Adhesive composition, protective film, surface protective film for image display device, and flexible image display device

Abstract

The present invention provides an adhesive composition that exhibits good adhesion before irradiation with active energy rays, good peelability after irradiation with active energy rays, and excellent transparency and conformability to deformation such as twisting over a wide temperature range. [Solution] An adhesive composition containing an acrylic resin (A), an active energy ray curable compound (B), and a crosslinking agent (C), The acrylic resin (A) contains an acrylic resin (A1) with a weight-average molecular weight of 900,000 or less. An adhesive composition in which the aforementioned adhesive composition is crosslinked to form an adhesive with a gel fraction of 30-80%, the glass transition temperature is -5°C or lower, and the elastic modulus at -20°C is 0.05-5 MPa.

Description

Technical Field

[0001] The present invention relates to an adhesive composition, a protective film, a surface protective film for an image display device, and a flexible image display device.

Background Art

[0002] In order to prevent scratches and the like on the surface, it is common practice to attach a protective film to an image display device equipped with a liquid crystal display, an organic EL display, or the like. As the protective film, from the viewpoints of scratch resistance and transparency, many are those in which an adhesive layer made of an adhesive obtained by crosslinking glass and an adhesive composition is laminated.

[0003] By the way, in recent years, the development of flexible terminals capable of bending or folding an image display screen (display) has been underway. For the protective film used in the image display device of such a flexible terminal, in addition to transparency, it is assumed to be used in various environments, and at a wide range of temperatures, followability corresponding to deformation such as easy bending against twisting and the like is required (for example, Patent Documents 1 and 2). Furthermore, the protective film is also required to have easy peelability so that it can be replaced when damaged or the like. As such a protective film having easy peelability, those that can be easily peeled by irradiating an adhesive layer with an active energy ray and curing are known (for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0005] However, the adhesive compositions described in Patent Documents 1 and 2 lacked easy peelability and could not be easily removed from the image display device. Furthermore, the adhesive composition described in Patent Document 3 lacked the ability to conform to deformation such as twisting, or sufficient transparency.

[0006] Therefore, against this background, the present invention aims to provide an adhesive composition that has good adhesion before irradiation with active energy rays, good peelability after irradiation with active energy rays, and excellent transparency and conformability to deformation such as twisting over a wide temperature range. [Means for solving the problem]

[0007] However, in view of these circumstances, the inventors conducted extensive research and, as a result, discovered that by providing an adhesive composition comprising an acrylic resin having a specific weight-average molecular weight, an active energy ray-curable compound, and a crosslinking agent, and by setting the glass transition temperature and elastic modulus of the adhesive within a specific range, an adhesive composition can be obtained that has good adhesive strength before irradiation with active energy rays, good peelability after irradiation with active energy rays, and excellent transparency and conformability to deformation such as twisting over a wide temperature range, thereby completing the present invention.

[0008] In other words, the present invention has the following aspects. [1] An adhesive composition containing an acrylic resin (A), an active energy ray curable compound (B), and a crosslinking agent (C), The acrylic resin (A) contains an acrylic resin (A1) with a weight-average molecular weight of 900,000 or less. An adhesive composition in which the aforementioned adhesive composition is crosslinked to form an adhesive with a gel fraction of 30-80%, the glass transition temperature is -5°C or lower, and the elastic modulus at -20°C is 0.05-5 MPa. [2] The adhesive composition according to [1], wherein the glass transition temperature of the acrylic resin (A1) is -30°C or lower. [3] The adhesive composition according to [1] or [2], wherein the weight-average molecular weight of the acrylic resin (A1) is 100,000 to 900,000. [4] The adhesive composition according to any one of [1] to [3], wherein the active energy ray curable compound (B) contains urethane (meth)acrylate (b). [5] The adhesive composition according to any one of [1] to [4], wherein the content of the active energy ray curable compound (B) is 1 to 200 parts by mass per 100 parts by mass of the acrylic resin (A). [6] The adhesive composition according to any one of [1] to [5] further contains an active energy ray polymerization initiator (D). A protective film having an adhesive layer in which the adhesive composition described in any of [1] to [6] is crosslinked. [8] The protective film according to [7], wherein the adhesive layer is hardened and peelable by irradiation with active energy rays. [9] A surface protective film for an image display device having an adhesive layer in which the adhesive composition described in any of [1] to [6] is crosslinked.

[10] The surface protective film for an image display device according to [9], wherein the adhesive layer is hardened and peelable by irradiation with active energy rays. A flexible image display device containing the surface protective film for image display devices described in

[11] [9]. [Effects of the Invention]

[0009] The adhesive composition of the present invention has good adhesive properties such as good tackiness, transparency, and conformability to deformation such as twisting over a wide temperature range before irradiation with active energy rays, and is easily peelable after irradiation with active energy rays. [Modes for carrying out the invention]

[0010] The present invention will be described below based on examples of embodiments for carrying out the present invention. However, the present invention is not limited to the embodiments described below. In this specification, "(meth)acryl" means acrylic and / or methacrylic, "(meth)acryloyl" means acryloyl and / or methacryloyl, and "(meth)acrylate" means acrylate and / or methacrylate, respectively. In this specification, "sheet" includes "tape" and "film".

[0011] In this specification, "X and / or Y (X, Y are arbitrary configurations)" means at least one of X and Y, and means three cases: only X, only Y, and X and Y. When expressed as "X to Y" (X, Y are arbitrary numbers) in this specification, unless otherwise specified, it includes the meaning of "X or more and Y or less" and also includes the meaning of "preferably exceeding X" or "preferably less than Y". When expressed as "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number) in this specification, it also includes the meaning of "preferably exceeding X" or "preferably less than Y". Regarding the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value of a numerical range at a certain step can be arbitrarily combined with the upper limit value or the lower limit value of a numerical range at another step. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range can be replaced with the value shown in the examples.

[0012] The adhesive composition according to an embodiment of the present invention (hereinafter, may be referred to as "this adhesive composition") is usually used as an adhesive layer of a protective film. The protective film is formed by applying this adhesive composition on a base sheet and crosslinking this adhesive composition to form an adhesive layer. After bonding to an adherend and protecting the surface of the adherend for a certain period, the adhesive layer is cured by irradiating active energy rays, and the adhesive force is reduced, and it can be easily peeled off from the adherend.

[0013] This adhesive composition contains an acrylic resin (A), an active energy ray curable compound (B), and a crosslinking agent (C). Hereinafter, each constituent component of this adhesive composition will be described.

[0014] <Acrylic resin (A)> The acrylic resin (A) is a resin obtained by polymerizing a polymerization component containing at least one (meth)acrylate monomer. Moreover, the content of the acrylic resin (A) in this adhesive composition (solid content) is usually 50 to 99% by mass, preferably 60 to 90% by mass.

[0015] The acrylic resin (A) contains an acrylic resin (A1) having a weight average molecular weight of 900,000 or less (hereinafter, may be referred to as "acrylic resin (A1)").

[0016] <Acrylic resin (A1)> The acrylic resin (A1) has a structural unit derived from an alkyl (meth)acrylate (a1) and preferably a structural unit derived from a functional group-containing monomer (a12), and may have a structural unit derived from other copolymerizable monomers (a3) as necessary. Such an acrylic resin (A1) is obtained by polymerizing a polymerization component containing an alkyl (meth)acrylate (a1), preferably a functional group-containing monomer (a2), and other copolymerizable monomers (a3) as necessary. In addition, the content of each monomer with respect to the entire polymerization component can be regarded as the content of the structural unit derived from the monomer in the acrylic resin (A1) which is a polymer. For example, the content of the alkyl (meth)acrylate (a1) with respect to the entire polymerization component can be regarded as the content of the structural unit derived from the alkyl (meth)acrylate (a1) in the acrylic resin (A1).

[0017] 〔Alkyl (meth)acrylate (a1)〕 The alkyl (meth)acrylate (a1) has an alkyl group with 1 to 20 carbon atoms, preferably 1 to 12, and more preferably 1 to 8 carbon atoms. If the alkyl group has too many carbon atoms, there tends to be a large amount of unreacted residual monomer, which tends to cause contamination of the coating when peeled off.

[0018] Specific examples of the alkyl(meth)acrylate (a1) include, for example, linear aliphatic alkyl(meth)acrylates such as methyl(meth)acrylate, ethyl(meth)acrylate, n-butyl(meth)acrylate, n-propyl(meth)acrylate, n-hexyl(meth)acrylate, n-octyl(meth)acrylate, lauryl(meth)acrylate, cetyl(meth)acrylate, and stearyl(meth)acrylate; aliphatic alkyl(meth)acrylates such as isobutyl(meth)acrylate, tert-butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, isooctylacrylate, isodecyl(meth)acrylate, and isostearyl(meth)acrylate; and alicyclic alkyl(meth)acrylates such as cyclohexyl(meth)acrylate and isobornyl(meth)acrylate. These can be used individually or in combination of two or more. Among them, aliphatic alkyl (meth)acrylates are preferred in terms of polymerizability, adhesive properties, ease of handling, and availability of raw materials, more preferably methyl (meth)acrylate, n-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, and particularly preferably methyl (meth)acrylate and n-butyl (meth)acrylate.

[0019] Furthermore, the content of alkyl (meth)acrylate (a1)-derived structural units in the acrylic resin (A1) is typically 30 to 99% by mass of the total structural units of the acrylic resin (A1), preferably 40 to 98% by mass, and more preferably 50 to 97% by mass. When the content is within the above range, the adhesive properties before irradiation with active energy rays tend to be good.

[0020] [Functional group-containing monomer (a2)] Examples of the functional group-containing monomer (a2) include carboxyl group-containing monomers, hydroxyl group-containing monomers, amino group-containing monomers, amide group-containing monomers, glycidyl group-containing monomers, sulfonic acid group-containing monomers, and acetoacetyl group-containing monomers. These can be used individually or in combination of two or more. Among these, carboxyl group-containing monomers and hydroxyl group-containing monomers are preferred.

[0021] When the acrylic resin (A1) has structural units derived from functional group-containing monomers (a2), the content is usually 30% by mass or less of the total structural units of the acrylic resin (A1), preferably 20% by mass or less, and more preferably 10% by mass or less. When the content is within the above range, storage stability is improved, crosslinking before the drying process is suppressed, and the coating properties tend to be excellent. The lower limit is usually 0.1% by mass, preferably 0.5% by mass.

[0022] [Carboxy group-containing monomers] The acrylic resin (A1) preferably contains structural units derived from carboxyl group-containing monomers. The presence of structural units derived from the carboxyl group-containing monomers in the acrylic resin (A1) tends to improve its adhesive properties before irradiation with active energy rays.

[0023] Examples of the carboxyl group-containing monomers include carboxyl group-containing (meth)acrylates such as (meth)acrylic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, and 2-(meth)acryloyloxyethyl phthalic acid, as well as crotonic acid, maleic acid, fumaric acid, citraconic acid, glutaconic acid, itaconic acid, and cinnamic acid. These can be used individually or in combination of two or more. Among these, carboxyl group-containing (meth)acrylates are preferred due to their ease of polymerization and their ability to improve tackiness before irradiation with active energy rays, and (meth)acrylic acid is more preferred.

[0024] When the acrylic resin (A1) has structural units derived from carboxyl group-containing monomers, the content thereof is preferably 0.1 to 30% by mass of the total structural units of the acrylic resin (A1), more preferably 0.5 to 20% by mass, even more preferably 1 to 15% by mass, and particularly preferably 1 to 8% by mass, in order to increase the adhesive strength before irradiation with active energy rays. If the content is too low, the cohesive force when used as an adhesive may be insufficient, or the adhesive strength before irradiation with active energy rays may be low, which tends to cause chipping and breakage. On the other hand, if the content is too high, the glass transition temperature of the acrylic resin (A1) may become too high, which tends to reduce adhesion to the coating and the ability to follow deformations such as twisting at low temperatures.

[0025] [Hydroxygroup-containing monomers] Examples of the hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate, as well as hydroxyl group-containing (meth)acrylates such as [4-(hydroxymethyl)cyclohexyl]methyl acrylate, cyclohexanedimethanol mono(meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. These can be used individually or in combination of two or more. Among these, hydroxyalkyl (meth)acrylate is preferred because it is easily polymerized, has good crosslinking properties with the crosslinking agent (C) described later, and is good at improving stain resistance after irradiation with active energy rays. Hydroxyalkyl (meth)acrylate with 2 to 10 carbon atoms in the alkyl group is more preferred, and 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred.

[0026] If the acrylic resin (A1) has structural units derived from hydroxyl group-containing monomers, the content thereof is preferably 30% by mass or less of the total structural units of the acrylic resin (A1), more preferably 20% by mass or less, and even more preferably 10% by mass or less. The lower limit is usually 0.01% by mass, preferably 0.1% by mass. If the content is too high, the stability of the acrylic resin (A1) tends to decrease, and the pot life tends to be shortened.

[0027] [Amino group-containing monomers] Examples of the amino group-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and N,N-dimethylaminopropyl (meth)acrylate. These can be used individually or in combination of two or more.

[0028] If the acrylic resin (A1) has structural units derived from amino group-containing monomers, the content thereof is usually 30% by mass or less, preferably 25% by mass or less, and more preferably 20% by mass or less, of the total structural units of the acrylic resin (A1). If the content is too high, crosslinking tends to occur before the drying process, which can easily lead to problems with coating properties.

[0029] [Amide group-containing monomers] Examples of the amide group-containing monomers include methoxydimethylpropanamide, ethoxymethyl(meth)acrylamide, n-butoxymethyl(meth)acrylamide, (meth)acryloylmorpholine, dimethyl(meth)acrylamide, diethyl(meth)acrylamide, dimethylaminopropyl(meth)acrylamide, (meth)acrylamide, N-methylol(meth)acrylamide, and other (meth)acrylamide monomers. These can be used individually or in combination of two or more.

[0030] When the acrylic resin (A1) has structural units derived from amide group-containing monomers, the content thereof is usually 30% by mass or less, preferably 25% by mass or less, and more preferably 20% by mass or less, of the total structural units of the acrylic resin (A1). Since monomers containing amide groups tend to have high glass transition temperatures, if the content is too high, the glass transition temperature of the polymer tends to rise, and the adhesive properties before irradiation with active energy rays tend to decrease.

[0031] [Glycidyl group-containing monomers] Examples of the glycidyl group-containing monomers include glycidyl (meth)acrylate and allyl glycidyl (meth)acrylate. These can be used individually or in combination of two or more.

[0032] When the acrylic resin (A1) has structural units derived from glycidyl group-containing monomers, the content of these units is usually 20% by mass or less of the total structural units of the acrylic resin (A1), preferably 10% by mass or less, and more preferably 5% by mass or less. If the content is too high, there is a tendency for polymerization to decrease and the stability of the acrylic resin (A1) to decrease.

[0033] [Sulfonic acid group-containing monomers] Examples of the sulfonic acid group-containing monomers include olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, 2-acrylamido-2-methylolpropanesulfonic acid, styrene sulfonic acid, or salts thereof. These can be used individually or in combination of two or more.

[0034] When the acrylic resin (A1) has structural units derived from sulfonic acid group-containing monomers, the content of these units is usually 10% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less, of the total structural units of the acrylic resin (A1). If the content is too high, the stability of the acrylic resin (A1) tends to decrease, and crosslinking progresses before the drying process, which tends to cause problems with coating properties.

[0035] [Acetoacetyl group-containing monomer] Examples of the acetoacetyl group-containing monomers include 2-(acetoacetoxy)ethyl (meth)acrylate and allyl acetoacetate. These can be used individually or in combination of two or more.

[0036] When the acrylic resin (A1) contains structural units derived from acetoacetyl group-containing monomers, the content of these units is usually 10% by mass or less, preferably 5% by mass or less, and more preferably 1% by mass or less, of the total structural units of the acrylic resin (A1). If the content is too high, there is a tendency for polymerization properties and adhesive properties to decrease.

[0037] [Other copolymerizable monomers (a3)] Examples of the aforementioned other polymerizable monomers (a3) ​​include unsaturated carboxylic acids such as maleic anhydride, itaconic anhydride, and acrylamide-N-glycolic acid; vinyl carboxylate monomers such as vinyl acetate, vinyl propionate, vinyl stearate, and vinyl benzoate; aromatic ring-containing monomers such as styrene and α-methylstyrene; and acrylonitrile, methacrylonitrile, vinyl chloride, vinylidene chloride, alkyl vinyl ethers, vinyltoluene, vinylpyridine, vinylpyrrolidone, dialkyl itaconic acid esters, dialkyl fumarate esters, allyl alcohol, acrylic chloride, methyl vinyl ketone, allyltrimethylammonium chloride, and dimethylallyl vinyl ketone. These can be used individually or in combination of two or more. Furthermore, the other polymerizable monomers (a3) ​​include, in addition to the monomers mentioned above, active energy ray crosslinkable monomers.

[0038] The aforementioned active energy ray crosslinkable monomers are monomers that generate radicals upon the action of light, and examples include (meth)acrylate monomers having a benzophenone structure, such as 4-(meth)acryloyloxybenzophenone, 4-(meth)acryloyloxyethoxybenzophenone, 4-(meth)acryloyloxy-4'-methoxybenzophenone, 4-(meth)acryloyloxy-4'-bromobenzophenone, 4-(meth)acryloyloxyethoxy-4'-bromobenzophenone, and mixtures thereof. These can be used individually or in combination of two or more. By using such active energy ray crosslinkable monomers as polymerization components, active energy ray crosslinkable structural sites can be formed in the acrylic resin (A1).

[0039] If the acrylic resin (A1) has structural units derived from other polymerizable monomers (a3), the content thereof is usually 30% by mass or less, preferably 20% by mass or less, of the total structural units of the acrylic resin (A1). Furthermore, if the other polymerizable monomer (a3) ​​has structural units derived from active energy ray crosslinkable monomers, its content is usually 10% by mass or less, preferably 5% by mass or less, of the total structural units of the acrylic resin (A1).

[0040] The acrylic resin (A1) is obtained by polymerizing a polymerization component containing alkyl (meth)acrylate (a1), preferably a functional group-containing monomer (a2), and optionally other copolymerizable monomers (a3). Conventional known polymerization methods such as solution radical polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization are typically used. Among these, solution radical polymerization and bulk polymerization are preferred, and solution radical polymerization is particularly preferred from the viewpoint of stably obtaining the acrylic resin (A1).

[0041] In the aforementioned solution radical polymerization, for example, the polymerization component and a thermal polymerization initiator can be mixed or added dropwise to an organic solvent, and polymerization can be carried out under reflux or at a temperature of 50 to 98°C for about 0.1 to 20 hours.

[0042] Examples of organic solvents used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, aliphatic alcohols such as N-propyl alcohol and isopropyl alcohol, and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. These can be used individually or in combination of two or more. Among these solvents, it is preferable to use an organic solvent with a boiling point of 80°C or lower, as this allows for efficient production of a solvent-free acrylic resin by distilling off the solvent from the acrylic resin solution obtained by solution polymerization.

[0043] Examples of organic solvents with a boiling point of 80°C or lower include hydrocarbon solvents such as n-hexane (67°C), alcohol solvents such as methanol (65°C), ester solvents such as ethyl acetate (77°C) and methyl acetate (54°C), ketone solvents such as methyl ethyl ketone (80°C) and acetone (56°C), diethyl ether (35°C), methylene chloride (40°C), and tetrahydrofuran (66°C). Among these, ethyl acetate, acetone, and methyl acetate are preferred in terms of versatility and safety, and ethyl acetate and acetone are particularly preferred. The numbers in parentheses following each organic solvent name indicate the boiling point of that solvent.

[0044] The amount of the aforementioned organic solvent used is typically 10 to 900 parts by mass per 100 parts by mass of the polymerization component.

[0045] As the thermal polymerization initiator used in the polymerization reaction, ordinary radical polymerization initiators such as azo polymerization initiators and peroxide polymerization initiators can be used. Examples of azo polymerization initiators include 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl)azodiphenylmethane, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), and 2 Examples of peroxide polymerization initiators include 2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and peroxide polymerization initiators include, for example, benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, t-butyl peroxypivalate, t-hexyl peroxypivalate, t-hexyl peroxyneodecanoate, diisopropyl peroxycarbonate, and diisobutyryl peroxide. These can be used individually or in combination of two or more.

[0046] The amount of thermal polymerization initiator used is usually 0.001 to 10 parts by mass, preferably 0.01 to 8 parts by mass, more preferably 0.05 to 6 parts by mass, and even more preferably 0.08 to 4 parts by mass, per 100 parts by mass of the polymerization component. If the amount of thermal polymerization initiator used is too small, the polymerization rate of the acrylic resin (A1) decreases, the residual monomers tend to increase, and the weight-average molecular weight of the acrylic resin (A1) tends to increase. If the amount used is too large, the time required for the final heating described later tends to be long and unproductive.

[0047] The polymerization temperature in the polymerization reaction is usually 40 to 120°C, but in this embodiment, 50 to 90°C is preferred, more preferably 55 to 75°C, and even more preferably 60 to 70°C, from the viewpoint of stable reaction. If the polymerization temperature is too high, the acrylic resin (A1) tends to gel easily, and if it is too low, the activity of the thermal polymerization initiator decreases, so the polymerization rate tends to decrease and the amount of residual monomer increases.

[0048] Furthermore, there are no particular restrictions on the polymerization time in the polymerization reaction (or the time until the start of the final heating if the final heating described later is performed), but it is preferably 0.5 hours or more from the addition of the last thermal polymerization initiator, more preferably 1 hour or more, even more preferably 2 hours or more, and particularly preferably 5 hours or more. The upper limit for the polymerization time is usually 72 hours. Furthermore, the polymerization reaction is preferably carried out while refluxing the solvent, as this facilitates heat removal.

[0049] In the production of the aforementioned acrylic resin (A1), it is preferable to decompose the thermal polymerization initiator by heating in a final heating process in order to reduce the amount of residual thermal polymerization initiator.

[0050] The final heating temperature is preferably higher than the 10-hour half-life temperature of the thermal polymerization initiator. Specifically, it is usually 40 to 150°C, preferably 55 to 130°C from the viewpoint of suppressing gelation, and more preferably 75 to 95°C. If the final heating temperature is too high, the acrylic resin (A1) tends to yellow, and if it is too low, polymerization components and thermal polymerization initiators remain, which tends to reduce the temporal stability and thermal stability of the acrylic resin (A1). Thus, an acrylic resin (A1) solution can be obtained.

[0051] The weight-average molecular weight (Mw) of the acrylic resin (A1) is 900,000 or less, preferably between 100,000 and 900,000, more preferably between 200,000 and 870,000, and even more preferably between 300,000 and 850,000. If the weight-average molecular weight is too small, the cohesive force of the resulting adhesive layer tends to decrease. If the weight-average molecular weight is too large, the compatibility with the activated energy ray curable compound (B) described later tends to decrease, the solution viscosity increases and the coating properties decrease, and the adhesive strength before activated energy ray irradiation and the ability to follow deformations such as twisting tend to decrease. If the weight-average molecular weight is within the above range, the adhesive properties and the ability to follow deformations such as twisting tend to be excellent.

[0052] Furthermore, the degree of dispersion [weight-average molecular weight (Mw) / number-average molecular weight (Mn)] of the acrylic resin (A1) is preferably 10 or less, and more preferably 7 or less. If the degree of dispersion is too high, the cohesive force tends to decrease. The lower limit of the degree of dispersion is usually 1.

[0053] The weight-average molecular weight of the acrylic resin (A1) is the weight-average molecular weight calculated on a standard polystyrene molecular weight scale. The high-performance liquid chromatograph (Waters Japan Co., Ltd., "Waters2695 (main unit)" and "Waters2414 (detector)") was used, and the column was ShodexGPCKF-806L (exclusion limit molecular weight: 2 × 10⁻¹⁶). 7 Separation range: 100~2×10 7 The measurement can be performed by connecting three units of a thermometer (theoretical plate count: 10,000 stages / unit, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm) in series, and the number-average molecular weight can be measured in the same way. Furthermore, the degree of dispersion can be determined from the measured values ​​of the weight-average molecular weight and the number-average molecular weight.

[0054] The glass transition temperature (Tg) of the acrylic resin (A1) is preferably -30°C or lower, more preferably -70 to -35°C, even more preferably -65 to -40°C, and particularly preferably -60 to -45°C. If the glass transition temperature is too low, the cohesive force of the adhesive layer tends to decrease, and the adhesive force before irradiation with active energy rays tends to decrease. If it is too high, the adhesion to the coated area tends to decrease, and the ability to follow deformations such as twisting at low temperatures tends to decrease.

[0055] The glass transition temperature (Tg) is calculated by applying the glass transition temperature and mass fraction of each monomer constituting the acrylic resin (A1) as a homopolymer to Fox's formula below.

[0056]

number

[0057] Here, the glass transition temperature of the monomers constituting the acrylic resin (A1) when they are homopolymers is usually measured using a differential scanning calorimeter (DSC), and can be measured according to methods conforming to JIS K 7121-1987 or JIS K 6240.

[0058] The acrylic resin (A) may contain other acrylic resins besides acrylic resin (A1). The content of the other acrylic resins is typically 30% by mass or less, preferably 10% by mass or less, and particularly preferably 0% by mass of acrylic resin (A). In other words, it is preferable that acrylic resin (A) consists only of acrylic resin (A1).

[0059] <Active energy ray curable compound (B)> Examples of the active energy ray curable compound (B) include urethane (meth)acrylate compounds (b), monofunctional (meth)acrylate compounds, and polyfunctional (meth)acrylate compounds. These can be used individually or in combination of two or more. Among these, urethane (meth)acrylate compounds (b) are preferred.

[0060] [Urethane (meth)acrylate compound (b)] Examples of the urethane (meth)acrylate compound (b) include urethane (meth)acrylate compound (b1), which is a reaction product of a hydroxyl group-containing (meth)acrylate compound and a polyvalent isocyanate compound; urethane (meth)acrylate compound (b2), which is a reaction product of a hydroxyl group-containing (meth)acrylate compound, a polyvalent isocyanate compound, and a polyol compound; and urethane (meth)acrylate compound (b3), which is a reaction product of a hydroxyl group-containing (meth)acrylate compound, a polyvalent isocyanate compound, a monofunctional alcohol, and optionally a polyol compound. These can be used individually or in combination of two or more.

[0061] Among these, urethane (meth)acrylate compounds (b1) and urethane (meth)acrylate compounds (b2) are preferred in terms of their compatibility with the acrylic resin (A), adhesive properties before irradiation with active energy rays, and stain resistance after irradiation with active energy rays, with urethane (meth)acrylate compound (b1) being particularly preferred.

[0062] [Hydroxyl group-containing (meth)acrylate compounds] The hydroxyl group-containing (meth)acrylate compound is not particularly limited as long as it is a (meth)acrylate compound having one or more hydroxyl groups, but a (meth)acrylate compound having one hydroxyl group is preferred.

[0063] The hydroxyl value of the hydroxyl group-containing (meth)acrylate compound is typically 10 to 1000 mg KOH / g, more preferably 20 to 500 mg KOH / g. When the hydroxyl value is within this range, it tends to be easier to achieve both easy peeling and stretchability after irradiation with active energy rays.

[0064] Specific hydroxyl group-containing (meth)acrylate compounds include, for example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate, as well as 2-hydroxyethyl acryloyl phosphate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, caprolactone-modified 2-hydroxyethyl (meth)acrylate, dipropylene glycol (meth)acrylate, fatty acid-modified glycidyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and 2-hydroxy-3-(meth)acryloyloxypropyl (meth)acrylate, which contain one ethylenically unsaturated group. Examples include hydroxyl group-containing (meth)acrylate compounds; hydroxyl group-containing (meth)acrylate compounds containing two ethylenically unsaturated groups, such as glycerin di(meth)acrylate and 2-hydroxy-3-acryloyloxypropyl methacrylate; hydroxyl group-containing (meth)acrylate compounds containing three or more ethylenically unsaturated groups, such as pentaerythritol tri(meth)acrylate, a mixture of pentaerythritol tetra(meth)acrylate and pentaerythritol tri(meth)acrylate, caprolactone-modified pentaerythritol tri(meth)acrylate, ethylene oxide-modified pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, caprolactone-modified dipentaerythritol penta(meth)acrylate, and ethylene oxide-modified dipentaerythritol penta(meth)acrylate. These can be used individually or in combination of two or more.In particular, hydroxyl group-containing (meth)acrylate compounds containing three or more ethylenically unsaturated groups are preferred due to their excellent reactivity and versatility, more preferably pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, a mixture of pentaerythritol tetra(meth)acrylate and pentaerythritol tri(meth)acrylate, and mixtures thereof, and even more preferably a mixture of pentaerythritol tri(meth)acrylate and pentaerythritol tetra(meth)acrylate.

[0065] [Polyvalent isocyanate compounds] The aforementioned polyvalent isocyanate compound is not particularly limited as long as it contains two or more isocyanate groups.

[0066] The isocyanate group content of the polyvalent isocyanate compound is typically 1 to 95% by mass, preferably 5 to 50% by mass. When the isocyanate group content is within this range, it tends to be easier to achieve both easy peelability after irradiation with active energy rays and compatibility with acrylic resin (A).

[0067] Specific examples of polyvalent isocyanate compounds include aromatic polyvalent isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, polyphenylmethane polyisocyanate, modified diphenylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, phenylylene diisocyanate, and naphthalene diisocyanate; and aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate, lysine triisocyanate, and dicyclohexylmethane-4,4'-diisocyanate. Examples include: alicyclic polyisocyanates such as hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate; or adduct compounds of these polyisocyanates with isocyanurates or polyhydroxyl compounds such as trimethylolpropane, or polymer compounds, allophanate-type polyisocyanates, burette-type polyisocyanates, and water-dispersible polyisocyanates (for example, "Aquanate 100", "Aquanate 110", "Aquanate 200", "Aquanate 210", etc. manufactured by Nippon Polyurethane Industries Co., Ltd.). These can be used individually or in combination of two or more. Among these, aliphatic diisocyanates, aromatic isocyanates, alicyclic diisocyanates, and their isocyanurate derivatives, adduct derivatives with polyhydric hydroxyl compounds, and allophanate derivatives are preferred in terms of reactivity, versatility, and excellence in stretchability after irradiation with active energy rays. More preferably are isophorone diisocyanate, tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, and their isocyanurate derivatives, adduct derivatives with polyhydric hydroxyl compounds, and allophanate derivatives. Even more preferably are isophorone diisocyanate, hexamethylene diisocyanate, and their isocyanurate derivatives, adduct derivatives with polyhydric hydroxyl compounds, and allophanate derivatives.

[0068] [Polyol compounds] The polyol compound is not particularly limited as long as it is a compound containing two or more hydroxyl groups.

[0069] The weight-average molecular weight of the polyol compound is typically 60 to 10,000, preferably 100 to 5,000, and more preferably 200 to 4,000. If the weight-average molecular weight of the polyol compound is too high, the compatibility between the resulting urethane (meth)acrylate compound (b) and the acrylic resin (A) tends to decrease, and the ease of peeling after irradiation with active energy rays tends to decrease.

[0070] The hydroxyl value of the polyol compound is preferably 10 to 1000 mg KOH / g, and more preferably 20 to 500 mg KOH / g. When the hydroxyl value is within this range, it tends to be easier to achieve both easy peeling after irradiation with active energy rays and compatibility with acrylic resin (A).

[0071] Examples of the polyol compounds include aliphatic polyols, alicyclic polyols, polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, polybutadiene polyols, polyisoprene polyols, (meth)acrylic polyols, and polysiloxane polyols. These can be used individually or in combination of two or more.

[0072] Examples of the aliphatic polyols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, dimethylolpropane, neopentyl glycol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-tetramethylenediol, 1,3-tetramethylenediol, 2-methyl-1,3-trimethylenediol, 1,5-pentamethylenediol, 1 Examples include aliphatic alcohols containing two hydroxyl groups, such as 6-hexamethylenediol, 3-methyl-1,5-pentamethylenediol, 2,4-diethyl-1,5-pentamethylenediol, pentaerythritol diacrylate, 1,9-nonanediol, and 2-methyl-1,8-octanediol; sugar alcohols such as xylitol and sorbitol; and aliphatic alcohols containing three or more hydroxyl groups, such as glycerin, trimethylolpropane, and trimethylolethane.

[0073] Examples of the alicyclic polyols include cyclohexanediols such as 1,4-cyclohexanediol and cyclohexyldimethanol, hydrogenated bisphenols such as hydrogenated bisphenol A, and tricyclodecanedimethanol.

[0074] Examples of the polyether polyol include polyalkylene glycols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polybutylene glycol, polypentamethylene glycol, and polyhexamethylene glycol, as well as random or block copolymers of these polyalkylene glycols.

[0075] Examples of the aforementioned polyester polyols include condensation polymers of polyhydric alcohols and polyhydric carboxylic acids; ring-opening polymers of cyclic esters (lactones); and reaction products of three components: polyhydric alcohols, polyhydric carboxylic acids, and cyclic esters.

[0076] Examples of the aforementioned polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, 1,4-tetramethylenediol, 1,3-tetramethylenediol, 2-methyl-1,3-trimethylenediol, 1,5-pentamethylenediol, neopentyl glycol, 1,6-hexamethylenediol, 3-methyl-1,5-pentamethylenediol, 2,4-diethyl-1,5-pentamethylenediol, glycerin, trimethylolpropane, trimethylolethane, cyclohexanediols (such as 1,4-cyclohexanediol), bisphenols (such as bisphenol A), sugar alcohols (such as xylitol and sorbitol), and the like. Examples of the polycarboxylic acids include aliphatic dicarboxylic acids such as malonic acid, maleic acid, fumaric acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedionic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, paraphenylenedicarboxylic acid, and trimellitic acid. Examples of the cyclic esters mentioned above include propiolactone, β-methyl-δ-valerolactone, and ε-caprolactone.

[0077] Examples of the polycarbonate polyol include reaction products of polyhydric alcohols and phosgene; and ring-opening polymers of cyclic carbonate esters (such as alkylene carbonates). Examples of the polyhydric alcohol include the polyhydric alcohols exemplified in the description of the polyester polyols. Examples of the alkylene carbonate include ethylene carbonate, trimethylene carbonate, tetramethylene carbonate, and hexamethylene carbonate. The polycarbonate polyol can be any compound having a carbonate bond within its molecule and a hydroxyl group at its terminus, and may also have ester bonds in addition to the carbonate bond.

[0078] Examples of the aforementioned polyolefin polyols include those having a homopolymer or copolymer of ethylene, propylene, butene, etc. as a saturated hydrocarbon backbone, and having hydroxyl groups at the molecular ends.

[0079] Examples of the polybutadiene polyols include those having a butadiene copolymer as the hydrocarbon backbone and having hydroxyl groups at the molecular ends. The polybutadiene-based polyol may also be a hydrogenated polybutadiene polyol in which all or part of the ethylenically unsaturated groups contained in its structure are hydrogenated.

[0080] Examples of the (meth)acrylic polyol include polymers or copolymers of (meth)acrylic acid esters that have at least two hydroxyl groups in the molecule. Examples of such (meth)acrylic acid esters include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, and octadecyl (meth)acrylate.

[0081] Examples of the polysiloxane polyols include dimethylpolysiloxane polyol and methylphenylpolysiloxane polyol.

[0082] Among these, aliphatic polyols and alicyclic polyols are preferred in terms of cost, while polyester polyols, polyether polyols, and polycarbonate polyols are preferred in terms of versatility.

[0083] [Monofungular alcohol] The monofunctional alcohol is not particularly limited, but examples include alcohols containing linear or branched alkyl groups having 1 to 36 carbon atoms, aromatic rings, alicyclic groups, heterocyclic groups, etc. Preferably, from the viewpoint of versatility, it is an alcohol containing linear or branched alkyl groups having 1 to 36 carbon atoms, and more preferably, it is an alcohol containing linear or branched alkyl groups having 4 to 18 carbon atoms. These can be used individually or in combination of two or more.

[0084] The urethane (meth)acrylate compound (b) can be produced by urethaneizing the above-mentioned components using known reaction methods. The following is an example of a method for producing urethane (meth)acrylate compound (b), but the method is not limited to this method. (1) When obtaining a urethane (meth)acrylate compound (b1) A method for urethane reaction between the hydroxyl group-containing (meth)acrylate compound and a polyhydric isocyanate compound. (2) When obtaining a urethane (meth)acrylate compound (b2) A method for urethane formation of the hydroxyl group-containing (meth)acrylate compound, a polyvalent isocyanate compound, and a polyol compound. (3) When obtaining a urethane (meth)acrylate compound (b3) A method for urethane-forming a hydroxyl group-containing (meth)acrylate compound, a polyhydric isocyanate compound, a polyol compound, and a monofunctional alcohol.

[0085] The aforementioned urethane formation reaction can be carried out by charging the aforementioned components into a reactor all at once or separately and carrying out the urethane formation reaction using known reaction methods. Furthermore, when producing urethane (meth)acrylate compounds (b2) and urethane (meth)acrylate compounds (b3), a method in which a hydroxyl group-containing (meth)acrylate compound or monofunctional alcohol is reacted with a reaction product obtained by pre-reacting a polyol compound with a polyvalent isocyanate compound is useful in terms of the stability of the urethane formation reaction and the reduction of by-products.

[0086] In the reaction between the hydroxyl group-containing (meth)acrylate compound and the polyvalent isocyanate compound, it is preferable to use a reaction catalyst to accelerate the reaction.

[0087] Examples of the reaction catalysts include organometallic compounds such as dibutyltin dilaurate, trimethyltin hydroxide, and tetra-n-butyltin; metal salts such as zinc octenoate, tin octenoate, tin octoate, cobalt naphthenate, stannous chloride, and stannous chloride; amine catalysts such as triethylamine, benzyldiethylamine, 1,4-diazabicyclo[2,2,2]octane, 1,8-diazabicyclo[5,4,0]undecene, N,N,N',N'-tetramethyl-1,3-butanediamine, and N-ethylmorpholine; bismuth nitrate, bismuth bromide, bismuth iodide, and bismuth sulfide; and organobismuth compounds such as dibutylbismuth dilaurate and dioctylbismuth dilaurate. Examples of catalysts include bismuth-based catalysts such as organic acid bismuth salts like bismuth 2-ethylhexanoate, bismuth naphthenate, bismuth isodecanate, bismuth neodecanoate, bismuth laurate, bismuth maleate, bismuth stearate, bismuth oleate, bismuth linoleate, bismuth acetate, bismuth lybisneodecanoate, bismuth disalicylate, and bismuth digallate; zirconium-based catalysts such as inorganic zirconium, organozirconium, and elemental zirconium; and combinations of two or more catalysts such as zinc 2-ethylhexanoate / zirconium tetraacetylacetonate. Among these, dibutyltin dilaurate and organic bismuth compounds are preferred. These catalysts can be used individually or in combination of two or more.

[0088] In the urethane reaction described above, organic solvents that do not have functional groups that react with isocyanate groups can be used, such as esters like ethyl acetate and butyl acetate, ketones like methyl ethyl ketone and methyl isobutyl ketone, and aromatics like toluene and xylene.

[0089] Furthermore, the reaction temperature for the urethane formation reaction is usually 30 to 90°C, preferably 40 to 80°C, and the reaction time is usually 2 to 10 hours, preferably 3 to 8 hours.

[0090] The urethane formation reaction described above is terminated when the residual isocyanate group content in the reaction system becomes 0.5% by mass or less, thereby yielding a urethane (meth)acrylate compound (b).

[0091] The concentration of (meth)acryloyl groups in the urethane (meth)acrylate compound (b) obtained in this way is usually 0.01 to 50% by mass, preferably 0.1 to 45% by mass, more preferably 1 to 40% by mass, and particularly preferably 5 to 35% by mass. By setting the concentration of (meth)acryloyl groups in the urethane (meth)acrylate compound (b) within the above range, it tends to be possible to achieve both easy peeling after irradiation with active energy rays and compatibility with acrylic resin (A). The acryloyl group concentration can be calculated using the following formula, and if two or more urethane (meth)acrylate compounds (b) are used, it can be calculated by summing the products of their respective mass fractions. Acryloyl group concentration (mass%) = 55 × N(UA) / Mw(UA) × 100 N(UA): Number of (mere) acryloyl groups in urethane (meth)acrylate. Mw(UA): Weight-average molecular weight of urethane (meth)acrylate

[0092] Furthermore, the number of ethylenically unsaturated groups in the urethane (meth)acrylate compound (b) is preferably 15 or less, more preferably 2 to 15, and particularly preferably 4 to 13, from the viewpoint of easy peeling after irradiation with active energy rays and compatibility with the acrylic resin (A). If the number of such ethylenically unsaturated groups is too small, sufficient crosslinking density cannot be obtained and the easy peeling properties tend to decrease, and if it is too large, the compatibility with the acrylic resin (A) tends to deteriorate.

[0093] The weight-average molecular weight of the urethane (meth)acrylate compound (b) is typically 200 to 10,000, preferably 400 to 5,000, and more preferably 600 to 4,000. If the weight-average molecular weight is too high, the compatibility between the urethane (meth)acrylate compound (b) and the (meth)acrylic resin (A) decreases, and the adhesive properties before and after irradiation with active energy rays tend to decrease. If the weight-average molecular weight is too low, the cohesive force of the adhesive layer tends to decrease, and the adhesive properties tend to decrease.

[0094] The weight-average molecular weight mentioned above is the weight-average molecular weight converted to the standard polystyrene molecular weight, and is measured using a high-performance liquid chromatograph (Waters, "ACQUITYAPC system") with four columns in series: one ACQUITYAPCXT450, one ACQUITYAPCXT200, and two ACQUITYAPCXT45.

[0095] The viscosity of the urethane (meth)acrylate compound (b) at 60°C is preferably 50 to 10,000 mPa·s, more preferably 100 to 7,000 mPa·s, and particularly preferably 200 to 4,000 mPa·s. If the viscosity is too low, the cohesive force tends to decrease, and if it is too high, there are problems with handling and solubility when mixed with acrylic resins. The viscosity can be measured using an E-type viscometer.

[0096] [Monofunctional (meth)acrylate compounds] The monofunctional (meth)acrylate compound excludes the urethane (meth)acrylate compound (b), and includes, for example, methyl (meth)acrylate, ethyl (meth)acrylate, acrylonitrile, 2-methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, phenoxyethyl (meth)acrylate, 2-phenoxy-2-hydroxypropyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, glycerin mono(meth)acrylate, glycidyl (meth)acrylate, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dicyclopentenyl (meth)acrylate. (T) acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)-methyl (meth)acrylate, cyclohexanespiro-2-(1,3-dioxolan-4-yl)-methyl (meth)acrylate, 3-ethyl-3-oxetanylmethyl (meth)acrylate, γ-butyrolactone (meth)acrylate, n-butyl (meth)acrylate )Acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate, octyl(meth)acrylate, nonyl(meth)acrylate, decyl(meth)acrylate, isodecyl(meth)acrylate, dodecyl(meth)acrylate, n-stearyl(meth)acrylate, benzyl(meth)acrylate, phenolethylene oxide modified (n=2)(meth)acrylate, nonylphenolpropylene oxide modified (n=2.5) Examples include (meth)acrylate monomers such as (meth)acrylate, 2-(meth)acryloyloxyethyl acid phosphate, 2-(meth)acryloyloxy-2-hydroxypropyl phthalate, half-(meth)acrylate, furfuryl(meth)acrylate, tetrahydrofurfuryl(meth)acrylate, carbitol(meth)acrylate, benzyl(meth)acrylate, butoxyethyl(meth)acrylate, allyl(meth)acrylate, (meth)acryloylmorpholine, polyoxyethylene secondary alkyl ether acrylate, 2-hydroxyethylacrylamide, N-methylol(meth)acrylamide, N-vinylpyrrolidone, 2-vinylpyridine, vinyl acetate, etc. These can be used individually or in combination of two or more.

[0097] [Polyfunctional (meth)acrylate compounds] The polyfunctional (meth)acrylate compound excludes the urethane (meth)acrylate compound (b), and examples include bifunctional (meth)acrylates, trifunctional or more functional acrylates, etc. These can be used individually or in combination of two or more.

[0098] Examples of the aforementioned bifunctional (meth)acrylates include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethylene oxide-modified bisphenol A type di(meth)acrylate, propylene oxide-modified bisphenol A type di(meth)acrylate, and cyclohexanedimethanol di(meth)acrylate. Examples include acrylates, ethoxylated cyclohexanedimethanol di(meth)acrylate, dimethylol dicyclopentane di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerin di(meth)acrylate, pentaerythritol di(meth)acrylate, ethylene glycol diglycidyl ether di(meth)acrylate, diethylene glycol diglycidyl ether di(meth)acrylate, diglycidyl phthalate diglycidyl ester di(meth)acrylate, hydroxypivalic acid-modified neopentyl glycol di(meth)acrylate, isocyanurate-modified ethylene oxide diacrylate, etc.

[0099] Examples of the three or more functional (meth)acrylates mentioned above include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tri(meth)acryloyloxyethoxytrimethylolpropane, glycerin polyglycidyl ether poly(meth)acrylate, isocyanurate ethylene oxide modified tri(meth)acrylate, and caprolactone modified dipentaerythritol penta(meth)acrylate. Examples include caprolactone-modified dipentaerythritol hexa(meth)acrylate, caprolactone-modified pentaerythritol tri(meth)acrylate, caprolactone-modified pentaerythritol tetra(meth)acrylate, ethylene oxide-modified dipentaerythritol penta(meth)acrylate, ethylene oxide-modified dipentaerythritol hexa(meth)acrylate, ethylene oxide-modified pentaerythritol tri(meth)acrylate, ethylene oxide-modified pentaerythritol tetra(meth)acrylate, and ethoxylated 15-glycerin tri(meth)acrylate.

[0100] In addition to these, other active energy ray curable compounds (B) that can be used include Michael adducts of (meth)acrylic acid or 2-(meth)acryloyloxyethyl dicarboxylic acid monoesters.

[0101] Examples of the Michael adducts of (meth)acrylic acid include (meth)acrylic acid dimers, (meth)acrylic acid trimers, and (meth)acrylic acid tetramers. Examples of the 2-(meth)acryloyloxyethyl dicarboxylic acid monoester include carboxylic acids having specific substituents, such as 2-(meth)acryloyloxyethyl succinic acid monoester, 2-(meth)acryloyloxyethyl phthalic acid monoester, 2-(meth)acryloyloxyethyl hexahydrophthalic acid monoester, and oligoester (meth)acrylate.

[0102] In this adhesive composition, the content of the active energy ray-curable compound (B) is preferably 1 to 200 parts by mass, more preferably 5 to 150 parts by mass, even more preferably 10 to 100 parts by mass, and even more preferably 15 to 80 parts by mass, per 100 parts by mass of the (meth)acrylic resin (A). If the content of the active energy ray-curable compound (B) is too low, the ease of peeling after irradiation with active energy rays tends to decrease.

[0103] Furthermore, the content of the urethane (meth)acrylate compound (b) in the active energy ray curable compound (B) is usually 50% by mass or more, preferably 80% by mass or more. The upper limit is usually 100% by mass. If the content is too low, the adhesive properties before irradiation with active energy rays tend to decrease.

[0104] Furthermore, the content of monofunctional (meth)acrylates and polyfunctional (meth)acrylates other than the urethane (meth)acrylate compound (b) in the active energy ray curable compound (B) is usually less than 50% by mass, preferably less than 20% by mass. The lower limit is usually 0% by mass. If the content is too high, the tackiness and durability before irradiation with active energy rays tend to deteriorate.

[0105] <Crosslinking agent (C)> This adhesive composition further contains a crosslinking agent (C). Examples of the crosslinking agent (C) include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, melamine-based crosslinking agents, aldehyde-based crosslinking agents, and amine-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred because they improve reactivity with acrylic resin (A) and adhesion to the substrate when used as a protective sheet. In addition, one or more of these crosslinking agents (C) can be used in combination.

[0106] Examples of the isocyanate-based crosslinking agents include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hexamethylene diisocyanate, diphenylmethane-4,4-diisocyanate, isophorone diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, tetramethyl xylylene diisocyanate, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, and adduct compounds of these polyisocyanate compounds with polyol compounds such as trimethylolpropane, as well as burette and isocyanurate compounds of these polyisocyanate compounds. Among these, the isocyanurate of hexamethylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, adduct of 2,6-tolylene diisocyanate and trimethylolpropane, isocyanurate of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, and adduct of tetramethylxylylene diisocyanate and trimethylolpropane are preferred in terms of reactivity with functional groups.

[0107] Examples of the epoxy crosslinking agent include bisphenol A-epichlorohydrin type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl erythritol, diglycerol polyglycidyl ether, 1,3'-bis(N,N-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidyl-m-xylenediamine.

[0108] Examples of the aziridine-based crosslinking agents include tetramethylolmethane-tri-β-aziridinylpropionate, trimethylolpropane-tri-β-aziridinylpropionate, N,N'-diphenylmethane-4,4'-bis(1-aziridincarboxyamide), and N,N'-hexamethylene-1,6-bis(1-aziridincarboxyamide).

[0109] Examples of the oxazoline-based crosslinking agents include 2,2'-bis(2-oxazoline), 1,2-bis(2-oxazoline-2-yl)ethane, 1,4-bis(2-oxazoline-2-yl)butane, 1,8-bis(2-oxazoline-2-yl)butane, 1,4-bis(2-oxazoline-2-yl)cyclohexane, 1,2-bis(2-oxazoline-2-yl)benzene, and 1,3-bis(2-oxazoline-2-yl). Examples include bisoxazoline compounds containing aliphatic or aromatic compounds such as benzene, and polymers of one or more addition polymerizable oxazolines such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0110] Examples of the melamine-based crosslinking agent include hexamethoxymethylmelamine, hexaethoxymethylmelamine, hexapropoxymethylmelamine, hexapoxymethylmelamine, hexapentyloxymethylmelamine, hexahexyloxymethylmelamine, and melamine resin.

[0111] Examples of the aldehyde-based crosslinking agents include glyoxal, malondialdehyde, succinidaldehyde, maleidaldehyde, glutardialdehyde, formaldehyde, acetaldehyde, and benzaldehyde.

[0112] Examples of the amine-based crosslinking agents include hexamethylenediamine, triethyldiamine, polyethyleneimine, hexamethylenetetraamine, diethylenetriamine, triethyltetraamine, isophoronediamine, amino resins, and polyamides.

[0113] The amount of the crosslinking agent (C) in this adhesive composition is usually 0.1 to 30 parts by mass, preferably 0.2 to 20 parts by mass, and more preferably 0.3 to 10 parts by mass, per 100 parts by mass of the acrylic resin (A). If the amount of crosslinking agent (C) is too small, the cohesive force of the adhesive layer decreases, and the adhesive properties tend to deteriorate. If the amount of crosslinking agent (C) is too large, the adhesive properties before irradiation with active energy rays tend to deteriorate, and the pot life shortens, making it easier for problems to occur during coating. Furthermore, if the amount of crosslinking agent (C) is too large, the ability to follow deformations such as twisting tends to decrease.

[0114] <Activated energy ray polymerization initiator (D)> This adhesive composition preferably contains an active energy ray polymerization initiator (D). The active energy ray polymerization initiator (D) can be any agent that generates radicals through the action of active energy rays. However, if the acrylic resin (A) has an active energy ray crosslinkable structural portion, it does not need to contain the active energy ray polymerization initiator (D).

[0115] Examples of the active energy ray polymerization initiator (D) include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone, 1-hydroxycyclohexylphenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-methyl-2-morpholino(4-thiomethylphenyl)propan- Acetophenones such as 1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, and 2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone oligomer; benzoins such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin isobutyl ether; benzophenone, o-benzoyl methyl benzoate, 4-phenylbenzophenone, and 4-benzoyl-4'-methyl-diphenylsulfate Benzophenones such as benzophenone, 3,3',4,4'-tetra(tert-butylperoxycarbonyl)benzophenone, 2,4,6-trimethylbenzophenone, 4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyloxy)ethyl]benzenemethanaminonium bromide, (4-benzoylbenzyl)trimethylammonium chloride; 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone Examples include thioxanthones such as 1-chloro-4-propoxythioxanthone and 2-(3-dimethylamino-2-hydroxy)-3,4-dimethyl-9H-thioxanthone-9-one mesochloride; and acyl phosphonate oxides such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide.Among these, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, and 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one are preferred because they do not sublimate when heated and are stable. These active energy ray polymerization initiators (D) can be used individually or in combination of two or more.

[0116] If the adhesive composition contains the active energy ray polymerization initiator (D), its content is preferably 0.005 to 10 parts by mass, particularly preferably 0.01 to 5 parts by mass, and especially preferably 0.01 to 3 parts by mass, per 100 parts by mass of the active energy ray curable compound (B). If the content of the active energy ray polymerization initiator (D) is too low, the ease of peeling after irradiation with active energy rays tends to decrease, and if it is too high, the stain resistance of the coated area tends to decrease after irradiation with active energy rays.

[0117] Furthermore, as auxiliary agents for these active energy ray polymerization initiators (D), for example, triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, 4-dimethylaminobenzoate ethyl, 4-dimethylaminobenzoate (n-butoxy)ethyl, 4-dimethylaminobenzoate isoamyl, 4-dimethylaminobenzoate 2-ethylhexyl, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, etc. may also be used in combination. These auxiliary agents can also be used one or more in combination.

[0118] <Other ingredients> The adhesive composition may further contain additives such as antistatic agents, antioxidants, plasticizers, fillers, pigments, diluents, anti-aging agents, UV absorbers, UV stabilizers, and tackifying resins, to the extent that they do not impair the effects of the present invention. These can be used individually or in combination of two or more. In addition to the additives, the adhesive composition may also contain small amounts of impurities contained in the raw materials used to manufacture the components of the adhesive composition.

[0119] As for the aforementioned additives, antioxidants are preferred because they enhance the stability when used as an adhesive, and plasticizers are preferred because they adjust viscosity and impart flexibility after crosslinking. If this adhesive composition contains an antioxidant, there are no particular restrictions on its content, but it is usually 0.01 to 5% by mass of the adhesive composition. Furthermore, if the adhesive composition contains a plasticizer, its content is preferably 0.5 to 30% by mass of the adhesive composition, and particularly preferably 1 to 20% by mass. If the plasticizer content is too low, the plasticizing effect cannot be obtained, and if it is too high, the stain resistance of the coated area tends to decrease.

[0120] <<Adhesive Composition>> The adhesive composition is obtained by mixing an acrylic resin (A) containing the aforementioned acrylic resin (A1), an active energy ray curable compound (B), a crosslinking agent (C), preferably an active energy ray polymerization initiator (D), and optionally other components. In particular, from the standpoint of productivity, it is preferable to first manufacture an acrylic resin (A) and then mix this acrylic resin (A) with components such as an active energy ray curable compound (B) and a crosslinking agent (C).

[0121] Furthermore, when this adhesive composition is crosslinked by the crosslinking agent (C), it exhibits the function of an adhesive, and the adhesive can be suitably used as the adhesive layer of a protective film described later.

[0122] The glass transition temperature of the adhesive is -5°C or lower, preferably -10°C or lower, and particularly preferably -15°C or lower. The lower limit is usually -40°C. When the glass transition temperature is within the above range, the material exhibits excellent flexibility in responding to deformations such as twisting at low temperatures. The glass transition temperature is determined by crosslinking the adhesive composition to create an adhesive with a gel fraction of 30-80%, and then measuring the dynamic viscoelasticity of this adhesive using a dynamic viscoelasticity measuring device in the shear deformation mode. The temperature at which the loss loss tangent (loss modulus G'' / storage modulus G'=tanδ) is maximized is read. The gel fraction can be determined by the method described later.

[0123] To set the glass transition temperature of the adhesive within the above range, methods include using an acrylic resin (A) whose glass transition temperature is within the range, or adding a plasticizer or the like.

[0124] Furthermore, the elastic modulus of the adhesive at -20°C is 0.05 to 5 MPa, preferably 0.5 to 4 MPa. The aforementioned modulus of elasticity is the value of the storage modulus of elasticity when the adhesive composition is crosslinked to form an adhesive with a gel fraction of 30-80%, and the dynamic viscoelasticity of this adhesive is measured in the shear deformation mode using a dynamic viscoelasticity measuring device.

[0125] To achieve the elastic modulus of the adhesive within the aforementioned range, methods such as lowering the glass transition temperature of the adhesive composition or reducing the degree of crosslinking can be employed.

[0126] <<Protective film>> A protective film according to one embodiment of the present invention (hereinafter referred to as "this protective film") has an adhesive layer in which the adhesive composition is crosslinked. This protective film can protect the surface of an object to which it is adhered, and after use, the adhesive layer hardens and the adhesive strength decreases when irradiated with active energy rays, making it possible to peel it off.

[0127] The adherend is not particularly limited, but examples include image display devices equipped with liquid crystal displays, organic EL displays, etc., and touch panels. Among these, image display devices are preferred, and flexible image display devices are more preferred. In other words, the protective film is preferably a surface protective film for an image display device. Furthermore, it is more preferable that the surface protective film for an image display device is attached to the surface of a flexible image display device.

[0128] This protective film typically comprises a base sheet, an adhesive layer made of this adhesive composition, and a release film. This protective film can be obtained, for example, by directly coating the adhesive composition onto a release film or base sheet, either as is or with its concentration adjusted using a suitable organic solvent, then crosslinking it by, for example, heat treatment at 80-105°C for 0.5-10 minutes, and finally attaching it to the base sheet or release film. Furthermore, the protective film may undergo further aging after drying to balance its adhesive properties.

[0129] Examples of the base sheet include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate, and polyethylene terephthalate / isophthalate copolymers; polyolefin resins such as polyethylene, polypropylene, and polymethylpentene; polyfluoroethylene resins such as polyvinyl fluoride, polyvinylidene fluoride, and polyfluoroethylene; polyamides such as nylon 6 and nylon 6,6; vinyl polymers such as polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, and vinylon; cellulose resins such as cellulose triacetate and cellophane; acrylic resins such as polymethyl methacrylate, polyethyl methacrylate, polyethyl acrylate, and polybutyl acrylate; polystyrene; polycarbonate; polyarylate; polyimide; and sheets made of at least one synthetic resin selected from the group consisting of these; and woven or nonwoven fabrics made of metal foils of aluminum, copper, and iron, paper such as fine paper and glassine paper, glass fibers, natural fibers, synthetic fibers, etc. These base sheets can be used as single layers or as multi-layered structures made by laminating two or more types. Among these, sheets made of synthetic resin are preferred from the viewpoint of weight reduction and other factors.

[0130] Furthermore, as the release film, for example, various synthetic resin sheets, paper, textiles, nonwoven fabrics, etc., as exemplified in the base sheet, can be used, which have been treated with a release agent.

[0131] The coating method for this adhesive composition is not particularly limited as long as it is a general coating method, and examples include roll coating, die coating, gravure coating, comma coating, and screen printing.

[0132] The thickness of the adhesive layer of the protective film obtained in this manner is typically 1 to 200 μm, preferably 3 to 100 μm, and more preferably 5 to 50 μm.

[0133] The gel fraction of the adhesive layer of this protective film is typically 30-80%, preferably 35-75%, and more preferably 40-70%. When the gel fraction is within the above range, the adhesive strength tends to be excellent before irradiation with active energy rays.

[0134] The gel fraction mentioned above serves as an indicator of the degree of crosslinking and can be calculated, for example, by the following method. The adhesive layer is removed from the protective film and its mass is measured. Then, this adhesive layer is wrapped in a 200-mesh stainless steel wire mesh and immersed in ethyl acetate at 23°C for 24 hours. After drying, the mass of the insoluble adhesive layer remaining in the wire mesh is measured. The gel fraction is calculated from the mass of the adhesive layer before immersion and the mass of the adhesive layer after immersion using the following formula. Gel fraction (%) = Mass of adhesive layer after immersion / Mass of adhesive layer before immersion × 100

[0135] Furthermore, the haze value of the adhesive layer of this protective film is usually 5% or less, preferably 3% or less, and more preferably 1% or less. The haze value is calculated by measuring the diffuse transmittance and total light transmittance of the adhesive layer using a haze meter, and using the following formula. Haze value (%) = Diffuse transmittance / Total light transmittance × 100

[0136] The adhesive strength (180-degree peel strength) of this protective film before irradiation with active energy rays varies depending on the type of base sheet, the type of coating, etc., but is usually 1 N / 25 mm or more, and preferably 3 N / 25 mm or more. The adhesive strength can be measured by the method described in the examples below.

[0137] The creep rate of this protective film at -20°C is typically 10% or more, preferably 13% or more. The upper limit is typically 30%. Furthermore, the creep rate of this protective film at 25°C is typically 20% or more, preferably 35% or more. The upper limit is typically 110%.

[0138] The creep rate is calculated by laminating the adhesive layer of the protective film to a thickness of 1000 μm, cutting it into a 9 mm diameter disc to form a test piece, placing it on a rheometer, and measuring the strain (%) after 600 seconds at temperatures of -20°C and 25°C under the conditions of a measuring jig: 8 mm diameter parallel plate, pressure: 10000 Pa.

[0139] As described above, this protective film can protect the surface of an object by being adhered to it. After use, the adhesive layer hardens and its adhesive strength decreases when irradiated with active energy rays, making it possible to peel it off.

[0140] As the aforementioned active energy rays, various types of light rays can be used, including far-ultraviolet, ultraviolet, near-ultraviolet, and infrared rays, as well as electromagnetic waves such as X-rays and gamma rays, and electron beams, proton beams, and neutron beams. However, ultraviolet light is advantageous due to its curing speed, ease of obtaining irradiation equipment, and cost.

[0141] The cumulative dose of ultraviolet radiation is typically 100 to 10,000 mJ / cm². 2 The concentration is preferably 500 to 7500 mJ / cm². 2 Furthermore, the irradiation time varies depending on the type of light source, the distance between the light source and the adhesive layer, the thickness of the adhesive layer, and other conditions, but it is usually only a few seconds, and in some cases even less than one second.

[0142] Furthermore, the adhesive strength (180-degree peel strength) after irradiation with active energy rays is lower than the adhesive strength before irradiation with active energy rays, and is usually 0.8 N / 25 mm or less, preferably 0.6 N / 25 mm or less.

[0143] A protective film using this adhesive composition as the adhesive layer can be easily peeled off the substrate after being bonded to the substrate, temporarily protecting the substrate's surface, and then irradiated with active energy rays. This hardens the adhesive layer and reduces its adhesive strength. [Examples]

[0144] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In the examples, "parts" means by mass.

[0145] [Manufacturing of acrylic resin (A1-1)] In a reactor equipped with a temperature controller, thermometer, stirrer, dropping funnel, and reflux condenser, 52 parts ethyl acetate, 44 parts toluene, and 0.045 parts AIBN were charged. The mixture was heated while stirring until reflux was achieved. Once the internal temperature stabilized, a mixture of 92 parts n-butyl acrylate (a1), 5 parts vinyl acetate (a3), 2.5 parts acrylic acid (a2), and 0.25 parts 2-hydroxyethyl methacrylate (a2) was added dropwise over 2 hours and the reaction was carried out under reflux. Subsequently, 14 parts ethyl acetate and 0.25 parts 2-hydroxyethyl methacrylate (a2) were added 3 hours after the start of the reaction, and then 3 parts ethyl acetate and 0.025 parts AIBN were added 3.5 hours after the start of the reaction. Furthermore, 13 parts of toluene and 0.025 parts of AIBN were added 5.5 hours after the start of the reaction, and 50 parts of toluene were added 7.5 hours after the start of the reaction to terminate the reaction and obtain an acrylic resin (A1-1) solution.

[0146] [Manufacturing of acrylic resin (A1'-1)] In a reactor equipped with a temperature controller, thermometer, stirrer, dropping funnel, and reflux condenser, 95 parts of n-butyl acrylate (a1), 5 parts of acrylic acid (a2), 15 parts of ethyl acetate, 40 parts of acetone, and 0.0125 parts of AIBN were charged. The mixture was heated while stirring, and the reaction was started when the internal temperature reached its peak. 0.5 hours after the start of the reaction, a mixture of 33 parts of ethyl acetate and 0.125 parts of AIBN was added dropwise over 1 hour. Then, 1.75 hours after the start of the reaction, 25 parts of ethyl acetate were added dropwise over 1 hour. 3.25 hours after the start of the reaction, ethyl acetate and 60 ppm of polymerization inhibitor (MEHQ) were added to terminate the reaction and obtain an acrylic resin (A1'-1) solution.

[0147] [Physical properties of acrylic resins (A1-1) and (A1'-1)] The polymerization components and physical properties of the acrylic resins (A1-1) and (A1'-1) obtained above are shown in Table 1 below. The weight-average molecular weight and glass transition temperature were measured as shown below.

[0148] (Weight-average molecular weight of acrylic resin (A)) The weight-average molecular weight of the acrylic resin (A) is the weight-average molecular weight calculated on a standard polystyrene molecular weight scale. The high-performance liquid chromatograph (Waters Japan Co., Ltd., "Waters2695 (main unit)" and "Waters2414 (detector)") was used, and the column was ShodexGPCKF-806L (exclusion limit molecular weight: 2 × 10⁻¹⁶). 7 Separation range: 100~2×10 7 The measurement was performed by connecting three units in series (theoretical plate count: 10,000 stages / unit, filler material: styrene-divinylbenzene copolymer, filler particle size: 10 μm).

[0149] (Glass transition temperature of acrylic resin (A)) The glass transition temperature (Tg) was calculated by applying the glass transition temperature and mass fraction of each monomer constituting the acrylic resin (A) as a homopolymer to Fox's formula below.

[0150]

number

[0151] [Table 1]

[0152] [Production of activated energy ray-curable compound (B-1)] A four-necked flask equipped with a temperature controller, thermometer, stirrer, water-cooled condenser, and nitrogen gas inlet contained 80.3 parts of a mixture of pentaerythritol tetraacrylate and pentaerythritol triacrylate (hydroxyl value: 119.1 mg KOH / g, manufactured by Osaka Organic Chemical Industry Co., Ltd.) as a hydroxyl group-containing (meth)acrylate compound, 19.7 parts of isophorone diisocyanate (isocyanate group content: 37.8%, manufactured by Evonik) as a polyvalent isocyanate compound, and 2,6-di-tert-butylcresol as a polymerization inhibitor. 0.04 parts of (BHT) and 0.02 parts of dibutyltin dilaurate (DBTL), a tin-based compound, as a reaction catalyst were charged and the reaction was carried out at 60°C. The reaction was terminated when the remaining isocyanate groups were 0.3% by mass or less, and an active energy ray-curable compound (B-1) [urethane (meth)acrylate compound (b1-1): 6 ethylenically unsaturated groups, weight-average molecular weight 1400, acryloyl group concentration 23.6% by mass] was obtained, with a ratio of hydroxyl group-containing (meth)acrylate compound to polyvalent isocyanate compound = 2.1:1 (mol).

[0153] [Crosslinking agent (C)] The following were prepared as crosslinking agents (C). • Isocyanate-based crosslinking agent (C-1): Isocyanurate derivative of hexamethylene diisocyanate (manufactured by Tosoh Corporation: Coronate HX)

[0154] [Activated energy ray polymerization initiator (D)] The following were prepared as active energy ray polymerization initiators (D). • Active energy ray polymerization initiator (D-1): 1-Hydroxycyclohexyl phenyl ketone (IGMresins: OMNIRAD184)

[0155] The adhesive compositions of the Examples and Reference Examples were prepared using the acrylic resin (A), active energy ray curable compound (B), crosslinking agent (C), and active energy ray polymerization initiator (D) prepared as described above.

[0156] <Example 1> To 100 parts of the acrylic resin (A1-1) obtained above, an active energy ray curable compound (B-1), a crosslinking agent (C-1), and an active energy ray polymerization initiator (D-1) were added in the proportions shown in Table 2 below and mixed to obtain an adhesive composition. Subsequently, ethyl acetate was added to the adhesive composition to prepare an adhesive composition solution.

[0157] <Reference example 1> The adhesive composition and adhesive composition solution of Reference Example 1 were prepared in the same manner as in Example 1, except that the composition of the adhesive composition was changed to the proportions shown in Table 2 below.

[0158] [Preparation of adhesive sheets with release film and PET sheets with adhesive layer] The adhesive composition solution obtained above was applied to a heavy release film (SP-PET3803-BU, manufactured by Mitsui Chemicals ICT Materia Co., Ltd.) as a substrate using an applicator, dried at 100°C for 5 minutes, cooled to room temperature, and then attached to a release film (SP-PET3801-BU, manufactured by Mitsui Chemicals ICT Materia Co., Ltd.). By aging at 40°C for 4 days, an adhesive sheet with a release film (adhesive layer thickness 25 μm) was obtained. Furthermore, a PET sheet with an adhesive layer (with an adhesive layer thickness of 25 μm) was obtained in the same manner as the above-mentioned adhesive sheet with release film, except that the base material was changed to polyethylene terephthalate film (film thickness 38 μm) (Toray Industries' "T60 Lumirror").

[0159] [Table 2]

[0160] The following measurements were performed and evaluated using the release film-coated adhesive sheet and the adhesive-coated PET sheet obtained above. The results are shown in Table 3 below.

[0161] [Gel fraction] From the 50mm x 50mm test specimen of the release film-coated adhesive sheet obtained above, only the adhesive layer was removed, sandwiched between 200-mesh stainless steel mesh, immersed in ethyl acetate, and left to stand at 23°C for 24 hours. After standing, it was removed and the ethyl acetate was completely evaporated using a drying oven. The gel fraction was calculated from the mass before and after immersion using the following formula. Gel fraction (%) = [Mass of adhesive layer (before immersion) - Mass of SUS mesh] / [Mass of adhesive layer (after immersion) - Mass of SUS mesh] × 100

[0162] [Glass transition temperature and elastic modulus at -20°C] An adhesive sheet with a thickness of approximately 1000 μm was fabricated by laminating the adhesive layers of the release film-attached adhesive sheet obtained above. The dynamic viscoelasticity of the fabricated adhesive sheet was measured under the following conditions, and the glass transition temperature (Tg) was determined from the temperature at which the storage modulus G' and the loss tangent (loss modulus G'' / storage modulus G'=tanδ) were maximized at -20°C. (Measurement conditions) • Measuring instrument: DVA-225 (manufactured by IT Measurement & Control Co., Ltd.) • Deformation mode: Shearing Distortion: 0.1% ·Measurement temperature: -80~20℃ ·Measurement frequency: 1Hz

[0163] [Creep rate] The adhesive layers of the release film-attached adhesive sheets obtained above were laminated to a thickness of 1000 μm, and then cut into discs with a diameter of 9 mm to prepare test specimens for creep measurement. The creep measurement specimens obtained as described above were placed on a rheometer (TA Instruments "MCR-301"), and the strain (%) after 600 seconds was measured at -20°C and 25°C under the conditions of a measuring jig: 8 mm diameter parallel plate, pressure: 10,000 Pa. This strain rate (%) was defined as the creep rate and evaluated according to the following evaluation criteria. (Evaluation criteria at -20℃) ○: 13% or more △: 10% or more, less than 13% ×: Less than 10% (Evaluation criteria at 25°C) ○: 35% or more △: 20% or more, less than 35% ×: Less than 20%

[0164] [Adhesion (before irradiation with activated energy rays)] The PET sheet with adhesive layer obtained above was cut to a size of 25 mm x 100 mm, the release film was peeled off, and the sheet was pressed onto a stainless steel plate (SUS304BA plate) by passing a 2 kg rubber roller back and forth twice in an atmosphere of 23°C and 50% relative humidity to prepare a test specimen. After the test specimen was left to stand for 30 minutes in an atmosphere of 23°C and 50% relative humidity, the 180-degree peel strength (N / 25 mm) was measured at a peeling speed of 300 mm / min and evaluated according to the following evaluation criteria. (Evaluation Criteria) 〇:5N / 25mm or more △: 1N / 25mm or more, less than 5N / 25mm ×: Less than 1N / 25mm

[0165] [Adhesion (after irradiation with active energy rays)] The adhesive sheet with release film obtained above was cut to a size of 25 mm x 100 mm, the release film was peeled off, and the sheet was pressed onto a stainless steel plate (SUS304BA plate) by passing a 2 kg rubber roller back and forth twice in an atmosphere of 23°C and 50% relative humidity to prepare a test specimen. Next, this test specimen was left to stand for 30 minutes in an atmosphere of 23°C and 50% relative humidity, and then irradiated with ultraviolet light from a height of 18 cm at a conveyor speed of 1.0 m / min using one 80 W high-pressure mercury lamp (cumulative irradiation dose of 1000 mJ / cm²). 2 ) 5 times (cumulative irradiation dose 5000 mJ / cm²) 2 The following tests were conducted. Furthermore, after UV irradiation, the test specimens were left to stand for 30 minutes in an atmosphere of 23°C and 50% relative humidity, and the 180° peel strength (N / 25mm) was measured at a peeling speed of 300 mm / min, and evaluated according to the following evaluation criteria. (Evaluation Criteria) ○: 0.8N / less than 25mm △: 0.8N / 25mm or more, less than 1.5N / 25mm ×:1.5N / 25mm or more

[0166] [Haze value] The diffuse transmittance and total light transmittance of only the adhesive layer of the release film-attached adhesive sheet were measured using HAZEMATERNDH4000 (manufactured by Nippon Denshoku Industries Co., Ltd.), and the haze value was calculated by substituting the obtained diffuse transmittance and total light transmittance values ​​into the following formula. A higher haze value indicates that the components in the adhesive composition are not uniform. Haze value (%) = Diffuse transmittance / Total light transmittance × 100

[0167] [Table 3]

[0168] As can be seen from Table 3 above, the adhesive sheet of Example 1, which used an adhesive composition containing an acrylic resin (A1) with a weight-average molecular weight below a specific amount, and whose glass transition temperature and elastic modulus at -20°C were within a specific range, exhibited excellent adhesive strength before active energy ray irradiation and excellent ease of peeling after active energy ray irradiation. Furthermore, the adhesive sheet of Example 1 also exhibited excellent creep rate and transparency at -20°C and 25°C. On the other hand, the adhesive sheet of Reference Example 1, which used an adhesive composition that did not contain an acrylic resin (A1) with a weight-average molecular weight below a specific amount, was inferior in creep rate at 25°C, even though its glass transition temperature and elastic modulus at -20°C were within a specific range. Therefore, it did not exhibit excellent conformability to deformation such as twisting over a wide range of temperatures. [Industrial applicability]

[0169] This adhesive composition exhibits excellent adhesion, transparency, and flexibility to conform to deformations such as twisting before irradiation with active energy rays, and is easily peelable after irradiation with active energy rays. Therefore, it can be suitably used as an adhesive layer for a protective film that protects the surface of an image display device.

Claims

1. An adhesive composition containing an acrylic resin (A), an active energy ray curable compound (B), and a crosslinking agent (C), The acrylic resin (A) contains an acrylic resin (A1) with a weight-average molecular weight of 900,000 or less. An adhesive composition in which the aforementioned adhesive composition is crosslinked to form an adhesive with a gel fraction of 30 to 80%, the glass transition temperature is -5°C or lower, and the elastic modulus at -20°C is 0.05 to 5 MPa.

2. The adhesive composition according to claim 1, wherein the glass transition temperature of the acrylic resin (A1) is -30°C or lower.

3. The adhesive composition according to claim 1, wherein the weight-average molecular weight of the acrylic resin (A1) is 100,000 to 900,000.

4. The adhesive composition according to claim 1, wherein the active energy ray curable compound (B) contains urethane (meth)acrylate (b).

5. The adhesive composition according to claim 1, wherein the content of the active energy ray curable compound (B) is 1 to 200 parts by mass per 100 parts by mass of the acrylic resin (A).

6. Furthermore, the adhesive composition according to claim 1 contains an active energy ray polymerization initiator (D).

7. A protective film having an adhesive layer in which the adhesive composition according to any one of claims 1 to 6 is crosslinked.

8. The protective film according to claim 7, wherein the adhesive layer is hardened and peelable by irradiation with active energy rays.

9. A surface protective film for an image display device having an adhesive layer in which the adhesive composition according to any one of claims 1 to 6 is crosslinked.

10. The surface protective film for an image display device according to claim 9, wherein the adhesive layer is hardened and peelable by irradiation with active energy rays.

11. A flexible image display device containing the surface protective film for image display devices described in claim 9.

Images