Optical pressure-sensitive adhesive sheet

Abstract

To provide an optical adhesive sheet having low temperature dependency of storage elastic modulus.SOLUTION: An optical pressure-sensitive adhesive sheet includes a first acrylic pressure-sensitive adhesive layer, an intermediate pressure-sensitive adhesive layer containing a silicone resin, and a second acrylic pressure-sensitive adhesive layer in this order.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an optical pressure-sensitive adhesive sheet. [Background technology]

[0002] In recent years, demand for touch panels has grown rapidly in fields such as smartphones, tablet PCs, portable game consoles, and car navigation devices. This has led to an increase in demand for optical adhesive sheets used to bond touch panels to other optical components. For example, a display device equipped with a touch panel typically has a laminated structure of optical components, such as a display panel such as a liquid crystal panel, a polarizing plate, a transparent component (touch panel body) having a surface layer made of a transparent conductive film such as ITO (indium tin oxide), and a cover panel that protects the transparent conductive film. Optical adhesive sheets are used to bond the optical components together. Adhesive sheets that are particularly highly transparent and suitable for bonding optical components are also called optically clear adhesive (OCA) sheets.

[0003] Patent Document 1 discloses a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer (A) on one side of a substrate, the pressure-sensitive adhesive layer (A) having a storage modulus G' measured at 1 Hz and 80°C of 1×10 Pa or less, and a silicone-based pressure-sensitive adhesive layer (B) on the other side of the substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-210930 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the investigations of the present inventors, depending on the type of pressure-sensitive adhesive layer, the storage modulus may be significantly lower in a high-temperature environment than at room temperature. When an attempt is made to increase the storage modulus in a high-temperature environment, the storage modulus at room temperature becomes too high, which may increase the possibility of display unevenness when used for bonding display panels or the like.

[0006] The present disclosure has been made in consideration of the above-mentioned current situation, and aims to provide an optical pressure-sensitive adhesive sheet having low temperature dependence of storage modulus. [Means for solving the problem]

[0007] (1) One embodiment of the present invention is an optical pressure-sensitive adhesive sheet comprising, in this order, a first acrylic pressure-sensitive adhesive layer, an intermediate pressure-sensitive adhesive layer containing a silicone resin, and a second acrylic pressure-sensitive adhesive layer.

[0008] (2) In one embodiment of the present invention, in addition to the configuration of (1), the intermediate pressure-sensitive adhesive layer contains the silicone resin and a curing agent, and has a storage modulus at 85°C calculated by the following formula (1) of 1×10 4 Pa or more, 10×10 4 It is an optical pressure-sensitive adhesive sheet with a tensile strength of 100 Pa or less. Storage modulus of the intermediate adhesive layer at 85°C (×10 4 Pa) = -40.0786 × mass ratio of hardener to silicone resin + 42.3105 (1)

[0009] (3) In one embodiment of the present invention, in addition to the configuration of (1) or (2), a storage modulus at 85°C of 1 × 10 4 Pa or more, and the storage modulus at 23°C is 10 x 10 4 It is an optical pressure-sensitive adhesive sheet with a tensile strength of 100 Pa or less.

[0010] (4) One embodiment of the present invention is an optical pressure-sensitive adhesive sheet having any one of the configurations (1) to (3) above, wherein the adhesive strength of the optical pressure-sensitive adhesive sheet is 10 N / 25 mm or more.

[0011] (5) One embodiment of the present invention is an optical pressure-sensitive adhesive sheet having the configuration of any one of the above (1) to (4), wherein the silicone resin is an addition reaction type silicone resin. [Effects of the Invention]

[0012] According to the present disclosure, an optical pressure-sensitive adhesive sheet having low temperature dependency of storage modulus can be provided. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a pressure-sensitive adhesive sheet according to an embodiment. [Figure 2] 1 is a graph showing the relationship between the mass ratio of a curing agent and a silicone-based resin. [Figure 3] This is a graph of the 95% confidence interval and predicted G´85℃ obtained from the regression analysis. [Figure 4] This is a graph comparing the predicted G'85°C of a silicone-based adhesive layer with the G'85°C of a three-layer OCA sheet. DETAILED DESCRIPTION OF THE INVENTION

[0014] Fig. 1 is a cross-sectional view schematically showing an example of a pressure-sensitive adhesive sheet according to an embodiment. As shown in Fig. 1, an optical pressure-sensitive adhesive sheet 10 according to an embodiment includes, in order from the observation side, a first acrylic pressure-sensitive adhesive layer 11, an intermediate pressure-sensitive adhesive layer 12, and a second acrylic pressure-sensitive adhesive layer 13. In this specification, the observation side refers to the side of the target member that is closer to the viewer when the target member is placed facing the viewer.

[0015] The optical pressure-sensitive adhesive sheet 10 has a first acrylic pressure-sensitive adhesive layer 11 and a second acrylic pressure-sensitive adhesive layer 13 on either side of an intermediate pressure-sensitive adhesive layer 12 containing a silicone resin. It has been difficult to ensure sufficient thickness and flexibility with only an acrylic pressure-sensitive adhesive layer. On the other hand, it has been difficult to obtain sufficient adhesive strength to an adherend such as glass with only a silicone pressure-sensitive adhesive layer. The optical pressure-sensitive adhesive sheet 10 according to this embodiment ensures thickness and flexibility with the intermediate pressure-sensitive adhesive layer 12 containing a silicone resin, while by disposing acrylic pressure-sensitive adhesive layers on both sides of the intermediate pressure-sensitive adhesive layer 12, it is possible to ensure adhesive strength to an adherend.

[0016] In addition, optical pressure-sensitive adhesive sheets may have a release film attached to one or both sides to protect the adhesive surface during transportation or storage. Commercially available release films include fluorine-based release films using fluorinated silicone as a release agent and silicone-based release films using fluorine-free silicone resins. Although silicone-based release films using fluorine-free silicone resins are inexpensive, when used as a release film for a pressure-sensitive adhesive sheet with a single silicone pressure-sensitive adhesive layer, the adhesion between the release film and the silicone pressure-sensitive adhesive layer becomes too strong due to the homogeneous material, which can cause damage to the surface of the silicone pressure-sensitive adhesive layer when peeling the release film, resulting in poor release. Therefore, fluorine-based release films, although expensive, are used as release films for pressure-sensitive adhesive sheets with a single silicone pressure-sensitive adhesive layer. The optical pressure-sensitive adhesive sheet 10 of this embodiment has acrylic pressure-sensitive adhesive layers on both sides of the intermediate pressure-sensitive adhesive layer 12 containing a silicone resin, allowing the use of inexpensive fluorine-free silicone release films, thereby expanding the range of materials available and reducing manufacturing costs.

[0017] <First and second acrylic pressure-sensitive adhesive layers> The first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13 preferably both constitute the outermost surface of the optical pressure-sensitive adhesive sheet 10. The first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13 contain an acrylic resin as a resin component. The first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13 are preferably formed by curing an acrylic resin composition. Examples of the acrylic resin composition include one containing an acrylic resin and a crosslinking agent.

[0018] Examples of the acrylic resin include (meth)acrylic acid ester polymers and copolymers thereof (hereinafter also referred to as (meth)acrylic copolymers).

[0019] The (meth)acrylic copolymer may be, for example, a copolymer of a (meth)acrylic acid alkyl ester and a carboxyl group-containing monomer.

[0020] The (meth)acrylic acid alkyl ester may be a (meth)acrylic acid alkyl ester (CH2=CR 1 -COOR 2 ;R 1 is a hydrogen atom or a methyl group, and R 2 is an alkyl group having 1 to 18 carbon atoms), and the alkyl group preferably has 4 to 12 carbon atoms.

[0021] Examples of (meth)acrylic acid alkyl esters having an alkyl group of 1 to 18 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undeca(meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, and isostearyl (meth)acrylate. These may be used alone or in combination of two or more.

[0022] Examples of the carboxyl group-containing monomer include carboxyl group-containing (meth)acrylates such as β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, succinic acid mono(meth)acryloyloxyethyl ester, and ω-carboxypolycaprolactone mono(meth)acrylate; acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid. These may be used alone or in combination of two or more.

[0023] The crosslinking agent may be, for example, a component capable of undergoing a crosslinking reaction with the crosslinkable functional group derived from the crosslinkable functional group-containing monomer possessed by the (meth)acrylic copolymer, and specific examples thereof include isocyanate compounds, metal chelate compounds, epoxy compounds, etc. The crosslinking agents may be used alone or in combination of two or more.

[0024] The thickness of each of the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13 is preferably 10 μm or more and 100 μm or less. A thickness of 10 μm or more provides sufficient adhesive strength. On the other hand, a thickness of 100 μm or less provides sufficient flexibility (also referred to as step-following ability) to the extent that the optical pressure-sensitive adhesive sheet can deform to follow steps present on the surface of an adherend to which it is attached. Furthermore, when the optical pressure-sensitive adhesive sheet is used to bond substrates with different elasticity in response to environmental changes, such as bonding a glass substrate and a resin substrate, the optical pressure-sensitive adhesive sheet can suitably follow dimensional changes in the substrates in response to environmental changes, thereby sufficiently suppressing peeling. The thickness of each of the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13 is more preferably 20 μm or more and 80 μm or less. Considering flexibility, a thickness of 25 μm or more and 50 μm or less is even more preferred. The thicknesses of the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13 may be the same or different from each other, but from the viewpoint of making the adhesive strength on both sides of the optical pressure-sensitive adhesive sheet equal, it is preferable that the thicknesses of the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13 are the same.

[0025] <Intermediate adhesive layer> The intermediate pressure-sensitive adhesive layer 12 is an intermediate layer disposed between the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13. The intermediate pressure-sensitive adhesive layer 12 preferably imparts flexibility and conformability to the optical pressure-sensitive adhesive sheet 10.

[0026] The intermediate pressure-sensitive adhesive layer 12 is a silicone-based pressure-sensitive adhesive layer containing a silicone-based resin. Silicone-based pressure-sensitive adhesive layers have a storage modulus G' that is less dependent on temperature than polyurethane layers, so by using a silicone-based pressure-sensitive adhesive layer as the intermediate pressure-sensitive adhesive layer 12, it is possible to obtain an optical pressure-sensitive adhesive sheet whose storage modulus G' is less likely to change even in high-temperature environments. In the case of a material whose storage modulus G' is highly dependent on temperature, such as a polyurethane layer, increasing the G' of the intermediate pressure-sensitive adhesive layer 12 at high temperatures will further increase the G' of the intermediate pressure-sensitive adhesive layer 12 at room temperature, which is thought to make it more likely to cause display unevenness when attached to an optical component.

[0027] The intermediate adhesive layer 12 is preferably a silicone-based adhesive layer containing an addition reaction type silicone-based resin, and more preferably a silicone-based adhesive layer containing an addition reaction type silicone-based resin that is also heat-curable. For example, if a condensation type silicone-based resin that cures with moisture is used, acetone, alcohol, and other condensation products are produced during curing, which can deteriorate the appearance of the optical adhesive sheet. Furthermore, condensation type silicone-based resins that cure with moisture have a long curing time. By using a silicone-based adhesive layer containing an addition reaction type silicone-based resin as the intermediate adhesive layer 12, the above condensation products are not produced during curing, resulting in a highly transparent adhesive sheet. Furthermore, the use of a catalyst such as a platinum catalyst allows for rapid heat curing.

[0028] The intermediate pressure-sensitive adhesive layer 12 contains a silicone resin (also referred to as a silicone pressure-sensitive adhesive) as a main component. Specifically, the content of the silicone resin in the intermediate pressure-sensitive adhesive layer 12 is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to the total mass of the intermediate pressure-sensitive adhesive layer 12.

[0029] Examples of the silicone resin include silicone resins having a polysiloxane skeleton. Examples of silicone resins include addition reaction type, condensation reaction type, ultraviolet curing type, and electron beam curing type. Among these, addition reaction type silicone resins are preferably used because of their high reactivity and excellent productivity.

[0030] Examples of the addition reaction type silicone resin include organopolysiloxanes having two or more alkenyl groups having 2 to 10 carbon atoms, such as vinyl groups, allyl groups, propenyl groups, and hexenyl groups, at the ends and / or side chains of the molecule. When using an addition reaction type silicone resin, it is preferable to use a curing agent and / or a catalyst in combination.

[0031] Examples of the curing agent include organopolysiloxanes having at least two hydrogen atoms bonded to silicon atoms in one molecule.Specific examples include dimethylhydrogensiloxy group-endblocked dimethylsiloxane-methylhydrogensiloxane copolymers, trimethylsiloxy group-endblocked dimethylsiloxane-methylhydrogensiloxane copolymers, trimethylsiloxy group-endblocked methylhydrogenpolysiloxanes, and poly(hydrogensilsesquioxanes).

[0032] Examples of the catalyst include fine particle platinum, fine particle platinum adsorbed on a carbon powder carrier, chloroplatinic acid, alcohol-modified chloroplatinic acid, olefin complexes of chloroplatinic acid, platinum group metal compounds such as palladium and rhodium, and the like.

[0033] The amount of curing agent is preferably 60 parts by mass or more and 110 parts by mass or less, more preferably 70 parts by mass or more and 100 parts by mass or less, and even more preferably 80 parts by mass or more and 100 parts by mass or less, per 100 parts by mass of the main resin (silicone-based resin). By using 60 parts by mass of curing agent per 100 parts by mass of the main resin, the adhesive strength of the silicone-based pressure-sensitive adhesive layer can be improved, and the adhesive strength between the silicone pressure-sensitive adhesive layer and the first and second acrylic pressure-sensitive adhesive layers can be improved.

[0034] The intermediate pressure-sensitive adhesive layer 12 contains the silicone resin and a curing agent, and has a storage modulus at 85°C calculated by the following formula (1) of 1×10 4 Pa or more, 10×10 4 The storage modulus (G') of the intermediate pressure-sensitive adhesive layer 12 at 85°C is preferably not more than 100 Pa. 85℃ When the storage modulus at 85°C is high, the storage modulus at room temperature becomes too high, which may increase the possibility of display unevenness when used to bond display panels or the like. Therefore, when the storage modulus at 85°C is high, the storage modulus at room temperature becomes too high, which may increase the possibility of display unevenness when used to bond display panels or the like, it is preferable to set the G' of the intermediate pressure-sensitive adhesive layer 12 obtained by the following formula (1) 85℃ is 10 x 10 4In addition, from the viewpoint of obtaining good creep characteristics that make it difficult to deform even when pressure is applied over time, G' of the intermediate pressure-sensitive adhesive layer 12 obtained by the following formula (1) is preferably 100 Pa or less. 85℃ is 1 x 10 4 Pa or more is preferred. The following formula (1) can be obtained by preparing a plurality of single-layer silicone pressure-sensitive adhesive layers with different mass ratios of curing agent to main agent (silicone-based resin) and performing regression analysis on the values ​​measured for storage modulus at 85°C. The above range of storage modulus corresponds to the 95% confidence interval of the regression equation obtained by the above regression analysis. In particular, when the thickness of the intermediate pressure-sensitive adhesive layer 12 is thicker than the first and second acrylic pressure-sensitive adhesive layers 11, 13, the physical properties of the intermediate pressure-sensitive adhesive layer 12 become dominant. Therefore, the storage modulus of the optical pressure-sensitive adhesive sheet can be controlled by adjusting the storage modulus of the intermediate pressure-sensitive adhesive layer 12 at 85°C. Storage modulus of the intermediate adhesive layer at 85°C (×10 4 Pa) = -40.0786 × mass ratio of hardener to silicone resin + 42.3105 (1)

[0035] The viscosity of the base agent is preferably 1000 mPa·s or more and 5000 mPa·s or less, and more preferably 1500 mPa·s or more and 4000 mPa·s or less. The viscosity of the curing agent is preferably 1000 mPa·s or more and 6000 mPa·s or less, and more preferably 2000 mPa·s or more and 6000 mPa·s or less. The viscosity of the mixture of the base agent and curing agent is preferably 1000 mPa·s or more and 5000 mPa·s or less, more preferably 1500 mPa·s or more and 4000 mPa·s or less, and even more preferably 2000 mPa·s or more and 3000 mPa·s or less. The absolute value of the difference in viscosity between the base agent and the curing agent is preferably 3000 mPa·s or less, more preferably 2000 mPa·s or less, and even more preferably 1000 mPa·s or less. The viscosity is measured at 23° C. by a method in accordance with JIS K 7117-2:1999. The viscosity can be measured using a measuring device such as a BII type viscometer (BMII manufactured by Toki Sangyo Co., Ltd.).

[0036] Examples of silicone adhesives that can be used include LUMISIL (registered trademark) 102 FC, 105FC, and ELASTOSIL (registered trademark) RT 601 manufactured by Wacker Asahi Kasei Silicone Co., Ltd.

[0037] Various additives such as tackifiers (tackifiers), stabilizers, antioxidants, antifungals, and flame retardants may be added to the intermediate pressure-sensitive adhesive layer 12 as needed, provided that they do not impair the required properties of the optical pressure-sensitive adhesive sheet. Each of the components contained in each layer may be used alone or in combination of two or more.

[0038] The intermediate pressure-sensitive adhesive layer 12 is preferably thicker than the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13. The thickness of the intermediate pressure-sensitive adhesive layer 12 is preferably 100 μm or more and 2000 μm or less. When the thickness is 100 μm or more, the flexibility of the entire pressure-sensitive adhesive sheet is improved, and when one side of the pressure-sensitive adhesive sheet is attached to the surface of an optical component, the pressure-sensitive adhesive sheet can effectively cover any irregularities or steps present on the surface of the optical component, enabling the other side of the pressure-sensitive adhesive sheet to be attached to the surface of another optical component with more sufficient adhesive strength. When the thickness is 2000 μm or less, it is easier to control the thickness accuracy of the intermediate pressure-sensitive adhesive layer 12. The thickness of the intermediate pressure-sensitive adhesive layer 12 is more preferably 200 μm or more and 1500 μm or less, even more preferably 250 μm or more and 1500 μm or less, and particularly preferably 500 μm or more and 1000 μm or less.

[0039] The optical pressure-sensitive adhesive sheet 10 according to this embodiment is suitable for use in bonding optical components. Examples of the optical components include various components constituting display devices, such as display panels, touch panels (glass substrates with ITO transparent conductive film), cover glasses, polarizing plates, and retardation films. The type of display panel is not particularly limited, and examples include liquid crystal panels and organic electroluminescence panels (organic EL panels). By bonding optical components using the optical pressure-sensitive adhesive sheet 10, it is possible to eliminate air gaps between the optical components, thereby improving the visibility of the display device.

[0040] The optical pressure-sensitive adhesive sheet 10 may have another layer such as a primer layer between the first acrylic pressure-sensitive adhesive layer 11 and the intermediate pressure-sensitive adhesive layer 12 and / or between the intermediate pressure-sensitive adhesive layer 12 and the second acrylic pressure-sensitive adhesive layer 13, but preferably has a three-layer structure of the first acrylic pressure-sensitive adhesive layer 11, the intermediate pressure-sensitive adhesive layer 12, and the second acrylic pressure-sensitive adhesive layer 13. That is, the first acrylic pressure-sensitive adhesive layer 11 and the intermediate pressure-sensitive adhesive layer 12 are preferably in contact with each other, and the second acrylic pressure-sensitive adhesive layer 13 and the intermediate pressure-sensitive adhesive layer 12 are preferably in contact with each other.

[0041] <Adhesive sheet> The thickness (total thickness) of the optical pressure-sensitive adhesive sheet 10 is preferably 120 μm or more and 2200 μm or less. When the thickness is 120 μm or more, the flexibility of the optical pressure-sensitive adhesive sheet 10 is improved. When the thickness is 2200 μm or less, it is easier to control the thickness accuracy of the entire optical pressure-sensitive adhesive sheet 10. The thickness of the optical pressure-sensitive adhesive sheet 10 is more preferably 240 μm or more and 1660 μm or less, even more preferably 300 μm or more and 1600 μm or less, and particularly preferably 550 μm or more and 1100 μm or less.

[0042] The optical pressure-sensitive adhesive sheet 10 preferably has a haze of 1% or less. It also preferably has a total light transmittance of 90% or more. The haze and total light transmittance can be measured, for example, using a turbidity meter "HazeMeter NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. The haze is measured according to a method in accordance with JIS K 7136:2000, and the total light transmittance is measured according to a method in accordance with JIS K 7361-1:1997.

[0043] The storage modulus of the optical pressure-sensitive adhesive sheet 10 at 85°C is 1 × 10 4 The storage modulus at 23°C is 10 × 10 4 The storage modulus (G') of the optical pressure-sensitive adhesive sheet 10 at 85°C is less than or equal to 100 Pa. 85℃ ) is 1×10 4 When the storage modulus (G') of the optical pressure-sensitive adhesive sheet 10 at 23°C is 1.0 Pa or more, the generation of delayed bubbles can be effectively suppressed. 23℃ ) is 10 x 104 When the elastic modulus is 1 Pa or less, the film has a suitable flexibility, and when used for bonding a display, for example, display unevenness is unlikely to occur.

[0044] The above G', and G" and tanδ described below can be measured using, for example, a viscoelasticity measuring device "Physica MCR301" manufactured by Anton Paar Germany GmbH. The loss tangent (tanδ) is expressed as the ratio (G" / G') of the storage modulus (G') to the loss modulus (G").

[0045] The storage modulus of the optical adhesive sheet 10 can be adjusted by the composition of the silicone-based adhesive layer, the mixing ratio of the main agent and crosslinking agent used in the silicone-based adhesive layer, the thickness of the silicone-based adhesive layer, the curing conditions, the composition of the acrylic adhesive layer, the ratio of the main agent and curing agent used in the acrylic adhesive layer, the thickness of the acrylic adhesive layer, etc.

[0046] Above G´ 85℃ A preferred upper limit is, for example, 10 × 10 4 Pa. The above G' 85℃ is 1 x 10 4 Pa or higher, 8×10 4 Pa or less is more preferable, and 1×10 4 Pa or higher, 6×10 4 Pa or less is more preferable. 23℃ A preferred lower limit is, for example, 2 × 10 4 Pa. The above G' 23℃ is 3 x 10 4 Pa or higher, 8×10 4 Pa or less is more preferable.

[0047] Ratio of storage modulus at 23°C to that at 85°C (G´ 23℃ / G´ 85℃ ) is preferably 3.0 or less. 23℃ / G´ 85℃ By making G' 3.0 or less, an optical pressure-sensitive adhesive sheet that is resistant to deformation while having good flexibility at room temperature and high temperatures can be obtained. 23℃ / G´ 85℃The lower limit of G' is, for example, 0.5. 23℃ / G´ 85℃ is more preferably 0.8 or more and 2.0 or less, further preferably 0.90 or more and 1.5 or less, and particularly preferably 1.3 or less.

[0048] The adhesive strength of the optical pressure-sensitive adhesive sheet 10 is preferably 10 N / 25 mm or more. When the adhesive strength of the optical pressure-sensitive adhesive sheet 10 is 10 N / 25 mm or more, it can exhibit good adhesive strength to an adherend. A higher adhesive strength is preferable, and the upper limit is not particularly limited, but is, for example, 100 N / 25 mm or less. The adhesive strength to an adherend of either the surface of the first acrylic pressure-sensitive adhesive layer 11 opposite the intermediate pressure-sensitive adhesive layer 12 or the surface of the second acrylic pressure-sensitive adhesive layer 13 opposite the intermediate pressure-sensitive adhesive layer 12 is preferably within the above range, and it is more preferable that the adhesive strength to an adherend of both the surfaces of the first and second acrylic pressure-sensitive adhesive layers 11, 13 opposite the intermediate pressure-sensitive adhesive layer 12 is within the above range.

[0049] The adhesive strength is measured according to the 180-degree peeling method of the peel adhesion strength test method specified in JIS K 6854-2: 1999. Specifically, a glass slide is attached to one surface of the optical pressure-sensitive adhesive sheet 10, a PET sheet is attached to the other surface, and the optical pressure-sensitive adhesive sheet 10 and the glass slide are peeled off at the interface between them to measure the adhesive strength.

[0050] A release film may be attached to one or both sides of the optical pressure-sensitive adhesive sheet 10. That is, for example, the optical pressure-sensitive adhesive sheet 10 may be a laminate in which the optical pressure-sensitive adhesive sheet 10, a first release film covering one side of the optical pressure-sensitive adhesive sheet 10, and a second release film covering the other side of the optical pressure-sensitive adhesive sheet 10 are laminated together.

[0051] The first and second release films are each subjected to an easy-peel treatment (release treatment) on the surface of the base film that contacts the optical pressure-sensitive adhesive sheet 10. A resin film such as a PET (polyethylene terephthalate) film is used as the base film. Examples of the release treatment include a method of applying a release agent to at least one surface of the base film.

[0052] The release agent preferably uses a fluorine-free silicone resin. Since the optical pressure-sensitive adhesive sheet of this embodiment has acrylic pressure-sensitive adhesive layers on both sides of the silicone-based pressure-sensitive adhesive layer, a silicone-based release film using a fluorine-free silicone resin as the release agent can be used. Such silicone-based release films are inexpensive, allowing for reduced production costs. Examples of the fluorine-free silicone resin include compounds having a low surface energy methyl group in a side chain, as shown in the following chemical formula (A), and not having a functional group containing a fluorine element in R in the side chain. Examples of fluorine-based release films include those using a silicone resin having a fluorine-containing functional group in R in the side chain of the following chemical formula (A). The addition of fluorine makes it difficult for silicone resins to bond together, thereby improving releasability.

[0053] [ka] (In the formula, n is a natural number representing the number of repeating units.)

[0054] <Method of manufacturing optical pressure-sensitive adhesive sheet> The method for producing the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13 is not particularly limited, and may be, for example, a method in which a pressure-sensitive adhesive composition is applied using a general-purpose film-forming device or film-forming method such as various coating devices, bar coaters, doctor blades, etc. Alternatively, the first acrylic pressure-sensitive adhesive layer 11 and the second acrylic pressure-sensitive adhesive layer 13 may be produced using a centrifugal molding method.

[0055] The method for producing the intermediate pressure-sensitive adhesive layer 12 is not particularly limited, but for example, a liquid or gel-like silicone pressure-sensitive adhesive composition is obtained by mixing a curing agent and / or catalyst with the main component of the silicone pressure-sensitive adhesive composition and stirring with a mixer, etc. The silicone pressure-sensitive adhesive composition is then sandwiched between first and second acrylic pressure-sensitive adhesive layers formed on a release film and heated in a drying oven, etc., to thermally cure (crosslink) the composition, thereby obtaining a silicone pressure-sensitive adhesive layer. [Example]

[0056] The present invention will be explained in more detail below by giving examples, but the present invention is not limited to these examples.

[0057] (Test Example 1) An acrylic resin composition was prepared by blending acrylic ester copolymers ("SK1838" and "SK1875" manufactured by Soken Chemical & Engineering Co., Ltd.) at a solids mass ratio of 5:5. 0.6 parts by mass of an isocyanate curing agent ("DY-70" manufactured by Soken Chemical & Engineering Co., Ltd.) was added to 100 parts by mass of the acrylic resin. Each of the acrylic resin compositions was applied to a release film using a comma coater to a dry thickness of 25 μm. After the solvent was dried, another release film was laminated and cured to produce first and second acrylic pressure-sensitive adhesive layers sandwiched between the release films. The release film used was a polyethylene terephthalate (PET) film substrate film, with one side treated with a fluorine-free silicone resin for release. Specifically, PET100-J2 manufactured by Nippa Corporation was used.

[0058] A silicone-based adhesive layer was prepared using a silicone-based adhesive composition containing an addition-reaction type silicone resin that cures upon heating. The silicone-based adhesive composition used was a mixture of LUMISIL® 102 FC base resin (liquid A) and LUMISIL 102 FC curing agent (liquid B) manufactured by Wacker Asahi Kasei Silicones, in a mass ratio (solids mass ratio) of 100:80. The viscosity of the base resin at 23°C was 2000 mPa·s, the viscosity of the curing agent was 2300 mPa·s, and the viscosity of the mixture of the base resin and curing agent was 2000 mPa·s.

[0059] One of the release PET films was peeled off from each of the first and second acrylic pressure-sensitive adhesive layers with release films.Then, the silicone-based pressure-sensitive adhesive composition was coated between the first acrylic pressure-sensitive adhesive layers so that the thickness after drying was 250 μm, and the second acrylic pressure-sensitive adhesive layer was laminated on the silicone-based pressure-sensitive adhesive composition.With the silicone-based pressure-sensitive adhesive composition sandwiched between the pair of acrylic pressure-sensitive adhesive layers, thermal curing was carried out at 105 ° C for 3 hours.In this way, an optical pressure-sensitive adhesive sheet having, in this order, a first acrylic pressure-sensitive adhesive layer, a silicone-based pressure-sensitive adhesive layer, and a second acrylic pressure-sensitive adhesive layer was produced.

[0060] (Test Examples 2 to 6) Optical pressure-sensitive adhesive sheets were produced in the same manner as in Test Example 1, except that the mass ratio of the curing agent to the main component of the silicone-based pressure-sensitive adhesive composition was changed as shown in Table 1 below.

[0061] (Test Example 7) In Test Example 7, the same first and second acrylic pressure-sensitive adhesive layers as in Test Example 1 were used, and the intermediate pressure-sensitive adhesive layer was a polyurethane layer prepared as follows.

[0062] (Thermosetting polyurethane layer) A thermosetting polyurethane composition having an α ratio of 1.5 was prepared by mixing and stirring 100 parts by weight of the following polyol component, 4.7 parts by weight of a hydrophilic polyisocyanate, 4.7 parts by weight of a hydrophobic polyisocyanate, 10 parts by weight of a tackifier, and 0.01 parts by weight of a catalyst using a reciprocating rotary mixer, Ajiter (manufactured by Shimazaki Engineering Co., Ltd.). Polyolefin polyol (EPOL (registered trademark) manufactured by Idemitsu Kosan Co., Ltd.) Hydrophilic polyisocyanate Modified polyisocyanate containing ethylene oxide units (Tosoh's "Coronate 4022") Hydrophobic polyisocyanate IPDI (isophorone diisocyanate) polyisocyanate ("Desmodur I" manufactured by Sumika Bayer Urethane Co., Ltd.) Tackifier Idemitsu Kosan's "Imarv P-100" ·catalyst Dimethyltin dilaurate (Momentive's "Fomrez catalyst UL-28")

[0063] The thermosetting polyurethane composition was sandwiched between a pair of release films and thermally cured at 85°C for 3 hours to produce a 950µm thick polyurethane layer with release films on both sides. Then, as in Test Example 1, first and second acrylic pressure-sensitive adhesive layers were attached to both sides of the polyurethane layer to produce an optical pressure-sensitive adhesive sheet.

[0064] (Test Example 8) In Test Example 8, an optical pressure-sensitive adhesive sheet was produced in the same manner as in Test Example 7, except that the thickness of the polyurethane layer was changed to 250 μm.

[0065] (Test Example 9) Optical pressure-sensitive adhesive sheets were prepared in the same manner as in Test Example 1, except that the type of silicone resin, the mixing ratio of the base agent and curing agent, and the curing conditions were changed. In Test Example 9, a silicone pressure-sensitive adhesive layer was also prepared using a silicone pressure-sensitive adhesive composition containing an addition-reaction type silicone resin that cures upon heating. The silicone pressure-sensitive adhesive composition used was LUMISIL® 105 FC manufactured by Wacker Asahi Kasei Silicones, mixed with the base agent and curing agent in a 100:100 mass ratio. At 23°C, the viscosity of the base agent was 3800 mPa·s, the viscosity of the curing agent was 5600 mPa·s, and the viscosity of the mixture of the base agent and curing agent was 4800 mPa·s. The silicone pressure-sensitive adhesive composition was cured under the curing conditions shown in Table 2 to prepare a silicone pressure-sensitive adhesive layer. Then, as in Test Example 1, first and second acrylic pressure-sensitive adhesive layers were bonded to both sides of the silicone pressure-sensitive adhesive layer to prepare an optical pressure-sensitive adhesive sheet.

[0066] (Test Examples 10-16) Optical pressure-sensitive adhesive sheets were produced in the same manner as in Test Example 1, except that the mass ratio of the curing agent to the main component of the silicone-based pressure-sensitive adhesive composition was changed as shown in Table 2 below.

[0067] (Test Example 17) The silicone-based adhesive composition prepared in Test Example 1 was coated onto the release film used in Test Example 1 so that the thickness after drying would be 300 μm, and the release film used in Test Example 1 was further laminated on top of it.With the silicone-based adhesive composition sandwiched between the pair of release films, thermal curing was carried out at 105°C for 3 hours to produce an optical adhesive sheet with a single silicone-based adhesive layer.

[0068] (Test Example 18) In Test Example 18, an optical pressure-sensitive adhesive sheet was prepared in the same manner as Test Example 1, except that a silicone pressure-sensitive adhesive layer was prepared using a silicone pressure-sensitive adhesive composition containing a silicone resin that is an addition reaction type different from the silicone pressure-sensitive adhesive composition used in Test Example 1 and that cures upon heating. The silicone pressure-sensitive adhesive composition used was RT601 manufactured by Wacker Asahi Kasei Silicone Co., Ltd., and was prepared by mixing the base agent and curing agent in a mass ratio of 100:11.1. The viscosity of the base agent at 23°C was 5000 mPa·s, the viscosity of the curing agent was 40 mPa·s, and the viscosity of the mixture of the base agent and curing agent was 3500 mPa·s. The silicone pressure-sensitive adhesive composition was sandwiched between the first and second pressure-sensitive adhesive layers and thermally cured under the curing conditions shown in Table 2. This produced an optical pressure-sensitive adhesive sheet having, in this order, a first acrylic pressure-sensitive adhesive layer, a silicone pressure-sensitive adhesive layer, and a second acrylic pressure-sensitive adhesive layer.

[0069] <Evaluation test> The storage modulus G', loss modulus G", and loss tangent (tanδ) of the optical pressure-sensitive adhesive sheets obtained in each test example were measured at 85°C and 23°C, respectively. The adhesive strength, total light transmittance, and haze of the optical pressure-sensitive adhesive sheets of the examples and comparative examples were also measured, and the results are shown in Tables 1 and 2. In test example 17, part of the silicone pressure-sensitive adhesive layer adhered to the release film, and the release film could not be properly peeled off from the silicone pressure-sensitive adhesive layer. In test example 18, peeling occurred at the interface between the acrylic pressure-sensitive adhesive layer and the silicone pressure-sensitive adhesive layer. Therefore, the following evaluation tests were not performed on test examples 17 and 18. The blend amounts of the main agent and curing agent in Tables 1 to 3 below are expressed in parts by mass.

[0070] (viscoelasticity) The storage modulus, loss modulus, and loss tangent were measured using an Anton Paar Physica MCR301 viscoelasticity measuring device. The measurement plate was a 12 mm diameter parallel plate (PP12), and the measurement conditions were a strain of 0.1%, a frequency of 1 Hz, and a cell temperature of 25°C to 100°C (heating rate of 3°C / min). The storage modulus (G´), loss modulus (G´´), and loss tangent (tanδ) were recorded at 23°C and 85°C.

[0071] (Adhesive strength) The adhesive strength (peel adhesion strength) of each optical pressure-sensitive adhesive sheet was measured by a 180° peel test according to JIS K 6854-2:1999. A 75 mm long x 25 mm wide test piece was prepared for each optical pressure-sensitive adhesive sheet. One side of the test piece was attached to a 75 mm long x 25 mm wide glass slide (alkali-free glass, product name Eagle XG, manufactured by Matsunami Glass Co., Ltd.) and held at a pressure of 0.4 MPa for 30 minutes to bond the optical pressure-sensitive adhesive sheet to the glass slide. Next, a 125 μm thick PET sheet ("Melinex (registered trademark) S" manufactured by Teijin DuPont Films) was attached to the side of the test piece opposite the glass slide. After leaving the test piece at room temperature and humidity (temperature 23 ° C, humidity 50%) for 12 hours, the PET sheet was pulled in the 180° direction at a rate of 300 mm / min, the optical pressure-sensitive adhesive sheet was peeled off at the interface with the glass slide, and the adhesive strength of the optical pressure-sensitive adhesive sheet to the glass slide was measured. For each test example, the average value of three measurements was calculated.

[0072] (Total light transmittance and haze) The haze and total light transmittance of each test example were measured using a turbidity meter "HazeMeter NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd. The haze was measured according to a method in accordance with JIS K 7136:2000, and the total light transmittance was measured according to a method in accordance with JIS K 7361-1:1997.

[0073] [Table 1]

[0074] [Table 2]

[0075] Single-layer silicone pressure-sensitive adhesive layers (1000 μm thick) were prepared as the following Study Examples 1 to 5. In Study Example 5, adhesiveness was not obtained and G' was significantly high. Therefore, regression analysis was performed as shown in Tables 4 to 6 below using the mass ratio (solid mass ratio) of the curing agent to the main component (silicone resin) and the storage modulus (G') at 85°C for Study Examples 1 to 4, and the graph shown in Figure 2 was obtained. Figure 2 is a graph showing the relationship between the mass ratio of the curing agent to the silicone resin. From the graph in Figure 2, the storage modulus (G') of the silicone pressure-sensitive adhesive layer at 85°C can be calculated. 85℃ The regression equation shown below (1) was obtained to calculate the predicted value of G´ 85℃ (×10 4 Pa) = -40.0786 × (mass ratio of hardener to base agent) + 42.3105 (1)

[0076] [Table 3]

[0077] [Table 4]

[0078] [Table 5]

[0079] [Table 6]

[0080] Using the regression equation obtained above, the predicted value of the storage modulus of the optical pressure-sensitive adhesive sheet at 85°C (predicted G' 85℃ ) were calculated and summarized in Table 7 below. [Table 7]

[0081] Figure 3 shows the 95% confidence intervals and predicted G´ obtained from the regression analysis. 85℃1 is a graph showing the predicted G' of the silicone-based pressure-sensitive adhesive layer calculated from the 95% confidence interval obtained above and the regression equation expressed by the above equation (1). 85℃ This is summarized in Figure 3. In Table 7 above, a mass ratio of curing agent to base agent of 0.636 corresponds to Test Example 2, and a mass ratio of curing agent to base agent of 0.11 corresponds to Test Example 18. In Test Example 2, the desired adhesive strength was obtained, but peeling occurred at the interface between the acrylic pressure-sensitive adhesive layer and the silicone-based pressure-sensitive adhesive layer. In addition, Test Example 18 is not preferred because G' at 85°C is too high, which also increases G' at room temperature and is thought to make it more likely to cause display unevenness when attached to an optical component. It is preferable that the silicone-based pressure-sensitive adhesive layer be within the 95% confidence interval obtained by the regression equation expressed by the above formula (1). Specifically, it is preferable that G' at 85°C of the silicone-based pressure-sensitive adhesive layer calculated by the above formula (1) is within the 95% confidence interval. 4 Pa or more, 10×10 4 It is preferable that the tensile strength is 100 Pa or less (the part surrounded by a bold frame in Table 7).

[0082] Figure 4 shows the predicted G´ of the silicone adhesive layer. 85℃ and G' of 3-layer OCA sheet 85℃ As shown in Figure 4, the predicted G' of the silicone-based pressure-sensitive adhesive layer calculated from the regression equation expressed by the above formula (1) is 85℃ And the G' of the 3-layer OCA sheet that was actually produced 85℃ It was confirmed that there is a correlation between the predicted G' of the silicone-based pressure-sensitive adhesive layer. 85℃ is in the 95% confidence interval 1×10 4 Pa or more, 10×10 4 Pa or less, the G´ of the three-layer OCA sheet actually produced 85℃ Also 1×10 4 Pa or more, preferably 10 × 10 4 It was confirmed that it was possible to achieve a temperature of less than Pa. [Explanation of symbols]

[0083] 10: Optical adhesive sheet 11: First acrylic adhesive layer 12: Intermediate adhesive layer 13: Second acrylic adhesive layer

Claims

1. An optical pressure-sensitive adhesive sheet comprising, in this order, a first acrylic pressure-sensitive adhesive layer, an intermediate pressure-sensitive adhesive layer containing a silicone resin, and a second acrylic pressure-sensitive adhesive layer.

2. the intermediate adhesive layer contains the silicone resin and a curing agent, The storage modulus at 85°C obtained by the following formula (1) is 1 x 10 ４ Pa or more, 10×10 ４ The optical pressure-sensitive adhesive sheet according to claim 1, wherein the viscosity is 0.05 Pa or less. Storage modulus of the intermediate adhesive layer at 85°C (×10 ４ Pa) = -40.0786 × mass ratio of hardener to silicone resin + 42.3105 (1)

3. Storage modulus at 85°C is 1 x 10 ４ Pa or more, and the storage modulus at 23°C is 10 x 10 ４ The optical pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the viscosity is 0.05 Pa or less.

4. The optical pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the adhesive strength of the optical pressure-sensitive adhesive sheet is 10 N / 25 mm or more.

5. The optical pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the silicone-based resin is an addition reaction type silicone-based resin.

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