JP2019077780A - Optically clear adhesive sheet, laminate, method for producing optically clear adhesive sheet, and laminated sheet - Google Patents

Abstract

To provide an optically clear adhesive sheet in which occurrence of delayed bubbles due to storage in a high-temperature environment is suppressed, by using a thermoset polyurethane excellent in flexibility and capable of being formed into a thick film.SOLUTION: The optically clear adhesive sheet is composed of a thermoset polyurethane. The thermoset polyurethane is a cured product of a thermosetting polyurethane composition containing a polyol component, a polyisocyanate component, and a silane coupling agent. The optically clear adhesive sheet has a loss tangent (tanδ) at 85°C of 0.50 or less.SELECTED DRAWING: Figure 4

Description

The present invention relates to an optically transparent pressure-sensitive adhesive sheet, a laminate, a method for producing an optically transparent pressure-sensitive adhesive sheet, and a laminated sheet.

An optically clear adhesive (OCA) sheet is a transparent adhesive sheet used for laminating optical members. In recent years, the demand for touch panels has been rapidly growing in the fields of smartphones, tablet PCs, portable game machines, car navigation devices, etc. With this, the demand for OCA sheets used to bond touch panels to other optical members Is also increasing. A display device provided with a touch panel generally includes a display panel such as a liquid crystal panel, a transparent member (touch panel main body) having a transparent conductive film made of ITO (indium tin oxide) or the like on the surface, and a cover for protecting the transparent conductive film. It has a structure where optical members, such as a panel, were laminated, and an OCA sheet is used for pasting between optical members. However, between the display panel and the touch panel main body, the end of the bezel, which is the housing of the display panel, is wider than the distance between the other optical members, and bonding with the OCA sheet is not performed. It was common to provide an air layer called.

However, if there is an air gap that is an air layer between the optical members, interface reflection occurs due to the difference in refractive index between the air layer and the optical members, and the visibility of the display panel is reduced. Therefore, a thick film OCA sheet suitable for bonding the display panel and the touch panel main body has been required. Moreover, covering the level difference formed by the thickness of a bezel is also calculated | required by the OCA sheet used for bonding of a display panel and a touch-panel main body. Therefore, an OCA sheet excellent in flexibility (step followability) and capable of being thickened is required.

Examples of documents disclosing prior art in the OCA sheet-related field include Patent Documents 1 and 2. The adhesive type optical film in which an adhesive layer is provided on an optical film is disclosed in Patent Document 1, wherein the adhesive layer comprises a polyol compound (a-1) having a weight average molecular weight of 500 to 4000, and an isocyanate compound (a-). 2), and a polyol compound (a-4) having two or more C = C bonds having radical polymerization property in one molecule, which are obtained by reaction, and the polyol (a-1) and the polyol compound (a-4) A polyurethane polymer (A) in which the compounding amount of the polyol compound (a-4) is 0.1 to 10% by weight with respect to the total amount of (A) as a base polymer, and the urethane polymer (A) 100 The adhesive type optical film characterized by containing 0.01-0.5 weight part of silane coupling agents (B) with respect to a weight part is disclosed.

Patent Document 2 describes 100 parts by weight of a pressure-sensitive adhesive resin (A) and silicone alkoxy oligomers (B) 0.1 to 20 having an epoxy equivalent of 100 to 2000 g / mol and an alkoxyl group content of 5 to 60% by weight. Acrylic pressure-sensitive adhesive resin (A1), urethane-based pressure-sensitive adhesive resin (A2), and polyester-based pressure-sensitive adhesive, which are obtained by polymerizing a monomer containing no carboxyl group, wherein the pressure-sensitive adhesive resin (A) contains parts by weight A pressure-sensitive adhesive composition is disclosed, which is one or more selected from the group consisting of an agent resin (A3). In addition, it is described that the pressure-sensitive adhesive composition may further contain 0.001 to 5 parts by weight of a silane coupling agent (D) with respect to 100 parts by weight of the pressure-sensitive adhesive resin (A). (See claim 7).

Patent No. 5016994 Specification JP, 2016-44291, A

As the OCA sheet, one formed of an ultraviolet curing adhesive is known. However, since an ultraviolet curing adhesive can not be irradiated with ultraviolet light at a portion to be a shadow of decorative printing or a portion to be a shadow of a material that absorbs ultraviolet light, it can not be cured sufficiently.

Therefore, the present inventors pay attention to using a thermosetting polyurethane composition which is film-formed without using a solvent and is cured by heating as a material of the OCA sheet which is excellent in flexibility and can be thickened. did. However, when various examinations were made on the OCA sheet obtained using the thermosetting polyurethane composition, after laminating the OCA sheet to the adherend, high temperature and high humidity environment (temperature 85 ° C., humidity 85%), etc. It has been found that when stored in a high temperature environment, air bubbles that are not present immediately after lamination but are generated later, that is, delayed bubbles (delay bubbles) are likely to be generated at the interface between the adherend and the OCA sheet. In recent years, not only glass substrates but also resin substrates composed of acrylic resins, polycarbonate resins and the like have come to be used as adherends.

As a result of investigations by the present inventors, the water generated inside the adherend is vaporized to cause delayed bubbles, and particularly when the adherend is a resin substrate which is likely to absorb moisture, delayed bubbles. Was found to occur easily. The generation of such delayed bubbles was a phenomenon unique to thermosetting polyurethanes. For example, an OCA sheet using an acrylic resin composition is likely to absorb moisture in a high temperature and high humidity environment, but has high adhesive strength and high gas permeability, so delayed bubbles are not a problem in particular. . Although the OCA sheet using silicone resin has low adhesion, it is very difficult to absorb moisture in a high temperature and high humidity environment, so delayed foam was not a problem in particular.

The present invention has been made in view of the above-mentioned present situation, and an optical fiber in which the generation of delayed bubbles caused by storage in a high temperature environment is suppressed by using a thermosetting polyurethane excellent in flexibility and capable of forming a thick film. It aims at providing a transparent adhesive sheet.

The present inventors examined the improvement of the environmental resistance of the optical transparent adhesive sheet using a thermosetting polyurethane, and by adding a silane coupling agent to the thermosetting polyurethane composition, the adhesion of the interface was improved. It has been found that the generation of delayed bubbles can be effectively suppressed by improving the cohesion of the sheet by controlling the loss tangent (tan δ) at 85 ° C. as 0.50 or less as the sheet physical property. completed.

The optical transparent adhesive sheet of the present invention is an optical transparent adhesive sheet composed of thermosetting polyurethane, and the thermosetting polyurethane is a thermosetting polyurethane composition containing a polyol component, a polyisocyanate component and a silane coupling agent. And a loss tangent (tan δ) at 85 ° C. of not more than 0.50.

The thickness of the optically transparent pressure-sensitive adhesive sheet of the present invention is preferably 250 to 2000 μm.

The optical transparent pressure-sensitive adhesive sheet of the present invention preferably has an initial adhesion of 5 N / 25 mm or less to a glass surface, and an adhesion of 10 N / 25 mm or more after holding at 50 ° C. for 2 hours. Moreover, it is preferable that initial stage adhesive force is 5 N / 25 mm or less with respect to the surface of a polycarbonate, and adhesive force after hold | maintaining at 50 degreeC for 2 hours is 10 N / 25 mm or more.

The polyol component preferably contains an olefin-based polyol.

The laminate of the present invention comprises the first adherend, the second adherend, and the optically transparent pressure-sensitive adhesive sheet of the present invention for bonding the first adherend and the second adherend. It is characterized by having.

The first adherend may be a glass substrate. The second adherend may be a resin base material. The resin substrate may contain a polycarbonate.

The method for producing an optical transparent pressure-sensitive adhesive sheet of the present invention is a method for producing the optical transparent pressure-sensitive adhesive sheet of the present invention, wherein the above-mentioned polyol component, the above-mentioned polyisocyanate component and the above-mentioned silane coupling agent are stirred and mixed The method comprises the steps of preparing a polyurethane composition and curing the thermosetting polyurethane composition.

The laminated sheet of the present invention comprises the optical transparent adhesive sheet of the present invention, a first release film covering one surface of the optical transparent adhesive sheet, and a second release film covering the other surface of the optical transparent adhesive sheet. It is characterized in that a mold film is laminated.

According to the optically transparent pressure-sensitive adhesive sheet of the present invention, it is possible to suppress the generation of delayed bubbles caused by storage in a high temperature environment while obtaining the superiority of a thermosetting polyurethane which is excellent in flexibility and can be thickened. . Moreover, according to the laminate of the present invention, it is possible to maintain a transparent, bubble-free bonding interface. According to the method for producing an optical transparent pressure-sensitive adhesive sheet of the present invention, the optical transparent pressure-sensitive adhesive sheet of the present invention can be suitably produced. According to the laminated sheet of the present invention, the handleability of the optical transparent pressure-sensitive adhesive sheet of the present invention can be improved.

It is a figure explaining the effect | action mechanism of a silane coupling agent. It is a schematic diagram for demonstrating the measuring method of the adhesive force of an optical transparent adhesive sheet. It is a schematic diagram for demonstrating the reason which a delayed bubble generate | occur | produces in the conventional laminated body. It is sectional drawing which showed typically an example of the display apparatus with a touch panel using the optical transparent adhesive sheet of this invention. It is a schematic diagram for demonstrating an example of the shaping | molding apparatus used for preparation of the optical transparent adhesive sheet of this invention.

The optical transparent adhesive sheet of the present invention is an optical transparent adhesive sheet composed of thermosetting polyurethane, and the thermosetting polyurethane is a thermosetting polyurethane composition containing a polyol component, a polyisocyanate component and a silane coupling agent. And a loss tangent (tan δ) at 85 ° C. of not more than 0.50. In addition, in this specification, an "optical transparent adhesive sheet" is synonymous with an "optical transparent adhesive film."

The optically transparent pressure-sensitive adhesive sheet of the present invention is composed of a thermosetting polyurethane. The optical transparent adhesive sheet made of polyurethane is flexible, stretches well and is very hard to break when a tensile stress is applied. For this reason, it is possible to peel off without adhesive residue. Moreover, since the optical transparent adhesive sheet of the present invention is flexible and can be thickened, it can be made excellent in impact resistance. Furthermore, since an optical transparent adhesive sheet made of polyurethane has a high dielectric constant and higher electrostatic capacitance than an optical transparent adhesive sheet made of a conventional acrylic resin composition, it is possible to use an electrostatic capacitive touch panel. It is suitably used for bonding.

The thermosetting polyurethane is preferably not acrylic-modified, and it is preferable that the main chain does not contain a site derived from an acrylic ester, a methacrylic ester or the like. When the thermosetting polyurethane is acrylic-modified, it becomes hydrophobic, and therefore, aggregation of water tends to occur under high temperature and high humidity. The aggregation of the water may cause whitening, foaming and the like, which may impair the optical properties. Therefore, by setting the thermosetting polyurethane not to be acrylic-modified, it is possible to prevent the deterioration of the optical characteristics due to whitening, foaming and the like under high temperature and high humidity. In the thermosetting polyurethane, the total amount of the monomer units derived from the polyol component and the monomer units derived from the polyisocyanate component is 80 mol% or more of the monomer units constituting the entire polyurethane. The monomer unit is preferably composed of only a monomer unit derived from a polyol component and a monomer unit derived from a polyisocyanate component.

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

Examples of the polyether polyols 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. And derivatives having a branched structure introduced, modified products, and mixtures of these.

Examples of the polycaprolactone polyol include polycaproate glycol, polycaprolactone triol, polycaprolactone tetraol, derivatives into which side chains are introduced or branched structures introduced into them, modified products, and mixtures of these, etc. It can be mentioned.

As said polycarbonate polyol, the reaction material of dialkyl carbonate and diol is mentioned, for example.

Examples of the dialkyl carbonate include dialkyl carbonates such as dimethyl carbonate and diethyl carbonate; diaryl carbonates such as diphenyl carbonate; and alkylene carbonates such as ethylene 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, 1,8-octanediol, 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 -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. As the diol, an alicyclic or alicyclic diol having 4 to 9 carbon atoms is preferable, and, for example, 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-1,1,5-heptanediol It is preferable to use 8-octanediol and 1,9-nonanediol singly or in combination of two or more. As the diol, a copolycarbonate diol consisting of 1,6-hexanediol and 3-methyl-1,5-pentanediol, and a copolycarbonate diol consisting of 1,6-hexanediol and 1,5-pentanediol are also available. preferable.

In addition, as the polycarbonate polyol, for example, polycarbonate glycol, polycarbonate triol, polycarbonate tetraol, derivatives in which a side chain is introduced or a branched structure is introduced thereto, modified products, and a mixture thereof can also be used. it can.

As said polyester polyol, what carried out dehydration condensation of the dicarboxylic acid and the glycol component is mentioned, for example.

Examples of dicarboxylic acids 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, sebacic acid and the like. Be

As the glycol component, for example, ethylene glycol, 1,4-butanediol, diethylene glycol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,5-pentanediol, 1,9-nonanediol, triethylene Aliphatic glycols such as glycols; alicyclic glycols such as 1,4-cyclohexanedimethanol; aromatic diols such as p-xylene diol; polyoxyalkylene glycols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol Be

The polyester polyol is a polyester having a linear molecular structure when formed by the dicarboxylic acid and glycol components exemplified above, but having a branched molecular structure using a trivalent or higher ester forming component. It 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 or more and 5,000 or less. 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, which makes it difficult to form the thermosetting polyurethane into a uniform sheet, or the flexibility of the thermosetting polyurethane becomes It may become brittle due to a decrease in the sex. When the number average molecular weight of the polyol component exceeds 5000, the viscosity of the polyol component becomes too high, which makes it difficult to form the thermosetting polyurethane into a uniform sheet, or the thermosetting polyurethane crystallizes and becomes cloudy. And other problems may occur. The number average molecular weight of the polyol component is more preferably 500 or more and 2000 or less.

The polyol component is preferably one having an olefin skeleton, that is, one whose main chain is constituted by a polyolefin or a derivative thereof. By using an olefin-based polyol as the polyol component, good heat resistance can be obtained, and since it is hydrophobic, the generation of outgassing due to moisture can be suppressed. 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 and 1,4-polychloroprene polyol, and polyisoprene Polyols and those having their double bonds saturated with hydrogen or halogen etc. may be mentioned. Further, the polyol component may be a polyol obtained by copolymerizing an olefin compound such as styrene, ethylene, vinyl acetate or acrylic ester with a polybutadiene type polyol or the like or a hydrogenated product thereof. The polyol component may have a linear structure or may have a branched structure. Only one type of polyol component having an olefin skeleton may be used, or two or more types may be used. The polyol component used for the polyurethane preferably contains 80 mol% or more of a polyol component having an olefin skeleton, and more preferably consists only of the polyol component having an olefin skeleton.

Among the known polyol components having an olefin skeleton, for example, a polyolefin polyol (“EPOL (registered trademark)”) obtained by hydrogenating hydroxyl-terminated polyisoprene manufactured by Idemitsu Kosan Co., Ltd., number average molecular weight: 2500), both-end hydroxyl group hydrogenated polybutadiene (“GI-1000”, number average molecular weight: 1500) manufactured by Nippon Soda Co., Ltd., polyhydroxy polyolefin oligomer (“Polytail (registered trademark)”) manufactured by Mitsubishi Chemical Corporation, etc. may be mentioned. .

[Polyisocyanate component]
The polyisocyanate component is not particularly limited, and conventionally known polyisocyanates can be used, and hydrophilic polyisocyanate having a hydrophilic unit (hydrophilic group) and hydrophobic polyisocyanate having no hydrophilic unit Either one or both may be used. The above-mentioned hydrophilic polyisocyanate is not a compound whose hydrophilicity is improved only by a structure derived from an isocyanate group like an isocyanurate structure or a biuret structure, but a functional group (hydrophilic group) for enhancing the hydrophilicity is added. It is preferable that it is a polyisocyanate.

An ethylene oxide unit is suitable as the hydrophilic unit. The action of suppressing whitening due to moisture absorption can be obtained by including the hydrophilic unit. It is preferable that content of the said ethylene oxide unit is 0.1 weight% or more and 20 weight% or less with respect to the whole thermosetting polyurethane composition. If the content is less than 0.1% by weight, whitening may not be sufficiently suppressed. When the content is more than 20% by weight, the compatibility with the low polar olefin-based polyol component, tackifier, plasticizer and the like is reduced, whereby the optical properties such as haze may be reduced. The content of the ethylene oxide unit is more preferably 0.1 to 5% by weight. When the content exceeds 5% by weight, the amount of moisture absorption in the high temperature and high humidity environment may be too large.

Examples of hydrophilic units other than ethylene oxide units include units containing a carboxylic acid group, an alkali metal base of carboxylic acid, a sulfonic acid group, an alkali metal base of sulfonic acid, a hydroxyl group, an amide group, an amino group and the like. 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, alkali metal of carboxymethylcellulose Salt, polyvinyl pyrrolidone and the like can be mentioned.

As a hydrophilic polyisocyanate which has the said hydrophilic unit, the modified polyisocyanate obtained by making aliphatic polyisocyanate and the ether compound which has an ethylene oxide unit react is used suitably, for example. By using the aliphatic polyisocyanate, it is possible to prevent the occurrence of coloration or discoloration of the optically transparent pressure-sensitive adhesive sheet, and to ensure the transparency of the optically transparent pressure-sensitive adhesive sheet for a long time more reliably. In addition, the polyisocyanate component can suppress whitening by the action of the hydrophilic portion (ethylene oxide unit) by forming a modified product in which an ether compound having an ethylene oxide unit is reacted, and the hydrophobic portion (other unit) The compatibility with low polarity tackifiers, plasticizers, etc. can be exhibited by the action of

Examples of the aliphatic polyisocyanate include hexamethylene diisocyanate, tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, lysine diisocyanate, trioxyethylene diisocyanate And isophorone diisocyanate, cyclohexyl diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, hydrogenated tetramethyl xylene diisocyanate, and modified products thereof. These may be used alone or in combination of two or more. In addition, as a modified body of hexamethylene diisocyanate, what carried out isocyanurate modification, allophanate modification, and / or urethane modification etc. of hexamethylene diisocyanate, etc. are mentioned, for example.

Examples of the ether compounds having ethylene oxide units include ethylene oxide adducts of alcohols, phenols and / or amines, and from the viewpoint of enhancing hydrophilicity, those having three or more ethylene oxide units per molecule It is preferably used.

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

Examples of the above-mentioned phenols include hydroquinone, bisphenols (bisphenol A, bisphenol F, etc.), and formalin low condensates of phenol compounds (novolak resin, intermediate of resole). 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. If the number of isocyanate groups is less than 2.0 on average, the decrease in the crosslink density may result in the thermosetting polyurethane composition not sufficiently curing.

The above-mentioned hydrophobic polyisocyanate is not particularly limited, but aliphatic isocyanates are suitably used. For example, hexamethylene diisocyanate (HDI), tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl -Pentane-1,5-diisocyanate, lysine diisocyanate, trioxyethylene diisocyanate, isophorone diisocyanate (IPDI), cyclohexyl diisocyanate, 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), norbornane diisocyanate (NBDI), hydrogenated tolylene And isocyanates, hydrogenated xylene diisocyanate, hydrogenated tetramethyl xylene diisocyanate, and modified products thereof. These may be used alone or in combination of two or more.

The compounding ratio of the hydrophilic polyisocyanate having the hydrophilic unit and the hydrophobic polyisocyanate not having the hydrophilic unit is preferably 9: 1 to 1: 1, from the viewpoint of achieving both the prevention of whitening and the reduction of the moisture absorption rate. 9, and more preferably 7: 3 to 3: 7.

The thermosetting polyurethane composition preferably has an α ratio of 1 or more (mole number of OH group derived from polyol component / mole number of NCO group derived from polyisocyanate component). 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 the thermosetting polyurethane becomes hard, and the flexibility required for the optical transparent adhesive sheet is It becomes difficult to secure. If the flexibility of the optical transparent pressure-sensitive adhesive sheet is low, in particular, when bonding an optical member such as a touch panel, it is not possible to cover the unevenness and the level difference present on the bonding surface. Moreover, there is a possibility that the adhesive force required for the optical transparent adhesive sheet can not be secured. 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 cured sufficiently.

[Silane coupling agent]
The above-mentioned silane coupling agent is not particularly limited, and has at least one reactive group (A) chemically bonded to the inorganic material and at least one reactive group (B) chemically bonded to the organic material in the molecule. Silane compounds can be used.

As said reactive group (A), a methoxy group and an ethoxy group are mentioned, for example. When at least one of the reactive groups (A) is an ethoxy group, the hydrolysis reaction can be delayed and outgassing causing delayed bubbles can be reduced.

As said reactive group (B), an epoxy group, an amino group, a ureido group, a mercapto group, and an isocyanate group are mentioned, for example. These functional groups are suitable for coupling with the polyol component or the polyisocyanate component.

As a preferable silane coupling agent, one having two or three ethoxy groups as a reactive group (A) and an epoxy group, an amino group, a ureido group, a mercapto group or an isocyanate group as a reactive group (B) Can be mentioned. According to such an ethoxy type silane coupling monomer, the properties of the resulting thermosetting polyurethane are stabilized without inhibiting the reaction between the polyol component and the polyisocyanate component. In addition, since the ethoxy group is easily segregated at the interface with the adherend, the ethoxy group can be strongly bonded to the adherend, and the generation of delayed bubbles can be effectively suppressed.

FIG. 1 is a view for explaining the action mechanism of the silane coupling agent. As shown in FIG. 1, the silane coupling agent is hydrolyzed by water to be silanol and then partially condensed to form an oligomer. Subsequently, the surface of the adherend 100 is adsorbed by an interaction such as hydrogen bonding. Thereafter, when a dehydration condensation reaction occurs due to heating or the like, it chemically strongly bonds to the surface of the adherend 100. As described above, the optical transparent pressure-sensitive adhesive sheet of the present invention does not exhibit high adhesive strength immediately after bonding, and by heating, the adhesive strength is significantly improved and can be firmly bonded to the adherend. Therefore, the optical transparent adhesive sheet of the present invention is excellent in reworkability, and can prevent the generation of delayed bubbles.

It is preferable that content of the said silane coupling agent is 0.2 weight% or more and 3 weight% or less with respect to a thermosetting polyurethane composition. When content of a silane coupling agent is less than 0.2 weight%, the effect of the adhesive force improvement of the optical transparent adhesive sheet by addition of a silane coupling agent may not fully be acquired. When content of a silane coupling agent exceeds 3 weight%, there exists a possibility that the adhesive force of an optical transparent adhesive sheet may fall because a silane coupling agent segregates on the surface of an optical transparent adhesive sheet.

[Tackfire]
The thermosetting polyurethane composition may further contain a tackifier (tackifier). A tackifier is an additive that is added to improve adhesion, and is usually an amorphous oligomer with a molecular weight of several hundred to several thousand, and is a thermoplastic resin that is liquid or solid at normal temperature. When the thermosetting polyurethane composition contains a tackifier, the adhesion of the optically transparent pressure-sensitive adhesive sheet formed of the cured product of the thermosetting polyurethane composition can be improved.

The above-mentioned tackifier is not particularly limited, and examples thereof include petroleum resin-based tackifiers, hydrocarbon resin-based tackifiers, rosin-based tackifiers, terpene-based tackifiers and the like. Only one type of these may be contained, or two or more types may be contained.

As the above-mentioned tackifier, a petroleum resin-based tackifier is suitably used since it is excellent in compatibility with the polyol component having the above-mentioned olefin skeleton. Among the above-mentioned petroleum resin-based tackifiers, a hydrogenated petroleum resin obtained by hydrogenating a copolymer of dicyclopentadiene and an aromatic compound is preferably used. Dicyclopentadiene is obtained from the C5 fraction. As said aromatic compound, vinyl aromatic compounds, such as styrene, (alpha)-methylstyrene, vinyl toluene, are mentioned, for example. The ratio of dicyclopentadiene to the vinyl aromatic compound is not particularly limited, but on a weight basis, it is preferable that dicyclopentadiene: vinyl aromatic compound = 70: 30 to 20:80, 60:40 to 40:60. It is more preferable that The preferable softening point of the above-mentioned hydrogenated petroleum resin is 90 to 160 ° C., the preferable vinyl aromatic compound unit content is 35 mass% or less, the preferable bromine number is 0 to 30 g / 100 g, and the preferable number average molecular weight is 500 to 1100. As a well-known thing among said hydrogenated petroleum resins, "Imarb P-100" by Idemitsu Kosan Co., Ltd. is mentioned, for example.

As said tackifier, since it is excellent in compatibility with the polyol component etc. which have the said olefin frame, a hydrocarbon resin type tackifier is used suitably. Among the above-mentioned hydrocarbon resin tackifiers, alicyclic saturated hydrocarbon resins are preferably used. Among the above-mentioned alicyclic saturated hydrocarbon resins, known ones include, for example, "Arcon P-100" manufactured by Arakawa Chemical Industries, Ltd.

It is preferable that content of the said tackifier is 1 weight% or more and 20 weight% or less with respect to a thermosetting polyurethane composition. When the content of the tackifier is less than 1% by weight, the adhesion of the optical transparent adhesive sheet may not be sufficiently improved, and in particular, the adhesion under high temperature and high humidity may be insufficient. . When the content of the tackifier exceeds 20% by weight, the reaction between the polyol component and the polyisocyanate component may be inhibited, and urethane crosslinking may not be sufficiently formed in the thermosetting polyurethane. As a result, the optical transparent pressure-sensitive adhesive sheet may be dissolved and the shape may change or the tackifier may be precipitated (bleed) under high temperature and high humidity. In addition, if the reaction time between the polyol component and the polyisocyanate component is increased to sufficiently form urethane crosslinking, the productivity is lowered.

[Plasticizer]
The thermosetting polyurethane composition may further contain a plasticizer. By the addition of the plasticizer, the hardness can be reduced, whereby the handling property and the level difference followability of the optical transparent pressure-sensitive adhesive sheet of the present invention can be improved.

The plasticizer is not particularly limited as long as it is a compound used to impart flexibility to a thermoplastic resin, but from the viewpoint of compatibility and weather resistance, it is preferable to include a carboxylic plasticizer. Examples of the carboxylic acid plasticizer include phthalic acid esters such as diundecyl phthalate, dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate, and dibutyl phthalate (phthalic acid plasticizers), and 1,2-cyclohexanedicarboxylic acid. Acid diisononyl ester, adipic acid ester, trimellitic acid ester, maleic acid ester, benzoic acid ester, poly-α-olefin and the like can be mentioned. Only one type of these may be contained, or two or more types may be contained. Among the above-mentioned carboxylic acid plasticizers, for example, “DINCH” manufactured by BASF, “San-sizer DUP” manufactured by Shin Nippon Rika, “Durasyn (registered trademark) 148” manufactured by Iones Oligomers, etc. Can be mentioned.

[catalyst]
The thermosetting polyurethane composition may further contain a catalyst. The catalyst is not particularly limited as long as it is a catalyst used for the urethanation reaction, for example, organic tin compounds such as di-n-butyl tin dilaurate, dimethyl tin dilaurate, dibutyl tin oxide, octane tin, etc .; organic titanium compounds Organic zirconium compounds; carboxylic acid tin salts; carboxylic acid bismuth salts; amine-based catalysts such as triethylenediamine.

In the above-mentioned thermosetting polyurethane composition, various additives such as a coloring agent, a stabilizer, an antioxidant, a mildew, a flame retardant and the like are optionally added within the range not to impair the required characteristics of the optical transparent pressure sensitive adhesive sheet. It may be added.

The optical transparent adhesive sheet of the present invention has a loss tangent (tan δ) at 85 ° C. of 0.50 or less. By setting the loss tangent at 85 ° C. to 0.50 or less, cohesion as a bulk of the sheet at high temperatures is secured, and therefore, foaming in the vicinity of the interface and in the sheet is suppressed. When the loss tangent at 85 ° C exceeds 0.50, the crosslink density is insufficient, so that foaming called cavitation due to the cohesion of the adhesive sheet may appear, and the foaming may impair the appearance of the display (display). is there. The preferred lower limit of loss tangent at 85 ° C. is 0.10. The loss tangent at 85 ° C. can be controlled by adjusting the composition of the thermosetting polyurethane composition and / or the heat curing conditions, and, for example, the α ratio (the number of moles of OH group derived from the polyol component / The number of moles of the NCO group derived from the polyisocyanate component), the silane coupling agent, the presence or absence of the addition of the plasticizer, the blending amount, the crosslinking temperature and the like can be controlled.

It is preferable that the thickness of the optical transparent adhesive sheet of this invention is 50-3000 micrometers. In the case where the thickness is less than 50 μm, when one surface of the optically transparent pressure-sensitive adhesive sheet is attached to the surface of the optical member, the optically transparent pressure-sensitive adhesive sheet may cover asperities or steps existing on the surface of the optical member In some cases, the other surface of the optical transparent pressure-sensitive adhesive sheet can not be attached to the surface of another optical member with sufficient adhesion. Further, the thicker the optical transparent adhesive sheet, the larger the amount of moisture absorption, and therefore delayed bubbles due to moisture absorption tend to occur, but if the thickness is 3000 μm or less, delayed bubbles due to moisture absorption can be sufficiently suppressed. The more preferable lower limit of the thickness of the optical transparent pressure-sensitive adhesive sheet is 200 μm, the more preferable lower limit is 250 μm, the particularly preferable lower limit is 300 μm, and the more preferable upper limit is 2000 μm. An optical transparent adhesive sheet having a thickness of 200 μm or more is suitable for preparation using a method of adjusting the thickness of a coating of a solventless thermosetting polyurethane composition by passing an air gap between rolls, If the thickness is 300 μm or more, the thickness accuracy is particularly excellent. Moreover, it is preferable that an optical transparent adhesive sheet has thickness 3 times or more with respect to the height of the unevenness | corrugation or level | step difference which exists in the sticking surface of a to-be-adhered body.

It is preferable that the optical transparent adhesive sheet of this invention is 5 N / 25 mm or less in initial stage adhesive force in 23 degreeC with respect to a glass surface. Moreover, it is preferable that the optical transparent adhesive sheet of this invention is 5 N / 25 mm or less in initial stage adhesive force in 23 degreeC with respect to the surface of a polycarbonate. If the initial adhesive strength is 5 N / 25 mm or less, when the optically transparent pressure-sensitive adhesive sheet is used for laminating optical members such as a touch panel, it can be peeled off without adhesive residue, so it is excellent in reworkability. Moreover, when the adhesive force of an optical transparent adhesive sheet becomes large too much, it may become difficult to pull out the bubble which entered between the optical transparent adhesive sheet and a to-be-adhered body at the time of bonding. In addition, when bonding optical members, such as a touch panel, with the optical transparent adhesive sheet of this invention, the autoclave process which removes a bubble and a vacuum void after bonding may be implemented at the temperature of about 50 degreeC. In order to be able to be reworked up to the autoclave treatment, it is preferable that the initial tackiness is low and the tackiness increase after the autoclave treatment. The optical transparent pressure-sensitive adhesive sheet of the present invention preferably has an adhesive strength of 10 N / 25 mm or more with respect to the glass surface after holding at 50 ° C. for 2 hours. Moreover, it is preferable that the adhesive force of the optical transparent adhesive sheet of this invention after holding for 2 hours at 50 degreeC with respect to the surface of a polycarbonate is 10 N / 25 mm or more. If the adhesive strength after holding at 50 ° C. for 2 hours is less than 10 N / 25 mm, the generation of delayed bubbles may not be suppressed.

The said adhesive force points out the value measured by the 180 degree peeling test which makes a base material made of glass or a polycarbonate a to-be-adhered body. The 180 ° peel test can be conducted by the following method to measure the adhesion (N / 25 mm). FIG. 2: is a schematic diagram for demonstrating the measuring method of the adhesive force of an optical transparent adhesive sheet. First, the optically transparent adhesive sheet 12 is attached to the base 31. Next, as shown to Fig.2 (a), the PET sheet 32 is affixed on the surface on the opposite side to the base material 31 of the optical transparent adhesive sheet 12. As shown in FIG. Thereafter, as shown in FIG. 2 (b), the PET sheet 32 is pulled in the direction of 180 ° to peel off the optically transparent adhesive sheet 12 at the interface with the substrate 31, and the adhesion of the optically transparent adhesive sheet 12 to the substrate 31 Measure

The optical transparent adhesive sheet of the present invention preferably has a haze of 0.5% or less and a total light transmittance of 90% or more in order to ensure the performance as an optical transparent adhesive sheet. . The haze and the total light transmittance can be measured, for example, using a turbidity meter “HazeMeter NDH 2000” manufactured by Nippon Denshoku Industries Co., Ltd. The haze is measured by the method according to JIS K 7136, and the total light transmittance is measured by the method according to JIS K 7361-1.

Moreover, the optical transparent adhesive sheet of this invention has a wide temperature range which can be used as an adhesive material, for example, is -40 degreeC-85 degreeC. This is because the tan δ peak of the thermosetting polyurethane constituting the optical transparent pressure-sensitive adhesive sheet of the present invention is as low as −40 ° C., and the low temperature characteristics are superior to the acrylic resin having a tan δ peak of approximately −6 ° C. For example, in the bonding reliability evaluation of an in-vehicle display, as a heat shock test, a reliability test in a temperature range of about -40 ° C to 85 ° C is performed, and a wide temperature range usable as an adhesive material is It has been demanded. Since the acrylic resin is in a glass state at around -6 ° C., if the display is distorted under an environment of -40 ° C., the acrylic resin adhesive material is easily peeled off. On the other hand, the thermosetting polyurethane used in the present invention is excellent in bonding reliability at low temperature because the glass transition point is on the lower temperature side.

A release film may be attached to both sides of the optical transparent adhesive sheet of the present invention. The optical transparent adhesive sheet of the present invention, a first release film covering one side of the optical transparent adhesive sheet, and a second release film covering the other side of the optical transparent adhesive sheet are laminated The laminated sheet (hereinafter, also referred to as "the laminated sheet of the present invention") which is one of them is also an aspect of the present invention. By attaching the first and second release films, the surface of the optical transparent pressure-sensitive adhesive sheet of the present invention can be protected until just before being attached to the adherend. As a result, it is possible to prevent the decrease in adhesiveness and the adhesion of foreign matter. Moreover, since it can prevent sticking other than a to-be-adhered body, the handleability of the optical transparent adhesive sheet of this invention can be improved.

For example, a polyethylene terephthalate (PET) film can be used as the first and second release films. The material and thickness of the first release film and the second release film may be the same or different.

The bonding strength (peel strength) of the optical transparent adhesive sheet of the present invention to the first release film and the bonding strength of the optical transparent adhesive sheet of the present invention to the second release film may be different from each other preferable. The optical transparent adhesion which peeled and exposed only one of the first and second release films (the release film with the weaker bonding strength) from the laminated sheet of the present invention due to the difference in the bonding strength. The first surface of the sheet and the first adherend were laminated, and then the other of the first and second release films (the release film with higher adhesion strength) was peeled off and exposed It becomes easy to bond together the 2nd surface and the 2nd adherend of an optical transparent adhesive sheet. The surface of the first release film in contact with the optical transparent adhesive sheet of the present invention, and the surface of the second release film in contact with the optical transparent adhesive sheet of the present invention, or both An easy peeling process (mold releasing process) may be performed. As an easy peeling process, a silicon process is mentioned, for example.

The application of the optical transparent pressure-sensitive adhesive sheet of the present invention is not particularly limited, and a first adherend, a second adherend, and the first adherend and the second adherend are joined. A laminate comprising the optical transparent pressure-sensitive adhesive sheet of the present invention is also an aspect of the present invention. As a 1st and 2nd to-be-adhered body, a glass base material and a resin base material are used suitably, for example. The materials of the first and second adherends may be the same or different. For example, the first adherend is a glass substrate and the second adherend is It may be a resin base material.

Here, when the glass base and the resin base were pasted together by the conventional optical transparent adhesive sheet, there was a case where delayed bubbles were generated mainly at the interface of the glass base and the optical transparent adhesive sheet . FIG. 3 is a schematic view for explaining the reason why delayed bubbles occur in the conventional laminate. As shown in FIG. 3, the moisture 61 contained inside the resin base material 52 due to moisture absorption etc. is vaporized under high temperature environment, released from the resin base material 52, transmitted through the optical transparent adhesive sheet 12, and glass base It gathers at the interface of the material 51 and the optical transparent adhesive sheet 12, and it will become air bubbles (delay foam | bubble) 60. FIG.

On the other hand, when the glass base and the resin base are pasted together by the optical transparent adhesive sheet of the present invention, the adhesion of the interface is improved by the addition of the silane coupling agent, and the loss tangent at 85 ° C. ( By improving the cohesion of the sheet by controlling tan δ) to 0.50 or less, it is possible to exhibit an excellent effect in preventing the generation of delayed bubbles.

The said glass base material will not be specifically limited if the surface which contact | connects an optical transparent adhesive sheet was comprised with glass, For example, Display apparatuses, such as a display panel, a touch panel (glass substrate with an ITO transparent conductive film), a cover glass The various members made of glass which comprise these are mentioned. The type of display panel is not particularly limited, and examples thereof include a liquid crystal panel and an organic electroluminescence panel (organic EL panel). By bonding various members in the display using the optically transparent adhesive sheet, the air layer (air gap) in the display can be eliminated, and the visibility of the display screen can be improved. Moreover, if an optical transparent adhesive sheet is stuck on a glass base material, the effect which prevents scattering of glass will be acquired.

The said resin base material will not be specifically limited if the surface which contact | connects an optical transparent adhesive sheet was comprised with resin (plastic), For example, Display apparatuses, such as a cover panel, a touch sensor film, a polarizing plate, retardation film The various resin-made members which comprise these are mentioned. The resin substrate may include a portion made of a material other than resin, but from the viewpoint of obtaining the effect of the present invention to suppress the generation of delayed bubbles, the thickness of the portion made of resin is 1 mm It is preferable that it is more than. If the thickness of the portion made of resin is less than 1 mm, the amount of water contained in the inside of the resin base material is small, so there is a possibility that the need to suppress the generation of delayed bubbles is small.

It does not specifically limit as resin which comprises the said resin base material, For example, a polycarbonate, polymethyl methacrylate resin (PMMA), triacetyl cellulose (TAC) etc. are mentioned. Among them, polycarbonate is preferable from the viewpoint of obtaining the effect of the present invention for suppressing the generation of delayed bubbles. In the case where the resin substrate contains a polycarbonate, delayed bubbles are likely to be generated remarkably, and the generation of delayed bubbles can be effectively suppressed by the present invention. Moreover, when the resin base material is a polarizing plate, the surface which contact | connects an optical transparent adhesive sheet may be comprised with a triacetyl cellulose.

As a laminated body of this invention, the display apparatus with a touch panel provided with the optical transparent adhesive sheet of this invention, a display panel, and a touch panel is mentioned, for example. FIG. 4: is sectional drawing which showed typically an example of the display apparatus with a touch panel using the optical transparent adhesive sheet of this invention. In the display device 10 shown in FIG. 4, the display panel 11, the optically transparent adhesive sheet 12, the touch panel (glass substrate with ITO transparent conductive film) 13, the optically transparent adhesive sheet 12, and the transparent cover panel 14 are sequentially stacked. The three optical members of the display panel 11, the touch panel 13 and the transparent cover panel 14 are integrated by two optically transparent adhesive sheets 12 of the present invention. The type of the display panel 11 is not particularly limited, and, for example, a liquid crystal panel, an organic electroluminescence panel (organic EL panel), or the like can be used. As the touch panel 13, for example, a detection method such as a resistance film method or a capacitance method is used.

The display panel 11 is housed in a bezel (a housing of the display panel 11) 11A having an opening on the display surface side, and a step corresponding to the thickness of the bezel 11A is present at the outer edge of the opening of the bezel 11A. Do. The optically transparent adhesive sheet 12 is attached to cover the display surface side of the display panel 11 and the bezel 11A, and covers a step corresponding to the thickness of the bezel 11A. According to the structure in which the optically transparent adhesive sheet 12 is disposed on the bezel so as to cover the step formed by the bezel 11A (hereinafter, also referred to as "bezel-on bonding structure"), the optically transparent adhesive sheet 12 is a step of the bezel 11A. Since the formation portion is covered, not only can the end portion of the optical transparent adhesive sheet 12 be prevented from being visually recognized, but the optical transparent adhesive sheet 12 is sandwiched between the step forming portion of the bezel 11A and the upper substrate (touch panel 13) Thus, peeling from the end of the optically transparent adhesive sheet 12 can be prevented. In order to cover the step formed by the thickness of the bezel 11A, the optical transparent adhesive sheet 12 is required to have flexibility to follow the step and a thickness greater than the thickness of the bezel 11A. Thus, it is preferable that the thickness of the optically 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 optical properties and flexibility even if it has a thickness of 700 μm or more, and is preferably used for bonding with the display panel 11 housed in the bezel 11A. it can.

In such a display device, since the optical transparent adhesive sheet of the present invention is used, the adhesive power of the optical transparent adhesive sheet is unlikely to decrease even when used under various environments, and the optical member is used for a long period of time It can be stuck to each other. As a result, since a space | gap does not generate | occur | produce between each optical member and an optical transparent adhesive sheet, the fall of the visibility by the increase of interface reflection etc. can be prevented. The optical transparent adhesive sheet of the present invention can be used, for example, in an on-vehicle display device such as a display device incorporated in a car navigation device or a display device for a portable device such as a smartphone.

The process for producing the transparent optical pressure-sensitive adhesive sheet of the present invention is not particularly limited. For example, after preparing a thermosetting polyurethane composition, a method may be mentioned in which the composition is thermally cured by a conventionally known method. And (ii) preparing a thermosetting polyurethane composition by stirring and mixing a polyol component, a polyisocyanate component and a silane coupling agent, and curing the thermosetting polyurethane composition.

As the polyol component, the polyisocyanate component and the silane coupling agent, 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 tackifiers can be added to either the polyol component and the polyisocyanate component, and are preferably added to the polyol component. Thus, when producing an optical transparent adhesive sheet using a thermosetting polyurethane composition, since removal of a solvent is unnecessary, a uniform sheet | seat can be thickly formed. For this reason, when using the optical transparent adhesive sheet of this invention for bonding of a display panel and the transparent member (touch panel) which has a transparent conductive film in surface layer, the level | step difference of a bezel can be covered.

As an example of the manufacturing method, first, a master batch is prepared by adding a predetermined amount of tackifier to the polyol component and dissolving it by heating and stirring. Subsequently, the obtained masterbatch, polyol component, polyisocyanate component, silane coupling agent, and, if necessary, other components such as a catalyst and the like are mixed and stirred by a mixer or the like to form a liquid or gel. A thermosetting polyurethane composition is obtained. Thereafter, the thermosetting polyurethane composition is immediately charged into a molding apparatus, and the thermosetting polyurethane composition is moved while being moved between the first and second release films, thereby causing crosslinking and curing. The polyurethane composition is semi-cured to obtain a sheet integrated with the first and second release films. Thereafter, a cross-linking reaction is carried out in a furnace for a fixed time to obtain an optically transparent pressure-sensitive adhesive sheet comprising a cured product of a thermosetting polyurethane composition, and the laminate sheet of the present invention is completed.

FIG. 5: is a schematic diagram for demonstrating an example of the shaping | molding apparatus used for preparation of the optical transparent adhesive sheet of this invention. In the forming apparatus 20 shown in FIG. 5, first, a pair of release films in which the liquid or gel thermosetting polyurethane composition 23 before curing is continuously fed out from a pair of forming rolls 22 disposed apart from each other. (PET film) 21 is poured into the gap. Then, while the thermosetting polyurethane composition 23 is held in the gap between the pair of release films 21, it is carried into the heating device 24 while advancing the curing reaction (crosslinking reaction). In the heating device 24, the thermosetting polyurethane composition 23 is thermally cured in a state of being held between a pair of release films (PET film) 21, and an optically transparent adhesive sheet comprising a cured product of the thermoplastic polyurethane composition The molding of 12 is completed.

As a process 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 apparatus, bar coat, doctor blade or the like and a film forming method are used. It may be. In addition, the optical transparent pressure-sensitive adhesive sheet of the present invention may be produced using a centrifugal molding method.

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

Example 1
100 parts by weight of a polyolefin polyol ("EPOL (registered trademark)" manufactured by Idemitsu Kosan Co., Ltd., number average molecular weight: 2500), 10 parts by weight of a modified polyisocyanate ("Coronato 4022" manufactured by Tosoh Corp.) having a hydrophilic unit, 1.3 parts by weight of 3-triethoxysilyl-N- (1,3-dimethyl-butylidene) propylamine, 20 parts by weight of hydrogenated petroleum resin-based tackifier (Iimab P-100 manufactured by Idemitsu Kosan Co., Ltd.), and And 0.05 parts by weight of dimethyltin dilaurate ("Fomrez catalyst UL-28" manufactured by Momentive) using a reciprocating rotary agitator, and a thermosetting polyurethane having an α ratio of 1.35. The composition was prepared.

Thereafter, the obtained thermosetting polyurethane composition was injected into the molding apparatus 20 shown in FIG. Then, while conveying the thermosetting polyurethane composition in a state of being sandwiched by a pair of release films (PET film whose surface has been subjected to release treatment) 21, conditions of an oven temperature of 70 ° C. and an oven time of 10 minutes It was cross-linked and hardened. Then, the crosslinking reaction was performed for 12 hours by the heating device 24 adjusted to 70 ° C., and an optically transparent adhesive sheet 12 made of a cured product of the thermosetting polyurethane composition was produced. The thickness of the optical transparent adhesive sheet 12 was 300 μm.

Optically bonded to a transparent glass substrate (soda glass manufactured by Matsunami Glass Co., Ltd.) by vacuum bonding one surface of the optical transparent adhesive sheet from which the mold release film was peeled off at a pressure of 0.15 MPa and peeling the mold release film Also on the other side of the transparent adhesive sheet, a transparent glass substrate (soda glass manufactured by Matsunami Glass Co., Ltd.) was vacuum bonded at a pressure of 0.15 MPa. By this bonding, a first laminate (glass / OCA / glass) in which the glass substrates were bonded to each other by the optically transparent adhesive sheet was obtained.

In addition, one side of the optical transparent adhesive sheet from which the mold release film is peeled is vacuum bonded to a transparent glass substrate (soda glass manufactured by Matsunami Glass Industrial Co., Ltd.) under a pressure of 0.15 MPa, and the mold release film is peeled off. A 2 mm-thick resin substrate was vacuum bonded to the other surface of the resulting optical transparent pressure-sensitive adhesive sheet at a pressure of 0.15 MPa. As a resin base material, hard coating is applied to both sides of "UW2-070" manufactured by Kuraray Co., Ltd., which is a resin board obtained by acrylic primer treatment of one side of a polycarbonate board ("MT2LX" manufactured by Kuraray Co., Ltd.) An optical transparent adhesive sheet was pasted to the side which has not been subjected to the acrylic primer treatment using the one to which "PMR" was applied. By this bonding, a second laminate (PC / OCA / glass) was obtained in which a polycarbonate resin base and a glass base were bonded by an optical transparent adhesive sheet.

Finally, the first and second laminates obtained were heated at 85 ° C. for 1 hour. Before heating, bonding of the glass substrate and the optical transparent adhesive sheet, and bonding of the resin substrate and the optical transparent adhesive sheet can be easily peeled off, and the optical transparent adhesive sheet may be used if necessary. It was possible to paste again. On the other hand, after heating, the optically transparent adhesive sheet is chemically bonded to the surfaces of the glass substrate and the resin substrate, and the glass substrates (in the case of the first laminate), and the glass substrate and the resin substrate (In the case of the second laminate) was firmly adhered by the optically clear pressure-sensitive adhesive sheet. In addition, although it heated in order to shorten the time which adhesion | attachment requires, sufficient adhesive strength is obtained only by leaving it to stand at normal temperature for about 1 day.

(Examples 2 to 4 and Comparative Examples 1 to 3)
As shown in Table 1 below, in the same manner as Example 1, except that the α ratio in the thermosetting polyurethane composition, the presence or absence of the addition of the silane coupling agent, and the thickness of the optical transparent adhesive sheet were changed. The optical transparent adhesive sheet with the release film which concerns on Examples 2-4 and Comparative Examples 1-3 was produced, respectively. And the 1st laminated body and the 2nd laminated body were obtained using the optical transparent adhesive sheet which concerns on Examples 2-4 and Comparative Examples 1-3.

(Evaluation test)
(1) Measurement of loss tangent (tan δ) The loss tangent of the optically transparent pressure-sensitive adhesive sheet was measured using a viscoelasticity measuring apparatus “Physica MCR 301” manufactured by Anton Paar Germany GmbH. The measurement plate was made of PP12, and the measurement conditions were: strain 0.1%, frequency 1 Hz, cell temperature 25 ° C. to 100 ° C. (heating rate 3 ° C./min). Table 1 below shows measured values of loss tangent at 85 ° C.

(2) Measurement of Adhesive Strength The 180 ° peel test was conducted by the method shown in FIG. 2 to measure the adhesive strength (N / 25 mm). Specifically, the optical transparent adhesive sheet with a release film was cut into a length of 75 mm × width 25 mm as a test piece. After peeling the release film on one side of this test piece, the optical transparent adhesive sheet 12 side is attached to the base material 31 of length 75 mm × width 25 mm, and held for 30 minutes at a pressure of 0.4 MPa. 12 and the base material 31 were bonded together. Next, the release film on the side opposite to the substrate 31 is peeled off, and as shown in FIG. 2 (a), a PET sheet with a thickness of 125 μm on the side opposite to the substrate 31 of the optical transparent adhesive sheet 12 ("Melinex (registered trademark) S" manufactured by Teijin DuPont Films, Inc.) 32 was laminated. Then, after standing for 12 hours under normal temperature and normal humidity (temperature 23 ° C., humidity 50%), as shown in FIG. 2 (b), the PET sheet 32 is pulled in the direction of 180 ° to make the optically transparent adhesive sheet 12 It was made to peel at the interface with the material 31, and the adhesion of the optical transparent adhesive sheet 12 to the substrate 31 was measured.

In addition, the measurement was performed about "the adhesion to glass force" when a glass plate is used as the base material 31, and "the adhesion to PC resistance" when a polycarbonate plate is used as the base material 31, respectively. Further, the adhesive strength immediately after bonding (initial adhesive strength) and the adhesive power after being put into an environment of 85 ° C. for 2 hours (adhesive strength after high temperature test) were measured. Each measurement was performed by preparing two test pieces for each example and comparative example, and the average value of the two measured values obtained was taken as the measurement result in each example and comparative example.

(3) Foam resistance test Each of the first laminate (glass / OCA / glass) and the second laminate (PC / OCA / glass) according to Examples 1 to 4 and Comparative Examples 1 to 3 was prepared. At the time, no bubbles of visible size were generated when viewed from the transparent glass substrate side. These laminates were stored at 85 ° C. and 10% RH for 96 hours, then, the laminates were visually observed from the transparent glass substrate side, and the occurrence of delayed bubbles was determined according to the following criteria. The test results are shown in Table 1 below.
◎: No delayed bubble was generated at the bonding interface between the resin base material (PC) and the glass base material.
○: No delayed bubble was generated at the bonding interface with the glass substrate.
Δ: Small spherical delayed bubbles were observed.
X: A large delayed bubble was generated on the entire surface of the bonding interface.

As can be seen from Table 1, the optically transparent pressure-sensitive adhesive sheets of Examples 1 to 4 in which a silane coupling agent was added and the loss tangent (tan δ) at 85 ° C. was 0.50 or less exhibited adhesion when heated. As a result, improved adhesion strength to the adherend is obtained, and delayed bubbles are generated in both the first laminate (glass / OCA / glass) and the second laminate (PC / OCA / glass). It was not. On the other hand, the optically transparent adhesive sheets of Comparative Examples 1 and 3 in which the loss tangent (tan δ) at 85 ° C. was greater than 0.50 did not generate delayed bubbles in the first laminate (glass / OCA / glass) However, delayed bubbles occurred in the second laminate (PC / OCA / glass). Moreover, although the loss tangent (tan δ) at 85 ° C. was 0.50 or less, the optically transparent adhesive sheet of Comparative Example 2 in which the silane coupling agent was not added was a first laminate (glass / OCA / In the second laminate (PC / OCA / glass), large delayed bubbles were generated in the entire surface of the bonding interface. In addition, the optical transparent pressure-sensitive adhesive sheet of Comparative Example 2 did not improve in adhesion even when heated, and sufficient adhesion strength to an adherend was not obtained.

DESCRIPTION OF SYMBOLS 10 display device 11 display panel 11A bezel 12 optical transparent adhesive sheet 13 touch panel 14 transparent cover panel 20 forming device 21 release film 22 forming roll 23 thermosetting polyurethane composition 24 heating device 31 base 32 PET sheet 51 glass base 52 Resin base material 60 air bubble (late bubble)
61 water 100 adherend

Claims (11)

It is an optical transparent adhesive sheet made of thermosetting polyurethane,
The thermosetting polyurethane is a cured product of a thermosetting polyurethane composition containing a polyol component, a polyisocyanate component and a silane coupling agent, and the loss tangent (tan δ) at 85 ° C. is 0.50 or less Optically transparent adhesive sheet characterized by. The thickness is 250-2000 micrometers, The optically transparent adhesive sheet of Claim 1 characterized by the above-mentioned. The optical transparency according to claim 1 or 2, wherein the initial adhesion is 5 N / 25 mm or less and the adhesion after holding for 2 hours at 50 ° C. is 10 N / 25 mm or more. Adhesive sheet. The adhesive strength to the surface of polycarbonate is 5 N / 25 mm or less, and the adhesive strength after holding for 2 hours at 50 ° C. is 10 N / 25 mm or more. Optical transparent adhesive sheet as described. The optically transparent adhesive sheet according to any one of claims 1 to 4, wherein the polyol component contains an olefin-based polyol. The optically transparent pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein a first adherend, a second adherend, the first adherend and the second adherend are joined. A laminate comprising: The laminate according to claim 6, wherein the first adherend is a glass substrate. The laminate according to claim 6 or 7, wherein the second adherend is a resin base material. The said resin base material contains a polycarbonate, The laminated body of Claim 8 characterized by the above-mentioned. It is a manufacturing method of the optical transparent adhesive sheet in any one of Claims 1-5, Comprising:
Preparing the thermosetting polyurethane composition by stirring and mixing the polyol component, the polyisocyanate component, and the silane coupling agent;
Curing the thermosetting polyurethane composition. The optical transparent adhesive sheet according to any one of claims 1 to 5, 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 laminated sheet characterized in that a release film and a laminated film are laminated.

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