JP2015030765A - Pressure-sensitive adhesive sheet, optical film with pressure-sensitive adhesive layer, and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure-sensitive adhesive sheet that suppresses display irregularity of an image display device and has little squeeze-out from an end face when used for bonding among a front transparent plate, a touch panel, and an image display panel, and to provide an optical film and an image display device including the pressure-sensitive adhesive sheet.SOLUTION: The pressure-sensitive adhesive sheet preferably shows a loss tangent tanδ of 0.60 or more at 50°C and 0.01 Hz and a loss tangent tanδ of 1.00 or less at 50°C and 0.001 Hz. A pressure-sensitive adhesive sheet 22 is used, for example, for bonding a front transparent plate 70 having a printed stepped portion 70a and an optical film 10 to be disposed on a surface of an image display panel 60.

Description

  The present invention relates to an adhesive sheet used for forming an image display device including a transparent plate, a touch panel, and the like on the front surface of an image display panel. Furthermore, this invention relates to the optical film with an adhesive layer provided with the said adhesive sheet, and an image display apparatus.

  Liquid crystal display devices and organic EL display devices are widely used as various image display devices such as mobile phones, car navigation devices, personal computer monitors, and televisions. For the purpose of preventing damage to the image display panel due to impact from the outer surface of the image display panel (liquid crystal panel or organic EL panel), a transparent front plate such as a transparent resin plate or glass plate (“ Also referred to as “window layer” or the like. In an image display device having a touch panel on the viewing side surface, a front transparent plate is provided on the viewing side of the touch panel.

  As a method of disposing a front transparent plate on the front surface of an image display panel or a touch panel, an “interlayer filling structure” in which both are bonded via an adhesive material layer is employed. In the interlayer filling structure, since the space between the panel and the front transparent plate is filled with an adhesive, the difference in the refractive index at the interface is reduced, and the reduction in visibility due to reflection and scattering is suppressed. Moreover, since the strength of the entire image display device is increased by filling the pressure-sensitive adhesive, even when the front transparent plate or the like is damaged, an effect of preventing scattering of glass or the like as a forming material can be obtained (for example, (See Patent Documents 1 and 2).

  A colored layer for the purpose of decoration and light shielding is formed by printing on the peripheral edge of the panel side surface of the front transparent plate. When a colored layer is formed on the peripheral edge of the transparent plate, a printing step of about 10 μm to several tens of μm occurs. When a sheet-like pressure-sensitive adhesive is used as an interlayer filler, bubbles are likely to be generated around the printed step. In view of such a problem, in Patent Document 3 and Patent Document 4, the storage elastic modulus and gel fraction of the pressure-sensitive adhesive are reduced to reduce the residual stress of the pressure-sensitive adhesive in the vicinity of the printing step, thereby making it possible to follow the step (step absorption). It has been proposed to suppress the generation of bubbles.

JP 2009-8851 A JP 2008-281997 A JP 2011-74308 A JP 2011-74308 A

  As described above, when a sheet-like pressure-sensitive adhesive is used as an interlayer filler, there is a problem that bubbles are likely to be generated around the printing step portion. In addition, when the front transparent plate having a printing step and the panel are bonded together via a sheet-like adhesive, due to stress strain applied to the adhesive around the printing step portion, the peripheral portion of the image display panel There is a problem that display unevenness is likely to occur.

  On the other hand, when an adhesive having a low storage elastic modulus and high fluidity is used for the purpose of suppressing display unevenness, the sheet tends to protrude from the end face when the sheet is cut to a predetermined size or bonded. is there. In addition, in the process of forming an image display device, in order to suppress the generation of bubbles (delay bubbles) around the printed step after bonding, pressurization / heating treatment such as autoclave treatment is often performed. At this time, the sticking out of the adhesive end face tends to occur.

  In view of the above, the present invention reduces display unevenness of the image display panel when sticking between layers of the front transparent plate, the touch panel, the image display panel, etc., and the adhesive protrudes from the end surface even in a high temperature environment. It is an object of the present invention to provide a pressure-sensitive adhesive sheet that is difficult to cause, an optical film including the pressure-sensitive adhesive sheet, and an image display device.

  As a result of investigations by the present inventors, it has been found that the above-mentioned problems can be solved by giving the adhesive sheet predetermined viscoelastic properties, and the present invention has been achieved. That is, the present invention relates to a pressure-sensitive adhesive sheet having a loss tangent tan δ at 50 ° C. and 0.01 Hz of 0.60 or more and a loss tangent tan δ at 50 ° C. and 0.001 Hz of 1.00 or less. In one embodiment, the thickness of the pressure sensitive adhesive sheet of the present invention is 25 micrometers or more.

  The pressure-sensitive adhesive sheet of the present invention is suitably used as an interlayer filler for bonding between the front transparent plate and the touch panel, between the front transparent plate and the image display panel, or between the touch panel and the image display panel. It is done.

  In the pressure-sensitive adhesive sheet of the present invention, the loss tangent tan δ at 50 ° C. and 0.001 Hz is preferably smaller than the loss tangent tan δ at 50 ° C. and 0.01 Hz. The pressure-sensitive adhesive sheet of the present invention preferably has a storage elastic modulus G ′ at 50 ° C. and 0.001 Hz of 0.2 kPa to 7 kPa. The pressure-sensitive adhesive sheet of the present invention preferably has a storage elastic modulus G ′ at 50 ° C. and 0.01 Hz of 0.7 kPa to 10 kPa.

  The pressure-sensitive adhesive constituting the pressure-sensitive adhesive sheet of the present invention preferably contains 50% by weight or more of an acrylic base polymer. As the acrylic base polymer, as a monomer unit, a (meth) acrylic acid alkyl ester having a linear alkyl group; a (meth) acrylic acid alkyl ester having a branched alkyl group; and a polymerization having an unsaturated double bond It is preferable to contain a polyfunctional monomer having two or more functional groups. The acrylic base polymer preferably further contains a nitrogen-containing monomer as a monomer unit.

  Furthermore, this invention relates to the optical film with an adhesive layer and image display apparatus provided with the said adhesive sheet.

  Since the tan δ at 50 ° C. and 0.01 Hz is 0.60 or more, the pressure-sensitive adhesive sheet of the present invention has air bubbles in the vicinity of the step portion even when the front transparent member having a printed step is used as an adherend. And the occurrence of display unevenness are suppressed. In addition, since tan δ at 50 ° C. and 0.001 Hz is 1.00 or less, even if the tan δ is exposed to a high temperature environment for a long time, the protrusion of the adhesive from the end face is suppressed.

It is sectional drawing which represents typically one Embodiment of an image display apparatus. It is sectional drawing which represents typically one Embodiment of the optical film with an adhesion layer. It is sectional drawing which represents typically one Embodiment of the optical film with an adhesion layer. It is a graph showing the frequency dependence of the loss tangent tan-delta in 50 degreeC of the adhesive sheet of an Example and a comparative example. It is a graph showing the frequency dependence of the storage elastic modulus G 'at 50 degreeC of the adhesive sheet of an Example and a comparative example.

[Physical properties of adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention is a sheet in which a pressure-sensitive adhesive is formed. The pressure-sensitive adhesive sheet preferably has a loss tangent tan δ at a measurement temperature of 50 ° C. and a frequency of 0.01 Hz of 0.60 or more and a loss tangent tan δ at a measurement temperature of 50 ° C. and a frequency of 0.001 Hz of 1.00 or less. The loss tangent tan δ is a ratio G ″ / G ′ of the storage shear modulus G ′ and the loss modulus G ″. The storage elastic modulus G ′ corresponds to a portion stored as elastic energy when the material is deformed, and is an index representing the degree of hardness. On the other hand, the loss elastic modulus G ″ corresponds to a loss energy portion that is dissipated due to internal friction or the like when the material is deformed, and represents the degree of viscosity. The larger tan δ, the stronger the tendency of viscosity, and the deformation behavior is liquid. Thus, the resilience energy tends to be small.

  The storage elastic modulus G ′ and the loss elastic modulus G ″ are 10 Hz to 0.001 Hz at a temperature of 50 ° C. in accordance with the method described in JIS K7244-1 “Plastics—Testing Method for Dynamic Mechanical Properties”. It is obtained by reading a value at a predetermined frequency (0.01 Hz and 0.001 Hz) when measurement is performed while changing the frequency in the range. In this specification, unless otherwise specified, the storage elastic modulus G ′, the loss elastic modulus G ″, and the loss tangent tan δ are measured values at 50 ° C.

  If tan δ at 0.01 Hz is 0.60 or more, display unevenness of the image display device tends to be suppressed when the adhesive sheet is used as an interlayer filler. The tan δ at 0.01 Hz is more preferably 0.70 or more, and further preferably 0.80 or more. The larger tan δ at 0.01 Hz, the easier it is for the adhesive to follow the shape of a non-flat part such as a step, so even when the front transparent member has a non-flat part, the generation of voids is suppressed, and the image display panel It is estimated that display unevenness is suppressed. On the other hand, if tan δ is excessively large, the fluidity of the pressure-sensitive adhesive in the heat-bonding environment increases, and problems such as transfer of the pressure-sensitive adhesive and protrusion from the end surface may occur. Therefore, tan δ at 0.01 Hz is preferably 1.50 or less, more preferably 1.40 or less, further preferably 1.30 or less, and particularly preferably 1.20 or less.

  If tan δ at 0.001 Hz is 1.00 or less, even if the pressure-sensitive adhesive sheet (or an optical member bonded through the pressure-sensitive adhesive sheet) is exposed to a high temperature (for example, about 85 ° C.) for a long time, the end face There is a tendency that the sticking out of the adhesive is suppressed. The tan δ at 0.001 Hz is more preferably 0.95 or less, and further preferably 0.90 or less. On the other hand, if tan δ is excessively small, the adhesive force is insufficient, and the pressure-sensitive adhesive sheet may be lifted or peeled off. Therefore, tan δ at 0.001 Hz is preferably 0.30 or more, more preferably 0.40 or more, and further preferably 0.50 or more.

  It is preferable that tan δ at 0.001 Hz of the pressure-sensitive adhesive sheet is smaller than tan δ at 0.01 Hz. The tan δ at 0.001 Hz is more preferably 0.95 times or less, and further preferably 0.92 times or less than tan δ at 0.01 Hz. When tan δ at 0.001 Hz is smaller than tan δ at 0.01 Hz, there is a tendency that suppression of display unevenness and suppression of the protrusion of the adhesive can be achieved more reliably.

  For viscoelasticity such as adhesives, a conversion rule is established between temperature and time (frequency). When the measurement temperature is constant, the frequency is increased (the time scale is shortened), and when the frequency is constant, the measurement temperature is decreased. In some cases, it is known to show similar behavior. Therefore, the value of tan δ at 0.001 Hz being smaller than the value of tan δ at 0.01 Hz means that tan δ is small in a higher temperature range (that is, the viscous behavior is small and the elastic behavior is large). The pressure-sensitive adhesive sheet of the present invention has a relatively large viscous behavior on the low temperature side, so that the pressure-sensitive adhesive easily follows steps, etc., and has a relatively large elastic behavior on the high temperature side, so that the pressure-sensitive adhesive protrudes at a high temperature. Is considered to be reduced.

  The storage elastic modulus G ′ at a frequency of 0.001 Hz of the pressure-sensitive adhesive sheet is preferably 0.1 kPa to 7 kPa, more preferably 0.3 kPa to 3 kPa, further preferably 0.5 kPa to 2 kPa, and particularly preferably 0.7 kPa to 1.8 kPa. preferable. The storage elastic modulus G 'at a frequency of 0.01 Hz is preferably 0.7 kPa to 10 kPa, more preferably 0.9 kPa to 7 kPa, and even more preferably 1.5 kPa to 5 kPa. If the storage elastic modulus G ′ is in the above range, the pressure-sensitive adhesive has an appropriate hardness, so that pressure-out of the pressure-sensitive adhesive from the end face when pressure is applied at the time of bonding or after heating is suppressed. Tend.

  The loss elastic modulus G ″ at a frequency of 0.001 Hz of the pressure-sensitive adhesive sheet is preferably from 0.1 kPa to 5 kPa, more preferably from 0.2 kPa to 2.5 kPa, and even more preferably from 0.3 kPa to 1.5 kPa. G ″ is preferably 0.8 kPa to 15 kPa, more preferably 1 kPa to 10 kPa, and even more preferably 1.8 kPa to 7 kPa. If the loss modulus G ″ is within the above range, the pressure-sensitive adhesive has an appropriate viscosity, so that elastic stress at the time of bonding is dissipated, and bubbles are generated due to concentration of stress on the pressure-sensitive adhesive in the vicinity of the stepped portion. There is a tendency that problems such as display unevenness are suppressed.

  G 'at 0.01 Hz is preferably in the range of 1.5 to 5 times G' at 0.001 Hz, more preferably in the range of 2 to 4 times, and still more preferably in the range of 2.5 to 3.6 times. G ″ at 0.01 Hz is preferably in the range of 2.5 to 6 times G ″ at 0.001 Hz, more preferably in the range of 2 to 5 times, and still more preferably in the range of 3 to 4.5 times. When the storage elastic modulus G ′ and the loss elastic modulus G ″ exhibit frequency dependency as described above, there is a tendency that both suppression of display unevenness and suppression of sticking out of the adhesive can be achieved more reliably.

[Adhesive Composition (Preparation of Adhesive Composition)]
The composition of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive sheet of the present invention is not particularly limited, and is an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate / vinyl chloride copolymer, modified polyolefin, epoxy-based, fluorine-based. Those having a base polymer of a rubber-based polymer such as natural rubber or synthetic rubber can be appropriately selected and used. In particular, an acrylic polymer containing an acrylic polymer as a base polymer from the viewpoint of excellent optical transparency, adhesive properties such as moderate wettability, cohesiveness, and adhesiveness, and excellent weather resistance and heat resistance. An adhesive is preferably used.

  The content of the acrylic base polymer in the pressure-sensitive adhesive sheet is preferably 50% by weight or more, more preferably 60% by weight or more. The acrylic base polymer has a monomer unit of (meth) acrylic acid alkyl ester as a main skeleton. In the present specification, “(meth) acryl” means acryl and / or methacryl.

  As said (meth) acrylic-acid alkylester, the (meth) acrylic-acid alkylester whose carbon number of an alkyl group is 1-20 is used suitably. For example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, s-butyl (meth) acrylate, t-butyl (meth) acrylate, (meta ) Pentyl acrylate, isopentyl (meth) acrylate, neopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, ( Isooctyl acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, (meth) ) Isotridodecyl acrylate, tetradecyl (meth) acrylate, (meta Isotetradecyl acrylate, pentadecyl (meth) acrylate, cetyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, isooctadecyl (meth) acrylate, nonadecyl (meth) acrylate, ( Examples include araalkyl methacrylate.

  From the viewpoint of imparting viscosity to the pressure-sensitive adhesive and increasing the loss tangent tan δ at 0.01 Hz, the acrylic base polymer has a branched alkyl group as a monomer unit of the (meth) acrylic acid alkyl ester (meth). It is preferable to contain an alkyl acrylate. Among the exemplified monomers, examples of the branched alkyl (meth) acrylate include 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, isodecyl (meth) acrylate, ( (Meth) isotetradecyl acrylate, isooctadecyl (meth) acrylate and the like are preferably used. In addition, 2 or more types of branched alkyl (meth) acrylic acid esters can be used in combination. Moreover, these branched alkyl (meth) acrylic acid esters may be used in combination with a linear alkyl (meth) acrylic acid ester.

  The content of the (meth) acrylic acid alkyl ester is preferably 40% by weight or more, more preferably 50% by weight or more, and still more preferably 60% by weight or more based on the total amount of monomer components constituting the base polymer. is there. Alkyl group has branching with respect to the total amount of (meth) acrylic acid alkyl ester component (total of (meth) acrylic acid alkyl ester with linear alkyl group and (meth) acrylic acid alkyl ester with alkyl group having branching) The content of the (meth) acrylic acid alkyl ester is preferably 20% by weight to 80% by weight, and more preferably 30% by weight to 70% by weight.

  The acrylic base polymer preferably contains a highly polar monomer unit in addition to the above (meth) acrylic acid alkyl ester. Examples of the polar monomer unit include a nitrogen-containing monomer, a hydroxyl group-containing monomer, and a carboxy group-containing monomer. Among these, a nitrogen-containing monomer and a hydroxyl group-containing monomer are preferably used because the pressure-sensitive adhesive has high adhesiveness and holding power and can maintain high transparency even when exposed to a high temperature environment.

  Examples of the nitrogen-containing monomer include N-vinylpyrrolidone, methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine, vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinyloxazole, vinylmorpholine, (meth) acryloylmorpholine, N- Examples thereof include vinyl monomers such as vinyl carboxylic acid amides and N-vinyl caprolactam, and cyanoacrylate monomers such as acrylonitrile and methacrylonitrile. Of these, N-vinylpyrrolidone and (meth) acryloylmorpholine are preferably used. By including a nitrogen-containing monomer unit in the adhesive, the cohesive force of the adhesive is improved and the adhesiveness of the adhesive sheet to the adherend is increased, and the whitening of the adhesive in a high-temperature, high-humidity environment is suppressed. it can.

  Examples of the hydroxy group-containing monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, (meth) Alcoholic hydroxy group-containing (meth) acrylic esters such as 8-hydroxyoctyl acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate and (4-hydroxymethylcyclohexyl) -methyl acrylate Is preferably used. Examples of the carboxyl group-containing monomer include (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid, and crotonic acid. By containing a hydroxy group-containing monomer unit or a carboxy group-containing monomer unit in the base polymer, the cohesive force of the pressure-sensitive adhesive is improved, and the adhesiveness of the pressure-sensitive adhesive sheet to the adherend is enhanced. In addition, since a crosslinking point is introduced into the base polymer, a crosslinked structure can be introduced between the polymer chains to enhance the cohesiveness.

  The proportion of the polar group-containing monomer component in the base polymer is not particularly limited, but is preferably 3 to 40% by weight, more preferably 5 to 35% by weight, and more preferably 10 to 30% by weight based on the total amount of the constituent monomer components. . If content of a polar group containing monomer is 3 weight% or more, while improving adhesiveness, the cloudiness of the adhesive in a high temperature, high humidity environment can be suppressed.

  The said polar group containing monomer can be used individually or in combination of 2 or more types. In particular, in the pressure-sensitive adhesive sheet of the present invention, the base polymer constituting the pressure-sensitive adhesive preferably contains a nitrogen-containing monomer component. The proportion of the nitrogen-containing monomer in the base polymer is preferably from 3 to 40% by weight, more preferably from 5 to 35% by weight, and even more preferably from 10 to 30% by weight, based on the total amount of the constituent monomer components. When the content of the polar group-containing monomer is excessively large, the cohesive force of the pressure-sensitive adhesive becomes too high, and tan δ is decreased, which may cause display unevenness in the image display device. In particular, when a crosslinking point is introduced by a hydroxy group-containing monomer or a carboxy group-containing monomer, the cohesive force tends to increase. Although depending on the content of the crosslinking agent and the polyfunctional monomer component, the total content of the hydroxy group-containing monomer component and the carboxy group-containing monomer component in the base polymer is preferably 30% by weight or less, more preferably 20% by weight or less. It is preferably 10% by weight or less.

  In addition to the above, an acid anhydride group-containing monomer, an acrylic acid caprolactone adduct, a sulfonic acid group-containing monomer, a phosphoric acid group-containing monomer, and the like can also be used as a copolymerization monomer component of the base polymer. Further, as the modifying monomer, vinyl monomers such as vinyl acetate, vinyl propionate, styrene, α-methylstyrene; epoxy group-containing acrylic monomers such as glycidyl (meth) acrylate; polyethylene glycol (meth) acrylate, ( Glycol acrylic ester monomers such as (meth) acrylic acid polypropylene glycol, (meth) acrylic acid methoxyethylene glycol, (meth) acrylic acid methoxypolypropylene glycol; (meth) acrylic acid tetrahydrofurfuryl, fluorine (meth) acrylate, silicone (meta ) Acrylic acid ester monomers such as acrylate and 2-methoxyethyl acrylate can also be used.

  The monomer component that forms the acrylic base polymer may contain a polyfunctional monomer as necessary in addition to the monofunctional monomer exemplified above. By having a polyfunctional monomer as a copolymerization monomer component, the storage elastic modulus G ′ of the pressure-sensitive adhesive tends to be increased, and tan δ tends to decrease. Therefore, the tan δ of the pressure-sensitive adhesive can be adjusted to a desired range by changing the content of the polyfunctional monomer component. Moreover, by containing a polyfunctional monomer as a copolymerization monomer component, tan δ at 0.001 Hz tends to exhibit viscoelastic behavior smaller than tan δ at 0.01 Hz. Therefore, by adjusting the content of the polyfunctional monomer in the copolymerization monomer component, it is possible to easily form an adhesive that can achieve both suppression of display unevenness and suppression of the protrusion of the adhesive.

  The polyfunctional monomer is a monomer having at least two polymerizable functional groups having an unsaturated double bond such as a (meth) acryloyl group or a vinyl group. For example, (poly) ethylene glycol di (methacrylate), (poly ) Propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, 1,2-ethylene glycol di (Meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,12-dodecanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylol methanetri (meth) acrelane Ester compounds of polyhydric alcohols such as (meth) acrylic acid; allyl (meth) acrylate, vinyl (meth) acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butyl di (meth) acrylate, hexyl di (meth) Among them, trimethylolpropane tri (meth) acrylate, hexanediol di (meth) acrylate, dipentaerythritol hexa (meth) acrylate can be suitably used. Can be used alone or in combination of two or more.

  The amount of the polyfunctional monomer used varies depending on the molecular weight and the number of functional groups, but is preferably 3% by weight or less, more preferably 2% by weight or less, and more preferably 1% by weight with respect to all monomer components forming the acrylic base polymer. % Or less is more preferable. When the amount of the polyfunctional monomer used exceeds 3% by weight, the tan δ of the pressure-sensitive adhesive is excessively lowered, and bubbles are likely to be mixed in the vicinity of the step portion and display unevenness of the image display panel is likely to occur.

  The above-mentioned acrylic base polymer can be prepared by a known polymerization method such as solution polymerization, UV polymerization, bulk polymerization, emulsion polymerization, or the like as described above. A solution polymerization method or an active energy ray polymerization method (for example, UV polymerization) is preferable in terms of transparency, water resistance, cost, and the like of the pressure-sensitive adhesive. As a solvent for solution polymerization, ethyl acetate, toluene or the like is generally used. The solution concentration is usually about 20 to 80% by weight. The reaction temperature is usually about 50 to 80 ° C., and the reaction time is usually about 1 to 8 hours.

  In preparing the acrylic base polymer, a polymerization initiator such as a photopolymerization initiator or a thermal polymerization initiator may be used depending on the type of polymerization reaction. The photopolymerization initiator is not particularly limited as long as it initiates photopolymerization. For example, benzoin ether photopolymerization initiator, acetophenone photopolymerization initiator, α-ketol photopolymerization initiator, aromatic sulfonyl Chloride photopolymerization initiator, photoactive oxime photopolymerization initiator, benzoin photopolymerization initiator, benzyl photopolymerization initiator, benzophenone photopolymerization initiator, ketal photopolymerization initiator, thioxanthone photopolymerization initiator An acylphosphine oxide photopolymerization initiator can be used. Examples of the thermal polymerization initiator include an azo initiator, a peroxide initiator, a redox initiator in which a peroxide and a reducing agent are combined (for example, a combination of a persulfate and sodium bisulfite, a peroxide) A combination of a product and sodium ascorbate).

  A polymerization initiator may be used independently and may be used in combination of 2 or more type. The amount of the polymerization initiator used is not particularly limited, but is preferably about 0.005 to 5 parts by weight, for example, 0.02 to 3 parts by weight with respect to 100 parts by weight of the total amount of monomer components forming the acrylic base polymer. The degree is more preferred.

  A chain transfer agent may be used to adjust the molecular weight of the base polymer. The chain transfer agent receives radicals from the growing polymer chain to stop the elongation of the polymer, and the chain transfer agent that receives the registrar can attack the monomer and start polymerization again. Therefore, by using a chain transfer agent, an increase in the molecular weight of the base polymer is suppressed without lowering the radical concentration in the reaction system, and an adhesive sheet having a high tan δ can be obtained.

  Examples of the chain transfer agent include thiols such as α-thioglycerol, lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. Are preferably used.

  A chain transfer agent may be used independently and may be used in mixture of 2 or more types. The amount of the chain transfer agent used is not particularly limited, but for example, it is preferably 2 parts by weight or less, more preferably 1 part by weight or less, based on 100 parts by weight of the total amount of monomer components forming the acrylic base polymer.

  The acrylic base polymer obtained may be any of a random copolymer, a block copolymer, a graft copolymer, and the like. The weight average molecular weight of the acrylic base polymer can be controlled by the amount of polymerization initiator used, the amount of chain transfer agent used, the reaction conditions, and the like.

  If the monomer component that forms the acrylic base polymer contains a polyfunctional monomer in addition to a monofunctional monomer, the monofunctional monomer is first polymerized to form a prepolymer composition with a low polymerization rate (preliminary polymerization) A polyfunctional monomer may be added to the syrup of the prepolymer composition to polymerize (post-polymerize) the prepolymer and the polyfunctional monomer. In this way, by performing prepolymerization of the prepolymer, branch points caused by the polyfunctional monomer component can be uniformly introduced into the base polymer. Moreover, after apply | coating the mixture (adhesive composition) of a prepolymer composition and an unpolymerized monomer component on a base material, post-polymerization may be performed on a base material and an adhesive sheet may be formed. Since the prepolymer composition has a low viscosity and excellent coating properties, the adhesive composition, which is a mixture of the prepolymer composition and the unpolymerized monomer, is subjected to post-polymerization on the substrate after coating, Productivity is improved and the thickness of the pressure-sensitive adhesive sheet can be made uniform.

  The prepolymer composition is, for example, a composition in which a monomer component (referred to as “monomer component A”) composing an acrylic base polymer and a polymerization initiator are mixed (referred to as “prepolymer-forming composition”), It can be prepared by partial polymerization (preliminary polymerization). The monomer component A in the prepolymer-forming composition is a monofunctional monomer component such as a (meth) acrylic acid alkyl ester or a polar group-containing monomer among the monomer components constituting the acrylic base polymer. preferable. The monomer component A may contain not only a monofunctional monomer but also a polyfunctional monomer. For example, a part of the polyfunctional monomer component used as the raw material for the base polymer may be contained in the prepolymer-forming composition, and the remainder of the polyfunctional monomer component may be added to the prepolymer after polymerization to be subjected to post-polymerization.

  The prepolymer-forming composition may contain a chain transfer agent or the like as necessary in addition to the monomer component A and the polymerization initiator. The polymerization method of the composition for forming a prepolymer is not particularly limited, but from the viewpoint of adjusting the reaction time and setting the molecular weight (polymerization rate) of the prepolymer to a desired range, polymerization by irradiation with actinic rays such as UV light is preferable. . The polymerization initiator and chain transfer agent used for the preliminary polymerization are not particularly limited, and for example, the above-described photopolymerization initiator and chain transfer agent can be used.

Although the polymerization rate of a prepolymer is not specifically limited, From the viewpoint of setting it as the viscosity suitable for application | coating on a base material, 3 to 50 weight% is preferable, More preferably, it is 5 to 40 weight%. The polymerization rate of the prepolymer can be adjusted to a desired range by adjusting the type and amount of the photopolymerization initiator, the irradiation intensity / irradiation time of actinic rays such as UV light, and the like. The polymerization rate of the prepolymer is calculated by the following formula from the weight before and after heating (drying) when the prepolymer composition is heated at 130 ° C. for 3 hours. In addition, when prepolymerization is performed by solution polymerization, a polymerization rate is calculated by subtracting the amount of the solvent from the total weight of the prepolymer composition as the weight before drying in the following formula.
Polymerization rate (%) of prepolymer composition = weight after drying / weight before drying × 100

  A monomer component constituting the acrylic base polymer (referred to as “monomer component B”) and, if necessary, a polymerization initiator, a chain transfer agent, a silane coupling agent, a crosslinking agent, etc., are mixed into the prepolymer composition. Then, an adhesive composition is formed. The monomer component B preferably contains a polyfunctional monomer. The monomer component B may contain a monofunctional monomer in addition to the polyfunctional monomer.

  The photopolymerization initiator and chain transfer agent used for post-polymerization are not particularly limited, and for example, the above-described photopolymerization initiator and chain transfer agent can be used. When the prepolymerization initiator remains in the prepolymer composition without being deactivated, the addition of the polymerization initiator for post-polymerization can be omitted.

  The base polymer may have a crosslinked structure as necessary. Formation of a crosslinked structure is performed, for example, by adding a crosslinking agent after preliminary polymerization or after polymerization of the base polymer. As the crosslinking agent, generally used ones such as an isocyanate crosslinking agent, an epoxy crosslinking agent, an oxazoline crosslinking agent, an aziridine crosslinking agent, a carbodiimide crosslinking agent, and a metal chelate crosslinking agent can be used.

  The content of the crosslinking agent is usually in the range of 0 to 5 parts by weight, preferably 0 to 3 parts by weight with respect to 100 parts by weight of the acrylic base polymer. If the content of the cross-linking agent is too large, tan δ may decrease as the storage elastic modulus G ′ increases, and bubbles may be mixed in or display unevenness may occur. Therefore, the content of the crosslinking agent is preferably 2 parts by weight or less, and more preferably 1 part by weight or less with respect to 100 parts by weight of the acrylic base polymer.

  When the pressure-sensitive adhesive composition contains a cross-linking agent, it is preferable that a cross-linking process is performed by heating before bonding to the adherend to form a cross-linked structure. Although the heating temperature and heating time in the crosslinking treatment are appropriately set according to the type of the crosslinking agent to be used, the crosslinking is usually performed in the range of 20 ° C. to 160 ° C. by heating for about 1 minute to 7 days.

  In the pressure-sensitive adhesive composition, a silane coupling agent can be added for the purpose of adjusting the adhesive force. A silane coupling agent can be used individually by 1 type or in combination of 2 or more types. When a silane coupling agent is added to the pressure-sensitive adhesive composition, the addition amount is usually about 0.01 to 5.0 parts by weight with respect to 100 parts by weight of the acrylic base polymer, and 0.03 to 2.0. The amount is preferably about parts by weight.

  A tackifier can be used for an adhesive composition as needed. Examples of tackifiers include terpene tackifiers, styrene tackifiers, phenol tackifiers, rosin tackifiers, epoxy tackifiers, dicyclopentadiene tackifiers, and polyamide tackifiers. An agent, a ketone tackifier, an elastomer tackifier, and the like can be used.

  In addition to the components exemplified above, additives such as plasticizers, softeners, deterioration inhibitors, fillers, colorants, ultraviolet absorbers, antioxidants, surfactants, antistatic agents, etc. It can be used as long as it is not impaired.

[Formation of adhesive sheet]
A pressure-sensitive adhesive sheet is formed by molding the pressure-sensitive adhesive composition into a sheet. The formation method of an adhesive sheet is not specifically limited. For example, as described above, after a pressure-sensitive adhesive composition containing a mixture of monomer components, a partial polymer (prepolymer), and an additive such as a polymerization initiator as necessary, is applied on a substrate, The method of superposing | polymerizing on a base material by actinic ray irradiation etc. is mentioned. In addition, a method of curing a composition (solution) containing a base polymer, a solvent, and, if necessary, an additive on a base material after coating and drying, may be employed.

  The method of applying the pressure-sensitive adhesive composition on the substrate is roll coat, kiss roll coat, gravure coat, reverse coat, roll brush, spray coat, dip roll coat, bar coat, knife coat, air knife coat, curtain coat. Various methods such as lip coat and die coater are used.

  As a method of drying the pressure-sensitive adhesive composition solution after coating, an appropriate method can be appropriately employed depending on the purpose. The heat drying temperature is preferably 40 ° C to 200 ° C, more preferably 50 ° C to 180 ° C, and particularly preferably 70 ° C to 170 ° C. As the drying time, an appropriate time can be adopted as appropriate. The drying time is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 15 minutes, and particularly preferably 10 seconds to 10 minutes.

  The thickness of the pressure-sensitive adhesive sheet is not particularly limited, but when a member having a printing step such as a front transparent plate is used as the adherend, the thickness of the pressure-sensitive adhesive sheet is preferably larger than the thickness of the printing step. Further, the thickness of the pressure-sensitive adhesive sheet is preferably 25 μm or more, more preferably 40 μm or more, and further preferably 50 μm or more. When the thickness of the pressure-sensitive adhesive sheet is smaller than the above range, problems such as bubble mixing near the printing step and display unevenness may occur. The upper limit of the thickness of the pressure-sensitive adhesive sheet is not particularly limited, but is preferably 300 μm or less and more preferably 250 μm or less from the viewpoint of productivity of the pressure-sensitive adhesive sheet.

  On the pressure-sensitive adhesive sheet, a protective sheet is detachably attached as necessary. The protective sheet is used for the purpose of protecting the exposed surface of the adhesive until the adhesive sheet is used for bonding to an adherend such as a film or a transparent plate. Examples of the constituent material of the protective sheath include plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and polyester films, porous materials such as paper, cloth, and nonwoven fabric, nets, foam sheets, metal foils, and laminates thereof. Although a suitable thin leaf body etc. are mentioned, a plastic film is used suitably from the point which is excellent in surface smoothness.

  Protective sheet can be removed with silicone, fluorine, long chain alkyl or fatty acid amide release agent, silica powder, etc. and antifouling treatment, coating type, kneading type, vapor deposition type, etc. The antistatic treatment can also be performed. In particular, when the surface of the protective sheet is appropriately subjected to release treatment such as silicone treatment, long-chain alkyl treatment, and fluorine treatment, the peelability from the pressure-sensitive adhesive sheet can be further enhanced when it is put to practical use. In addition, you may use the base material used at the time of formation (application | coating) of an adhesive sheet as a protective sheet of an adhesive sheet as it is.

[Use of adhesive sheet]
The pressure-sensitive adhesive sheet of the present invention is suitably used for bonding image display device forming members such as an image display panel, a touch panel, and a front transparent plate.

<Image display device>
FIG. 1 is a cross-sectional view schematically showing an image display device which is a usage example of the pressure-sensitive adhesive sheet of the present invention. An image display device 100 shown in FIG. 1 includes an optical film 10 such as a polarizing plate on the viewing side of an image display cell 61 such as a liquid crystal cell or an organic EL cell, and further includes a front transparent member 70 on the viewing side. The image display cell 61 is bonded to the optical film 10 via the first pressure-sensitive adhesive layer 21, and the front transparent plate 70 is bonded to the optical film 10 via the second pressure-sensitive adhesive layer 22. Note that an optical film such as a polarizing plate or an optical element (not shown) such as a backlight may be provided on the opposite side of the image display cell 61 from the viewing side.

  Examples of the front transparent member 70 include a front transparent plate (window layer) and a touch panel. As the front transparent plate, a transparent plate having appropriate mechanical strength and thickness is used. As such a transparent plate, for example, a transparent resin plate such as an acrylic resin or a polycarbonate resin, or a glass plate is used. As the touch panel, a touch panel of an arbitrary system such as a resistive film system, a capacitance system, an optical system, and an ultrasonic system is used.

  In such an image display device, display unevenness is caused by using the pressure-sensitive adhesive sheet of the present invention as the second pressure-sensitive adhesive layer 22 for bonding the optical film 10 on the surface of the image display panel 60 and the front transparent member 70 together. It is suppressed.

  The order of bonding these optical members is not particularly limited. For example, after the image display cell 61 and the optical film 10 are bonded together via the first pressure-sensitive adhesive layer 21 to form the image display panel 60, the second pressure-sensitive adhesive layer 22 (the pressure-sensitive adhesive sheet of the present invention) is used. Then, the optical film 10 on the surface of the image display panel 60 and the front transparent member 70 are bonded together. Before the image display cell 61 and the optical film 10 are bonded together, the front transparent member 70 and the optical film 10 may be bonded first. Moreover, both can be bonded simultaneously.

  From the viewpoint of improving the workability of the bonding and the accuracy (axial accuracy) of the arrangement angle of the optical film, the first bonding in which the optical film 10 and the image display cell 61 are bonded through the first pressure-sensitive adhesive layer 21. It is preferable that a process is performed and the 2nd bonding process by which the optical film 10 and a front transparent member are bonded through the 2nd adhesive layer 22 is performed after that.

  When the front transparent member 70 is bonded, bubbles are likely to be generated in the vicinity due to the step of the printing unit 70a provided at the peripheral edge of the front transparent member. Therefore, when bonding with the optical film 10 and the front transparent member 70 using the adhesive sheet of this invention, it is preferable to bond together under vacuum.

  After the optical film 10 and the front transparent member 70 are bonded to each other, the interface between the second pressure-sensitive adhesive layer 22 and the front transparent member 70 and the vicinity of a non-flat portion such as the printing portion 70a formed on the front transparent member 70 In order to remove bubbles, it is preferable that defoaming is performed. As the defoaming method, an appropriate method such as heating, pressurization, or reduced pressure can be employed. For example, it is preferable that bonding is performed while suppressing mixing of bubbles under reduced pressure and heating, and then pressurization is performed simultaneously with heating by autoclave treatment or the like for the purpose of suppressing delay bubbles. In the pressure-sensitive adhesive sheet of the present invention, since tan δ at 0.01 Hz is 0.6 or more, the pressure-sensitive adhesive easily follows the shape of a non-flat part such as a step, and even when the front transparent member has a non-flat part, And the display unevenness of the image display panel is suppressed.

  When defoaming is performed by heating, the heating temperature is generally about 30 ° C to 100 ° C, preferably 40 ° C to 90 ° C, more preferably 50 ° C to 80 ° C. Moreover, when pressurization is performed, the pressure is generally in the range of about 0.05 MPa to 2 MPa, preferably 0.1 MPa to 1.5 MPa, more preferably 0.2 MPa to 1 MPa. Since the tan δ at 0.001 Hz of the pressure-sensitive adhesive sheet of the present invention is 1.0 or less, even when a heating / pressurizing process is performed for the purpose of defoaming or the like, the sticking-out of the pressure-sensitive adhesive from the end surface is suppressed. .

<Optical film with adhesive layer>
When forming an image display apparatus using the adhesive sheet of this invention, it can also use for practical use as an optical film with an adhesive layer which laminated | stacked the adhesive sheet and the optical film. FIG. 2 schematically shows an embodiment of an optical film with a double-sided pressure-sensitive adhesive layer that includes a first pressure-sensitive adhesive layer 21 on one surface of the optical film 10 and a second pressure-sensitive adhesive layer 22 on the other surface of the optical film 10. It is sectional drawing to represent. Protection sheets 31 and 32 are temporarily attached to the surfaces of the pressure-sensitive adhesive layers 21 and 22.

  In the optical film 50 with a double-sided pressure-sensitive adhesive layer, the first pressure-sensitive adhesive layer 21 is used for bonding with a liquid crystal cell or the like, and the second pressure-sensitive adhesive layer 22 is used for bonding with a viewing-side touch panel, a front transparent plate, or the like. . In the optical film with a double-sided pressure-sensitive adhesive layer, the second pressure-sensitive adhesive layer 22 is preferably the pressure-sensitive adhesive sheet of the present invention.

  The pressure-sensitive adhesive constituting the first pressure-sensitive adhesive layer 21 includes acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate / vinyl chloride copolymer, modified polyolefin, epoxy-based, fluorine-based, natural rubber, What uses rubber-type polymers, such as a synthetic rubber, as a base polymer can be selected suitably, and can be used. In particular, an acrylic pressure-sensitive adhesive is preferably used from the viewpoint that it is excellent in optical transparency, exhibits adhesive properties such as appropriate wettability, cohesiveness and adhesiveness, and is excellent in weather resistance and heat resistance.

  The thickness of the 1st adhesive layer 21 is not specifically limited, It can determine suitably according to a use purpose, adhesive force, etc. For example, when the first pressure-sensitive adhesive layer 21 is used for bonding with a liquid crystal cell, the thickness is preferably about 3 μm to 30 μm, more preferably 5 μm to 27 μm, and even more preferably 10 μm to 25 μm.

(Optical film)
Examples of the optical film 10 include various optical films used for forming an image display device such as a polarizing plate, a phase difference plate, a viewing angle widening film, a viewing angle limiting (preventing peeping) film, and a brightness enhancement film. The optical film 10 may be formed by laminating a plurality of optical films via an appropriate adhesive layer or pressure-sensitive adhesive layer as necessary.

  The surface of the optical film 10 may be subjected to a hard coat layer, antireflection treatment, antisticking treatment, or treatment for diffusion or antiglare. In addition, a surface modification treatment may be performed on the surface of the optical film 10 for the purpose of adhesion or the like before attaching the pressure-sensitive adhesive layers 21 and 22. Specific examples of the treatment include corona treatment, plasma treatment, flame treatment, ozone treatment, primer treatment, glow treatment, saponification treatment, and treatment with a coupling agent. Further, an antistatic layer can be appropriately formed.

(Attachment of adhesive layer to optical film)
As a method for forming the first pressure-sensitive adhesive layer 21 and the second pressure-sensitive adhesive layer 22 on the optical film 10, for example, the pressure-sensitive adhesive composition is applied to a substrate that has been subjected to a release treatment, and dried or cured as necessary. A method of forming a pressure-sensitive adhesive layer (pressure-sensitive adhesive sheet) after the treatment, and then transferring it onto the optical film 10; or applying a pressure-sensitive adhesive composition to the optical film 10, and drying or curing the optical film as necessary. And a method of forming a pressure-sensitive adhesive layer on an optical film.

  On the adhesive layers 21 and 22, protective sheets 31 and 32 are detachably attached as necessary. In addition, even if it uses the separator (base material for adhesive layer application | coating) used when transferring the adhesive layers 21 and 22 on the optical film 10 as it is as the protective sheets 31 and 32 of the optical film with an adhesive layer. Good.

(Cutting optical film with adhesive layer)
The optical film with the pressure-sensitive adhesive layer is cut into a desired size as necessary and is put to practical use. In general, an optical film with an adhesive layer formed in a long shape is cut into a product size that matches the size (screen size) of the image display device. Examples of the cutting method include a method of punching using a Thomson blade and the like, a cutter such as a round blade and a countersink, a method of using laser light and water pressure, and the like.

  In the optical film with an adhesive layer, since the protective sheets 31 and 32 are attached to the surfaces of the adhesive layers 21 and 22, the surface of the adhesive layer is protected. On the other hand, the side surface of the pressure-sensitive adhesive layer is generally exposed to the outside. For this reason, when cutting, transporting, handling, etc., the side of the adhesive layer that is exposed to the outside comes into contact with some object, causing the adhesive to fall off as if the adhesive at the end is missing (glue) In some cases, such as chipping) or the removed adhesive may contaminate the surface of the optical film (glue stain). In particular, since the second pressure-sensitive adhesive layer 22 used for pasting the front transparent plate 70 is large in thickness, the second pressure-sensitive adhesive layer 22 is likely to adhere to the cutting blade or cause chipping or stains during cutting. Tend.

  In one embodiment, the optical film 55 with a double-sided pressure-sensitive adhesive layer is formed such that at least one side surface of the first pressure-sensitive adhesive layer 21 and the second pressure-sensitive adhesive layer 22 is the optical film 10 as schematically shown in FIGS. It exists inside the side. In addition to being inside the optical film 10, at least a part of the side surfaces 21 e and 22 e of the first pressure-sensitive adhesive layer 21 and / or the second pressure-sensitive adhesive layer 22 is inside the protective sheets 31 and 32. Is preferred. If the side surface (edge) of the adhesive layer is inside the side surface of the optical film or protective sheet, adhesive stains and chipping on processing lines such as transportation and bonding with image display cells are suppressed. Is done. In the present invention, the side surface 22e of the second pressure-sensitive adhesive layer 22 is particularly preferably inside the optical film 10, and both the side surface 21e of the first pressure-sensitive adhesive layer 21 and the side surface 22e of the second pressure-sensitive adhesive layer 22 are optical. It is preferable to be inside the film 10.

  In particular, the second pressure-sensitive adhesive layer 22 (the pressure-sensitive adhesive sheet of the present invention) has a large thickness and is liable to cause adhesive chipping or paste stains. Therefore, at least a part of the side surface 22e of the second pressure-sensitive adhesive layer 22 is a side surface of the optical film 10. It is preferable to be inside, and it is preferable that at least a part of the side surface 22 e of the second pressure-sensitive adhesive layer 22 is inside the side surface of the protective sheet 32. By having the side surface of the second pressure-sensitive adhesive layer 22 on the inner side of the side surface of the optical film 10 or the protective sheet 32, problems due to the sticking out of the pressure-sensitive adhesive are further suppressed.

  Of the side surface 22e of the second pressure-sensitive adhesive layer, the portion inside the side surface of the optical film 10 is preferably 1/2 or more of the side circumferential length of the pressure-sensitive adhesive layer 22, and 3/4 or more of the side circumferential length. It is more preferable that the total length of the side periphery is particularly preferable. Similarly to the second pressure-sensitive adhesive layer 22, the side surface 21 e of the first pressure-sensitive adhesive layer 21 also has a side circumferential length of ½ or more, more preferably 3/4 or more, and particularly preferably over the entire length of the optical film 10. And / or preferably inside the protective sheet 31.

  When the side surfaces 21e and 22e of the pressure-sensitive adhesive layers 21 and 22 are inside the side surfaces of the optical film 10 and / or the protective sheets 31 and 32, for example, the shape shown in FIG. is there. In addition, as shown in FIG. 3, in the vicinity of the interface between the pressure-sensitive adhesive layers 21 and 22 and the optical film 10 and / or the protective sheets 31 and 32, the side surface of the pressure-sensitive adhesive layer is almost the same as the side surface of the optical film and / or protective sheet. It can also be made into the shape which exists inside the side surface of an optical film and / or a protection sheet in the thickness direction center part vicinity of an adhesive layer. In addition, the presence or absence and shape of the part inside the optical film and / or protective sheet on the side surface of the pressure-sensitive adhesive layer are not limited to the above, and can be set as appropriate.

  As a method of providing the side surface of the pressure-sensitive adhesive layer inside the side surface of the optical film or the side surface of the protective sheet, a method of controlling the attachment area of the pressure-sensitive adhesive layer on the optical film, or a pressure-sensitive adhesive layer after attaching the pressure-sensitive adhesive layer There is a method of removing only the part.

  As a particularly preferable method, after attaching the protective sheets 31 and 32 on the pressure-sensitive adhesive layers 21 and 22, the optical film with a double-sided pressure-sensitive adhesive layer is pressed from above the protective sheets 31 and 32, so that the end of the pressure-sensitive adhesive layer is the end of the optical film. After the adhesive layer protrudes from the part and the adhesive layer protrudes, the pressure-sensitive adhesive layer is cut together with the optical film 10 and the protective sheets 31 and 32, and then the pressure is released so that the side surfaces 21e and 22e of the adhesive layers 21 and 21 are removed. The method of making it retreat inside from the side surface of the optical film 10 and / or the protection sheets 31 and 32 is mentioned. In this case, for example, after punching the optical film formed in a long shape with a Thomson blade or the like, in a state where a plurality of punched optical films with an adhesive layer are stacked, pressure is applied from the stacking direction, and the adhesive layer Preferably, a method of cutting the inside of the cut surface by punching and finishing to a product size using a rotary blade or the like while protruding from the side surface is preferably used.

On the side surfaces of the pressure-sensitive adhesive layers 21 and 22, the distance (longest portion) W ₁ and W ₂ from the side of the optical film on the inner side of the side of the optical film 10, while suppressing chipping and paste stains, From the viewpoint of preventing image display and bonding problems from occurring, the thickness is preferably about 10 μm to 300 μm, more preferably about 20 μm to 250 μm, and still more preferably about 30 μm to 200 μm. In the method of releasing the pressure after cutting the pressure-sensitive adhesive layer together with the optical film and the protective sheet under pressure, the distance W is desired by adjusting the pressure applied to the pressure-sensitive adhesive layer and the elastic modulus of the pressure-sensitive adhesive layer. Range. Distance W ₁ and W ₂ may be the same or different.

(Lamination with image display cell and front transparent plate)
The bonding method of the optical film 55 with the double-sided pressure-sensitive adhesive layer, the image display cell 61 and the front transparent member 70 is not particularly limited, and is attached to the respective surfaces of the first pressure-sensitive adhesive layer 21 and the second pressure-sensitive adhesive layer 22. After the protective sheets 31 and 32 are peeled off, they can be bonded together by various known methods. Although the order of bonding is not particularly limited, as described above, the first bonding step in which the optical film 10 and the image display cell 61 are bonded via the first pressure-sensitive adhesive layer 21 is performed, and then the optical It is preferable that the 2nd bonding process in which the film 10 and the front transparent member 70 are bonded through the 2nd adhesive layer 22 is performed. Further, when the optical film 10 and the front transparent member 70 are bonded through the second pressure-sensitive adhesive layer 22, it is preferable that the bonding is performed under vacuum as described above. It is preferable that defoaming is performed by an appropriate method such as heating, pressurization, and decompression.

  As described above, by using the pressure-sensitive adhesive sheet of the present invention, it is possible to suppress the display unevenness of the image display panel and the sticking of the pressure-sensitive adhesive from the end face in a high-temperature environment, and the optical film with the pressure-sensitive adhesive layer of the present invention. By using this, it is possible to simplify the bonding process in the manufacture of an image display device employing an interlayer filling structure.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Measuring method]
<Storage modulus of adhesive sheet>
The separator was peeled off from the pressure-sensitive adhesive sheets of each Example and Comparative Example, and a plurality of pressure-sensitive adhesive sheets were laminated to obtain a thickness of about 1.5 mm as a measurement sample. Using “Advanced Rheometric Expansion System (ARES)” manufactured by Rheometric Scientific, dynamic viscoelasticity measurement was performed under the following conditions. From the measurement results, storage elastic modulus G ′ at 0.01 Hz and 0.001 Hz, loss The values of elastic modulus G ″ and loss tangent tan δ were read.

(Measurement condition)
Deformation mode: Torsion Measurement temperature: 50 ° C
Measurement frequency: 10Hz to 0.001Hz
Shape: Parallel plate 7.9mmφ

[Example 1]
(Preparation of adhesive composition)
As monomer components, 41 parts by weight of isostearyl acrylate, 41 parts by weight of 2-ethylhexyl acrylate, and 18 parts by weight of N-vinylpyrrolidone, and as a photopolymerization initiator, 1-hydroxy-cyclohexyl-phenyl-ketone (trade name “Irgacure 184” ", 0.1 part by weight of Ciba Japan Co., Ltd.) was put into a four-necked flask and irradiated with ultraviolet rays in a nitrogen atmosphere to obtain a prepolymer composition having a polymerization rate of 10%. To 100 parts by weight of this prepolymer, 0.06 part by weight of trimethylolpropane triacrylate as a polyfunctional monomer and 0.3 part by weight of α-thioglycerol as a chain transfer agent were added, and these were mixed uniformly. A pressure-sensitive adhesive composition was prepared.

(Coating and post-polymerization)
The pressure-sensitive adhesive composition is applied to a release surface of a 75 μm thick polyester film that has been peeled with silicone on one side to form a coating layer having a thickness of 150 μm. The peel-treated surface of the peel-treated polyester film having a thickness of 38 μm was bonded. Thereafter, UV irradiation is performed from the surface on the side of the polyester film having a thickness of 38 μm with a black light whose position is adjusted so that the irradiation intensity on the irradiation surface immediately below the lamp is 5 mW / cm ² until the integrated light quantity becomes 3000 mJ / cm ^2. The polymerization was advanced to produce an acrylic pressure-sensitive adhesive sheet having a thickness of 150 μm.

[Examples 2-7, Comparative Examples 1-4]
The composition of the prepolymer-forming composition and the composition added afterwards to the prepolymer composition were changed as shown in Table 1. Other than that was carried out similarly to the said Example 1, the prepolymer superposition | polymerization, adjustment of an adhesive composition, application | coating, and post-polymerization were performed, and the 150-micrometer-thick acrylic adhesive sheet was produced.

In Table 1, each component is described by the following abbreviations.
ISA: Isostearyl acrylate 2EHA: 2-ethylhexyl acrylate NVP: N-vinylpyrrolidone 4HBA: 4-hydroxybutyl acrylate DPHA: dipentaerystol hexaacrylate ATMPT: trimethylolpropane triacrylate Irg184: Irgacure 184

[Evaluation]
<Evaluation of image display unevenness>
After the pressure-sensitive adhesive sheets prepared in the above Examples and Comparative Examples were cut to a size of 50 mm × 80 mm, the 38 μm thick polyester film was peeled off. After removing the backlight part from the replacement upper liquid crystal panel of Nintendo 3DS, overlay the adhesive exposed surface of the above adhesive sheet on the center of the surface opposite to the backlight of the liquid crystal panel and use a hand roller And pressed to bond.

  After the 75 μm thick polyester film was peeled off from the surface of the pressure-sensitive adhesive sheet after bonding, a glass plate (0.7 mm × 50 mm × 100 mm, ink printing thickness = 15 μm, both short) Sides (long side direction) ink printing width: 15 mm each, both long sides (short side direction) ink printing width: 5 mm each were placed on the exposed surface of the adhesive, and vacuum thermocompression bonding apparatus (A temperature of 25 ° C., an internal pressure of 50 Pa, a pressure of 0.3 MPa, and a pressure holding time of 10 seconds). Thereafter, autoclaving (50 ° C., 0.5 MPa, 15 minutes) was performed to produce a panel for evaluating image display unevenness.

  This image display unevenness evaluation panel was replaced with the image display panel of the Nintendo 3DS main body, and electrical connection was made to visually confirm the presence or absence of display unevenness near the printing frame when the display panel was white. . The results are shown in Table 1, with ◯ indicating no display unevenness and x indicating display unevenness.

<Evaluation of adhesive sticking>
(Preparation of cell side adhesive layer)
In a separable flask equipped with a thermometer, stirrer, reflux condenser and nitrogen gas inlet tube, 97 parts of butyl acrylate, 3 parts of acrylic acid, 0.2 part of azobisisobutyronitrile as a polymerization initiator and 233 parts of ethyl acetate Then, nitrogen gas was introduced and nitrogen substitution was performed for about 1 hour while stirring. Thereafter, the flask was heated to 60 ° C. and reacted for 7 hours to obtain an acrylic polymer having a weight average molecular weight (Mw) of 1.1 million.

  0.8 parts by weight of trimethylolpropane tolylene diisocyanate (“Coronate L” manufactured by Nippon Polyurethane Industry Co., Ltd.) as an isocyanate-based crosslinking agent in the acrylic polymer solution (with a solid content of 100 parts by weight), silane coupling 0.1 part of an agent (“KBM-403” manufactured by Shin-Etsu Chemical Co., Ltd.) was added to prepare an adhesive composition (solution).

  On the 38 μm-thick polyethylene terephthalate film whose surface has been release-treated, the above-mentioned pressure-sensitive adhesive composition solution is applied so that the thickness after drying is 20 μm, and dried at 100 ° C. for 3 minutes to remove the solvent. Thus, an adhesive layer was obtained. Then, it heated at 50 degreeC for 48 hours, and the crosslinking process was performed. (Hereinafter, this pressure-sensitive adhesive layer is referred to as “pressure-sensitive adhesive layer A”)

(Preparation of optical film with double-sided adhesive layer)
Said adhesive layer A was bonded together as a cell side adhesive layer on one surface of the polarizing plate. As the polarizing plate, a polarizing plate (degree of polarization 99.995) in which a transparent protective film was bonded to both sides of a polarizer made of a stretched polyvinyl alcohol film having a thickness of 25 μm impregnated with iodine was used. The transparent protective film on one side (image display cell side) of the polarizer is a retardation film made of a triacetyl cellulose film having a thickness of 40 μm, and the transparent protective film on the other side (viewing side) is 60 μm in thickness. It was a triacetyl cellulose film.

  The pressure-sensitive adhesive sheet prepared in each of Examples and Comparative Examples was bonded to the other surface of the polarizing plate as a visible-side pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer having a thickness of 20 μm and the other were bonded to one surface of the polarizing plate (optical film). An optical film with a double-sided pressure-sensitive adhesive layer in which a 150 μm-thick pressure-sensitive adhesive layer was bonded to the surface and a separator was temporarily attached onto each pressure-sensitive adhesive layer was obtained.

(Production of pseudo panel for evaluation)
The optical film with a double-sided pressure-sensitive adhesive layer was cut to 60 mm × 100 mm, the separator on the cell-side pressure-sensitive adhesive layer was peeled off, and then bonded onto a glass plate (0.7 mm × 50 mm × 100 mm). Then, the optical film with a double-sided pressure-sensitive adhesive layer was cut with a cutter knife, and the optical film with a double-sided pressure-sensitive adhesive layer in the region of 10 mm from both short sides to the long side of the glass plate And peeled off.

  Then, the separator of the visual recognition side adhesive layer surface of the optical film with a double-sided adhesive layer bonded together to the glass plate was peeled. Similar to the above-mentioned image display unevenness evaluation panel production, a glass plate with black ink printed in a frame shape on the periphery is pasted together with a vacuum thermocompression bonding apparatus, and then autoclaved to produce an evaluation pseudo panel. did.

(Evaluation of adhesive sticking out)
The pseudo panels for evaluation of each example and comparative example were put into a dryer at 85 ° C. for 500 hours, then taken out to a room temperature environment, and the protruding state of the adhesive layer from both end faces in the short side direction was observed with a digital microscope. did. The maximum value of the protruding amount of the pressure-sensitive adhesive layer from each end face was measured, and the average value was within 0.3 mm, and the case where the average value exceeded 0.3 mm was marked with x.

[Evaluation results]
Table 1 shows the composition and viscoelasticity of each of the above Examples and Comparative Examples, and the results of image display unevenness and protrusion evaluation. 4 and 5 show the frequency dependence of the loss tangent tan δ and the storage elastic modulus G ′ of the pressure-sensitive adhesive sheets of Examples 1, 4, 5, 6, and 7 and Comparative Examples 2 and 3. FIG.

  According to the comparison between Example 1 and Example 2, the comparison between Example 3 and Comparative Example 4, the comparison between Example 4 and Comparative Example 3, and the comparison between Example 5 and Example 6, the pressure-sensitive adhesive It can be seen that tan δ decreases as the amount of polyfunctional monomer in the composition increases. Further, according to the comparison between Example 2 and Example 3, it can be seen that tan δ increases as the monomer unit (2EHA) in which the acrylic group has a branch is increased. From the comparison between Example 3 and Comparative Example 2, it can be seen that when the content of the nonpolar monomer (2HEA) is decreased and the content of the polar monomer (4HBA) is increased, tan δ is decreased. Thus, it turns out that the adhesive which has the required viscoelastic property is obtained by changing the composition of an adhesive.

  In Comparative Example 2, the content of 2HEA was increased and the content of polyfunctional monomer (ATMPT) was decreased as compared with Examples 1 to 7, but tan δ was reduced as compared with each Example. . This is presumably because the polymer had a higher molecular weight because no chain transfer agent was used in either the prepolymer polymerization or post-polymerization. From this result, it can be seen that the polymerization rate can be adjusted and the viscoelasticity can be controlled by using the chain transfer agent. Even if a chain transfer agent is not used, the polymerization rate can also be adjusted by adjusting the monomer composition (preparation ratio), the temperature during polymerization, the amount of active light irradiation, the time, and the like. When using a chain transfer agent for the purpose of adjusting viscoelasticity by controlling the polymerization rate, as shown in Example 7, the chain transfer agent can be added at any stage of prepolymerization and post-polymerization. I understand.

  As shown in Table 1, in Comparative Examples 1 and 2, since the value of tan δ at 0.01 Hz of the adhesive sheet was small, the liquid crystal display was uneven. On the other hand, in Comparative Example 3 and Comparative Example 4, although the tan δ value at 0.001 Hz of the pressure-sensitive adhesive sheet was large and display unevenness did not occur, the pressure-sensitive adhesive protruded from the end face when exposed to a high temperature environment. It was. On the other hand, as in each example, by using an adhesive sheet having a tan δ at 0.01 Hz of 0.60 or more and a tan δ at 0.001 Hz of 1.00 or less, there is no display unevenness, and It can be seen that the adhesive does not protrude from the end face even when exposed to a high temperature environment for a long time.

  Referring to FIG. 5, regarding the frequency dependence of the storage elastic modulus G ′, no clear difference tendency was observed between the examples and the comparative examples. On the other hand, referring to FIG. 4, in each example, the loss tangent tan δ tends to increase between 0.001 Hz and 0.01 Hz, and the pressure-sensitive adhesive sheet exhibiting such viscoelastic behavior has a low frequency ( Since tan δ is small on the high temperature side and elastic behavior is preferential, sticking out of the adhesive is suppressed, and on the high frequency (low temperature side) tan δ is large and viscous behavior is preferential, suppressing display unevenness due to stress. It is estimated that.

DESCRIPTION OF SYMBOLS 10 Optical film 21,22 Adhesive layer 31,32 Protective sheet 55 Optical film with an adhesive layer 61 Image display cell 70 Front transparent member 70a Printing part 100 Image display apparatus

Claims (11)

An adhesive sheet used between the front transparent plate and the touch panel, between the front transparent plate and the image display panel, or between the touch panel and the image display panel,
A pressure-sensitive adhesive sheet having a loss tangent tan δ at 50 ° C. and 0.01 Hz of 0.60 or more; and a loss tangent tan δ at 50 ° C. and 0.001 Hz of 1.00 or less.   The pressure-sensitive adhesive sheet according to claim 1, wherein a loss tangent tan δ at 50 ° C and 0.001 Hz is smaller than a loss tangent tan δ at 50 ° C and 0.01 Hz.   The pressure sensitive adhesive sheet according to claim 1 or 2 whose storage elastic modulus G 'in 50 ° C and 0.001 Hz is 0.2 kPa-7 kPa.   The sheet | seat adhesive sheet of any one of Claims 1-3 whose storage elastic modulus G 'in 50 degreeC and 0.01 Hz is 0.7 kPa-10 kPa.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive constituting the pressure-sensitive adhesive sheet contains 50% by weight or more of an acrylic base polymer.   The acrylic base polymer has, as monomer units, an alkyl group with a linear alkyl group (meth) acrylic acid alkyl ester; an alkyl group with a branched (meth) acrylic acid alkyl ester; and a polymerization with an unsaturated double bond The pressure-sensitive adhesive sheet according to claim 5, comprising a polyfunctional monomer having two or more functional functional groups.   The pressure-sensitive adhesive sheet according to claim 6, further comprising a nitrogen-containing monomer as the monomer unit.   The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, having a thickness of 25 µm or more.   An optical film with an adhesive layer, comprising the adhesive sheet according to any one of claims 1 to 8 on at least one surface of the optical film.   It is an optical film with a double-sided adhesive layer which has an adhesive layer on both surfaces of an optical film, Comprising: The adhesive layer of at least one surface is the adhesive sheet of any one of Claims 1-8, With a double-sided adhesive layer Optical film.     The pressure-sensitive adhesive sheet according to any one of claims 1 to 8, wherein either the front transparent plate and the touch panel, the front transparent plate and the image display panel, or the touch panel and the image display panel are used. An image display device bonded together.