adhesive sheet

Abstract

To provide an adhesive sheet capable of providing reliable adhesion property even upon exposure to cosmetics, chemicals and the like containing polar compounds.SOLUTION: An adhesive sheet provided by this invention has an adhesive layer comprising a polyester-based polymer. The adhesive sheet has a 180° peel strength of 1 N / 5 mm or greater after ethanol immersion.SELECTED DRAWING: None

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 hereinafter) are in a soft solid (viscoelastic) state at temperatures around room temperature and have the property of easily adhering to an adherend when pressure is applied. Utilizing these properties, adhesives are widely used for purposes such as joining, fixing, and protecting components in mobile phones and other portable devices, for example, in the form of substrate-attached adhesive sheets having an adhesive layer on a supporting substrate, or substrate-less adhesive sheets. Patent Documents 1 and 2 are technical documents relating to adhesive tapes used in portable electronic devices. In these documents, an acrylic adhesive is used as the adhesive. Patent Documents 3 and 4 are prior art documents relating to polyester-based adhesives. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-215355 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-100485 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-115149 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-134906 Summary of the Invention [Problem to be solved by the invention]

[0004] Because mobile devices are used while being carried, they are prone to adhesion of secretions such as sebum and fingerprints, as well as oils contained in cosmetics, hair styling products, moisturizing creams, sunscreens, and other chemicals, and oils contained in foods. In particular, touch-panel mobile devices, which have become increasingly popular in recent years, feature a display / input unit that also functions as an input unit. Because users operate the display / input unit by directly touching the surface with their fingertips, there are many opportunities for oils to adhere to the device through their fingertips. Furthermore, some so-called wearable devices are worn in contact with the skin, and in such usage, they are frequently exposed to oils such as sebum and chemicals applied to the skin. For example, in such applications, if the above-mentioned oils (sebum, cosmetics, etc.) come into contact with the adhesive layer of a pressure-sensitive adhesive sheet that secures components, problems such as a decrease in adhesive strength or adhesive extrusion can occur. Regarding this issue, for example, Patent Document 1 studies an acrylic adhesive sheet that is resistant to softening and swelling even when penetrated by oils, and therefore does not extrude when used to secure components.

[0005] In recent years, adhesive sheets used in mobile devices have been required to have a higher level of chemical resistance. Specifically, not only the oils mentioned above, but also perfumes, insect repellent sprays, hand-washing detergents, disinfectant wipes, and the like may come into contact with mobile devices through, for example, human operation. Many of these cosmetics, chemicals, and the like contain alcohol (typically ethanol) as a solvent or dispersion medium. However, it is difficult for acrylic adhesives such as those described in Patent Documents 1 and 2 to achieve durability against polar solvents such as alcohol. This is because the improvement in oil resistance of the above-mentioned acrylic adhesives is due to the polarity of the adhesive (e.g., the introduction of polar functional groups into the base polymer or tackifier resin). Looking beyond acrylic adhesives, rubber-based adhesives and urethane-based adhesives are considered as potential candidates, but it is difficult for either of them to achieve good durability against both low-polarity components such as oils and polar components. Furthermore, it is also difficult to achieve adhesive properties (e.g., peel strength and holding power) comparable to those of acrylic adhesives.

[0006] Against this background, the present inventors discovered that polyester-based PSAs can exhibit good durability against both low-polarity components and polar components, and as a result of further investigation, they have completed the present invention. That is, an object of the present invention is to provide a PSA sheet that can exhibit good adhesive reliability even when exposed to cosmetics, chemicals, etc. that contain polar components. [Means for solving the problem]

[0007] According to the present specification, a pressure-sensitive adhesive sheet is provided that includes a pressure-sensitive adhesive layer containing a polyester-based polymer. This pressure-sensitive adhesive sheet has a 180-degree peel strength of 1 N / 5 mm or more after immersion in ethanol. Because the pressure-sensitive adhesive sheet uses a pressure-sensitive adhesive containing a polyester-based polymer as the adhesive, it is able to exhibit excellent durability against both low-polarity and polar components, unlike acrylic pressure-sensitive adhesives. Furthermore, because the pressure-sensitive adhesive sheet exhibits a peel strength after immersion in ethanol that is equal to or greater than a predetermined value, it can exhibit good adhesion reliability even when exposed to cosmetics, chemicals, etc. that contain polar components such as ethanol (hereinafter also referred to as "polar chemicals, etc."). This can be a particularly significant feature in mobile device applications that are likely to come into contact with oils (low-polarity components) such as sebum, cosmetics, and sunscreen cream, and may also be exposed to perfumes, insect repellent sprays, hand detergents, disinfectant wipes, etc. that contain polar solvents (typically ethanol).

[0008] A preferred embodiment of the pressure-sensitive adhesive sheet has an adhesive strength retention rate of 50% or more after immersion in ethanol. A pressure-sensitive adhesive sheet that satisfies this characteristic can exhibit stable adhesive reliability even when it comes into contact with polar chemicals, etc.

[0009] A preferred embodiment of the PSA sheet has a 180-degree peel strength of 2 N / 5 mm or more after immersion in oleic acid. PSA sheets that satisfy this characteristic do not lose their adhesive reliability even when exposed to low-polarity components such as oils. In other words, they have excellent durability against the low-polarity components. The technology disclosed herein makes it possible to improve adhesive reliability when contacting polar chemicals and the like, in addition to a configuration that has durability against low-polarity components. This has not been possible with conventional acrylic PSAs, and is particularly significant from a practical standpoint.

[0010] A preferred embodiment of the PSA sheet exhibits a slippage of 0.5 mm or less in a shear holding strength test conducted under conditions of a load of 1 kg, a temperature of 60°C, and 1 hour. PSA sheets that satisfy this characteristic also have excellent holding strength, making them suitable for use in a variety of applications requiring holding strength. The technology disclosed herein can improve adhesive reliability when contacting polar chemicals and the like in a configuration with excellent holding strength. This has not been possible with conventional acrylic PSAs, and is particularly significant from a practical standpoint.

[0011] A preferred embodiment of the pressure-sensitive adhesive sheet has an initial 180-degree peel strength of 10 N / 25 mm or more. A pressure-sensitive adhesive sheet that satisfies this characteristic can exert sufficient adhesive strength to an adherend.

[0012] In a preferred embodiment of the PSA sheet disclosed herein, the content of the tackifier resin in the PSA layer is less than 80 parts by weight per 100 parts by weight of the polyester polymer. By limiting the amount of tackifier resin used to less than a predetermined amount, good adhesive reliability can be preferably exhibited even when contacting polar chemicals, etc., and adhesive properties such as peel strength and holding power after immersion in oleic acid can also be preferably improved.

[0013] In a preferred embodiment of the PSA sheet disclosed herein, the tackifier resin comprises a tackifier resin having a hydroxyl value of 30 mgKOH / g or more. Tackifier resins having a hydroxyl value of a predetermined value or more are highly compatible with polyester-based polymers and can preferably satisfy desired properties.

[0014] In a preferred embodiment of the pressure-sensitive adhesive sheet disclosed herein, the polyester polymer is crosslinked with a crosslinking agent. By structuring the polymer in the pressure-sensitive adhesive layer with the crosslinking agent in this manner, it becomes easier to block the penetration of oils, polar solvents, etc. Furthermore, the polyester polymer crosslinked with the crosslinking agent has increased cohesive strength, and the holding power can also be preferably improved. In a preferred embodiment, the pressure-sensitive adhesive layer has a gel fraction of 20% by weight or more.

[0015] The PSA sheet disclosed herein can be preferably used, for example, to bond components of portable electronic devices. As described above, portable electronic devices often come into contact with oils such as sebum, and may also come into contact with polar chemicals such as perfume. Therefore, it is particularly meaningful to apply the technology disclosed herein to configure a device that can exhibit good durability not only against low-polarity components such as oils, but also against polar chemicals. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a cross-sectional view schematically showing one example of the configuration of a pressure-sensitive adhesive sheet. [Figure 2] FIG. 10 is a cross-sectional view schematically showing another example of the configuration of the pressure-sensitive adhesive sheet. [Figure 3] FIG. 10 is a cross-sectional view schematically showing another example of the configuration of the pressure-sensitive adhesive sheet. [Figure 4] FIG. 10 is a cross-sectional view schematically showing another example of the configuration of the pressure-sensitive adhesive sheet. [Figure 5] FIG. 10 is a cross-sectional view schematically showing another example of the configuration of the pressure-sensitive adhesive sheet. [Figure 6] FIG. 10 is a cross-sectional view schematically showing another example of the configuration of the pressure-sensitive adhesive sheet. DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred embodiments of the present invention are described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings for carrying out the invention described in this specification and the common general technical 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 technical knowledge in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic 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] As used herein, the term "adhesive" refers to a material that is in a soft solid (viscoelastic) state in a temperature range around room temperature and has the property of easily adhering to an adherend by pressure, as described above.

[0019] <Adhesive sheet composition> The PSA sheet disclosed herein may be a substrate-attached PSA sheet having the PSA layer on one or both sides of a substrate (support), or may be a substrate-less PSA sheet having the PSA layer supported on a release liner. The concept of PSA sheet here includes what are called PSA tapes, PSA labels, PSA films, etc. The PSA sheet disclosed herein may be in the form of a roll or sheets. Alternatively, it may be a PSA sheet processed into various shapes.

[0020] The pressure-sensitive adhesive sheets disclosed herein may have, for example, cross-sectional structures as schematically shown in Figs. 1 to 6. Of these, Figs. 1 and 2 show structural examples of double-sided pressure-sensitive adhesive substrate-attached pressure-sensitive adhesive sheets. The pressure-sensitive adhesive sheet 1 shown in Fig. 1 has a configuration in which pressure-sensitive adhesive layers 21 and 22 are provided on each side (both of which are non-releasable) of a substrate 10, and these pressure-sensitive adhesive layers are protected by release liners 31 and 32, at least the pressure-sensitive adhesive layer side of which is a release surface. The pressure-sensitive adhesive sheet 2 shown in Fig. 2 has a configuration in which pressure-sensitive adhesive layers 21 and 22 are provided on each side (both of which are non-releasable) of a substrate 10, and one of these pressure-sensitive adhesive layers 21 is protected by a release liner 31, both of which have release surfaces. This type of pressure-sensitive adhesive sheet 2 can be configured so that the pressure-sensitive adhesive layer 22 is also protected by the release liner 31 by rolling the pressure-sensitive adhesive sheet and abutting the other pressure-sensitive adhesive layer 22 against the back surface of the release liner 31.

[0021] Figures 3 and 4 show examples of the configuration of a substrate-less double-sided PSA sheet. PSA sheet 3 shown in Figure 3 has a configuration in which both sides 21A and 21B of substrate-less PSA layer 21 are protected by release liners 31 and 32, respectively, with at least the PSA layer side serving as a release surface. PSA sheet 4 shown in Figure 4 has a configuration in which one surface (adhesive surface) 21A of substrate-less PSA layer 21 is protected by release liner 31, with both surfaces serving as release surfaces. When rolled up, the other surface (adhesive surface) 21B of PSA layer 21 abuts against the back surface of release liner 31, so that the other surface 21B is also protected by release liner 31.

[0022] Figures 5 and 6 show examples of the configuration of a single-sided adhesive substrate-attached adhesive sheet. The adhesive sheet 5 shown in Figure 5 has an adhesive layer 21 provided on one surface 10A (non-releasable) of a substrate 10, and a surface (adhesive surface) 21A of the adhesive layer 21 protected by a release liner 31, at least the adhesive layer side of which is a release surface. The adhesive sheet 6 shown in Figure 6 has an adhesive layer 21 provided on one surface 10A (non-releasable) of a substrate 10. The other surface 10B of the substrate 10 is a release surface, and when the adhesive sheet 6 is rolled up, the adhesive layer 21 abuts against the other surface 10B, so that the surface (adhesive surface) 21B of the adhesive layer is protected by the other surface 10B of the substrate.

[0023] <Characteristics of adhesive sheets> The PSA sheet disclosed herein is characterized by a 180-degree peel strength after ethanol immersion (peel strength after ethanol immersion) of 1 N / 5 mm or more. PSA sheets that satisfy this characteristic can exhibit good adhesion reliability even when exposed to polar chemicals, etc. The inventors have discovered that the peel strength after ethanol immersion can be used to evaluate durability against polar chemicals such as perfume, and the effects of the peel strength after ethanol immersion are based on this discovery. The peel strength after ethanol immersion is preferably approximately 1.4 N / 5 mm or more, more preferably approximately 1.7 N / 5 mm or more, even more preferably approximately 2 N / 5 mm or more, and particularly preferably approximately 2.5 N / 5 mm or more (e.g., approximately 3 N / 5 mm or more). There is no particular upper limit to the peel strength after ethanol immersion, and from a practical standpoint, it may be approximately 8 N / 5 mm or less (e.g., approximately 5 N / 5 mm or less). The peel strength after ethanol immersion is measured by the method described in the Examples below.

[0024] The PSA sheet disclosed herein preferably has a 180-degree peel strength after immersion in oleic acid (peel strength after immersion in oleic acid) of approximately 2 N / 5 mm or more. PSA sheets that satisfy this characteristic can exhibit good adhesion reliability even when exposed to low-polarity components such as oils. The peel strength after immersion in oleic acid is more preferably approximately 2.4 N / 5 mm or more, even more preferably approximately 2.7 N / 5 mm or more, and particularly preferably approximately 3 N / 5 mm or more (e.g., approximately 4 N / 5 mm or more). There are no particular limitations on the upper limit of the peel strength after immersion in oleic acid, and from a practical standpoint, it may be approximately 8 N / 5 mm or less (e.g., approximately 5 N / 5 mm or less). The peel strength after immersion in oleic acid is measured by the method described in the Examples below.

[0025] The pressure-sensitive adhesive sheet disclosed herein preferably has an initial 180-degree peel strength (initial peel strength) of approximately 10 N / 25 mm or more. Pressure-sensitive adhesive sheets that satisfy this characteristic can exhibit sufficient adhesive strength to adherends, and are therefore preferably used for fixing and joining applications. The initial peel strength is more preferably approximately 12 N / 25 mm or more (e.g., approximately 15 N / 25 mm or more). There is no particular upper limit to the initial peel strength, and from a practical standpoint, it may be approximately 30 N / 25 mm or less (e.g., approximately 25 N / 25 mm or less). The initial peel strength can be measured by the method described in the Examples below. When the width of the pressure-sensitive adhesive sheet used for measurement is not 25 mm, as in the Examples below, the peel strength [N / 25 mm] can be obtained by dividing the measured peel strength [N] by the width [mm] of the pressure-sensitive adhesive sheet used for measurement and multiplying by 25.

[0026] Furthermore, the PSA sheet disclosed herein has a 180-degree peel strength S after ethanol immersion relative to a 180-degree peel strength S before ethanol immersion. EtOHIt is preferable that the adhesive strength retention rate after ethanol immersion, expressed as the ratio of S to S, is approximately 50% or more. A pressure-sensitive adhesive sheet that satisfies this characteristic can exhibit stable adhesive reliability even when it comes into contact with polar chemicals, etc. The adhesive strength retention rate after ethanol immersion is preferably approximately 60% or more, more preferably approximately 70% or more, even more preferably approximately 80% or more, and particularly preferably approximately 90% or more. The adhesive strength retention rate [%] is calculated using the formula: S EtOH / S0 × 100; 180 degree peel strength after immersion in ethanol S EtOH is as described above, and the 180-degree peel strength S0 before ethanol immersion can be the above-mentioned initial 180-degree peel strength (however, the unit is N / 5 mm).

[0027] The PSA sheet disclosed herein is a sheet having a 180-degree peel strength S after immersion in oleic acid relative to a 180-degree peel strength S before immersion in oleic acid. OA It is preferable that the adhesive strength retention rate after immersion in oleic acid, expressed as the ratio of S to S, is approximately 70% or more. A PSA sheet that satisfies this characteristic can exhibit stable adhesive reliability even when it comes into contact with low-polarity components such as oils. The adhesive strength retention rate after immersion in oleic acid is preferably approximately 80% or more, more preferably approximately 90% or more, and even more preferably approximately 95% or more (for example, approximately 100% or more). The adhesive strength retention rate [%] is calculated using the formula: S OA / S0 × 100; The 180-degree peel strength S after immersion in oleic acid is calculated. OA is as described above, and the 180-degree peel strength S0 before immersion in oleic acid can be the above-mentioned initial 180-degree peel strength (however, the unit is N / 5 mm).

[0028] Furthermore, a pressure-sensitive adhesive sheet according to a preferred embodiment suitably exhibits a displacement distance of approximately 1 mm or less in a shear holding strength test carried out under conditions of a load of 1 kg, a temperature of 60°C, and 1 hour. Pressure-sensitive adhesive sheets that satisfy this characteristic have excellent holding strength and are therefore suitable for use in fixing and bonding applications. The displacement distance in the shear holding strength test is preferably approximately 0.5 mm or less, more preferably approximately 0.3 mm or less, even more preferably approximately 0.2 mm or less, and particularly preferably approximately 0.1 mm or less. The shear holding strength test is carried out by the method described in the Examples below.

[0029] <Adhesive layer> (Polyester polymer) The pressure-sensitive adhesive sheet disclosed herein includes a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive containing a polyester-based polymer. The polyester-based polymer is typically included in the pressure-sensitive adhesive layer as a base polymer. Here, the base polymer refers to the main component of the rubber-like polymer (a polymer that exhibits rubber elasticity in a temperature range around room temperature) included in the pressure-sensitive adhesive layer. In this specification, unless otherwise specified, the term "main component" refers to a component that is included in an amount of more than 50% by weight. In this specification, the term "polyester-based polymer" refers to a polymer obtained by polycondensation of a polycarboxylic acid and a polyol.

[0030] The polycarboxylic acid used in the synthesis of the polyester polymer can be any of aromatic polycarboxylic acids, alicyclic polycarboxylic acids, aliphatic polycarboxylic acids, and unsaturated polycarboxylic acids. Any of dicarboxylic acids containing two carboxyl groups in one molecule, tricarboxylic acids (tricarboxylic acids) containing three carboxyl groups, and tetracarboxylic or higher polycarboxylic acids containing four or more carboxyl groups can be used.

[0031] Specific examples of polycarboxylic acids include aromatic dicarboxylic acids such as isophthalic acid, terephthalic acid, orthophthalic acid, benzylmalonic acid, 2,2'-biphenyldicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-dicarboxydiphenyl ether, and naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as 1,2-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, norbornanedicarboxylic acid, and adamantanedicarboxylic acid; Examples of the polycarboxylic acid derivatives include aliphatic dicarboxylic acids such as carboxylic acid, succinic acid, glutaric acid, dimethylglutaric acid, adipic acid, trimethyladipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, thiodipropionic acid, and diglycolic acid; unsaturated dicarboxylic acids such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, and citraconic acid; trivalent or higher polycarboxylic acids such as trimellitic acid, pyromellitic acid, adamantanetricarboxylic acid, and trimesic acid; dimer acids and trimer acids obtained by dimerizing or trimerizing fatty acids such as oleic acid; and derivatives thereof. These may be used alone or in combination of two or more. The derivatives of the polycarboxylic acids include derivatives such as carboxylic acid salts, carboxylic acid anhydrides, carboxylic acid halides, and carboxylic acid esters.

[0032] As the polycarboxylic acid, aromatic polycarboxylic acids (typically aromatic dicarboxylic acids) are preferably used. The use of aromatic polycarboxylic acids tends to make it easier to prevent the penetration of polar chemicals and the like. In addition, the cohesive strength of the adhesive tends to increase, improving holding power. Suitable examples include isophthalic acid, terephthalic acid, and orthophthalic acid, with isophthalic acid being more preferred. These can be used alone or in combination of two or more. For example, isophthalic acid and terephthalic acid can be used in combination.

[0033] The molar ratio of aromatic carboxylic acid to the total number of moles of polycarboxylic acid in the monomer component of polyester polymer is not particularly limited, but is suitably about 1 mol% or more. From the viewpoint of durability and holding power against polar chemicals, etc., it is preferably about 10 mol% or more, more preferably about 30 mol% or more, even more preferably about 40 mol% or more, for example, about 50 mol% or more, or even about 60 mol% or more. Furthermore, the molar ratio of the aromatic carboxylic acid is suitably about 95 mol% or less, and from the viewpoint of adhesive properties such as peel strength, it is preferably about 85 mol% or less, more preferably about 80 mol% or less, even more preferably about 75 mol% or less (e.g., 70 mol% or less). The molar ratio of the aromatic carboxylic acid may be about 65 mol% or less (e.g., about 55 mol% or less).

[0034] Furthermore, as the polycarboxylic acid, an aliphatic polycarboxylic acid (typically an aliphatic dicarboxylic acid) is also preferably used. Suitable examples include dimethylglutaric acid, adipic acid, trimethyladipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. Among these, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid are more preferred, and adipic acid and sebacic acid are even more preferred.

[0035] The molar ratio of aliphatic carboxylic acids to the total number of moles of polycarboxylic acids in the monomer components of polyester polymers is not particularly limited, and is suitably about 1 mol% or more. From the viewpoint of adhesive properties such as peel strength, it is preferably about 10 mol% or more, more preferably about 15 mol% or more, even more preferably about 20 mol% or more, particularly preferably about 25 mol% or more, and may be about 35 mol% or more (for example, about 50 mol% or more). Furthermore, the molar ratio of the aliphatic carboxylic acids is suitably about 90 mol% or less. From the viewpoint of durability against polar chemicals, etc., it is preferably about 70 mol% or less, more preferably about 60 mol% or less, for example, it may be about 50 mol% or less, or may be about 40 mol% or less.

[0036] From the viewpoint of obtaining a glass transition temperature (Tg) suitable for the adhesive, it is preferable to use an aliphatic polycarboxylic acid (typically an aliphatic dicarboxylic acid) in combination with an aromatic polycarboxylic acid (typically an aromatic dicarboxylic acid). A and aromatic polycarboxylic acid C B The molar ratio of A :C B ) is suitably about 1:49 to 49:1, and may be about 5:45 to 45:5. In a preferred embodiment, the molar ratio (C A :C B ) is approximately 5:45 to 40:10, more preferably approximately 10:40 to 35:15 (for example, approximately 15:35 to 30:20), and may be, for example, approximately 5:45 to 25:25 or approximately 10:40 to 20:30 (for example, approximately 15:35 to 20:30).

[0037] Furthermore, it is preferable that the polycarboxylic acid is primarily composed of a dicarboxylic acid. While not intended to be limiting, the use of a trivalent or higher polycarboxylic acid tends to form polar functional groups within the polymer structure, which may allow the infiltration of polar chemicals and the like. From the perspective of preventing the infiltration of polar chemicals and the like, it is considered desirable to use a dicarboxylic acid as the main skeleton and suppress the formation of polar functional groups within the polymer structure. Furthermore, since trivalent or higher polycarboxylic acids contribute to improving cohesive strength, they may result in reduced adhesion to the adherend, which may lead to the infiltration of polar solvents and the like from the adhesive interface. From the above perspectives, the proportion of dicarboxylic acids in the total amount of polycarboxylic acids in the monomer components of the polyester-based polymer is suitably approximately 90 mol% or more, preferably approximately 95 mol% or more, more preferably approximately 98 mol% or more, even more preferably approximately 99 mol% or more (e.g., 99 to 100 mol%), and typically 99.9 mol% or more (in other words, the polycarboxylic acid is substantially composed of dicarboxylic acids). The proportion of trivalent or higher polycarboxylic acids in the total amount of the polycarboxylic acids is suitably approximately 10 mol% or less, preferably approximately 5 mol% or less, more preferably approximately 3 mol% or less, even more preferably approximately 1 mol% or less, and particularly preferably approximately 0.1 mol% or less (in other words, the polycarboxylic acids do not substantially contain trivalent or higher polycarboxylic acids).

[0038] The polyol used in the synthesis of the polyester polymer disclosed herein may be any of aliphatic polyols, alicyclic polyols, aromatic polyols, and unsaturated polyols. Any of diols containing two hydroxy groups in one molecule, triols containing three hydroxy groups, and tetrahydric or higher polyols containing four or more hydroxy groups may be used.

[0039] Specific examples of the polyol include aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,3-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, and 1,8-octanediol; 1,2-cyclohexanedimethanol; Alicyclic diols such as cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecanedimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol; aromatic diols such as 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, o-, m-, and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and their ethylene oxide and propylene oxide adducts; dimer diol; trivalent or higher polyols such as pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, trimethylolpropane, trimethylolethane, 1,3,6-hexanetriol, and adamantanetriol. These can be used alone or in combination of two or more.

[0040] As the polyol, aliphatic polyols (typically aliphatic diols) and alicyclic polyols (typically alicyclic diols) are preferred, with aliphatic polyols being more preferred. By combining these polyols (preferably aliphatic diols) with the above-mentioned polycarboxylic acids (preferably polycarboxylic acids containing aromatic dicarboxylic acids), a polyester-based polymer with excellent adhesive properties can be preferably obtained. Suitable examples include ethylene glycol, propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. From the viewpoint of reactivity, etc., ethylene glycol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol are more preferred. These can be used alone or in combination of two or more. For example, a combination of ethylene glycol, 2,2-dimethyl-1,3-propanediol, and 1,6-hexanediol may be mentioned.

[0041] The molar ratio of aliphatic polyols and alicyclic polyols (preferably the molar ratio of aliphatic polyols) to the total number of moles of polyols in the monomer components of the polyester polymer is not particularly limited, and is suitably about 50 mol% or more. From the viewpoint of obtaining good adhesive properties, it is preferably about 70 mol% or more, more preferably about 80 mol% or more, even more preferably about 90 mol% or more, and particularly preferably about 95 mol% or more (for example, 99 to 100 mol%). The molar ratio of the aliphatic polyols and alicyclic polyols (preferably the molar ratio of aliphatic polyols) may be, for example, about 95 mol% or less.

[0042] Furthermore, it is preferable that the polyol is primarily composed of a diol. While not intended to be limiting, the use of a trivalent or higher polyol tends to form polar functional groups (typically hydroxyl groups) within the polymer structure, which may allow the infiltration of polar chemicals and the like. From the perspective of preventing the infiltration of polar chemicals and the like, it is considered desirable to use a diol as the main skeleton and suppress the formation of polar functional groups within the polymer structure. Furthermore, since trivalent or higher polyols contribute to improving cohesive strength, they may result in reduced adhesion to the adherend, potentially allowing polar solvents and the like to infiltrate through the adhesive interface. From these perspectives, the proportion of diols in the total amount of polyols in the monomer components of the polyester polymer is suitably approximately 90 mol% or more, preferably approximately 95 mol% or more, more preferably approximately 98 mol% or more, even more preferably approximately 99 mol% or more (e.g., 99 to 100 mol%), and typically 99.9 mol% or more (in other words, the polyol is substantially composed of diols). The proportion of trihydric or higher polyols in the total amount of the polyols is suitably approximately 10 mol% or less, preferably approximately 5 mol% or less, more preferably approximately 3 mol% or less, even more preferably approximately 1 mol% or less, and particularly preferably approximately 0.1 mol% or less (in other words, the polyol does not substantially contain trihydric or higher polyols).

[0043] The polyester polymer may be substantially composed of the polycarboxylic acid and polyol described above. However, for the purpose of introducing desired functional groups or adjusting molecular weight, other copolymerization components (e.g., monocarboxylic acids or alcohols) other than the polycarboxylic acid and polyol may be copolymerized within a range that does not impair the effects of the technology disclosed herein. The proportion of the other copolymerization components is, for example, approximately less than 3 mol%, typically approximately less than 1 mol% (even less than 0.1 mol%). The technology disclosed herein can also be preferably implemented in an embodiment in which the monomer components of the polyester polymer do not substantially contain the other copolymerization components.

[0044] The method for obtaining the polyester polymer disclosed herein is not particularly limited, and any polymerization method known as a synthetic method for polyester polymers can be appropriately adopted. From the viewpoints of polymerization efficiency, molecular weight control, and the like, it is appropriate to blend the monomer raw material used in the synthesis of the polyester polymer so that 1 equivalent or more (e.g., 1 to 2 equivalents) of polyol is blended per equivalent of polycarboxylic acid. In a preferred embodiment, the blending amount of polyol per equivalent of polycarboxylic acid is more than 1 equivalent and 1.8 equivalents or less (e.g., 1.2 to 1.7 equivalents).

[0045] The polyester polymer in the technology disclosed herein can be obtained by polycondensation of a polycarboxylic acid and a polyol, similar to general polyesters. More specifically, a polyester polymer can be synthesized by proceeding with the reaction between a carboxyl group of a polycarboxylic acid and a hydroxyl group of a polyol, typically while removing water (produced water) produced by the reaction from the reaction system. Methods for removing the produced water from the reaction system include a method of blowing an inert gas into the reaction system and removing the produced water together with the inert gas from the reaction system, and a method of distilling the produced water from the reaction system under reduced pressure (reduced pressure method). The reduced pressure method is preferably employed because it is suitable for shortening the synthesis time and improving productivity.

[0046] The reaction temperature during the above reaction (including esterification and polycondensation) and the degree of vacuum (pressure within the reaction system) when a reduced pressure method is used can be appropriately set so as to efficiently obtain a polyester polymer with the desired properties (e.g., molecular weight). While not particularly limited, the reaction temperature is typically set to 180°C to 260°C, for example, 200°C to 220°C. Setting the reaction temperature within the above range ensures a good reaction rate, improves productivity, and facilitates the prevention or suppression of deterioration of the resulting polyester polymer. While not particularly limited, the degree of vacuum is typically set to 10 kPa or less (typically 10 kPa to 0.1 kPa), for example, 4 kPa to 0.1 kPa. Setting the pressure within the reaction system within the above range allows the water produced by the reaction to be efficiently distilled out of the system, making it easy to maintain a good reaction rate. Furthermore, when the reaction temperature is relatively high, setting the pressure within the reaction system to at least the above lower limit can easily prevent the raw materials, polycarboxylic acid and polyol, from distilling out of the system. From the viewpoint of maintaining a stable pressure in the reaction system, it is usually appropriate to set the pressure in the reaction system to 0.1 kPa or more.

[0047] In the above reaction, as in the synthesis of general polyesters, a known or conventional catalyst can be used in an appropriate amount for esterification and condensation. Examples of such catalysts include various metal compounds, such as titanium-based, germanium-based, antimony-based, tin-based, and zinc-based compounds; strong acids, such as p-toluenesulfonic acid and sulfuric acid; and the like. Among these, titanium-based metal compounds (titanium compounds) are preferred. Specific examples of such titanium compounds include titanium tetraalkoxides, such as titanium tetrabutoxide, titanium tetraisopropoxide, titanium tetrapropoxide, and titanium tetraethoxide; alkyl titanates, such as tetraisopropyl titanate, tetrabutyl titanate, octaalkyltrititanate, and hexaalkylditanate; and titanium acetate.

[0048] In the above process of synthesizing a polyester polymer by reacting a polycarboxylic acid with a polyol, a solvent may or may not be used. The synthesis can be carried out substantially without using an organic solvent (meaning, for example, that an organic solvent is intentionally used as a reaction solvent during the reaction is excluded). Synthesizing a polyester polymer substantially without using an organic solvent and preparing a polyester pressure-sensitive adhesive using such a polyester polymer are preferable because they meet the demand for reducing the use of organic solvents in the production process.

[0049] In the above reaction, there is generally a correlation between the molecular weight of the polyester polymer synthesized and the viscosity of the reaction system, and this can be utilized to control the molecular weight of the polyester polymer. For example, by continuously or intermittently measuring (monitoring) the torque of the stirrer and the viscosity of the reaction system during the reaction, it is possible to synthesize a polyester polymer having a target molecular weight with high accuracy.

[0050] Although not particularly limited, the polyester polymer used in the technology disclosed herein may be a polyester polymer having a hydroxyl value of less than 30 mgKOH / g (e.g., less than 15 mgKOH / g). Using a polyester polymer having a hydroxyl value less than a predetermined value makes it easier to block the penetration of polar chemicals and the like. The hydroxyl value of the polyester polymer is preferably less than 12 mgKOH / g, more preferably less than 10 mgKOH / g, and may be, for example, less than 8 mgKOH / g or less than 5 mgKOH / g. The lower limit of the hydroxyl value is 0 mgKOH / g or more (e.g., 1 mgKOH / g or more). The hydroxyl value of the polyester polymer can be measured in accordance with JIS K0070:1992. Measurements are also performed in the examples described below using a similar method.

[0051] Furthermore, the acid value of the polyester polymer in the technology disclosed herein is not particularly limited, and for example, a polyester polymer of less than 10 mgKOH / g can be used. By using a polyester polymer with an acid value less than a predetermined value, it is easy to block the penetration of polar chemicals and the like. The acid value of the polyester polymer is preferably less than 5 mgKOH / g, more preferably less than 3 mgKOH / g, and even more preferably less than 2 mgKOH / g, and may be, for example, less than 1 mgKOH / g. The lower limit of the acid value is 0 mgKOH / g. The acid value of the polyester polymer can be measured in accordance with JIS K0070:1992. The same method is used in the examples described below.

[0052] From the viewpoint of adhesion to an adherend, the Tg of the polyester polymer is advantageously about 15° C. or less, preferably about 0° C. or less, more preferably about −10° C. or less, even more preferably about −15° C. or less, and may be, for example, about −20° C. or less. From the viewpoint of cohesive strength of the pressure-sensitive adhesive layer, the Tg of the polyester polymer is usually about −80° C. or more, preferably about −60° C. or more, more preferably about −40° C. or more, even more preferably about −30° C. or more (for example, −20° C. or more). The Tg of the polyester polymer can be adjusted by appropriately changing the monomer composition (i.e., the types and amount ratios of monomers used in synthesizing the polymer). In the technology disclosed herein, any of high Tg type (for example, Tg of -20°C or higher, typically Tg of -20°C to 15°C), medium Tg type (for example, Tg of -40°C or higher but lower than -20°C), and low Tg type (for example, Tg of lower than -40°C, typically -80°C or higher but lower than -40°C) polyester polymers can be used as the base polymer of the pressure-sensitive adhesive layer. Of these, medium Tg type and high Tg type polyester polymers are preferred. The Tg of a polyester polymer can be measured using a commercially available differential scanning calorimeter (e.g., TA Instruments, model "DSC Q20"). Measurement conditions include a shear strain frequency of 1 Hz, a temperature range of -90°C to 100°C, and a heating rate of 10°C / min. Measurements are also performed in the examples described below using a similar method.

[0053] The number average molecular weight (Mn) of the polyester polymer is not particularly limited and may be, for example, approximately 5,000 or more. Here, Mn refers to a value calculated in terms of standard polystyrene obtained by GPC (gel permeation chromatography). As a GPC device, for example, a model "HLC-8320GPC" (column: TSKgelGMH-H(S), manufactured by Tosoh Corporation) can be used. From the viewpoint of durability against polar chemicals and the like, cohesive strength, retention strength, etc., Mn of the polyester polymer is preferably approximately 7,000 or more, more preferably approximately 9,000 or more, and may be, for example, approximately 12,000 or more, approximately 15,000 or more, or approximately 18,000 or more (e.g., approximately 24,000 or more). Mn of the polyester polymer is usually approximately 10 × 10 4 It is appropriate that the thickness is equal to or less than 5×10 4 Less than or equal to 3×10 4 For example, approximately 2 × 10 4 It may be less than or equal to approximately 1.5 × 10 4 It may be the following:

[0054] (tackifying resin) The tackifier resin can be one or more selected from various known tackifier resins such as phenolic tackifier resins, terpene tackifier resins, modified terpene tackifier resins, rosin tackifier resins, hydrocarbon tackifier resins, epoxy tackifier resins, polyamide tackifier resins, elastomer tackifier resins, ketone tackifier resins, etc. Use of a tackifier resin can improve the adhesion of the PSA layer to the adherend and effectively prevent polar chemicals and oils from penetrating from the outer edge of the PSA sheet to the adhesive interface.

[0055] 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 terpene residues and phenol residues, and is a concept that encompasses both copolymers of terpenes and phenolic compounds (terpene-phenol copolymer resins) and phenol-modified terpene resins (phenol-modified terpene resins) of terpenes or their homopolymers or copolymers. 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- (dipentene) forms). Hydrogenated terpene phenolic resins have a structure obtained by hydrogenating such terpene phenolic resins. They are also sometimes called hydrogenated terpene phenolic resins. 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 various rosin derivatives described above (including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters). Examples of rosin phenolic resins include those obtained by adding phenol to rosins or the various rosin derivatives described above using an acid catalyst and then thermally polymerizing the resulting mixture. Of these phenolic tackifying resins, terpene phenol resins, hydrogenated terpene phenol resins and alkylphenol resins are preferred, terpene phenol resins and hydrogenated terpene phenol resins are more preferred, and terpene phenol resins are particularly preferred.

[0056] Examples of terpene-based tackifying resins include polymers of terpenes (e.g., monoterpenes) such as α-pinene, β-pinene, d-limonene, l-limonene, and dipentene. They may be homopolymers of one type of terpene, or copolymers of two or more types of terpenes. Examples of homopolymers of one type of terpene include α-pinene polymers, β-pinene polymers, and dipentene polymers. Examples of modified terpene resins include those obtained by modifying the above-mentioned terpene resins, such as styrene-modified terpene resins and hydrogenated terpene resins.

[0057] The concept of rosin-based tackifying resins herein encompasses 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.).

[0058] Rosin derivative resins are typically derivatives of the rosins described above. The term "rosin-based resin" as used herein encompasses derivatives of unmodified rosin and derivatives of modified rosin (including hydrogenated rosin, disproportionated rosin, and polymerized rosin). Examples include 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, which are rosin esters modified with unsaturated fatty acids; unsaturated fatty acid-modified rosin esters, which are rosin esters modified with unsaturated fatty acids; rosin alcohols, which are obtained by reducing the carboxyl groups of rosins or the various rosin derivatives described above (including rosin esters, unsaturated fatty acid-modified rosins, and unsaturated fatty acid-modified rosin esters); and metal salts of rosins or the various rosin derivatives described above. 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.).

[0059] Examples of hydrocarbon-based tackifying resins include various hydrocarbon-based 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.

[0060] The softening point of the tackifier resin is not particularly limited. From the viewpoint of improving cohesive strength, in one embodiment, a tackifier resin having a softening point (softening temperature) of approximately 80°C or higher (preferably approximately 100°C or higher) can be preferably used. The technology disclosed herein can be preferably implemented in an embodiment in which the tackifier resin having the above softening point accounts for more than 50% by weight (more preferably more than 70% by weight, for example, more than 90% by weight) of the total tackifier resin contained in the PSA layer. For example, a phenolic tackifier resin (such as a terpene phenol resin) having such a softening point can be preferably used. In a preferred embodiment, a terpene phenol resin having a softening point of approximately 135°C or higher (even approximately 140°C or higher) 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, in one embodiment, a tackifier resin having a softening point of approximately 200°C or lower (more preferably approximately 180°C or lower) 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.

[0061] In one preferred embodiment, the tackifier resin comprises one or more phenolic tackifier resins (e.g., terpene phenolic resins). Phenolic tackifier resins tend to have better compatibility with polyester polymers than other tackifier resins (e.g., rosin-based tackifier resins). They also tend to have lower affinity for low-polarity components (typically oils). The technology disclosed herein can be preferably implemented, for example, in an embodiment in which approximately 25% by weight or more (more preferably approximately 30% by weight or more) of the total tackifier resin is a terpene phenolic resin. Approximately 50% by weight or more of the total tackifier resin may be a terpene phenolic resin, or approximately 80% by weight or more (e.g., approximately 90% by weight or more) may be a terpene phenolic resin. Substantially all of the tackifier resin (e.g., approximately 95% by weight to 100% by weight, or even approximately 99% by weight to 100% by weight) may be a terpene phenolic resin.

[0062] Although not particularly limited, the tackifying resin used in the technology disclosed herein may be a tackifying resin having a hydroxyl value of less than 30 mgKOH / g (e.g., less than 20 mgKOH / g). Hereinafter, a tackifying resin having a hydroxyl value of less than 30 mgKOH / g may be referred to as a "low hydroxyl value resin." The hydroxyl value of the low hydroxyl value resin may be approximately 15 mgKOH / g or less, or approximately 10 mgKOH / g or less. The lower limit of the hydroxyl value of the low hydroxyl value resin is not particularly limited, and may be substantially 0 mgKOH / g.

[0063] In a preferred embodiment, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more is used as the tackifier resin in the technology disclosed herein. Hereinafter, a tackifier resin having a hydroxyl value of 30 mgKOH / g or more may be referred to as a "high hydroxyl value resin." The hydroxyl value of the high hydroxyl value resin can be approximately 50 mgKOH / g or more (e.g., approximately 60 mgKOH / g or more) from the viewpoints of compatibility with polyester-based polymers, durability against low-polarity components, etc. The upper limit of the hydroxyl value of the high hydroxyl value resin is not particularly limited. From the viewpoints of compatibility with polyester-based polymers, durability against polar chemicals, etc., the hydroxyl value of the high hydroxyl value resin is usually approximately 200 mgKOH / g or less, preferably approximately 180 mgKOH / g or less, more preferably approximately 160 mgKOH / g or less, and even more preferably approximately 140 mgKOH / g or less.

[0064] Here, the hydroxyl value can 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) For the acetylation reagent, take about 12.5 g (about 11.8 mL) of acetic anhydride, add pyridine to make a total volume of 50 mL, and stir thoroughly before use. Alternatively, take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to make a total volume of 100 mL, and stir thoroughly before use. (2) The measurement reagent is a 0.5 mol / L potassium hydroxide ethanol solution. (3) In addition, prepare toluene, pyridine, ethanol, and distilled water. 2.Operation (1) Accurately weigh 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 condenser 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) Potentiometric titration is performed 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 the above steps (1) to (5) without adding any sample. 3.Calculation The hydroxyl value is calculated using the following formula. Hydroxyl value (mgKOH / g) = [(BC) × f × 28.05] / S + D where: B: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test. C: Amount (mL) of 0.5 mol / L potassium hydroxide ethanol solution used for the sample. f: Factor of 0.5 mol / L potassium hydroxide ethanol solution, S: sample weight (g), D: acid number, 28.05: 1 / 2 of the molecular weight of potassium hydroxide, 56.11 is.

[0065] The low hydroxyl value resin and the high hydroxyl value resin can be any of the above-mentioned tackifier resins having the corresponding hydroxyl values. The low hydroxyl value resin and the high hydroxyl value resin can be used alone or in combination of two or more. For example, a phenolic tackifier resin with a hydroxyl value of less than 30 mgKOH / g can be used as the low hydroxyl value resin. Furthermore, for example, a phenolic tackifier resin with a hydroxyl value of 30 mgKOH / g or more can be preferably used as the high hydroxyl value resin. Among these, terpene phenolic resins are preferred. Terpene phenolic resins are advantageous because the hydroxyl value can be freely controlled by the copolymerization ratio of phenol.

[0066] In embodiments using a tackifier resin, the content of the tackifier resin is not particularly limited. The content of the tackifier resin can be, for example, more than 0 parts by weight per 100 parts by weight of the polyester-based polymer, and may be approximately 3 parts by weight or more (e.g., approximately 5 parts by weight or more). The upper limit of the content of the tackifier resin is not particularly limited. From the viewpoint of compatibility with the polyester-based polymer and adhesiveness, in one embodiment, the content of the tackifier resin per 100 parts by weight of the polyester-based polymer is typically approximately 120 parts by weight or less, preferably less than 80 parts by weight, and more preferably approximately 70 parts by weight or less (e.g., approximately 50 parts by weight or less). In another preferred embodiment, the content of the tackifier resin per 100 parts by weight of the polyester-based polymer is suitably less than 20 parts by weight (typically less than 15 parts by weight, for example, less than 10 parts by weight).

[0067] In the technology disclosed herein, in an embodiment using a high Tg type polyester polymer (e.g., Tg of -20°C or higher, typically Tg of -20°C to 15°C) as the base polymer, the content of the tackifier resin per 100 parts by weight of the polyester polymer is suitably about 0 parts by weight or more (typically more than 0 parts by weight), preferably about 1 part by weight or more, more preferably about 3 parts by weight or more, and suitably less than 10 parts by weight, preferably about 8 parts by weight or less, more preferably about 6 parts by weight or less. Furthermore, in an embodiment using a medium Tg type polyester polymer (e.g., Tg of -40°C or higher but less than -20°C) as the base polymer, the content of the tackifier resin per 100 parts by weight of the polyester polymer is suitably about 5 parts by weight or more, preferably about 10 parts by weight or more, more preferably about 13 parts by weight or more, and may be, for example, about 20 parts by weight or more, or may be about 25 parts by weight or more. In this embodiment, the content of the tackifier resin per 100 parts by weight of the polyester polymer is suitably less than 50 parts by weight, preferably less than 40 parts by weight, and more preferably about 35 parts by weight or less. In an embodiment in which a low Tg type (e.g., Tg less than -40°C, typically -80°C or more and less than -40°C) polyester polymer is used as the base polymer, the content of the tackifier resin per 100 parts by weight of the polyester polymer is about 10 parts by weight or more, preferably about 20 parts by weight or more, more preferably about 30 parts by weight or more, and even more preferably about 35 parts by weight or more (e.g., about 50 parts by weight or more), and is suitably less than 80 parts by weight, preferably about 70 parts by weight or less (e.g., about 65 parts by weight or less).

[0068] (Crosslinking agent) The pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer preferably contains a crosslinking agent as an optional component. 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 partially crosslinked form, or an intermediate or composite form thereof. The crosslinking agent is usually contained in the pressure-sensitive adhesive layer exclusively in a form after crosslinking reaction. Note that the crosslinking agent used to crosslink the polyester polymer may also function as a chain extender.

[0069] The type of crosslinking agent is not particularly limited, and can 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, and metal chelate-based crosslinking agents. The crosslinking agents can be used alone or in combination of two or more. Among these, isocyanate-based crosslinking agents are preferred.

[0070] 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.

[0071] Examples of polyfunctional isocyanates 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.

[0072] 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.

[0073] 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.

[0074] A preferred example of a polyfunctional isocyanate is one having an average of three or more isocyanate groups per molecule. Such a tri- or higher functional isocyanate may be a multimer (e.g., a dimer or trimer) of a bifunctional or tri- or higher functional isocyanate, a derivative (e.g., an addition reaction product of a polyhydric alcohol with two or more molecules of a polyfunctional isocyanate), a polymer, or the like. Examples of polyfunctional isocyanates include 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 the like. Commercially available products of such polyfunctional isocyanates include those manufactured by Asahi Kasei Chemicals Corporation under the trade name "Duranate TPA-100," and those manufactured by Tosoh Corporation under the trade names "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096."

[0075] In embodiments in which an isocyanate-based crosslinking agent is used, the amount used is not particularly limited. The amount of isocyanate-based crosslinking agent used can be, for example, approximately 0.5 parts by weight or more and approximately 10 parts by weight or less per 100 parts by weight of polyester-based polymer. From the viewpoint of durability against polar chemicals, etc., the amount of isocyanate-based crosslinking agent used per 100 parts by weight of polyester-based polymer is usually approximately 1 part by weight or more, and preferably approximately 1.5 parts by weight or more (e.g., approximately 3 parts by weight or more). Furthermore, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of polyester-based polymer is usually approximately 8 parts by weight or less, and preferably approximately 5 parts by weight or less.

[0076] The total amount of crosslinking agent used is not particularly limited, and can be selected, for example, from a range of approximately 0.005 parts by weight or more (e.g., 0.01 parts by weight or more, typically 0.1 parts by weight or more) to approximately 10 parts by weight or less (e.g., approximately 8 parts by weight or less, preferably approximately 5 parts by weight or less) per 100 parts by weight of the base polymer.

[0077] (Other additives) In addition to the above-mentioned components, the pressure-sensitive adhesive composition may optionally contain various additives commonly used in the field of pressure-sensitive adhesives, such as leveling agents, crosslinking aids, fillers, plasticizers, softeners, antistatic agents, antioxidants, UV absorbers, antioxidants, and light stabilizers. The polyester-based pressure-sensitive adhesive composition disclosed herein may contain an appropriate amount of a hydrolysis stabilizer such as a carbodiimide, or may be substantially free of it. Here, "substantially free of a hydrolysis stabilizer" means that the content of the hydrolysis stabilizer in the pressure-sensitive adhesive composition is less than 0.01 wt % (e.g., less than 0.003 wt %). Conventionally known additives can be used in the usual manner as the above-mentioned additives do not particularly characterize the present invention, and therefore detailed description thereof will be omitted.

[0078] The PSA layer disclosed herein can be formed by a conventionally known method. For example, a method (direct method) can be used in which a PSA composition is directly applied (typically coated) to a non-releasable substrate and then dried to form a PSA layer. Alternatively, a method (transfer method) can be used in which a PSA composition is applied to a releasable surface (release surface) and then dried to form a PSA layer on the surface, and then the PSA layer is transferred to a non-releasable substrate. From the viewpoint of productivity, the transfer method is preferred. In a substrate-less configuration, a PSA layer can be formed by applying a PSA composition to a releasable surface (release surface) and drying it, and then covering it with a release liner, if necessary. The release surface can be the surface of a release liner, the back surface of a release-treated substrate, or the like. The PSA layer disclosed herein is typically formed continuously, but is not limited to this form. For example, the PSA layer may be formed in a regular or random pattern, such as a striped pattern.

[0079] The pressure-sensitive adhesive composition can be applied using a conventionally known coater such as a gravure roll coater, a die coater, a bar coater, etc. Alternatively, the pressure-sensitive adhesive composition may be applied by impregnation or curtain coating. The pressure-sensitive adhesive composition can be dried at room temperature or under heating. From the viewpoints of promoting the crosslinking reaction and improving production efficiency, the pressure-sensitive adhesive composition is preferably dried under heating. The drying temperature can be, for example, about 40 to 150°C, and is usually preferably about 40 to 100°C. After drying the pressure-sensitive adhesive composition, it is preferable to perform aging for the purposes of adjusting component migration within the pressure-sensitive adhesive layer, promoting the crosslinking reaction, and alleviating distortion that may exist in the substrate or pressure-sensitive adhesive layer. The aging conditions are not particularly limited, and can be, for example, about 70°C or less (typically about 40 to 70°C) for one day or more (e.g., three days or more).

[0080] The thickness of the pressure-sensitive adhesive layer is not particularly limited. To prevent the pressure-sensitive adhesive sheet from becoming excessively thick, the thickness of the pressure-sensitive adhesive layer is typically approximately 100 μm or less, preferably approximately 70 μm or less, more preferably approximately 50 μm or less, and even more preferably approximately 30 μm or less. Generally, as the thickness of the pressure-sensitive adhesive layer decreases, adhesion to the adherend decreases, and polar chemicals and oils tend to penetrate more easily from the interface with the adherend. Therefore, it is particularly meaningful to apply the technology disclosed herein. In a preferred embodiment of the pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive layer is approximately 25 μm or less (usually less than 25 μm, more preferably approximately 22 μm or less, for example, approximately 20 μm or less). There is no particular lower limit to the thickness of the pressure-sensitive adhesive layer, and from the viewpoint of adhesion to the adherend, it is advantageous to set the thickness to approximately 4 μm or more, preferably approximately 6 μm or more, more preferably approximately 10 μm or more (for example, approximately 15 μm or more).

[0081] (Tg of adhesive layer) In addition, from the viewpoint of favorably exhibiting the effects of the technology disclosed herein, it is preferable that the Tg of the pressure-sensitive adhesive layer, calculated from the Tg of the polyester polymer contained in the pressure-sensitive adhesive layer and the softening point of the tackifier resin that may be contained as an optional component, be within a predetermined range. The Tg of the pressure-sensitive adhesive layer is preferably about −35° C. or higher, more preferably about −30° C. or higher, even more preferably about −25° C. or higher, and particularly preferably about −20° C. or higher, and may be, for example, about −15° C. or higher or about −12° C. or higher. The Tg of the pressure-sensitive adhesive layer is preferably about 10° C. or lower, more preferably about 0° C. or lower, even more preferably about −5° C. or lower, and may be, for example, about −10° C. or lower.

[0082] The Tg of the pressure-sensitive adhesive layer is a value determined using the Fox equation, with the Tg of the polyester polymer and the softening point of the tackifier resin regarded as the Tg of each component. 1 / Tg(PSA)=[(W(p) / Tg(p))+(W(t) / Tg(t))] In the above formula, Tg(PSA) represents the glass transition temperature (unit: K) of the PSA layer (a PSA layer essentially composed mainly of a polyester polymer and a tackifying resin); W(p) represents the weight fraction of the polyester polymer relative to the total amount of the polyester polymer and tackifying resin contained in the PSA layer; Tg(p) represents the glass transition temperature (unit: K) of the polyester polymer; W(t) represents the weight fraction of the tackifying resin relative to the total amount of the polyester polymer and tackifying resin contained in the PSA layer; and Tg(t) represents the softening point of the tackifying resin (unit: K).

[0083] (gel fraction) Although not particularly limited, the gel fraction of the pressure-sensitive adhesive layer disclosed herein can be, for example, 20% or more by weight, and is usually 30% or more, preferably 35% or more, and more preferably 40% or more (e.g., 45% or more). By increasing the gel fraction of the pressure-sensitive adhesive layer within an appropriate range, it is easy to prevent the penetration of polar chemicals and the like. Holding power also tends to be improved. On the other hand, by adjusting the gel fraction to a predetermined value or less, it is possible to increase adhesion to the adherend and prevent the penetration of polar chemicals and the like. From this perspective, the gel fraction of the pressure-sensitive adhesive layer is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less (e.g., 65% or less).

[0084] 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.

[0085] [Gel fraction measurement method] Approximately 0.1 g of adhesive sample (weight Wg1) is wrapped in a porous polytetrafluoroethylene membrane (weight Wg2) with an average pore size of 0.2 μm, and the opening is tied with string (weight Wg3). The porous polytetrafluoroethylene (PTFE) membrane is available from Nitto Denko Corporation under the trade name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent. The package is immersed in 50 mL of ethyl acetate and kept at room temperature (typically 23°C) for 7 days to allow only the sol component in the adhesive layer to elute out of the film. The package is then removed 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 (Wg4) of the package is measured. G can be calculated by substituting each value into the following formula: A similar method is also used in the examples described later. Gel fraction F G (%) = [(Wg4 - Wg2 - Wg3) / Wg1] x 100

[0086] <Base material> In embodiments in which the PSA sheet disclosed herein is in the form of a single-sided or double-sided PSA sheet with a substrate, the substrate supporting (backing) the PSA layer can be a resin film, paper, cloth, rubber sheet, foam sheet, metal foil, or a composite thereof. Examples of resin films include polyolefin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester films such as polyethylene terephthalate (PET); vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluororesin films; polyurethane films; and cellophane. Examples of paper include Japanese paper, kraft paper, glassine paper, fine paper, synthetic paper, and top-coated paper. Examples of fabrics include woven fabrics and nonwoven fabrics made from 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, and polyolefin fiber. Examples of rubber sheets include natural rubber sheets, butyl rubber sheets, etc. Examples of foam sheets include foamed polyurethane sheets, foamed polychloroprene rubber sheets, etc. Examples of metal foils include aluminum foils, copper foils, etc.

[0087] The term "nonwoven fabric" as used herein refers to a nonwoven fabric for adhesive sheets that is primarily used in the field of adhesive tapes and other adhesive sheets, and typically refers to a nonwoven fabric (sometimes referred to as "paper") that is produced using a general papermaking machine. The term "resin film" as used herein typically refers to a non-porous resin sheet, and is a concept that is distinguished from, for example, nonwoven fabric (i.e., does not include nonwoven fabric). The resin film may be any of a non-stretched film, a uniaxially stretched film, and a biaxially stretched film. The surface of the substrate on which the adhesive layer is to be formed may be subjected to a surface treatment such as application of a primer, corona discharge treatment, or plasma treatment.

[0088] The technology disclosed herein can be preferably implemented in the form of a substrate-attached PSA sheet having the PSA layer on at least one surface of a substrate film (support), for example, a substrate-attached double-sided PSA sheet having the PSA layers on one and the other surfaces of a substrate film.

[0089] The substrate film preferably includes a resin film as a base film. The base film is typically a member that can independently maintain its shape (independent). The substrate film in the technology disclosed herein may be substantially composed of such a base film. Alternatively, the substrate film may include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include an undercoat layer, an antistatic layer, a colored layer, etc., provided on the surface of the base film.

[0090] The resin film is a film whose main component is a resin material (a component contained in the resin film at more than 50% by weight). Examples of resin films include polyolefin-based resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester-based resin films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); vinyl chloride-based resin films; vinyl acetate-based resin films; polyimide-based resin films; polyamide-based resin films; fluororesin films; cellophane; and the like. The resin film may also be a rubber-based film such as a natural rubber film or a butyl rubber film. Among these, polyester films are preferred from the viewpoint of handling and processability, and PET films are particularly preferred. In this specification, the term "resin film" refers to a typically non-porous sheet, a concept distinguished from so-called nonwoven fabrics and woven fabrics (in other words, a concept excluding nonwoven fabrics and woven fabrics).

[0091] The resin film (e.g., PET film) may contain various additives, such as fillers (inorganic fillers, organic fillers, etc.), colorants, dispersants (surfactants, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, plasticizers, etc. The blending ratio of the various additives is usually about less than 30% by weight (e.g., less than 20% by weight, preferably less than 10% by weight).

[0092] The resin film may have a single layer structure, or a multilayer structure of two, three or more layers. From the viewpoint of shape stability, the resin film preferably has a single layer structure. In the case of a multilayer structure, at least one layer (preferably all layers) preferably has 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, as appropriate. 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.

[0093] The thickness of the substrate film disclosed herein is not particularly limited. To prevent the pressure-sensitive adhesive sheet from becoming excessively thick, the thickness of the substrate film can be, for example, approximately 200 μm or less, preferably approximately 150 μm or less, and more preferably approximately 100 μm or less. Depending on the intended use and manner of use of the pressure-sensitive adhesive sheet, the thickness of the substrate film may be approximately 70 μm or less, approximately 50 μm or less, or approximately 30 μm or less (e.g., approximately 25 μm or less). In one embodiment, the thickness of the substrate film may be approximately 20 μm or less, approximately 15 μm or less, or approximately 10 μm or less (e.g., approximately 5 μm or less). By reducing the thickness of the substrate film, the thickness of the pressure-sensitive adhesive layer can be increased even if the total thickness of the pressure-sensitive adhesive sheet is the same. This can be advantageous from the perspective of improving adhesion to the substrate. There is no particular lower limit on the thickness of the substrate film. From the viewpoint of the handleability and processability of the PSA sheet, the thickness of the base film 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 one embodiment, the thickness of the base film can be about 6 μm or more, or may be about 8 μm or more, or may be about 10 μm or more (e.g., more than 10 μm).

[0094] In embodiments using a foam substrate as the substrate, the thickness of the foam substrate is not particularly limited and can be appropriately set depending on the strength, flexibility, and intended use of the PSA sheet. From the viewpoint of thinning the bonded portion, the thickness of the foam substrate is typically approximately 0.70 mm or less, preferably approximately 0.40 mm or less, and more preferably approximately 0.30 mm or less. From the viewpoint of processability when processing the PSA sheet to a narrow width, the technology disclosed herein can be preferably implemented in an embodiment in which the thickness of the foam substrate is approximately 0.20 mm or less (typically 0.18 mm or less, e.g., 0.16 mm or less). Furthermore, from the viewpoint of reducing the amount of oil penetration into the adhesive interface, the thickness of the foam substrate is approximately 0.05 mm or more, preferably approximately 0.06 mm or more, and more preferably approximately 0.07 mm or more (e.g., approximately 0.08 mm or more). The technology disclosed herein can be preferably implemented in an embodiment in which the thickness of the foam substrate is approximately 0.10 mm or more (typically greater than 0.10 mm, preferably 0.12 mm or more, for example, 0.13 mm or more). As the thickness of the foam substrate increases, the impact resistance also improves, and the desired impact resistance tends to be exhibited even in a narrower configuration.

[0095] The surface (typically the surface on the PSA layer side) of the substrate (e.g., substrate film layer) may be subjected to a conventionally known surface treatment such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, application of a primer, etc. Such a surface treatment may be a treatment for improving the adhesion between the substrate and the PSA layer, in other words, the anchoring ability of the PSA layer to the substrate.

[0096] The thickness of the substrate can be selected appropriately depending on the purpose and type, but is generally about 2 μm or more (e.g., 10 μm or more, typically 20 μm or more) and about 1000 μm or less (e.g., 500 μm or less, typically 200 μm or less).

[0097] <Release liner> In the technology disclosed herein, a release liner can be used during the formation of the adhesive layer, the production of the adhesive sheet, and the storage, distribution, and shaping of the adhesive sheet before use. The release liner is not particularly limited, and examples that can be used include release liners having a release treatment layer on the surface of a liner substrate such as a resin film or paper, and release liners made of low-adhesion materials such as fluorine-based polymers (polytetrafluoroethylene, etc.) and polyolefin-based resins (polyethylene, polypropylene, 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.

[0098] <Total thickness of adhesive sheet> The total thickness of the PSA sheet disclosed herein (excluding the release liner) is not particularly limited. The total thickness of the PSA sheet can be, for example, approximately 500 μm or less, and is usually approximately 350 μm or less, preferably approximately 250 μm or less (e.g., approximately 200 μm or less). The technology disclosed herein can be preferably implemented in the form of a PSA sheet having a total thickness of approximately 150 μm or less (more preferably approximately 100 μm or less, even more preferably less than approximately 60 μm, for example, approximately 55 μm or less). The total thickness of a PSA sheet according to one embodiment (e.g., a substrateless PSA sheet) is preferably approximately 50 μm or less, more preferably approximately 30 μm or less. There are no particular lower limits on the thickness of the PSA sheet, and from the viewpoint of adhesion to the adherend, it is advantageous to set it to approximately 4 μm or more, preferably approximately 6 μm or more, and more preferably approximately 10 μm or more (e.g., approximately 15 μm or more). The total thickness of the pressure-sensitive adhesive sheet (for example, a pressure-sensitive adhesive sheet with a substrate) may be approximately 10 μm or more, approximately 20 μm or more, or approximately 30 μm or more.

[0099] <Application> The pressure-sensitive adhesive sheet disclosed herein can exhibit good adhesive reliability even when exposed to polar chemicals, etc. Utilizing these characteristics, the pressure-sensitive adhesive sheet can be preferably used for fixing various components that may come into contact with oil. A typical example of such an application is fixing components in various portable devices. For example, it is suitable for fixing components in portable electronic devices. Non-limiting examples of the portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (e.g., wristwear devices worn on the wrist like a wristwatch, modular devices worn on a part of the body with a clip or strap, eyewear devices including eyeglasses (monocular and binocular, including head-mounted devices), clothing devices attached to shirts, socks, hats, etc. as accessories, and earwear devices attached to the ears like earphones), digital cameras, digital video cameras, audio devices (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, e-books, in-car information devices, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. Non-limiting examples of portable devices other than portable electronic devices include mechanical wristwatches and pocket watches, flashlights, hand mirrors, pass cases, etc. In this specification, the term "portable" does not simply mean that something can be carried around, but rather means that it has a level of portability that allows an individual (average adult) to carry it relatively easily.

[0100] A particularly preferred embodiment of the pressure-sensitive adhesive sheet is used for joining and fixing components of a mobile electronic device with a touch panel. The mobile electronic device is equipped with a display / input unit (typically a touch panel) whose display also functions as an input unit, and is operated by a user directly touching the surface of the display / input unit with their fingertips. Therefore, the mobile electronic device is prone to adhesion of secretions such as sebum and fingerprints, chemicals such as cosmetics, hair styling products, moisturizing creams, and sunscreens, and low-polarity components such as oils contained in food. The mobile electronic device may also be exposed to polar chemicals containing polar solvents (typically ethanol), such as perfumes, insect repellent sprays, hand washing detergents, and disinfectant wipes. The pressure-sensitive adhesive sheet disclosed herein can be advantageously used for mobile electronic devices that frequently come into contact with such low-polarity components and polar chemicals.

[0101] The PSA sheets (typically double-sided PSA sheets) disclosed herein can be used in the form of bonding materials processed into various shapes to fasten components constituting portable devices. Particularly preferred applications include applications for fastening components constituting portable electronic devices. In particular, they can be preferably used in portable electronic devices having liquid crystal display devices. For example, in such portable electronic devices, they are suitable for applications such as joining a display unit (which may be the display unit of a liquid crystal display device) or a display unit protection member to a housing.

[0102] A preferred embodiment of such a bonding material is one having a narrow portion with a width of 4.0 mm or less (e.g., 2.0 mm or less, usually less than 2.0 mm). The pressure-sensitive adhesive sheet disclosed herein can have excellent cohesive strength in addition to oil resistance, and can therefore secure members well even when used as a bonding material having a shape (e.g., a frame shape) that includes such a narrow portion. In one embodiment, the width of the narrow portion may be 1.5 mm or less, 1.0 mm or less, or about 0.5 mm or less. There is no particular lower limit to the width of the narrow portion, but from the viewpoint of ease of handling of the pressure-sensitive adhesive sheet, a width of 0.1 mm or more (e.g., 0.2 mm or more) is usually appropriate.

[0103] The narrow width portion is typically linear. Here, the term "linear" refers to a concept that includes straight, curved, or folded (e.g., L-shaped) shapes, as well as ring shapes such as frame shapes and circles, and composite or intermediate shapes among these. The ring shape is not limited to shapes formed by curves, but also includes ring shapes that are partially or entirely linear, such as a shape that follows the periphery of a rectangle (frame shape) or a shape that follows the periphery of a fan shape. The length of the narrow width portion is not particularly limited. For example, the effects of applying the technology disclosed herein can be suitably exhibited in a configuration in which the length of the narrow width portion is 10 mm or more (more preferably 20 mm or more, e.g., 30 mm or more).

[0104] The matters disclosed by this specification include the following: (1) A portable electronic device, The display is equipped with a touch panel that also functions as an input unit, the touch panel can be operated by directly touching it with a fingertip; The members constituting the portable electronic device are joined together via an adhesive sheet, the pressure-sensitive adhesive sheet includes a pressure-sensitive adhesive layer containing a polyester-based polymer, The portable electronic device, wherein the pressure-sensitive adhesive sheet has a 180-degree peel strength of 1 N / 5 mm or more after immersion in ethanol. (2) The portable electronic device according to (1) above, which is a mobile phone. (3) The mobile electronic device according to (1) above, which is a smartphone. (4) The portable electronic device according to (1) above, which is a tablet computer. (5) The portable electronic device according to (1) above, which is a wearable device. (6) The portable electronic device according to (1) above, which is a digital camera. (7) The portable electronic device according to (1) above, which is a portable music player. (8) The portable electronic device according to (1) above, which is a portable game device. (9) The portable electronic device according to (1) above, which is an electronic dictionary. (10) The portable electronic device according to (1) above, which is an electronic book.

[0105] (11) A pressure-sensitive adhesive layer containing a polyester polymer, An adhesive sheet with a 180-degree peel strength of 1N / 5mm or more after immersion in ethanol. (12) The pressure-sensitive adhesive sheet according to (11) above, which has an adhesive strength retention rate of 50% or more after immersion in ethanol. (13) The pressure-sensitive adhesive sheet according to (11) or (12) above, which has a 180° peel strength of 2 N / 5 mm or more after immersion in oleic acid. (14) The pressure-sensitive adhesive sheet according to any one of (11) to (13) above, which exhibits a displacement distance of 0.5 mm or less in a shear holding strength test carried out under conditions of a load of 1 kg, a temperature of 60°C, and 1 hour. (15) The pressure-sensitive adhesive sheet according to any one of (11) to (14) above, which has an initial 180-degree peel strength of 10 N / 25 mm or more. (16) The pressure-sensitive adhesive sheet according to any one of (11) to (15) above, wherein the content of the tackifier resin in the pressure-sensitive adhesive layer is less than 80 parts by weight per 100 parts by weight of the polyester polymer. (17) The pressure-sensitive adhesive sheet according to (16) above, wherein the tackifier resin comprises a tackifier resin having a hydroxyl value of 30 mgKOH / g or more. (18) The pressure-sensitive adhesive sheet according to any one of (11) to (17) above, wherein the polyester polymer is crosslinked with a crosslinking agent. (19) The pressure-sensitive adhesive sheet according to any one of (11) to (18) above, wherein the pressure-sensitive adhesive layer has a gel fraction of 20% by weight or more.

[0106] (20) The pressure-sensitive adhesive sheet according to any one of (11) to (19) above, wherein the polyester polymer is a polycondensation product of a polycarboxylic acid and a polyol, and the polycarboxylic acid includes an aromatic dicarboxylic acid. (21) The pressure-sensitive adhesive sheet according to (20), wherein the aromatic dicarboxylic acid includes at least one of isophthalic acid and terephthalic acid. (22) The pressure-sensitive adhesive sheet according to any one of (11) to (21) above, wherein the polyester polymer is a polycondensation product of a polycarboxylic acid and a polyol, and the polycarboxylic acid includes an aliphatic dicarboxylic acid. (23) The pressure-sensitive adhesive sheet according to (22) above, wherein the aliphatic dicarboxylic acid includes at least one of adipic acid and sebacic acid. (24) The pressure-sensitive adhesive sheet according to any one of (11) to (23) above, wherein the polyester polymer is a polycondensation product of a polycarboxylic acid and a polyol, and the polyol contains an aliphatic diol. (25) The pressure-sensitive adhesive sheet according to (24) above, wherein the aliphatic diol is at least one selected from the group consisting of ethylene glycol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol. (26) The pressure-sensitive adhesive sheet according to any one of (11) to (25) above, wherein the polyester polymer has a hydroxyl value of less than 12 mgKOH / g. (27) The pressure-sensitive adhesive sheet according to any one of (11) to (26) above, wherein the polyester polymer has an acid value of less than 5 mgKOH / g. (28) The pressure-sensitive adhesive sheet according to any one of (11) to (27) above, wherein the glass transition temperature of the polyester polymer is −50° C. or higher and 0° C. or lower. (29) The number average molecular weight of the polyester polymer is 7000 or more and 5 × 10 4 The pressure-sensitive adhesive sheet according to any one of (11) to (28) above, which is: (30) The pressure-sensitive adhesive sheet according to any one of (11) to (29) above, wherein the polyester polymer is crosslinked with a crosslinking agent, and the crosslinking agent includes an isocyanate crosslinking agent. (31) The pressure-sensitive adhesive sheet according to any one of (11) to (30) above, wherein the pressure-sensitive adhesive layer contains a tackifier resin, and 50% by weight or more of the tackifier resin is a phenol-based tackifier resin (for example, a terpene phenol resin). (32) The pressure-sensitive adhesive sheet according to any one of (11) to (31) above, wherein the pressure-sensitive adhesive layer contains a tackifier resin, and the softening point of the tackifier resin is 135° C. or higher. (33) The pressure-sensitive adhesive sheet according to any one of (11) to (32) above, wherein the pressure-sensitive adhesive layer has a glass transition temperature of -35°C or higher and 10°C or lower. (34) The pressure-sensitive adhesive sheet according to any one of (11) to (33) above, wherein the pressure-sensitive adhesive layer has a thickness of 10 μm or more and 25 μm or less. (35) The pressure-sensitive adhesive sheet according to any one of (11) to (34) above, which is a substrate-less double-sided pressure-sensitive adhesive sheet consisting only of the pressure-sensitive adhesive layer. (36) The pressure-sensitive adhesive sheet according to any one of (11) to (34) above, which is configured as a substrate-attached pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer on at least one surface of a substrate.

[0107] (37) The pressure-sensitive adhesive sheet according to any one of (11) to (36) above, which is used for fixing members in a portable device. (38) A mobile device comprising the adhesive sheet according to any one of (11) to (36) above and a component joined by the adhesive sheet. [Example]

[0108] Several 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.

[0109] Evaluation Method [Initial 180° peel strength] Under a measurement environment of 23°C and 50% RH, a 50 μm thick PET film is attached to one adhesive side of a double-sided PSA sheet to form a backing, and the sheet is then cut to a size of 5 mm wide and 100 mm long to obtain a PSA sheet test specimen. Under the same conditions, the other adhesive side of the PSA sheet test specimen is pressed against the surface of a stainless steel plate (SUS304BA plate) using a 2 kg roller, moving back and forth once, to form the measurement sample. The measurement sample is then cured under the same conditions for 30 minutes. After a further 24 hours under the same conditions, the initial peel strength [N / 5 mm] is measured using a universal tension and compression tester in accordance with JIS Z 0237:2000, at a tension speed of 300 mm / min and a peel angle of 180°. The universal tension and compression tester used is a Minebea "Tension and Compression Tester, TG-1kN" or equivalent. For single-sided PSA sheets, a PET film backing is not required.

[0110] [Peel strength after immersion in ethanol] A measurement sample was obtained in the same manner as in the measurement of the initial 180-degree peel strength, and this was aged in the same environment for 30 minutes. Next, the measurement sample was immersed in a container containing ethanol at room temperature (23°C) for 24 hours. The measurement sample was then removed from the ethanol bath, and the ethanol adhering to the periphery was lightly wiped off with a dry cloth. The peel strength [N / 5 mm] after ethanol immersion was measured in the same manner as in the measurement of the initial 180-degree peel strength.

[0111] [Peel strength after immersion in oleic acid] A measurement sample was obtained using the same method as in the measurement of the initial 180-degree peel strength, and then aged in the same environment for 30 minutes. The measurement sample was then immersed in a container containing oleic acid for 24 hours at room temperature (23°C). The measurement sample was then removed from the oleic acid bath, and any oleic acid adhering to the periphery was lightly wiped off with a dry cloth. The peel strength [N / 5 mm] after immersion in oleic acid was measured using the same method as in the measurement of the initial 180-degree peel strength.

[0112] [Shear holding strength] The holding power test was conducted in accordance with JIS Z 0237 (2004). Specifically, a 50 μm thick PET film was attached to one adhesive surface of a double-sided PSA sheet at 23°C and 50% RH, and the sheet was then cut to a width of 10 mm to prepare a measurement sample. The other adhesive surface of the measurement sample was attached to a Bakelite plate as an adherend, with an adhesive area of ​​10 mm wide and 20 mm long. The sample was pressed against the adherend by a 2 kg roller, which was then reciprocated. The measurement sample was then draped in a 60°C environment for 30 minutes, after which a 1 kg load was applied to the free end of the measurement sample. After the sample was left in a 60°C environment for 1 hour with the load applied, the displacement distance [mm] from the initial attachment position was measured. For single-sided PSA sheets, a PET film backing is not required.

[0113] <Synthesis Example 1> A polycarboxylic acid and a polyol were charged into a reactor equipped with a stirrer, thermometer, and outflow condenser in a ratio of 1.5 equivalents of polyol to 1 equivalent (molar equivalent) of polycarboxylic acid. Titanium tetraisopropoxide (Wako Pure Chemical Industries, Ltd.) was added as a polymerization catalyst at 0.05 parts per 100 parts of the total polycarboxylic acid and polyol. The reaction was carried out at 200°C and 0.1 kPa for approximately 7 hours to obtain Polymer A with an Mn of 9,300. The polycarboxylic acids used were sebacic acid (SB), isophthalic acid (IP), and terephthalic acid (TP) in a molar ratio of SB:IP:TP = 37:13:0.1. The polyol used was neopentyl glycol (NPG) and a mixture of 1,4-butanediol (BD) and 1,6-hexanediol (HD) in a molar ratio of 23:27. Polymer A had a Tg of −50° C., a hydroxyl value of 2 to 5 mgKOH / g, and an acid value of less than 1 mgKOH / g.

[0114] <Synthesis Example 2> Polymer B was obtained in the same manner as in Synthesis Example 1, except that SB, IP, and TP were used as the polycarboxylic acids in a molar ratio of SB:IP:TP = 29:20:1, and NPG and a BD / HD mixture were used as the polyol in a molar ratio of 20:30. Polymer B had an Mn of 23,000, a Tg of -25°C, a hydroxyl value of 1 to 3 mgKOH / g, and an acid value of less than 1 mgKOH / g.

[0115] <Synthesis Example 3> Polymer C was obtained in the same manner as in Synthesis Example 1, except that adipic acid (AD), IP, and TP were used as the polycarboxylic acids in a molar ratio of AD:IP:TP = 19:30:1, and NPG, HD, and ethylene glycol (EG) were used as the polyol in a molar ratio of NPG:HD:EG = 16:14:20. Polymer C had an Mn of 13,000, a Tg of 0°C, a hydroxyl value of 6 to 9 mgKOH / g, and an acid value of less than 1 mgKOH / g.

[0116] <Example 1 to Example 9> (Preparation of Pressure-Sensitive Adhesive Composition) Any of the polyester polymers A to C obtained in Synthesis Examples 1 to 3 above, a terpene phenol resin (manufactured by Yasuhara Chemical Co., Ltd., trade name "YS Polystar S-145", softening point approximately 145°C, hydroxyl value 70 to 110 mgKOH / g), and an isocyanate crosslinking agent (trade name "Coronate L", 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation) were stirred and mixed in the composition shown in Table 1 to prepare the pressure-sensitive adhesive compositions of each example.

[0117] (Preparation of adhesive sheet) The adhesive composition according to each example was applied to the release surface of a 38 μm thick polyester release film (trade name "Diafoil MRF", manufactured by Mitsubishi Polyester Corporation) and dried at 110°C for 2 minutes to form an adhesive layer with a thickness of 20 μm. The release surface of a 25 μm thick polyester release film (trade name "Diafoil MRF", thickness 25 μm, manufactured by Mitsubishi Polyester Corporation) was then bonded to this adhesive layer. This was then aged at 50°C for 96 hours. In this way, a substrateless double-sided adhesive sheet with a thickness of 20 μm, both sides of which were protected by the two release films, was obtained.

[0118] <Reference example> A reaction vessel equipped with a stirrer, thermometer, nitrogen gas inlet tube, reflux condenser, and dropping funnel was charged with 95 parts of n-butyl acrylate and 5 parts of acrylic acid as monomer components, and 233 parts of ethyl acetate as a polymerization solvent, 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 2,2'-azobisisobutyronitrile was added as a polymerization initiator, and solution polymerization was carried out at 60°C for 8 hours to obtain an acrylic polymer solution. The Mw of this acrylic polymer was approximately 70 x 10 4 It was. To 100 parts of the obtained acrylic polymer, 30 parts of terpene phenol resin B (manufactured by Yasuhara Chemical Co., Ltd., trade name "YS Polystar S-145", softening point approximately 145°C, hydroxyl value 70 to 110 mgKOH / g), 2 parts of isocyanate-based crosslinking agent (trade name "Coronate L", 75% ethyl acetate solution of trimethylolpropane / tolylene diisocyanate trimer adduct, manufactured by Tosoh Corporation), and 0.01 parts of epoxy-based crosslinking agent (trade name "TETRAD-C", 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, manufactured by Mitsubishi Gas Chemical Co., Inc.; hereinafter referred to as "epoxy-based crosslinking agent B") were added and mixed with stirring to prepare a pressure-sensitive adhesive composition according to this example. A substrate-less double-sided PSA sheet having a thickness of 20 μm was produced in the same manner as in Example 1, except that this acrylic PSA composition was used.

[0119] For each PSA sheet, the shear strength [mm], initial peel strength [N / 5mm], peel strength after immersion in oleic acid [N / 5mm], and peel strength after immersion in ethanol [N / 5mm] were measured. Furthermore, the adhesive strength retention rate [%] after immersion in oleic acid and ethanol was calculated from the obtained results. The results are shown in Table 1.

[0120] [Table 1]

[0121] As shown in Table 1, the peel strength after ethanol immersion for the acrylic pressure-sensitive adhesive (Reference Example) was significantly lower than the initial peel strength, whereas among the examples using polyester pressure-sensitive adhesives, Examples 2, 3, and 6 to 8 maintained a peel strength of 1 N / 5 mm or more after ethanol immersion. In these examples, the adhesive strength retention rate after ethanol immersion was also 50% or higher. Furthermore, the polyester pressure-sensitive adhesives of Examples 2, 3, and 6 to 8 had a peel strength of 2 N / 5 mm or more after immersion in oleic acid, demonstrating excellent durability against low-polarity components. Furthermore, in these examples, the shear holding strength test showed a displacement distance of 0.5 mm or less, demonstrating holding strength comparable to that of acrylic pressure-sensitive adhesives. In particular, the pressure-sensitive adhesive sheets of Examples 7 and 8 had high peel strength and adhesive strength retention rate after ethanol immersion, and also had excellent oil resistance and holding strength.

[0122] Although specific examples of the present invention have been described above in detail, these are merely examples and should not be construed as limiting the scope of the claims. The technology described in the claims includes various examples of the above-mentioned examples. This includes modifications and alterations to the above. [Explanation of symbols]

[0123] 1,2,3,4,5,6 Adhesive sheet 10 Base material 21, 22 Adhesive layer 31,32 Release liner

Claims

1. a pressure-sensitive adhesive layer containing a polyester-based polymer as a base polymer (excluding those containing 1 to 30 mol % of a polyalkylene glycol having a number average molecular weight of 200 to 2000 relative to 100 mol % of a glycol component constituting the polyester-based polymer); The polyester polymer is a polymer obtained by polycondensation of a polycarboxylic acid and a polyol, a ratio of dicarboxylic acids to the total amount of the polycarboxylic acids is 90 mol % or more, and the dicarboxylic acids include isophthalic acid and / or terephthalic acid; the proportion of the diol in the total amount of the polyol is 90 mol % or more; the pressure-sensitive adhesive layer contains a terpene phenol resin as a tackifier resin, The hydroxyl value of the terpene phenol resin is 30 mgKOH / g or more, the content of the tackifier resin in the pressure-sensitive adhesive layer is more than 0 parts by weight and less than 80 parts by weight relative to 100 parts by weight of the polyester-based polymer, the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer contains a crosslinking agent, The PSA composition does not contain a hydrolysis stabilizer or contains the hydrolysis stabilizer in an amount of less than 0.003 wt %; A PSA sheet having a 180-degree peel strength after ethanol immersion of 1 N / 5 mm or more, wherein the 180-degree peel strength after ethanol immersion is measured in an environment of 23°C and 50% RH by pressing the PSA sheet against the surface of a stainless steel plate by rolling a 2 kg roller back and forth once, allowing it to cure for 30 minutes, and then immersing it in ethanol for 24 hours, in accordance with JIS Z 0237:2000, under conditions of a pulling speed of 300 mm / min and a peel angle of 180°.

2. The pressure-sensitive adhesive sheet according to claim 1, which has an adhesive strength retention rate of 50% or more after immersion in ethanol.

3. 3. The pressure-sensitive adhesive sheet according to claim 1, which has a 180-degree peel strength of 2 N / 5 mm or more after immersion in oleic acid.

4. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, which exhibits a displacement distance of 0.5 mm or less in a shear holding strength test carried out under conditions of a load of 1 kg, a temperature of 60°C, and 1 hour.

5. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, having an initial 180 degree peel strength of 10 N / 25 mm or more.

6. The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein the pressure-sensitive adhesive layer has a gel fraction of 20% by weight or more.

7. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, which is used to fix members in a portable device.

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