the (meth)acrylic polymer (A).

[0045] Other comonomers (a4) may also be used in the monomer component. Other comonomers (a4) may have polymerizable functional groups, such as (meth)acrylic or vinyl unsaturated double bonds. By using other comonomers (a4), the adhesion and heat resistance of the adhesive layer can be improved. Other comonomers (a4) may be used alone or in combination.

[0046] Other comonomers (a4) can improve the adhesion and durability of the adhesive layer by using amino-containing monomers, amide-containing monomers, and nitrile-containing monomers. Examples of amino-containing monomers include N,N-dimethylaminoethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate. Examples of amide-containing monomers include: (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-isopropylacrylamide, N-methyl (meth)acrylamide, N-butyl (meth)acrylamide, N-hexyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-hydroxymethyl-N-propane (meth)acrylamide, aminomethyl (meth)acrylamide, etc. Acrylamide monomers include methyl methacrylamide, aminoethyl methacrylamide, mercaptomethyl methacrylamide, mercaptoethyl methacrylamide, etc.; N-acrylyl heterocyclic monomers include N-(meth)acrylamide morphofolin, N-(meth)acrylamide piperidine, N-(meth)acrylamide pyrrolidine, etc.; N-vinylpyrrolidone, N-vinyl-ε-caprolactam, etc., containing N-vinyl lactone monomers. Acrylonitrile monomers include, for example, (meth)acrylonitrile.

[0047] Other comonomers (a4) may also be multifunctional monomers. By using multifunctional monomers, the gel fraction of the adhesive layer or the cohesive force can be adjusted or controlled. Examples of multifunctional monomers include: hexanediol di(meth)acrylate (1,6-hexanediol di(meth)acrylate), butanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, neopentyl tetraethylene di(meth)acrylate, neopentyl tetraethylene tri(meth)acrylate, dinepentyl tetraethylene hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl methacrylate, vinyl methacrylate, epoxy acrylate, polyester acrylate, carbamate acrylate, and other multifunctional acrylates; and divinylbenzene. The polyfunctional acrylates are preferably 1,6-hexanediol diacrylate or dinepentylenetetrol hexa(meth)acrylate.

[0048] Other comonomers (a4) besides those mentioned above may include, for example: 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, methoxytriethylene glycol methacrylate, 3-methoxypropyl methacrylate, 3-ethoxypropyl methacrylate, 4-methoxybutyl methacrylate, 4-ethoxybutyl methacrylate, and other alkoxyalkyl methacrylates; cyclizable monomers such as methyl 2-(allyloxymeth)acrylate; and epoxy methacrylates. Acrylic acid ester, methyl methacrylate, and other epoxy-containing monomers; sodium vinyl sulfonate and other sulfonic acid-containing monomers; phosphate-containing monomers; cyclopentyl methacrylate, cyclohexyl methacrylate, isoborneol methacrylate, and other (meth)acrylates with alicyclic hydrocarbon groups; vinyl acetate, vinyl propionate, and other vinyl esters; styrene, vinyltoluene, and other aromatic vinyl compounds; olefins or dienes such as ethylene, propylene, butadiene, isoprene, and isobutylene; vinyl ethers such as vinyl alkyl ethers; vinyl chloride.

[0049] Relative to 100 parts by weight of the total monomer content forming the (meth)acrylic polymer (A), the content of other comonomers (a4) in the (meth)acrylic polymer (A) should preferably be 20 parts by weight or less, preferably 10 parts by weight or less, more preferably 8 parts by weight or less, and especially preferably 5 parts by weight or less.

[0050] The (meth)acrylic polymer (A) may also contain a monomer (a5) with an unsaturated carbon double bond and a glass transition temperature of 0°C or higher as a monomer component. Examples of monomers (a5) with an unsaturated carbon double bond and a glass transition temperature of 0°C or higher for the homopolymer include alkyl methacrylate monomers and (meth)acrylic acid. The monomer (a5) is preferably a monomer with an unsaturated carbon double bond and a glass transition temperature of 20°C or higher for the homopolymer, and more preferably a monomer with an unsaturated carbon double bond and a glass transition temperature of 40°C or higher for the homopolymer.

[0051] Monomers (a5) may include, for example, methyl acrylate (Tg: 8℃), methyl methacrylate (Tg: 105℃), ethyl methacrylate (Tg: 65℃), n-propyl acrylate (Tg: 3℃), n-propyl methacrylate (Tg: 35℃), n-amyl acrylate (Tg: 22℃), n-tetradecyl acrylate (Tg: 24℃), n-hexadecyl acrylate (Tg: 35℃), n-hexadecyl methacrylate (Tg: 15℃), n-octadecyl acrylate (Tg: 30℃), and n-octadecyl methacrylate (Tg: 38℃). Straight-chain alkyl esters of (meth)acrylate, such as methyl methacrylate (Tg: 43℃), methyl methacrylate (Tg: 48℃), isopropyl methacrylate (Tg: 81℃), and isobutyl methacrylate (Tg: 48℃); branched-chain alkyl esters of (meth)acrylate, such as cyclohexyl acrylate (Tg: 19℃), cyclohexyl methacrylate (Tg: 65℃), isoborneol acrylate (Tg: 94℃), and isoborneol methacrylate (Tg: 180℃); acrylic acid (Tg: 106℃), etc. These can be used alone or in combination.

[0052] C-3. Method for manufacturing (meth)acrylic polymer (A) The (meth)acrylic polymer (A) can be manufactured by any suitable method. Specific examples of manufacturing methods include radiation polymerization such as electron beam or UV polymerization, solution polymerization, bulk polymerization, emulsion polymerization, and various free radical polymerizations. The resulting (meth)acrylic polymer (A) can be any of random copolymers, block copolymers, graft copolymers, etc.

[0053] In solution polymerization, the polymerization solvent can be, for example, ethyl acetate or toluene. The solution polymerization reaction can be carried out, for example, by adding a polymerization initiator to the monomer component under a stream of inert gas such as nitrogen, and typically at around 50°C to 70°C for about 5 to 30 hours.

[0054] The polymerization initiator, chain transfer agent, emulsifier, etc. used for free radical polymerization can be appropriately selected according to the purpose. The weight average molecular weight of the (meth)acrylic polymer (A) can be controlled by the amount of polymerization initiator and chain transfer agent used and the reaction conditions, and the type and amount of them can be adjusted according to the desired weight average molecular weight.

[0055] As polymerization initiators, examples include azo-based initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-amidinylpropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-methylpropanediamine) disulfate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropanediamine] hydrate (manufactured by Wako Pure Chemical Industries, Ltd., VA-057), potassium persulfate, ammonium persulfate, di(2-ethylhexyl) peroxydicarbonate, and di(4-tert-butylcyclohexyl) peroxydicarbonate. Dicarbonate oxide, di-dibutyl peroxide, tert-butyl peroxyneodecanate, tert-hexyl peroxytrimethylacetic acid, tert-butyl peroxytrimethylacetic acid, dilauryl peroxide, di-n-octyl peroxide, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(4-methylbenzoyl)peroxide, dibenzoyl peroxide, tert-butyl perisobutyrate, 1,1-di(tert-hexylperoxy)cyclohexane, tert-butyl hydrogen peroxide, hydrogen peroxide and other peroxide-based initiators; combinations of persulfate and sodium bisulfite; combinations of peroxide and sodium ascorbate and other peroxide-reducing agents to form redox initiators, etc.

[0056] The polymerization initiator can be used alone or in combination. The total amount of polymerization initiator used relative to 100 parts by weight of monomer components should preferably be about 0.005 parts by weight to 1 part by weight, and more preferably about 0.01 parts by weight to 0.5 parts by weight.

[0057] Examples of chain transfer agents include lauryl thiol, epichlorohydrin, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolic acid, and 2,3-dimercapto-1-propanol. Chain transfer agents can be used alone or in combination of two or more. The total amount of chain transfer agent used is approximately 0.1 parts by weight or less per 100 parts by weight of the monomer component.

[0058] Examples of emulsifiers used in emulsified polymerization include anionic emulsifiers such as sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, polyoxyethylene alkyl ether ammonium sulfate, and polyoxyethylene alkylphenyl ether sodium sulfate, as well as nonionic emulsifiers such as polyoxyethylene alkyl ether, polyoxyethylene ethyl alkylphenyl ether, polyoxyethylene fatty acid ester, and polyoxyethylene ethyl-polyoxypropylene block polymer. Emulsifiers can be used alone or in combination.

[0059] Reactive emulsifiers may include, for example, emulsifiers incorporating free radical polymerizable functional groups such as propylene groups and allyl ether groups. Specific examples include Aqualon HS-10, HS-20, KH-10, BC-05, BC-10, and BC-20 (all manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), and ADEKA REASOAP SE10N (manufactured by ADEKA Corporation). Since reactive emulsifiers incorporate into the polymer chain after polymerization, good water resistance is preferred. The amount of emulsifier used relative to 100 parts by weight of the total monomer components is preferably 0.3 parts by weight to 5 parts by weight, more preferably 0.5 parts by weight to 1 part by weight. If the amount of emulsifier used is within the above range, the polymerization stability and the mechanical stability of the resulting adhesive layer are good.

[0060] When manufacturing (meth)acrylic acid polymers (A) using radiation polymerization, the monomer components can be polymerized by irradiating them with radiation such as electron beams or UV rays. When performing radiation polymerization using UV polymerization, the monomer components can contain photopolymerization initiators. This can shorten the polymerization time. When performing radiation polymerization using electron beams, it is not necessary to specifically contain photopolymerization initiators in the monomer components.

[0061] Any suitable photopolymerization initiator may be used. Specific examples include: benzoin ether-based, acetophenone-based, α-ketool-based, photoactive oxime-based, benzoin-based, benzyl-based, diphenyl ketone-based, ketal-based, and 9-oxosulfur-based photopolymerization initiators. The amount of photopolymerization initiator used relative to 100 parts by weight of the total monomer components is preferably 0.02 parts by weight to 1.5 parts by weight, more preferably 0.1 parts by weight to 1 part by weight. The photopolymerization initiator may be used alone or in combination.

[0062] The weight average molecular weight (Mw) of the (meth)acrylic polymer (A) is preferably 1 million to 3 million, more preferably 2 million to 3 million, and even more preferably 2 million to 2.8 million. If the weight average molecular weight (Mw) is less than 1 million, insufficient glue production may not be adequately suppressed. If the weight average molecular weight (Mw) is greater than 3 million, viscosity may increase and / or gelation may occur during polymer polymerization.

[0063] The polydispersity (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the (meth)acrylic polymer (A) should preferably be 5.0 or less, more preferably 1.05 to 5.0, and even more preferably 1.05 to 4.0. When the polydispersity (Mw / Mn) is large (e.g., greater than 5.0), there are more low molecular weight polymers. Even if the same constituent materials are used to form the adhesive layer, the amount of uncrosslinked polymers or oligomers (sol components) will still increase, and the toughness of the adhesive layer will decrease (become more brittle), resulting in insufficient adhesive during irregular processing or peeling under high temperature and high humidity conditions. In addition, the polydispersity (Mw / Mn), like the weight average molecular weight, can be determined by GPC (gel permeation chromatography) and obtained from the value calculated by converting to styrene.

[0064] C-4. Silane coupling agent adhesive compositions containing functional groups may contain silane coupling agents containing functional groups. Examples of functional groups include epoxy, mercapto, amino, isocyanate, triisocyanate, vinyl, styrene, acetoacetyl, urea, thiourea, (meth)acrylyl, heterocyclic, anhydride, and combinations thereof. The silane coupling agent containing functional groups may be used alone or in combination.

[0065] Examples of functionalized silane coupling agents include: 3-epoxypropoxypropyltrimethoxysilane, 3-epoxypropoxypropyltriethoxysilane, 3-epoxypropoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, etc., epoxy-containing silane coupling agents; 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, etc., mercapto-containing silane coupling agents; 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilane... Silicon coupling agents containing amino groups, such as propyl-N-(1,3-dimethylbutylene)propylamine and N-phenyl-γ-aminopropyltrimethoxysilane; silicone coupling agents containing isocyanate groups, such as propyltriethoxysilane; vinyl-containing silicone coupling agents, such as vinyltrimethoxysilane and vinyltriethoxysilane; styrene-containing silicone coupling agents, such as p-styrenetrimethoxysilane; and silicone coupling agents containing (meth)acrylic acid, such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane. Among these, silicone coupling agents containing epoxy groups and silicone coupling agents containing mercapto groups are preferred. For example, commercially available silicone coupling agents include "KBM-403" manufactured by Shin-Etsu Chemical Co., Ltd.

[0066] Silicon coupling agents containing functional groups can also be those with multiple alkoxysilane groups within the molecule (oligomeric silicone coupling agents). Specifically, examples include: epoxy-containing oligomeric silicone coupling agents manufactured by Shin-Etsu Chemical Co., Ltd., trade names "X-41-1053", "X-41-1059A", "X-41-1056", and "X-40-2651"; and mercapto-containing oligomeric silicone coupling agents "X-41-1818", "X-41-1810", and "X-41-1805". Because oligomeric silicone coupling agents are less volatile and have multiple alkoxysilane groups, they can effectively improve durability.

[0067] When a functionalized silane coupling agent is incorporated into an adhesive composition, the amount of the functionalized silane coupling agent incorporated is typically 0.001 parts by weight or more and 5 parts by weight or less relative to 100 parts by weight of the (meth)acrylic polymer (A).

[0068] C-5. Crosslinking Agent In this embodiment of the invention, the adhesive composition (adhesive) constituting the adhesive layer contains an isocyanate-based crosslinking agent. By containing an isocyanate-based crosslinking agent, adhesive failure can be suppressed. For example, an isocyanate-based crosslinking agent can be a compound having at least two isocyanate groups (including isocyanate-regenerated functional groups whose isocyanate groups are temporarily protected by end-capping agents or polymerization). For example, any suitable aliphatic polyisocyanate, alicyclic polyisocyanate, aromatic polyisocyanate, etc., that can be used for carbamate reactions can be used.

[0069] Aliphatic polyisocyanates include, for example, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-epoxypropyl diisocyanate, 1,3-epoxybutyl diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0070] Examples of alicyclic isocyanates include 1,3-cyclopentene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, isoflavone diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated benzoyl diisocyanate, toluene diisocyanate, and hydrogenated tetramethyl benzoyl diisocyanate.

[0071] Examples of aromatic diisocyanates include phenylene diisocyanate, toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, and phenylene diisocyanate.

[0072] Other examples of isocyanate-based crosslinking agents include the carbamate-modified products, urea-modified products, biuret-modified products, urea-modified products, triisocyanate-modified products, and carbodiimide-modified products obtained by reacting the above-mentioned diisocyanate polymers (dimers, trimers, pentamers, etc.) with polyols such as trimethylolpropane.

[0073] Commercially available isocyanate-based crosslinking agents include, for example, those manufactured by Tosoh (stock) under the trade names “Millionate MT”, “Millionate MTL”, “Millionate MR-200”, “Millionate MR-400”, “CORONATE L”, “CORONATE HL”, and “CORONATE HX”; and those manufactured by Mitsui Chemicals (stock) under the trade names “Takenate D-110N”, “Takenate D-120N”, “Takenate D-140N”, “Takenate D-160N”, “Takenate D-165N”, “Takenate D-170HN”, “Takenate D-178N”, “Takenate 500”, and “Takenate 600”.

[0074] Isocyanate-based crosslinking agents are preferably aromatic polyisocyanates and their modified aromatic polyisocyanates, and aliphatic polyisocyanates and their modified aliphatic polyisocyanates. Aromatic polyisocyanate compounds have a good balance between crosslinking speed and pot life, making them suitable for use. Toluene diisocyanate and its modified aromatic polyisocyanates are particularly preferred (sometimes these are collectively referred to as toluene diisocyanate-based crosslinking agents).

[0075] The amount of isocyanate-based crosslinking agent in the adhesive composition is 2 to 20 parts by weight relative to 100 parts by weight of (meth)acrylic polymer (A), preferably 2 to 18 parts by weight, and more preferably 2 to 15 parts by weight. If the amount of isocyanate-based crosslinking agent is within the above range, an adhesive layer with an excellent balance between insufficient adhesive and haze can be formed. If the amount of isocyanate-based crosslinking agent is too small, insufficient adhesive may not be adequately suppressed. If the amount of isocyanate-based crosslinking agent is too large, the resulting adhesive layer may have increased haze.

[0076] In one embodiment, both isocyanate-based crosslinking agents and peroxide-based crosslinking agents can be used as crosslinking agents in the adhesive composition.

[0077] Any suitable peroxide-based crosslinking agent can be used, as long as it generates free radical active species upon heating or light irradiation, thereby crosslinking the base polymer ((meth)acrylic polymer (A)) of the adhesive composition. A peroxide with a 1-minute half-life temperature of 80°C to 160°C is preferred, and more preferably, a peroxide with a 1-minute half-life temperature of 90°C to 140°C is also preferred. This type of peroxide exhibits good workability and stability.

[0078] Examples of the peroxides mentioned above include di(2-ethylhexyl)peroxydicarbonate (1-minute half-life temperature: 90.6℃), di(4-tert-butylcyclohexyl)peroxydicarbonate (1-minute half-life temperature: 92.1℃), di-secondary butyl peroxydicarbonate (1-minute half-life temperature: 92.4℃), tert-butyl peroxyneodecanate (1-minute half-life temperature: 103.5℃), tert-hexyl peroxytrimethylacetic acid (1-minute half-life temperature: 109.1℃), tert-butyl peroxytrimethylacetic acid (1-minute half-life temperature: 110.3℃), and dilauryl peroxide. The following compounds were selected for their cross-linking efficiency: di(n-octyl)peroxide (1-minute half-life temperature: 117.4℃), 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate (1-minute half-life temperature: 124.3℃), di(4-methylbenzoyl)peroxide (1-minute half-life temperature: 128.2℃), dibenzoylperoxide (1-minute half-life temperature: 130.0℃), tributyl perisobutyrate (1-minute half-life temperature: 136.1℃), and 1,1-di(tri-hexylperoxy)cyclohexane (1-minute half-life temperature: 149.2℃). Among these, di(4-tri-butylcyclohexyl)peroxydicarbonate, dilauryl peroxide, and dibenzoylperoxide were preferred.

[0079] Furthermore, the half-life of a peroxide is an indicator of the rate of decomposition of the peroxide, meaning the time when the residual amount of the peroxide becomes half. The decomposition temperature required to reach the half-life at any time, or the half-life time at any temperature, is described in the manufacturer's catalogue, such as the "Organic Peroxide Catalogue, 9th Edition (May 2003)" of Nippon Oils & Fats Co., Ltd.

[0080] When a peroxide-based crosslinking agent is incorporated into the adhesive composition, the amount of the peroxide-based crosslinking agent incorporated is preferably 0.01 to 2 parts by weight, or 0.1 to 0.5 parts by weight, relative to 100 parts by weight of the (meth)acrylic polymer (A). Within this range, processability and crosslinking stability can be easily adjusted.

[0081] It can also replace peroxide-based crosslinking agents, or in addition to peroxide-based crosslinking agents, other crosslinking agents can be used in combination with isocyanate-based crosslinking agents. Other crosslinking agents include, for example, multifunctional metal chelates, epoxy-based crosslinking agents, and imine-based crosslinking agents. Multifunctional metal chelates are compounds in which multivalent metals are covalently or coordinately bonded to organic compounds. Examples of multivalent metal atoms include Al, Cr, Zr, Co, Cu, Fe, Ni, V, Zn, In, Ca, Mg, Mn, Y, Ce, Sr, Ba, Mo, La, Sn, Ti, etc. Examples of organic compounds that can be covalently or coordinately bonded include oxygen atoms, and examples of organic compounds include alkyl esters, alcohols, carboxylic acids, ethers, ketones, etc.

[0082] C-6. Other components. The adhesive composition may also contain (meth)acrylic oligomers. (Meth)acrylic oligomers may be obtained by polymerizing the monomer components described in section C-2 of the (meth)acrylic polymer individually or by copolymerizing two or more of them. The type, quantity, combination, and polymerization molar ratio of the monomer components may be appropriately set according to the purpose and desired characteristics. The weight average molecular weight (Mw) of the (meth)acrylic oligomer is preferably 1000-8000, more preferably 2000-7000, and even more preferably 3000-6000. When (meth)acrylic oligomers are blended into the adhesive composition, the amount of (meth)acrylic oligomers blended relative to 100 parts by weight of the (meth)acrylic polymer (A) is preferably 5-35 parts by weight.

[0083] The adhesive composition may contain an ionic compound. Any suitable ionic compound may be used. Examples of suitable ionic compounds include those described in Japanese Patent Application Publication No. 2015-4861, among which lithium (perfluoroalkylsulfonyl)imidinium salt is preferred, and lithium bis(trifluoromethanesulfonylimidinium) is even more preferred. The amount of ionic compound incorporated can be appropriately set according to the purpose. For example, relative to 100 parts by weight of the (meth)acrylic polymer (A), the amount of ionic compound incorporated is preferably 10 parts by weight or less, preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and especially preferably 1 part by weight or less.

[0084] The adhesive composition may also contain additives. Specific examples of additives include colorants, pigments and other powders, dyes, surfactants, plasticizers, tackifiers, surface lubricants, leveling agents, softeners, antioxidants, anti-aging agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, inorganic or organic fillers, metal powders, granules, foils, etc. Furthermore, redox systems with added reducing agents may be used within a controllable range. The type, quantity, combination, and content of additives can be appropriately set according to the purpose. The content of additives relative to 100 parts by weight of the (meth)acrylic polymer (A) should preferably be 5 parts by weight or less, more preferably 3 parts by weight or less, and even more preferably 1 part by weight or less.

[0085] D. Image Display Device The optical thin film with adhesive layer in the embodiments of the present invention, as described above, is suitable for use in image display devices. Therefore, image display devices comprising optical thin films with adhesive layers are also included in the embodiments of the present invention. An image display device typically includes an image display unit and an optical thin film with an adhesive layer bonded to the image display unit through an adhesive layer. Examples of image display devices include liquid crystal display devices, organic electroluminescent (EL) display devices, and quantum dot display devices. Organic EL display devices are preferred. This is due to the significant effect brought about by the optical thin film with adhesive layers.

[0086] Examples The present invention will be specifically described below by way of examples, but the present invention is not limited to these examples. The evaluation items of the examples are as follows. Furthermore, unless otherwise specified, "parts" and "%" in the examples refer to weight.

[0087] (1) The amount of adhesive missing was determined by observing the cross-sectional state of the adhesive layer of the irregularly shaped processing part of the optical film with adhesive layer obtained in the examples and comparative examples using an optical microscope. The length of the part with the largest defect in the adhesive layer from the outer edge to the inner side of the surface was measured, and this length was taken as the amount of adhesive missing (µm). (2) The haze was measured by using a haze meter (Murakami Color Science Research Institute Co., Ltd., trade name "HM-150") according to the method specified in JIS K 7136.

[0088] <Manufacturing Example 1: Preparation of Acrylic Polymer A1> A monomer mixture containing 74.9 parts butyl acrylate, 20 parts benzyl acrylate, 5 parts acrylic acid, and 0.1 parts 4-hydroxybutyl acrylate was fed into a four-necked flask equipped with a stirring blade, thermometer, nitrogen inlet pipe, and cooler. 0.1 parts 2,2'-azobisisobutyronitrile (2,2'-azobisisobutyronitrile), used as a polymerization initiator, and 100 parts ethyl acetate were added to each 100 parts of the monomer mixture. Nitrogen substitution was carried out by slowly stirring and introducing nitrogen gas. The liquid temperature in the flask was maintained at approximately 55°C, and the polymerization reaction was carried out for 8 hours to prepare a solution of acrylic polymer A1 with a weight average molecular weight (Mw) of 2.1 million.

[0089] <Manufacturing Example 2: Preparation of Acrylic Polymer A2> Except for using a monomer mixture containing 82.9 parts of butyl acrylate, 12 parts of benzyl acrylate, 5 parts of acrylic acid and 0.1 parts of 4-hydroxybutyl acrylate, a solution of acrylic polymer A2 with a yield of Mw205 was prepared in the same manner as in Manufacturing Example 1.

[0090] <Manufacturing Example 3: Preparation of Acrylic Polymer A3> Except for using a monomer mixture containing 79.9 parts of butyl acrylate, 15 parts of phenoxyethyl acrylate, 5 parts of acrylic acid and 0.1 parts of 4-hydroxybutyl acrylate, a solution of acrylic polymer A3 with a yield of Mw2.6 million was prepared in the same manner as in Manufacturing Example 1.

[0091] <Manufacturing Example 4: Preparation of Acrylic Polymer A4> Except for replacing a portion of the ethyl acetate fed during polymerization with toluene, a solution of acrylic polymer A4 with a yield of Mw 1.2 million was prepared in the same manner as in Manufacturing Example 1.

[0092] <Manufacturing Example 5: Preparation of Acrylic Polymer A5> Except for using a monomer mixture containing 94.9 parts of butyl acrylate, 5 parts of acrylic acid and 0.1 parts of 4-hydroxybutyl acrylate, a solution of acrylic polymer A5 with a yield of Mw2.2 million was prepared in the same manner as in Manufacturing Example 1.

[0093] <Manufacturing Example 6: Fabrication of Polarizing Plate> (with Fabrication of TAC Film of HC) In a resin solution (manufactured by DIC Corporation, trade name: UNIDIC 17-806, solids concentration: 80%) obtained by dissolving a UV-curable resin monomer or oligomer with carbamate acrylate as the main component in butyl acetate, 5 parts of photopolymerization initiator (manufactured by BASF Corporation, trade name: IRGACURE 907) and 0.1 parts of leveling agent (manufactured by DIC Corporation, trade name: GRANDIC PC4100) are added per 100 parts of solids in the solution. Cyclopentanone and propylene glycol monomethyl ether are added to the solution at a ratio of 45:55 to make the solids concentration in the solution 36%, thereby preparing a hard coating forming material. The hard coating material was applied to a TAC film (manufactured by FUJIFILM, product name: TJ40UL, thickness: 40µm) to form a hard coating with a cured thickness of 7µm. The coating was dried at 90°C for 1 minute and then irradiated with ultraviolet light at a cumulative intensity of 300mJ / cm² using a high-pressure mercury lamp to harden the coating and form a hard coating, thus producing an HC-coated TAC film. The resulting HC-coated TAC film was then subjected to a saponification treatment.

[0094] (Preparation of a polarizing plate) A 45µm thick polyvinyl alcohol film was dyed for 1 minute in a 0.3% iodine solution at 30°C and stretched to 3 times its original length between rollers with different speed ratios. Then, it was immersed in an aqueous solution containing 4% boric acid and 10% potassium iodide at 60°C for 0.5 minutes while being stretched to a total elongation of 6 times. Next, it was washed by immersion in an aqueous solution containing 1.5% potassium iodide at 30°C for 10 seconds and then dried at 50°C for 4 minutes to obtain a 18µm thick polarizing element. The obtained HC-coated TAC film was bonded to one side of the polarizing element using a polyvinyl alcohol-based adhesive, and a 40µm thick TAC film (KC4CT, manufactured by Konica Minolta) that had undergone saponification treatment was bonded to the other side to produce a polarizing plate.

[0095] <Example 1> (Preparation of adhesive composition) 100 parts of the solid component of the acrylic polymer A1 solution obtained in Manufacturing Example 1 were mixed with 2 parts of isocyanate crosslinking agent (trimethylolpropane / toluene diisocyanate adduct: manufactured by Tosoh Corporation, trade name "Coronate L"), 0.2 parts of peroxide crosslinking agent (manufactured by Nippon Yushi Co., Ltd., trade name "NYPER BMT") and 0.2 parts of silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KBM-403") to prepare an acrylic adhesive composition solution.

[0096] (Preparation of the polarizing plate with adhesive layer) To achieve a dry adhesive layer thickness of 20µm, a solution of the aforementioned acrylic adhesive composition was coated onto one side of a polyethylene terephthalate film (Mitsubishi Chemical Polyester Film, trade name "MRF38", release film) treated with a polysiloxane release agent, and dried at 155°C for 1 minute to form an adhesive layer on the surface of the release film. Next, the adhesive layer formed on the release film was transferred to the TAC film (KC4CT) side of the polarizing plate prepared in Manufacturing Example 6 to produce an optical film with an adhesive layer (polarizing plate with adhesive layer). The obtained polarizing film with adhesive layer was then subjected to irregular shaping processing. At this point, the laminated body with a surface protective film (manufactured by Nitto Denko, trade name "PPF-100T") on the TAC film side of the obtained adhesive layer polarizing film is used as the workpiece for irregular shape processing. More specifically, the laminated bodies are stacked to a layer height of 10 mm, and the formed laminate is clamped and fixed. Then, a through hole is cut from the surface protective film side using an end mill with a cutting diameter of 2.0 mm, and the hole diameter is cut to a shape corresponding to the center of the lower section of Figure 2. The cutting is performed at a cutting speed of 2500 rpm and a feed rate of 50 mm / min. The polarizing plate with the adhesive layer after irregular shape processing is provided for evaluation in (1) above, and the adhesive layer used to make the optical film with the adhesive layer is provided for evaluation in (2) above. The results are listed in Table 1.

[0097] <Examples 2-9 and Comparative Examples 1-2> Except that the composition of the adhesive component forming the adhesive layer was changed as shown in Table 1, optical films with adhesive layers were fabricated in the same manner as in Example 1. The adhesive layer used to fabricate the optical film with adhesive layers and the polarizing plate with the adhesive layers formed by the adhesive layers were subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[0098] [Table 1]

[0099] The abbreviations in Table 1 are as follows. Furthermore, the blending amounts of each component in Table 1 are relative to 100 parts of the polymer. BA: Butyl acrylate; BzA: Benzyl acrylate; PEA: Phenoxyethyl acrylate; AA: Acrylic acid; HBA: 4-Hydroxybutyl acrylate; C / L: Trimethylolpropane / Toluene diisocyanate adduct (manufactured by Tosoh Corporation, trade name "CORONATE L"); Peroxide: Peroxide crosslinking agent (manufactured by Nippon Yushi Co., Ltd., trade name "NYPER BMT"); Si-cup agent: Epoxy-containing silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KBM-403").

[0100] <Example 9> (Preparation of a polarizing plate) A long roll of 30µm thick polyvinyl alcohol film (Kuraray's product name "PE3000") was uniaxially stretched along its length by a roll stretcher to a length of 5.9 times, while simultaneously undergoing swelling, dyeing, crosslinking, and washing treatments, and finally dried to produce a polarizing element with a thickness of 12µm. Specifically, the swelling treatment was carried out in pure water at 20°C while stretching to a length of 2.2 times. Next, the dyeing treatment was carried out in an aqueous solution at 30°C with an iodine to potassium iodide weight ratio of 1:7, adjusted to achieve a transmittance of 45.0% for the polarizing film, while stretching to a length of 1.4 times. Then, the crosslinking treatment employed a two-stage crosslinking process. The first stage of crosslinking was carried out in an aqueous solution of boric acid and potassium iodide dissolved at 40°C while stretching to a length of 1.2 times. The boric acid content in the aqueous solution for the first-stage crosslinking treatment was set to 5.0% by weight, and the potassium iodide content was set to 3.0% by weight. The second-stage crosslinking treatment involved extending the crosslinking layer by 1.6 times while being treated in an aqueous solution of boric acid and potassium iodide dissolved at 65°C. The boric acid content in the aqueous solution for the second-stage crosslinking treatment was set to 4.3% by weight, and the potassium iodide content was set to 5.0% by weight. Furthermore, the washing treatment was performed using a potassium iodide aqueous solution at 20°C. The potassium iodide content in the washing treatment aqueous solution was set to 2.6% by weight. Finally, the drying treatment involved drying the polarizer at 70°C for 5 minutes to obtain the polarizing element. A TAC film (product name: KC2UA, thickness: 25µm) manufactured by Konica Minolta AG and an HC-TAC film (thickness: 32µm) with an HC layer on one side of the TAC film were bonded to both sides of the obtained polarizing element using a polyvinyl alcohol adhesive, respectively, to obtain a polarizing plate 1 with protective films bonded to both sides of the polarizing element.

[0101] (Preparation of Phase Difference Layer A) 10g of a polymerizable liquid crystal (manufactured by BASF, product name "Paliocolor LC242", denoted by the following formula) displaying a nematic liquid crystal phase and 3g of a photopolymerization initiator for the polymerizable liquid crystal compound (manufactured by Ciba Specialty Chemicals, product name "IRGACURE 907") were dissolved in 40g of toluene to prepare a liquid crystal composition (coating solution). [Chemical Formula 1] The surface of a polyethylene terephthalate (PET) film (thickness 38µm) was wiped with a wiping cloth to perform an orientation treatment. The orientation treatment conditions were: 1 rub (number of rub rollers), 76.89mm radius of the rub rollers r, 1500rpm rotation of the rub rollers nr, and 83mm / s film transport speed v.

[0102] The orientation treatment direction is set to be -75° relative to the absorption axis of the polarizer when viewed from the viewing side when attached to the polarizing plate. The above-mentioned coating liquid is applied to the orientation-treated surface using a bar coater and heated to 90°C for 2 minutes to dry, thereby orienting the liquid crystal compound. A metal halide lamp is used to irradiate the liquid crystal layer formed in the above manner with light of 1 mJ / cm² to harden the liquid crystal layer, thereby forming a phase retardation layer A on the PET film. The phase retardation layer A has a thickness of 2 µm and an in-plane phase retardation Re of 270 nm. Furthermore, the phase retardation layer A has a refractive index distribution of nx > ny = nz.

[0103] (Fabrication of Phase Retardation Layer B) The surface of a polyethylene terephthalate (PET) film (38µm thick) was wiped with a wiping cloth to perform an orientation treatment. The orientation treatment direction was set to be -15° relative to the absorption axis of the polarizer when viewed from the viewing side. The same liquid crystal coating liquid as described above was applied to the orientation-treated surface, and the liquid crystal was oriented and cured in the same manner as described above to form a phase retardation layer B on the PET film. The thickness of the phase retardation layer B is 1.2µm, and the in-plane phase difference Re is 140nm. Furthermore, the phase retardation layer B has a refractive index distribution of nx > ny = nz.

[0104] (Fabrication of a polarizing plate with a phase retardation layer) The TAC film surface of the polarizing plate and the phase retardation layer A are bonded together using an ultraviolet-curing adhesive such that the angle between the absorption axis of the polarizing plate and the slow axis of the phase retardation layer A is 75°. Next, the phase retardation layer A and the phase retardation layer B are bonded together using the same adhesive (5µm thick) as in Example 14 such that the angle between the absorption axis of the polarizing plate and the slow axis of the phase retardation layer B is 15°, thereby obtaining a polarizing plate with a phase retardation layer. Adhesive layers identical to those in Examples 1-8 and Comparative Examples 1-2 are formed on the outer side of the phase retardation layer B. The obtained polarizing plate with a phase retardation layer is shaped in the same manner as in Example 1 and is subjected to the same evaluation as in Example 1. The results confirmed that, for polarizing plates with a phase retardation layer, those using adhesive layers corresponding to Examples 1-8 had good adhesive shortage and haze, those using adhesive layers corresponding to Comparative Example 1 had high haze, and those using adhesive layers corresponding to Comparative Example 2 had a large amount of adhesive shortage.

[0105] <Evaluation> As can be clearly seen from Table 1, according to the embodiments of the present invention, an optical film with an adhesive layer that can significantly suppress adhesive deficiency in irregularly shaped processing sections and has excellent transparency can be practically obtained. Comparative Example 1, which did not use aromatic (meth)acrylate in the adhesive constituting the adhesive layer, had a high haze in its adhesive layer, resulting in insufficient transparency of the optical film with the adhesive layer. Comparative Example 2, which had a small amount of isocyanate-based crosslinking agent, had a large amount of adhesive deficiency.

[0106] Industrial Applicability The optical film with adhesive layer of the present invention is suitable for use in image display devices, especially for image display devices with irregularly shaped processing parts, such as car dashboards, smartphones, tablet PCs or smartwatches. [Simplified Explanation of the Diagram]

[0007] FIG1 is a schematic top view illustrating an example of an irregularly shaped or irregularly shaped processing section of an optical thin film with an adhesive layer according to an embodiment of the present invention. FIG2 is a schematic top view illustrating a modified example of an irregularly shaped or irregularly shaped processing section of an optical thin film with an adhesive layer according to an embodiment of the present invention. FIG3 is a schematic top view illustrating another modified example of an irregularly shaped or irregularly shaped processing section of an optical thin film with an adhesive layer according to an embodiment of the present invention. FIG4 is a schematic top view illustrating another modified example of an irregularly shaped or irregularly shaped processing section of an optical thin film with an adhesive layer according to an embodiment of the present invention.

Claims

1. An optical film with an adhesive layer, comprising an optical film and an adhesive layer on one side of the optical film; the optical film with the adhesive layer having an irregular shape other than a rectangle; the adhesive composition constituting the adhesive layer comprising a (meth)acrylate-based polymer and an isocyanate-based crosslinking agent; the (meth)acrylate-based polymer comprising aromatic (meth)acrylate, a carboxyl-containing monomer, and a hydroxyl-containing monomer as monomer components; the adhesive comprising, relative to 100 parts by weight of the (meth)acrylate-based polymer, 5 to 20 parts by weight of the isocyanate-based crosslinking agent; the haze of the adhesive layer being 2.0% or less; the weight average molecular weight of the (meth)acrylate-based polymer being 1 million to 3 million, and the polydispersity being 5.0 or less.

2. The optical film with the adhesive layer as claimed in claim 1, wherein the aforementioned isocyanate-based crosslinking agent is a toluene diisocyanate-based crosslinking agent.

3. The optical film of the adhesive layer as claimed in claim 1 or 2, wherein the aforementioned (meth)acrylate-based base polymer contains 10 to 30 parts by weight of the aforementioned aromatic (meth)acrylate relative to 100 parts by weight of the total monomer content.

4. The optical film of the adhesive layer as claimed in claim 3, wherein the aforementioned (meth)acrylic base polymer contains 0.1 to 1 part by weight of the aforementioned hydroxyl-containing monomer relative to 100 parts by weight of the total monomer content.

5. The optical film with the adhesive layer as claimed in claim 4, wherein the aforementioned (meth)acrylic base polymer contains 2 to 8 parts by weight of the aforementioned carboxyl-containing monomer relative to 100 parts by weight of the total monomer content.

6. The optical film with an adhesive layer as claimed in claim 1 or 2, wherein the weight average molecular weight of the aforementioned (meth)acrylic acid-based base polymer is 2 million to 3 million.

7. An optical film with an adhesive layer as claimed in claim 1 or 2, wherein the optical film includes a polarizing element.

8. The optical film with the adhesive layer as described in claim 7, wherein the optical film further comprises a phase retardation layer.

9. An image display device comprising an optical film with an adhesive layer as claimed in any one of claims 1 to 8.

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