Adhesive sheet

Abstract

To provide a novel adhesive sheet which is excellent in durability under high temperature and humidity (less air bubbles, less cracking and discoloration of a base material when TAC is used as a base material) even if attached to a plastic plate.SOLUTION: There is provided an adhesive sheet comprising an adhesive layer, wherein the adhesive layer is composed of an adhesive composition comprising an acrylic adhesive, an adhesion-imparting agent having a fluoroalkyl group, an aluminum chelate compound and a curing agent, the curing agent includes an isocyanate-based curing agent or an epoxy-based curing agent and the content of the aluminum chelate compound based on 100 pts.mass of the total content of the acrylic adhesive and the adhesion-imparting agent having a fluoroalkyl group is 0.3 to 1.8 pts.mass.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet. [Background technology]

[0002] In the past, functional films applied to display surface protection panels were often made with a base material of polyethylene terephthalate (PET), but in recent years, triacetyl cellulose (TAC) and polycarbonate (PC) have also been used. In addition, glass plates and plastic plates (polycarbonate, acrylic, ABS, etc.) are used as materials for display surface protection panels. For example, Patent Document 1 discloses that glass plates and plastic plates such as acrylic plates and polycarbonate plates can also be used for surface protection panels. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-23695 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a functional film based on TAC is attached to a plastic plate, problems such as outgassing from the plastic plate and the formation of air bubbles, or yellowing and cracking of the TAC film can occur, especially under high temperature and humidity conditions.

[0005] The present invention relates to providing a novel pressure-sensitive adhesive sheet that has excellent durability under high temperature and high humidity conditions (few air bubbles, and when TAC is used as the substrate, less cracking and discoloration of the substrate) even when attached to a plastic plate. [Means for solving the problem]

[0006] The present invention relates to the following [1]. [1] A pressure-sensitive adhesive sheet having an adhesive layer, the pressure-sensitive adhesive layer being made of an adhesive composition including an acrylic pressure-sensitive adhesive, a tackifier having a fluoroalkyl group, an aluminum chelate compound, and a curing agent, the curing agent including an isocyanate-based curing agent or an epoxy-based curing agent, and the content of the aluminum chelate compound per 100 parts by mass of the total content of the acrylic pressure-sensitive adhesive and the tackifier having a fluoroalkyl group is 0.3 to 1.8 parts by mass. Effect of the Invention

[0007] According to the present invention, a novel pressure-sensitive adhesive sheet can be provided that has excellent durability under high temperature and high humidity conditions (few air bubbles, and when TAC is used as the substrate, less cracking and discoloration of the substrate) even when attached to a plastic plate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] As a result of intensive research into the above-mentioned problems, the inventors of the present invention have found that when a specific adhesive composition containing a tackifier having a fluoroalkyl group or an aluminum chelate compound is used as an adhesive layer, the adhesive layer has excellent durability. Although the mechanism is unclear, it is presumed that the tackifier having a fluoroalkyl group, which has higher heat resistance than the main polymer of the acrylic adhesive, is segregated on the surface of the adhesive sheet, and when the adhesive sheet is laminated on a plastic plate, a barrier effect is generated at the interface with the plastic plate.

[0009] The pressure-sensitive adhesive sheet of the present invention includes a pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet of the present invention may be an embodiment having only a pressure-sensitive adhesive layer, or an embodiment having a laminated structure with a substrate or a release material. For example, the pressure-sensitive adhesive sheet may be an embodiment having a substrate / adhesive layer / release material laminated in this order, a substrate / adhesive layer / substrate laminated in this order, or a release material / adhesive layer / release material laminated in this order.

[0010] The adhesive layer is made of an adhesive composition containing an acrylic adhesive, a tackifier having a fluoroalkyl group, an aluminum chelate compound, and a curing agent. The adhesive layer can be formed by coating and drying the adhesive composition.

[0011] Examples of the acrylic adhesive include a polymer of a monomer derived from a (meth)acrylic acid ester, and a copolymer of a monomer derived from a (meth)acrylic acid ester and a monomer having a polymerizable functional group. From the viewpoint of durability and adhesiveness, the glass transition temperature of the polymer is preferably from -80°C to 0°C, more preferably from -75°C to -20°C, and even more preferably from -70°C to -20°C. The weight average molecular weight of the acrylic adhesive is preferably 100,000 or more, more preferably 200,000 or more, and even more preferably 400,000 or more. Also, it is preferably 2 million or less, more preferably 1.5 million or less, and even more preferably 1 million or less.

[0012] Examples of monomers derived from (meth)acrylic acid esters include (meth)acrylic acid alkyl esters having an alkyl group of (meth)acrylic acid esters having an acrylic carbon number of 4 to 12. For example, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, lauryl (meth)acrylate, and the like can be mentioned, and one or a combination of two or more of these can be mentioned.

[0013] The monomer having a polymerizable functional group is preferably one having a functional group capable of reacting with a crosslinking agent to form a chemical bond. The functional group may be a hydroxyl group, a carboxyl group, an amino group, an amide group, or the like, and may be any one or a combination of two or more of these. From the viewpoint of easy control of reactivity with the crosslinking agent, a hydroxyl group or a carboxyl group is preferred. For attachment to a film sensor using a metal film, a hydroxyl group is preferred from the viewpoint of metal corrosion. The monomer having a polymerizable functional group to be copolymerized may be 1 to 30% by mass of the total 100% by mass of the monomers derived from the acrylic acid ester. Examples of monomers having a polymerizable functional group include (meth)acrylic acid, ethacrylic acid, maleic acid, fumaric acid, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, polyethylene-polypropylene glycol mono(meth)acrylate, dimethylaminomethyl (meth)acrylate, diethylaminomethyl (meth)acrylate, 2-dimethylaminoethyl (meth)acrylate, 3-dimethylaminopropyl (meth)acrylate, (meth)acrylamide, 2-dimethylaminoacrylamide (meth)acrylate, N-methylol acrylamide, N-methoxymethyl acrylamide, N-methoxybutyl acrylamide, and diacetone acrylamide, and combinations of one or more of these may be used.

[0014] Examples of tackifiers having a fluoroalkyl group include trifluoromethyl (meth)acrylate, pentafluoroethyl (meth)acrylate, heptafluoropropyl (meth)acrylate, nonafluorobutyl (methyl)acrylate, undecafluoropentyl (meth)acrylate, and tridecafluorohexyl (meth)acrylate. From the viewpoint of durability, pentafluoroethyl (meth)acrylate and the like are preferred.

[0015] From the viewpoint of durability, the content of the tackifier having a fluoroalkyl group in the pressure-sensitive adhesive composition is preferably 1.0 to 50 parts by mass, more preferably 2.0 to 40 parts by mass, and even more preferably 3.0 to 30 parts by mass, per 100 parts by mass of the acrylic pressure-sensitive adhesive.

[0016] Examples of the aluminum chelate compound include aluminum trisethylacetoacetate, alkylacetoacetate aluminum diisopropylate, aluminum monoacetylacetate bis(ethyl acetylacetate), and aluminum tris(acetylacetate). From the viewpoint of durability, alkylacetoacetate aluminum diisopropylate is preferred.

[0017] From the viewpoint of durability, the content of the aluminum chelate compound in the pressure-sensitive adhesive composition is 0.3 to 1.8 parts by mass, preferably 0.6 to 1.6 parts by mass, and more preferably 0.8 to 1.4 parts by mass, per 100 parts by mass of the total content of the acrylic pressure-sensitive adhesive and the tackifier having a fluoroalkyl group.

[0018] The curing agent may be an isocyanate-based curing agent or an epoxy-based curing agent.

[0019] As the isocyanate-based hardening agent, various isocyanates having two or more isocyanate groups, such as aromatic polyisocyanates, aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic aliphatic polyisocyanates, are used. As the isocyanate-based hardening agent, 1,3-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,4'-diphenylmethane diisocyanate, 2,4'-tolylene diisocyanate, naphthalene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, tolidine diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexa Examples include methylene diisocyanate, lysine diisocyanate, lysine triisocyanate, isophorone diisocyanate, cyclohexyl diisocyanate, ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate. These are used when the acrylic adhesive does not contain a carboxy group.

[0020] Examples of epoxy curing agents include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidyl aniline, and diglycidyl amine, and are used when the acrylic adhesive contains a carboxy group.

[0021] From the viewpoint of durability, the content of the curing agent in the pressure-sensitive adhesive composition is preferably 0.03 to 30 parts by mass, more preferably 0.09 to 15 parts by mass, and even more preferably 0.15 to 6 parts by mass, relative to 100 parts by mass of the total content of the acrylic pressure-sensitive adhesive and the tackifier having a fluoroalkyl group.

[0022] The reaction retarder is one having two or more carbonyl groups in the molecule. Examples of the reaction retarder having two or more carbonyl groups in the molecule include diketone, dicarboxylic acid, keto acid, etc. For example, acetylacetone, dibenzoylmethane, methyl acetoacetate, ethyl acetoacetate, n-propyl acetoacetate, isopropyl acetoacetate, etc. are included, and from the viewpoint of durability, acetylacetone, etc. is preferred.

[0023] From the viewpoint of durability, the content of the reaction retarder in the pressure-sensitive adhesive composition is preferably 0.04 to 40 parts by mass, more preferably 0.2 to 20 parts by mass, and even more preferably 0.4 to 12 parts by mass, relative to 100 parts by mass of the total content of the acrylic pressure-sensitive adhesive and the tackifier having a fluoroalkyl group.

[0024] The pressure-sensitive adhesive composition may contain any of the following components: an ultraviolet absorber, a colorant (dye, pigment), an antistatic agent, a silane coupling agent, an antioxidant, and an antirust agent.

[0025] The adhesive composition can be prepared by mixing the above-mentioned components. Here, a commercially available product containing an acrylic adhesive and a tackifier having a fluoroalkyl group can also be used. Examples of such commercially available products include "MPT-25" manufactured by Toagosei Co., Ltd., "MPT-54" manufactured by Toagosei Co., Ltd., and "MPT-57" manufactured by Toagosei Co., Ltd. In addition, a solvent such as toluene, xylene, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, or methyl isobutyl ketone may be blended.

[0026] The thickness of the adhesive layer is preferably 2 to 1000 μm, more preferably 5 to 500 μm, and further preferably 10 to 200 μm.

[0027] The storage modulus (G') of the adhesive layer at 100°C is preferably 10 3 ~10 6 Pa, more preferably 10 4 ~10 5In this specification, the storage modulus (G') is a value measured in accordance with JIS K 7244. More specifically, the storage modulus was measured at 100°C using a dynamic viscoelasticity measuring device (manufactured by Anton Paar, model number: MCR301) in the temperature range of -40°C to 190°C, at a heating rate of 3°C / min and a frequency of 1 Hz.

[0028] The adhesive strength of the adhesive layer to glass at 23°C and 50% RH is preferably 1 to 50 N / 25 mm, more preferably 2 to 40 N / 25 mm. The adhesive strength of the adhesive layer to polycarbonate at 23°C and 50% RH is preferably 1 to 50 N / 25 mm, more preferably 2 to 40 N / 25 mm. The tack value of the adhesive layer in a ball tack test at 23°C and 50% RH is preferably 1 to 10, more preferably 1 to 8. In this specification, the adhesive strength is measured in accordance with JIS Z 0237:2009. The ball tack test is also in accordance with JIS Z 0237. Specifically, after fixing a test piece to a 30° inclined plate, a ball is rolled on the surface of the test piece, and the maximum ball number that stops within the measurement area is taken as the tack value.

[0029] The substrate is preferably made of TAC, but other polymer resin sheets can also be used. As other polymer resin sheets, known plastic materials such as polyethylene terephthalate, polyvinylidene chloride, polyethylene, polypropylene, polycarbonate, and polystyrene can be used. The substrate can be formed by any method such as a solvent casting method or an extrusion method.

[0030] The release material may be a suitable thin material such as a synthetic resin film, such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, or polyethylene terephthalate, a rubber sheet, a foam sheet, a metal foil, paper, a nonwoven fabric, or a laminate of these. The surface of the release material may be subjected to a release treatment such as silicone treatment, long-chain alkyl treatment, or fluorine treatment, as necessary, in order to improve the releasability from the adhesive layer. The releasability of the release material can be controlled by adjusting at least one of the parameters of the type of agent used in the release treatment and the amount of coating.

[0031] The pressure-sensitive adhesive sheet of the present invention has excellent durability under high temperature and high humidity conditions (few air bubbles, and when TAC is used as the substrate, less cracking and discoloration of the substrate) even when attached to a plastic plate. Therefore, it is preferable to use it for purposes such as attaching to plastic surface protection panels for displays, ornamental plastic panels (protective boxes), etc. Furthermore, it can also be used for purposes such as attaching to a glass plate or the like on the other side of the side to which the TAC substrate is attached, and has excellent durability under high temperature and high humidity conditions for both TAC and glass substrates. EXAMPLES

[0032] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples. The amount of each component below is the amount converted to solid content. In addition, for those containing only a solvent component such as acetylacetone used as a reaction retarder, the amount added is indicated.

[0033] Example 1 [Preparation of Adhesive Composition] To 100 parts by mass of an acrylic adhesive containing a tackifier having a fluoroalkyl group ("MPT-54", manufactured by Toagosei Co., Ltd.), 0.21 parts by mass of xylylene diisocyanate as a curing agent, 2.0 parts by mass of acetylacetone as a reaction retarder, and 0.4 parts by mass of alkylacetoacetate aluminum diisopropylate as a chelating agent were added and mixed to obtain an adhesive composition.

[0034] [Manufacturing of substrate-less adhesive sheets] The adhesive composition was applied to a polyethylene terephthalate film release sheet (trade name "Diafoil MRF75" 75μm, manufactured by Mitsubishi Chemical Corporation) so that the thickness after drying would be 25μm, and this adhesive layer was laminated with a polyethylene terephthalate film release sheet (trade name "Cosmo Peel E7006" 75μm, manufactured by Toyobo Co., Ltd.) and left to stand at 40°C for 3 days to prepare a substrateless adhesive sheet. The obtained substrateless adhesive sheet was subjected to various measurements and evaluations using the following methods. The coating suitability was evaluated visually based on the gelation state of the coating liquid and the presence or absence of streaks and unevenness on the coated surface, and the storage modulus and ball tack of the adhesive layer were measured using the methods described above. The results are shown in Tables 1 and 2.

[0035] Details of the components used in Table 1 are shown below. Isocyanate hardener: "Takenate D110N" manufactured by Mitsui Chemicals Reaction retarder: "Acetylacetone" manufactured by Daicel Corporation Aluminum chelate: "Aluminum chelate M" manufactured by Kawaken Fine Chemicals Co., Ltd.

[0036] [Preparation of adhesive film for testing] The light release separator E7006 was peeled off from the obtained substrate-less adhesive sheet, and the adhesive layer was attached to the easy-adhesion surface of a single-sided easy-adhesion polyethylene terephthalate film (product name "Cosmoshine A4160" 100 μm, Toyobo Co., Ltd.) to obtain a test adhesive film.

[0037] <Adhesive strength> The above test adhesive film was cut to a width of 25 mm, and after peeling off the heavy release separator MRF75, it was laminated and pressed onto a commercially available soda lime glass plate (2.0 mm thick) and a polycarbonate plate (Teijin PC1600, 2.0 mm thick). Using a tensile tester (Shimadzu Corporation AGS-500NG), the 180 degree peel strength of the adhesive sheet was measured at a peel speed of 300 mm / min in accordance with JISZ-0237:2009, and this was taken as the adhesive strength.

[0038] <Total light transmittance> The above test adhesive film was cut into a 50 mm square. After peeling off the heavy release separator MRF75, it was bonded to a polycarbonate plate (PC1600 manufactured by Teijin, 2.0 mm thick). Then, using an autoclave treatment device (manufactured by Kurihara Seisakusho), it was pressure-bonded under the conditions of 0.5 MPa and 50 °C for 30 minutes to obtain a sample for optical evaluation. The total light transmittance of the above sample for optical evaluation was measured under the following conditions. Apparatus: Ultraviolet-visible-infrared spectrophotometer (UV-3150 manufactured by Shimadzu Corporation) Wavelength range: 380 - 780 nm Viewing angle: 2 degrees Light source: D65

[0039] <Haze> The haze of the above sample for optical evaluation was measured under the following conditions. Apparatus: Haze meter (manufactured by Nippon Denshoku Industries Co., Ltd.) Light source: D65

[0040] <Durability> The heavy release separator MRF75 of the adhesive film obtained by changing the one-sided easy-adhesion polyethylene terephthalate film in the production of the above test adhesive film to a triacetyl cellulose film and bonding them was peeled off, and it was bonded to a polycarbonate plate (PC1600 manufactured by Teijin, 2.0 mm thick). Then, using an autoclave treatment device (manufactured by Kurihara Seisakusho), it was pressure-bonded under the conditions of 0.5 MPa and 50 °C for 30 minutes to obtain a sample for durability evaluation. The above sample for durability evaluation was left standing in a thermo-hygrostat at 85 °C and 85% RH for 1500 hours, and the generation status of bubbles and the cracking and discoloration status of the TAC film were visually evaluated. The evaluation criteria are shown below.

[0041] <Plastic plate bubbles> ◎: No bubbles generated 〇: A very small part of microbubbles are present △: Microbubbles are present on the entire surface ×: Large bubbles are present

[0042] <TAC film cracking> ◎: None 〇: There is a part with microcracks △: There is a part with cracks ×: There are cracks all over

[0043] <TAC Film Discoloration> ◎: None 〇: Light yellow △: Yellow ×: Brown

[0044] Examples 2, 5, 6, Comparative Examples 1 - 3 A base material pressure - sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the types and ratios of the curing agent, reaction retardant, and chelating agent were changed as shown in Table 1. Also, a test adhesive film was prepared in the same manner as above, and the same measurements as in Example 1 were performed. The results are shown in Tables 1 and 2.

[0045] Example 3 A base material pressure - sensitive adhesive sheet was obtained in the same manner as in Example 2, except that an acrylic pressure - sensitive adhesive containing a tackifier having a fluoroalkyl group and having different glass transition temperatures (manufactured by Toagosei Co., Ltd., "MPT - 57") was used. Also, a test adhesive film was prepared in the same manner as above, and the same measurements as in Example 1 were performed. The results are shown in Tables 1 and 2.

[0046] Example 4 A base material pressure - sensitive adhesive sheet was obtained in the same manner as in Example 2, except that an acrylic pressure - sensitive adhesive containing a tackifier having a fluoroalkyl group and having different glass transition temperatures (manufactured by Toagosei Co., Ltd., "MPT - 25") was used. Also, a test adhesive film was prepared in the same manner as above, and the same measurements as in Example 1 were performed. The results are shown in Tables 1 and 2.

[0047]

Table 1

[0048]

Table 2

[0049] As shown in Tables 1 and 2, the adhesive sheets of Examples 1 to 6, in which the adhesive layer was made of an adhesive composition containing an acrylic adhesive, a tackifier having a fluoroalkyl group, an aluminum chelate compound, and an isocyanate-based curing agent, and in which the content of the aluminum chelate compound was 0.3 to 1.8 parts by mass per 100 parts by mass of the total content of the acrylic adhesive and the tackifier having a fluoroalkyl group, all had excellent durability.

[0050] Although not shown in Tables 1 and 2, the same results as in Examples 1 to 6 were obtained when an acrylic ester copolymerized with an acrylic adhesive polymer was used as the acrylic adhesive, and an epoxy curing agent was used as the curing agent. When a rosin ester tackifier or a terpene phenol tackifier was used instead of a tackifier having a fluoroalkyl group, no discoloration or cracking was observed in the TAC, but large bubbles were observed when the TAC was attached to a plastic plate. When a titanium chelate compound or a zirconia chelate compound was used instead of an aluminum chelate compound, there were few bubbles when the TAC was attached to a plastic plate, but discoloration and cracking were observed. [Industrial Applicability]

[0051] The pressure-sensitive adhesive sheet of the present invention is suitably used as a functional film to be attached to a surface protection panel of a display.

Claims

1. A pressure-sensitive adhesive sheet having an adhesive layer, the pressure-sensitive adhesive layer being made of a pressure-sensitive adhesive composition (excluding those containing an epoxy-based curing agent) containing an acrylic pressure-sensitive adhesive, a tackifier having a fluoroalkyl group, an aluminum chelate compound, and a curing agent, the curing agent containing an isocyanate-based curing agent, and the content of the aluminum chelate compound per 100 parts by mass of the total content of the acrylic pressure-sensitive adhesive and the tackifier having a fluoroalkyl group is 0.3 to 1.8 parts by mass.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive composition further comprises a reaction retarder.

3. The pressure-sensitive adhesive sheet according to claim 1 , further comprising a substrate.

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