TW201837133A - Optically clear adhesive sheet, method for manufacturing optically clear adhesive sheet, laminate, and bonded structure - Google Patents

Abstract

The present invention uses a thermosetting polyurethane that has excellent flexibility and can be made into a thick film to provide an optically clear adhesive sheet which has excellent creep properties under high temperature environments and in which whitening that occurs due to storage under high temperature and high humidity environments is suppressed. This optically clear adhesive sheet comprises a thermosetting polyurethane, wherein the thermosetting polyurethane is a cured product of a thermosetting polyurethane composition comprising a polyol component and a polyisocyanate component, the polyisocyanate component containing a first polyisocyanate having a hydrophilic unit and a second polyisocyanate that does not have a hydrophilic unit. The optically clear adhesive sheet has a shear storage modulus at 85 DEG C of 5*103 to 5*104 Pa and an adhesive strength measured by a 180 DEG peel test of 1.5 to 30 N/25 mm.

Description

Optical transparent adhesive sheet, method for manufacturing optical transparent adhesive sheet, laminated body and laminated structure

The present invention relates to an optical transparent adhesive sheet, a method for producing an optically transparent adhesive sheet, a laminate, and a bonded structure.

An OVA (Optical Clear Adhesive) sheet is a transparent adhesive sheet used for bonding optical members. In recent years, the demand for touch panels has increased rapidly in the fields of smart phones, personal computers (Personal Computers, PCs), portable game consoles, and car navigation devices, and the touch panels have been attached thereto. The demand for optically transparent adhesive sheets for other optical components has also increased. A display device including a touch panel usually has a display panel such as a liquid crystal panel, a transparent member (a touch panel body) including a transparent conductive film such as Indium Tin Oxide (ITO), and a transparent conductive layer. The structure of an optical member such as a cover panel of a film, and an optically transparent adhesive sheet is used for bonding between optical members.

For example, Patent Document 1 discloses a two-liquid-curing urethane adhesive obtained by using a urethane prepolymer and a crosslinking agent, and having the following characteristics. • A urethane prepolymer is obtained using a polyol and a polyisocyanate. The average functional group number f of the polyol is 1.7 or less. The relationship between the average functional group number f of the polyol and the addition amount Eq (equivalent) of the crosslinking agent satisfies the following formula (a). 1-(f-1.7)×10<Eq<20-(f-1.7)×20 (a) (where Eq>0) • The modulus of elasticity at 1 Hz and 25°C is 2×10 ⁵ Pa or less The modulus of elasticity at a frequency of 1 Hz and 80 ° C is 2 × 10 ⁴ Pa or more.

Further, Patent Document 2 discloses an optical film having an adhesive on both sides, which is disposed between a front transparent plate or a touch panel and an image display unit, and has the following features. An optical film including a polarizing plate, a first adhesive layer provided on a surface of the optical film that is bonded to the image display unit, and a transparent plate or a touch panel disposed on the optical film. A second layer of adhesive on the side of one side. A protective sheet is detachably attached to each of the first adhesive layer and the second adhesive layer. The thickness of the second adhesive layer is 30 μm or more. [Prior Art Document] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. Hei. No. Hei. No. Hei. No. Hei. No. 2014-115468.

[Problems to be Solved by the Invention] In the display device including the touch panel, as described above, the optical transparent adhesive sheet is used for bonding between the optical members, and the display panel and the touch panel main body are used. There is an end portion of a bezel as a frame of the display panel, and thus the distance from other optical members is wide, and the optical transparent adhesive sheet is not used for bonding. Usually, an air called an air gap is provided. Floor. However, when an air gap, that is, an air gap exists between the optical members, interface reflection occurs due to a difference in refractive index between the air layer and the optical member, and visibility of the display panel is lowered. Therefore, an optically transparent adhesive sheet which is applied to a thick film of a display panel and a touch panel main body is proposed. In addition, for the optically transparent adhesive sheet used for bonding the display panel and the touch panel main body, it is also required to cover the step formed by the thickness of the bezel. Therefore, an optically transparent adhesive sheet which is excellent in flexibility (step followability) and can be thickened is required.

On the other hand, the inventors of the present invention have focused on a thermosetting polyurethane which can form a film without using a solvent, and is an optically transparent adhesive sheet which is excellent in flexibility and can be thickened. However, various studies have been conducted on an optically transparent adhesive sheet obtained by using a thermosetting polyurethane, and as a result, it is understood that there is still room for improvement in the holding power (creep property) in a high temperature environment. Specifically, when a heavy object (load) is attached to the optically-transparent adhesive sheet and the adherend, the creep test is performed in a high-temperature environment, and peeling occurs at the interface between the optically transparent adhesive sheet and the adherend, and the weight falls. .

In addition, according to the study by the inventors of the present invention, it has been found that when the optically transparent adhesive sheet is stored in a high-temperature and high-humidity environment, whitening may occur depending on the constituent material of the thermosetting polyurethane, and optical characteristics (for example, Transparency) declines.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an optically transparent adhesive sheet which is excellent in softness and thick film-forming thermosetting polyurethane and excellent in creep properties in a high temperature environment. The whitening caused by storage in a high-temperature and high-humidity environment is suppressed. [Means for solving the problem]

The present inventors have found that it is effective for the inhibition of whitening to use both a polyisocyanate having a hydrophilic unit and a polyisocyanate having no hydrophilic unit as a constituent material of a thermosetting polyurethane (polyisocyanate). A thermosetting polyurethane composition of the composition). Further, it has been found that by controlling the storage shear modulus at 85 ° C and the adhesion in the 180° peel test to a specific range, excellent creep properties can be obtained even in a high temperature environment, thereby completing the present invention. invention.

The optically transparent adhesive sheet of the present invention is an optically transparent adhesive sheet comprising a thermosetting polyurethane, and the optically transparent adhesive sheet is characterized in that the thermosetting polyurethane is a polyol-containing component and A cured product of a thermosetting polyurethane composition of a polyisocyanate component comprising a first polyisocyanate having a hydrophilic unit and a second polyisocyanate having no hydrophilic unit at 85 ° C The storage elastic modulus under the storage is 5×10 ³ Pa to 5×10 ⁴ Pa, and the adhesion in the 180° peeling test is 1.5 N/25 mm to 30 N/25 mm.

In the thermosetting polyurethane composition, the mixing of the first polyisocyanate and the second polyisocyanate defined by the following formula (M) is preferably from 0.5 to 9.0. "mixing ratio" = "the number of moles of the second polyisocyanate" / "the number of moles of the first polyisocyanate" (M)

The thickness of the optically transparent adhesive sheet is preferably from 250 μm to 1500 μm.

The method for producing an optically transparent adhesive sheet of the present invention is characterized by comprising the steps of: preparing the thermosetting polyurethane composition by stirring and mixing the polyol component and the polyisocyanate component; The step of hardening the thermosetting polyurethane composition.

The laminate of the present invention is characterized in that an optically transparent adhesive sheet of the present invention, a first release film covering one side of the optically transparent adhesive sheet, and a second release covering the other side of the optically transparent adhesive sheet are laminated. Mold film.

The bonded structure of the present invention is characterized by comprising: a first adhesive body, a second adhesive body, and an optically transparent adhesive sheet of the present invention in which the first adhesive body and the second adhesive body are joined. [Effects of the Invention]

According to the optically transparent adhesive sheet of the present invention, an optically transparent adhesive sheet can be obtained which has an advantage of obtaining a thermosetting polyurethane which is excellent in flexibility and can be thickened, and has excellent creep properties in a high temperature environment. Whitening caused by storage in a high-temperature and high-humidity environment is suppressed. According to the method for producing an optically transparent adhesive sheet of the present invention, the optically transparent adhesive sheet of the present invention can be preferably produced. According to the laminate of the present invention, the operability of the optically transparent adhesive sheet of the present invention can be improved. According to the bonded structure of the present invention, the bonded structure can be obtained in which the creep property in a high-temperature environment is excellent, and whitening caused by storage in a high-temperature and high-humidity environment is suppressed.

The optically transparent adhesive sheet of the present invention is an optically transparent adhesive sheet comprising a thermosetting polyurethane, and the optically transparent adhesive sheet is characterized in that the thermosetting polyurethane is a polyol-containing component and A cured product of a thermosetting polyurethane composition of a polyisocyanate component comprising a first polyisocyanate having a hydrophilic unit and a second polyisocyanate having no hydrophilic unit at 85 ° C The storage elastic modulus under the storage is 5×10 ³ Pa to 5×10 ⁴ Pa, and the adhesion in the 180° peeling test is 1.5 N/25 mm to 30 N/25 mm.

In the present specification, "X to Y" means "X or more and Y or less".

In the present specification, the term "optical transparent adhesive sheet" is synonymous with "optical transparent adhesive film".

The optically clear adhesive sheet of the present invention comprises a thermosetting polyurethane. The thermosetting polyurethane is a cured product of a thermosetting polyurethane composition containing a polyol component and a polyisocyanate component. The cured product of the thermosetting polyurethane composition is obtained by reacting a polyol component with a polyisocyanate component, and has a structure represented by the following formula (A).

[Chemical 1]

In the formula (A), R represents a portion of the polyisocyanate component from which the NCO group is removed. R' represents a portion of the polyol component from which the OH group is removed. n represents the number of repeating units.

The thermosetting polyurethane is preferably not modified with acrylic acid, and preferably does not contain a portion derived from an acrylate, a methacrylate or the like in the main chain. When the thermosetting polyurethane is modified by acrylic acid, it is hydrophobized, so that moisture condensation is likely to occur in a high-temperature and high-humidity environment. There is a case where the aggregation of the water causes whitening, foaming, or the like, and the optical properties (for example, transparency) are impaired. Therefore, by setting the thermosetting polyurethane to be unmodified with acrylic acid, it is possible to prevent deterioration of optical characteristics due to whitening, foaming, or the like in a high-temperature and high-humidity environment. The thermosetting polyurethane preferably has a total amount derived from a monomer unit derived from a polyol component and a unit body unit derived from a polyisocyanate component, and is a single unit constituting the thermosetting polyurethane. More than 80% by mole of the unit cell, more preferably only a monomer unit derived from the polyol component and a monomer unit derived from the polyisocyanate component.

As the polyol component and the polyisocyanate component, those which are liquid at normal temperature (23 ° C) can be used, and a thermosetting polyurethane can be obtained without using a solvent. Other components such as a tackifier may be added to any of the polyol component and the polyisocyanate component, and are preferably added to the polyol component. Thus, in the case of producing an optically transparent adhesive sheet using thermosetting polyamic acid, since it is not necessary to remove the solvent, a uniform thick sheet can be formed. Therefore, in the case where the optically transparent adhesive sheet of the present invention is used for bonding a display panel and a transparent member (touch panel) having a transparent conductive film on the surface layer, the step of the bezel can be covered. Further, the optically transparent pressure-sensitive adhesive sheet of the present invention can maintain the optical characteristics even when a thick sheet is formed, and can sufficiently suppress the decrease in transparency, coloring, and foaming (bubbles are generated at the interface with the adherend).

The optically clear adhesive sheet of the present invention contains a thermosetting polyurethane and is therefore soft, and when stretch stress is applied, it extends well and is extremely hard to be torn. Therefore, it can be peeled off without residue. Moreover, since the optically transparent adhesive sheet of the present invention is soft and can be thickened, it can be used for bonding a transparent member having a transparent conductive film on the surface layer and a cover panel, and further using other members. It can also be used for the display panel or the bonding of a transparent member having a transparent conductive film on the surface layer to other members. Further, since the optically transparent adhesive sheet of the present invention contains a thermosetting polyurethane, the dielectric constant is high, and an electrostatic capacitance higher than that of the optically transparent adhesive sheet containing the acrylic resin composition can be obtained. Therefore, the optically transparent adhesive sheet of the present invention can be preferably used for the bonding of a capacitive touch panel.

[Polyol component] The polyol component is not particularly limited, and examples thereof include a polyether polyol, a polycaprolactone polyol, a polycarbonate polyol, and a polyester polyol. These may be used alone or in combination of two or more.

Examples of the polyether polyol include polyolefins such as polyethylene glycol, polypropylene glycol, polyglycerol, polypropanediol, polytetramethylene glycol, polytetramethylene triol, and copolymers thereof. A diol, a derivative obtained by introducing a side chain or a branched structure, a modified body, and a mixture thereof.

Examples of the polycaprolactone polyol include polycaprolactone diol, polycaprolactone triol, and polycaprolactone tetraol, and a derivative obtained by introducing a side chain or introducing a branched structure into the polycaprolactone diol. A modified body, a mixture of these, and the like.

Examples of the polycarbonate polyol include a reaction product of a dialkyl carbonate and a diol.

Examples of the dialkyl carbonate include a dialkyl carbonate such as dimethyl carbonate or diethyl carbonate; a diaryl carbonate such as diphenyl carbonate; and an alkylene carbonate such as ethyl carbonate. These may be used alone or in combination of two or more.

Examples of the diol include 1,4-butanediol, diethylene glycol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octane. Glycol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-dodecanediol, 2-ethyl-1,6-hexanediol, 3-methyl Base-1,5-pentanediol, 2,4-dimethyl-1,5-pentanediol, neopentyl glycol, 1,3-cyclohexanediol, 1,4-cyclohexanediol 1,4-cyclohexanedimethanol, 2,2'-bis(4-hydroxycyclohexyl)-propane, and the like. These may be used alone or in combination of two or more. The diol is preferably an alicyclic or alicyclic diol having 4 to 9 carbon atoms. For example, it is preferred to use only one or less kinds of diols or two or more of the following diols: 1,4-butane Alcohol, diethylene glycol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2,4-dimethyl-1,5-pentane Alcohol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, and the like. Further, as the diol, a copolycarbonate diol comprising 1,6-hexanediol and 3-methyl-1,5-pentanediol, and 1,6-hexanediol and 1,5 are also preferred. a copolycarbonate diol of pentanediol or the like.

Further, as the polycarbonate polyol, for example, a polycarbonate diol, a polycarbonate triol, a polycarbonate tetraol, a derivative in which a side chain or a branched structure is introduced, and a modified product can be used. And further mixtures of these and the like.

Examples of the polyester polyol include those obtained by dehydrating and condensing a dicarboxylic acid and a diol component.

Examples of the dicarboxylic acid include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and 2,6-naphthalene dicarboxylic acid; oxalic acid; malonic acid; succinic acid; glutaric acid; Diacid; azelaic acid; azelaic acid.

Examples of the diol component include ethylene glycol, 1,4-butanediol, diethylene glycol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 1,5-pentane. An aliphatic diol such as an alcohol, 1,9-nonanediol or triethylene glycol; an alicyclic diol such as 1,4-cyclohexanedimethanol; an aromatic diol such as p-xylene glycol; A polyoxyalkylene glycol such as an alcohol, a polypropylene glycol or a polytetramethylene glycol.

The polyester polyol has a linear molecular structure when formed of the dicarboxylic acid and the diol component exemplified above, but may be a polyester having a branched molecular structure using a trivalent or higher ester forming component. . The dicarboxylic acid and the diol component may be reacted at a molar ratio of 1.1 to 1.3 at 150 to 300 °C.

The number average molecular weight of the polyol component is preferably from 300 to 5,000. When the number average molecular weight of the polyol component is less than 300, the reaction between the polyol component and the polyisocyanate component is too fast, and it is difficult to form the thermosetting polyurethane into a uniform sheet, or to thermally harden the polyamine group. The softness of the formate decreases and becomes brittle. When the number average molecular weight of the polyol component exceeds 5,000, the viscosity of the polyol component becomes too high, and it is difficult to form the thermosetting polyurethane into a uniform sheet, or to produce a thermosetting polyaminocarboxylic acid. A case where the ester is crystallized and white turbidity or the like is caused. The number average molecular weight of the polyol component is more preferably from 500 to 2,000.

The polyol component preferably has an olefin skeleton, that is, the main chain is composed of a polyolefin or a derivative thereof. Examples of the polyol component having an olefin skeleton include 1,2-polybutadiene polyol, 1,4-polybutadiene polyol, and 1,2-polychlorobutadiene by hydrogen or halogen. A polybutadiene-based polyol such as an alcohol or a 1,4-polychloropren polyhydric alcohol; a polyisoprene-based polyol; and a double bond-saturated or the like. Further, the polyol component may be a polyol obtained by copolymerizing an olefin compound such as styrene, ethylene, vinyl acetate or acrylate with a polybutadiene polyol or the like, or may be a hydrogenated product thereof. The polyol component may have a linear structure or a branched structure. The polyol component having an olefin skeleton may be used alone or in combination of two or more. The polyol component preferably contains 80 mol% or more of a polyol component having an olefin skeleton, and more preferably contains only a polyol component having an olefin skeleton.

As a known example of the polyol component having an olefin skeleton, a polyolefin polyol "Epol (registered trademark)" obtained by hydrogenating a hydroxyl-terminated polyisoprene manufactured by Idemitsu Kosan Co., Ltd. is mentioned. A number average molecular weight: 2,500), a two-terminal hydrogenated polybutadiene "GI-1000" manufactured by Japan's Soda Corporation (quantitative average molecular weight: 1,500), and a polyhydroxy polyolefin oligomer manufactured by Mitsubishi Chemical Corporation. (polytail) (registered trademark) and so on.

[Polyisocyanate Component] The polyisocyanate component contains a first polyisocyanate having a hydrophilic unit (hydrophilic group) and a second polyisocyanate having no hydrophilic unit. According to the polyisocyanate component, whitening can be suppressed by the action of a hydrophilic portion (hydrophilic unit: first polyisocyanate) (hygroscopic action), and the hydrophobic portion (other unit: second polyisocyanate) can be used. It exhibits high compatibility with a polyol component, a first polyisocyanate, a tackifier, a plasticizer, and the like.

The hydrophilic unit is a constituent unit having a solubility parameter (SP (solubility parameter value) of 8.5 MPa ^1/2 or more, and preferably a constituent unit having a solubility parameter of 9.0 MPa ^1/2 or more. Solubility parameters can be determined by the Fedors method (refer to RF Fedors: Polymer Engineering and Science, Polym. Eng. Sci., 14 [2], 147-154). (1974)) and calculated. In addition, regarding the calculation method of the solubility parameter by the Fedors method, for example, in the paper "Investigation on Solubility Parameters of Additives" in "Research No. 152 of Coatings" issued by Kansai Paint Co., Ltd. (issued in October 2010) There are records. Further, the hydrophilic unit is different from the isocyanate group-derived structure as in the isomeric isocyanate structure or the biuret structure, and refers to a portion in which a hydrophilic functional group is added to the polyisocyanate. .

As the hydrophilic unit, an ethylene oxide unit is preferred. The content of the ethylene oxide unit is preferably from 0.1% by weight to 20% by weight based on the total amount of the thermosetting polyurethane composition. When the content of the ethylene oxide unit is less than 0.1% by weight, whitening may not be sufficiently suppressed. When the content of the ethylene oxide unit exceeds 20% by weight, the compatibility with the low-polarity olefin-based polyol component (polyol component having an olefin skeleton), a tackifier, a plasticizer, or the like may be lowered. The optical characteristics such as transparency are degraded. Further, since the optically transparent adhesive sheet has a large amount of moisture absorption, the adhesive property in a high temperature environment may be adversely affected. The content of the ethylene oxide unit is more preferably from 0.1% by weight to 5% by weight. When the content of the ethylene oxide unit exceeds 5% by weight, the amount of moisture absorption in a high-temperature/high-humidity environment may be excessive.

Examples of the hydrophilic unit include, in addition to the ethylene oxide unit, an alkali metal salt group including a carboxylic acid group or a carboxylic acid, a sulfonic acid group, an alkali metal salt group of a sulfonic acid, a hydroxyl group, a guanamine group, an amine group, and the like. Unit. More specifically, polyacrylic acid, an alkali metal salt of polyacrylic acid, a sulfonic acid group-containing copolymer, an alkali metal salt of a sulfonic acid group-containing copolymer, polyvinyl alcohol, polypropylene decylamine, carboxymethyl group Cellulose, alkali metal salt of carboxymethyl cellulose, polyvinylpyrrolidone, and the like.

(First Polyisocyanate) As the first polyisocyanate having a hydrophilic unit, for example, a modified polyisocyanate can be preferably used: an aliphatic polyisocyanate or an alicyclic polyisocyanate and an ethylene oxide unit Obtained by reacting an ether compound. By using an aliphatic polyisocyanate or an alicyclic polyisocyanate, coloring, discoloration, and the like of the optically transparent adhesive sheet are more difficult to occur, and the transparency of the optically transparent adhesive sheet can be maintained over a long period of time.

Examples of the aliphatic polyisocyanate include Hexamethylene Diisocyanate (HDI), tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, and 3-methyl group. Pentane-1,5-diisocyanate, lysine diisocyanate, trioxyethylene diisocyanate, modified bodies thereof, and the like. These may be used alone or in combination of two or more. Further, examples of the modified form of hexamethylene diisocyanate include modification of hexamethylene diisocyanate with iso-polycyanate, modification of allophanate, and/or amine group. The formate is modified and so on.

Examples of the alicyclic polyisocyanate include isophorone diisocyanate (IPDI) and 4,4'-dicyclohexylmethane diisocyanate (Diphenyl Methane Diisocyanate, MDI). )), norbornane diisocyanate (NBDI (norbornane diisocyanate), refer to the following chemical formula (B)), hydrogenated xylene diisocyanate, hydrogenated tetramethyl xylene diisocyanate, modified bodies thereof, and the like. These may be used alone or in combination of two or more.

[Chemical 2]

Examples of the ether compound having an ethylene oxide unit include an ethylene oxide adduct of an alcohol, a phenol, and/or an amine. As the ether compound having an ethylene oxide unit, an ether compound having three or more ethylene oxide units per molecule can be preferably used from the viewpoint of improving hydrophilicity.

Examples of the alcohols include monohydric alcohols and glycols (ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,3). - Butanediol, neopentyl glycol, etc.), triols (glycerol, trimethylolpropane, etc.). These may be used alone or in combination of two or more.

Examples of the phenols include hydroquinone, bisphenols (bisphenol A, bisphenol F, etc.), and formalin low condensates of phenol compounds (novolac resin, intermediates of resol), and the like. ). These may be used alone or in combination of two or more.

The number of isocyanate groups per molecule of the modified polyisocyanate is preferably 2.0 or more on average. When the number of isocyanate groups is less than 2.0 on average, there is a case where the thermosetting polyurethane composition is not sufficiently cured due to a decrease in the crosslinking density.

(Second Polyisocyanate) As the second polyisocyanate containing no hydrophilic unit, an aliphatic polyisocyanate or an alicyclic polyisocyanate can be preferably used.

Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate (HDI), tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, and 3-methyl-pentane. -1,5-diisocyanate, leucine diisocyanate, trioxyethylene diisocyanate, modified bodies thereof, and the like. These may be used alone or in combination of two or more. Further, examples of the modified form of hexamethylene diisocyanate include modification of hexamethylene diisocyanate with isomeric cyanurate, modification of urea resin, and/or urethane. Reformed and so on.

Examples of the alicyclic polyisocyanate include isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), and norbornane diisocyanate (NBDI, see the following chemical formula). (B)), hydrogenated xylene diisocyanate, hydrogenated tetramethyl xylene diisocyanate, these modified bodies, and the like. These may be used alone or in combination of two or more.

[Chemical 3]

In the thermosetting polyurethane composition, the mixing ratio (mole ratio) of the first polyisocyanate and the second polyisocyanate defined by the following formula (M) causes whitening inhibition and compatibility. From the viewpoint of ensuring coexistence, it is preferably from 0.5 to 9.0, more preferably from 0.5 to 3.0. When the mixing ratio exceeds 9.0, whitening may not be sufficiently suppressed. "mixing ratio" = "molar number of second polyisocyanate" / "molar number of first polyisocyanate" (M)

The α ratio of the thermosetting polyurethane composition (the number of moles of the OH group derived from the polyol component / the number of moles of the NCO group derived from the polyisocyanate component) is preferably 1 or more. When α is less than 1, the amount of the polyisocyanate component is excessive with respect to the amount of the polyol component, so that the thermosetting polyurethane is hard, and it is difficult to ensure an optically transparent adhesive sheet. The condition of the required softness. When the flexibility of the optically transparent pressure-sensitive adhesive sheet is low, in particular, when it is attached to an optical member such as a touch panel, it is difficult to coat the unevenness and the step difference of the attachment surface of the optical member. In addition, there is a case where it is difficult to secure the adhesive force required for the optically transparent adhesive sheet. The α ratio is more preferably such that 1.3 < α < 2.0 is satisfied. When the α ratio is 2.0 or more, the thermosetting polyurethane composition may not be sufficiently cured.

[Tackifier] The thermosetting polyurethane composition may further contain a tackifier (adhesive imparting agent). The tackifier is an additive added for the purpose of improving the adhesion, and is usually an amorphous oligomer having a molecular weight of several hundreds to several thousands, and is a liquid or solid thermoplastic resin at normal temperature. According to the tackifier, the adhesion of the optically transparent adhesive sheet can be improved.

The tackifier is not particularly limited, and examples thereof include a petroleum resin-based tackifier, a hydrocarbon resin-based tackifier, a rosin-based tackifier, and a terpene-based tackifier. These may be used alone or in combination of two or more.

As a tackifier, a petroleum resin-based tackifier can be preferably used from the viewpoint of excellent compatibility with the polyol component having an olefin skeleton or the like. Among the petroleum resin-based tackifiers, a hydrogenated petroleum resin obtained by hydrogenating a copolymer of dicyclopentadiene and an aromatic compound can be preferably used. Dicyclopentadiene is obtained from the C5 fraction. Examples of the aromatic compound include vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyltoluene. The ratio of dicyclopentadiene to vinyl aromatic compound (dicyclopentadiene: vinyl aromatic compound) is not particularly limited, and is preferably 70:30 to 20:80 by weight, more preferably 60:40~40:60. With respect to the hydrogenated petroleum resin, a preferred softening temperature is from 90 ° C to 160 ° C, preferably a vinyl aromatic compound content of 35% by weight or less, and a preferred bromine number is from 0 g / 100 g to 30 g / 100 g. Preferably, the number average molecular weight is from 500 to 1100. A well-known example of a hydrogenated petroleum resin-based tackifier is "IMARV (registered trademark) P-100" manufactured by Kokusai Co., Ltd., and the like.

As the tackifier, a hydrocarbon resin-based tackifier can be preferably used from the viewpoint of excellent compatibility with the polyol component having an olefin skeleton. Among the hydrocarbon resin-based tackifiers, an alicyclic saturated hydrocarbon resin can be preferably used. As a known example of the alicyclic saturated hydrocarbon resin, "Arkon P-100" manufactured by Arakawa Chemical Industries Co., Ltd., or the like can be given.

The acid value of the tackifier is preferably 1 mgKOH/g or less. When the acid value of the tackifier is 1 mgKOH/g or less, the tackifier can be sufficiently prevented from inhibiting the reaction between the polyol component and the polyisocyanate component.

The content of the tackifier is preferably from 1% by weight to 20% by weight based on the total amount of the thermosetting polyurethane composition. When the content of the tackifier is less than 1% by weight, the adhesion of the optically transparent adhesive sheet may not be sufficiently improved, and in particular, the adhesive strength in a high-temperature environment may be insufficient. In the optically transparent adhesive sheet of the present invention, even if the tackifier is not formulated in the thermosetting polyurethane composition, the storage shear modulus at 85 ° C is stripped from 180°. The adhesion control in the test is within a specific range, and the adhesion in a high temperature environment is sufficiently ensured. In the case where the content of the tackifier exceeds 20% by weight, the tackifier hinders the reaction of the polyol component with the polyisocyanate component, and the urethane crosslink cannot be sufficiently formed in the thermosetting polyurethane. Case. As a result, there is a case where the optically transparent adhesive sheet is dissolved in a high-temperature and high-humidity environment, the shape is changed, or the tackifier is precipitated (bleeded). On the other hand, when the reaction time of the polyol component and the polyisocyanate component is extended in order to fully form a urethane crosslink, productivity is fall.

[Plasticizer] The thermosetting polyurethane composition may further contain a plasticizer. According to the plasticizer, the hardness of the thermosetting polyurethane is lowered, so that the workability and flexibility (step followability) of the optically transparent adhesive sheet can be improved. Further, since the adhesiveness is lowered by the addition of the plasticizer, the optically transparent adhesive sheet according to the present invention can ensure sufficient adhesion even if the adhesive force is slightly lowered.

The plasticizer is not particularly limited as long as it imparts flexibility to the thermosetting polyurethane, and a carboxylic acid system can be preferably used from the viewpoint of compatibility and weather resistance. Plasticizer. Examples of the carboxylic acid plasticizer include di-undecyl phthalate, dioctyl phthalate, diisononyl phthalate, diisononyl phthalate, and Phthalates such as dibutyl phthalate (phthalic acid plasticizer); diisodecyl 1,2-cyclohexanedicarboxylate; adipate; trimellitate ; maleic acid ester; benzoic acid ester; poly-α-olefin, etc. These may be used alone or in combination of two or more.

As a well-known example of the carboxylic acid-based plasticizer, "Dingchi (DINCH) (registered trademark)" manufactured by BASF Corporation, "SANSOCIZER" (registered by Shin-Nippon Chemical Co., Ltd.) Trademark) DUP", "DURASYN (registered trademark) 148" manufactured by INEOS Oligomers.

[Ceramic Medium] The thermosetting polyurethane composition may further contain a catalyst. The catalyst is not particularly limited as long as it is a compound which can be used for the urethanization reaction, and examples thereof include di-n-butyltin dilaurate, dimethyltin dilaurate, and dibutyltin oxide. An organotin compound such as octane tin; an organic titanium compound; an organic zirconium compound; a tin carboxylate; a cerium carboxylate; an amine catalyst such as triethylenediamine.

As the catalyst, a non-amine catalyst is preferred. In the case of using an amine-based catalyst, there is a case where the optically transparent adhesive sheet is easily discolored. Among the non-amine-based catalysts, dimethyltin dilaurate is preferred.

The content of the catalyst is, for example, 0.01% by weight to 0.1% by weight based on the total amount of the polyol component and the polyisocyanate component.

The thermosetting polyurethane composition may further contain a monoisocyanate component. The monoisocyanate component is a compound having one isocyanate group per molecule. Examples of the monoisocyanate component include octadecyl diisocyanate (ODI), 2-methacryloyloxy ethyl isocyanate (MOI), and 2-acryloxyloxyethyl bromide. 2-acryloyloxy ethyl isocyanate (AOI), octyl isocyanate, heptyl isocyanate, ethyl 3-isocyanatopropionate, cyclopentyl isocyanate, cyclohexyl isocyanate, 2- Methoxyethane isocyanate, ethyl isocyanate, butyl isocyanate, p-toluenesulfonyl isocyanate, and the like. These may be used alone or in combination of two or more. Further, the thermosetting polyurethane composition preferably contains no monoisocyanate component.

In the thermosetting polyurethane composition, various additives such as a coloring agent, a stabilizer, an antioxidant, an antifungal agent, and a flame retardant may be added as needed within a range that does not inhibit the required characteristics of the optically transparent adhesive sheet. additive.

The optically transparent adhesive sheet of the present invention has a storage shear elastic modulus at 85 ° C of 5 × 10 ³ Pa to 5 × 10 ⁴ Pa. According to the study by the inventors of the present invention, it is effective to set the storage shear elastic modulus at 85 ° C as an index of creep characteristics. When the storage shear modulus at 85 ° C is less than 5 × 10 ³ Pa, the optically transparent adhesive sheet changes significantly in a high-temperature environment, so that peeling of the interface with the adherend is liable to occur. When the storage shear modulus at 85 ° C exceeds 5 × 10 ⁴ Pa, the hardness of the optically transparent adhesive sheet is too high, and the shape is not easily changed in a high temperature environment, so that it is liable to change with the shape of the adherend. The difference results in peeling of the interface with the adherend. Further, the optically transparent adhesive sheet is less likely to be coated with irregularities and steps on the surface of the adherend, and the possibility of poor adhesion is improved. The storage shear modulus at 85 ° C is preferably from 1 × 10 ⁴ Pa to 4 × 10 ⁴ Pa.

The storage shear modulus at 85 ° C can be controlled by adjusting the composition and/or thermosetting conditions of the thermosetting polyurethane composition as a raw material of the thermosetting polyurethane. For example, the α ratio, the content of the hydrophilic unit in the polyisocyanate component, the kind (molecular weight) of the hydrophilic unit, the first polyisocyanate having a hydrophilic unit, and the second polyisocyanate containing no hydrophilic unit may be mixed. The storage shear modulus at 85 ° C is controlled by the ratio (for example, molar ratio), the presence or absence of the addition of a plasticizer, the amount of the plasticizer, the crosslinking temperature, and the like.

The optically transparent adhesive sheet of the present invention has an adhesive force of 1.5 N/25 mm to 30 N/25 mm in the 180 peel test. According to the study by the inventors of the present invention, it is effective to set the adhesive force in the 180° peeling test as an index of creep characteristics. In the case where the adhesion in the 180° peeling test is less than 1.5 N/25 mm, the adhesion of the optically transparent adhesive sheet in a high temperature environment is remarkably lowered, so that it is easy to be in the optically transparent adhesive sheet and the adherend in a high temperature environment. The interface is peeled off. In the case where the adhesion in the 180° peeling test exceeds 30 N/25 mm, the hardness of the optically transparent adhesive sheet becomes too low, so that it is liable to deviate from the surface of the adherend at the time of the creep test. Further, when the optically transparent adhesive sheet is peeled off from the adherend, residual glue is likely to be generated. Further, it is difficult to remove the bubbles entering between the optically transparent adhesive sheet and the adherend, and the workability is lowered. The adhesion in the 180° peel test is preferably from 3 N/25 mm to 15 N/25 mm, more preferably from 5 N/25 mm to 15 N/25 mm.

In the optically transparent adhesive sheet of the present invention, as described above, both the storage shear modulus at 85 ° C and the adhesion in the 180 ° peel test are within a specific range, and thus creep properties in a high temperature environment Significantly excellent. Details of the method for measuring the storage shear modulus at 85 ° C and the method for measuring the adhesion in the 180 ° peel test will be described later.

In the optically transparent adhesive sheet of the present invention, the thermosetting polyurethane composition preferably contains no compound having a softening temperature of 100 ° C or less. According to the study by the inventors of the present invention, in the case where a compound having a softening temperature of 100 ° C or less is blended in the thermosetting polyurethane composition, the obtained optically transparent adhesive sheet is used in a high temperature environment. In the creep test (usually a creep test in an environment of 80 ° C to 100 ° C), there is a case where the compound is softened by a high temperature environment and does not contribute to the polymer (thermosetting polyurethane) The influence of the bonding, the hardness of the optically transparent adhesive sheet is lowered, and the shape is liable to change. Therefore, the optically transparent adhesive sheet and the adhesive body are likely to be peeled off at the interface in a high temperature environment. On the other hand, in the case where a compound having a softening temperature of 100 ° C or less is not blended in the thermosetting polyurethane composition, the compound does not have a softening effect in a high temperature environment, and thus is in a high temperature environment. The creep characteristics are further improved. Here, the softening temperature refers to a temperature at which deformation begins to soften as the temperature rises.

In the compound which can be blended in the thermosetting polyurethane composition, the compound having a softening temperature of 100 ° C or lower is, for example, a hydrogenated petroleum resin-based tackifier (for example, "Ai", manufactured by Idemitsu Kosan Co., Ltd. IMARV P-100" (softening temperature: 100 ° C)). The hydrogenated petroleum resin-based tackifier can be preferably used from the viewpoint of excellent compatibility with a polyol component having an olefin skeleton or the like, and is highly transparent to the optically transparent adhesive sheet. Therefore, when a hydrogenated petroleum resin-based tackifier (a compound having a softening temperature of 100 ° C or less) is not blended in a thermosetting polyurethane composition, the optically transparent adhesive sheet is in a high-temperature environment. The creep properties are improved, but there is a drop in optical properties (transparency). On the other hand, in the optically transparent adhesive sheet of the present invention, a second polyisocyanate having high compatibility with a polyol component or the like and containing no hydrophilic unit is blended as a polyisocyanate component to a thermosetting polyamine group. In the acid ester composition, even when a hydrogenated petroleum resin-based tackifier (a compound having a softening temperature of 100 ° C or lower) is blended in a thermosetting polyurethane composition, excellent results can be obtained. Optical properties (transparency).

The thickness of the optically transparent adhesive sheet of the present invention is not particularly limited, and may be, for example, 50 μm to 2500 μm, or preferably 250 μm to 1500 μm. When the thickness of the optically transparent adhesive sheet is 250 μm or more, when one side of the optically transparent adhesive sheet is attached to the adhesive body, the unevenness or step of the surface of the adhesive body is easily covered, so that sufficient adhesion can be utilized. The other side of the optically transparent adhesive sheet is attached to the other adhesive body. On the other hand, the thicker the optically transparent adhesive sheet, the more easily the decrease in optical properties (transparency) and the decrease in the adhesiveness due to an increase in the moisture absorption amount. However, if the thickness of the optically transparent adhesive sheet is 1500 μm or less, the formulation material of the thermosetting polyurethane composition is studied as in the present invention, and the storage shear elastic modulus at 85 ° C is studied. The adhesion control in the 180° peel test is controlled within a specific range, whereby the decrease in optical properties (transparency) and the decrease in the adhesion due to an increase in the moisture absorption amount can be sufficiently suppressed. Further, it is preferable that the optically transparent adhesive sheet has a thickness which is three times or more with respect to the height of the unevenness or the step of the adhesion surface present on the adherend.

The micro-rubber A hardness of the optically transparent adhesive sheet of the present invention is preferably from 0.5 to 25 . When the micro-rubber A hardness of the optically transparent adhesive sheet is less than 0.5°, the workability when attached to the adhesive body may be poor, and the optical transparent adhesive sheet may be deformed. In the case where the micro-rubber A of the optically transparent adhesive sheet has a hardness of more than 25°, there is a case where the optically transparent adhesive sheet has low flexibility, and when attached to the adhesive body, it cannot follow the surface shape of the adhesive body and enters the air. Therefore, it becomes the cause of peeling off from the adherend. Further, when the optically transparent adhesive sheet has low flexibility, in particular, when an optical member such as a touch panel is attached, irregularities and steps existing on the attached surface cannot be covered. A more preferable upper limit of the micro rubber A hardness of the optically transparent adhesive sheet of the present invention is 15°. For example, the micro rubber A hardness can be measured using a micro rubber hardness meter "MD-1 type A" manufactured by Kobunshi Corporation. The micro rubber hardness tester "MD-1 type A" is a hardness tester designed and manufactured in the form of a reduction model of about one-fifth of a type of durometer type rubber durometer. Even if the measurement object is thin, it can be obtained. The measured value of the spring type rubber hardness tester type A is consistent.

The optically transparent adhesive sheet of the present invention preferably has a haze of 0.5% or less, and the total light transmittance is preferably 90% or more to ensure performance (transparency) as an optically transparent adhesive sheet. For example, haze and total light transmittance can be measured using a haze meter "HazeMeter NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. The haze is measured by a method according to "Japanese Industrial Standards (JIS) K 7361". The total light transmittance is measured by the method according to "JIS K 7361-1".

A release film may also be attached to both sides of the optically transparent adhesive sheet of the present invention. Further, as an optically transparent adhesive sheet of the present invention, a first release film covering one surface of the optically transparent adhesive sheet, and a second release film covering the other surface of the optically transparent adhesive sheet The body (hereinafter also referred to as "the laminate of the present invention") is also an aspect of the present invention. According to the laminate of the present invention, both sides of the optically transparent adhesive sheet of the present invention can be protected by the first release film and the second release film until they are attached to the adherend. Thereby, the adhesion of the optically transparent adhesive sheet of the present invention and the adhesion of foreign matter can be prevented. Further, it is possible to prevent the optically transparent adhesive sheet of the present invention from adhering to the outside of the adherend, and thus the workability is improved.

Examples of the first release film and the second release film include a polyethylene terephthalate (PET) film. The material and thickness of the first release film and the second release film may be the same or different.

The bonding strength (peeling strength) of the optically clear adhesive sheet and the first release film of the present invention and the bonding strength (peeling strength) of the optically transparent adhesive sheet and the second release film of the present invention are preferably different from each other. In this way, the bonding strength is different from each other, and it is easy to peel off only one of the first release film and the second release film (release film having a low bonding strength) from the laminate of the present invention. The first surface of the exposed optically transparent adhesive sheet is bonded to the first adhesive body, and then the other of the first release film and the second release film (the release film having a high bonding strength) is peeled off. The second side of the exposed optically transparent adhesive sheet is bonded to the second adhesive body.

At least one of a surface of the first release film that is in contact with the optically transparent adhesive sheet of the present invention and a surface of the second release film that is in contact with the optically transparent adhesive sheet of the present invention The person performs an easy peeling treatment (release treatment). As the easy peeling treatment, for example, a hydrazine treatment or the like can be mentioned.

The use of the optically transparent adhesive sheet of the present invention is not particularly limited, and further includes a first adhesive body, a second adhesive body, and an optically transparent adhesive sheet of the present invention in which the first adhesive body and the second adhesive body are joined. The bonded structure (hereinafter also referred to as "the bonded structure of the present invention") is also an aspect of the present invention.

Examples of the first adhesive body and the second adhesive body include various panels in a display device such as a display panel, a touch panel, and a cover panel; a polarizing plate; a resin plate; a glass plate. When the various panels in the display device are bonded to each other by using the optically transparent adhesive sheet of the present invention, the air layer (air gap) in the display device can be prevented from occurring, and the visibility of the display screen can be improved.

The bonding structure of the present invention includes, for example, a display device with a touch panel including the optically transparent adhesive sheet, the display panel, and the touch panel of the present invention. Further, the attachment surface of the polarizing plate includes triacetyl cellulose (TAC), etc., and the attachment surface of the resin plate contains polycarbonate (Polycarbonate, PC) or the like, but the optically transparent adhesive sheet of the present invention is not only It can be used for glass, and it also exerts good adhesion to these resins. Further, when the optically transparent adhesive sheet of the present invention is attached to a glass plate, an effect of preventing scattering of the glass can be obtained.

1 is a cross-sectional view schematically showing an example of a display device with a touch panel using the optically transparent adhesive sheet of the present invention. As shown in FIG. 1, in the display device 10, a display panel 11, an optical transparent adhesive sheet 12, a touch panel (a glass substrate with a transparent conductive film) 13, an optical transparent adhesive sheet 12, and a transparent cover panel 14 are sequentially laminated. . The three optical members of the display panel 11, the touch panel 13, and the transparent cover panel 14 are integrated by the two optical transparent adhesive sheets 12.

The display panel 11 is housed in a bezel (frame of the display panel 11) 11A in which an opening is provided on the display surface side. At the outer edge of the opening of the bezel 11A, there is a step corresponding to the thickness of the bezel 11A. The optically transparent adhesive sheet 12 is attached to cover the display surface side of the display panel 11 and the bezel 11A, and is covered with a step corresponding to the thickness of the bezel 11A. The optically transparent adhesive sheet 12 is required to follow the softness (step followability) of the step portion and the thickness thicker than the thickness of the bezel 11A to cover the step corresponding to the thickness of the bezel 11A. As described above, the thickness of the optically transparent adhesive sheet 12 to be bonded to the display panel 11 accommodated in the bezel 11A is preferably, for example, 700 μm or more. The optically transparent adhesive sheet of the present invention has sufficient flexibility and optical characteristics (for example, transparency) even when it is 700 μm or more, and can be used for the display panel 11 and the touch panel housed in the bezel 11A. 13 is preferably used when it is attached.

The type of the display panel 11 is not particularly limited, and examples thereof include a liquid crystal panel and an organic electroluminescence panel (organic electroluminescence panel).

As the touch panel 13, for example, a touch panel of a detection method such as a resistive film method or a capacitive method can be cited.

In such a display device, since the optically transparent adhesive sheet of the present invention is used, the adhesion of the optically transparent adhesive sheet is hardly lowered even under various environments, and the optical members can be closely adhered to each other for a long period of time. As a result, no void is formed between each of the optical members and the optically transparent adhesive sheet, so that deterioration in visibility due to an increase in interface reflection or the like can be prevented. The optically transparent adhesive sheet of the present invention can be preferably used, for example, in a vehicle display device such as a display device incorporated in a car navigation device, a display device for a portable device such as a smart phone, or the like.

The method for producing the optically transparent pressure-sensitive adhesive sheet of the present invention is not particularly limited. For example, after preparing a thermosetting polyurethane composition, the thermosetting polyurethane is formed by a conventionally known method. Preferably, the method of forming the thermosetting hardening comprises: a step of preparing a thermosetting polyurethane composition by stirring and mixing a polyol component and a polyisocyanate component; and thermosetting a polyamic acid. The step of hardening the ester composition.

As an example of the method for producing an optically transparent adhesive sheet of the present invention, first, a predetermined amount of a tackifier is added to a polyol component, and the mixture is heated, stirred, and dissolved to prepare a tackifier master batch. Then, the obtained tackifier master batch, polyol component, polyisocyanate component, and other components (additives) such as an optional catalyst are mixed and stirred by a mixer or the like to obtain a liquid or gel. A thermosetting polyurethane composition. Immediately thereafter, the thermosetting polyurethane composition is put into a molding apparatus, and the thermosetting polyamine group is placed while being sandwiched by the first release film and the second release film. The acid ester composition moves while hardening it by crosslinking. As a result, a sheet in which the thermosetting polyurethane composition is semi-hardened and integrated with the first release film and the second release film can be obtained. Then, the thermosetting polyurethane composition is subjected to a crosslinking reaction in a furnace for a certain period of time, whereby a cured product containing a thermosetting polyurethane composition (thermosetting polyamine group) is obtained. An optically transparent adhesive sheet of an acid ester) to complete the laminate of the present invention.

Fig. 2 is a schematic view schematically showing an example of a molding apparatus used in the production of the optically transparent adhesive sheet of the present invention. As shown in FIG. 2, in the molding apparatus 20, first, the liquid or gel-like thermosetting polyurethane composition 23 before curing is poured into a pair of forming rolls 22 which are disposed apart from each other. A gap between a pair of release films (for example, PET film) 21 that are continuously fed. In addition, while the thermosetting polyurethane composition 23 is held in the gap between the pair of release films 21, the curing reaction (crosslinking reaction) is carried out and carried into the heating device 24. Thereafter, in the heating device 24, the thermosetting polyurethane composition 23 is thermally cured in a state of being held between the pair of release films 21, thereby completing the thermosetting polyamic acid. The formation of the optically transparent adhesive sheet 12 of the cured product (thermosetting polyurethane) of the ester composition 23. As a result, a laminate (optical transparent adhesive sheet with a release film) 25 in which the release film 21 is formed on both areas of the optically transparent adhesive sheet 12 is completed.

As a method for producing the optically transparent adhesive sheet of the present invention, after a thermosetting polyurethane composition before curing, a general film forming apparatus such as various coating apparatuses, bar coatings, and doctor blades can be used. A method of forming a film formation method. Further, the optically transparent adhesive sheet of the present invention can also be produced by a centrifugal molding method. [Examples]

Hereinafter, the present invention will be described in more detail by way of examples, but the invention is not limited to the examples.

[Materials] The materials for preparing the thermosetting polyurethane composition in the examples and comparative examples are abbreviated as follows.

(Polyol content) · "P1" Polyolefin polyol "Epol" (EPOL) manufactured by Idemitsu Kosan Co., Ltd.

(Polyisocyanate component) · "Q1" Modified polyisocyanate (first polyisocyanate) having an ethylene oxide unit (EO (ethylene oxide unit)) Coronate manufactured by Tosoh Corporation (registered trademark) 4022" · "Q2" Isophorone diisocyanate (IPDI) polyisocyanate (second polyisocyanate) Desmodur (registered by Sumika Bayer urethane) Trademark) I" · "Q3" · Hexamethylene diisocyanate (HDI) polyisocyanate (second polyisocyanate) "Coronate 2760" manufactured by Tosoh Corporation

"Coronate 4022" manufactured by Tosoh Corporation is an ether polyol having an average of three or more ethylene oxide units per molecule, and hexamethylene diisocyanate and/or The hexamethylene diisocyanate monomer is obtained by reacting a polyisocyanate of a starting material. In addition, "Coronate 2760" manufactured by Tosoh Corporation is a mixture of urea-form modified hexamethylene diisocyanate and hexamethylene diisocyanate trimer.

(Tackifier) · "S1" Hydrogenated Petroleum Resin Tackifier "IMARV P-100" manufactured by Idemitsu Kosan Co., Ltd.

(catalyst) · "T1" Dimethyltin dilaurate "Fomrez Catalyst UL-28" manufactured by Momentive

(Example 1) First, 75 parts by weight of a polyolefin polyol "P1" and 4.6 parts by weight of a modified polyisocyanate "Q1" having an EO unit, 2.4 parts by weight, using a reciprocating rotary mixer AJITER The IPDI-based polyisocyanate "Q2", 17 parts by weight of the tackifier "S1", and 1 part by weight of the catalyst "T1" were stirred and mixed to prepare a thermosetting polyurethane composition having an α ratio of 1.7. . Further, in the thermosetting polyurethane composition, the mixing ratio (Mohr ratio) of the first polyisocyanate and the second polyisocyanate defined by the following formula (M) is 1. "mixing ratio" = "molar number of second polyisocyanate" / "molar number of first polyisocyanate" (M)

Thereafter, the prepared thermosetting polyurethane composition (thermosetting polyurethane composition 23) is injected into the molding apparatus 20 shown in Fig. 2 . In the state in which the thermosetting polyurethane composition is held by a pair of release films (PET film having a release treatment on the surface) 21 while being conveyed, the temperature in the furnace is maintained. The sheet with the release film 21 was produced by crosslinking and hardening at 70 ° C for 10 minutes in the furnace. Thereafter, the thermosetting polyurethane composition in the sheet was subjected to a cross-linking reaction for 12 hours in a heating device 24 adjusted to 70 ° C to complete a composition comprising a thermosetting polyurethane composition. The formation of an optically transparent adhesive sheet 12 of a cured product (thermosetting polyurethane). As a result, a laminate (optical transparent adhesive sheet with a release film) 25 in which the release film 21 is formed on both areas of the optically transparent adhesive sheet 12 is completed.

Fig. 3 is a cross-sectional view schematically showing a laminated body of the first embodiment. As shown in FIG. 3, a release film 21, an optically transparent adhesive sheet 12, and a release film 21 are laminated in this order. The optically transparent adhesive sheet 12 has a thickness of 250 μm.

(Examples 2 to 9 and Comparative Examples 1 to 9) The composition of the thermosetting polyurethane composition and the thickness of the optically transparent adhesive sheet were changed as shown in Tables 1 to 4. An optically transparent adhesive sheet of each example was produced in the same manner as in Example 1.

[Evaluation] The following evaluations were performed on the optically transparent adhesive sheets of the respective examples. The results are shown in Tables 1 to 4.

(1) Storage Shear Elastic Modulus The storage shear elastic modulus of the optically transparent adhesive sheet was measured using a viscoelasticity measuring device "Physica MCR301" manufactured by Anton Paar Germany GmbH. As the measuring plate, PP12 was used. The measurement conditions were strain 0.1%, frequency 1 Hz, and cell temperature 25 ° C to 100 ° C (temperature up rate 3 ° C / min). The measured values of the storage shear elastic modulus at 85 ° C are shown in Tables 1 to 4.

(2) Adhesion The 180° peel test was performed by the following method, and the adhesive force (N/25 mm) was measured. 4(a) and 4(b) are schematic views for explaining a method of evaluating the adhesion of the optically transparent adhesive sheet.

First, a laminate (an optically transparent adhesive sheet with a release film) was cut into a length of 75 mm × a width of 25 mm, and used as a test piece. Further, after peeling off the release film of one side of the test piece, the optically transparent adhesive sheet 12 side was attached to a slide glass 31 having a length of 75 mm × a width of 25 mm, and held at a pressure of 0.4 MPa for 30 minutes. The optically transparent adhesive sheet 12 is attached to the slide glass 31. Thereafter, the release film on the opposite side of the slide glass 31 is peeled off, and as shown in FIG. 4(a), a thickness of 125 μm is attached to the surface of the optically transparent adhesive sheet 12 opposite to the slide glass 31. PET film 32 (Melinex (registered trademark) S" manufactured by Teijin Dupont Film Co., Ltd.).

Next, the state shown in Fig. 4 (a) is placed in an environment of normal temperature and normal humidity (temperature 23 ° C, humidity 50%) for 12 hours, and as shown in Fig. 4 (b), the PET sheet 32 is oriented to 180. The optically transparent adhesive sheet 12 is peeled off in the direction of the surface, and the optically transparent adhesive sheet 12 is peeled off from the interface with the slide glass 31 to measure the adhesion of the optically transparent adhesive sheet 12 to the slide glass 31. Further, two test pieces were prepared for each example to measure the adhesion. Further, the average value of the two measured values obtained was taken as the measurement result of the adhesive force in each example.

(3) Optical characteristics First, after peeling off the single-sided release film of a laminated body (optical transparent adhesive sheet with a release film), the optical transparent adhesive sheet side is attached to a glass slide (made of soda glass), The optically clear adhesive sheet was attached to the slide glass at a pressure of 0.4 MPa for 30 minutes. Further, the release film on the opposite side to the slide glass was peeled off, and after standing for 168 hours in an environment of high temperature and high humidity (temperature: 85 ° C, humidity: 85%), the appearance of the optically transparent adhesive sheet was visually observed. The determination criteria are as follows. ○: No whitening occurred. ×: Whitening occurred.

(4) Creep characteristics The creep test was carried out by the following method to evaluate the creep characteristics. Fig. 5 is a schematic view for explaining a method of evaluating creep characteristics of an optically transparent adhesive sheet.

First, a laminate (an optically transparent adhesive sheet with a release film) was cut into a length of 25 mm × a width of 25 mm (25 mm square) and used as a test piece. Further, after peeling off the release film of one side of the test piece, the optically transparent adhesive sheet 12 side was attached to a slide glass 31 having a length of 75 mm × a width of 25 mm, and held at a pressure of 0.4 MPa for 30 minutes. The optically transparent adhesive sheet 12 is attached to the slide glass 31. Thereafter, the release film on the opposite side of the slide glass 31 was peeled off, and a PET sheet 32 having a thickness of 125 μm was attached to the surface of the optically transparent adhesive sheet 12 opposite to the slide glass 31 (Teijin Dupont) "Melinex (registered trademark) S" manufactured by Membrane Corporation. Next, as shown in Fig. 5, the state in which the weight 33 of 150 g was fixed was hung on the side of the PET sheet 32, and left in an environment of high temperature and normal humidity (temperature: 85 ° C, humidity: 50%) for 120 minutes. Then, the optically transparent adhesive sheet 12 was peeled off from the interface with the slide glass 31 or the PET sheet 32, whereby the weight 33 was observed to fall, and the holding time (unit: minute) from the start of the suspension to the fall of the weight 33 was measured. In addition, in Tables 1 to 4, when the weight 33 has not fallen for 120 minutes, the holding time is set to 120 minutes, and the position at the start of suspension of the optically transparent adhesive sheet 12 is shown (attachment position: The starting point) is a measured value (unit: mm) which is an offset amount downward, that is, a displacement amount of the optically transparent adhesive sheet 12. In addition, when the weight 33 fell after 120 minutes, the holding time was set to 120 minutes, and the offset amount was expressed as "(drop)". As a criterion for determination, the holding time was 120 minutes (corresponding to the case where the weight 33 did not fall at 120 minutes), and the case where the offset amount was 0 mm to 8 mm was set as a suitable level. Among them, it is preferable that the optically transparent adhesive sheet has a moderate flexibility corresponding to the heat shrinkability of the adherend (the slide glass 31 and the PET sheet 32 in the evaluation), and is not limited to the offset. The case of 0 mm is the best.

[Table 1]

[Table 2]

[table 3]

[Table 4]

As shown in Tables 1 and 2, in Examples 1 to 9, the creep property in a high-temperature environment was high, and whitening did not occur after standing in a high-temperature and high-humidity environment. Further, in Examples 1 to 9, the thickness of the optically transparent adhesive sheet was evaluated to be 250 μm to 1500 μm thicker than before, and even when the optically transparent adhesive sheet was thick and the moisture absorption amount was easily increased. The creep property in a high-temperature environment is also high, and whitening does not occur after being placed in a high-temperature and high-humidity environment.

In Example 3, Example 4, and Example 9, the tackifier was not formulated in the thermosetting polyurethane composition, but the second polyisocyanate containing no hydrophilic unit was formulated, and thus the polyol was mixed with the polyol. The composition and the first polyisocyanate have high compatibility, and do not cause whitening after being placed in a high-temperature and high-humidity environment. Further, in Example 3, Example 4, and Example 9, the compound having a softening temperature of 100 ° C or less was not blended in the thermosetting polyurethane composition (the light produced in Example 1 and the like) The company's "IMARV P-100") has a high storage shear modulus at 85 ° C, which significantly contributes to the improvement of creep properties in high temperature environments.

On the other hand, as shown in Tables 3 and 4, in Comparative Examples 1 to 9, the creep property in a high-temperature environment was low, or whitening occurred after being placed in a high-temperature and high-humidity environment.

In Comparative Examples 1 to 3, the storage shear elastic modulus at 85 ° C was less than 5 × 10 ³ Pa, and therefore the creep property in a high temperature environment was low.

In Comparative Example 4 and Comparative Example 6, since the adhesive force in the 180° peeling test exceeded 30 N/25 mm, the creep property in a high temperature environment was low.

In Comparative Example 5, the adhesive strength in the 180° peeling test was less than 1.5 N/25 mm, so the creep property in a high temperature environment was low.

In Comparative Example 7, the second polyisocyanate and the tackifier which do not contain a hydrophilic unit are not simultaneously blended in the thermosetting polyurethane composition, and thus the compatibility with the polyol component is lowered, and the temperature is high. • Whitening occurs after placement in a high-humidity environment.

In Comparative Example 8 and Comparative Example 9, since the first polyisocyanate having a hydrophilic unit was not blended in the thermosetting polyurethane composition, whitening occurred after standing in a high-temperature and high-humidity environment.

10‧‧‧ display device

11‧‧‧ display panel

11A‧‧‧Border

12‧‧‧Optical transparent adhesive sheet

13‧‧‧Touch panel

14‧‧‧ Transparent cover panel

20‧‧‧Forming device

21‧‧‧ release film

22‧‧‧Forming rolls

23‧‧‧ Thermosetting polyurethane varnish composition

24‧‧‧ heating device

25‧‧‧Laminated body (optical transparent adhesive sheet with release film)

31‧‧‧Slides

32‧‧‧PET film

33‧‧‧ Heavy objects

1 is a cross-sectional view schematically showing an example of a display device with a touch panel using the optically transparent adhesive sheet of the present invention. Fig. 2 is a schematic view schematically showing an example of a molding apparatus used in the production of the optically transparent adhesive sheet of the present invention. Fig. 3 is a cross-sectional view schematically showing a laminated body of the first embodiment. 4(a) and 4(b) are schematic views for explaining a method of evaluating the adhesion of the optically transparent adhesive sheet. Fig. 5 is a schematic view for explaining a method of evaluating creep characteristics of an optically transparent adhesive sheet.

Claims (6)

An optically transparent adhesive sheet comprising a thermosetting polyurethane, and the optically transparent adhesive sheet is characterized in that: the thermosetting polyurethane is a heat hardening comprising a polyol component and a polyisocyanate component A cured product of a polyurethane component comprising a first polyisocyanate having a hydrophilic unit and a second polyisocyanate having no hydrophilic unit, storage shear elasticity at 85 ° C The modulus is 5 × 10 ³ Pa to 5 × 10 ⁴ Pa, and the adhesion in the 180° peel test is 1.5 N/25 mm to 30 N/25 mm. The optically transparent adhesive sheet according to claim 1, wherein in the thermosetting polyurethane composition, the first polyisocyanate defined by the following formula (M) is as described The mixing ratio of the second polyisocyanate is from 0.5 to 9.0: "mixing ratio" = "the number of moles of the second polyisocyanate" / "the number of moles of the first polyisocyanate" (M). The optically transparent adhesive sheet according to claim 1 or 2, wherein the optically transparent adhesive sheet has a thickness of from 250 μm to 1500 μm. A method of producing an optically transparent adhesive sheet according to any one of claims 1 to 3, wherein the optical transparent adhesive sheet is produced by the method of manufacturing the optically transparent adhesive sheet. The method includes the steps of: preparing the thermosetting polyurethane composition by stirring and mixing the polyol component and the polyisocyanate component; and hardening the thermosetting polyurethane composition A step of. A laminate having an optically transparent adhesive sheet according to any one of claims 1 to 3, a first release film covering one side of the optically transparent adhesive sheet, and a cover layer. a second release film on the other side of the optically transparent adhesive sheet. A bonding structure, comprising: a first adhesive body, a second adhesive body, and the first adhesive body and the second adhesive body joined as in the first to third aspects of the patent application scope An optically transparent adhesive sheet as described.