JP6371922B1 - Optical transparent adhesive sheet, optical transparent adhesive sheet manufacturing method, laminate, and bonded structure - Google Patents

Abstract

The present invention is an optically transparent adhesive that uses a thermosetting polyurethane that is excellent in flexibility and can be made thick, has excellent creep characteristics in a high temperature environment, and is suppressed in whitening caused by storage in a high temperature and high humidity environment. Provide a sheet. The optically transparent adhesive sheet of the present invention is an optically transparent adhesive sheet made of a thermosetting polyurethane, and the thermosetting polyurethane is a cured product of a thermosetting polyurethane composition containing a polyol component and a polyisocyanate component, The polyisocyanate component includes a first polyisocyanate having a hydrophilic unit and a second polyisocyanate not having a hydrophilic unit, and a storage shear elastic modulus at 85 ° C. of 5 × 10 3 to 5 × 10 4 Pa. Yes, the adhesive strength in the 180 ° peel test is 1.5 to 30 N / 25 mm.

Description

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

An optical transparent adhesive (OCA) sheet is a transparent adhesive sheet used for bonding optical members. In recent years, the demand for touch panels has rapidly increased in the fields of smartphones, tablet PCs, portable game machines, car navigation devices, and the like, and accordingly, an optical transparent adhesive sheet used for bonding touch panels to other optical members. Demand is also increasing. A display device provided with a touch panel is usually a display panel such as a liquid crystal panel, a transparent member (touch panel body) having a transparent conductive film made of ITO (indium tin oxide) or the like as a surface layer, and a cover panel that protects the transparent conductive film The optical transparent adhesive sheet is used for bonding between optical members.

For example, Patent Document 1 discloses a two-component curable urethane pressure-sensitive adhesive obtained by using a urethane prepolymer and a crosslinking agent and having the following characteristics.
-A urethane prepolymer is obtained by using a polyol and a polyisocyanate.
-The average functional group number f of a 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)
(However, Eq> 0)
The elastic modulus at a frequency of 1 Hz and 25 ° C. is 2 × 10 ⁵ Pa or less, and the elastic modulus at a frequency of 1 Hz and 80 ° C. is 2 × 10 ⁴ Pa or more.

Moreover, in patent document 2, the optical film with a double-sided adhesive which is arrange | positioned and used between a front transparent plate or a touch panel and an image display cell, and has the following characteristics is disclosed.
An optical film including a polarizing plate, a first pressure-sensitive adhesive layer provided on the surface of the optical film to be bonded to the image display cell, and a surface of the optical film to be bonded to the transparent plate or the touch panel. A second pressure-sensitive adhesive layer.
A protective sheet is detachably attached to each of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer.
-The thickness of a 2nd adhesive layer is 30 micrometers or more.

JP, 2006-204467, A JP 2014-115468 A

In a display device including a touch panel, as described above, an optical transparent adhesive sheet may be used for bonding between optical members, while the space between the display panel and the touch panel body is a housing of the display panel. Since the end portion of the bezel is present, it is wider than the interval between the other optical members and is not bonded by the optical transparent adhesive sheet, and it is common to provide an air layer called an air gap. However, when an air gap that is an air layer exists between the optical members, interface reflection occurs due to a difference in refractive index between the air layer and the optical member, and thus the visibility of the display panel is lowered. For this reason, a thick-film optically transparent adhesive sheet suitable for bonding the display panel and the touch panel body has been demanded. Further, the optical transparent adhesive sheet used for bonding the display panel and the touch panel body is also required to cover a step formed by the thickness of the bezel. Therefore, an optically transparent pressure-sensitive adhesive sheet that is excellent in flexibility (step difference followability) and can be thickened is required.

On the other hand, the present inventors have focused on thermosetting polyurethane that can be formed without using a solvent as a material for an optically transparent adhesive sheet that is excellent in flexibility and can be made thick. However, various studies were made on the optically transparent adhesive sheet obtained by using thermosetting polyurethane, and it was found that there was room for improvement in the holding power (creep characteristics) in a high temperature environment. Specifically, when a creep test is performed in a high temperature environment by suspending a weight (load) on the bonded optical transparent adhesive sheet and adherend, the interface between the optical transparent adhesive sheet and the adherend is measured. It was found that peeling occurred and the weight dropped.

Further, according to the study by the present inventors, depending on the constituent material of the thermosetting polyurethane, the optical transparent adhesive sheet may be whitened when stored in a high temperature and high humidity environment, and optical characteristics (for example, transparency) ) Will decrease.

The present invention has been made in view of the above-described situation, and uses a thermosetting polyurethane that is excellent in flexibility and capable of thickening, has excellent creep characteristics in a high temperature environment, and is in a high temperature / high humidity environment. An object of the present invention is to provide an optically transparent adhesive sheet in which whitening caused by storage is suppressed.

The present inventors use a thermosetting polyurethane composition containing both a polyisocyanate having a hydrophilic unit and a polyisocyanate not having a hydrophilic unit as a constituent material (polyisocyanate component) of the thermosetting polyurethane. Has been found to be effective in suppressing whitening. Furthermore, it has been found that excellent creep characteristics can be obtained even in a high temperature environment by controlling the storage shear modulus at 85 ° C. and the adhesive strength in the 180 ° peel test within a specific range. The present invention has been completed.

The optically transparent adhesive sheet of the present invention is an optically transparent adhesive sheet made of a thermosetting polyurethane, and the thermosetting polyurethane is a cured product of a thermosetting polyurethane composition containing a polyol component and a polyisocyanate component, The polyisocyanate component includes a first polyisocyanate having a hydrophilic unit and a second polyisocyanate not having a hydrophilic unit, and a storage shear modulus at 85 ° C. of 5 × 10 ^{3 to} 5 × 10. ⁴ Pa, and the adhesive strength in the 180 ° peel test is 1.5 to 30 N / 25 mm.

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

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

The method for producing an optically transparent pressure-sensitive adhesive sheet of the present invention includes a step of stirring and mixing the polyol component and the polyisocyanate component to prepare the thermosetting polyurethane composition, and a step of curing the thermosetting polyurethane composition. It is characterized by including.

The laminate of the present invention comprises an optically transparent adhesive sheet of the present invention, a first release film that covers one surface of the optically transparent adhesive sheet, and a second release that covers the other surface of the optically transparent adhesive sheet. It is characterized by being laminated with a mold film.

The bonded structure of the present invention includes a first adherend, a second adherend, the optically transparent adhesive sheet of the present invention that joins the first adherend and the second adherend. It is characterized by providing.

According to the optically transparent pressure-sensitive adhesive sheet of the present invention, it has superior flexibility and a superior thermosetting polyurethane that can be thickened, and has excellent creep characteristics in a high temperature environment, and can be stored in a high temperature and high humidity environment. Thus, an optically transparent pressure-sensitive adhesive sheet in which whitening caused by is suppressed is obtained.
According to the method for producing an optical transparent adhesive sheet of the present invention, the optical transparent adhesive sheet of the present invention can be preferably produced.
According to the laminate of the present invention, the handleability of the optically transparent adhesive sheet of the present invention can be improved.
According to the bonded structure of the present invention, it is possible to obtain a bonded structure that is excellent in creep characteristics in a high temperature environment and is suppressed from whitening caused by storage in a high temperature and high humidity environment.

It is sectional drawing which shows typically an example of the display apparatus with a touch panel using the optically transparent adhesive sheet of this invention. It is sectional drawing which shows typically an example of the shaping | molding apparatus used for manufacture of the optically transparent adhesive sheet of this invention. FIG. 3 is a cross-sectional view schematically showing a laminated body of Example 1. It is a schematic diagram for demonstrating the evaluation method of the adhesive force of an optical transparent adhesive sheet. It is a schematic diagram for demonstrating the evaluation method of the creep characteristic of an optical transparent adhesive sheet.

The optically transparent adhesive sheet of the present invention is an optically transparent adhesive sheet made of a thermosetting polyurethane, and the thermosetting polyurethane is a cured product of a thermosetting polyurethane composition containing a polyol component and a polyisocyanate component, The polyisocyanate component includes a first polyisocyanate having a hydrophilic unit and a second polyisocyanate not having a hydrophilic unit, and a storage shear modulus at 85 ° C. of 5 × 10 ^{3 to} 5 × 10. ⁴ Pa, and the adhesive strength in the 180 ° peel test is 1.5 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 “optical transparent adhesive sheet” has the same meaning as the “optical transparent adhesive film”.

The optically transparent pressure-sensitive adhesive sheet of the present invention is made of thermosetting polyurethane. The thermosetting polyurethane is a cured product of a thermosetting polyurethane composition containing a polyol component and a polyisocyanate component. A cured product of the thermosetting polyurethane composition is obtained by reacting a polyol component and a polyisocyanate component, and has a structure as shown in the following formula (A).

In said formula (A), R represents the site | part except the NCO group of the polyisocyanate component. R 'represents a site excluding the OH group of the polyol component. n represents the number of repeating units.

It is preferable that the thermosetting polyurethane is not acrylic-modified, and it is preferable that a site derived from an acrylate ester, a methacrylate ester or the like is not included in the main chain. When the thermosetting polyurethane is acrylic-modified, it becomes hydrophobic, and moisture aggregation tends to occur in a high temperature and high humidity environment. This aggregation of moisture may cause whitening, foaming, and the like, and may impair optical properties (for example, transparency). Accordingly, by making the thermosetting polyurethane unmodified with acrylic, it is possible to prevent deterioration of optical characteristics due to whitening, foaming, etc. in a high temperature / high humidity environment. In the thermosetting polyurethane, the total amount of the monomer unit derived from the polyol component and the monomer unit derived from the polyisocyanate component is 80 mol% or more of the monomer unit constituting the entire thermosetting polyurethane. It is preferable that there are, more preferably, only monomer units derived from the polyol component and monomer units derived from the polyisocyanate component.

As the polyol component and the polyisocyanate component, those that 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 can be added to either the polyol component or the polyisocyanate component, and are preferably added to the polyol component. Thus, when manufacturing an optically transparent adhesive sheet using thermosetting polyurethane, since removal of a solvent is unnecessary, a uniform sheet | seat can be formed thickly. For this reason, when using the optical transparent adhesive sheet of this invention for bonding with the transparent member (touch panel) which has a display panel and a transparent conductive film in a surface layer, the level | step difference of a bezel can be coat | covered. Further, the optically transparent pressure-sensitive adhesive sheet of the present invention can maintain optical properties even when it is formed thick, resulting in reduced transparency, coloring, and foaming (occurrence of bubbles at the interface with the adherend). It can be sufficiently suppressed.

Since the optically transparent adhesive sheet of the present invention is made of thermosetting polyurethane, it is flexible, stretches well when applied with tensile stress, and is very difficult to break. For this reason, it is possible to peel off without leaving glue. In addition, since the optically transparent adhesive sheet of the present invention is flexible and can be thickened, it has excellent impact resistance and can be used for bonding a transparent member having a transparent conductive film as a surface layer to a cover panel. In the case of using another member, it can also be used for bonding a display panel or a transparent member having a transparent conductive film on its surface and another member. Furthermore, since the optically transparent pressure-sensitive adhesive sheet of the present invention is made of thermosetting polyurethane, the dielectric constant is high, and a higher capacitance can be obtained than an optically transparent pressure-sensitive adhesive sheet made of a conventional acrylic resin composition. For this reason, the optical transparent adhesive sheet of this invention is preferably used for bonding of a capacitive touch panel.

[Polyol component]
It does not specifically limit as a polyol component, For example, polyether polyol, polycaprolactone polyol, polycarbonate polyol, polyester polyol etc. are mentioned. These may be used alone or in combination of two or more.

Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polypropylene triol, polypropylene tetraol, polytetramethylene glycol, polytetramethylene triol, polyalkylene glycols such as copolymers thereof, and side chains introduced into these. Examples thereof include derivatives, modified products, and mixtures thereof in which a branched structure is introduced.

Examples of the polycaprolactone polyol include polycaprotectone glycol, polycaprolactone triol, polycaprolactone tetraol, derivatives in which side chains are introduced or branched structures are introduced, modified products, and mixtures thereof. It is done.

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

Examples of the dialkyl carbonate include dialkyl carbonates such as dimethyl carbonate and diethyl carbonate; diaryl carbonates such as diphenyl carbonate; alkylene carbonates such as ethylene carbonate, and the like. 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, 1,8-octanediol, and 2-methyl-1,8. -Octanediol, 1,9-nonanediol, 1,10-dodecanediol, 2-ethyl-1,6-hexanediol, 3-methyl-1,5-pentanediol, 2,4-dimethyl-1,5- Examples include 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, such as 1,4-butanediol, diethylene glycol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl. -1,5-pentanediol, 2,4-dimethyl-1,5-pentanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 2-methyl-1, It is preferable to use only one type of 8-octanediol, 1,9-nonanediol, or a combination of two or more types. Examples of the diol include a copolycarbonate diol composed of 1,6-hexanediol and 3-methyl-1,5-pentanediol, a copolycarbonate diol composed of 1,6-hexanediol and 1,5-pentanediol, and the like. Is also preferable.

As the polycarbonate polyol, for example, polycarbonate glycol, polycarbonate triol, polycarbonate tetraol, derivatives in which side chains are introduced or branched structures are introduced, modified products, and mixtures thereof can be used. .

Examples of the polyester polyol include those obtained by dehydration condensation of a dicarboxylic acid and a glycol component.

Examples of the dicarboxylic acid include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; oxalic acid; malonic acid; succinic acid; glutaric acid; adipic acid; azelaic acid; It is done.

Examples of the glycol component include ethylene glycol, 1,4-butanediol, diethylene glycol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,5-pentanediol, 1,9-nonanediol, and triethylene. Aliphatic glycols such as glycol; alicyclic glycols such as 1,4-cyclohexanedimethanol; aromatic diols such as p-xylenediol; polyoxyalkylene glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; Can be mentioned.

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

The number average molecular weight of the polyol component is preferably 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, making it difficult to form the thermosetting polyurethane into a uniform sheet, or the flexibility of the thermosetting polyurethane. It may fall and become 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 becomes difficult to form the thermosetting polyurethane into a uniform sheet, or the thermosetting polyurethane crystallizes and becomes cloudy. May occur. The number average molecular weight of the polyol component is more preferably 500 to 2,000.

The polyol component preferably has an olefin skeleton, that is, the main chain is composed of polyolefin or a derivative thereof. Examples of the polyol component having an olefin skeleton include polybutadiene-based polyols such as 1,2-polybutadiene polyol, 1,4-polybutadiene polyol, 1,2-polychloroprene polyol, 1,4-polychloroprene polyol; and polyisoprene polyol. And those in which those double bonds are saturated with hydrogen, halogen or the like. Further, the polyol component may be a polyol obtained by copolymerizing an olefin compound such as styrene, ethylene, vinyl acetate, and acrylate with a polybutadiene-based polyol or the like, or a hydrogenated product thereof. The polyol component may have a linear structure or a branched structure. The polyol component which has an olefin frame | skeleton may be used only by 1 type, and may be used together by 2 or more types. The polyol component preferably contains 80 mol% or more of a polyol component having an olefin skeleton, and more preferably comprises only a polyol component having an olefin skeleton.

As a known example of a polyol component having an olefin skeleton, a polyolefin polyol “EPOL (registered trademark)” (number average molecular weight: 2500) obtained by hydrogenating a hydroxyl-terminated polyisoprene manufactured by Idemitsu Kosan Co., Ltd., manufactured by Nippon Soda Co., Ltd. Examples thereof include hydroxyl-terminated hydrogenated polybutadiene “GI-1000” (number average molecular weight: 1500), polyhydroxy polyolefin oligomer “Polytail (registered trademark)” manufactured by Mitsubishi Chemical Corporation, and the like.

[Polyisocyanate component]
A polyisocyanate component contains the 1st polyisocyanate which has a hydrophilic unit (hydrophilic group), and the 2nd polyisocyanate which does not have a hydrophilic unit. According to such a polyisocyanate component, whitening can be suppressed by the action (hygroscopic action) of the hydrophilic part (hydrophilic unit: first polyisocyanate), and the hydrophobic part (other unit: second unit). The polyisocyanate) can exhibit high compatibility with the polyol component, the first polyisocyanate, the tackifier, the plasticizer, and the like.

The hydrophilic unit means a structural unit having a solubility parameter (SP value) of 8.5 MPa ^1/2 or more, preferably a structural unit having a solubility parameter of 9.0 MPa ^1/2 or more. The solubility parameter can be calculated by the Fedors method (see RF Fedors: Polym. Eng. Sci., 14 [2], 147-154 (1974)). In addition, as for the calculation method of solubility parameter by Fedors method, for example, the paper “Consideration on solubility parameter of additive” in “Paint Research No. 152” (October, 2010) published by Kansai Paint Co., Ltd. Have been described. The hydrophilic unit is different from the structure derived from an isocyanate group, such as an isocyanurate structure or a biuret structure, and means a portion in which a hydrophilic functional group is added and incorporated into polyisocyanate.

As the hydrophilic unit, an ethylene oxide unit is preferable. The content of the ethylene oxide unit is preferably 0.1 to 20% by weight with respect to 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 low-polar olefinic polyol components (polyol components having an olefin skeleton), tackifiers, plasticizers, etc. decreases, so that the optical properties such as transparency The characteristics may deteriorate. Moreover, since the amount of moisture absorption of the optical transparent pressure-sensitive adhesive sheet increases, the pressure-sensitive adhesive performance under a high temperature environment may be adversely affected. As for content of an ethylene oxide unit, it is more preferable that it is 0.1 to 5 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 units containing a carboxylic acid group, an alkali metal base of a carboxylic acid, a sulfonic acid group, an alkali metal base of a sulfonic acid, a hydroxyl group, an amide group, an amino group and the like in addition to the ethylene oxide unit. It is done. More specifically, polyacrylic acid, alkali metal salt of polyacrylic acid, sulfonic acid group-containing copolymer, alkali metal salt of sulfonic acid group-containing copolymer, polyvinyl alcohol, polyacrylamide, carboxymethylcellulose, and alkali metal of carboxymethylcellulose Examples thereof include salts and polyvinyl pyrrolidone.

(First polyisocyanate)
As the first polyisocyanate having a hydrophilic unit, for example, a modified polyisocyanate obtained by reacting an aliphatic polyisocyanate or an alicyclic polyisocyanate with an ether compound having an ethylene oxide unit is preferably used. By using an aliphatic polyisocyanate or an alicyclic polyisocyanate, the optical transparent pressure-sensitive adhesive sheet is less likely to be colored or discolored, and the transparency of the optical transparent pressure-sensitive 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, 3-methyl-pentane-1,5-diisocyanate, lysine diisocyanate, trioxy Examples thereof include ethylene diisocyanate and modified products thereof. These may be used alone or in combination of two or more. Examples of the modified product of hexamethylene diisocyanate include hexamethylene diisocyanate modified with isocyanurate, allophanate, and / or urethane.

Examples of the alicyclic polyisocyanate include isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI), norbornane diisocyanate (NBDI, see the following chemical formula (B)), hydrogenated xylene diisocyanate, hydrogen. Examples thereof include added tetramethylxylene diisocyanate and modified products thereof. These may be used alone or in combination of two or more.

Examples of ether compounds having an ethylene oxide unit include alcohols, phenols, and / or amine oxide adducts of amines. As the ether compound having an ethylene oxide unit, an ether compound having 3 or more ethylene oxide units per molecule is preferably used from the viewpoint of enhancing hydrophilicity.

Examples of alcohols include monohydric alcohols, dihydric alcohols (ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,3-butylenediol, Peopentyl glycol, etc.) and trihydric alcohols (glycerin, trimethylolpropane, etc.). These may be used alone or in combination of two or more.

Examples of the phenols include hydroquinone, bisphenols (such as bisphenol A and bisphenol F), and phenolic formalin low condensates (such as novolac resins and resol intermediates). 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, the thermosetting polyurethane composition may not be sufficiently cured due to a decrease in crosslinking density.

(Second polyisocyanate)
As the second polyisocyanate having no hydrophilic unit, an aliphatic polyisocyanate, an alicyclic polyisocyanate, or the like is preferably used.

Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate (HDI), tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine diisocyanate, trioxy Examples thereof include ethylene diisocyanate and modified products thereof. These may be used alone or in combination of two or more. Examples of the modified product of hexamethylene diisocyanate include hexamethylene diisocyanate modified with isocyanurate, allophanate, and / or urethane.

Examples of the alicyclic polyisocyanate include isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI), norbornane diisocyanate (NBDI, see the following chemical formula (B)), hydrogenated xylene diisocyanate, hydrogen. Examples thereof include added tetramethylxylene diisocyanate and modified products thereof. These may be used alone or in combination of two or more.

In the thermosetting polyurethane composition, the mixing ratio (molar ratio) of the first polyisocyanate and the second polyisocyanate defined by the following formula (M) achieves both suppression of whitening and ensuring compatibility. From the viewpoint of making it, 0.5 to 9.0 is preferable, and 0.5 to 3.0 is more preferable. When the mixing ratio exceeds 9.0, whitening may not be sufficiently suppressed.
“Mixing ratio” = “number of moles of second polyisocyanate” / “number of moles of first polyisocyanate” (M)

The thermosetting polyurethane composition preferably has an α ratio (number of moles of OH group derived from polyol component / number of moles of NCO group derived from polyisocyanate component) of 1 or more. When the α ratio 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 becomes hard and the flexibility required for the optically transparent adhesive sheet is secured. It may be difficult. When the flexibility of the optical transparent adhesive sheet is low, it may be difficult to cover unevenness and a step present on the attachment surface of the optical member, particularly when the optical transparent adhesive sheet is attached to an optical member such as a touch panel. Moreover, the adhesive force requested | required of an optical transparent adhesive sheet may become difficult to be ensured. The α ratio more preferably satisfies 1.3 <α <2.0. When the α ratio is 2.0 or more, the thermosetting polyurethane composition may not be sufficiently cured.

[Tackfire]
The thermosetting polyurethane composition may further contain a tackifier (tackifier). The tackifier is an additive that is added to increase the adhesive force, and is usually an amorphous oligomer having a molecular weight of several hundred to several thousand, and is a thermoplastic resin that is liquid or solid at room temperature. According to the tackifier, the adhesive strength of the optical transparent adhesive sheet can be increased.

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

As the tackifier, a petroleum resin tackifier is preferably used from the viewpoint of excellent compatibility with the above-described polyol component having an olefin skeleton. Of the petroleum resin tackifiers, hydrogenated petroleum resins obtained by hydrogenating a copolymer of dicyclopentadiene and an aromatic compound are preferably used. Dicyclopentadiene is obtained from the C5 fraction. Examples of the aromatic compound include vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyl toluene. The ratio of dicyclopentadiene and vinyl aromatic compound (dicyclopentadiene: vinyl aromatic compound) is not particularly limited, but is preferably 70:30 to 20:80 on a weight basis, and 60:40 to 40: 60 is more preferable. For hydrogenated petroleum resins, the preferred softening temperature is 90 to 160 ° C., the preferred vinyl aromatic compound unit content is 35% by mass or less, the preferred bromine number is 0 to 30 g / 100 g, and the preferred number average molecular weight is 500-1100. Known examples of hydrogenated petroleum resin tackifiers include “Imabe (registered trademark) P-100” manufactured by Idemitsu Kosan Co., Ltd.

As the tackifier, a hydrocarbon resin-based tackifier is also preferably used from the viewpoint of excellent compatibility with the above-described polyol component having an olefin skeleton. Among the hydrocarbon resin tackifiers, alicyclic saturated hydrocarbon resins are preferably used. Known examples of the alicyclic saturated hydrocarbon resin include “Arcon P-100” manufactured by Arakawa Chemical Industries, Ltd.

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 sufficiently prevent the reaction between the polyol component and the polyisocyanate component.

It is preferable that content of a tackifier is 1 to 20 weight% with respect to the whole quantity of a thermosetting polyurethane composition. When the content of the tackifier is less than 1% by weight, the adhesive strength of the optically transparent adhesive sheet may not be sufficiently increased, and in particular, the adhesive strength in a high temperature environment may be insufficient. However, in the optically transparent adhesive sheet of the present invention, the storage shear elastic modulus at 85 ° C. and the adhesive strength in the 180 ° peel test are specified even if the tackifier is not blended in the thermosetting polyurethane composition. By controlling within the range, the adhesive strength in a high temperature environment is sufficiently ensured. When the content of the tackifier exceeds 20% by weight, the tackifier may inhibit the reaction between the polyol component and the polyisocyanate component, and urethane crosslinking may not be sufficiently formed in the thermosetting polyurethane. As a result, the optical transparent pressure-sensitive adhesive sheet dissolves and changes its shape in a high temperature and high humidity environment, and tackifier may precipitate (bleed). On the other hand, if the reaction time between the polyol component and the polyisocyanate component is increased in order to sufficiently form urethane crosslinks, the productivity is lowered.

[Plasticizer]
The thermosetting polyurethane composition may further contain a plasticizer. According to the plasticizer, since the hardness of the thermosetting polyurethane is lowered, the handleability and flexibility (step following ability) of the optical transparent pressure-sensitive adhesive sheet can be improved. In addition, although there exists a possibility that adhesive force may fall by addition of a plasticizer, according to the optically transparent adhesive sheet of this invention, sufficient adhesive force can be ensured even if adhesive force falls somewhat.

Although it will not specifically limit if it is a compound used in order to provide a softness | flexibility to thermosetting polyurethane as a plasticizer, From a compatibility and a weather resistance viewpoint, a carboxylic acid type plasticizer is used preferably. Examples of the carboxylic acid plasticizer include phthalic acid esters (phthalic plasticizers) such as diundecyl phthalate, dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate, and dibutyl phthalate; diisononyl 1,2-cyclohexanedicarboxylate Adipic acid ester; trimellitic acid ester; maleic acid ester; benzoic acid ester; poly-α-olefin, and the like. These may be used alone or in combination of two or more.

Known examples of carboxylic acid plasticizers include "DINCH (registered trademark)" manufactured by BASF, "Sunsocizer (registered trademark) DUP" manufactured by Shin Nippon Chemical Co., Ltd., and "DURASYN (registered trademark)" manufactured by Iones Oligomers. 148 "and the like.

[catalyst]
The thermosetting polyurethane composition may further contain a catalyst. The catalyst is not particularly limited as long as it is a compound used in the urethanization reaction. For example, organic tin compounds such as di-n-butyltin dilaurate, dimethyltin dilaurate, dibutyltin oxide, and octane tin; An organic zirconium compound; a carboxylic acid tin salt; a carboxylic acid bismuth salt; and an amine-based catalyst such as triethylenediamine.

As the catalyst, a non-amine catalyst is preferable. When an amine-based catalyst is used, the optically transparent adhesive sheet may be easily discolored. Among non-amine catalysts, dimethyltin dilaurate is preferable.

Content of a catalyst is 0.01 to 0.1 weight% with respect to the total amount of a polyol component and a polyisocyanate component, for example.

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-methacryloyloxyethyl isocyanate (MOI), 2-acryloyloxyethyl isocyanate (AOI), octyl isocyanate, heptyl isocyanate, ethyl 3-isocyanate propionate, Examples include cyclopentyl isocyanate, cyclohexyl isocyanate, 2-methoxyethane isocyanate, ethyl isocyanate acetate, butyl isocyanate acetate, and p-toluenesulfonyl isocyanate. These may be used alone or in combination of two or more. In addition, it is preferable that a thermosetting polyurethane composition does not contain a monoisocyanate component.

Various additives such as colorants, stabilizers, antioxidants, antifungal agents, flame retardants, etc. are added to the thermosetting polyurethane composition as needed, as long as the required properties of the optically transparent adhesive sheet are not impaired. May be.

The optical transparent adhesive sheet of the present invention has a storage shear modulus at 85 ° C. of 5 × 10 ^{3 to} 5 × 10 ⁴ Pa. According to the study by the present inventors, it is effective to use the storage shear modulus at 85 ° C. as an indicator of creep characteristics. When the storage shear modulus at 85 ° C. is less than 5 × 10 ³ Pa, the optically transparent adhesive sheet undergoes a great change in shape under a high temperature environment, and therefore, peeling at the interface with the adherend tends 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 it is difficult for the shape to change under a high temperature environment. Peeling at the interface with the adherend tends to occur. Moreover, it becomes difficult for the optical transparent pressure-sensitive adhesive sheet to cover the unevenness and the steps present on the surface of the adherend, and the possibility of poor bonding increases. The storage shear modulus at 85 ° C. is preferably 1 × 10 ⁴ to 4 × 10 ⁴ Pa.

The storage shear modulus at 85 ° C. can be controlled by adjusting the composition of the thermosetting polyurethane composition that is the raw material of the thermosetting polyurethane and / or the thermosetting conditions. For example, α ratio, content of hydrophilic unit in polyisocyanate component, type of hydrophilic unit (molecular weight), first polyisocyanate having hydrophilic unit and second polyisocyanate not having hydrophilic unit The storage shear modulus at 85 ° C. can be controlled by the mixing ratio (for example, molar ratio), the presence or absence of the addition of a plasticizer, the blending amount of the plasticizer, the crosslinking temperature, and the like.

The optically transparent adhesive sheet of the present invention has an adhesive strength of 1.5 to 30 N / 25 mm in a 180 ° peel test. According to the study by the present inventors, it is effective that the adhesive strength in the 180 ° peel test is also used as an index of creep characteristics. When the adhesive strength in the 180 ° peel test is less than 1.5 N / 25 mm, the adhesive strength in the high temperature environment of the optical transparent adhesive sheet is remarkably reduced. Therefore, in the high temperature environment, the optical transparent adhesive sheet and the adherend are Peeling at the interface is likely to occur. When the adhesive strength in the 180 ° peel test exceeds 30 N / 25 mm, the hardness of the optically transparent adhesive sheet is too low, so that it is easily displaced from the surface of the adherend during the creep test. Further, when the optical transparent pressure-sensitive adhesive sheet is peeled off from the adherend, adhesive residue tends to occur. Furthermore, it becomes difficult to remove air bubbles that have entered between the optically transparent pressure-sensitive adhesive sheet and the adherend, and the handleability is reduced. The adhesive strength in the 180 ° peel test is preferably 3 to 15 N / 25 mm, more preferably 5 to 15 N / 25 mm.

In the optical transparent pressure-sensitive adhesive sheet of the present invention, as described above, both the storage shear modulus at 85 ° C. and the pressure-sensitive adhesive force in the 180 ° peel test are within a specific range. Remarkably superior. Details of the method for measuring the storage shear modulus at 85 ° C. and the method for measuring the adhesive strength in the 180 ° peel test will be described later.

In the optically transparent adhesive sheet of the present invention, the thermosetting polyurethane composition preferably does not contain a compound having a softening temperature of 100 ° C. or lower. According to the study by the present inventors, when a compound having a softening temperature of 100 ° C. or less is blended in the thermosetting polyurethane composition, a creep test is performed in a high-temperature environment using the obtained optically transparent adhesive sheet ( In general, when a creep test in an environment of 80 to 100 ° C. is performed, the compound softens in a high temperature environment, and does not contribute to the bonding of the polymer (thermosetting polyurethane). The hardness of the steel may decrease, and the shape may change easily. Therefore, the optical transparent adhesive sheet may be easily peeled off at the interface with the adherend in a high temperature environment. On the other hand, when a compound having a softening temperature of 100 ° C. or less is not blended with the thermosetting polyurethane composition, the effect of softening the compound under a high temperature environment is eliminated, so that creep characteristics under a high temperature environment are eliminated. Will increase. Here, the softening temperature refers to a temperature at which a substance softens as the temperature rises and begins to deform.

Among the compounds that can be blended in the thermosetting polyurethane composition, examples of the compound having a softening temperature of 100 ° C. or lower include hydrogenated petroleum resin tackifiers (for example, “Imabe P-100” manufactured by Idemitsu Kosan Co., Ltd.). (Softening temperature: 100 ° C.)). The hydrogenated petroleum resin-based tackifier is preferably used from the viewpoint of excellent compatibility with a polyol component having an olefin skeleton, and imparts high transparency to the optically transparent adhesive sheet. Therefore, when the hydrogenated petroleum resin tackifier (compound having a softening temperature of 100 ° C. or less) is not blended in the thermosetting polyurethane composition, the creep property of the optically transparent adhesive sheet in a high temperature environment is enhanced, but the optical There is a concern that the characteristics (transparency) will decrease. On the other hand, in the optically transparent pressure-sensitive adhesive sheet of the present invention, the second polyisocyanate that does not have a hydrophilic unit and exhibits high compatibility with a polyol component or the like as a polyisocyanate component is a thermosetting polyurethane composition. Even if the hydrogenated petroleum resin tackifier (compound with a softening temperature of 100 ° C. or less) is not blended in the thermosetting polyurethane composition, it has excellent optical properties (transparent Property).

The thickness of the optically transparent pressure-sensitive adhesive sheet of the present invention is not particularly limited, and may be, for example, 50-2500 μm, but is preferably 250-1500 μm. If the thickness of the optical transparent pressure-sensitive adhesive sheet is 250 μm or more, it becomes easy to cover the unevenness and the step existing on the surface of the adherend when one surface of the optical transparent pressure-sensitive adhesive sheet is attached to the adherend. The other surface of the transparent adhesive sheet and the other adherend can be bonded together with sufficient adhesive force. On the other hand, the thicker the optically transparent adhesive sheet, the easier it is for the optical properties (transparency) to decrease and the adhesiveness to decrease due to an increase in moisture absorption. However, if the thickness of the optically transparent pressure-sensitive adhesive sheet is 1500 μm or less, as in the present invention, the compounding material of the thermosetting polyurethane composition is devised, and the storage shear elastic modulus at 85 ° C. and the adhesion in the 180 ° peel test are used. By controlling the force within a specific range, it is possible to sufficiently suppress a decrease in optical properties (transparency) and a decrease in adhesiveness due to an increase in moisture absorption. In addition, it is preferable that an optical transparent adhesive sheet has a thickness 3 times or more with respect to the height of the unevenness | corrugation and level | step difference which exist in the sticking surface of a to-be-adhered body.

The micro rubber A hardness of the optically transparent adhesive sheet of the present invention is preferably 0.5 to 25 °. When the micro rubber A hardness of the optical transparent pressure-sensitive adhesive sheet is less than 0.5 °, the handleability when affixed to the adherend is poor, and the optical transparent pressure-sensitive adhesive sheet may be deformed. When the micro rubber A hardness of the optical transparent adhesive sheet exceeds 25 °, the optical transparent adhesive sheet has low flexibility and cannot follow the surface shape of the adherend when being attached to the adherend. It may cause peeling from the adherend by biting air. Moreover, when the flexibility of the optical transparent adhesive sheet is low, it may be difficult to cover unevenness and a step present on the attachment surface of the optical member, particularly when attaching to an optical member such as a touch panel. The upper limit with more preferable micro rubber | gum A hardness of the optical transparent adhesive sheet of this invention is 15 degrees. The micro rubber A hardness is measured using, for example, a micro rubber hardness meter “MD-1 type A” manufactured by Kobunshi Keiki Co., Ltd. The micro rubber hardness tester “MD-1 Type A” is a hardness tester designed and manufactured as a reduced model of about 1/5 of the spring type rubber hardness tester (durometer) A type. It is possible to obtain a measurement value that matches the spring type rubber hardness tester A type.

In order to ensure the performance (transparency) of the optically transparent adhesive sheet of the present invention, the haze is preferably 0.5% or less, and the total light transmittance is 90% or more. Preferably there is. The haze and total light transmittance are measured using, for example, a turbidimeter “HazeMeter NDH2000” manufactured by Nippon Denshoku Industries Co., Ltd. The haze is measured by a method based on “JIS K 7136”. The total light transmittance is measured by a method according to “JIS K 7361-1”.

A release film may be attached to both surfaces of the optically transparent adhesive sheet of the present invention. The 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 were laminated. A laminated body (hereinafter, also referred to as “laminated body of the present invention”) is also an embodiment of the present invention. According to the laminate of the present invention, the first release film and the second release film can protect both surfaces of the optical transparent pressure-sensitive adhesive sheet of the present invention until just before being attached to the adherend. Thereby, the adhesive fall with respect to the optical transparent adhesive sheet of this invention, and adhesion of a foreign material are prevented. Moreover, since the optical transparent adhesive sheet of the present invention is prevented from sticking to other than the adherend, the handleability is improved.

Examples of the first release film and the second release film include a polyethylene terephthalate (PET) film. The materials and thicknesses of the first release film and the second release film may be the same as or different from each other.

The bonding strength (peeling strength) of the optically transparent 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 mutually Preferably they are different. Since the bonding strengths are different from each other in this way, only one of the first release film and the second release film (the release film having the lower bonding strength) is peeled from the laminate of the present invention. Then, the first surface of the exposed optically transparent adhesive sheet and the first adherend are bonded together, and then the other of the first release film and the second release film (the bonding strength is It becomes easy to bond the second surface of the exposed optically transparent adhesive sheet and the second adherend to each other by peeling the higher release film).

At least one of the surface of the first release film on the side in contact with the optical transparent adhesive sheet of the present invention and the surface of the second release film on the side of contact with the optical transparent adhesive sheet of the present invention is easy. A peeling treatment (mold release treatment) may be performed. As an easy peeling process, a silicon process etc. are mentioned, for example.

The use of the optically transparent adhesive sheet of the present invention is not particularly limited, and the first adherend, the second adherend, the first adherend and the second adherend are joined together. A bonded structure including the optically transparent adhesive sheet of the invention (hereinafter also referred to as “bonded structure of the present invention”) is also an embodiment of the present invention.

Examples of the first adherend and the second adherend 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. For example, if the various panels in the display device are bonded together using the optical transparent adhesive sheet of the present invention, the air layer (air gap) in the display device can be eliminated, and the visibility of the display screen can be improved. it can.

As a bonding structure of this invention, the display apparatus with a touch panel provided with the optically transparent adhesive sheet of this invention, a display panel, and a touch panel, etc. are mentioned, for example. In addition, although the sticking surface of a polarizing plate is comprised with triacetyl cellulose (TAC) etc. and the sticking surface of a resin board is comprised with polycarbonate (PC) etc., the optical transparent adhesive sheet of this invention is not only glass. In addition, good adhesion performance can be exhibited even for these resins. Moreover, if the optically transparent adhesive sheet of this invention is affixed on a glass plate, the effect which prevents scattering of glass will be acquired.

FIG. 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 apparatus 10, the display panel 11, the optical transparent adhesive sheet 12, the touch panel (glass substrate with a transparent conductive film) 13, the optical transparent adhesive sheet 12, and the transparent cover panel 14 are laminated in order. Yes. Three optical members of the display panel 11, the touch panel 13, and the transparent cover panel 14 are integrated by two optical transparent adhesive sheets 12.

The display panel 11 is accommodated in a bezel (a casing of the display panel 11) 11A having an opening on the display surface side. A step corresponding to the thickness of the bezel 11A exists at the outer edge of the opening of the bezel 11A. The optical transparent adhesive sheet 12 is attached so as to cover the display surface side of the display panel 11 and the bezel 11A, and covers the step corresponding to the thickness of the bezel 11A. The optically transparent adhesive sheet 12 is required to have flexibility (step following ability) that can follow the step portion and to be thicker than the thickness of the bezel 11A in order to cover the step corresponding to the thickness of the bezel 11A. It is done. Thus, it is preferable that the thickness of the optical transparent adhesive sheet 12 used for bonding with the display panel 11 accommodated in the bezel 11A is, for example, 700 μm or more. The optical transparent pressure-sensitive adhesive sheet of the present invention has sufficient flexibility and optical characteristics (for example, transparency) even if it has a thickness of 700 μm or more, and the display panel 11 and the touch panel 13 accommodated in the bezel 11A It is preferably used when bonding.

The kind of display panel 11 is not specifically limited, For example, a liquid crystal panel, an organic electroluminescent panel (organic EL panel), etc. are mentioned.

Examples of the touch panel 13 include detection systems such as a resistance film system and a capacitance system.

In such a display device, since the optically transparent adhesive sheet of the present invention is used, the adhesive force of the optically transparent adhesive sheet is hardly reduced even under various environments, and each optical member is used over a long period of time. Can be brought into close contact with each other. As a result, no gap is generated between each optical member and the optical transparent pressure-sensitive adhesive sheet, and it is possible to prevent a decrease in visibility due to an increase in interface reflection or the like. The optically transparent pressure-sensitive adhesive sheet of the present invention is preferably used in, for example, an in-vehicle display device such as a display device incorporated in a car navigation device, a display device for portable equipment such as a smartphone, and 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, there is a method in which the thermosetting polyurethane composition is molded while being thermoset by a conventionally known method. Preferably, the method includes a step of preparing a thermosetting polyurethane composition by stirring and mixing a polyol component and a polyisocyanate component, and a step of curing the thermosetting polyurethane composition.

As an example of the method for producing the optically transparent pressure-sensitive adhesive sheet of the present invention, a tackifier masterbatch is first prepared by adding a predetermined amount of tackifier to a polyol component and dissolving it by heating and stirring. Subsequently, by mixing the obtained tackifier masterbatch, polyol component, polyisocyanate component, and other components (additives) such as a catalyst, if necessary, and stirring with a mixer or the like, a liquid or gel The thermosetting polyurethane composition is obtained. Immediately after that, the thermosetting polyurethane composition is put into a molding apparatus, and is crosslinked and cured while moving the thermosetting polyurethane composition while being sandwiched between the first release film and the second release film. . As a result, the thermosetting polyurethane composition is semi-cured, and a sheet integrated with the first release film and the second release film is obtained. Subsequently, an optically transparent pressure-sensitive adhesive sheet made of a cured product of the thermosetting polyurethane composition (thermosetting polyurethane) is obtained by crosslinking reaction of the thermosetting polyurethane composition in a furnace for a certain period of time. Complete.

FIG. 2 is a cross-sectional view schematically showing an example of a molding apparatus used for producing the optically transparent adhesive sheet of the present invention. As shown in FIG. 2, in the shaping | molding apparatus 20, first, a pair of liquid or gel-like thermosetting polyurethane composition 23 before hardening is continuously sent out from a pair of shaping | molding rolls 22 spaced apart. Pour into a gap between release films (for example, PET film) 21. Then, while the thermosetting polyurethane composition 23 is held in the gap between the pair of release films 21, the curing reaction (crosslinking reaction) is allowed to proceed and is carried into the heating device 24. Thereafter, in the heating device 24, the thermosetting polyurethane composition 23 is thermoset while being held between the pair of release films 21, and is obtained from a cured product (thermosetting polyurethane) of the thermosetting polyurethane composition 23. The forming of the optical transparent pressure-sensitive adhesive sheet 12 is completed. As a result, the laminated body (optical transparent adhesive sheet with a release film) 25 in which the release film 21 is laminated on both surfaces of the optical transparent adhesive sheet 12 is completed.

As a method for producing the optically transparent adhesive sheet of the present invention, after preparing a thermosetting polyurethane composition before curing, a general-purpose film forming apparatus such as various coating apparatuses, bar coats, doctor blades, and the like are used. It may be. Moreover, you may manufacture the optical transparent adhesive sheet of this invention using a centrifugal molding method.

EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail about this invention, this invention is not limited only to these Examples.

[Composition material]
In Examples and Comparative Examples, materials used for preparing thermosetting polyurethane compositions and their abbreviations are as follows.

(Polyol component)
・ "P1"
“EPOL” manufactured by Idemitsu Kosan Co., Ltd.

(Polyisocyanate component)
・ "Q1"
Modified polyisocyanate (first polyisocyanate) having ethylene oxide unit (EO unit)
"Coronate (registered trademark) 4022" manufactured by Tosoh Corporation
・ "Q2"
Isophorone diisocyanate (IPDI) polyisocyanate (second polyisocyanate)
"Death Module (registered trademark) I" manufactured by Sumika Bayer Urethane Co., Ltd.
・ "Q3"
Hexamethylene diisocyanate (HDI) polyisocyanate (second polyisocyanate)
"Coronate 2760" manufactured by Tosoh Corporation

"Coronate 4022" manufactured by Tosoh Corporation is obtained by reacting polyisocyanate starting from hexamethylene diisocyanate and / or hexamethylene diisocyanate monomer with an ether polyol having an average of 3 or more ethylene oxide units per molecule. It is a thing. Further, “Coronate 2760” manufactured by Tosoh Corporation is a mixture of allophanate-modified hexamethylene diisocyanate and hexamethylene diisocyanate trimer.

(Tack Fire)
・ "S1"
“Imabe P-100” manufactured by Idemitsu Kosan Co., Ltd.

(catalyst)
・ "T1"
Dimethyl tin dilaurate “Fomrez catalyst UL-28” manufactured by Momentive)

Example 1
First, 75 parts by weight of polyolefin polyol “P1”, 4.6 parts by weight of modified polyisocyanate “Q1” having an EO unit, 2.4 parts by weight of IPDI polyisocyanate “Q2”, 17 parts by weight of tackifier “S1”, and 1 part by weight of catalyst “T1” was stirred and mixed using a reciprocating rotary stirrer agitator to prepare a thermosetting polyurethane composition having an α ratio of 1.7. In the thermosetting polyurethane composition, the mixing ratio (molar ratio) between the first polyisocyanate and the second polyisocyanate defined by the following formula (M) was 1.
“Mixing ratio” = “number of moles of second polyisocyanate” / “number of moles of first polyisocyanate” (M)

Thereafter, the prepared thermosetting polyurethane composition (thermosetting polyurethane composition 23) was injected into the molding apparatus 20 shown in FIG. And while transporting the thermosetting polyurethane composition in a state of being sandwiched between a pair of release films (PET film whose surface has been subjected to a release treatment) 21, the temperature in the furnace is 70 ° C. and the furnace time is 10 minutes. Under cross-linking and curing, a sheet with a release film 21 was produced. Thereafter, the thermosetting polyurethane composition in the sheet is subjected to a crosslinking reaction for 12 hours with the heating device 24 adjusted to 70 ° C., and the optically transparent adhesive sheet 12 made of a cured product (thermosetting polyurethane) of the thermosetting polyurethane composition. Was completed. As a result, the laminated body (optical transparent adhesive sheet with a release film) 25 in which the release films 21 were laminated on both surfaces of the optical transparent adhesive sheet 12 was completed.

FIG. 3 is a cross-sectional view schematically showing the laminate of Example 1. As shown in FIG. 3, in the laminated body 25, the release film 21, the optical transparent adhesive sheet 12, and the release film 21 were laminated | stacked in order. The thickness of the optically transparent adhesive sheet 12 was 250 μm.

(Examples 2-9 and Comparative Examples 1-9)
The optical transparent adhesive sheet of each example was manufactured like Example 1 except having changed the composition of the thermosetting polyurethane composition and the thickness of the optical transparent adhesive sheet as shown in Tables 1-4.

[Evaluation]
The following evaluation was performed about the optical transparent adhesive sheet of each example. The results are shown in Tables 1-4.

(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. PP12 was used as the measurement plate. The measurement conditions were a strain of 0.1%, a frequency of 1 Hz, and a cell temperature of 25 to 100 ° C. (temperature increase rate of 3 ° C./min). Tables 1 to 4 show the measured values of the storage shear modulus at 85 ° C.

(2) Adhesive strength A 180 ° peel test was performed by the following method, and the adhesive strength (N / 25 mm) was measured. FIG. 4 is a schematic diagram for explaining a method for evaluating the adhesive strength of the optical transparent adhesive sheet.

First, the laminate (optical transparent adhesive sheet with a release film) was cut into a length of 75 mm and a width of 25 mm to obtain a test piece. And after peeling off the release film on one side of this test piece, the optically transparent adhesive sheet 12 side is attached to a slide glass 31 having a length of 75 mm × width of 25 mm, and held at a pressure of 0.4 MPa for 30 minutes, and optically transparent The adhesive sheet 12 and the slide glass 31 were bonded together. Thereafter, the release film on the side opposite to the slide glass 31 is peeled off, and the PET sheet 32 having a thickness of 125 μm is formed on the surface of the optically transparent adhesive sheet 12 opposite to the slide glass 31 as shown in FIG. (“Melinex (registered trademark) S” manufactured by Teijin DuPont Films Ltd.) was attached.

Next, after leaving the state shown in FIG. 4 (a) for 12 hours in an environment of normal temperature and normal humidity (temperature 23 ° C., humidity 50%), as shown in FIG. 4 (b), a PET sheet 32 was pulled in the 180 ° direction, the optical transparent adhesive sheet 12 was peeled off at the interface with the slide glass 31, and the adhesive strength of the optical transparent adhesive sheet 12 to the slide glass 31 was measured. In addition, the measurement of adhesive force was performed by preparing two test pieces for each example. And the average value of the obtained two measured values was used as the measurement result of the adhesive strength in each example.

(3) Optical characteristics First, after peeling off the release film on one side of the laminate (optical transparent adhesive sheet with release film), the optical transparent adhesive sheet side is attached to a slide glass (made of soda glass), and the pressure is set to 0. Holding at 4 MPa for 30 minutes, the optically transparent adhesive sheet and the slide glass were bonded together. Then, the release film on the side opposite to the slide glass was peeled off and allowed to stand for 168 hours in a high temperature and high humidity (temperature 85 ° C., humidity 85%) environment, and then the appearance of the optical transparent adhesive sheet was visually observed. Judgment criteria were as follows.
○: Whitening did not occur.
X: Whitening occurred.

(4) Creep characteristics Creep tests were conducted by the following methods to evaluate the creep characteristics. FIG. 5 is a schematic diagram for explaining a method for evaluating creep characteristics of an optically transparent adhesive sheet.

First, the laminate (optical transparent adhesive sheet with a release film) was cut into a length of 25 mm × width of 25 mm (25 mm square) to obtain a test piece. And after peeling off the release film on one side of this test piece, the optically transparent adhesive sheet 12 side is attached to a slide glass 31 having a length of 75 mm × width of 25 mm, and held at a pressure of 0.4 MPa for 30 minutes, and optically transparent The adhesive sheet 12 and the slide glass 31 were bonded together. Thereafter, the release film on the side opposite to the slide glass 31 is peeled off, and a 125 μm-thick PET sheet 32 (“Melenex (Teijin DuPont Films” (Registered trademark) S "). Next, as shown in FIG. 5, the one with a 150 g weight 33 fixed on the PET sheet 32 side is suspended and left in a high temperature / normal humidity (temperature 85 ° C., humidity 50%) environment for 120 minutes. . Then, the optical transparent adhesive sheet 12 is observed at the interface with the slide glass 31 or the PET sheet 32 to observe whether the weight 33 falls, and the holding time (unit: from the start of the suspension until the weight 33 falls) Minute). In Tables 1 to 4, when the weight 33 does not fall for 120 minutes, the holding time is set to 120 minutes, and the position from the position at which the optical transparent adhesive sheet 12 starts to be hung (attached position: zero point) is below. The measurement value (unit: mm) of the amount of deviation to the surface, that is, the amount of deformation movement of the optical transparent adhesive sheet 12 is shown. Further, when the weight 33 dropped after 120 minutes, the holding time was set to 120 minutes, and the deviation amount was indicated as “(falling)”. As a determination criterion, a case where the holding time is 120 minutes (corresponding to the case where the weight 33 does not fall for 120 minutes) and the deviation amount is 0 to 8 mm was set as the conforming level. However, from the viewpoint that it is desirable that the optical transparent adhesive sheet has an appropriate flexibility corresponding to the heat shrinkability of the adherend (in this evaluation, the slide glass 31 and the PET sheet 32), the deviation amount is 0 mm. Is not always the best.

As shown in Tables 1 and 2, Examples 1 to 9 had high creep characteristics in a high temperature environment, and no whitening occurred after being left in a high temperature and high humidity environment. In Examples 1 to 9, the thickness of the optical transparent pressure-sensitive adhesive sheet was evaluated to be 250 to 1500 μm and thicker than conventional, but even when the optical transparent pressure-sensitive adhesive sheet is thick and the moisture absorption amount is likely to increase, The creep property was high in a high temperature environment, and no whitening occurred after being left in a high temperature and high humidity environment.

In Examples 3, 4, and 9, the tackifier was not blended in the thermosetting polyurethane composition, but the second polyisocyanate having no hydrophilic unit was blended. It was highly compatible with polyisocyanate, and no whitening occurred after being left under high temperature and high humidity. In Examples 3, 4, and 9, a compound having a softening temperature of 100 ° C. or less (“Imabe P-100” manufactured by Idemitsu Kosan Co., Ltd., blended in Example 1) is a thermosetting polyurethane composition. Therefore, the storage shear modulus at 85 ° C. was high, which greatly contributed to the improvement of creep characteristics in a high temperature environment.

On the other hand, as shown in Tables 3 and 4, in Comparative Examples 1 to 9, whitening occurred after the creep characteristics were low in a high temperature environment or left in a high temperature and high humidity environment.

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

In Comparative Examples 4 and 6, since the adhesive strength in the 180 ° peel test exceeded 30 N / 25 mm, the creep characteristics in a high temperature environment were low.

In Comparative Example 5, since the adhesive strength in the 180 ° peel test was less than 1.5 N / 25 mm, the creep characteristics in a high temperature environment were low.

In Comparative Example 7, since the thermosetting polyurethane composition was not blended with the second polyisocyanate having no hydrophilic unit and the tackifier, the compatibility with the polyol component was reduced, and the Whitening occurred after being left in a high humidity environment.

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

10: Display device 11: Display panel 11A: Bezel 12: Optical transparent adhesive sheet 13: Touch panel 14: Transparent cover panel 20: Molding device 21: Release film 22: Molding roll 23: Thermosetting polyurethane composition 24: Heating device 25: Laminate (optical transparent adhesive sheet with release film)
31: Slide glass 32: PET sheet 33: Weight

Claims (6)

An optically transparent adhesive sheet made of thermosetting polyurethane,
The thermosetting polyurethane is a cured product of a thermosetting polyurethane composition containing a polyol component and a polyisocyanate component,
The polyisocyanate component includes a first polyisocyanate having an ethylene oxide unit and a second polyisocyanate not having an ethylene oxide unit ;
In the thermosetting polyurethane composition, the α ratio expressed by the number of moles of OH groups derived from the polyol component / the number of moles of NCO groups derived from the polyisocyanate component is larger than 1.3 and smaller than 2.0. And
The storage shear modulus at 85 ° C. is 5 × 10 ^{3 to} 5 × 10 ⁴ Pa,
180 ° adhesive strength in peeling test Ri 1.5~30N / 25mm der,
An optical transparent pressure-sensitive adhesive sheet having a thickness of 250 to 2500 μm . In the thermosetting polyurethane composition, the mixing ratio of the first polyisocyanate and the second polyisocyanate defined by the following formula (M) is 0.5 to 9.0. The optical transparent pressure-sensitive adhesive sheet according to claim 1.
“Mixing ratio” = “number of moles of the second polyisocyanate” / “number of moles of the first polyisocyanate” (M) The optical transparent adhesive sheet according to claim 1 or 2, wherein the optical transparent adhesive sheet has a thickness of 250 to 1500 µm. A method for producing the optically transparent adhesive sheet according to any one of claims 1 to 3,
A step of stirring and mixing the polyol component and the polyisocyanate component to prepare the thermosetting polyurethane composition;
And a step of curing the thermosetting polyurethane composition. The optical transparent adhesive sheet according to any one of claims 1 to 3, a first release film covering one surface of the optical transparent adhesive sheet, and a second covering the other surface of the optical transparent adhesive sheet. A laminate comprising a release film and a laminate. The optically transparent adhesive sheet according to any one of claims 1 to 3, wherein the first adherend, the second adherend, the first adherend, and the second adherend are joined. A bonded structure characterized by comprising:

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