Adhesive composition and method for producing laminate using the same

Abstract

To provide an adhesive composition which can retain a coating shape after UV irradiation and has good adhesive strength after curing, and a method for producing a laminate using the same.SOLUTION: The adhesive composition contains 45 to 70% by mass of an epoxy resin, at least one first (meth) acrylate component selected from the group consisting of an aromatic (meth) acrylate, an alicyclic (meth) acrylate, and a heterocyclic (meth) acrylate, a second (meth) acrylate component composed of a hydroxyl group-containing (meth) acrylate, a radical photopolymerization initiator, and a cationic photopolymerization initiator. The adhesive composition may contain more than 30% by mass and 70% by mass or less of a hydrogenated epoxy resin, at least one first (meth) acrylate component selected from the group consisting of an aromatic (meth) acrylate, an alicyclic (meth) acrylate, and a heterocyclic (meth) acrylate, a second (meth) acrylate component composed of a hydroxyl group-containing (meth) acrylate, a radical photopolymerization initiator, and a cationic photopolymerization initiator.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present technology relates to an adhesive composition and a method for producing a laminate using the same. [Background technology]

[0002] There are known techniques for bonding and fixing adherends, such as an image display device and a front cover, an image display device and a touch panel, and a front cover and a touch panel, using optically transparent adhesives such as OCR (Optical Clear Resin) and LOCA (Liquid Optically Clear Adhesive), respectively (see, for example, Patent Documents 1 to 3). Among these, UV delayed-curing adhesives have also been proposed as a method for curing UV (ultraviolet) opaque parts. Furthermore, with the recent emergence of displays other than rectangular, there has been an increasing need for irregularly shaped adhesive coating. One solution to this problem is inkjet coating. Adhesives used in inkjet coating are required to have low viscosity and typically contain a monomer as the main component.

[0003] Patent Documents 1 and 2 describe a resin composition containing a polyfunctional epoxy resin, a monofunctional epoxy resin, and a polyfunctional oxetane resin as a UV delayed-cure adhesive. Patent Document 3 describes a photocurable resin composition containing a radical polymerizable group-containing compound, a cationically polymerizable group-containing compound, a photoradical initiator, and a photoacid generator, in which the content of the radical polymerizable group-containing compound is greater than the content of the cationically polymerizable group-containing compound, the photoradical initiator is at least one of an α-hydroxyalkylphenone-based photoradical initiator and a benzyl methyl ketal-based photoradical initiator, and the mass ratio of the photoradical initiator to the photoacid generator (photoradical initiator / photoacid generator) is 0.5 to 30.

[0004] The UV-curable resin compositions described in Patent Documents 1 and 2 are epoxy-cationic curing systems, and therefore have a slower start of curing than acrylic-radical curing systems. Monofunctional epoxy monomers in particular have a slow start of curing. Therefore, when the epoxy-cationic curing adhesives described in Patent Documents 1 and 2 are used as low-viscosity adhesives for inkjet coating, curing does not start immediately after UV irradiation, which raises concerns about difficulty in maintaining the coating shape.

[0005] On the other hand, conventional acrylic-radical curing UV-curable resin compositions are resistant to deformation of the coated shape after UV irradiation, but if the elastic modulus after curing is high, bonding of adherends to each other tends to be difficult due to repulsion. Therefore, conventional acrylic-radical curing UV-curable resin compositions need to have a low elastic modulus after curing, making it difficult to obtain sufficient adhesive strength. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5919574 [Patent Document 2] Patent No. 6080064 [Patent Document 3] Japanese Patent Application Publication No. 2017-218515 Summary of the Invention [Problem to be solved by the invention]

[0007] The present technology has been proposed in view of the above-mentioned conventional situation, and provides an adhesive composition that can retain its coating shape after UV irradiation and has good adhesive strength after curing, as well as a method for producing a laminate using the same. [Means for solving the problem]

[0008] The adhesive composition according to the present technology contains 45 to 70 mass % of an epoxy resin, at least one first (meth)acrylate component selected from the group consisting of aromatic (meth)acrylates, alicyclic (meth)acrylates, and heterocyclic (meth)acrylates, a second (meth)acrylate component consisting of a hydroxyl group-containing (meth)acrylate, a radical photopolymerization initiator, and a cationic photopolymerization initiator.

[0009] The adhesive composition according to the present technology contains more than 30% by mass and not more than 70% by mass of a hydrogenated epoxy resin, at least one first (meth)acrylate component selected from the group consisting of aromatic (meth)acrylates, alicyclic (meth)acrylates, and heterocyclic (meth)acrylates, a second (meth)acrylate component consisting of a hydroxyl group-containing (meth)acrylate, a radical photopolymerization initiator, and a cationic photopolymerization initiator.

[0010] The method for producing a bonded body according to the present technology includes step A of applying the above-described adhesive composition to a first adherend to form an adhesive composition layer, step B of irradiating the adhesive composition layer with ultraviolet light to form a cured adhesive layer, and step C of placing a second adherend on the surface of the cured adhesive layer and joining the first adherend and the second adherend via the cured adhesive layer. [Effects of the Invention]

[0011] This technology can provide an adhesive composition that can maintain its applied shape after UV irradiation and has good adhesive strength after curing. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a graph illustrating the change in elastic modulus of the adhesive composition over time. [Figure 2] FIG. 2 is a perspective view illustrating an example of a method for producing a laminate using an adhesive composition, where (A) is a perspective view illustrating step A, (B) is a perspective view illustrating step B, and (C) and (D) are perspective views illustrating step C. [Figure 3]FIG. 3 is a perspective view illustrating another example of a method for producing a laminate using an adhesive composition, where (A) is a perspective view illustrating step A, (B) is a perspective view illustrating step B, and (C) and (D) are perspective views illustrating step C. [Figure 4] FIG. 4 is a perspective view for explaining the method of the high-temperature retention test. DETAILED DESCRIPTION OF THE INVENTION

[0013] The adhesive composition according to the present technology contains 45 to 70 mass % of an epoxy resin, at least one first (meth)acrylate component selected from the group consisting of aromatic (meth)acrylates, alicyclic (meth)acrylates, and heterocyclic (meth)acrylates, a second (meth)acrylate component consisting of a hydroxyl group-containing (meth)acrylate, a radical photopolymerization initiator, and a cationic photopolymerization initiator.

[0014] FIG. 1 is a graph illustrating the change in elastic modulus of an adhesive composition over time. The horizontal axis in FIG. 1 represents time, and the vertical axis represents elastic modulus. Also, A in FIG. 1 represents the elastic modulus at which bonding is possible (Dahlquist standard). Graph (i) in FIG. 1 represents the change in elastic modulus over time when a conventional epoxy-cationic curing UV-curable resin composition, such as those described in Patent Documents 1 and 2, is used. Graph (ii) in FIG. 1 represents the change in elastic modulus over time when a conventional acrylic-radical curing UV-curable resin composition is used. And graph (iii) in FIG. 1 represents the change in elastic modulus over time when an adhesive composition according to the present technology (a combination of an epoxy-cationic curing system and an acrylic-radical curing system) is used.

[0015] The adhesive composition according to the present technology contains a first (meth)acrylate component and a radical photopolymerization initiator, and as shown in B in Figure 1, curing begins immediately after UV irradiation, allowing the adhesive composition to immediately exhibit adhesive strength and shape retention after UV irradiation. Furthermore, immediately after UV irradiation, the epoxy resin in the adhesive composition according to the present technology does not completely cure, but rather acts as a plasticizing component, contributing to reducing the elasticity of the adhesive composition. Thus, the adhesive composition according to the present technology exhibits improved adhesiveness and lamination properties after UV irradiation.

[0016] Furthermore, the adhesive composition according to the present technology exhibits delayed curing properties due to the inclusion of an epoxy resin and a cationic photopolymerization initiator, and therefore, the adhesive composition according to the present technology initiates delayed curing by being left at room temperature (and heated as necessary) after UV irradiation, thereby exhibiting high adhesive strength.

[0017] Furthermore, the adhesive composition according to the present technology can more effectively exhibit adhesion (adhesive strength) and delayed curing properties by using a first (meth)acrylate component and a second (meth)acrylate component in combination.

[0018] In this way, the adhesive composition according to the present technology can maintain its applied shape after UV irradiation and can also provide good adhesive strength after curing.

[0019] Specific examples of the components of the adhesive composition according to the present technology will be described below.

[0020] <Epoxy resin> The epoxy resin may be a monofunctional epoxy compound having one epoxy group per molecule, or a polyfunctional epoxy compound having two or more epoxy groups per molecule. In particular, from the viewpoint of reactivity, the epoxy resin is preferably a polyfunctional epoxy compound, and more preferably a bifunctional epoxy resin.

[0021] The epoxy resin may be solid or liquid at room temperature. Room temperature refers to the range of 15 to 25°C as specified in JIS K 0050:2019 (General rules for chemical analysis methods). The epoxy group contained in the epoxy resin may be an alicyclic epoxy group or a non-alicyclic epoxy group.

[0022] Specific examples of epoxy resins include bisphenol-type epoxy compounds such as polybutadiene epoxy resin, bisphenol A-type epoxy resin, and bisphenol F-type epoxy resin, naphthalene-type epoxy compounds, aliphatic epoxy compounds, biphenyl-type epoxy, glycidylamine-type epoxy compounds, and alcohol-type epoxy compounds such as hydrogenated bisphenol A-type epoxy compounds, epoxy-modified silicones, novolac-type epoxy compounds such as phenol novolac-type epoxy compounds and cresol novolac-type epoxy compounds, alicyclic epoxy compounds, multifunctional epoxy compounds, glycidyl ether-type epoxy compounds, glycidyl ester-type epoxy compounds, halogenated epoxy compounds such as brominated epoxy compounds, rubber-modified epoxy compounds, urethane-modified epoxy compounds, epoxidized polybutadiene, epoxidized styrene-butadiene-styrene block copolymers, epoxy group-containing polyester compounds, epoxy group-containing polyurethane compounds, and epoxy group-containing acrylic compounds. Among these, bisphenol F-type epoxy resins are preferred from the viewpoint of maintaining the delayed curing properties of the adhesive composition after UV irradiation.

[0023] Furthermore, as the epoxy resin, a hydrogenated epoxy resin (hydrogenated epoxy resin) can also be used. From the viewpoint of transmittance and coloring resistance after curing of the adhesive composition, hydrogenated epoxy resin is preferred.

[0024] The epoxy equivalent of the epoxy resin can be, for example, 150 to 300 g / eq, or can also be 180 to 220 g / eq.

[0025] The viscosity of the epoxy resin at 25°C is preferably 500 to 10,000 mPa·s.

[0026] Examples of epoxy resin products include jER YX8000 and YX8034 (both manufactured by Mitsubishi Chemical Corporation), EPICLON EXA-830CRP (manufactured by DIC Corporation), etc. One type of epoxy resin may be used alone, or two or more types may be used in combination.

[0027] The content of the epoxy resin in the adhesive composition is 45% by mass or more, and may be 50% by mass or more, or may be 53% by mass or more. When the content of the epoxy resin in the adhesive composition is 45% by mass or more, high adhesive strength can be exhibited after UV irradiation. The upper limit of the content of the epoxy resin in the adhesive composition is 70% by mass or less, and may be 65% by mass or less, or may be 60% by mass or less. When the content of the epoxy resin in the adhesive composition is 70% by mass or less, the amount of other components (e.g., the first (meth)acrylate component and the second (meth)acrylate component) is not too small relatively, and adhesive strength and shape retention can be exhibited after UV irradiation. In particular, it is preferable that the content of the hydrogenated epoxy resin in the adhesive composition satisfies the above numerical range. Note that when the adhesive composition contains two or more epoxy resins, it is preferable that the total amount of the epoxy resins satisfies the above numerical range.

[0028] <First (meth)acrylate component> The first (meth)acrylate component is selected from the group consisting of aromatic (meth)acrylates, alicyclic (meth)acrylates, and heterocyclic (meth)acrylates. The first (meth)acrylate component may be used alone or in combination of two or more. The first (meth)acrylate component may be monofunctional or bifunctional or higher, but is preferably monofunctional.

[0029] The aromatic (meth)acrylate is a (meth)acrylate having an aromatic hydrocarbon group. The number of carbon atoms in the aromatic hydrocarbon group in the aromatic (meth)acrylate can be 6 to 30, or optionally 6 to 18. The aromatic hydrocarbon group may have a monocyclic structure or a polycyclic structure. The aromatic hydrocarbon group may have a substituent or may be unsubstituted. Specific examples of aromatic (meth)acrylates include benzyl (meth)acrylate, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxy polyethylene glycol (meth)acrylate, nonylphenoxy polyethylene glycol (meth)acrylate, phenoxy polypropylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. Among these, benzyl (meth)acrylate is preferred, and benzyl acrylate is more preferred, from the viewpoint of more effectively exhibiting the adhesive strength and shape retention of the adhesive composition after UV irradiation. An example of a product of aromatic (meth)acrylate is Viscoat 160 (manufactured by Osaka Organic Chemical Industry Co., Ltd.).

[0030] The alicyclic (meth)acrylate is a (meth)acrylate having an alicyclic structure. The number of carbon atoms constituting the alicyclic structure in the alicyclic (meth)acrylate can be, for example, 4 to 30, or may be 4 to 20, 4 to 10, or 4 to 8. The alicyclic structure in the alicyclic (meth)acrylate may be a monocyclic structure or a polycyclic structure. The alicyclic structure in the alicyclic (meth)acrylate may be saturated or unsaturated. The alicyclic hydrocarbon group may have a substituent or may be unsubstituted. Specific examples of alicyclic (meth)acrylates include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxy (meth)acrylate, dicyclopentenyloxyethyl acrylate, adamantyl (meth)acrylate, 2-alkyl-2-adamantyl (meth)acrylate, 3-hydroxy-1-adamantyl (meth)acrylate, and 1-perfluoroadamantyl (meth)acrylate. Among these, cyclohexyl (meth)acrylate is preferred, and cyclohexyl acrylate is more preferred, from the viewpoint of more effectively exhibiting the adhesive strength and shape retention of the adhesive composition after UV irradiation. An example of a product of alicyclic (meth)acrylate is Viscoat 155 (manufactured by Osaka Organic Chemical Industry Co., Ltd.).

[0031] The heterocyclic (meth)acrylate has at least one heteroatom of the heterocycle, such as a nitrogen atom, an oxygen atom, or a sulfur atom. The number of carbon atoms constituting the heterocycle can be 3 to 10, or can be 3 to 8. The heterocycle may have a monocyclic structure or a polycyclic structure. The heterocycle may have a substituent or may be unsubstituted. Specific examples of heterocyclic (meth)acrylates include tetrahydrofurfuryl (meth)acrylate, 4-tetrahydropyranyl acrylate, and 2-tetrahydropyranylmethyl acrylate. Among these, tetrahydrofurfuryl (meth)acrylate is preferred, and tetrahydrofurfuryl acrylate is more preferred, from the viewpoint of more effectively exhibiting the adhesive strength and shape retention of the adhesive composition after UV irradiation. An example of a heterocyclic (meth)acrylate product is Viscoat 150 (manufactured by Osaka Organic Chemical Industry Ltd.).

[0032] The content of the first (meth)acrylate component in the adhesive composition is preferably 20% by mass or more, and may be 25% by mass or more, 30% by mass or more, 35% by mass or more, or 40% by mass or more. Having a first (meth)acrylate component content of 20% by mass or more in the adhesive composition can further improve adhesion and bonding properties after UV irradiation. The upper limit of the content of the first (meth)acrylate component in the adhesive composition is preferably 50% by mass or less, and may be 45% by mass or less, or 42% by mass or less. By setting the amount of the first (meth)acrylate component in the adhesive composition to 50% by mass or less, the elastic modulus after curing can be prevented from becoming too high, thereby enabling good bonding between adherends. Furthermore, the amount of other components (e.g., epoxy resin) in the adhesive composition is not too small relative to each other, which more effectively exhibits delayed curing properties and results in high adhesive strength. When the adhesive composition contains two or more types of first (meth)acrylate components, it is preferable that the total amount of the first (meth)acrylate components falls within the above numerical range.

[0033] <Second (meth)acrylate component> The second (meth)acrylate component is a hydroxyl group-containing (meth)acrylate. The hydroxyl group-containing (meth)acrylate has one or more hydroxyl groups in one molecule, and may have two or more hydroxyl groups in one molecule. The second (meth)acrylate component may be used alone or in combination of two or more types.

[0034] Specific examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, etc. Among these, from the viewpoint of more effectively exhibiting the adhesiveness and delayed curing properties of the adhesive composition after UV irradiation, 4-hydroxybutyl (meth)acrylate is preferred, and 4-hydroxybutyl acrylate is more preferred.

[0035] The content of the second (meth)acrylate component in the adhesive composition is preferably 2% by mass or more, and may be 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more. By having the content of the second (meth)acrylate component in the adhesive composition be 2% by mass or more, adhesion and delayed curing properties can be more effectively exhibited, thereby improving the retention of the applied shape and adhesive strength. The upper limit of the content of the second (meth)acrylate component in the adhesive composition is preferably 30% by mass or less, and may be 25% by mass or less, or 22% by mass or less. By having the content of the second (meth)acrylate component in the adhesive composition be 30% by mass or less, the amount of other components (e.g., epoxy resin) in the adhesive composition is not too small relative to the amount of the second (meth)acrylate component, and therefore delayed curing properties can be more effectively exhibited, resulting in high adhesive strength. When the adhesive composition contains two or more second (meth)acrylate components, it is preferable that the total amount of the second (meth)acrylate components be within the above-mentioned range.

[0036] <Radical photopolymerization initiator> The radical photopolymerization initiator is a polymerization initiator for the first (meth)acrylate component and the second (meth)acrylate component described above. Examples of the radical photopolymerization initiator include an α-hydroxyalkylphenone radical photopolymerization initiator and a benzyl methyl ketal radical photopolymerization initiator. Examples of the α-hydroxyalkylphenone radical photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)-benzyl]phenyl}-2-methyl-1-one, and oligo[2-hydroxy-2-methyl-[1-(methylvinyl)phenyl]propanone]. Commercially available radical photopolymerization initiators include Irgacure 184 (1-hydroxycyclohexylphenyl ketone, manufactured by BASF), Irgacure 1173 (2-hydroxy-2-methyl-1-phenylpropan-1-one, manufactured by BASF), Irgacure 2959 (1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, manufactured by BASF), Irgacure 127 (2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)-benzyl]phenyl}-2-methyl-1-one, manufactured by BASF), and Esacureone (oligo[2-hydroxy-2-methyl-[1-(methylvinyl)phenyl]propanone], manufactured by Lamberti). The radical photopolymerization initiators may be used alone or in combination of two or more.

[0037] The content of the radical photopolymerization initiator in the adhesive composition can be appropriately selected depending on the purpose, and can be, for example, 0.1% by mass or more, or can be 0.1 to 2.0% by mass.

[0038] <Cationic photopolymerization initiator> The cationic photopolymerization initiator is a polymerization initiator for the epoxy resin described above. As the cationic photopolymerization initiator, onium salts such as azonium salts, iodonium salts, and sulfonium salts can be used.

[0039] Examples of diazonium salts include benzenediazonium hexafluoroantimonate, benzenediazonium hexafluorophosphate, and benzenediazonium hexafluoroborate.

[0040] Examples of iodonium salts include diphenyliodonium tetrakis(pentafluorophenyl)borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, di(4-nonylphenyl)iodonium hexafluorophosphate, di(4-t-butylphenyl)iodonium hexafluorophosphate, di(4-t-butylphenyl)iodonium hexafluoroantimonate, tolylcumyliodonium tetrakis(pentafluorophenyl)borate, and (4-methylphenyl)[4-(2-methylpropyl)phenyl]iodonium hexafluorophosphate.

[0041] Examples of sulfonium salts include triarylsulfonium hexafluorophosphate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis(pentafluorophenyl)borate, diphenyl[4-(phenylthio)phenyl]sulfonium hexafluoroantimonate, 4,4'-bis[diphenylsulfonio]diphenyl sulfide bishexafluorophosphate, 4,4'-bis[di(β-hydroxyethoxy)phenylsulfonio]diphenyl sulfide bishexafluoroantimonate, and 4,4'-bis[di(β-hydroxyethoxy)phenylsulfonio]diphenyl sulfide Examples of the hexafluorophosphate include bishexafluorophosphate, 7-[di(p-toluyl)sulfonio]-2-isopropylthioxanthone hexafluoroantimonate, 7-[di(p-toluyl)sulfonio]-2-isopropylthioxanthone tetrakis(pentafluorophenyl)borate, 4-phenylcarbonyl-4'-diphenylsulfonio-diphenylsulfide hexafluorophosphate, 4-(p-tert-butylphenylcarbonyl)-4'-diphenylsulfonio-diphenylsulfide hexafluoroantimonate, and 4-(p-tert-butylphenylcarbonyl)-4'-di(p-toluyl)sulfonio-diphenylsulfide tetrakis(pentafluorophenyl)borate.

[0042] From the viewpoint of heat resistance (resistance to discoloration) after curing of the adhesive composition, the cationic photopolymerization initiator is preferably a cationic photopolymerization initiator whose anion species is phosphorus-based. Specific examples of phosphorus-based cationic photopolymerization initiators include Omnicat 250 (manufactured by IGM Resin) and AT-6992 (manufactured by Tomoe Engineering Co., Ltd.). One type of cationic photopolymerization initiator may be used alone, or two or more types may be used in combination.

[0043] The content of the cationic photopolymerization initiator in the adhesive composition can be appropriately selected depending on the purpose, and can be, for example, 0.1% by mass or more, or can be 0.1 to 2.0% by mass.

[0044] As described above, the adhesive composition contains 45 to 70 mass % of an epoxy resin, a first (meth)acrylate component, a second (meth)acrylate component, a radical photopolymerization initiator, and a cationic photopolymerization initiator, and therefore, even when an epoxy-cationic curing adhesive is used, the applied shape can be maintained after UV irradiation and good adhesive strength can be achieved after curing.

[0045] In another embodiment, the adhesive composition may contain more than 30% by mass and not more than 70% by mass of a hydrogenated epoxy resin, a first (meth)acrylate component, a second (meth)acrylate component, a radical photopolymerization initiator, and a cationic photopolymerization initiator. Such adhesive compositions can also achieve the effects of the present technology described above. When the content of the hydrogenated epoxy resin in the adhesive composition is more than 30% by mass, high adhesive strength can be achieved after UV irradiation. When the content of the hydrogenated epoxy resin in the adhesive composition is not more than 70% by mass, the amount of other components (e.g., the first (meth)acrylate component and the second (meth)acrylate component) is not too low, allowing the adhesive composition to exhibit adhesive strength and shape retention after UV irradiation.

[0046] The adhesive composition may further contain other components in addition to the above-mentioned components, provided that the effects of the present technology are not impaired. Examples of other components include (meth)acrylates other than the first (meth)acrylate component and the second (meth)acrylate component described above, plasticizers, tackifiers, sensitizers, etc.

[0047] However, it is preferable that the adhesive composition is substantially free of any other (meth)acrylate components than the first (meth)acrylate component and the second (meth)acrylate component described above. For example, the content of any other (meth)acrylate components than the first (meth)acrylate component and the second (meth)acrylate component in the adhesive composition can be 10% by mass or less, 5% by mass or less, or 1% by mass or less.

[0048] To achieve good inkjet suitability under normal inkjet ejection conditions, the adhesive composition has a viscosity of 5 mPa·s or more, preferably 10 mPa·s or more, and more preferably 15 mPa·s or more, at 25°C, and a viscosity of 50 mPa·s or less, preferably 30 mPa·s or less, and more preferably 20 mPa·s or less, at 60°C. If the adhesive composition has a viscosity of less than 5 mPa·s at 25°C, it tends to drip easily from the inkjet nozzle. If the adhesive composition has a viscosity of more than 50 mPa·s at 60°C, it tends to fail to eject. Preferably, the adhesive composition has a viscosity of 50 mPa·s or less at 25°C. Preferably, the adhesive composition has a viscosity of 5 mPa·s or more at 60°C. Preferably, the adhesive composition has a viscosity of 5 to 50 mPa·s in the temperature range of 25 to 60°C. The viscosity of the adhesive composition can be measured by the method described in the Examples below.

[0049] <Method of manufacturing the laminated body> A method for producing a bonded body using an adhesive composition according to the present technology includes the following steps A, B, and C. Specific examples of the method for producing a bonded body will be described below in the order of a first embodiment and a second embodiment.

[0050] [First embodiment] <Process A> FIG. 2 is a perspective view illustrating an example of a method for producing a laminate using an adhesive composition. In step A, as shown in FIG. 2(A), an adhesive composition 2 according to the present technology is applied to a first adherend 1 to form an adhesive composition layer 3. When the adhesive composition 2 has the viscosity characteristics described above, good inkjet suitability can be achieved under normal inkjet discharge conditions. Therefore, in step A, the adhesive composition 2 can be applied using an inkjet head 4. The method for applying the adhesive composition 2 is not limited to the inkjet method and can be appropriately selected depending on the purpose, and may be, for example, a jet dispensing method, a spray method, a spin coating method, or the like.

[0051] Specifically, in step A, a first adherend 1 is prepared, and as shown in FIG. 2(A), an adhesive composition 2 is applied to the surface of the first adherend 1 from the nozzle of an inkjet head 4 to form an adhesive composition layer 3. The thickness of the adhesive composition layer 3 can be appropriately set depending on the surface conditions of the first adherend 1 and the second adherend 5 (described below), the required physical properties of the cured adhesive layer 6, and the like. The adhesive composition 2 may be applied multiple times to obtain the required thickness. Furthermore, because the adhesive composition 2 is liquid under inkjet conditions, even if there is distortion in the surface shape of the first adherend 1 or the surface shape of the second adherend 5, the distortion can be canceled out.

[0052] The first adherend 1 may be a light-transmitting or non-light-transmitting member. In the example shown in FIG. 2, the first adherend 1 is a light-transmitting member that allows the image formed on the image display member to be visible. Examples of light-transmitting members include plate-shaped or sheet-shaped materials such as glass, acrylic resin, polyethylene terephthalate, polyethylene naphthalate, and polycarbonate. These materials can be subjected to hard coating treatment, anti-reflection treatment, etc. on one or both sides. The physical properties of the first adherend 1, such as thickness and elasticity, can be appropriately determined depending on the intended use. The first adherend 1 also includes the above-mentioned plate-shaped or sheet-shaped material to which a position input element such as a touchpad is integrated via a cured resin layer of a known adhesive or the adhesive composition according to the present technology.

[0053] The shape of the first adherend 1 can be appropriately selected depending on the purpose. The first adherend 1 may have a curved shape, or the surface may be flat. The curved shape may be, for example, a shape that is concavely curved in one direction, a convexly curved shape, a paraboloid of revolution, a hyperbolic paraboloid, or other quadratic curved shape, and the curved shape or quadratic curved shape may also have a flat portion in part.

[0054] <Process B> In step B, as shown in FIG. 2(B), ultraviolet light 8 is irradiated from an ultraviolet irradiation unit 7 onto the adhesive composition layer 3 to form a cured adhesive layer 6. Specifically, ultraviolet light 8 is irradiated from the ultraviolet irradiation unit 7 onto the adhesive composition layer 3 obtained in step A from the side of the first adherend 1, thereby forming a light-transmitting cured adhesive layer 6. Furthermore, as shown by A in FIG. 1, it is preferable to adopt irradiation conditions for ultraviolet light 8 such that the elastic modulus of the adhesive composition layer 3 after irradiation with ultraviolet light 8 is equal to or less than the elastic modulus at which lamination is possible in step C. As an example, in step B, the integrated light dose of ultraviolet light 8 is set to 2000 to 8000 mJ / cm. 2 can range from 4000 to 6000 mJ / cm 2 It can also be in the range of

[0055] The higher the curing rate of the adhesive cured layer 6, the more preferable it is, and can be, for example, 90% or higher, when no step of irradiating with ultraviolet light 8 is performed after step B. Here, the curing rate of the adhesive cured layer 6 is a value defined as the ratio (consumption rate) of the amount of (meth)acryloyl groups present in the first (meth)acrylate component and the second (meth)acrylate component in the adhesive composition layer 3 after ultraviolet light irradiation to the amount of (meth)acryloyl groups present in the first (meth)acrylate component and the second (meth)acrylate component in the adhesive composition layer 3 before ultraviolet light irradiation. A higher curing rate value indicates a more advanced curing.

[0056] As the ultraviolet irradiation unit 7, for example, a device having an LED with an emission peak wavelength in the range of 360 to 430 nm (for example, an emission wavelength of 365±5 nm) can be used.

[0057] <Process C> In step C, as shown in Fig. 2(C), a second adherend 5 is placed on the surface of the cured adhesive layer 6, and the first adherend 1 and the second adherend 5 are joined via the cured adhesive layer 6. Step C results in a laminate 9 in which the first adherend 1, the cured adhesive layer 6, and the second adherend 5 are laminated in this order.

[0058] In step C, the second adherend 2 is bonded to the first adherend 1 from the side of the cured adhesive layer 6. Specifically, in step C, as shown in FIG. 2(D), at least one of autoclave treatment and heat treatment can be performed to accelerate the curing of the cured adhesive layer 6. When heat treatment is performed in step C, it can be performed at normal pressure and a temperature of 10 to 80°C. In step C, autoclave treatment and heat treatment may be performed in combination. For example, in step C, autoclave treatment can be performed under conditions of a pressure of 0.2 to 0.6 MPa and a temperature of 25 to 80°C. In step C, autoclave treatment may be performed without heating. For example, in step C, the laminate 9 may be pressurized under conditions of a pressure of 0.2 to 0.6 MPa and a temperature of 10 to 30°C.

[0059] The second adherend 5 is, for example, an image display member such as a liquid crystal display panel, an organic EL display panel, a plasma display panel, or a touch panel. A touch panel is a device in which a display element such as a liquid crystal display panel and a position input element such as a touchpad are integrated via a known adhesive or a cured resin layer 6. If a touchpad is already integrated into the first adherend 1, a touch panel does not need to be used as the second adherend 5. The shape of the second adherend 5 can be appropriately selected depending on the purpose, as with the first adherend 1. The second adherend 5 may have a curved shape or a flat surface.

[0060] The manufacturing method of a bonded body according to the present technology may further include step D, in which the adhesive cured layer 6 is left standing between step B and step C. Since the manufacturing method of a bonded body according to the present technology can further include step D, it is not necessary to perform step C immediately after irradiating the adhesive composition layer 3 with ultraviolet light 8 in step B, and therefore the manufacturing process has a greater degree of freedom compared to manufacturing methods of a bonded body that do not include step D. In step D, for example, after irradiating the adhesive composition layer 3 with ultraviolet light 8 using an ultraviolet light irradiation unit 7 in step B, the adhesive composition layer 3 may be left standing as is. Furthermore, when a drawer-type (batch-type) ultraviolet light irradiation device is used as the ultraviolet light irradiation unit 7, in step D, after irradiating the adhesive composition layer 3 with ultraviolet light 8 using the ultraviolet light irradiation unit 7 in step B, the first adherend 1 coated with the adhesive composition layer 3 may be drawn out from the ultraviolet light irradiation unit 7 and left standing. Thus, the manufacturing method of a bonded body according to the present technology can include step D regardless of the type of ultraviolet light irradiation unit 7. The leaving time in step D can be, for example, within 5 minutes.

[0061] [Second embodiment] 3 is a perspective view illustrating another example of the method for producing a bonded body using the adhesive composition 2. In the second embodiment, the first adherend 1 and the second adherend 5 are members that do not have optical transparency.

[0062] In step A, as shown in FIG. 3(A), an inkjet head 4 is used to partially apply an adhesive composition 2 to a first adherend 1 to form a plurality of rectangular adhesive composition layers 3.

[0063] In step B, as shown in Fig. 3(B), ultraviolet light 8 is irradiated from an ultraviolet irradiation unit 7 onto the plurality of adhesive composition layers 3 to form a plurality of rectangular cured adhesive layers 6. Specifically, ultraviolet light 8 is irradiated from the ultraviolet irradiation unit 7 onto the plurality of adhesive composition layers 3 obtained in step A from the first adherend 1 side to form a plurality of cured adhesive layers 6. The ultraviolet light irradiation conditions can be the same as those in the first embodiment.

[0064] In step C, as shown in FIG. 3(C), a second adherend 5 is placed on the surface of the plurality of cured adhesive layers 6, and the first adherend 1 and the second adherend 5 are bonded together via the cured adhesive layer 6. In step C, for example, a heat treatment is performed to bond the first adherend 1 and the plurality of second adherends 5 together via the cured adhesive layer 6. The heat treatment conditions can be the same as those in the first embodiment. In step C, a laminate 10 is obtained in which the first adherend 1, the cured adhesive layer 6, and the second adherend 5 are laminated in this order. In step C, as shown in FIG. 3(D), a heat treatment may be performed to further promote curing of the cured adhesive layer 6. The heat treatment conditions can be the same as those in the first embodiment. [Example]

[0065] Hereinafter, examples of the present technology will be described, but the present technology is not limited to these examples.

[0066] The components used in this example are as follows:

[0067] jER YX8000: Hydrogenated epoxy resin, manufactured by Mitsubishi Chemical Corporation EPICLON EXA-830CRP: Bisphenol F type epoxy resin, manufactured by DIC Viscoat 160: Aromatic acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. Viscoat 155: alicyclic acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. Viscoat 150: heterocyclic acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. LA: Aliphatic acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd. 4HBA: hydroxyl group-containing acrylate, manufactured by Osaka Organic Chemical Industry Ltd. Denacol EX-121, monofunctional epoxy resin, manufactured by Nagase ChemteX Corporation Aron Oxetane OXT-221: Multifunctional oxetane resin, manufactured by Toagosei Co., Ltd. PI-184: Radical photopolymerization initiator, manufactured by Hunan AT-6992: Phosphorus-based cationic photopolymerization initiator, manufactured by Tomoe Engineering Co., Ltd. Omnicat 250: Phosphorus-based cationic photoinitiator, manufactured by IGM Resin

[0068] [viscosity] An adhesive composition was prepared by uniformly mixing the components shown in Table 1. The viscosity of the resulting adhesive composition at 25°C was measured using a rheometer (HaakeRheoSress600, Thermo Fisher Scientific; measurement conditions: cone rotor, φ=35 mm, rotor angle 2°, shear rate 120 1 / s). The results are shown in Table 1. For inkjet coating, the viscosity of the adhesive composition is desirably less than 50 mPa·s.

[0069] [Temporary pasting properties] An adhesive composition was prepared by uniformly mixing the components shown in Table 1. Two glass slides (26 mm wide x 76 mm long x 1.0 to 1.2 mm thick) were prepared, and the adhesive composition was applied to the center of one of the glass slides to form an adhesive composition layer. This adhesive composition layer was irradiated with an integrated light dose of 5000 mJ / cm from a UV-LED. 2 The light with a peak at a wavelength of 365 nm is 1000 mW / cm 2 The sample was irradiated with UV light for 5 seconds at a high intensity. Next, the other glass slide was placed perpendicular to the first glass slide and heated at 60°C for 10 minutes to obtain a sample for the temporary adhesion test with a cured adhesive layer approximately 0.2 mm thick. The temporary adhesion of the sample was evaluated as OK if the glass slides were successfully bonded together, in other words, if no repulsion (a phenomenon in which the glass slides once bonded peel off) occurred after UV irradiation; otherwise, it was evaluated as NG. The results are shown in Table 1.

[0070] [Transmittance] An adhesive composition was prepared by uniformly mixing the components shown in Table 1. Two glass slides (40 mm wide x 70 mm long x 0.4 mm thick) were prepared, and the adhesive composition was applied to the center of one of the glass slides to form an adhesive composition layer. This adhesive composition layer was irradiated with an integrated light dose of 5000 mJ / cm from a UV-LED. 2The light with a peak at a wavelength of 365 nm is 1000 mW / cm 2 The other slide glass was placed on the other slide glass and heated at 60°C for 10 minutes to obtain a light transmittance test sample having a cured adhesive layer approximately 0.1 mm thick. The visible light transmittance of this sample was measured. Specifically, the light transmittance of the cured adhesive layer of the light transmittance test sample was measured in a wavelength range of 400 to 800 nm, and the minimum light transmittance was determined. For optical applications, it is desirable that the cured adhesive layer have a light transmittance of 90% or more. The results are shown in Table 1. In Table 1, for example, "OK (100)" in Example 1 indicates that the minimum light transmittance in the wavelength range of 400 to 800 nm is 100%, indicating a good evaluation. Furthermore, "NG (44)" in Comparative Example 2 indicates that the minimum light transmittance in the wavelength range of 400 to 800 nm is 44%, indicating a poor evaluation.

[0071] [Heat resistance] The transmittance test sample described above was further heated at 200°C for 1 hour, and then the visible light transmittance of the cured adhesive layer was measured. Specifically, the transmittance test sample was further heated at 200°C for 1 hour, and then the cured adhesive layer was measured for light transmittance in the wavelength range of 400 to 800 nm, and the minimum light transmittance was determined. For optical applications, it is desirable that the cured adhesive layer have a light transmittance of 90% or more. The results are shown in Table 1.

[0072] [High temperature holding power] FIG. 4 is a perspective view illustrating the method of the high-temperature holding power test. An adhesive composition was prepared by uniformly mixing the components shown in Table 1. Two glass slides (width 26 mm × length 76 mm × thickness 1.0 to 1.2 mm) were prepared, and the adhesive composition was applied to one of the glass slides to form an adhesive composition layer. This adhesive composition layer was irradiated with an integrated light intensity of 5000 mJ / cm from a UV-LED. 2 The light with a peak at a wavelength of 365 nm is 1000 mW / cm 2The glass slide was irradiated with a high intensity for 5 seconds. Next, the other glass slide was placed on the first glass slide and heated at 60°C for 10 minutes. As a result, a laminate 9A was obtained, in which the adhesive cured layer 6 between the glass slides 1A and 5A had an adhesion area of ​​26 mm x 26 mm, as shown in Figure 4. A 1 kg load 11 was then lowered onto the glass slide 5A, and the presence or absence of displacement of the glass slide 1A after 1 hour in an 85°C atmosphere was evaluated using a holding force tester (device name: BE-501, manufactured by Tester Sangyo Co., Ltd.). If the glass slide 5A did not displace, it was evaluated as OK, and if not, it was evaluated as NG. The results are shown in Table 1.

[0073] [Table 1]

[0074] In Examples 1 to 6, adhesive compositions containing 45 to 70% by mass of an epoxy resin, a first (meth)acrylate component, a second (meth)acrylate component, a radical photopolymerization initiator, and a cationic photopolymerization initiator were used, or adhesive compositions containing more than 30% by mass but not more than 70% by mass of a hydrogenated epoxy resin, a first (meth)acrylate component, a second (meth)acrylate component, a radical photopolymerization initiator, and a cationic photopolymerization initiator were used, and it was found that these compositions exhibited good temporary adhesion and high-temperature holding power. Thus, the adhesive compositions used in Examples 1 to 6, which contain a first (meth)acrylate component, a second (meth)acrylate component, and a radical photopolymerization initiator, began curing immediately after UV irradiation, as shown in graph (iii) in Figure 1, and were therefore able to maintain the coating shape after UV irradiation. Furthermore, it was found that the adhesive compositions used in Examples 1 to 6 contained an epoxy resin and a cationic photopolymerization initiator, which allowed delayed curing after UV irradiation, resulting in good adhesive strength after curing. It was also found that the adhesive compositions used in Examples 1 to 6 had good transmittance and heat resistance.

[0075] Furthermore, the results of Examples 1 and 6 show that adhesive compositions using hydrogenated epoxy resins as the epoxy resins have better transmittance and heat resistance.

[0076] In Comparative Example 1, an adhesive composition not containing a second (meth)acrylate component was used, and it was found that the high-temperature holding power did not show good results.

[0077] In Comparative Example 2, an adhesive composition not containing the first (meth)acrylate component was used, and therefore, in addition to the poor high-temperature holding power results, it was found that the transmittance and heat resistance were also poor.

[0078] In Comparative Example 3, an adhesive composition was used that did not contain an epoxy resin, a cationic photopolymerization initiator, and a first (meth)acrylate component, and therefore the high-temperature holding power was poor. This is thought to be because in Comparative Example 3, delayed curing properties were not exhibited after UV irradiation, as shown in graph (ii) in Figure 1, for example.

[0079] In Comparative Example 4, an adhesive composition was used that did not contain a first (meth)acrylate component, a second (meth)acrylate component, or a radical photopolymerization initiator and had an epoxy resin content of 45 mass% or less, and therefore it was found that the curing properties were poor and it was difficult to form a cured adhesive layer. This is thought to be because in Comparative Example 4, curing did not start immediately after UV irradiation, as shown in graph (i) in Figure 1, for example.

[0080] In Comparative Example 5, an adhesive composition containing 45% or less by mass of epoxy resin was used, and therefore, in addition to the poor high-temperature holding power, it was found that rebound occurred after ultraviolet irradiation, i.e., the bonded joints peeled off. [Explanation of symbols]

[0081] REFERENCE SIGNS LIST 1 First adherend, 1A Slide glass, 2 Adhesive composition, 3 Adhesive composition layer, 4 Inkjet head, 5 Second adherend, 5A Slide glass, 6 Cured adhesive layer, 7 Ultraviolet irradiation unit, 8 Ultraviolet light, 9 Laminate, 9A Laminate, 10 Laminate, 11 Load

Claims

1. 45 to 70% by mass of an epoxy resin; at least one first (meth)acrylate component selected from the group consisting of aromatic (meth)acrylates, alicyclic (meth)acrylates, and heterocyclic (meth)acrylates; a second (meth)acrylate component consisting of a hydroxyl group-containing (meth)acrylate; a radical photopolymerization initiator; and a cationic photopolymerization initiator.

2. 2. The adhesive composition according to claim 1, wherein the epoxy resin is a hydrogenated epoxy resin.

3. 3. The adhesive composition according to claim 1, wherein the cationic photopolymerization initiator is a cationic photopolymerization initiator whose anion species is phosphorus-based.

4. The first (meth)acrylate component is contained in an amount of 20 to 50% by mass, The adhesive composition according to any one of claims 1 to 3, comprising 2 to 30 mass% of the second (meth)acrylate component.

5. The adhesive composition according to any one of claims 1 to 4, which has a viscosity at 25°C of 50 mPa·s or less.

6. More than 30% by mass and 70% by mass or less of a hydrogenated epoxy resin; at least one first (meth)acrylate component selected from the group consisting of aromatic (meth)acrylates, alicyclic (meth)acrylates, and heterocyclic (meth)acrylates; a second (meth)acrylate component consisting of a hydroxyl group-containing (meth)acrylate; a radical photopolymerization initiator; and a cationic photopolymerization initiator.

7. Step A: applying the adhesive composition according to any one of claims 1 to 6 to a first adherend to form an adhesive composition layer; Step B of irradiating the adhesive composition layer with ultraviolet light to form a cured adhesive layer; and C. placing a second adherend on the surface of the cured adhesive layer and joining the first adherend and the second adherend via the cured adhesive layer.

8. The method for producing a bonded body according to claim 7 , wherein in the step C, at least one of an autoclave treatment and a heat treatment is performed.

9. The method for producing a bonded body according to claim 8, wherein in the step C, the heat treatment is performed at normal pressure and a temperature of 10 to 80°C.

10. The method for producing a bonded body according to claim 8, wherein in the step C, the autoclave treatment is carried out at a temperature of 10 to 30°C.

11. The method for producing a bonded body according to any one of claims 7 to 10, further comprising a step D of leaving the adhesive cured layer between the step B and the step C.

12. The method for producing a bonded body according to claim 11, wherein in the step D, the material is left as it is after being irradiated with ultraviolet light in the step B.

13. The method for producing a bonded body according to claim 11, wherein in the step D, after the ultraviolet ray is irradiated using the ultraviolet ray irradiation unit in the step B, the laminated body is pulled out from the ultraviolet ray irradiation unit and left as it is.

14. The method for producing a bonded body according to any one of claims 7 to 13, wherein in the step A, the adhesive composition is applied using an inkjet head.

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