Adhesive sheet

Abstract

To provide an adhesive sheet in which both of high-temperature holding power and an ability to follow a complex shape can be achieved.SOLUTION: An adhesive sheet has an adhesive layer. The adhesive layer includes: a polymer having a weight-average molecular weight exceeding 70×104; and at least one selected from oligomers and tackifier resins with a softening point of less than 145°C. The adhesive layer has a storage modulus G' (25°C) at 25°C of less than 0.15 MPa.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet. [Background technology]

[0002] Generally, adhesives (also called pressure-sensitive adhesives; the same applies below) are in a soft solid (viscoelastic) state in a temperature range around room temperature, and have the property of easily adhering to an adherend by pressure. Taking advantage of such properties, adhesives are widely used for purposes such as joining, fixing, and protecting members in smartphones and other portable electronic devices, for example in the form of a substrate-attached adhesive sheet having an adhesive layer on a supporting substrate, or in the form of a substrate-less adhesive sheet without a supporting substrate. Patent documents 1 and 2 are cited as technical documents related to adhesive tapes used to fix members in portable electronic devices. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-70102 A [Patent Document 2] JP 2018-28051 A Summary of the Invention [Problem to be solved by the invention]

[0004] Adhesive sheets used in environments exposed to high temperatures are required to have good adhesive properties even at high temperatures. For example, the above-mentioned portable electronic devices may be used in high-temperature environments, and the internal space may become hot due to heat generation from electronic components, so that adhesive sheets used for such applications must have sufficient adhesive reliability even at high temperatures. In addition, since the adhesive area is usually small for fixing members inside portable electronic devices due to restrictions on size, weight, etc., the adhesive sheets used for such applications must have adhesive reliability that can achieve good fixing even in small areas, and the required performance is at a higher level due to the demand for weight reduction and miniaturization. In particular, portable electronic devices equipped with touch panel displays, such as smartphones, are becoming smaller and thinner in the products themselves, while the screens are becoming larger in terms of visibility and operability of the displays, and adhesives used therein are required to have adhesive fixing performance under harsher conditions. For fixing members inside portable electronic devices, it is desirable to use adhesive sheets that have excellent adhesive fixing performance (e.g., high-temperature retention) not only in the normal temperature range but also in the high temperature range.

[0005] In recent years, in addition to the above-mentioned miniaturization and thinning, the development of portable electronic devices having curved shapes such as three-dimensional shapes has progressed, and the shapes of the components thereof tend to become more complex. The adhesive to be attached to the above-mentioned complex shapes is required to have the ability to conform well to the shape and adhere to it. For example, in the above-mentioned portable electronic devices, an adhesive for fixing a member such as a cover glass having a complex surface shape (which may be a curved shape) needs to exhibit a good fixing function while maintaining a state of conforming to the complex shape without any gaps. If the adhesive does not conform to the curved shape of the adherend and a gap is generated between the adhesive and the adherend, there is a risk of problems such as water entering through the gap and impairing the waterproofing. The ability to conform to the complex surface shape of the adherend can be improved by utilizing the flexibility of the adhesive sheet, but a highly flexible adhesive tends to have a lower adhesive fixing performance (especially high-temperature retention) at the above-mentioned high temperatures, and it is not easy to achieve both. It would be beneficial to provide an adhesive sheet that can achieve both conformability to the complex shape of the adherend and high-temperature retention.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a pressure-sensitive adhesive sheet that is capable of achieving both the ability to conform to complex shapes and high-temperature retention. [Means for solving the problem]

[0007] According to the present specification, there is provided a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer has a weight average molecular weight of 70×10 4 and further at least one selected from an oligomer and a tackifier resin having a softening point of less than 145° C. The pressure-sensitive adhesive layer has a storage modulus G'(25° C.) of less than 0.15 MPa at 25° C. The polymer contained in the pressure-sensitive adhesive is preferably a polymer having a weight average molecular weight (Mw) of 70×10 4 By using a polymer having a storage modulus G' (25°C) of less than 0.15 MPa at 25°C, and at least one selected from an oligomer and a tackifier resin having a softening point of less than 145°C, a pressure-sensitive adhesive layer having a storage modulus G' (25°C) of less than 0.15 MPa at 25°C can be formed, utilizing the cohesive force based on the entanglement of the polymers and the effect of adding the oligomer and low-softening point tackifier resin, while retaining flexibility capable of conforming to complex shapes of adherends, and achieving good high-temperature retention. In other words, a pressure-sensitive adhesive sheet is provided that can achieve both conformability to complex shapes and high-temperature retention.

[0008] In some preferred embodiments, the pressure-sensitive adhesive layer has a gel fraction of more than 35% by weight. By making the gel fraction of the pressure-sensitive adhesive layer more than 35% by weight, high-temperature retention can be improved.

[0009] In some preferred embodiments, the pressure-sensitive adhesive layer has a ratio (G'(80°C) / G'(25°C)) of the storage modulus G'(25°C) at 25°C to the storage modulus G'(80°C) at 80°C that is greater than 0.20. A pressure-sensitive adhesive having a ratio of the 25°C storage modulus to the 80°C storage modulus within a predetermined range as described above can preferably achieve both complex shape conformability and high temperature retention.

[0010] In some embodiments, the dispersity (Mw / Mn) of the polymer is equal to or less than 40. By setting the dispersity of the polymer to a predetermined value or less, a flocculation action having a predetermined flexibility based on entanglement of high molecular weight polymers is preferably exhibited.

[0011] In some preferred embodiments, the polymer is an acrylic polymer. The adhesive layer disclosed herein may be an acrylic adhesive layer containing an acrylic polymer as the polymer. By using an acrylic polymer, which has a wide range of molecular design options and is relatively easy to design, it is easy to obtain a polymer suitable for both complex shape conformability and high temperature retention. In a configuration including an acrylic adhesive layer, the technology disclosed herein is preferably implemented.

[0012] In some preferred embodiments, the pressure-sensitive adhesive layer contains both the oligomer and the tackifier resin. In a composition containing a high molecular weight polymer, a tackifier resin having a softening point of less than 145° C. and an oligomer are used in combination, thereby achieving a better balance between conformability to complex shapes and high-temperature retention.

[0013] In some embodiments, the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer includes an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent. By using an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent in combination as crosslinking agents, flexibility and cohesive strength that are compatible with complex shape conformability and high temperature retention can be preferably realized.

[0014] In some preferred embodiments, the pressure-sensitive adhesive sheet is a substrate-less double-sided adhesive pressure-sensitive adhesive sheet made of the pressure-sensitive adhesive layer. Substrate-less double-sided pressure-sensitive adhesive sheets can be made thinner because they do not have a substrate, and can contribute to the miniaturization and space-saving of products to which the double-sided pressure-sensitive adhesive sheet is applied. In addition, substrate-less pressure-sensitive adhesive sheets can maximize the effects of the pressure-sensitive adhesive layer, such as flexibility and holding power. The compatibility of complex shape conformability and high-temperature holding power by the technology disclosed herein is preferably realized in substrate-less pressure-sensitive adhesive sheets.

[0015] The adhesive sheet disclosed herein has good high-temperature retention, and therefore may be used in a high-temperature environment, and is suitable for use in fixing members in portable electronic devices whose internal space may become heated due to heat generated by electronic components. In addition, portable electronic devices such as smartphones may include members having a three-dimensional curved surface, and therefore the adhesive sheet disclosed herein is suitable for use in fixing members in such portable electronic devices. The adhesive sheet disclosed herein is suitable for use in a portable electronic device, where the adhesive sheet is attached to the step and / or curved surface of a member having a step and / or curved surface. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a cross-sectional view showing a schematic configuration example of a pressure-sensitive adhesive sheet. [Diagram 2] FIG. 1 is an exploded perspective view illustrating a configuration example of a display device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] A preferred embodiment of the present invention will be described below. Matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention can be understood by a person skilled in the art based on the teachings on carrying out the invention described in this specification and the common general knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general knowledge in the field. In addition, in the following drawings, members and parts that perform the same function may be described by using the same reference numerals, and duplicated descriptions may be omitted or simplified. In addition, the embodiments described in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the pressure-sensitive adhesive sheet of the present invention that is actually provided as a product.

[0018] In this specification, the term "adhesive" refers to a material that exhibits a soft solid (viscoelastic) state at temperatures near room temperature and that has the property of easily adhering to an adherend by pressure, as described above. The adhesive referred to here is generally a material having a complex tensile modulus E * (1Hz)<10 7 dyne / cm 2 The material may be a material having the properties satisfying the above (typically, a material having the above properties at 25°C).

[0019] <Adhesive sheet configuration example> The adhesive sheet disclosed herein may be a substrate-attached adhesive sheet having the above-mentioned adhesive layer on one or both sides of a non-releasable substrate (support substrate), or may be a substrate-less adhesive sheet (i.e., an adhesive sheet without a non-releasable substrate) having the above-mentioned adhesive layer held by a release liner. The concept of adhesive sheet here may include those called adhesive tapes, adhesive labels, adhesive films, etc. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be an adhesive sheet in the form of a processed form into various shapes.

[0020] An example of the structure of a double-sided adhesive substrateless adhesive sheet (substrateless double-sided adhesive sheet) is shown in FIG. 1. The adhesive sheet 1 shown in FIG. 1 has a structure in which both sides 21A, 21B of a substrateless adhesive layer 21 are protected by release liners 31, 32, each of which has at least the adhesive layer side as a release surface. Alternatively, the adhesive sheet may have a structure in which one surface (adhesive surface, first adhesive surface) of the substrateless adhesive layer is protected by a release liner having both sides as release surfaces, and when the adhesive sheet is rolled up, the other surface (adhesive surface, second adhesive surface) of the adhesive layer abuts against the back surface of the release liner, so that the second adhesive surface of the adhesive layer is also protected by the release liner. The technology disclosed herein can be preferably implemented in such a substrateless form from the viewpoint of reducing the thickness of the adhesive sheet. Substrateless adhesive sheets are advantageous in that they are easy to form thin layers and can maximize adhesive properties such as adhesive strength, impact resistance, flexibility, and holding power.

[0021] <Adhesive layer> (25℃ storage modulus) The adhesive layer disclosed herein is characterized by a storage modulus G'(25°C) at 25°C of less than 0.15 MPa. An adhesive having the above G'(25°C) can have flexibility capable of conforming to a complex shape of an adherend. The above G'(25°C) is preferably less than 0.14 MPa, more preferably 0.12 MPa or less, and may be 0.11 MPa or less. In addition, the above G'(25°C) is suitably 0.03 MPa or more, and from the viewpoint of compatibility with high temperature holding power, it is preferably 0.05 MPa or more, more preferably 0.09 MPa or more, even more preferably 0.10 MPa or more, and may be, for example, 0.11 MPa or more.

[0022] (Loss modulus at 25℃) Furthermore, although not particularly limited, it is appropriate that the pressure-sensitive adhesive layer disclosed herein generally has a loss modulus at 25°C G"(25°C) of 2.0 MPa or less. From the viewpoint of cohesive strength, the above G"(25°C) is preferably 1.0 MPa or less, more preferably 0.50 MPa or less, and even more preferably 0.30 MPa or less (e.g., 0.20 MPa or less). The above G"(25°C) may be 0.10 MPa or less (e.g., 0.07 MPa or less). Furthermore, it is appropriate that the above G"(25°C) is generally greater than 0.01 MPa, and from the viewpoint of wettability to the adherend surface and thus conformability to the shape of the adherend, it is preferably 0.03 MPa or more, more preferably 0.05 MPa or more, and even more preferably 0.07 MPa or more, and may be, for example, 0.08 MPa or more.

[0023] (25℃ tan δ) The tan δ(25°C) at 25°C of the pressure-sensitive adhesive layer disclosed herein can be appropriately set in consideration of the adhesion to an adherend at room temperature, the followability, the cohesive strength, and the like. Here, the tan δ (loss tangent) of the pressure-sensitive adhesive (layer) refers to the ratio of the loss modulus G" to the storage modulus G' of the pressure-sensitive adhesive (layer). That is, tan δ=G" / G'. For example, it is appropriate that tan δ(25°C) is about 0.1 or more, and from the viewpoint of followability and the like, it is preferably about 0.3 or more, more preferably about 0.5 or more, and may be about 0.7 or more. For example, it is appropriate that tan δ(25°C) is about 3 or less, and from the viewpoint of improving the cohesive strength, it is preferably about 1.5 or less, more preferably about 1.2 or less, even more preferably about 1.0 or less (for example, 0.90 or less), and may be about 0.80 or less (for example, 0.60 or less).

[0024] (80℃ storage modulus) In some embodiments, the storage modulus G'(80°C) of the pressure-sensitive adhesive layer at 80°C may be 0.01 MPa or more. A pressure-sensitive adhesive layer having a G'(80°C) of a predetermined value or more tends to have excellent high-temperature retention. The G'(80°C) is preferably 0.020 MPa or more, more preferably 0.025 MPa or more, even more preferably about 0.030 MPa or more (e.g., 0.035 MPa or more), particularly preferably 0.040 MPa or more, and may be 0.045 MPa or more (e.g., 0.050 MPa or more). The G'(80°C) is usually suitably less than 0.10 MPa, and may be, for example, less than 0.08 MPa, less than 0.06 MPa, or less than 0.05 MPa.

[0025] (Loss modulus at 80℃) Furthermore, although not particularly limited, it is appropriate that the loss modulus G"(80°C) of the pressure-sensitive adhesive layer at 80°C is 1.0 MPa or less. From the viewpoint of high-temperature cohesive strength, the above G"(80°C) is preferably 0.30 MPa or less, more preferably 0.10 MPa or less, even more preferably 0.05 MPa or less, and particularly preferably 0.03 MPa or less (for example, less than 0.02 MPa). The above G"(80°C) is usually appropriately greater than 0.001 MPa, and may be 0.005 MPa or more, or may be 0.010 MPa or more.

[0026] (80℃ tan δ) In addition, the tan δ(80°C) of the adhesive layer disclosed herein at 80°C can be appropriately set in consideration of the adhesion, conformability, cohesive strength, etc. to the adherend at high temperatures. For example, tan δ(80°C) is appropriately set to about 0.03 or more, preferably about 0.08 or more, more preferably about 0.10 or more, and even more preferably 0.20 or more (e.g., 0.30 or more). In addition, tan δ(80°C) is appropriately set to about 1.0 or less, preferably about 0.80 or less, more preferably about 0.60 or less, and even more preferably 0.50 MPa or less (e.g., about 0.40 or less).

[0027] ((G´(80℃) / G´(25℃)) In some preferred embodiments, the pressure-sensitive adhesive layer has a ratio (G'(80°C) / G'(25°C)) of the storage modulus G'(25°C) at 25°C to the storage modulus G'(80°C) at 80°C that is greater than 0.20. As described above, a pressure-sensitive adhesive having a ratio of the storage modulus G'(25°C) to the storage modulus G'(80°C) within a predetermined range tends to have relatively high flexibility at room temperature and maintain relatively high cohesive strength at high temperatures. Therefore, a pressure-sensitive adhesive that satisfies the above characteristics can preferably achieve both complex shape conformability and high temperature retention. The ratio (G'(80°C) / G'(25°C)) may be 0.22 or more, 0.25 or more, or 0.27 or more, more preferably 0.30 or more, even more preferably 0.35 or more, and particularly preferably 0.40 or more (e.g., 0.42 or more). The upper limit of the ratio (G'(80°C) / G'(25°C)) is not particularly limited, and is usually 0.80 or less, and may be, for example, 0.60 or less, or 0.50 or less.

[0028] Although not particularly limited, the glass transition temperature (Tg) of the adhesive layer is suitably controlled to about 20° C. or less from the viewpoint of adhesion to the adherend. An adhesive layer having the above Tg also tends to have excellent impact resistance. From the viewpoint of conformability to a complex adherend shape, the Tg of the adhesive layer is preferably about 10° C. or less, more preferably about 5° C. or less, and may be about 0° C. or less or may be about -5° C. or less (for example, -10° C. or less). From the viewpoint of improving cohesive force, the Tg of the adhesive layer is suitably about -25° C. or more, and from the viewpoint of obtaining good high-temperature retention, it is preferably about -15° C. or more, more preferably about -12° C. or more, and may be about -7° C. or more or may be about -3° C. or more (for example, -1° C. or more). In this specification, the Tg of the adhesive layer refers to the glass transition temperature determined from the peak temperature of tan δ in dynamic viscoelasticity measurement.

[0029] The specific numerical ranges of the viscoelastic properties of the above-mentioned adhesive layer (25°C storage modulus, 25°C loss modulus, 25°C tan δ, 80°C storage modulus, 80°C loss modulus, 80°C tan δ and Tg (peak top temperature of tan δ)) can be the numerical ranges of the viscoelastic properties of the adhesive sheet (25°C storage modulus, 25°C loss modulus, 25°C tan δ, 80°C storage modulus, 80°C loss modulus, 80°C tan δ and Tg (peak top temperature of tan δ)) when the adhesive sheet is a substrateless adhesive sheet consisting essentially of an adhesive layer alone.

[0030] The viscoelastic properties of the above-mentioned adhesive layer are, based on the contents of this specification, Mw of 70 × 10 4 and at least one selected from an oligomer and a tackifier resin having a softening point of less than 145°C, and the proportions used are adjusted, and the adhesive composition containing other components (such as a crosslinking agent) as necessary is appropriately set, and adjustment can be made by adjusting the polymerization conditions of the polymer and the manufacturing conditions of the adhesive layer, etc.

[0031] In the technology disclosed herein, the 25°C storage modulus, 25°C loss modulus, 25°C tan δ, 80°C storage modulus, 80°C loss modulus, 80°C tan δ, and Tg (peak top temperature of tan δ) of the adhesive layer can be determined by dynamic viscoelasticity measurement. Specifically, a plurality of adhesive layers (adhesive sheets in the case of a substrate-less adhesive sheet) to be measured are stacked to prepare an adhesive layer having a thickness of about 2 mm. The adhesive layer is punched into a disk shape having a diameter of 7.9 mm, and a sample is sandwiched and fixed between parallel plates. Dynamic viscoelasticity measurement is performed under the following conditions using a viscoelasticity tester (e.g., ARES or an equivalent product manufactured by TA Instruments), and the 25°C storage modulus, 25°C loss modulus, 25°C tan δ, 80°C storage modulus, 80°C loss modulus, 80°C tan δ, and Tg (peak top temperature of tan δ) are determined. Measurement mode: Shear mode Temperature range: -70℃~150℃ Heating rate: 5℃ / min ·Measurement frequency: 1Hz The above method is also used for the measurements in the Examples described later. The pressure-sensitive adhesive layer to be measured can be formed by applying the corresponding pressure-sensitive adhesive composition in a layer shape and drying or curing it.

[0032] (Adhesive) In the technology disclosed herein, the type of adhesive constituting the adhesive layer is not particularly limited. The adhesive may contain one or more of various rubber-like polymers such as acrylic polymers, rubber polymers (natural rubber, synthetic rubber, a mixture thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers as adhesive polymers (meaning structural polymers that form the adhesive, hereinafter also referred to as "base polymers"). From the viewpoint of adhesive performance, cost, etc., an adhesive containing an acrylic polymer or a rubber polymer as a base polymer may be preferably adopted. Among them, an adhesive having an acrylic polymer as a base polymer (acrylic adhesive) is preferable. The technology disclosed herein is preferably implemented in an embodiment using an acrylic adhesive.

[0033] Hereinafter, the following description will be mainly focused on an adhesive layer made of an acrylic adhesive, i.e., an adhesive sheet having an acrylic adhesive layer, however, it is not intended to limit the adhesive layer of the adhesive sheet disclosed herein to one made of an acrylic adhesive.

[0034] (polymer) The adhesive layer disclosed herein has a Mw of 70×10 4 The polymer is characterized by including a polymer having a Mw of 90×10 or more. By using a polymer having the above Mw, the cohesive force based on the entanglement of the polymer is exerted, and good high-temperature retention is easily obtained. In addition, the cohesive force based on the high molecular weight of the polymer has a high degree of freedom in the molecular structure compared to general chemical crosslinking, and can maintain a certain degree of flexibility. Therefore, it tends to be easy to realize good conformability to complex adherend shapes while maintaining high-temperature retention. The Mw of the polymer is preferably about 90×10 4More preferably, 100×10 4 or more (e.g. 100×10 4 More preferably, approximately 110×10 4 More preferably, about 120×10 4 or more (for example, about 130 x 10 4 The Mw is usually about 500×10 4 Less than or equal to 300×10 4 From the viewpoint of improving flexibility, the above Mw is preferably about 200×10 4 Less than or equal to 150×10 4 Less than (for example, about 140×10 4 The polymer may be one or more of the various polymers exemplified above as the rubber-like polymer. For example, in the case of an acrylic polymer obtained by solution polymerization, it is preferable to set the Mw within the above range.

[0035] The above polymer is typically a component used as a base polymer in the adhesive layer. The polymer is preferably an acrylic polymer. Here, the "base polymer" of the adhesive refers to the main component of the rubber-like polymer contained in the adhesive, and is not otherwise limited to this. The rubber-like polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, the "main component" refers to a component contained in an amount of more than 50% by weight, unless otherwise specified.

[0036] In addition, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer". Therefore, in this specification, an acrylic polymer is defined as a polymer containing a monomer unit derived from an acrylic monomer. A typical example of an acrylic polymer is an acrylic polymer in which the proportion of an acrylic monomer in the total monomer components used in the synthesis of the acrylic polymer is more than 50% by weight. In addition, the term "(meth)acryloyl" refers collectively to acryloyl and methacryloyl. Similarly, the term "(meth)acrylate" refers collectively to acrylate and methacrylate, and the term "(meth)acrylic" refers collectively to acrylic and methacrylic.

[0037] (Acrylic polymer) In the technology disclosed herein, the acrylic polymer used as the polymer is preferably, for example, a polymer of a monomer raw material that contains an alkyl (meth)acrylate as a main monomer and may further contain a sub-monomer copolymerizable with the main monomer. Here, the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition in the monomer raw material.

[0038] As the alkyl(meth)acrylate, for example, a compound represented by the following formula (1) can be suitably used. CH 2 =C(R 1 )COOR 2 (1) Here, R in the above formula (1) 1 is a hydrogen atom or a methyl group. 2 is a chain alkyl group having 1 to 20 carbon atoms. Hereinafter, this range of carbon atoms will be referred to as "C 1-20 From the viewpoint of the storage modulus of the adhesive, R 2 C 1-14 (For example, C1-10 , typically C 4-8 It is appropriate to use alkyl (meth)acrylate, which is a chain alkyl group of R, as the main monomer. 2 In addition, from the viewpoint of adhesive properties, alkyl (meth)acrylates in which R is a butyl group or a 2-ethylhexyl group are preferred. 1 is a hydrogen atom and R 2 C 4-8 Alkyl acrylate, which is a chain alkyl group of 4-8 It is preferable to use alkyl acrylate as the main monomer.

[0039] R 2 C 1-20Specific examples of the alkyl(meth)acrylate, which is a chain alkyl group, include, but are not limited to, methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate, s-butyl(meth)acrylate, t-butyl(meth)acrylate, pentyl(meth)acrylate, isopentyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl ... Examples of the alkyl (meth)acrylate include isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. These alkyl (meth)acrylates can be used alone or in combination of two or more. Suitable examples of the alkyl (meth)acrylate include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA). Particularly preferred alkyl (meth)acrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA).

[0040] The proportion of alkyl (meth)acrylate in the monomer components constituting the acrylic polymer is typically more than 50% by weight, and can be, for example, 70% by weight or more, 85% by weight or more, or 90% by weight or more. The upper limit of the proportion of alkyl (meth)acrylate is not particularly limited, but is preferably 99.5% by weight or less (for example, 99% by weight or less), or may be 98% by weight or less (for example, less than 97% by weight) from the viewpoint of favorably exerting the characteristics (for example, cohesive force) based on the secondary monomer such as a carboxyl group-containing monomer. Alternatively, the acrylic polymer may be substantially a polymer of only alkyl (meth)acrylate.

[0041] In addition, C is used as a monomer component. 4-8 When using an alkyl acrylate, the alkyl (meth)acrylate C contained in the monomer component 4-8 The proportion of alkyl acrylate is preferably 70% by weight or more, and more preferably 90% by weight or more.

[0042] The technology disclosed herein can be preferably implemented in an embodiment in which the monomer component constituting the acrylic polymer contains at least one of BA and 2EHA, and the total amount of BA and 2EHA among the alkyl(meth)acrylates contained in the monomer component is 75% by weight or more (usually 85% by weight or more, for example 90% by weight or more, or even 95% by weight or more). The technology disclosed herein can be implemented, for example, in an embodiment in which the alkyl(meth)acrylate contained in the monomer component is BA alone, 2EHA alone, or a combination of BA and 2EHA.

[0043] In some preferred embodiments, the monomer components constituting the acrylic polymer are 1-6 The acrylic polymer contains 50% by weight or more of alkyl (meth)acrylate. 1-6 The polymerization ratio of the alkyl (meth)acrylate is preferably 50% by weight or more. 1-6By using alkyl (meth)acrylate as the main monomer, the 80°C storage modulus can be favorably improved, thereby improving the high-temperature cohesive strength and achieving compatibility with flexibility. 1-6 The proportion of alkyl (meth)acrylate (in other words, the polymerization proportion) is preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 92% by weight or more (for example, more than 95% by weight). 1-6 The upper limit of the proportion of alkyl (meth)acrylate is not particularly limited, but is usually 99% by weight or less, and in relation to the proportion of other copolymerizable monomers used, it is appropriate to set it to 98% by weight or less, preferably 97% by weight or less, and may be less than 95% by weight. 1-6 The alkyl (meth)acrylates may be used alone or in combination of two or more. 1-6 As alkyl (meth)acrylate, C 1-6 Alkyl acrylates are preferred, C 2-6 Alkyl acrylates are more preferred, C 4-6 More preferred are alkyl acrylates. 1-6 The alkyl (meth)acrylate is preferably 1-4 Alkyl acrylate, more preferably C 2-4 It is an alkyl acrylate. 1-6 A suitable example of the alkyl (meth)acrylate is BA.

[0044] In some other preferred embodiments, the monomer components constituting the acrylic polymer are 7-10 The acrylic polymer contains 50% by weight or more of alkyl (meth)acrylate. 7-10 The copolymerization ratio of alkyl (meth)acrylate is preferably 50% by weight or more. 7-10By using alkyl (meth)acrylate as the main monomer, the 25°C storage modulus can be reduced to a desired level, which increases flexibility and improves conformability to the adherend, while also achieving high-temperature retention. 7-10 The proportion of alkyl (meth)acrylate (in other words, copolymerization proportion) may be more than 60% by weight, or may be more than 70% by weight, more preferably more than 80% by weight, even more preferably 90% by weight or more, and particularly preferably 92% by weight or more (for example, 95% by weight or more). 7-10 The upper limit of the proportion of alkyl (meth)acrylate is not particularly limited, but is usually 99% by weight or less, and considering the proportion of other copolymerizable monomers (e.g., acidic group-containing monomers) used, it is appropriate to set it to 97% by weight or less, and preferably 96% by weight or less. 7-10 The alkyl (meth)acrylates may be used alone or in combination of two or more. 7-10 Suitable examples of alkyl (meth)acrylates include C acrylates such as 2EHA, isooctyl acrylate, and isononyl acrylate. 7-10 Among them, 2EHA is preferable.

[0045] The acrylic polymer in the technology disclosed herein may be copolymerized with a secondary monomer. Examples of secondary monomers that can introduce functional groups that can be crosslinking base points into the acrylic polymer or contribute to improving adhesive strength include carboxyl group-containing monomers, hydroxyl group (OH group)-containing monomers (2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc.), acid anhydride group-containing monomers, amide group-containing monomers ((meth)acrylamide, N,N-dimethyl (meth)acrylamide, etc.), amino group-containing monomers (aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), epoxy group-containing monomers, cyano group-containing monomers, keto group-containing monomers, monomers having nitrogen atom-containing rings (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), alkoxysilyl group-containing monomers, imide group-containing monomers, etc. The secondary monomers may be used alone or in combination of two or more.

[0046] When the monomer component constituting the acrylic polymer contains the functional group-containing monomer, the content of the functional group-containing monomer in the monomer component is not particularly limited. From the viewpoint of appropriately exerting the effect of using the functional group-containing monomer, the content of the functional group-containing monomer in the monomer component can be, for example, 0.1% by weight or more, suitably 0.5% by weight or more, and may be 1% by weight or more. In addition, from the viewpoint of easily balancing the adhesive performance in relation to the main monomer, the content of the functional group-containing monomer in the monomer component is suitably 40% by weight or less, preferably 20% by weight or less, and may be 10% by weight or less (for example, 5% by weight or less).

[0047] In some preferred embodiments, an acidic group-containing monomer is used as a monomer copolymerizable with the main monomer, alkyl (meth)acrylate. The acidic group-containing monomer can improve cohesion based on its polarity and exhibit good bonding strength to polar adherends. In addition, when a crosslinking agent such as an isocyanate-based or epoxy-based crosslinking agent is used, the acidic group (typically a carboxy group) becomes a crosslinking point of the acrylic polymer. These actions make it possible to suitably realize conformability to complex adherend shapes and high-temperature retention.

[0048] As the acidic group-containing monomer, a carboxyl group-containing monomer is preferably used. Examples of the carboxyl group-containing monomer include ethylenically unsaturated monocarboxylic acids such as acrylic acid (AA), methacrylic acid (MAA), carboxyethyl (meth)acrylate, crotonic acid, and isocrotonic acid; and ethylenically unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and citraconic acid, and their anhydrides (maleic anhydride, itaconic anhydride, etc.). The acidic group-containing monomer may also be a monomer having a metal salt (e.g., an alkali metal salt) of a carboxyl group. Among them, AA and MAA are preferred, and AA is more preferred.

[0049] In the technology disclosed herein, the content of the acidic group-containing monomer (typically a carboxyl group-containing monomer) in the monomer components (in other words, the copolymerization ratio of the acidic group-containing monomer in the acrylic polymer) is suitably 1.0% by weight or more. By using a predetermined amount or more of the acidic group-containing monomer, the cohesive strength (particularly high temperature cohesive strength) of the adhesive layer can be improved. The copolymerization ratio of the acidic group-containing monomer in the acrylic polymer is preferably 1.5% by weight or more, more preferably 2.0% by weight or more, even more preferably 2.5% by weight or more, and particularly preferably 3.0% by weight or more. In some preferred embodiments, the copolymerization ratio of the acidic group-containing monomer in the acrylic polymer is 4.0% by weight or more, may be more than 5.0% by weight, may be 6.0% by weight or more, or may be 6.5% by weight or more. The copolymerization ratio of the acidic group-containing monomer in the acrylic polymer is usually appropriate to be 20% by weight or less, and from the viewpoint of improving adhesion to an adherend and therefore tracking ability, it is preferably less than 10% by weight, more preferably less than 8.0% by weight, even more preferably less than 7.0% by weight, particularly preferably less than 6.0% by weight, and may be less than 5.0% by weight (for example, less than 4.0% by weight).

[0050] The acrylic polymer preferably used in the technology disclosed herein may be a copolymer in which an alkyl (meth)acrylate as a main monomer and an acidic group-containing monomer as a sub-monomer are copolymerized. In such an acrylic polymer, the proportion of copolymerization components other than the alkyl (meth)acrylate and the acidic group-containing monomer may be less than 10% by weight, less than 3% by weight, less than 1% by weight, less than 0.1% by weight, or less than 0.03% by weight (e.g., less than 0.01% by weight). The monomer components constituting the acrylic polymer may be substantially free of functional group-containing monomers other than the acidic group-containing monomer. The acrylic polymer substantially composed of an alkyl (meth)acrylate and an acidic group-containing monomer can maximize the effects of the alkyl (meth)acrylate and the acidic group-containing monomer.

[0051] Alternatively, in some embodiments, the monomer components forming the acrylic polymer may contain, for example, a hydroxyl group-containing monomer as a functional group-containing monomer other than the acid group-containing monomer. The ratio of the hydroxyl group-containing monomer in the monomer components may be, for example, about 0.01% by weight or more and less than 1% by weight, and may be less than 0.5% by weight or less than 0.1% by weight.

[0052] The monomer components constituting the acrylic polymer may contain other copolymerization components other than the above-mentioned secondary monomers for the purpose of improving cohesive strength, etc. Examples of other copolymerization components include vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, cyclopentyl (meth)acrylate, and isobornyl (meth)acrylate; aromatic ring-containing (meth)acrylates such as aryl (meth)acrylates (e.g., phenyl (meth)acrylate), aryloxyalkyl (meth)acrylates (e.g., phenoxyethyl (meth)acrylate), and arylalkyl (meth)acrylates (e.g., benzyl (meth)acrylate); olefin monomers; chlorine-containing monomers; isocyanate group-containing monomers such as 2-(meth)acryloyloxyethyl isocyanate; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; and the like. The other copolymerization components may be used alone or in combination of two or more.

[0053] The amount of such other copolymerization components is not particularly limited and may be appropriately selected depending on the purpose and application, but from the viewpoint of appropriately exerting the effect of use, it is appropriate to set it to 0.05 wt% or more, and it may be 0.5 wt% or more. In addition, from the viewpoint of easily balancing the adhesive performance, the content of other copolymerization components in the monomer component is appropriate to be 20 wt% or less, and it may be 10 wt% or less (for example, 5 wt% or less). The technology disclosed herein can also be preferably implemented in an embodiment in which the monomer component does not substantially contain other copolymerization components. Here, "the monomer component does not substantially contain other copolymerization components" means that other copolymerization components are not used at least intentionally, and it is acceptable for other copolymerization components to be unintentionally contained, for example, about 0.01 wt% or less.

[0054] The acrylic polymer may contain a polyfunctional monomer having at least two polymerizable functional groups (typically radically polymerizable functional groups) having an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, as another monomer component. By using a polyfunctional monomer as a monomer component, the cohesive force of the adhesive layer can be increased. The polyfunctional monomer can be used as a crosslinking agent. The polyfunctional monomer is not particularly limited, and examples thereof include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, neopentyl glycol di(meth)acrylate, and the like. The polyfunctional monomer can be used alone or in combination of two or more kinds.

[0055] The amount of the polyfunctional monomer used is not particularly limited, and can be appropriately set so that the purpose of using the polyfunctional monomer is achieved. The amount of the polyfunctional monomer used can be about 3% by weight or less of the monomer component, preferably about 2% by weight or less, and more preferably about 1% by weight or less (for example, about 0.5% by weight or less). When using a polyfunctional monomer, the lower limit of the amount used is not particularly limited as long as it is greater than 0% by weight. Usually, the effect of using the polyfunctional monomer can be appropriately exhibited by setting the amount of the polyfunctional monomer used to about 0.001% by weight or more (for example, about 0.01% by weight or more) of the monomer component.

[0056] The composition of the monomer components constituting the acrylic polymer is suitably designed so that the glass transition temperature (Tg) of the acrylic polymer is about -15°C or less (for example, about -70°C or more and -15°C or less). Here, the Tg of the acrylic polymer refers to the Tg calculated by the Fox formula based on the composition of the monomer components. The Fox formula, as shown below, is a relational expression between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer. 1 / Tg=Σ(Wi / Tgi) In the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi represents the glass transition temperature (unit: K) of the homopolymer of monomer i.

[0057] The glass transition temperature of the homopolymer used to calculate Tg is a value described in a publicly known document. For example, for the monomers listed below, the following values ​​are used as the glass transition temperatures of the homopolymers of the monomers. 2-Ethylhexyl acrylate -70℃ n-Butyl acrylate -55℃ 2-Hydroxyethyl acrylate -15℃ 4-Hydroxybutyl acrylate -40℃ Vinyl acetate 32℃ Acrylic acid 106℃ Methacrylic acid 228℃

[0058] For the glass transition temperature of homopolymers of monomers other than those exemplified above, the values ​​described in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989) shall be used. For monomers for which multiple values ​​are described in this document, the highest value shall be adopted. If the value is not described in the Polymer Handbook, the value obtained by the measurement method described in JP-A-2007-51271 shall be used.

[0059] Although not particularly limited, from the viewpoint of adhesion and flexibility, the Tg of the acrylic polymer is advantageously about -25°C or less, preferably about -35°C or less, more preferably about -40°C or less, and even more preferably about -45°C or less, for example, it may be -50°C or less, or it may be -55°C or less. In addition, from the viewpoint of the cohesive strength of the adhesive layer, the Tg of the acrylic polymer is usually about -75°C or more, preferably about -70°C or more. In some embodiments, the Tg of the acrylic polymer may be -60°C or less, or it may be -62°C or less (for example, -64°C or less). In addition, from the viewpoint of the cohesive strength of the adhesive layer, the Tg of the acrylic polymer may be about -65°C or more, or it may be about -60°C or more (for example, about -55°C or more). The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (i.e., the type and amount ratio of the monomers used in the synthesis of the polymer).

[0060] The dispersity (Mw / Mn) of the polymer (preferably an acrylic polymer) disclosed herein is not particularly limited. The dispersity (Mw / Mn) here refers to the dispersity (Mw / Mn) expressed as the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn). In some preferred embodiments, the dispersity (Mw / Mn) of the polymer is 40 or less, and may be less than 20, less than 15 (e.g., 12 or less), less than 10, or less than 7.0. By restricting the molecular weight distribution within an appropriate range, stable characteristics are easily obtained. In a polymer (preferably an acrylic polymer) having a Mw of more than 700,000, by setting the Mw / Mn within the above range, the cohesive force and flexibility based on the entanglement of the high molecular weight substance in the polymer tend to be accurately expressed. The lower limit of the Mw / Mn is not particularly limited, and may be, for example, 3.0 or more, 5.0 or more, or 7.0 or more. By having a certain degree of molecular weight distribution, the effects of the low molecular weight substance and the high molecular weight substance tend to be well balanced. Such polymers also tend to be more manufacturable.

[0061] Mw, Mn and Mw / Mn can be adjusted by the polymerization conditions (time, temperature, etc.), the concentration of non-volatile matter (monomer components) during polymerization, the amount of polymerization initiator used, the use of a chain transfer agent, the selection of a polymerization solvent based on the chain transfer constant, etc. Mw and Mn can be calculated from the standard polystyrene-equivalent values ​​obtained by GPC (gel permeation chromatography). As a GPC device, for example, a model named "HLC-8320GPC" (column: TSKgelGMH-H(S), manufactured by Tosoh Corporation) can be used.

[0062] The method for obtaining a polymer (e.g., an acrylic polymer) is not particularly limited, and various polymerization methods known as polymer synthesis methods, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately adopted. For example, a solution polymerization method can be preferably adopted. The polymerization temperature when carrying out solution polymerization can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, and the like, and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0063] The solvent (polymerization solvent) used in the solution polymerization can be appropriately selected from conventionally known organic solvents (toluene, ethyl acetate, etc.). The initiator used in the polymerization can be appropriately selected from conventionally known polymerization initiators (for example, azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN), peroxide-based initiators, etc.) depending on the type of polymerization method. The amount of the polymerization initiator used may be a normal amount, and can be selected, for example, from the range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) relative to 100 parts by weight of the monomer component.

[0064] (tackifier resin) The adhesive layer in the technology disclosed herein can contain a tackifier resin. This can increase the peel strength of the adhesive sheet. As the tackifier resin, one or more selected from tackifier resins such as phenol-based tackifier resins, terpene-based tackifier resins, modified terpene-based tackifier resins, rosin-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, and ketone-based tackifier resins can be used. Among these, phenol-based tackifier resins, terpene-based tackifier resins, and modified terpene-based tackifier resins are preferred, and phenol-based tackifier resins (preferably terpene phenol resins) are more preferred.

[0065] Examples of phenolic tackifying resins include terpene phenolic resins, hydrogenated terpene phenolic resins, alkyl phenolic resins, and rosin phenolic resins. Terpene phenolic resin refers to a polymer containing a terpene residue and a phenol residue, and is a concept that includes both a copolymer of a terpene and a phenolic compound (terpene-phenol copolymer resin) and a homopolymer or copolymer of a terpene modified with phenol (phenol-modified terpene resin). Suitable examples of terpenes that constitute such terpene phenolic resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-, l-, and d / l-forms (dipentene)). Hydrogenated terpene phenolic resin refers to a hydrogenated terpene phenolic resin having a structure obtained by hydrogenating such a terpene phenolic resin. It is also called hydrogenated terpene phenolic resin. Alkylphenol resins are resins (oil-based phenolic resins) obtained from alkylphenols and formaldehyde. Examples of alkylphenol resins include novolac and resol types. Rosin phenolic resins are typically phenol-modified products of rosins or the above-mentioned various rosin derivatives (including rosin esters, unsaturated fatty acid modified rosins, and unsaturated fatty acid modified rosin esters). Examples of rosin phenolic resins include rosin phenolic resins obtained by adding phenol to rosins or the above-mentioned various rosin derivatives using an acid catalyst and then thermally polymerizing the resulting mixture.

[0066] Examples of terpene-based tackifier resins include polymers of terpenes (typically monoterpenes) such as α-pinene, β-pinene, d-limonene, l-limonene, and dipentene. The resin may be a homopolymer of one type of terpene, or a copolymer of two or more types of terpenes. Examples of homopolymers of one type of terpene include α-pinene polymer, β-pinene polymer, and dipentene polymer. Examples of modified terpene resins include those obtained by modifying the above-mentioned terpene resins. Specific examples include styrene-modified terpene resins and hydrogenated terpene resins.

[0067] The concept of rosin-based tackifier resins as used herein includes both rosins and rosin derivative resins. Examples of rosins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; and modified rosins obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, other chemically modified rosins, etc.).

[0068] The rosin derivative resin is typically a derivative of rosins as described above. The concept of rosin resin here includes derivatives of unmodified rosin and derivatives of modified rosin (including hydrogenated rosin, disproportionated rosin, and polymerized rosin). For example, rosin esters such as unmodified rosin esters, which are esters of unmodified rosin and alcohols, and modified rosin esters, which are esters of modified rosin and alcohols; unsaturated fatty acid modified rosins obtained by modifying rosin with unsaturated fatty acid; unsaturated fatty acid modified rosin esters obtained by modifying rosin esters with unsaturated fatty acid; rosin alcohols obtained by reducing the carboxyl groups of rosins or the above-mentioned various rosin derivatives (including rosin esters, unsaturated fatty acid modified rosins, and unsaturated fatty acid modified rosin esters); and metal salts of rosins or the above-mentioned various rosin derivatives. Specific examples of rosin esters include methyl esters, triethylene glycol esters, glycerin esters, pentaerythritol esters, and the like of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.).

[0069] Examples of hydrocarbon-based tackifying resins include various hydrocarbon resins such as aliphatic hydrocarbon resins, aromatic hydrocarbon resins, aliphatic cyclic hydrocarbon resins, aliphatic / aromatic petroleum resins (styrene-olefin copolymers, etc.), aliphatic / alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, and coumarone-indene resins.

[0070] The softening point of the tackifier resin is not particularly limited. From the viewpoint of improving the cohesive force, a tackifier resin having a softening point (softening temperature) of about 80° C. or more (preferably about 100° C. or more) can be preferably used. For example, a phenol-based tackifier resin (such as a terpene phenol resin) having such a softening point can be preferably used. In some embodiments, a terpene phenol resin having a softening point of about 135° C. or more (even more preferably about 140° C. or more) can be used. The upper limit of the softening point of the tackifier resin is not particularly limited. From the viewpoint of adhesion to an adherend or a substrate, a tackifier resin having a softening point of about 200° C. or less (more preferably about 180° C. or less) can be preferably used. The softening point of the tackifier resin can be measured based on the softening point test method (ring and ball method) specified in JIS K2207.

[0071] In some preferred embodiments, the tackifier resin is a tackifier resin T having a softening point of less than 145° C. L Tackifying resin T with a softening point of less than 145°C is used. L By using the tackifier resin T, it is possible to preferably form a pressure-sensitive adhesive that has both high-temperature retention and ability to conform to complex shapes. L The softening point of the tackifier resin T is preferably less than 135° C., more preferably less than 125° C., and may be 120° C. or less. L The lower limit of the softening point of the tackifier resin T is not particularly limited, and is, for example, 60° C. or higher (hence, solid at 30° C.), suitably 80° C. or higher, and from the viewpoint of achieving both high-temperature retention and ability to conform to complex shapes, preferably 90° C. or higher, more preferably 100° C. or higher, and may be 110° C. or higher. In the following, the softening point of the tackifier resin T having a softening point of 60° C. or higher but less than 145° C. L Tackifying resin T L1 Tackifier Resin T L (Specifically, tackifier resin T L1 As the tackifier resin T, an appropriate type can be selected from the above-mentioned tackifier resins, and among them, terpene phenol resins are preferably used. L can be used alone or in combination of two or more.

[0072] The adhesive layer is made of tackifier resin T L1 In the case where the tackifier resin T L1 The content of tackifier resin T L1 From the viewpoint of favorably exerting the effect of using the tackifier resin T, it is appropriate that the amount is 1 part by weight or more per 100 parts by weight of the polymer (e.g., acrylic polymer) in the adhesive layer, preferably 5 parts by weight or more, more preferably 10 parts by weight or more, even more preferably 15 parts by weight or more (e.g., more than 15 parts by weight), and particularly preferably 18 parts by weight or more. Also, from the viewpoint of cohesive force, the amount of the tackifier resin T per 100 parts by weight of the polymer is preferably 1 part by weight or more, more preferably 10 parts by weight or more, even more preferably 15 parts by weight or more (e.g., more than 15 parts by weight), and particularly preferably 18 parts by weight or more. L1 The amount of is suitably less than 50 parts by weight, and from the viewpoint of high temperature retention, is preferably less than 40 parts by weight, more preferably less than 30 parts by weight, and may be less than 25 parts by weight.

[0073] In addition, tackifier resin T L As a result, the liquid tackifier resin (liquid resin) T, which is liquid at 30°C, L2 Liquid resin T can be used. L2 By using the liquid resin T, the storage modulus at 25°C of the pressure-sensitive adhesive layer can be preferably reduced. L2 For example, the liquid resin T may be a tackifier resin having a softening point of less than 60° C., preferably about 50° C. or less, and more preferably about 40° C. or less. L2 As the tackifier resin, an appropriate type can be selected from the above-mentioned tackifier resins, and among them, tackifier resins such as rosin-based, terpene-based, and hydrocarbon-based tackifier resins are preferred, and rosin-based tackifier resins such as hydrogenated rosin methyl ester are particularly preferred. L2 The liquid resin T may be used alone or in combination of two or more. L2 is the above tackifier resin T L1 It is preferable to use it in combination with

[0074] Adhesive layer is liquid resin T L2 In the case where liquid resin T L2 The content of liquid resin T L2From the viewpoint of favorably exerting the effect of using the liquid resin T, it is appropriate that the amount of the liquid resin T is 0.1 parts by weight or more relative to 100 parts by weight of the polymer (e.g., acrylic polymer) in the adhesive layer, preferably 1 part by weight or more, more preferably 2 parts by weight or more, and even more preferably 3 parts by weight or more. Also, from the viewpoint of cohesive force, the amount of the liquid resin T relative to 100 parts by weight of the polymer is 0.1 parts by weight or more, more preferably 1 part by weight or more, more preferably 2 parts by weight or more, and even more preferably 3 parts by weight or more. L2 The amount of is suitably less than 20 parts by weight, and from the viewpoint of high temperature retention, is preferably less than 10 parts by weight, more preferably less than 8 parts by weight, and may be 5 parts by weight or less.

[0075] The adhesive layer is made of tackifier resin T L In the case where the tackifier resin T L The total content of tackifier resin T L From the viewpoint of favorably exerting the effect of using, it is appropriate that the amount of the tackifier resin is 1 part by weight or more relative to 100 parts by weight of the polymer (e.g., acrylic polymer) in the adhesive layer, preferably 5 parts by weight or more, more preferably 10 parts by weight or more, even more preferably 15 parts by weight or more (e.g., 18 parts by weight or more), and particularly preferably 20 parts by weight or more (e.g., 22 parts by weight or more). From the viewpoint of cohesive strength, the amount of the tackifier resin relative to 100 parts by weight of the polymer is appropriate to be 60 parts by weight or less, and from the viewpoint of high temperature retention, it is preferably 50 parts by weight or less, more preferably 40 parts by weight or less, and may be 30 parts by weight or less (e.g., 28 parts by weight or less).

[0076] Tackifier resin T with a softening point of less than 145°C L In an embodiment in which a tackifier resin T having a softening point of less than 145° C. is used, the pressure-sensitive adhesive layer L High softening point tackifier resins that do not fall under the above (typically tackifier resins with a softening point of 145°C or higher) H The adhesive layer may or may not contain a tackifier resin T L In addition to tackifier resin T H When it contains tackifier resin T H The content of tackifier resin T LIt is appropriate that the amount is less than 100 parts by weight, preferably less than 50 parts by weight, more preferably less than 30 parts by weight, and even more preferably less than 10 parts by weight, and may be less than 1 part by weight or less than 0.1 part by weight. L Tackifier resin T H By limiting the amount of, the storage modulus at 25°C of the pressure-sensitive adhesive layer can be easily reduced.

[0077] Some preferred embodiments include an embodiment in which the tackifier resin contains one or more phenol-based tackifier resins (typically terpene phenol resins). The technology disclosed herein can be preferably implemented, for example, in an embodiment in which, assuming the total amount of the tackifier resins to be 100% by weight, about 25% by weight or more (more preferably about 30% by weight or more) of the tackifier resins is a terpene phenol resin. About 50% by weight or more of the total amount of the tackifier resins may be a terpene phenol resin, or about 70% by weight or more (for example, about 80% by weight or more) may be a terpene phenol resin. Substantially all of the tackifier resins (for example, about 95 to 100% by weight, or even about 99 to 100% by weight) may be a terpene phenol resin.

[0078] Although not particularly limited, in some embodiments, the tackifier resin may include a tackifier resin having a hydroxyl value of more than 20 mgKOH / g. Among them, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more is preferable. Hereinafter, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more may be referred to as a "high hydroxyl value resin". By using a tackifier resin containing such a high hydroxyl value resin, a pressure-sensitive adhesive layer having excellent adhesion to an adherend and high cohesive strength can be realized. The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoint of compatibility with a polymer, the hydroxyl value of the high hydroxyl value resin is suitably about 200 mgKOH / g or less, preferably about 100 mgKOH / g or less, may be about 70 mgKOH / g or less, or may be about 65 mgKOH / g or less. The high hydroxyl value resin may be used alone or in combination of two or more types. The technology disclosed herein can be preferably implemented in an embodiment in which the tackifier resin contains a high hydroxyl value resin (e.g., a phenol-based tackifier resin, preferably a terpene phenol resin) having a hydroxyl value of more than 20 mgKOH / g (e.g., 30 to 65 mgKOH / g). In some preferred embodiments, the high hydroxyl value resin is a tackifier resin T having a softening point of less than 145°C. L It could be.

[0079] Here, the hydroxyl value may be a value measured by potentiometric titration as specified in JIS K0070: 1992. The specific measurement method is as follows. [Method for measuring hydroxyl value] 1. Reagents (1) As the acetylation reagent, take about 12.5 g (about 11.8 mL) of acetic anhydride, add pyridine to make the total volume 50 mL, and stir thoroughly before use. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to make the total volume 100 mL, and stir thoroughly before use. (2) Use a 0.5 mol / L potassium hydroxide ethanol solution as the measurement reagent. (3) In addition, prepare toluene, pyridine, ethanol and distilled water. 2.Operation (1) Accurately weigh out approximately 2 g of sample into a flat-bottom flask, add 5 mL of acetylation reagent and 10 mL of pyridine, and attach an air condenser. (2) Heat the flask in a 100°C bath for 70 minutes, then allow it to cool, add 35 mL of toluene as a solvent from the top of the cooling tube and stir, then add 1 mL of distilled water and stir to decompose the acetic anhydride. Heat again in the bath for 10 minutes to complete the decomposition, then allow it to cool. (3) Wash the cooling tube with 5 mL of ethanol and remove it. Then, add 50 mL of pyridine as a solvent and stir. (4) Add 25 mL of 0.5 mol / L potassium hydroxide ethanol solution using a volumetric pipette. (5) Perform potentiometric titration with 0.5 mol / L potassium hydroxide ethanol solution. The inflection point of the obtained titration curve is the endpoint. (6) A blank test is carried out by carrying out steps (1) to (5) above without adding any sample. 3.Calculation The hydroxyl value is calculated according to the following formula. Hydroxyl value (mgKOH / g) = [(BC) x f x 28.05] / S + D Where: B: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test. C: Amount of 0.5 mol / L potassium hydroxide ethanol solution used for the sample (mL), f: Factor of 0.5 mol / L potassium hydroxide ethanol solution, S: weight of sample (g), D: acid number, 28.05: 1 / 2 the molecular weight of potassium hydroxide, 56.11. It is.

[0080] When the adhesive layer contains a tackifier resin, the amount (total amount) of the tackifier resin used is not particularly limited, and may be appropriately set within the range of about 1 to 100 parts by weight per 100 parts by weight of the polymer. From the viewpoint of favorably exhibiting the effect of improving peel strength, the amount of the tackifier resin used per 100 parts by weight of the polymer (e.g., acrylic polymer) is suitably 5 parts by weight or more, preferably 10 parts by weight or more, and may be 15 parts by weight or more. In addition, from the viewpoint of impact resistance and cohesive strength, the amount of the tackifier resin used per 100 parts by weight of the polymer (e.g., acrylic polymer) is suitably 50 parts by weight or less, may be 40 parts by weight or less, or may be 30 parts by weight or less.

[0081] (Oligomer) In some preferred embodiments, the pressure-sensitive adhesive layer contains an oligomer. By including an oligomer in the pressure-sensitive adhesive layer, in addition to the effect of improving the adhesive properties such as improving the adhesive strength, it is possible to preferably achieve both high temperature retention and complex shape conformability. The type of oligomer is not particularly limited, and is appropriately selected in consideration of compatibility and the like according to the type of polymer. The oligomer is typically an acrylic oligomer. The acrylic oligomer is preferably used in an embodiment in which an acrylic polymer is used as the polymer. As the oligomer, it is preferable to use a polymer having a higher Tg than the Tg of a copolymer corresponding to the composition of the monomer components of the polymer (typically roughly corresponding to the Tg of the acrylic polymer contained in the pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition). By including an oligomer, the adhesive strength of the pressure-sensitive adhesive can be improved. The oligomer can be used alone or in combination of two or more types.

[0082] The oligomer (typically an acrylic oligomer) has a Tg of about 0°C or more and about 300°C or less, preferably about 20°C or more and about 300°C or less, more preferably about 40°C or more and about 300°C or less. By having the Tg within the above range, the adhesive strength can be suitably improved. In some preferred embodiments, from the viewpoint of the cohesiveness of the adhesive, the Tg of the oligomer is about 30°C or more, more preferably about 50°C or more (e.g. about 60°C or more), and from the viewpoint of adhesiveness, etc., it is preferably about 200°C or less, more preferably about 150°C or less, and even more preferably about 100°C or less (e.g. about 80°C or less). The Tg of the oligomer is a value calculated based on the Fox formula, like the Tg of the copolymer corresponding to the composition of the above monomer components.

[0083] The weight average molecular weight (Mw) of the oligomer (typically an acrylic oligomer) can typically be about 1000 or more and less than about 30000, preferably about 1500 or more and less than about 20000, and more preferably about 2000 or more and less than about 10000. It is preferable that Mw is within the above range because good adhesive strength and retention properties can be obtained. In some preferred embodiments, from the viewpoint of high temperature retention, Mw of the oligomer is about 2500 or more (e.g., about 3000 or more), and from the viewpoint of adhesiveness, etc., it is preferably about 7000 or less, more preferably about 5000 or less (e.g., about 4500 or less, typically about 4000 or less). Mw of the oligomer can be measured by gel permeation chromatography (GPC) and calculated as a value in terms of standard polystyrene. Specifically, the measurement is performed using 2 columns of TSKgel GMH-H(20) on a Tosoh HPLC8020 with a tetrahydrofuran solvent at a flow rate of about 0.5 mL / min.

[0084] Examples of monomers constituting the acrylic oligomer used as the oligomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isobutyl (meth)acrylate, butyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, ... isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth)acrylate, isobutyl (meth Examples of the (meth)acrylate include alkyl (meth)acrylates such as sononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, and dodecyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and dicyclopentanyl (meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate and benzyl (meth)acrylate; and (meth)acrylates obtained from terpene compound derivative alcohols. Such (meth)acrylates can be used alone or in combination of two or more.

[0085] The acrylic oligomer preferably contains, as a monomer unit, an acrylic monomer having a relatively bulky structure, typified by alkyl (meth)acrylates in which the alkyl group has a branched structure, such as isobutyl (meth)acrylate and t-butyl (meth)acrylate; esters of (meth)acrylic acid and alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates), such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate and dicyclopentanyl (meth)acrylate; and (meth)acrylates having a cyclic structure, such as aryl (meth)acrylates, such as phenyl (meth)acrylate and benzyl (meth)acrylate, from the viewpoint of further improving the adhesiveness of the pressure-sensitive adhesive layer. In addition, when ultraviolet light is used in synthesizing an acrylic oligomer or preparing an adhesive layer, those having saturated bonds are preferred in that they are less likely to cause polymerization inhibition, and alkyl (meth)acrylates in which the alkyl group has a branched structure, or esters with alicyclic alcohols (alicyclic hydrocarbon group-containing (meth)acrylates) can be suitably used as monomers constituting the acrylic oligomer. The above-mentioned branched alkyl (meth)acrylates, alicyclic hydrocarbon group (meth)acrylates, and aryl (meth)acrylates all fall under the category of (meth)acrylate monomers in the technology disclosed herein. The alicyclic hydrocarbon group may be a saturated or unsaturated alicyclic hydrocarbon group.

[0086] The proportion of (meth)acrylate monomers (e.g., alicyclic hydrocarbon group-containing (meth)acrylates) in all monomer components constituting the acrylic oligomer is typically more than 50% by weight, preferably 60% by weight or more, and more preferably 70% by weight or more (e.g., 80% by weight or more, or even 90% by weight or more). In some preferred embodiments, the acrylic oligomer has a monomer composition consisting essentially of (meth)acrylate monomers.

[0087] As the constituent monomer component of the acrylic oligomer, in addition to the above (meth)acrylate monomer, a functional group-containing monomer can be used. Suitable examples of the functional group-containing monomer include monomers having a nitrogen atom-containing ring (typically a nitrogen atom-containing heterocycle) such as N-vinyl-2-pyrrolidone and N-acryloylmorpholine; amino group-containing monomers such as N,N-dimethylaminoethyl (meth)acrylate; amide group-containing monomers such as N,N-diethyl (meth)acrylamide; carboxy group-containing monomers such as AA and MAA; and hydroxy group-containing monomers such as 2-hydroxyethyl (meth)acrylate. These functional group-containing monomers can be used alone or in combination of two or more. Among them, carboxy group-containing monomers are preferred, and AA is particularly preferred.

[0088] When all monomer components constituting the acrylic oligomer contain a functional group-containing monomer, the proportion of the functional group-containing monomer (e.g., a carboxy group-containing monomer such as AA) in the above all monomer components is suitably about 1 wt % or more, preferably 2 wt % or more, more preferably 3 wt % or more, and is suitably about 15 wt % or less, preferably 10 wt % or less, more preferably 7 wt % or less.

[0089] An oligomer (typically an acrylic oligomer) can be formed by polymerizing its constituent monomer components. The polymerization method and polymerization mode are not particularly limited, and various conventionally known polymerization methods (e.g., solution polymerization, emulsion polymerization, bulk polymerization, photopolymerization, radiation polymerization, etc.) can be used in an appropriate mode. The type of polymerization initiator (e.g., azo-based polymerization initiator such as AIBN) that can be used as necessary is generally as exemplified in the synthesis of an acrylic polymer, and the amount of the polymerization initiator and the amount of a chain transfer agent such as n-dodecyl mercaptan that is optionally used are appropriately set based on technical common sense so as to obtain a desired molecular weight, so detailed explanations are omitted here.

[0090] From the above viewpoint, suitable acrylic oligomers include, for example, homopolymers of dicyclopentanyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), dicyclopentanyl acrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA), as well as copolymers of CHMA and isobutyl methacrylate (IBMA), copolymers of CHMA and IBXMA, copolymers of CHMA and acryloylmorpholine (ACMO), copolymers of CHMA and diethylacrylamide (DEAA), copolymers of CHMA and AA, copolymers of ADA and methyl methacrylate (MMA), copolymers of DCPMA and IBXMA, and copolymers of DCPMA and MMA.

[0091] When the adhesive layer disclosed herein contains an oligomer (preferably an acrylic oligomer), the content is suitably, for example, 0.1 parts by weight or more (e.g., 1 part by weight or more) relative to 100 parts by weight of the polymer (typically an acrylic polymer). From the viewpoint of better exerting the effect of the oligomer, the content of the oligomer is preferably about 5 parts by weight or more, more preferably about 8 parts by weight or more, and may be 12 parts by weight or more. In addition, from the viewpoint of compatibility with the polymer (typically an acrylic polymer), the content of the oligomer (typically an acrylic oligomer) is suitably less than 50 parts by weight, preferably less than 30 parts by weight, more preferably less than 20 parts by weight, and may be less than 15 parts by weight (e.g., less than 12 parts by weight).

[0092] In some preferred embodiments, the adhesive layer is made of the above-mentioned tackifier resin (typically a tackifier resin T having a softening point of less than 145° C. L) and one or more oligomers (preferably acrylic oligomers). By using the above tackifier resin and oligomer in combination, it is possible to achieve both high temperature retention and conformability to the adherend while exhibiting the desired adhesive properties. The above tackifier resin (typically, tackifier resin T having a softening point of less than 145° C.) L ) content C T and oligomer content C O The ratio is not particularly limited, and may be, for example, T / C O is suitably about 0.2 or more, preferably about 1 or more (e.g., more than 1), more preferably 1.2 or more, and even more preferably 1.5 or more, and may be 2.0 or more, or may be 2.3 or more. T / C O is suitably about 20 or less, preferably 10 or less, more preferably 5 or less, and further preferably 3 or less. Within the above ratio range, the effect of using the tackifier resin and oligomer in combination can be preferably exhibited.

[0093] In order to preferably exert the effects of the technology disclosed herein, the combined amount (total amount) of tackifier resin and oligomer (preferably acrylic oligomer) contained in the adhesive layer in some preferred embodiments is suitably approximately 1 part by weight or more per 100 parts by weight of polymer (preferably acrylic polymer), preferably approximately 10 parts by weight or more, more preferably approximately 20 parts by weight or more, even more preferably 30 parts by weight or more, and particularly preferably 35 parts by weight or more, and is suitably less than 120 parts by weight (for example, approximately 80 parts by weight or less), preferably less than 60 parts by weight, more preferably approximately 50 parts by weight or less, and even more preferably approximately 45 parts by weight or less.

[0094] (Crosslinking agent) In the technology disclosed herein, the adhesive composition used to form the adhesive layer may contain a crosslinking agent as necessary. The type of crosslinking agent is not particularly limited, and may be appropriately selected from conventionally known crosslinking agents. Examples of such crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, amine-based crosslinking agents, and silane coupling agents. Among these, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and melamine-based crosslinking agents are preferred, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are more preferred, and isocyanate-based crosslinking agents are particularly preferred. By appropriately selecting and using a crosslinking agent, the adhesive layer can obtain cohesive strength, have good high-temperature retention, and improve the followability and adhesive strength to the adherend. The pressure-sensitive adhesive layer in the technology disclosed herein may contain the crosslinking agent in a form after crosslinking reaction, a form before crosslinking reaction, a form partially crosslinked, an intermediate or composite form thereof, etc. The crosslinking agent is typically contained in the pressure-sensitive adhesive layer exclusively in a form after crosslinking reaction.

[0095] As the isocyanate-based crosslinking agent, a polyfunctional isocyanate (which refers to a compound having an average of two or more isocyanate groups per molecule, including those having an isocyanurate structure) can be preferably used. The isocyanate-based crosslinking agent can be used alone or in combination of two or more kinds.

[0096] Examples of the polyfunctional isocyanate include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates. Specific examples of aliphatic polyisocyanates include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,5-hexamethylene diisocyanate; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

[0097] Specific examples of alicyclic polyisocyanates include isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyl diisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0098] Specific examples of aromatic polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, Examples of the diisocyanate include 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, and xylylene-1,3-diisocyanate.

[0099] A preferred example of the polyfunctional isocyanate is a polyfunctional isocyanate having an average of three or more isocyanate groups per molecule. Such a trifunctional or higher isocyanate may be a multimer (typically a dimer or trimer) of a bifunctional or trifunctional or higher isocyanate, a derivative (for example, an addition reaction product of a polyhydric alcohol and two or more molecules of a polyfunctional isocyanate), a polymer, etc. For example, a dimer or trimer of diphenylmethane diisocyanate, an isocyanurate of hexamethylene diisocyanate (a trimer adduct of an isocyanurate structure), a reaction product of trimethylolpropane and tolylene diisocyanate, a reaction product of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanate, polyether polyisocyanate, polyester polyisocyanate, and other polyfunctional isocyanates may be mentioned. Commercially available examples of such polyfunctional isocyanates include those manufactured by Asahi Kasei Chemicals Corporation under the trade names "Duranate TPA-100," and those manufactured by Tosoh Corporation under the trade names "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096."

[0100] The amount of the isocyanate-based crosslinking agent used is not particularly limited. For example, it can be about 0.1 parts by weight or more relative to 100 parts by weight of the polymer. From the viewpoint of compatibility between cohesive strength and adhesion and impact resistance, the amount of the isocyanate-based crosslinking agent used relative to 100 parts by weight of the polymer can be, for example, more than 0.5 parts by weight, and more than 1.0 parts by weight is appropriate, preferably 1.5 parts by weight or more, more preferably more than 2.0 parts by weight, and even more preferably more than 2.5 parts by weight (for example, 2.8 parts by weight or more). By adopting the amount of the isocyanate-based crosslinking agent in the above range, it is possible to preferably achieve both high temperature retention and complex shape followability. On the other hand, from the viewpoint of improving adhesion and followability to the adherend, the amount of the isocyanate-based crosslinking agent used is appropriately 10 parts by weight or less relative to 100 parts by weight of the polymer, and is preferably less than 5 parts by weight, more preferably less than 4.5 parts by weight, even more preferably less than 4.0 parts by weight, and particularly preferably less than 3.5 parts by weight (for example, 3.0 parts by weight or less).

[0101] In some preferred embodiments, the crosslinking agent is a combination of an isocyanate-based crosslinking agent and at least one crosslinking agent having a different type of crosslinking functional group from that of the isocyanate-based crosslinking agent. According to the technology disclosed herein, a crosslinking agent other than an isocyanate-based crosslinking agent (i.e., a crosslinking agent having a different type of crosslinking reactive group from that of an isocyanate-based crosslinking agent. Hereinafter, also referred to as a "non-isocyanate-based crosslinking agent") is used in combination with an isocyanate-based crosslinking agent, thereby making it possible to favorably achieve both high temperature retention and complex shape conformability.

[0102] The type of non-isocyanate crosslinking agent that can be used in combination with the isocyanate crosslinking agent is not particularly limited, and can be appropriately selected from the above-mentioned crosslinking agents. The non-isocyanate crosslinking agent can be used alone or in combination of two or more.

[0103] In some preferred embodiments, an epoxy-based crosslinking agent can be used as the non-isocyanate-based crosslinking agent. For example, by using an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent in combination, it is easy to achieve both cohesiveness and impact resistance. As the epoxy-based crosslinking agent, a compound having two or more epoxy groups in one molecule can be used without any particular limitation. An epoxy-based crosslinking agent having 3 to 5 epoxy groups in one molecule is preferred. The epoxy-based crosslinking agents can be used alone or in combination of two or more.

[0104] Non-limiting specific examples of epoxy crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc. Commercially available epoxy crosslinking agents include Mitsubishi Gas Chemical Company's product names "TETRAD-C" and "TETRAD-X," DIC Corporation's product name "Epicron CR-5L," Nagase ChemteX Corporation's product name "Denacol EX-512," Nissan Chemical Industries' product name "TEPIC-G," etc.

[0105] The amount of the epoxy crosslinking agent used is not particularly limited. The amount of the epoxy crosslinking agent used can be, for example, more than 0 part by weight and about 1 part by weight or less (typically about 0.001 to 0.5 parts by weight) relative to 100 parts by weight of the polymer. From the viewpoint of favorably exhibiting the effect of improving the cohesive force, the amount of the epoxy crosslinking agent used is suitably about 0.005 parts by weight or more relative to 100 parts by weight of the polymer, preferably about 0.01 parts by weight or more, and more preferably about 0.02 parts by weight or more. In addition, from the viewpoint of improving the adhesion and the followability to the adherend, the amount of the epoxy crosslinking agent used is suitably about 0.2 parts by weight or less relative to 100 parts by weight of the polymer, preferably about 0.1 parts by weight or less, and more preferably less than about 0.05 parts by weight. By reducing the amount of the epoxy crosslinking agent used, there is a tendency that the crosslinking agent will follow the complicated shape of the adherend well and the impact resistance will be improved.

[0106] In the technology disclosed herein, the relationship between the content of the isocyanate crosslinking agent and the content of the non-isocyanate crosslinking agent (e.g., epoxy crosslinking agent) is not particularly limited. The content of the non-isocyanate crosslinking agent can be, for example, about 1 / 50 or less of the content of the isocyanate crosslinking agent. From the viewpoint of more suitably achieving both adhesion to the adherend and cohesive strength, the content of the non-isocyanate crosslinking agent is suitably about 1 / 75 or less of the content of the isocyanate crosslinking agent on a weight basis, preferably about 1 / 100 or less, and may be 1 / 120 or less. In addition, from the viewpoint of optimally exerting the effect of using an isocyanate-based crosslinking agent in combination with a non-isocyanate-based crosslinking agent (e.g., an epoxy-based crosslinking agent), the content of the non-isocyanate-based crosslinking agent is suitably approximately 1 / 1000 or more of the content of the isocyanate-based crosslinking agent, for example, approximately 1 / 500 or more, preferably 1 / 300 or more, and more preferably 1 / 150 or more.

[0107] The total amount of the crosslinking agent used (total amount) is not particularly limited, and can be, for example, about 10 parts by weight or less, preferably about 0.005 to 10 parts by weight, and more preferably about 0.01 to 5 parts by weight, per 100 parts by weight of the polymer (preferably an acrylic polymer).

[0108] (rust inhibitor) The adhesive layer according to some embodiments may contain a rust inhibitor. The rust inhibitor is not particularly limited, and examples thereof include azole-based rust inhibitors, amine compounds, nitrites, ammonium benzoate, ammonium phthalate, ammonium stearate, ammonium palmitate, ammonium oleate, ammonium carbonate, dicyclohexylamine benzoate, urea, urotropine, thiourea, phenyl carbamate, and cyclohexylammonium-N-cyclohexylcarbamate (CHC). The rust inhibitor may be used alone or in combination of two or more.

[0109] As the rust inhibitor, an azole-based rust inhibitor can be preferably used. As the azole-based rust inhibitor, a five-membered aromatic compound containing two or more heteroatoms, at least one of which is a nitrogen atom, is preferably used as an active ingredient of an azole-based compound. As a suitable example of a compound that can be used as an azole-based rust inhibitor, there is a benzotriazole-based rust inhibitor containing a benzotriazole-based compound as an active ingredient. As a suitable example of a benzotriazole-based compound, there is 1,2,3-benzotriazole, 5-methylbenzotriazole, 4-methylbenzotriazole, carboxybenzotriazole, etc.

[0110] The content of the rust inhibitor is not particularly limited, and can be, for example, 0.01 parts by weight or more (typically 0.05 parts by weight or more) relative to 100 parts by weight of the polymer. From the viewpoint of obtaining a better metal corrosion prevention effect, the content may be 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more. On the other hand, from the viewpoint of increasing the cohesive force of the adhesive, the content of the rust inhibitor is suitably less than 8 parts by weight relative to 100 parts by weight of the polymer, and may be 5 parts by weight or less, or 2 parts by weight or less.

[0111] (Other additives) The adhesive composition may contain various additives that are common in the field of adhesives, such as leveling agents, crosslinking assistants, plasticizers, softeners, fillers, colorants, antistatic agents, antiaging agents, UV absorbers, antioxidants, and light stabilizers, as necessary. The adhesive layer disclosed herein may contain a colorant such as a black colorant (e.g., carbon black particles) that can help improve light blocking properties, or may not contain the above colorant from the viewpoint of optical properties such as light transmittance. As for the various additives, those that are conventionally known can be used in a conventional manner, and detailed explanations will be omitted since they do not particularly characterize the present invention.

[0112] The adhesive layer (layer made of adhesive) disclosed herein may be an adhesive layer formed from an aqueous adhesive composition, a solvent-based adhesive composition, a hot melt-type adhesive composition, or an active energy ray curable adhesive composition that is cured by irradiation with active energy rays such as ultraviolet rays or electron beams. The aqueous adhesive composition refers to an adhesive composition in a form containing an adhesive (adhesive layer forming component) in a solvent (aqueous solvent) mainly composed of water, and typically includes those called water-dispersed adhesive compositions (compositions in which at least a part of the adhesive is dispersed in water). The solvent-based adhesive composition refers to an adhesive composition in a form containing an adhesive in an organic solvent. As the organic solvent contained in the solvent-based adhesive composition, one or more of the organic solvents (toluene, ethyl acetate, etc.) that can be used in the above-mentioned solution polymerization can be used without particular limitation. The technology disclosed herein can be preferably implemented in an embodiment having an adhesive layer formed from a solvent-based adhesive composition from the viewpoint of adhesion properties and the like. In an embodiment having a solvent-based pressure-sensitive adhesive layer formed from a solvent-based pressure-sensitive adhesive composition, the effects of the technology disclosed herein are preferably realized.

[0113] The adhesive layer disclosed herein can be formed by a conventionally known method. For example, a method can be adopted in which an adhesive composition is applied to a surface (release surface) having releasability and then dried to form an adhesive layer. In the case of an adhesive sheet having a substrate, for example, a method (direct method) can be adopted in which an adhesive composition is directly applied (typically coated) to the substrate and then dried to form an adhesive layer. In addition, a method (transfer method) can be adopted in which an adhesive composition is applied to a surface (release surface) having releasability and then dried to form an adhesive layer on the surface, and the adhesive layer is transferred to a substrate. For example, the surface of a release liner described later can be preferably used as the release surface. The adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, and may be an adhesive layer formed in a regular or random pattern such as a dotted or striped pattern.

[0114] The application of the adhesive composition can be carried out using a conventionally known coater such as a gravure roll coater, a die coater, a bar coater, etc. Alternatively, the adhesive composition may be applied by impregnation, the curtain coating method, or the like. From the viewpoints of promoting the crosslinking reaction, improving the production efficiency, etc., it is preferable to dry the adhesive composition under heating. The drying temperature can be, for example, about 40 to 150 °C, and preferably about 60 to 130 °C. After drying the adhesive composition, aging may be carried out for the purpose of adjusting the component migration in the adhesive layer, promoting the crosslinking reaction, relaxing the strain that may exist in the adhesive layer, etc.

[0115] The adhesive layer disclosed herein may have a single-layer structure or a multilayer structure having two or more layers. From the viewpoint of productivity, etc., the adhesive layer preferably has a single-layer structure.

[0116] The thickness of the adhesive layer is not particularly limited. The thickness of the adhesive layer is usually about 300 μm or less, suitably about 150 μm or less, preferably about 100 μm or less, more preferably about 70 μm or less, and may be about 60 μm or less (for example, 55 μm or less). The adhesive layer with a limited thickness can be well adapted to the requirements of thinning and weight reduction. The lower limit of the thickness of the adhesive layer is not particularly limited, but from the viewpoints of adhesiveness and followability to the adherend, it is, for example, about 3 μm or more, and suitably about 10 μm or more. In some preferred embodiments, the thickness of the adhesive layer is about 20 μm or more, more preferably about 30 μm or more, and may be about 40 μm or more. By increasing the thickness of the adhesive layer, more excellent adhesive properties can be easily obtained, and there is a tendency to be excellent in followability to an adherend having a complex shape. In the adhesive sheet having adhesive layers (the first adhesive layer and the second adhesive layer) on each surface of the substrate, the thicknesses of the respective adhesive layers may be the same or different.

[0117] (gel fraction) Although not particularly limited, the gel fraction of the pressure-sensitive adhesive layer disclosed herein can be, for example, 20% or more, and is usually suitably 30% or more, and is preferably greater than 35%, based on weight. By increasing the gel fraction of the pressure-sensitive adhesive layer within a moderate range, it is possible to improve high-temperature retention while maintaining conformability to the adherend. In the technology disclosed herein, the gel fraction is more preferably 45% or more, even more preferably 50% or more, and particularly preferably 55% or more, and may be 60% or more. On the other hand, from the viewpoint of conformability to the adherend, the gel fraction of the pressure-sensitive adhesive layer is suitably 90% or less, preferably 70% or less (for example, 65% or less), and may be less than 60%.

[0118] Here, the "gel fraction of the pressure-sensitive adhesive layer" refers to a value measured by the following method. The gel fraction can be understood as the weight ratio of ethyl acetate-insoluble matter in the pressure-sensitive adhesive layer. [Gel fraction measurement method] Approximately 0.1 g of adhesive sample (weight Wg 1 ) was applied to a porous polytetrafluoroethylene membrane (weight Wg 2 ) into a pouch shape, and the opening is closed with a string (weight Wg 3 As the porous polytetrafluoroethylene (PTFE) membrane, a product name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) available from Nitto Denko Corporation or an equivalent product is used. The package is immersed in 50 mL of ethyl acetate and kept at room temperature (typically 23° C.) for 7 days to elute only the sol component in the adhesive layer out of the film. The package is then taken out and the ethyl acetate adhering to the outer surface is wiped off. The package is then dried at 130° C. for 2 hours, and the weight of the package (Wg 4 ) is measured. The gel fraction F of the adhesive layer G can be calculated by substituting each value into the following formula: A similar method is used in the examples described later. Gel fraction F G (%) = [(Wg 4 -Wg 2 -Wg 3 ) / Wg 1 ] x 100

[0119] <Base material> In an embodiment in which the adhesive sheet disclosed herein is in the form of a single-sided or double-sided adhesive substrate-attached adhesive sheet, the substrate that supports (backs) the adhesive layer can be a resin film, a foam film (foam substrate), paper, cloth, metal foil, a composite of these, or the like.

[0120] The technology disclosed herein can be implemented in the form of a substrate-attached PSA sheet having the PSA layer on at least one surface of a substrate (support).For example, the technology can be implemented in the form of a substrate-attached double-sided PSA sheet having the PSA layers on one and the other surfaces of a substrate.

[0121] As the substrate, a substrate containing a resin film as a base film can be preferably used. The base film is typically a member that can independently maintain its shape (independent). The substrate in the technology disclosed herein may be substantially composed of such a base film. Alternatively, the substrate may contain an auxiliary layer in addition to the base film. Examples of the auxiliary layer include an undercoat layer, an antistatic layer, a colored layer, and the like provided on the surface of the base film.

[0122] The resin film is a film containing a resin material as a main component (a component contained in the resin film in an amount of more than 50% by weight). Examples of the resin film include polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester resin films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluororesin films; cellophane; and the like. The resin film may be a rubber film such as a natural rubber film or a butyl rubber film. Among them, polyester films are preferred from the viewpoint of handling and processability, and PET films are particularly preferred.

[0123] The resin film may have a single-layer structure, or may have a multi-layer structure of two, three or more layers. From the viewpoint of shape stability, the resin film is preferably a single-layer structure. In the case of a multi-layer structure, at least one layer (preferably all layers) is preferably a layer having a continuous structure of the resin (e.g., polyester-based resin). The method for producing the resin film is not particularly limited and may be any conventionally known method. For example, conventionally known general film forming methods such as extrusion molding, inflation molding, T-die casting molding, and calendar roll molding may be appropriately used.

[0124] In some other embodiments, paper or cloth is used as the substrate material. Examples of paper that can be used as the substrate include Japanese paper, craft paper, glassine paper, fine paper, synthetic paper, topcoat paper, etc. Examples of cloth include woven fabrics and nonwoven fabrics made of various fibrous materials, either alone or in combination. Examples of the fibrous materials include cotton, staple fiber, Manila hemp, pulp, rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber, polyolefin fiber, etc.

[0125] Note that the nonwoven fabric referred to here is a concept referring to a nonwoven fabric for an adhesive sheet mainly used in the field of adhesive tapes and other adhesive sheets, and typically refers to a nonwoven fabric (sometimes referred to as "paper") produced using a general papermaking machine. Also, the resin film referred to here is typically a non-porous resin sheet, and is a concept that is distinguished from, for example, a nonwoven fabric (that is, does not include a nonwoven fabric). The above resin film may be any of an unstretched film, a uniaxially stretched film, and a biaxially stretched film. Further, the surface of the substrate on which the adhesive layer is provided may be subjected to surface treatments such as application of a primer, corona discharge treatment, plasma treatment, etc.

[0126] On the above substrate (such as a resin film like a PET film), various additives such as a filler (inorganic filler, organic filler, etc.), a colorant, a dispersant (surfactant, etc.), an anti-aging agent, an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, and a plasticizer may be blended as necessary. The blending ratio of the various additives is usually about less than approximately 30% by weight (for example, less than approximately 20% by weight, preferably less than approximately 10% by weight).

[0127] The surface of the substrate may be subjected to conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, application of a primer, etc. Such a surface treatment can be a treatment for improving the adhesion between the substrate and the adhesive layer, in other words, the anchoring property of the adhesive layer to the substrate.

[0128] The thickness of the substrate disclosed herein is not particularly limited. The thickness of the substrate (e.g., resin film) can be, for example, about 200 μm or less, preferably about 100 μm or less, more preferably about 50 μm or less. Depending on the purpose and mode of use of the pressure-sensitive adhesive sheet, the thickness of the substrate may be about 30 μm or less, about 15 μm or less, or about 10 μm or less (e.g., about 5 μm or less). By reducing the thickness of the substrate, the thickness of the pressure-sensitive adhesive layer can be made larger even if the total thickness of the pressure-sensitive adhesive sheet is the same. This can be advantageous from the viewpoint of improving adhesion to the adherend. The lower limit of the thickness of the substrate is not particularly limited. From the viewpoint of the handleability (handling property) and processability of the pressure-sensitive adhesive sheet, the thickness of the substrate is usually about 0.5 μm or more (e.g., 1 μm or more), preferably about 2 μm or more, for example, about 4 μm or more. In some embodiments, the thickness of the substrate may be about 10 μm or more.

[0129] <Release liner> In the technology disclosed herein, a release liner can be used during the formation of the adhesive layer, the preparation of the adhesive sheet, the storage, distribution, and shaping of the adhesive sheet before use. The release liner is not particularly limited, and examples of the release liner include a release liner having a release treatment layer on the surface of a liner substrate such as a resin film or paper, and a release liner made of a low-adhesion material such as a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin-based resin (PE, PP, etc.). The release treatment layer can be formed by surface-treating the liner substrate with a release treatment agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide.

[0130] <Adhesive sheet> Some preferred embodiments of the pressure-sensitive adhesive sheet are substrate-less double-sided adhesive sheets (substrate-less double-sided pressure-sensitive adhesive sheets) that are substantially composed of only a pressure-sensitive adhesive layer. Such substrate-less pressure-sensitive adhesive sheets have excellent conformability, and therefore can adhere well to adherends having steps, for example, and can exhibit excellent adhesive performance. In particular, they can exhibit good conformability to adherends having complex surfaces such as three-dimensional curved shapes. The substrate-less double-sided pressure-sensitive adhesive sheet is composed of the pressure-sensitive adhesive layer over its entire thickness, and therefore can exhibit better adhesive properties (particularly high-temperature retention) in a limited thickness space. Therefore, they can be particularly preferably used for fixing components of portable electronic devices that tend to be limited in thickness and may be exposed to high temperatures.

[0131] The total thickness of the adhesive sheet (not including the release liner) disclosed herein is not particularly limited. The total thickness of the adhesive sheet can be, for example, about 500 μm or less, and is usually about 350 μm or less, preferably about 250 μm or less (for example, about 200 μm or less). The technology disclosed herein can be preferably implemented in the form of an adhesive sheet (typically a double-sided adhesive sheet) having a total thickness of about 150 μm or less (more preferably about 100 μm or less, even more preferably less than about 60 μm, for example about 55 μm or less). The lower limit of the total thickness of the adhesive sheet is not particularly limited, and is usually about 10 μm or more, and from the viewpoint of adhesion and adherend followability, about 20 μm or more is preferable, about 30 μm or more is more preferable, and about 40 μm or more is even more preferable. By increasing the thickness of the adhesive sheet, better adhesive properties are easily obtained, and followability to adherends having complex shapes tends to be improved. When the pressure-sensitive adhesive sheet comprises a foam substrate, the upper limit of the total thickness of the pressure-sensitive adhesive sheet is usually appropriately set to 1.5 mm or less, preferably 1 mm or less, and more preferably 0.5 mm or less.

[0132] <Application> The adhesive sheet disclosed herein has good high-temperature retention and can conform well to the surface of an adherend having a complex shape. By utilizing such characteristics, the adhesive sheet can be used in various applications requiring high-temperature retention and adherend conformability. For example, it is suitable for use in fixing various portable electronic devices having members with curved shapes such as three-dimensional shapes. Portable electronic devices may be used in high-temperature environments, and the internal space may become heated due to heat generation from electronic components, so there is a great advantage in improving high-temperature retention using the adhesive sheet disclosed herein. Non-limiting examples of the portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wristwear-type devices worn on the wrist like a wristwatch, modular-type devices worn on a part of the body with a clip or strap, eyewear-type devices including glasses-type devices (monocular and binocular types, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. in the form of accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio devices (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, electronic books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" does not mean that it is sufficient to simply be portable, but rather that it has a level of portability that allows an individual (average adult) to carry it relatively easily.

[0133] In addition, the adhesive sheet disclosed herein is preferably used in a portable electronic device for fixing a member such as a cover glass having a three-dimensional shape (typically a curved shape) constituting the portable electronic device. It is also suitable for fixing an adherend surface having a step. The adhesive sheet disclosed herein has excellent conformability to the adherend, so it can conform well and adhere to the above-mentioned three-dimensional shape or a complex shape having a step. It can adhere closely to such an adherend surface having a three-dimensional shape or a step without any gaps and exhibit a good fixing function, while imparting excellent waterproofness to products that require waterproofness (for example, electronic devices such as portable electronic devices).

[0134] The adhesive sheet (typically a double-sided adhesive sheet) disclosed herein can be used in the form of a bonding material processed into various shapes to fix members constituting the above-mentioned portable electronic device. In particular, it can be preferably used in electronic devices (typically portable electronic devices) equipped with an organic EL display device or a liquid crystal display device. For example, the adhesive sheet disclosed herein is preferably used to fix members of electronic devices (typically portable electronic devices such as smartphones) having a display unit such as a touch panel display, and the like, having a large-screen display unit.

[0135] FIG. 2 is an exploded perspective view showing a typical example of a configuration of a display device to which the adhesive sheet disclosed herein can be applied. As shown in FIG. 2, the display device 200 included in the portable electronic device 100 includes a display unit 220 including a cover member, an organic EL unit, and the like, and a support unit 240. The display device 200 is configured to further include an adhesive sheet 230. In this configuration example, the adhesive sheet 230 is in the form of a double-sided adhesive sheet (double-sided adhesive sheet) that fixes the members that make up the display unit 220 and the support unit 240. The support unit 240 is configured to include a substrate (a metal plate such as a stainless steel plate or an aluminum plate) and the like. Alternatively, the adhesive sheet disclosed herein may fix a member such as a cover member or an organic EL unit. The adhesive sheet disclosed herein is preferably used as a component of the display device described above.

[0136] The matters disclosed by this specification include the following: [1] A portable electronic device including a display device including a display unit including a cover member and an organic EL unit, and a support unit, An adhesive sheet is bonded to the cover member, The pressure-sensitive adhesive sheet has a pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer is Weight average molecular weight is 70×10 4 and At least one selected from an oligomer and a tackifier resin having a softening point of less than 145°C; Including, The pressure-sensitive adhesive layer has a storage modulus G'(25°C) of less than 0.15 MPa. [2] The portable electronic device according to [1] above, wherein the display unit is provided with a touch panel that also functions as an input unit. [3] The portable electronic device according to [1] or [2] above, wherein the cover member has a three-dimensional curved shape. [4] The portable electronic device according to any one of the above [1] to [3], wherein the pressure-sensitive adhesive layer has a gel fraction of more than 35% by weight. [5] The portable electronic device according to any one of the above [1] to [4], wherein the pressure-sensitive adhesive layer has a ratio (G'(80°C) / G'(25°C)) of the storage modulus G'(25°C) at 25°C to the storage modulus G'(80°C) at 80°C greater than 0.20. [6] The portable electronic device according to any one of the above [1] to [5], wherein the polydispersity (Mw / Mn) of the polymer is 40 or less. [7] The portable electronic device according to any one of the above [1] to [6], wherein the polymer is an acrylic polymer. [8] The portable electronic device according to any one of the above [1] to [7], wherein the pressure-sensitive adhesive layer contains both the oligomer and the tackifier resin. [9] The mobile electronic device according to any one of the above [1] to [8], wherein the adhesive composition for forming the adhesive layer contains an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent.

[10] The portable electronic device according to any one of the above [1] to [9], which is a substrateless double-sided adhesive sheet comprising the adhesive layer.

[0137]

[11] A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, The pressure-sensitive adhesive layer is Weight average molecular weight is 70×10 4 and At least one selected from an oligomer and a tackifier resin having a softening point of less than 145°C; Including, The pressure-sensitive adhesive layer has a storage modulus G'(25°C) of less than 0.15 MPa.

[12] The pressure-sensitive adhesive sheet according to the above-mentioned

[11] , wherein the pressure-sensitive adhesive layer has a gel fraction of more than 35% by weight.

[13] The pressure-sensitive adhesive sheet according to the above-mentioned

[11] or

[12] , wherein the pressure-sensitive adhesive layer has a ratio (G'(80°C) / G'(25°C)) of the storage modulus G'(25°C) at 25°C to the storage modulus G'(80°C) at 80°C of greater than 0.20.

[14] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[13] , wherein the polydispersity (Mw / Mn) of the polymer is 40 or less.

[15] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[14] , wherein the polymer is an acrylic polymer.

[16] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[15] , wherein the pressure-sensitive adhesive layer contains both the oligomer and the tackifier resin.

[17] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[16] , wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent.

[18] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[17] , which is a substrateless double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.

[19] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[18] , which is used for fixing components in a portable electronic device.

[20] The pressure-sensitive adhesive sheet according to any one of the above

[11] to

[19] , which is attached to a stepped and / or curved surface of a member having a stepped and / or curved shape in a portable electronic device. EXAMPLES

[0138] Some examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0139] <Example 1> (Preparation of Acrylic Polymer) In a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel, 95 parts of 2-ethylhexyl acrylate (2EHA) and 5 parts of acrylic acid (AA) as monomer components, and ethyl acetate as a polymerization solvent were charged, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, 0.1 parts of 2,2'-azobisisobutyronitrile (AIBN) was added as a polymerization initiator, and solution polymerization was carried out at 60°C for 6 hours to obtain a solution of acrylic polymer (P1). The above polymerization reaction was carried out by adjusting the amount of polymerization solvent to control the concentration of the non-volatile content (monomer component). The Mw of the acrylic polymer (P1) was 126 x 10 4 and the Mw / Mn was 8.7.

[0140] (Preparation of Pressure-Sensitive Adhesive Composition) To this acrylic polymer solution, 20 parts of tackifier resin (T1), 5 parts of tackifier resin (T2), 10 parts of oligomer, 3 parts of isocyanate-based crosslinking agent and 0.03 parts of epoxy-based crosslinking agent as crosslinking agents were added to 100 parts of acrylic polymer (P1) contained in the solution, and the mixture was stirred to prepare an adhesive composition. As the tackifier resin (T1), a terpene phenol resin (trade name "YS Polystar T-115", manufactured by Yasuhara Chemical Co., Ltd., softening point about 115°C, hydroxyl value 30 to 60 mgKOH / g) was used. As the tackifier resin (T2), a liquid resin (manufactured by Nissei Rinsan Kagaku Co., Ltd., trade name "M-HDR", hydrogenated rosin methyl ester resin) was used. As the isocyanate-based crosslinking agent, a trade name "Coronate L" (manufactured by Tosoh Corporation, 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct) was used. The epoxy crosslinking agent used was trade name "TETRAD-C" (manufactured by Mitsubishi Gas Chemical Co., Ltd., 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane). The oligomer used was an acrylic oligomer prepared by the following method. Specifically, 95 parts of cyclohexyl methacrylate (CHMA), 5 parts of AA, 10 parts of AIBN as a polymerization initiator, and toluene as a polymerization solvent were charged into a reaction vessel equipped with a stirrer, a thermometer, a nitrogen gas inlet tube, a reflux condenser, and a dropping funnel, and the mixture was stirred in a nitrogen stream for 1 hour to remove oxygen from the polymerization system, and then heated to 85°C and reacted for 5 hours to obtain an acrylic oligomer with a solid content concentration of 50%. The Mw of the obtained acrylic oligomer was 3600.

[0141] (Preparation of adhesive sheet) As the release liner A, a polyester release film (trade name "Diafoil MRV", thickness 75 μm, manufactured by Mitsubishi Polyester Corporation) with one side being release-treated to form a release surface was prepared, and as the release liner B, a polyester release film (trade name "Diafoil MRF", thickness 38 μm, manufactured by Mitsubishi Polyester Corporation) with one side being release-treated to form a release surface was prepared. The pressure-sensitive adhesive composition obtained above was applied to the release surface of the release liner A and dried at 100° C. for 2 minutes to form a pressure-sensitive adhesive layer with a thickness of 50 μm. The exposed adhesive surface of this pressure-sensitive adhesive layer was covered with the release liner B so that the release surface was on the pressure-sensitive adhesive layer side, and a substrate-less double-sided adhesive pressure-sensitive adhesive sheet according to this example was produced.

[0142] <Example 2> The monomer composition was changed to 93 parts of n-butyl acrylate (BA), 7 parts of AA, and 0.05 parts of 4-hydroxybutyl acrylate (4HBA), and the concentration of the non-volatile matter (monomer component) was controlled by adjusting the amount of the polymerization solvent. Except for this, an acrylic polymer (P2) was synthesized in a manner basically similar to that of the acrylic polymer (P1), and a solution of the acrylic polymer (P2) was obtained. The Mw of the acrylic polymer (P2) was 132×10 4 The Mw / Mn was 5.85. To this acrylic polymer solution, 20 parts of tackifier resin (T1), 5 parts of tackifier resin (T2), 15 parts of oligomer, 1.5 parts of isocyanate-based crosslinking agent and 0.01 parts of epoxy-based crosslinking agent were added to 100 parts of acrylic polymer (P2) contained in the solution, and the mixture was stirred to prepare a pressure-sensitive adhesive composition. The tackifier resin (T1) (T2), oligomer, isocyanate-based crosslinking agent, and epoxy-based crosslinking agent were the same as those used in Example 1. A 50 μm-thick substrateless double-sided PSA sheet, both sides of which were protected with the two polyester release liners, was obtained in the same manner as in Example 1, except that the obtained PSA composition was used.

[0143] <Example 3> The monomer composition was changed to 97 parts BA and 3 parts AA, and the concentration of the non-volatile matter (monomer component) was controlled by adjusting the amount of the polymerization solvent. In a manner basically similar to the synthesis of the acrylic polymer (P1), except for this, an acrylic polymer (P3) was synthesized and a solution of the acrylic polymer (P3) was obtained. The Mw of the acrylic polymer (P3) was 100×10 4 The Mw / Mn was 4.5. 20 parts of tackifier resin (T1), 3 parts of isocyanate crosslinking agent and 0.02 parts of epoxy crosslinking agent as crosslinking agents were added to 100 parts of acrylic polymer (P3) contained in the acrylic polymer solution, and the mixture was stirred to prepare a pressure-sensitive adhesive composition. The tackifier resin (T1), isocyanate crosslinking agent, and epoxy crosslinking agent were the same as those used in Example 1. A 50 μm-thick substrateless double-sided PSA sheet, both sides of which were protected with the two polyester release liners, was obtained in the same manner as in Example 1, except that the obtained PSA composition was used.

[0144] <Example 4> In a reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel, 70 parts of BA, 30 parts of 2EHA, and 3 parts of AA as monomer components, and ethyl acetate as a polymerization solvent were charged, and the mixture was stirred for 2 hours while introducing nitrogen gas. After removing oxygen from the polymerization system in this manner, 0.2 parts of AIBN was added as a polymerization initiator, and solution polymerization was carried out at 60°C for 8 hours to obtain a solution of acrylic polymer (P4). The Mw of the acrylic polymer (P4) was 44×10 4 The Mw / Mn was 8.8. 30 parts of tackifier resin (T3) and 3 parts of an isocyanate-based crosslinking agent as a crosslinking agent were added to this acrylic polymer solution relative to 100 parts of the acrylic polymer (P4) contained in the solution, and the mixture was stirred to prepare a pressure-sensitive adhesive composition. As the tackifier resin (T3), a polymerized rosin ester (manufactured by Arakawa Chemical Industries, Ltd., product name "PENSEL D125") with a softening point of 125°C was used. As the isocyanate-based crosslinking agent, the same type as that used in Example 1 was used. A 50 μm-thick substrateless double-sided PSA sheet, both sides of which were protected with the two polyester release liners, was obtained in the same manner as in Example 1, except that the obtained PSA composition was used.

[0145] <Example 5> Acrylic polymer (P5) was synthesized in a manner similar to that of acrylic polymer (P4), except that the monomer composition was changed to 95 parts BA and 5 parts AA, and a solution of acrylic polymer (P5) was obtained. The Mw of acrylic polymer (P5) was 68×10 4 The Mw / Mn was 4.4. To this acrylic polymer solution, 30 parts of tackifier resin (T4) and 2 parts of isocyanate-based crosslinking agent and 0.01 parts of epoxy-based crosslinking agent as crosslinking agents were added to 100 parts of acrylic polymer (P5) contained in the solution, and the mixture was stirred and mixed to prepare a pressure-sensitive adhesive composition. The isocyanate-based crosslinking agent and the epoxy-based crosslinking agent were the same as those used in Example 1. As the tackifier resin (T4), a terpene phenol resin (trade name "YS Polystar S-145" manufactured by Yasuhara Chemical Co., Ltd., softening point about 145°C, hydroxyl value 70 to 110 mgKOH / g) was used. A 50 μm-thick substrateless double-sided PSA sheet, both sides of which were protected with the two polyester release liners, was obtained in the same manner as in Example 1, except that the obtained PSA composition was used.

[0146] <Evaluation> [High temperature retention test] A high-temperature retention test was conducted at a temperature of 80°C in accordance with JIS Z0237:2009. That is, in an environment of 23°C and 50% RH, a 50μm thick PET film was attached to one adhesive surface of a double-sided pressure-sensitive adhesive sheet to back it up, and the sheet was cut to a width of 10mm to prepare a measurement sample. The other adhesive surface of the measurement sample was attached to a Bakelite plate as an adherend by rolling a 2kg roller back and forth once. The adhesion area between the measurement sample and the adherend was 10mm wide and 20mm long. The measurement sample thus attached to the adherend was dangling in an environment of 80°C and left for 30 minutes, and then a load of 1kg was applied to the free end of the measurement sample, and the measurement sample was left in an environment of 80°C for 1 hour with the load applied. If the measurement sample was still held by the adherend after 1 hour, it was judged to be "passed", and if the measurement sample peeled off from the adherend and fell within 1 hour, it was judged to be "failed". In the case of a single-sided pressure-sensitive adhesive sheet, the above-mentioned PET film backing is not necessary.

[0147] [Step waterproofing test] The adhesive sheet (double-sided adhesive sheet) was cut into a window frame shape (picture frame shape) having a square outer edge of 24.5 mm × 24.5 mm and a width of 2 mm to obtain a window frame-shaped adhesive sheet. This window frame-shaped adhesive sheet was attached to a square acrylic plate of 50 mm × 50 mm and a thickness of 2 mm to produce an acrylic plate with a window frame-shaped adhesive sheet. A polycarbonate plate having a size larger than the acrylic plate was prepared, and a step tape (width 5 mm, height 20 μm) was attached to the surface of the polycarbonate plate. This step tape is used for the purpose of providing a convex (step) on the surface of the polycarbonate plate. Here, an adhesive sheet having an adhesive layer on one side of a PET substrate was used as the step tape. Then, the acrylic plate with the window frame-shaped adhesive sheet prepared above was placed on the polycarbonate plate so that the center of the two parallel sides of the window frame-shaped adhesive sheet crossed the step tape (so that the two parallel sides of the window frame-shaped adhesive sheet intersected (orthogonal) with the step tape), and pressure-bonded under conditions of 0.2 MPa and 1 minute. In this way, an evaluation sample was obtained. When the window frame-shaped adhesive sheet is in close contact with the adherend (acrylic plate, polycarbonate plate, and step tape), the inside of the obtained evaluation sample becomes a space sealed from the outside. The step waterproofing was evaluated by submerging the evaluation sample in water in an autoclave, applying a pressure of 0.5 MPa at 25°C for 30 minutes in the autoclave, and visually observing whether water penetrated into the evaluation sample (inside the window frame-shaped adhesive sheet). If water penetration into the evaluation sample was observed, it was judged as "failed," and if not, it was judged as "passed." The step waterproofing test was carried out after aging the evaluation sample under standard conditions (23° C., 50% RH) for 30 minutes.

[0148] Table 1 shows an overview of the adhesive for each example, and the evaluation results of the adhesive layer's G' (25°C) [MPa], G" (25°C) [MPa], tan δ (25°C), G' (80°C) [MPa], G" (80°C) [MPa], tan δ (80°C), glass transition temperature (Tg) (temperature of the peak top of tan δ) [°C], G' (80°C) / G' (25°C), high temperature holding power, and step waterproofing.

[0149] [Table 1]

[0150] As shown in Table 1, Mw is 70 × 10 4In Examples 1 to 3, which used a polymer exceeding Mw and at least one of an oligomer and a low-softening point tackifier resin (softening point less than 145°C) and had a pressure-sensitive adhesive layer with a 25°C storage modulus G' (25°C) of less than 0.15 MPa, the high temperature retention and step waterproofing properties were all acceptable. 4 Example 4, in which a low-softening point tackifier resin (softening point less than 145°C) was used instead of a polymer having a molecular weight of more than 70, and in which the adhesive layer had a G' (25°C) of less than 0.15 MPa, passed the step waterproofing test but failed the evaluation of high temperature retention. The adhesive sheet of Example 5, in which the adhesive layer had a G' (25°C) of 0.15 MPa or more, passed the evaluation of high temperature retention but failed the step waterproofing test. The adhesive layer of Example 5 had a Mw of 70×10 4 It contained no ultra-thin polymers and no low softening point tackifying resins. From the above results, Mw is 70×10 4 and further at least one selected from an oligomer and a low softening point tackifier resin (softening point less than 145°C), and the adhesive layer has a storage modulus G'(25°C) of less than 0.15 MPa at 25°C, and it can be seen that a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer having a storage modulus G'(25°C) of less than 0.15 MPa at 25°C can achieve both conformability to complex shapes and high temperature retention.

[0151] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above. [Explanation of symbols]

[0152] 1 Adhesive sheet 21 Adhesive layer 31,32 Release liner

Claims

1. A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer, The total thickness of the pressure-sensitive adhesive sheet is less than 60 μm, The pressure-sensitive adhesive layer is Weight average molecular weight is 90 x 10 4 or more (however, excluding polymers of monomer components containing 50 to 97% by weight of an alkyl (meth)acrylate having a branched alkyl group having 8 to 18 carbon atoms at an ester group terminal and a homopolymer glass transition temperature of -50°C or lower, and 3 to 50% by weight of a (meth)acrylate having an ether bond in the molecular skeleton and a homopolymer glass transition temperature of -40°C or lower), At least one selected from an acrylic oligomer and a tackifier resin; Including, The acrylic polymer is a polymer of a monomer component containing 90% by weight or more of alkyl (meth)acrylate, The alkyl (meth)acrylate includes at least one of n-butyl acrylate and 2-ethylhexyl acrylate, the total amount of n-butyl acrylate and 2-ethylhexyl acrylate in the alkyl (meth)acrylate is 75% by weight or more; the monomer component contains an acidic group-containing monomer copolymerizable with the alkyl (meth)acrylate in an amount of 1.5% by weight or more and less than 10% by weight; In the case where the pressure-sensitive adhesive layer contains the tackifier resin, the tackifier resin contains a tackifier resin T L having a softening point of 60° C. or more and less than 135° C. and does not contain a xylene-based resin; The pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent, the amount of the isocyanate-based crosslinking agent is more than 0.5 parts by weight and less than 5 parts by weight based on 100 parts by weight of the acrylic polymer; The pressure-sensitive adhesive layer has a storage modulus G'(25°C) of less than 0.15 MPa at 25°C, measured at a frequency of 1 Hz.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive layer has a gel fraction of greater than 35% by weight.

3. 3. The pressure-sensitive adhesive layer according to claim 1, wherein the ratio (G'(80°C) / G'(25°C)) of the storage modulus G'(25°C) at 25°C to the storage modulus G'(80°C) at 80°C is greater than 0.20, wherein the storage modulus G'(25°C) and the storage modulus G'(80°C) are measured at a frequency of 1 Hz.

4. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the dispersity (Mw / Mn) of the acrylic polymer is 40 or less.

5. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer contains both the acrylic oligomer and the tackifier resin.

6. The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein the pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer further comprises an epoxy-based crosslinking agent.

7. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, which is a substrate-less double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.

8. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, which is used for fixing members in a portable electronic device.

9. The pressure-sensitive adhesive sheet according to any one of claims 1 to 8, which is attached to a stepped and / or curved surface of a member having a stepped and / or curved shape in a portable electronic device.

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