Adhesive sheet

Abstract

This invention provides an adhesive sheet having an adhesive layer comprising an acrylic polymer and a tackifying resin. The acrylic polymer is a polymer containing a monomeric component of n-heptyl acrylate. The content of the tackifying resin is greater than 10 parts by weight relative to 100 parts by weight of the acrylic polymer. The swelling degree of the adhesive layer to ethyl acetate is less than 100.

Description

Technical Field

[0001] This invention relates to adhesive sheets.

[0002] This application claims priority based on Japanese Patent Application No. 2022-108034, filed on July 4, 2022, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Typically, adhesives (also known as pressure-sensitive adhesives, hereinafter the same) are soft solids (viscoelastics) in a temperature range near room temperature, possessing the property of adhering to the substrate by pressure. Utilizing this property, adhesives are widely used in various industries, from household appliances to automobiles, various machinery, and electronic equipment, typically in the form of adhesive sheets containing layers of the adhesive for purposes such as component bonding and surface protection.

[0004] Among adhesive sheets are those used to secure components in portable devices such as mobile phones, smartphones, and tablets. Since these portable devices are carried around, secretions such as sebum and hand dirt, as well as chemicals such as cosmetics, hair products, moisturizers, and sunscreens, and oils from food, easily adhere to them. Especially in recent years, portable devices with touch panels have displays / input sections that function as both displays and input sections, and users operate them by directly contacting the surface of these sections with their fingertips, thus increasing the chance of oil adhering through the fingertips. Furthermore, wearable devices are worn in contact with the skin, increasing the chance of exposure to oils such as sebum and chemicals applied to the skin. Therefore, adhesive sheets used in portable devices preferably exhibit minimal reduction in adhesive strength due to contact with oils. Patent Document 1 and Patent Document 2 are examples of technical documents that address the reduction in adhesive strength caused by contact with oils.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-132911

[0008] Patent Document 2: Japanese Patent Application Publication No. 2017-165977 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] With the increasing performance and functionality of portable devices, there is a growing demand for improved adhesive strength in adhesive sheets used to secure components. Furthermore, due to increased hygiene awareness in recent years, there is a growing tendency to use water-based solvents such as water and lower alcohols to keep portable devices clean. Therefore, adhesive sheets used in portable devices are expected to exhibit minimal reduction in adhesive strength even upon contact with water-based solvents. However, in the adhesive field, there is usually a trade-off between resistance to water-based solvents and resistance to oils. Therefore, achieving adhesive sheets with high adhesive strength and minimal reduction in adhesive strength even upon contact with oils or water-based solvents is not an easy task.

[0011] The present invention was made in view of the above circumstances, and its object is to provide an adhesive sheet that can simultaneously achieve a high level of adhesive strength, suppression of adhesive strength reduction caused by contact with oil, and suppression of adhesive strength reduction caused by contact with aqueous solvents.

[0012] means for solving problems

[0013] According to this specification, an adhesive sheet having an adhesive layer comprising an acrylic polymer and a tackifying resin is provided. The acrylic polymer is a polymer containing a monomer component of n-heptyl acrylate. The content of the tackifying resin in the adhesive layer is greater than 10 parts by weight relative to 100 parts by weight of the acrylic polymer. The swelling degree of the adhesive layer with ethyl acetate is 100 or less. By using an acrylic polymer containing n-heptyl acrylate as a monomer component, and ensuring that the content of the tackifying resin relative to 100 parts by weight of the acrylic polymer is greater than 10 parts by weight while maintaining a swelling degree of 100 or less in the adhesive layer, the adhesive strength can be effectively improved, and the reduction in adhesive strength due to contact with oil can be suppressed. Furthermore, by using n-heptyl acrylate as a monomer component of the acrylic polymer, the reduction in adhesive strength due to contact with aqueous solvents can be appropriately suppressed. That is, according to the above configuration, a high level of balance can be achieved between adhesive strength, suppression of the reduction in adhesive strength due to contact with oil (oil resistance), and suppression of the reduction in adhesive strength due to contact with aqueous solvents (water solvent resistance).

[0014] In some preferred embodiments, the monomer component comprises 5.0% by weight or more of a carboxyl-containing monomer. Depending on the monomer composition, there is a tendency to obtain adhesive sheets with higher adhesive strength.

[0015] In some preferred embodiments, the adhesive composition used to form the adhesive layer comprises an isocyanate crosslinker and an epoxy crosslinker. By using both isocyanate and epoxy crosslinkers, the swelling degree of the adhesive layer can be appropriately adjusted, and an adhesive sheet that balances high levels of adhesion, oil resistance, and water solvent resistance can be appropriately achieved.

[0016] In some preferred embodiments, the adhesive layer comprises a phenolic tackifying resin as the tackifying resin. By combining an acrylic polymer containing n-heptyl acrylate as a monomer component with a phenolic tackifying resin, the adhesive strength can be effectively improved.

[0017] In some preferred embodiments, the adhesive layer comprises a terpene phenolic resin as the aforementioned phenolic tackifying resin. By including the terpene phenolic resin in the adhesive layer, the adhesive strength can be effectively improved. The content of the terpene phenolic resin is preferably 20 parts by weight or more relative to 100 parts by weight of the acrylic polymer.

[0018] In some embodiments, the adhesive composition used to form the adhesive layer comprising the aforementioned phenolic tackifying resin preferably contains a combination of isocyanate crosslinking agents and epoxy crosslinking agents. By combining an acrylic polymer containing n-heptyl acrylate as a monomer component, a phenolic tackifying resin, an isocyanate crosslinking agent, and an epoxy crosslinking agent, it is possible to more appropriately achieve an adhesive sheet that balances high levels of adhesion, oil resistance, and water solvent resistance.

[0019] In some embodiments, the weight-average molecular weight (Mw) of the aforementioned acrylic polymer is preferably greater than 500,000. According to this method, adhesive sheets that achieve a high level of adhesion, oil resistance, and water solvent resistance can be readily obtained.

[0020] Some preferred adhesive sheets exhibit a 180-degree peel strength (SUS adhesion) of 8.0 N / 10 mm or higher against stainless steel sheets. Adhesive sheets with this SUS adhesion strength can achieve high component fixation performance.

[0021] Some preferred embodiments of the adhesive sheet are configured as double-sided adhesive sheets. Double-sided adhesive sheets are used by attaching one surface of the adhesive sheet to the substrates separately; therefore, oils and aqueous solvents can easily penetrate the adhesive interface with these substrates. Therefore, it is particularly meaningful to apply the techniques disclosed herein to suppress the reduction in adhesive strength caused by the aforementioned oils.

[0022] Some preferred embodiments of the adhesive sheet are configured as a double-sided adhesive sheet having a resin film as a support substrate and an adhesive layer disposed on one surface and the other surface of the support substrate. This configuration of the double-sided adhesive sheet is advantageous from the viewpoint of processability to the desired shape and shape retention (e.g., suppression of protrusion).

[0023] The adhesive sheet disclosed herein can achieve a high level of balance between adhesive strength, suppression of adhesive strength reduction due to contact with oil, and suppression of adhesive strength reduction due to contact with aqueous solvents, and is therefore suitable for fixing components in, for example, portable devices (e.g., portable electronic devices such as smartphones). Therefore, according to this specification, a portable device using any of the adhesive sheets disclosed herein is provided; in other words, a portable device incorporating such an adhesive sheet is provided. Attached Figure Description

[0024] Figure 1 A cross-sectional view illustrating the structure of an adhesive sheet according to one embodiment.

[0025] Figure 2 A cross-sectional view illustrating the composition of an adhesive sheet according to another embodiment.

[0026] Figure 3 A cross-sectional view illustrating the composition of an adhesive sheet according to another embodiment.

[0027] Figure 4 A front view illustrating an example of a portable device (portable electronic device) comprising an adhesive sheet. Detailed Implementation

[0028] The preferred embodiments of the present invention will now be described. It should be noted that matters not specifically mentioned in this specification but necessary for implementing the invention can be understood by those skilled in the art based on the teachings for implementing the invention described in this specification and common technical knowledge at the time of application. The present invention can be implemented based on the disclosure in this specification and common technical knowledge in the field. Furthermore, in the following drawings, components / parts that perform the same function are sometimes labeled with the same reference numerals, and repeated descriptions may be omitted or simplified. Additionally, for the purpose of clearly illustrating the present invention, the embodiments described in the drawings are schematic and do not necessarily accurately represent the dimensions or scale of the adhesive sheet of the present invention actually provided as a product.

[0029] In this specification, "adhesive" refers to a material that, as described above, is a soft solid (viscoelastic) in a temperature range near room temperature and has the property of easily adhering to the substrate under pressure. As defined in "CADahlquist, 'Adhesion: Fundamental and Practice', McLaren & Sons, (1966) p. 143", the adhesive referred to here is generally a material having a complex tensile modulus E. * (1Hz) < 10 7 dyne / cm 2Materials with the properties described above (typically materials that have the properties described above at 25°C).

[0030] In this specification, carbon derived from biomass refers to carbon from biomass materials, that is, materials from renewable organic resources (renewable carbon). Biomass materials typically refer to materials from biological resources (typically photosynthetic plants) that can continuously reproduce as long as sunlight, water, and carbon dioxide are available. Therefore, materials from fossil resources depleted through extraction (fossil materials) are not included in the concept of biomass materials as used herein. The biomass carbon ratio of the adhesive layer and adhesive sheet, i.e., the proportion of carbon derived from biomass in the total carbon contained in the adhesive layer and adhesive sheet, can be estimated based on the carbon isotope content of mass number 14 as determined according to ASTM D6866.

[0031] <Composition of Adhesive Sheets>

[0032] The adhesive sheet disclosed herein is constructed by containing an adhesive layer. For example, the adhesive sheet may be a substrate-free double-sided adhesive sheet having a first adhesive surface formed by one surface of the adhesive layer and a second adhesive surface formed by the other surface of the adhesive layer. Alternatively, the adhesive sheet disclosed herein may be a substrate-supported adhesive sheet obtained by laminating the adhesive layer on one or both surfaces of a supporting substrate. Hereinafter, the supporting substrate will sometimes be simply referred to as "substrate". It should be noted that the concept of adhesive sheet as used herein may include articles referred to as adhesive tape, adhesive labels, adhesive films, etc. The adhesive sheet disclosed herein may be in roll form or in sheet form. Alternatively, it may be an adhesive sheet further processed into various shapes.

[0033] The structure of an adhesive sheet according to one embodiment is schematically shown. Figure 1 The adhesive sheet 1 is a substrate-free double-sided adhesive sheet consisting of an adhesive layer 21. The adhesive sheet 1 is used to adhere a first adhesive surface 21A (first surface) of the adhesive layer 21 and a second adhesive surface 21B (second surface) of the adhesive layer 21 to different parts of an object being adhered. The locations where adhesive surfaces 21A and 21B are adhered can be individual parts of different components or different parts within a single component. Figure 1As shown, the adhesive sheet 1 before use (i.e., before being pasted onto the object) can be an adhesive sheet 100 with release liner, in which the first adhesive surface 21A and the second adhesive surface 21B are protected by release liner 31, 32, respectively, on the side opposite to the adhesive layer 21, which respectively serve as the release surface. As the release liner 31, 32, for example, it is preferable to use a release liner formed by providing a release layer of release agent on one side of a sheet-like substrate (liner substrate), so that the single side serves as the release surface. Alternatively, the release liner 32 can be omitted, and the release liner 31 with two sides serving as release surfaces can be used, overlapped with the adhesive sheet 1 and wound into a spiral shape, thereby forming an adhesive sheet with release liner in which the second adhesive surface 21B is protected by contact with the back of the release liner 31 (roll shape).

[0034] The structure of the adhesive sheet according to another embodiment is schematically shown in Figure 2 The adhesive sheet 2 is configured as a single-sided adhesive sheet with a substrate, comprising: a sheet-like support substrate (e.g., a resin film) 10 having a first side 10A and a second side 10B, and an adhesive layer 21 disposed on the first side 10A. The adhesive layer 21 is fixedly disposed on the first side 10A of the support substrate 10, i.e., it is not intended to separate the adhesive layer 21 from the support substrate 10. Figure 2 As shown, the adhesive sheet 2 before use can be a component of an adhesive sheet 200 with a release liner, in which the surface (adhesive surface) 21A of the adhesive layer 21 is protected by a release liner 31 with at least one side opposite to the adhesive layer 21 as the release surface. Alternatively, it can be a roll form where the release liner 31 is omitted, and a support substrate 10 with a second surface 10B as the release surface is used, and the adhesive surface 21A is protected by contacting the second surface (back surface) 10B of the support substrate 10 when the adhesive sheet 2 is wound around it.

[0035] The structure of the adhesive sheet according to another embodiment is schematically shown in Figure 3 The adhesive sheet 3 is constructed as a double-sided adhesive sheet with a substrate, which includes: a sheet-like support substrate (e.g., a resin film) 10 having a first side 10A and a second side 10B; a first adhesive layer 21 fixedly disposed on the first side 10A; and a second adhesive layer 22 fixedly disposed on the second side 10B. Figure 3As shown, the adhesive sheet 3 before use can be an adhesive sheet 300 in which the surface (first adhesive surface) 21A of the first adhesive layer 21 and the surface (second adhesive surface) 22A of the second adhesive layer 22 are protected by release liner 31, 32. Alternatively, the release liner 32 can be omitted, and the release liner 31 with two surfaces as release surfaces can be used. It can be overlapped with the adhesive sheet 3 and wound into a spiral shape, thereby forming an adhesive sheet with release liner in which the second adhesive surface 22A is in contact with the back of the release liner 31 and protected (roll form).

[0036] It should be noted that in the double-sided adhesive sheet with a substrate, at least one of the first adhesive layer and the second adhesive layer (e.g., the first adhesive layer) can be the adhesive layer described below, and the other adhesive layer (e.g., the second adhesive layer) can be the adhesive layer disclosed herein, or it can be an adhesive layer with a different composition from the adhesive layer disclosed herein (specifically, the aforementioned adhesive layer, e.g., the first adhesive layer). Such another adhesive layer can, for example, be formed from a known or conventional adhesive.

[0037] <Adhesive layer>

[0038] The adhesive layer constituting the adhesive sheet disclosed herein comprises an acrylic polymer and a tackifying resin. The aforementioned adhesive layer is typically an adhesive layer using the aforementioned acrylic polymer as the base polymer. Such an adhesive layer is also referred to as an acrylic adhesive layer. It should be noted that the base polymer of the adhesive layer refers to the main component of the rubbery polymer (a polymer exhibiting rubber elasticity in a temperature range near room temperature) contained in the adhesive layer. Furthermore, in this specification, unless otherwise specified, "main component" refers to a component with a content greater than 50% by weight. Additionally, the following description regarding the components that may be contained in the adhesive and adhesive layer applies to adhesive compositions used to form the adhesive (layer), unless otherwise specified.

[0039] Furthermore, in this specification, "acrylic polymer" refers to a polymer containing monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule as the monomer units constituting the polymer. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule will also be referred to as an "acrylic monomer." Therefore, the acrylic polymer in this specification is defined as a polymer containing monomer units derived from acrylic monomers. It should be noted that in this specification, "(meth)acryloyl" refers to both acryloyl and methacryloyl groups. Similarly, "(meth)acrylate" refers to both acrylate and methacrylate, and "(meth)acrylic acid" refers to both acrylic acid and methacrylic acid.

[0040] (Acrylic polymers)

[0041] The acrylic polymers used in the disclosed technology are polymers containing a monomer component of n-heptyl acrylate (n-HpA). The inventors have found that acrylic polymers obtained by polymerizing monomer components containing n-HpA (i.e., alkyl acrylates with a n-heptyl group at the ester terminus) are more suitable for achieving adhesive sheets that balance high levels of adhesion, oil resistance, and water solvent resistance, for example, compared to compositions where n-HpA is replaced with 2EHA. The rationale is not specifically limited, but it is believed that polymers containing n-HpA as monomer units have a low glass transition temperature, which allows the adhesive layer to adhere well to the substrate and easily inhibits the penetration of oils and aqueous solvents into the interface. Furthermore, due to the relatively long linear side chains derived from n-HpA, it has good compatibility with tackifying resins. Therefore, even with an increased content of tackifying resin, it is easy to suppress the decrease in adhesive strength caused by contact with oils. Moreover, the side chains from n-HpA are less oleophilic than those from alkyl acrylates with more carbon atoms, thus easily suppressing swelling. Additionally, the side chains from n-HpA are less hydrophilic than those from alkyl acrylates with fewer carbon atoms (e.g., BA), thus easily suppressing the decrease in adhesive strength caused by contact with aqueous solvents (e.g., a mixture of water and lower alcohols).

[0042] In some embodiments, it is appropriate for n-HpA to constitute 50% by weight or more (e.g., greater than 50% by weight) of the monomer component of the acrylic polymer, preferably 70% by weight or more, more preferably 80% by weight or more, further preferably 85% by weight or more, particularly preferably 90% by weight or more, and can be 91% by weight or more, 92% by weight or more, 94% by weight or more, or 94.5% by weight or more. Increasing the amount of n-HpA used tends to result in a more effective performance. In some embodiments, the proportion of n-HpA in the monomer component can be 98% by weight or more, 99% by weight or more, or even 100% by weight. On the other hand, from the viewpoint of easily suppressing the swelling of the adhesive layer and easily adjusting the balance of properties, in some ways, it is appropriate for the proportion of n-HpA in the monomer component to be 99.5% by weight or less, preferably 97% by weight or less (e.g., less than 97% by weight), more preferably 96% by weight or less, further preferably 95% by weight or less, and can be 94% by weight or less, 93% by weight or less, or 91% by weight or less.

[0043] Acrylic polymers may copolymerize alkyl (meth)acrylates other than n-HpA (hereinafter also referred to as "optional alkyl (meth)acrylates"). As an optional alkyl (meth)acrylate, a compound represented by formula (1) may be preferred, for example.

[0044] CH2=C(R 1 COOR 2 (1)

[0045] Here, R in equation (1) above 1 It can be a hydrogen atom or a methyl group. Additionally, R... 2 It is a chain alkyl group having 1 to 20 carbon atoms (except for n-heptyl).

[0046] Examples of optional alkyl methacrylates include: methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, pentyl methacrylate, isoamyl methacrylate, hexyl methacrylate, heptyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isooctyl methacrylate, nonyl methacrylate, isononyl methacrylate, decyl methacrylate, isodecanyl methacrylate, undecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecanyl methacrylate, heptadecanyl methacrylate, octadecyl methacrylate, nonadecanyl methacrylate, eicosyl methacrylate, etc. These optional alkyl (meth)acrylates can be used alone or in combination of two or more. Examples of preferred alkyl (meth)acrylates include n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA). These optional alkyl (meth)acrylates can be used alone or in combination of two or more.

[0047] In some approaches, from the viewpoint of facilitating the use of n-HpA, it is appropriate for the proportion of optional alkyl (meth)acrylates in the monomer component (the total proportion when two or more are used) to be less than 50% by weight (e.g., 49.5% by weight or less), preferably less than 47% by weight, more preferably 45% by weight or less, even more preferably 40% by weight or less, and can be 30% by weight or less, 10% by weight or less, 5% by weight or less, or 1% by weight or less. Regarding R in formula (1) above... 2 For optional (meth)acrylates that are alkyl acrylates with 8 or more carbon atoms or alkyl methacrylates with 7 or more carbon atoms, from the viewpoint of oil resistance, it is appropriate for the proportion of the above-mentioned optional (meth)acrylates contained in the monomer component (the total proportion when two or more are used) to be 30% by weight or less, preferably 20% by weight or less, more preferably 10% by weight or less, and can be 5% by weight or less, 1% by weight or less, or 0.5% by weight or less. Furthermore, regarding R in formula (1) above... 2For optional alkyl methacrylates having 6 or fewer carbon atoms, from the viewpoint of resistance to aqueous solvents, it is appropriate for the proportion of the aforementioned optional alkyl methacrylates contained in the monomer component (the total proportion when using two or more) to be 30% by weight or less of the monomer component, preferably 20% by weight or less, more preferably 10% by weight or less, and can be 5% by weight or less, 1% by weight or less, or 0.5% by weight or less. In some embodiments, the technology disclosed herein can preferably be implemented in a manner where the monomer component substantially does not contain optional alkyl methacrylates.

[0048] It should be noted that, in this specification, "monomer component does not substantially contain monomer A (e.g., the optional (meth)acrylate)" means that monomer A is not used intentionally, and it is permissible to unintentionally contain, for example, less than about 0.01% by weight of monomer A.

[0049] In some embodiments, the aforementioned monomeric components may be contained in alkyl (meth)acrylates (hereinafter also referred to as "biomass (meth)acrylates") having an alkyl group derived from biomass at the ester terminus. In recent years, environmental issues such as global warming have received increasing attention, with a desire to reduce the use of fossil fuels such as petroleum. Under these circumstances, there is also a need to reduce the use of fossil fuels in the field of adhesives. By using biomass (meth)acrylates, it is possible to appropriately achieve acrylic adhesives that take into account the reduction of dependence on fossil fuels.

[0050] There are no particular limitations on the use of biomass (meth)acrylate esters, such as esters of alkanols derived from biomass and (meth)acrylates derived from or not derived from biomass. Examples of alkanols derived from biomass include bioethanol, alkanols derived from plant sources such as palm oil or palm kernel oil, coconut oil, and castor oil. When the alkanol derived from biomass has 3 or more carbon atoms, the alkanol can be straight-chain or branched. In some cases, as a biomass (meth)acrylate ester used in the synthesis of acrylic polymers, an ester of alkanol derived from biomass and (meth)acrylates not derived from biomass can be used. In such biomass (meth)acrylate esters, the more carbon atoms the alkanol has, the higher the proportion of carbon atoms derived from biomass in the total carbon number contained in the biomass (meth)acrylate ester, i.e., the higher the biomass carbon ratio of the (meth)acrylate ester. Therefore, in the above-mentioned biomass (meth)acrylate esters, from the perspective of reducing dependence on fossil resources, it is desirable to have a high number of carbon atoms in the alkyl group derived from biomass. On the other hand, when the alkyl group constituting the (meth)acrylate has too many carbon atoms, it tends to swell excessively upon contact with oil, leading to a decrease in oil resistance. Furthermore, it may become disadvantageous from the perspectives of synthesis, operability, cost, and productivity. In methods using alkanols derived from biomass and esters of (meth)acrylate not derived from biomass as biomass (meth)acrylate alkyl esters, it is desirable to use materials that balance adhesive properties with reduced dependence on fossil resources (more specifically, the biomass carbon ratio of the aforementioned (meth)acrylate alkyl ester).

[0051] In some preferred embodiments, n-heptyl acrylate derived from biomass (biomass n-HpA) can be used as n-heptyl acrylate. By using biomass n-HpA, the effects of the technology disclosed herein can be achieved while reducing dependence on fossil-based materials. The aforementioned biomass n-HpA is an ester of an alkanol derived from biomass and acrylic acid derived from or not derived from biomass; for example, an ester of an alkanol derived from biomass and acrylic acid derived from or not derived from biomass can be used. In this compound, only the straight-chain heptyl group is derived from biomass.

[0052] The proportion of alkyl methacrylate (preferably biomass n-HpA) in the monomer components of the aforementioned acrylic polymer is, for example, 50% by weight or more in some embodiments (e.g., greater than 50% by weight), preferably 70% by weight or more, more preferably 80% by weight or more, further preferably 85% by weight or more, particularly preferably 90% by weight or more, and can be 92% by weight or more, 94% by weight or more, or 96% by weight or more. Furthermore, the proportion of alkyl methacrylate (preferably biomass n-HpA) in the monomer components is less than 97% by weight, and in some embodiments, can be 95% by weight or less, 93% by weight or less, or 91% by weight or less. In other embodiments, the proportion of alkyl methacrylate in the monomer components can be 90% by weight or less, 70% by weight or less, 50% by weight or less, 30% by weight or less, 10% by weight or less, or 1% by weight or less.

[0053] In some embodiments, the monomer component of the acrylic polymer preferably includes carboxyl-containing monomers. Besides contributing to improved adhesion through enhanced cohesiveness based on its polarity, carboxyl-containing monomers can also suppress excessive swelling of the adhesive layer by oils, thus suppressing the reduction in adhesion caused by contact with oils (e.g., adhesion retention rate R, described later). A (This improves the efficiency of the adhesive layer). Furthermore, the aforementioned carboxyl groups can serve as crosslinking points for acrylic polymers, thus offering the advantage of easily adjusting the swelling degree of the adhesive layer.

[0054] Examples of carboxyl-containing monomers include: acrylic acid (AA), methacrylic acid (MAA), carboxyethyl methacrylate, carboxypentyl methacrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc. Among these, AA and MAA are preferred carboxyl-containing monomers. AA is particularly preferred. One carboxyl-containing monomer may be used alone or in combination of two or more.

[0055] The proportion of carboxyl-containing monomers in the monomer composition of acrylic polymers can be, for example, 0.5% by weight or more, or 1.0% by weight or more, or 2.0% by weight or more. In some embodiments, it is appropriate for the proportion of carboxyl-containing monomers in the monomer composition of acrylic polymers to be greater than 3.0% by weight, preferably 3.5% by weight or more, more preferably 4.0% by weight or more, and more preferably 4.5% by weight or more or 5.0% by weight or more. By increasing the amount of carboxyl-containing monomers, the tendency to suppress the decrease in adhesive strength caused by contact with oils is better suppressed, and the tendency to suppress swelling is also suppressed. In some embodiments, the proportion of carboxyl-containing monomers in the monomer composition can be greater than 5.0% by weight, or 5.5% by weight or more, 6.0% by weight or more, 7.0% by weight or more, 8.0% by weight or more (e.g., greater than 8.0% by weight), or 9.0% by weight or more. Furthermore, it is appropriate for the amount of carboxyl-containing monomer to be, for example, 20% by weight or less of the total monomer composition. From the viewpoint of suppressing the reduction in adhesive strength caused by contact with aqueous solvents, it is preferably 15% by weight or less, and more preferably 12% by weight or less. In some embodiments, the amount of the carboxyl-containing monomer may be less than 10% by weight, less than 9% by weight, less than 8% by weight, less than 6% by weight, or less than 5% by weight. By appropriately adjusting the amount of carboxyl-containing monomer within the above range, a balanced approach can be taken into account adhesive strength, oil resistance, and water solvent resistance.

[0056] Acrylic polymers can copolymerize monomers containing functional groups other than those containing carboxyl groups. Hereinafter, monomers containing functional groups other than those containing carboxyl groups will also be referred to as "functional group monomer B". Monomers B containing functional groups that can be introduced into acrylic polymers as crosslinking sites or help improve adhesive strength include: hydroxyl (OH) monomers ((meth)acrylate 2-hydroxyethyl ester, (meth)acrylate 2-hydroxypropyl ester, (meth)acrylate 3-hydroxypropyl ester, (meth)acrylate 2-hydroxybutyl ester, (meth)acrylate 4-hydroxybutyl ester, etc. (meth)acrylate hydroxyalkyl esters; polypropylene glycol mono(meth)acrylate, etc.), anhydride monomers, amide monomers ((meth)acrylamide, N,N-dimethyl(meth)acrylamide, etc.), amino monomers ((meth)acrylate aminoethyl ester, (meth)acrylate N,N-dimethylaminoethyl ester, etc.), epoxy monomers, cyano monomers, ketone monomers, monomers with nitrogen-containing rings (N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), alkoxysilyl monomers, and imide monomers, etc. The aforementioned functional group-containing monomer B can be used alone or in combination of two or more. In the manner in which the monomer component constituting the acrylic polymer includes the functional group-containing monomer B, the aforementioned monomer component may include carboxyl-containing monomers or may substantially not contain carboxyl-containing monomers.

[0057] When the monomer component constituting the acrylic polymer includes the aforementioned functionalized monomer B, the content of functionalized monomer B in this monomer component is not particularly limited. From the viewpoint of appropriately utilizing the effects based on the use of functionalized monomer B, the content of functionalized monomer B in the monomer component can be, for example, 0.1% by weight or more, 0.5% by weight or more, and 1% by weight or more. Furthermore, from the viewpoint of easily obtaining a balance between oil resistance and water solvent resistance in monomer components containing n-HpA, the content of functionalized monomer B in the monomer component is suitable to be 40% by weight or less, preferably 20% by weight or less, and can be 10% by weight or less (e.g., 5% by weight or less). In some embodiments, the content of functionalized monomer B in the monomer component is, for example, less than 3% by weight, less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, or less than 0.1% by weight. The technology disclosed herein can preferably be implemented in a manner where the monomer component of the acrylic polymer substantially does not contain functionalized monomer B.

[0058] Furthermore, when using a hydroxyl-containing monomer as the aforementioned functionalized monomer B, its content can be, for example, about 0.001% by weight or more, about 0.01% by weight or more, or about 0.02% by weight or more of the total monomer composition. Additionally, it is suitable for the content of the hydroxyl-containing monomer to be about 10% by weight or less of the total monomer composition, preferably about 5% by weight or less, and more preferably about 2% by weight or less. In some embodiments, the content of the hydroxyl-containing monomer in the monomer composition can be, for example, less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, less than 0.1% by weight, or less than 0.01% by weight. The monomer composition of the acrylic polymer may substantially not contain the hydroxyl-containing monomer. According to the technology disclosed herein, the desired effect can be achieved without relying on the hydroxyl-containing monomer.

[0059] In cases where the monomer component constituting the acrylic polymer includes a carboxyl-containing monomer, from the viewpoint of effectively copolymerizing the carboxyl-containing monomer, it is appropriate for the carboxyl-containing monomer to account for 30% by weight or more of the total number of functionalized monomers (including the carboxyl-containing monomer) in the monomer component. Preferably, this is 50% by weight or more, more preferably 70% by weight or more, further preferably 80% by weight or more, particularly preferably 90% by weight or more, for example, 95% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more (e.g., 99.9% by weight or more). The upper limit for the proportion of the carboxyl-containing monomer in the total number of functionalized monomers is 100% by weight, which is equivalent to not using functionalized monomer B. In some cases, the proportion of the carboxyl-containing monomer in the total number of functionalized monomers may be, for example, 95% by weight or less.

[0060] For purposes such as improving cohesiveness, the monomer components constituting acrylic polymers may also contain other copolymer components besides the aforementioned functionalized monomers. Examples of other copolymer components include: vinyl ester monomers such as vinyl acetate; aromatic vinyl compounds such as styrene; cycloalkyl methacrylates such as cyclohexyl methacrylate, cyclopentyl methacrylate, and isobornyl methacrylate; aromatic ring-containing methacrylates such as aryl methacrylates (e.g., phenyl methacrylate), aryloxyalkyl methacrylates (e.g., phenoxyethyl methacrylate), and arylalkyl methacrylates (e.g., benzyl methacrylate); olefin monomers; chlorinated monomers; isocyanate-containing monomers such as 2-(methacryloyloxyethyl isocyanate); alkoxy-containing monomers such as methoxyethyl methacrylate and ethoxyethyl methacrylate; vinyl ether monomers such as methyl vinyl ether and ethyl vinyl ether; etc. The aforementioned other copolymer components may be used alone or in combination of two or more.

[0061] The amount of the other copolymer components can be appropriately selected according to the purpose and use, and there is no particular limitation. From the viewpoint of properly utilizing the effects brought about by the use of other copolymer components, it is appropriate for the amount to be 0.05% by weight or more in the monomer component, and it can be 0.5% by weight or more. In addition, from the viewpoint of easily achieving a balanced balance of oil resistance and water solvent resistance in the monomer component containing n-HpA, it is appropriate for the content of other copolymer components in the monomer component to be 20% by weight or less, preferably 10% by weight or less, more preferably 8% by weight or less, and even more preferably less than 5% by weight, for example, less than 3% by weight or less than 1% by weight. The technology disclosed herein can preferably be implemented in a manner in which the monomer component does not substantially contain other copolymer components.

[0062] The monomer components constituting acrylic polymers can include polyfunctional monomers with polymerizable functional groups (typically free radical polymerizable functional groups) having at least two (meth)acryloyl groups, vinyl groups, or other unsaturated double bonds. Using polyfunctional monomers as monomer components can improve the cohesiveness of the adhesive layer and suppress swelling. There are no particular limitations on polyfunctional monomers; examples include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and neopentyl glycol di(meth)acrylate. One polyfunctional monomer can be used alone or in combination of two or more.

[0063] When using multifunctional monomers, the lower limit of the usage amount is only greater than 0% by weight, and there is no particular restriction. The amount of multifunctional monomer can be appropriately set in a way that achieves the intended use of the multifunctional monomer. Generally, by using a multifunctional monomer at a level of about 0.001% by weight or more (e.g., about 0.01% by weight or more) of the monomer component, the effect of the multifunctional monomer can be appropriately exerted. In addition, in some embodiments, from the viewpoint of easily obtaining good adhesive strength, it is appropriate for the amount of multifunctional monomer to be about 3% by weight or less of the monomer component, preferably about 2% by weight or less, and more preferably about 1% by weight or less (e.g., about 0.5% by weight or less). The monomer component constituting the acrylic polymer can be substantially composed of monofunctional monomers. That is, the monomer component may not contain multifunctional monomers.

[0064] The biomass carbon ratio of the monomer components constituting the aforementioned acrylic polymer (the biomass carbon ratio of the acrylic polymer) can be, for example, 1% or more, 10% or more is appropriate, preferably 30% or more, more preferably 50% or more (e.g., greater than 50%), 70% or more, 80% or more, or 90% to 100%. With this design, an acrylic adhesive that takes into account the reduction of dependence on fossil resources can be obtained.

[0065] There are no particular limitations on the methods for obtaining acrylic polymers; various known polymerization methods, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization is preferred. As for the monomer supply method during solution polymerization, appropriate methods include one-time feeding of the total monomer feedstock, continuous feeding (dropwise addition), and batch feeding (dropwise addition). The polymerization temperature can be appropriately selected based on the type of monomer and solvent used, as well as the type of polymerization initiator; for example, it can be approximately 20°C to approximately 170°C (typically approximately 40°C to approximately 140°C).

[0066] The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, any one or a mixture of two or more solvents can be used, selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetates such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; haloalkanes such as 1,2-dichloroethane; lower alcohols such as isopropanol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc.

[0067] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators, depending on the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) are preferred. Other examples of polymerization initiators include: persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide (BPO) and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; etc. Further examples of polymerization initiators include redox initiators based on combinations of peroxides and reducing agents. Such polymerization initiators can be used alone or in combination of two or more. The amount of polymerization initiator used can be the usual amount, for example, selected from about 0.005 parts by weight to about 1 part by weight (typically about 0.01 parts by weight to about 1 part by weight) relative to 100 parts by weight of the total monomer content.

[0068] The weight-average molecular weight (Mw) of acrylic polymers is not particularly limited, and can be, for example, about 300,000 or more and about 5,000,000 or less. The Mw of acrylic polymers is generally preferably greater than 500,000 (e.g., 550,000 or more), more preferably 600,000 or more or greater than 600,000 (e.g., 650,000 or more). With acrylic polymers having this Mw, adhesive sheets that balance high levels of adhesion, oil resistance, and water solvent resistance can be readily obtained. In some cases, the Mw of the acrylic polymer can be 700,000 or more, 800,000 or more, 900,000 or more, 950,000 or more, 1,000,000 or more, 1,050,000 or more, 1,150,000 or more, 1,200,000 or more, or greater than 1,200,000. Furthermore, considering the ease of synthesis of acrylic polymers, the ease of preparation of adhesive compositions, and coatability, it is generally appropriate for the Mw of acrylic polymers to be about 3,000,000 or less (e.g., 2,500,000 or less). From the viewpoint of improving the adhesion between the adhesive layer and the adherend, and easily suppressing the penetration of oil and aqueous solvents into the interface between the two, in some embodiments, the Mw of the acrylic polymer is preferably less than 2 million, more preferably less than 1.8 million, less than 1.6 million, less than 1.5 million, less than 1.4 million, less than 1.3 million, less than 1.2 million or less than 1.2 million, less than 1.1 million, less than 1 million, less than 900,000 or less than 900,000, less than 850,000, or less than 750,000.

[0069] The Mw of acrylic polymers can be determined by gel permeation chromatography (GPC) and calculated as a standard polystyrene equivalent. Specifically, the Mw can be determined using a GPC measuring device (manufactured by Tosoh Corporation) under the conditions described below. The same applies to the examples described later.

[0070] [GPC Measurement Conditions]

[0071] Sample concentration: 0.2% by weight (tetrahydrofuran solution)

[0072] Sample injection volume: 10 μL

[0073] Eluent: Tetrahydrofuran (THF)

[0074] Flow rate: 0.6 mL / min

[0075] Column temperature (measurement temperature): 40℃

[0076] column:

[0077] Sample columns: 1 "TSKguardcolumn SuperHZ-H" column + 2 "TSKgel SuperHZM-H" columns (manufactured by Tosoh Corporation)

[0078] Reference column: 1 piece of "TSKgel SuperH-RC" (manufactured by Tosoh Corporation)

[0079] Detector: Differential refractometer (RI)

[0080] Standard sample: polystyrene

[0081] (Tackifying resin)

[0082] The adhesive layer disclosed herein contains more than 10 parts by weight of tackifying resin relative to 100 parts by weight of the aforementioned acrylic polymer, which is a monomeric component of n-HpA. The adhesive strength can be effectively improved by containing this amount of tackifying resin. The content of tackifying resin relative to 100 parts by weight of the acrylic polymer can be, for example, 12 parts by weight or more, or 15 parts by weight or more, or 18 parts by weight or more. In some embodiments, from the viewpoint of obtaining a higher performance, the content of tackifying resin relative to 100 parts by weight of the acrylic polymer is appropriate, preferably 20 parts by weight or more, and can be 25 parts by weight or more, or 30 parts by weight or more. The acrylic polymer containing n-HpA as a monomeric unit has good compatibility with the tackifying resin, thus enabling improved adhesive strength by containing more tackifying resin while maintaining cohesive strength suitable for suppressing the reduction of oil and water solvent resistance. In addition, relative to 100 parts by weight of acrylic polymer, the content of tackifying resin can be, for example, 100 parts by weight or less or 90 parts by weight or less. From the viewpoint of better suppressing the reduction of adhesive strength caused by contact with oil, it is appropriate to be 80 parts by weight or less, preferably 60 parts by weight or less (e.g., 55 parts by weight or less), more preferably 50 parts by weight or less, and can be 45 parts by weight or less, 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, or 25 parts by weight or less.

[0083] There are no particular restrictions on the type of tackifying resin used. For example, various tackifying resins can be used, such as phenolic tackifying resins, rosin-based tackifying resins, terpene-based tackifying resins, hydrocarbon-based tackifying resins, epoxy-based tackifying resins, polyamide-based tackifying resins, elastomer-based tackifying resins, ketone-based tackifying resins, etc. Such tackifying resins can be used alone or in combination of two or more.

[0084] Examples of phenolic tackifying resins include: terpene phenol resins, hydrogenated terpene phenol resins, alkylphenol resins, and rosin phenol resins.

[0085] Terpene phenol resins refer to polymers containing both terpene and phenol residues. This concept encompasses both copolymers of terpenes and phenolic compounds (terpene-phenol copolymer resins) and resins obtained by modifying homopolymers or copolymers of terpenes with phenol (phenol-modified terpene resins). Specific examples of terpenes constituting such terpene phenol resins include monoterpenes such as α-pinene, β-pinene, and limonene (including d-form, l-form, and d / l-form (terpinene)). Hydrogenated terpene phenol resins refer to hydrogenated terpene phenol resins having a structure obtained by hydrogenating such terpene phenol resins. They are sometimes also called hydrogenated terpene phenol resins.

[0086] Alkylphenol resin is a resin obtained from alkylphenol and formaldehyde (oil-based phenolic resin). Examples of alkylphenol resins include phenolic varnish-type alkylphenol resin and methyl phenolic type alkylphenol resin.

[0087] Rosin phenol resins are typically phenol-modified products of rosin or various rosin derivatives (including rosin esters, unsaturated fatty acid-modified rosin, and unsaturated fatty acid-modified rosin esters). Examples of rosin phenol resins include those obtained by thermal polymerization of rosin or various rosin derivatives with phenol using an acid catalyst.

[0088] Among these phenolic tackifying resins, terpene phenol resins, hydrogenated terpene phenol resins, and alkylphenol resins are preferred, with terpene phenol resins and hydrogenated terpene phenol resins being more preferred, and terpene phenol resins being the most preferred.

[0089] Examples of rosin-based tackifying resins include: unmodified rosin (raw rosin), such as resin rosin, wood rosin, and top-oil rosin; modified rosin obtained by modifying these unmodified rosin through hydrogenation, disproportionation, polymerization, etc. (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosin, etc. The same applies below); various other rosin derivatives; etc. Examples of the aforementioned rosin derivatives include: rosin esters, such as substances obtained by esterifying unmodified rosin with alcohols (i.e., rosin esters) and substances obtained by esterifying modified rosin with alcohols (i.e., modified rosin esters); unsaturated fatty acid-modified rosin, obtained by modifying unmodified or modified rosin with unsaturated fatty acids; unsaturated fatty acid-modified rosin esters, obtained by modifying rosin esters with unsaturated fatty acids; rosin alcohols, obtained by reducing the carboxyl groups in unmodified rosin, modified rosin, unsaturated fatty acid-modified rosin, or unsaturated fatty acid-modified rosin esters; metal salts of rosin derivatives (especially rosin esters); etc. Among these, rosin esters are preferred. Specific examples of rosin esters include esters of unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), such as methyl esters, triethylene glycol esters, glyceryl esters, pentaerythritol esters, etc., but there are no particular limitations.

[0090] Examples of terpene-based tackifying resins include polymers of terpenes (e.g., monoterpenes), such as α-pinene, β-pinene, d-limonene, l-limonene, and terpinene. These can be homopolymers of a single terpene or copolymers of two or more terpenes. Examples of terpene homopolymers include α-pinene polymers, β-pinene polymers, and terpinene polymers.

[0091] Examples of hydrocarbon tackifying resins include: aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, aliphatic / aromatic copolymers (C5 / C9) petroleum resins, their hydrogenates (e.g., alicyclic petroleum resins obtained by hydrogenating aromatic petroleum resins), their various modifiers (e.g., maleic anhydride modifiers), coumarone resins, coumarone-indene resins, and other hydrocarbon resins.

[0092] In some methods, phenolic tackifying resins are preferably used as tackifying resins. By using phenolic tackifying resins, the adhesive strength can be satisfactorily improved while suppressing the increase in swelling. Among these, terpene phenol resins are preferred. As tackifying resins, only one or more phenolic tackifying resins may be used, or a combination of phenolic tackifying resins and other tackifying resins (e.g., rosin-based tackifying resins) may be used. The proportion of phenolic tackifying resin (e.g., terpene phenol resin) in the total tackifying resin contained in the adhesive layer may be, for example, about 35% by weight or more, and from the viewpoint of properly utilizing the effect of phenolic tackifying resins, it is preferably greater than about 50% by weight, about 70% by weight or more, or about 80% by weight or more. The technology disclosed herein can preferably be implemented in a manner where substantially all of the tackifying resin (e.g., about 97% by weight or more, or about 99% by weight or more, or even 100% by weight) is a phenolic tackifying resin.

[0093] In methods of using terpene phenol resin as a tackifying resin, the content of the terpene phenol resin relative to 100 parts by weight of the acrylic polymer can be, for example, 1 part by weight or more, 3 parts by weight or more, 5 parts by weight or more, 7 parts by weight or more, 9 parts by weight or more, 12 parts by weight or more, 15 parts by weight or more, or 18 parts by weight or more. In some methods, from the viewpoint of obtaining a better performance, it is appropriate for the content of terpene phenol resin to be 18.5 parts by weight or more relative to 100 parts by weight of the acrylic polymer, preferably 20 parts by weight or more, and 25 parts by weight or more. In other methods, from the viewpoint of oil resistance, etc., it is appropriate for the content of terpene phenol resin to be 80 parts by weight or less relative to 100 parts by weight of the acrylic polymer, preferably 60 parts by weight or less (e.g., 55 parts by weight or less), more preferably 50 parts by weight or less, and can be 45 parts by weight or less, 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, or 25 parts by weight or less. Here, the statement that the content of terpene phenol resin is X parts by weight or less relative to 100 parts by weight of acrylic polymer is used to mean both that the adhesive layer does not contain terpene phenol resin and that it contains terpene phenol resin in a proportion of X parts by weight or less relative to 100 parts by weight of acrylic polymer. In some embodiments, the content of terpene phenol resin in the adhesive layer may be 10 parts by weight or less, or 5 parts by weight or less, 3 parts by weight or less, or 1 part by weight or less (e.g., 0 to 0.1 parts by weight) relative to 100 parts by weight of acrylic polymer.

[0094] When using a phenolic tackifying resin as the tackifying resin, the proportion of tackifying resins other than the phenolic tackifying resin (non-phenolic tackifying resins, such as rosin-based tackifying resins) in the adhesive layer is appropriately 40 parts by weight or less relative to 100 parts by weight of the acrylic polymer. This facilitates the appropriate application of the phenolic tackifying resin. In some embodiments, the amount of non-phenolic tackifying resin used relative to 100 parts by weight of the acrylic polymer is preferably about 20 parts by weight or less (e.g., less than 20 parts by weight), more preferably about 15 parts by weight or less, and can be about 10 parts by weight or less, or even about 5 parts by weight or less.

[0095] In some methods, from the viewpoint of adhesion to the adhered object, a tackifying resin T with a softening point of less than 150°C is used as the tackifying resin. L Tackifying resin T L There is no particular limitation on the lower limit of the softening point. In some approaches, from the viewpoint of achieving moderate cohesiveness, the tackifying resin T... L A softening point of approximately 60°C or higher is suitable; for example, it could be approximately 80°C or higher, approximately 90°C or higher, or even approximately 100°C or higher. As a tackifying resin T... L One or more tackifying resins with a softening point of less than 150°C, selected from the tackifying resins exemplified above, may be used alone.

[0096] In some methods, tackifying resin T L Preferably, it contains a phenolic tackifying resin. Tackifying resin T L It may contain only one type of phenolic tackifying resin, or it may contain two or more types of phenolic tackifying resins. Tackifying resin T L It is possible to combine phenolic tackifying resins and non-phenolic tackifying resins. As the aforementioned non-phenolic tackifying resin, one or more tackifying resins selected from those excluding phenolic tackifying resins and having a softening point of less than 150°C can be used alone or in combination. In some embodiments, the phenolic tackifying resin is present in the tackifying resin T... L The proportion of the total component can be, for example, greater than about 50% by weight, more than about 65% by weight, or more than about 75% by weight. The technology disclosed herein preferably uses tackifying resin T. L It is implemented in a manner in which virtually all (e.g., more than 97% by weight, or more than 99% by weight, or even 100% by weight) is a phenolic tackifying resin.

[0097] Tackifying resin T L The content of (containing two or more tackifying resins T) LIn the case of their total amount, there is no particular limitation, but it is appropriate to be 80 parts by weight or less relative to 100 parts by weight of acrylic polymer. From the viewpoint of adhesion to the adhered object, it is preferable to be 60 parts by weight or less (e.g., 55 parts by weight or less), more preferably 50 parts by weight or less, and can be 45 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, or 25 parts by weight or less. In addition, relative to 100 parts by weight of acrylic polymer, the tackifying resin T L The amount used can be, for example, 5 parts by weight or more, 7 parts by weight or more, 9 parts by weight or more, 12 parts by weight or more, 15 parts by weight or more, or 18 parts by weight or more. In some methods, from the viewpoint of improving adhesion, the tackifying resin T is used relative to 100 parts by weight of the acrylic polymer. L The amount used is appropriate, for example, 18.5 parts by weight or more, preferably 20 parts by weight or more, and may also be 25 parts by weight or more.

[0098] In some embodiments, the adhesive layer described above may be combined with a tackifying resin T L Tackifying resins T with a softening point of 150°C or higher (e.g., 150°C to 200°C) H As a tackifying resin T H One or more of the tackifying resins with a softening point of 150°C or higher can be used alone.

[0099] It should be noted that the softening point of the tackifying resin in this specification is defined as the value determined according to the softening point test method (ring and ring method) specified in JIS K5902 and JIS K2207. Specifically, the sample is rapidly melted at the lowest possible temperature and filled into a ring placed on a flat metal plate, taking care not to generate air bubbles. After cooling, the raised portion is cut off from the plane containing the upper end of the ring with a slightly heated knife. Next, a support (ring stand) is placed in a glass container (heating bath) with a diameter of 85 mm or more and a height of 127 mm or more, and glycerol is poured in until the depth reaches 90 mm or more. Next, a steel ball (9.5 mm in diameter, 3.5 g in weight) and the ring filled with the sample are immersed in glycerol without touching each other, and the temperature of the glycerol is maintained at 20 °C ± 5 °C for 15 minutes. Then, the steel ball is placed in the center of the sample surface in the ring and placed in a fixed position on the support. Next, maintaining a distance of 50 mm from the top of the ring to the glycerin surface, place a thermometer with the center of the thermometer's mercury bulb at the same height as the center of the ring, and heat the container. The flame of the Bunsen burner used for heating should be positioned between the center and the edge of the bottom of the container to ensure uniform heating. It should be noted that the bath temperature rise after reaching 40°C must be at a rate of 5.0°C ± 0.5°C per minute. The sample gradually softens and flows down the ring; the temperature at which it finally contacts the base plate is recorded as the softening point. The softening point should be determined at least twice, and the average value should be used.

[0100] In some methods, tackifying resin T L Preferably, the tackifying resin constitutes more than 50% by weight of the total amount of tackifying resin in the adhesive layer. This readily and effectively demonstrates the presence of tackifying resin T. L The effect of more effectively utilizing the tackifying resin T. L From the perspective of usage effect, tackifying resin T L The proportion of the total amount of tackifying resin contained in the adhesive layer is preferably 60% by weight or more, more preferably 70% by weight or more, further preferably 80% by weight or more, particularly preferably 90% by weight or more, and can be 95% by weight or more, or 98% by weight or more. In some preferred embodiments, the tackifying resin contained in the adhesive layer substantially consists only of tackifying resin T. L In this method, the tackifying resin T L The total amount of tackifying resin contained in the adhesive layer is in the range of 99% to 100% by weight.

[0101] In some embodiments, the aforementioned tackifying resin may contain a hydroxyl value of 40 mg KOH / g or higher (e.g., greater than 40 mg KOH / g, preferably 45 mg KOH / g or higher, more preferably 50 mg KOH / g or higher). Hereinafter, the tackifying resin having this hydroxyl value is sometimes referred to as a "high hydroxyl value resin." Acrylic polymers containing n-HpA as a monomer unit have good compatibility with such high hydroxyl value resins, thus enabling improved adhesion while maintaining a balanced balance of oil resistance and water solvent resistance through the use of such high hydroxyl value resins. In some embodiments, the hydroxyl value of the high hydroxyl value resin may be 60 mg KOH / g or higher, 80 mg KOH / g or higher, 90 mg KOH / g or higher, or 100 mg KOH / g or higher. There is no particular upper limit to the hydroxyl value of the high hydroxyl value resin; for example, it may be about 200 mg KOH / g or lower, about 160 mg KOH / g or lower, or about 140 mg KOH / g or lower. In some approaches, from the viewpoint of adhesion to the adherend, the hydroxyl value of the high hydroxyl value resin is preferably about 125 mg KOH / g or less, can be about 115 mg KOH / g or less, or can be about 90 mg KOH / g or less.

[0102] As a high hydroxyl value resin, one or more tackifying resins appropriately selected from the tackifying resins exemplified above, having a hydroxyl value equivalent to that of a high hydroxyl value resin, can be used alone or in combination. In some embodiments, the high hydroxyl value resin preferably comprises a phenolic tackifying resin (e.g., a terpene phenolic resin). The high hydroxyl value resin may contain only one phenolic tackifying resin or may contain a combination of two or more phenolic tackifying resins. Furthermore, the high hydroxyl value resin may be the aforementioned tackifying resin T. L It can also be a tackifying resin T H In some methods, T can be preferably used as the tackifying resin. L High hydroxyl value resin. Based on T as a tackifying resin... L High hydroxyl value resins can improve adhesive strength by containing more tackifying resins while inhibiting the reduction of oil resistance, water resistance, and solvent resistance.

[0103] Although there are no particular limitations, when using a high hydroxyl value resin (e.g., a high hydroxyl value resin with a hydroxyl value greater than 40 mg KOH / g, preferably 45 mg KOH / g or more, more preferably 50 mg KOH / g or more), the amount of the high hydroxyl value resin used (the total amount of the two or more high hydroxyl value resins) relative to 100 parts by weight of the acrylic polymer can be, for example, 5 parts by weight or more. From the viewpoint of obtaining a higher effect, it is preferably 10 parts by weight or more (e.g., greater than 10 parts by weight), more preferably 12 parts by weight or more, 15 parts by weight or more, 18 parts by weight or more (e.g., 18.5 parts by weight or more), 20 parts by weight or more, or 25 parts by weight or more. In addition, from the viewpoint of suppressing swelling and oil resistance, in some methods, it is appropriate for the amount of high hydroxyl value resin used to be 80 parts by weight or less relative to 100 parts by weight of acrylic polymer, preferably 60 parts by weight or less (e.g., 55 parts by weight or less), more preferably 50 parts by weight or less, and can be 45 parts by weight or less, 40 parts by weight or less, 35 parts by weight or less, 30 parts by weight or less, or 25 parts by weight or less.

[0104] In some embodiments, the high hydroxyl value resin (e.g., a high hydroxyl value resin with a hydroxyl value greater than 40 mg KOH / g, preferably 45 mg KOH / g or more, more preferably 50 mg KOH / g or more) preferably accounts for more than 30% by weight of the total amount of tackifying resin contained in the adhesive layer, and more preferably more than 50% by weight. This satisfactorily achieves the effect of improving adhesion while maintaining a balanced oil resistance and water / solvent resistance. In some embodiments, from the viewpoint of more easily utilizing the effect of the high hydroxyl value resin, the proportion of the high hydroxyl value resin in the total amount of tackifying resin contained in the adhesive layer is preferably 60% by weight or more, more preferably 70% by weight or more, further preferably 80% by weight or more, particularly preferably 90% by weight or more, and can be 95% by weight or more, or 98% by weight or more. In some preferred embodiments, the tackifying resin contained in the adhesive layer substantially consists only of the high hydroxyl value resin. In this embodiment, the proportion of the high hydroxyl value resin in the total amount of tackifying resin contained in the adhesive layer is in the range of 99% by weight to 100% by weight.

[0105] In some embodiments, the aforementioned tackifying resin may comprise a tackifying resin with a hydroxyl value less than 40 mg KOH / g (e.g., less than 30 mg KOH / g). Hereinafter, a tackifying resin having this hydroxyl value is sometimes referred to as a "low hydroxyl value resin." The hydroxyl value of a low hydroxyl value resin can be less than about 20 mg KOH / g, less than about 15 mg KOH / g, or less than about 10 mg KOH / g. There is no particular limitation on the lower limit of the hydroxyl value of a low hydroxyl value resin; it can be substantially 0 mg KOH / g. Low hydroxyl value resins are preferably used in combination with high hydroxyl value resins, which can help adjust adhesive properties, etc. Alternatively, the techniques disclosed herein can also be implemented by using only a low hydroxyl value resin as the tackifying resin.

[0106] As a low hydroxyl value resin, one or more tackifying resins appropriately selected from the tackifying resins exemplified above, having a hydroxyl value equivalent to that of a low hydroxyl value resin, can be used alone or in combination. In some embodiments, the low hydroxyl value resin preferably comprises a rosin-based tackifying resin. For example, the hydroxyl value resin may comprise only one rosin-based tackifying resin, or it may comprise a combination of two or more rosin-based tackifying resins. Furthermore, the low hydroxyl value resin may be the aforementioned tackifying resin T. L It can also be a tackifying resin T H In some methods, T can be preferably used as the tackifying resin. L Low hydroxyl value resin.

[0107] While there are no particular restrictions, the amount of low-hydroxyl value resin used (the total amount of two or more low-hydroxyl value resins) relative to 100 parts by weight of the acrylic polymer can be, for example, 1 part by weight or more, 3 parts by weight or more, 5 parts by weight or more, 7 parts by weight or more, or 9 parts by weight or more. Furthermore, the amount of low-hydroxyl value resin used relative to 100 parts by weight of the acrylic polymer is generally appropriate to be 50 parts by weight or less, and can be 40 parts by weight or less, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, 8 parts by weight or less, 4 parts by weight or less, or 2 parts by weight or less. Low-hydroxyl value resin may also be omitted.

[0108] Here, the hydroxyl value mentioned above can be determined by potentiometric titration as specified in JIS K0070:1992. The specific determination method is as follows.

[0109] [Method for determining hydroxyl value]

[0110] 1. Reagents

[0111] (1) As an acetylation reagent, use the following acetylation reagent: take about 12.5 g (about 11.8 mL) of acetic anhydride, add pyridine to it to make a total volume of 50 mL and stir thoroughly. Alternatively, use the following acetylation reagent: take about 25 g (about 23.5 mL) of acetic anhydride, add pyridine to it to make a total volume of 100 mL and stir thoroughly.

[0112] (2) Use 0.5 mol / L potassium hydroxide ethanol solution as the assay reagent.

[0113] (3) In addition, prepare toluene, pyridine, ethanol and distilled water.

[0114] 2. Operation

[0115] (1) Accurately weigh about 2g of the sample into a flat-bottomed flask, add 5mL of acetylation reagent and 10mL of pyridine, and install an air cooling tube.

[0116] (2) Heat the above flask in a bath at 100°C for 70 minutes, then allow it to cool naturally. Add 35 mL of toluene as a solvent from the top of the cooling tube and stir. Then add 1 mL of distilled water and stir to decompose the acetic anhydride. To ensure complete decomposition, heat the flask again in the bath for 10 minutes and allow it to cool naturally.

[0117] (3) Clean the cooling tube with 5 mL of ethanol and remove it. Then, add 50 mL of pyridine as a solvent and stir.

[0118] (4) Add 25 mL of 0.5 mol / L potassium hydroxide ethanol solution using a volumetric pipette.

[0119] (5) Perform potentiometric titration with 0.5 mol / L potassium hydroxide ethanol solution. Take the inflection point of the obtained titration curve as the endpoint.

[0120] (6) In the blank test, the above (1) to (5) are carried out without adding the sample.

[0121] 3. Calculation

[0122] The hydroxyl value is calculated using the following formula.

[0123] Hydroxyl value (mgKOH / g) = [(BC) × f × 28.05] / S + D

[0124] Here,

[0125] B: The volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test.

[0126] C: The volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the sample.

[0127] f: Factor of 0.5 mol / L potassium hydroxide ethanol solution

[0128] S: Weight of the sample (g)

[0129] D: Acid value,

[0130] 28.05: Half of the molecular weight of potassium hydroxide, which is 56.11.

[0131] From the viewpoint of increasing the biomass carbon ratio of the adhesive layer, the tackifying resin contained in the adhesive layer disclosed herein is preferably a tackifying resin derived from plants (plant-based tackifying resin). Examples of plant-based tackifying resins include, for instance, the aforementioned rosin-based tackifying resins and terpene-based tackifying resins. One type of plant-based tackifying resin may be used alone, or two or more may be used in combination. The proportion of plant-based tackifying resin in the total amount of tackifying resin is preferably 30% by weight or more (e.g., 50% by weight or more, typically 80% by weight or more). In some embodiments, the proportion of plant-based tackifying resin in the total amount of tackifying resin is 90% by weight or more (e.g., 95% by weight or more, typically 99% to 100% by weight). The technology disclosed herein can preferably be implemented in a manner that substantially does not contain tackifying resins other than plant-based tackifying resins.

[0132] In the technology disclosed herein, the total content of acrylic polymers and tackifying resins in the adhesive layer is appropriately set to achieve the effects brought about by the technology disclosed herein, without limitation to a specific range. From the viewpoint of better achieving the effects brought about by the technology disclosed herein, in some preferred embodiments, the total amount (total quantity) of acrylic polymers and tackifying resins contained in the adhesive layer is appropriate to be greater than 50% by weight, preferably about 70% by weight or more, more preferably about 90% by weight or more, further preferably about 95% by weight or more (e.g., 95% by weight or more and 100% by weight or greater than or equal to 95% by weight and less than 100% by weight), and can be 97% by weight or more.

[0133] (Cross-linking agent)

[0134] In the technology disclosed herein, the adhesive composition used in the formation of the adhesive layer may include a crosslinking agent as needed. There are no particular limitations on the type of crosslinking agent; examples include epoxy crosslinking agents, isocyanate crosslinking agents, etc. Crosslinking agents include zopyridine crosslinking agents, melamine crosslinking agents, peroxide crosslinking agents, urea crosslinking agents, metal alkoxide crosslinking agents, metal chelate crosslinking agents, metal salt crosslinking agents, carbodiimide crosslinking agents, hydrazine crosslinking agents, amine crosslinking agents, and silane coupling agents. One crosslinking agent can be used alone or in combination of two or more. Among these, epoxy crosslinking agents and isocyanate crosslinking agents are preferred. Azoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, and more preferably epoxy-based or isocyanate-based crosslinking agents are used. By appropriately selecting the crosslinking agent, a cohesion degree of 100 or less can be satisfactorily achieved. It should be noted that the adhesive layer in the disclosed technology may contain the aforementioned crosslinking agent in the form after the crosslinking reaction, in the form before the crosslinking reaction, in the form after a partial crosslinking reaction, in an intermediate or composite form, etc. The aforementioned crosslinking agent is typically mainly contained in the adhesive layer in the form after the crosslinking reaction.

[0135] As epoxy crosslinking agents, compounds having two or more epoxy groups in one molecule can be used without particular limitation. Epoxy crosslinking agents having three to five epoxy groups in one molecule are preferred. One epoxy crosslinking agent can be used alone or in combination of two or more.

[0136] Specific examples of epoxy crosslinking agents are not particularly limited, but can include: N,N,N',N'-tetraglycidyl-m-phenylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc. Commercially available epoxy crosslinking agents include: Mitsubishi Gas Chemical Co., Ltd.'s trade names "TETRAD-C" and "TETRAD-X", DIC Corporation's trade name "EPICRON CR-5L", Nagase Chemte X Co., Ltd.'s trade name "DENACOL EX-512", and Nissan Chemical Industries Co., Ltd.'s trade name "TEPIC-G", etc.

[0137] There is no particular limitation on the amount of epoxy crosslinking agent used. For example, relative to 100 parts by weight of acrylic polymer, the amount of epoxy crosslinking agent can be greater than 0 parts by weight and less than or equal to about 1 part by weight (typically about 0.001 parts by weight to about 1 part by weight). From the viewpoint of appropriately exerting the effect of improving cohesion, it is appropriate to use about 0.005 parts by weight or more of epoxy crosslinking agent relative to 100 parts by weight of acrylic polymer, preferably about 0.01 parts by weight or more (e.g., greater than 0.01 parts by weight, or 0.015 parts by weight or more), and more preferably about 0.02 parts by weight or more (e.g., greater than 0.02 parts by weight, or 0.025 parts by weight or more). Furthermore, from the viewpoint of improving adhesion to the adhered object, it is appropriate for the amount of epoxy crosslinking agent used to be about 0.5 parts by weight or less relative to 100 parts by weight of acrylic polymer, preferably about 0.2 parts by weight or less, more preferably about 0.1 parts by weight or less (e.g., less than 0.1 parts by weight), and can be 0.07 parts by weight or less, 0.05 parts by weight or less, 0.04 parts by weight or less (e.g., less than 0.04 parts by weight), less than 0.035 parts by weight, or 0.03 parts by weight or less.

[0138] As isocyanate crosslinking agents, polyfunctional isocyanates (compounds having an average of two or more isocyanate groups per molecule, including substances with isocyanurate structures) are preferred. Isocyanate crosslinking agents can be used alone or in combination of two or more.

[0139] Examples of polyfunctional isocyanates include aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates.

[0140] Specific examples of aliphatic polyisocyanates include: 1,2-ethylidene diisocyanate; 1,2-butylidene diisocyanate, 1,3-butylidene diisocyanate, 1,4-butylidene diisocyanate, and other butylidene diisocyanates; 1,2-hexylidene diisocyanate, 1,3-hexylidene diisocyanate, 1,4-hexylidene diisocyanate, 1,5-hexylidene diisocyanate, 1,6-hexylidene diisocyanate, 2,5-hexylidene diisocyanate, and other hexylidene diisocyanates; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, lysine diisocyanate, etc.

[0141] 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 diphenylmethylene diisocyanate, hydrogenated toluene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0142] Specific examples of aromatic polyisocyanates include: 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrobiphenyl-4,4'-diisocyanate, and 2,2'-diphenylpropane-4,4'-diisocyanate. Isocyanates, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, terephthalene diisocyanate, naphthyl-1,4-diisocyanate, naphthyl-1,5-diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, phenylenediamine-1,4-diisocyanate, phenylenediamine-1,3-diisocyanate, etc.

[0143] Preferred polyfunctional isocyanates include those having an average of three or more isocyanate groups per molecule. These trifunctional or higher isocyanates can be polymers (typically dimers or trimers) of difunctional or trifunctional or higher isocyanates, derivatives (e.g., addition reaction products of polyols with two or more molecules of polyfunctional isocyanates), polymers, etc. Examples include: dimers or trimers of diphenylmethane diisocyanate, isocyanurates of hexamethylene diisocyanate (trimeric adducts of isocyanurate structures), reaction products of trimethylolpropane and toluene diisocyanate, reaction products of trimethylolpropane and hexamethylene diisocyanate, polymethylene polyphenyl isocyanates, polyether polyisocyanates, polyester polyisocyanates, and other polyfunctional isocyanates. Commercially available products of this polyfunctional isocyanate include: "DURANATETPA-100" manufactured by Asahi Kasei Chemicals, "Coronate L" manufactured by Tosoh Corporation, "Coronate HL" manufactured by Tosoh Corporation, "Coronate HK" manufactured by Tosoh Corporation, "Coronate HX" manufactured by Tosoh Corporation, and "Coronate 2096" manufactured by Tosoh Corporation.

[0144] There is no particular limitation on the amount of isocyanate crosslinking agent used; for example, it can be about 0.1 parts by weight or more relative to 100 parts by weight of acrylic polymer. From the viewpoint of balancing adhesion, oil resistance, and water and solvent resistance, the amount of isocyanate crosslinking agent used relative to 100 parts by weight of acrylic polymer can be, for example, 0.5 parts by weight or more, 1.0 parts by weight or more is appropriate, 1.5 parts by weight or more is advantageous, preferably 2.0 parts by weight or more, more preferably greater than 2.5 parts by weight, 2.8 parts by weight or more, 3.0 parts by weight or more, or 3.5 parts by weight or more. Furthermore, relative to 100 parts by weight of acrylic polymer, the amount of the aforementioned isocyanate crosslinking agent used is appropriate to be 10 parts by weight or less, preferably less than 8.0 parts by weight, more preferably less than 7.0 parts by weight, and even more preferably less than 6.0 parts by weight. It can be less than 5.0 parts by weight or less than 4.5 parts by weight.

[0145] In some preferred embodiments, as a crosslinking agent, an epoxy crosslinking agent and at least one crosslinking agent with a different type of crosslinking functional group than the epoxy crosslinking agent can be used in combination. According to the technology disclosed herein, by combining a crosslinking agent other than an epoxy crosslinking agent (i.e., a crosslinking agent with a different type of crosslinking reactive group than the epoxy crosslinking agent; hereinafter also referred to as a "non-epoxy crosslinking agent") with an epoxy crosslinking agent, it is possible to appropriately balance adhesive strength and high holding power for different types of materials.

[0146] There are no particular restrictions on the types of non-epoxy crosslinking agents that can be used in combination with epoxy crosslinking agents; appropriate selections can be made from the aforementioned crosslinking agents. One non-epoxy crosslinking agent can be used alone, or two or more can be used in combination.

[0147] In some preferred embodiments, isocyanate crosslinking agents can be used as non-epoxy crosslinking agents. For example, by using both epoxy and isocyanate crosslinking agents, superior adhesive properties can be achieved. There are no particular limitations on the relationship between the content of the epoxy crosslinking agent and the content of the non-epoxy crosslinking agent (preferably an isocyanate crosslinking agent). The content of the epoxy crosslinking agent can, for example, be about 1 / 10 or less of the content of the non-epoxy crosslinking agent (preferably an isocyanate crosslinking agent). From the viewpoint of more appropriately balancing adhesion and cohesion of the adhered objects, it is appropriate for the content of the epoxy crosslinking agent to be about 1 / 30 or less of the content of the non-epoxy crosslinking agent, preferably about 1 / 50 or less (e.g., about 1 / 60 or less), more preferably about 1 / 75 or less, and can be about 1 / 90 or less. Furthermore, from the viewpoint of properly maximizing the effect of using epoxy crosslinking agents and non-epoxy crosslinking agents (preferably isocyanate crosslinking agents) in combination, it is generally appropriate for the content of epoxy crosslinking agent to be about 1 / 1000 or more, for example, about 1 / 500 or more, preferably about 1 / 300 or more, more preferably 1 / 180 or more (for example, 1 / 150 or more), and even more preferably 1 / 120 or more.

[0148] There is no particular limitation on the total amount of crosslinking agent used. For example, it can be selected from a range of more than about 0.005 parts by weight (e.g., more than about 0.01 parts by weight, typically more than about 0.1 parts by weight) and less than about 10 parts by weight (e.g., less than about 8 parts by weight, preferably less than about 5 parts by weight) relative to 100 parts by weight of acrylic polymer.

[0149] (Other additives)

[0150] In addition to the components mentioned above, the adhesive composition may contain, as needed, various additives commonly used in the adhesive field, such as leveling agents, crosslinking aids, plasticizers, softeners, fillers, colorants (pigments, dyes, etc.), antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, and light stabilizers. These additives can be made using conventional methods and are not characteristic of this invention; therefore, detailed descriptions are omitted.

[0151] (Swelling degree)

[0152] The adhesive layer in the disclosed technology has a swelling degree of 100 or less with ethyl acetate. By using an acrylic polymer containing n-HpA as a monomer component, and ensuring that the content of the tackifying resin is greater than 10 parts by weight relative to 100 parts by weight of the acrylic polymer while maintaining a swelling degree of 100 or less, the adhesive strength can be effectively improved, and the reduction in adhesive strength caused by contact with oils and aqueous solvents can be suppressed. Thus, an adhesive sheet that balances high levels of adhesive strength, oil resistance, and water solvent resistance can be achieved. In some embodiments, from the viewpoint of improving oil resistance, the swelling degree of the adhesive layer is preferably 90 or less, more preferably 80 or less, and can be 75 or less, 70 or less, 65 or less, or 60 or less (e.g., less than 60). There is no particular limitation on the lower limit of the swelling degree; for example, it can be 10 or more. From the viewpoint of adhesion to the adhered object, in some embodiments, a swelling degree of 30 or more with the adhesive layer is appropriate, preferably 35 or more, more preferably 40 or more, 45 or more (e.g., greater than 45), or 50 or more. The swelling degree of the adhesive layer was measured by adjusting the swelling degree appropriately within the above range, using the method described in the examples below. The swelling degree can be adjusted by the composition of the adhesive, including the monomer composition of the acrylic polymer, Mw, tackifying resin, crosslinking agent, etc.

[0153] (Formation of the adhesive layer)

[0154] The adhesive layer (layer containing the adhesive) disclosed herein can be an adhesive layer formed from an aqueous adhesive composition, a solvent-based adhesive composition, a hot-melt adhesive composition, or an active energy radiation-curable adhesive composition. An aqueous adhesive composition refers to an adhesive composition in which the adhesive (adhesive layer forming component) is contained in a solvent (aqueous solvent) with water as the main component, typically including an aqueous adhesive composition such as a water-dispersible adhesive composition (a composition in which at least a portion of the adhesive is dispersed in water). A solvent-based adhesive composition refers to an adhesive composition in which the adhesive is contained in an organic solvent. As the organic solvent contained in the solvent-based adhesive composition, one or more examples of organic solvents (toluene, ethyl acetate, etc.) that can be used in the above-described solution polymerization can be used without particular limitation. From the viewpoint of adhesive properties, the technology disclosed herein is preferably implemented in a manner having an adhesive layer formed from a solvent-based adhesive composition.

[0155] The adhesive layer disclosed herein can be formed using methods known in the art. For example, it can be formed by applying an adhesive composition to a peelable surface (peel surface) or a non-peelable surface and allowing it to dry. For adhesive sheets having a substrate, for example, it can be formed by directly applying (typically coating) an adhesive composition to the substrate and allowing it to dry (direct method). Alternatively, it can be formed by applying an adhesive composition to a peelable surface (peel surface) and allowing it to dry, and then transferring the adhesive layer to the substrate (transfer method). From a productivity point of view, the transfer method is preferred. The peel surface can be the surface of a release liner, the back of a substrate that has undergone a peeling treatment, etc. It should be noted that the adhesive layer disclosed herein is typically formed continuously, but is not limited to this manner; for example, it can also be formed as a regular or irregular pattern such as dots or stripes.

[0156] The adhesive composition can be coated using conventionally known coating machines such as gravure roller coaters, die coaters, and bar coaters. Alternatively, the adhesive composition can be coated using methods such as dip coating or curtain coating.

[0157] From the viewpoint of promoting cross-linking reactions and improving manufacturing efficiency, the drying of the adhesive composition is preferably carried out under heating. The drying temperature can be, for example, about 40°C to about 150°C, and is generally preferred to be about 60°C to about 130°C. After the adhesive composition is dried, it can be further cured for purposes such as adjusting the transfer of components within the adhesive layer, proceeding with the cross-linking reaction, and relaxing any strain that may exist within the adhesive layer.

[0158] There is no particular limitation on the thickness of the adhesive layer. Depending on the application and intended use, an adhesive layer with an appropriate thickness, for example, ranging from 0.1 μm to 500 μm, can be used. In some embodiments, from the viewpoint of avoiding excessive thickness of the adhesive sheet, a thickness of about 100 μm or less is suitable, preferably about 70 μm or less, more preferably about 50 μm or less, and even more preferably about 35 μm or less. In some preferred embodiments of the adhesive sheet, the thickness of the adhesive layer can be about 30 μm or less (e.g., less than 30 μm), about 25 μm or less (e.g., less than 25 μm), about 22 μm or less, or about 20 μm or less (e.g., less than 20 μm). Adhesive layers with limited thickness can effectively address the requirements of thickness reduction and weight reduction. Furthermore, as the thickness of the adhesive layer decreases, there is a tendency for reduced adhesive strength. Additionally, there is a tendency for reduced adhesion to the adhered objects and for oils and aqueous solvents to easily penetrate the interface. According to the technology disclosed herein, by constructing an adhesive layer with a limited thickness, it is possible to achieve an adhesive sheet that balances high levels of adhesive strength, oil resistance, and water solvent resistance. From the viewpoint of adhesion to the adhered objects, in some embodiments, a lower limit of the adhesive layer thickness of about 0.5 μm or more is appropriate; about 1 μm or more is advantageous; about 3 μm or more is preferred; about 7 μm or more is more preferred; about 10 μm or more is even more preferred; about 12 μm or more (e.g., greater than 12 μm) is even more preferred; about 15 μm or more is also possible; and about 18 μm or more is also possible. A greater adhesive layer thickness tends to facilitate achieving the target adhesive strength. In some embodiments, the adhesive layer thickness can be greater than 20 μm, or more than 24 μm or 27 μm.

[0159] The adhesive sheet disclosed herein can be an adhesive sheet having adhesive layers of the aforementioned thickness on both sides of a substrate. Furthermore, in a double-sided adhesive sheet with a substrate having a first adhesive layer and a second adhesive layer on each side of the substrate, the first adhesive layer and the second adhesive layer can be of the same thickness or of different thicknesses.

[0160] (Surface free energy γ)

[0161] In some embodiments, the surface free energy γ of the adhesive layer is preferably less than 40 mJ / m 2 The surface free energy γ of the adhesive layer is expressed by the following formula: γ = γ d +γ p +γ h Here, γ in the above formula... d γ p and γ hThese represent the dispersive, polar, and hydrogen-bonding components of the surface free energy, respectively. The surface free energy γ of the adhesive layer can be determined using water, diiodomethane, and 1-bromonaphthalene as probe solutions, according to the Kitasaki-Hata method (Journal of the Japan Adhesives Association, Vol. 8, No. 3, 1972, pp. 131-141). The contact angle can be measured using a commercially available contact angle meter. A contact angle meter manufactured by Kyowa Interface Science Co., Ltd. under the product name "CA-X" can be used. The measurement uses the droplet method, determining the contact angle based on the droplet shape after 1500 ms. The same method is used in the examples described later.

[0162] When the surface free energy γ of the adhesive layer decreases, the wettability of the adhesive layer to the adherend increases, and the adhesion at the interface (adhesive interface) between the adhesive layer and the adherend tends to increase. By improving the adhesion at the adhesive interface in this way, it is possible to suppress the penetration of oil and aqueous solvents from the outer edge of the adhesive sheet into the adhesive interface. Therefore, from the viewpoint of suppressing the decrease in adhesive strength caused by contact with oil and aqueous solvents, it is preferable to improve the adhesion at the interface between the adhesive layer and the adherend.

[0163] From the viewpoint of easily achieving higher adhesion, in some approaches, the surface free energy γ of the adhesive layer is preferably about 35 mJ / m². 2 Below, approximately 30 mJ / m is preferred. 2 The following can be 27 mJ / m 2 The following can be 25 mJ / m 2 The following can also be 20 mJ / m 2 The lower limit of the surface free energy γ of the adhesive layer is not particularly limited, and is typically about 7 mJ / m. 2 The above is preferably about 10 mJ / m 2 That's all. In some methods, the surface free energy γ of the adhesive layer can be 15 mJ / m. 2 The above can also be 20 mJ / m 2 The surface free energy γ of the adhesive layer can be adjusted, for example, by the composition of the monomer components constituting the acrylic polymer, the type and amount of tackifying resin used, etc.

[0164] (Gel fraction)

[0165] The gel fraction of the adhesive layer disclosed herein is not particularly limited, and can be, for example, in the range of 20% to 80% (by weight). By increasing the gel fraction of the adhesive layer within a suitable range, the adhesive layer can be given cohesiveness, suppressing the reduction in adhesive strength caused by contact with oils or aqueous solvents. In some embodiments, a gel fraction of more than 30% is suitable, more than 40% is advantageous, more than 45%, more than 50%, more than 55%, more than 60%, and for example, more than 63%. Furthermore, from the viewpoint of adhesion to the adherend, in some embodiments, the gel fraction of the adhesive layer is preferably 75% or less, more preferably 70% or less (e.g., less than 70%), less than 68%, and less than 66% by weight.

[0166] The gel fraction was determined by the following method. Approximately 0.1 g of the adhesive sample (weight Wg1) was wrapped in a porous polytetrafluoroethylene (PTFE) membrane with an average pore size of 0.2 μm (weight Wg2) into a pouch shape, and the opening was tied with kite string (weight Wg3). The porous PTFE membrane used was "NITOFLON (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent product, available from Nitto Denko Corporation. The package was immersed in 50 mL of ethyl acetate and kept at room temperature (approximately 23°C) for 7 days. The package was then removed, the ethyl acetate adhering to the outer surface was wiped off, and the package was dried at 130°C for 2 hours. The weight of the package (Wg4) was measured. The gel fraction of the adhesive layer was calculated by substituting the values ​​into the following formula.

[0167] Gel fraction (%) = [(Wg4 - Wg2 - Wg3) / Wg1] × 100

[0168] (Biomass carbon ratio)

[0169] In some embodiments, the adhesive layer comprises materials derived from biomass, and the biomass carbon ratio can be a specified value or higher. The biomass carbon ratio of the adhesive layer is, for example, 1% or more, 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio in the adhesive indicates a lower amount of fossil resources, such as petroleum, used. From this perspective, a higher biomass carbon ratio in the adhesive is preferred. For example, the biomass carbon ratio of the adhesive layer can be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or greater than 80%. The upper limit of the biomass carbon ratio is defined as 100%, but it can be 99% or less. From the viewpoint of material availability, it can be 95% or less, or 90% or less. From the viewpoint of easily achieving good adhesive performance, in some embodiments, the biomass carbon ratio of the adhesive layer can be, for example, 90% or less, 85% or less, or 80% or less.

[0170] <Substrate>

[0171] In the form of adhesive sheets disclosed herein, which are single-sided or double-sided adhesive sheets with a substrate, the substrate used as the supporting (backing) adhesive layer can be resin film, paper, cloth, rubber sheet, foam sheet, metal foil, or composites 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; fluorinated resin films; and cellophane. Examples of paper include: Japanese paper, kraft paper, cellophane, high-quality paper, synthetic paper, and surface-coated paper. Examples of cloth include woven fabrics and non-woven fabrics obtained by weaving various fibrous materials alone or in blends. Examples of the aforementioned fibrous materials include: cotton, synthetic staple fibers, Manila hemp, pulp, rayon, cellulose acetate, polyester fibers, polyvinyl alcohol fibers, polyamide fibers, and polyolefin fibers. Examples of rubber sheets include natural rubber sheets and butyl rubber sheets. Examples of foam sheets include foamed polyolefin sheets, foamed polyurethane sheets, and foamed neoprene sheets. Examples of metal foils include aluminum foil and copper foil. It should be noted that the substrate supporting the adhesive layer is also referred to as the substrate layer in adhesive sheets.

[0172] The substrate can be formed from biomass-derived materials or from non-biomass-derived materials. From the viewpoint of producing adhesive sheets that take into account reducing dependence on fossil-based materials, it is preferable to use biomass-derived substrate materials (typically resin films).

[0173] Alternatively, the substrate can also be formed using recyclable materials or recycled materials (also known as recycled materials). Resin films are preferably used as such recycled materials. Since resin films (e.g., polyester films such as PET films) can be reused, continuous reproduction is possible by reusing used resin films, regardless of whether plant-derived materials are used, and environmental impact can be reduced. Such reusable resin films or recycled resin films are also called recycled films. The aforementioned recycled materials (e.g., recycled films) can be formed from materials derived from biomass or from materials not derived from biomass.

[0174] As the substrate constituting the adhesive sheet with a substrate, a substrate containing a resin film as the base film is preferably used. The base film is typically a (non-dependent) component that can independently maintain its shape. The substrate in the disclosed technology can be substantially composed of such a base film. Alternatively, the substrate may include auxiliary layers in addition to the base film. Examples of such auxiliary layers include a coloring layer, a reflective layer, a primer layer, an antistatic layer, etc., disposed on the surface of the base film.

[0175] The aforementioned resin film is a film in which a resin material is the main component (e.g., a component with a content greater than 50% by weight in the resin film). Examples of resin films include: polyolefin resin films such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer; polyester resin films such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); vinyl chloride resin films; vinyl acetate resin films; polyimide resin films; polyamide resin films; fluorinated resin films; cellophane; etc. The resin film can also be a rubber film such as a natural rubber film or a butyl rubber film. Among these, polyester films are preferred from the viewpoint of operability and processability, and PET films are particularly preferred.

[0176] It should be noted that in this specification, "resin film" typically refers to a non-porous sheet, distinct from the concepts of nonwoven fabric and woven fabric (in other words, a concept other than nonwoven fabric and woven fabric). The aforementioned resin film can be any of the following: non-stretch film, uniaxial stretch film, or biaxial stretch film. Furthermore, such a resin film can be non-foamed. Here, non-foamed resin film refers to a resin film that has not undergone any intentional treatment to form a foam. Specifically, non-foamed resin film can be a resin film with a foaming ratio of less than 1.1 times (e.g., less than 1.05 times, typically less than 1.01 times).

[0177] The aforementioned substrate (e.g., resin film) can be formulated with various additives as needed, including fillers (inorganic fillers, organic fillers, etc.), colorants, dispersants (surfactants, etc.), anti-aging agents, antioxidants, UV absorbers, antistatic agents, lubricants, and plasticizers. The proportion of each additive can be less than approximately 30% by weight (e.g., less than approximately 20% by weight, typically less than approximately 10% by weight).

[0178] The aforementioned substrate (e.g., a resin film) can be a single-layer structure or a multi-layer structure with two, three, or more layers. From the viewpoint of shape stability, a single-layer structure is preferred. In the case of a multi-layer structure, it is preferable that at least one layer (preferably all layers) is a layer having a continuous structure of the aforementioned resin (e.g., a polyester resin). The manufacturing method of the substrate (typically a resin film) can appropriately employ conventionally known methods without particular limitation. For example, conventionally known film forming methods such as extrusion molding, blow molding, T-die casting, and calendering roll forming can be appropriately employed.

[0179] For the surface of the substrate, conventional surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and application of primer can be performed. Such surface treatments can be used to improve the adhesion between the substrate and the adhesive layer, in other words, the anchoring effect of the adhesive layer on the substrate.

[0180] Furthermore, when the disclosed technology is implemented in the form of a single-sided adhesive sheet with a substrate, a peeling process can be performed on the back side of the substrate as needed. The peeling process can be, for example, applying a typical silicone, long-chain alkyl, or fluorinated peeling agent in the form of a thin film typically about 0.01 μm to about 1 μm (e.g., 0.01 μm to 0.1 μm). By performing this peeling process, effects such as easy unwinding of the adhesive sheet into a roll can be achieved.

[0181] In adhesive sheets that include a substrate, the thickness of the substrate is not particularly limited. From the viewpoint of avoiding an excessively thick adhesive sheet, the substrate thickness can be, for example, about 200 μm or less, preferably about 150 μm or less, and more preferably about 100 μm or less. Depending on the intended use and application of the adhesive sheet, the substrate thickness can be about 70 μm or less, about 50 μm or less, or about 30 μm or less (e.g., about 25 μm or less). In some embodiments, the thickness of the substrate film layer can be about 20 μm or less, about 15 μm or less, or about 10 μm or less (e.g., about 5 μm or less). By reducing the substrate thickness, even with the same total thickness of the adhesive sheet, the thickness of the adhesive layer can be further increased. From the viewpoint of improving adhesion to the adhered object and substrate, further increasing the thickness of the adhesive layer is advantageous. There is no particular limitation on the lower limit of the substrate thickness. From the viewpoint of the operability (handleability) and processability of the adhesive sheet, a substrate thickness of about 0.5 μm or more (e.g., 1 μm or more) is appropriate, preferably about 2 μm or more, for example about 6 μm or more, and can be about 8 μm or more, or about 10 μm or more. In some embodiments, the substrate thickness can be about 15 μm or more, or about 25 μm or more.

[0182] <Removing Liner>

[0183] In the disclosed technology, release liner can be used in the formation of the adhesive layer, the fabrication of the adhesive sheet, the storage, distribution, and shaping of the adhesive sheet before use. There are no particular limitations on the release liner; for example, a release liner with a release treatment layer on the surface of the liner substrate such as a resin film or paper can be used; a release liner containing a fluoropolymer (such as polytetrafluoroethylene) can also be used. The release treatment layer can be formed, for example, by surface treatment of the liner substrate with release agents such as silicone, long-chain alkyl, fluorinated, or molybdenum sulfide. As for the liner substrate, similar to the substrate of the aforementioned adhesive sheet, a substrate formed from biomass or a recycled material (such as a recycled film) is preferably used.

[0184] <Total thickness of adhesive sheet>

[0185] The total thickness of the adhesive sheet disclosed herein (which includes an adhesive layer and may also include a substrate layer, but does not include a release liner) is not particularly limited. The total thickness of the adhesive sheet can be, for example, less than about 1 mm, less than about 500 μm, less than about 300 μm, and from a thinning point of view, less than about 200 μm is suitable, and less than about 150 μm (e.g., less than about 100 μm). In some preferred embodiments, the thickness of the adhesive sheet can be less than about 70 μm, for example, less than about 55 μm. The lower limit of the thickness of the adhesive sheet is, for example, more than 0.1 μm (e.g., more than 0.5 μm), more than about 3 μm is suitable, more preferably more than about 10 μm, more than about 15 μm, more than about 20 μm, and more than about 40 μm. Adhesive sheets with thicknesses of the specified values ​​or higher tend to have good adhesion to the adhered object and also tend to have excellent operability. It should be noted that in the adhesive sheet without a substrate, the thickness of the adhesive layer is the total thickness of the adhesive sheet.

[0186] <Properties of Adhesive Sheets>

[0187] (Regarding SUS adhesion (initial adhesion F0))

[0188] In some embodiments of the adhesive sheet disclosed herein, the 180-degree peel strength (SUS adhesion) of the adhesive sheet to a stainless steel sheet is preferably 8.0 N / 10 mm or more. Adhesive sheets exhibiting such SUS adhesion can provide good fastening performance, for example, in applications involving the fixing of components. More preferably, the aforementioned SUS adhesion is about 8.2 N / 10 mm or more, further preferably 8.5 N / 10 mm or more, and can be 8.8 N / 10 mm or more, 9.0 N / 10 mm or more, 9.2 N / 10 mm or more, 9.5 N / 10 mm or more, or 9.7 N / 10 mm or more. Higher SUS adhesion is advantageous in fixing small or narrow components, or in fixing components where a relatively large load can be applied to the joint due to their own weight or external forces. There is no particular upper limit to the SUS adhesion strength mentioned above. Considering other requirements (such as reducing the thickness of the adhesive layer), it can be below 20 N / 10 mm, below 18 N / 10 mm, or below 16 N / 10 mm. The SUS adhesion strength described above was measured using an SUS sheet as the substrate at 23°C and 50% RH, under conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees. The SUS adhesion strength described above was measured after bonding to the substrate without the supply of oil or aqueous solvents. To indicate the adhesion strength F after impregnation as described later... A F BRegarding the relationship, the above-mentioned adhesion to SUS is sometimes referred to hereinafter as "initial adhesion force F0". The initial adhesion force F0 is more specifically measured by the method described in the examples below.

[0189] (Adhesion retention rate R) A )

[0190] In some of the methods disclosed herein, the adhesive sheet is composed of the following formula:

[0191] Adhesion retention rate R A [%] = (Adhesive strength after impregnation F) A (initial adhesion force F0) × 100

[0192] The adhesive strength retention rate R is represented by A Preferably, it is 60% or more. Here, the adhesive force F after impregnation in the above formula... A To measure the 180-degree peel strength after bonding the adhesive sheet of the evaluated object to a stainless steel plate and immersing it in oleic acid at 40°C and 90% RH for 2 weeks, the initial adhesive force F0 in the above formula is the adhesive force to SUS described above. The adhesive force F after immersion... A More specifically, the method described in the examples below is used for determination. Adhesive retention rate R A Based on the above-mentioned adhesive strength F after impregnation A The initial adhesive force F0 mentioned above is calculated using the above formula.

[0193] From the viewpoint of better suppressing the decrease in adhesion caused by contact with oil, in some ways, the aforementioned adhesion retention rate R A More preferably, it is 63% or more (e.g., 65% or more), even more preferably 67% or more (e.g., 70% or more), and can be 73% or more, 75% or more, 80% or more, or 85% or more. Adhesive retention rate R A There is no specific upper limit. Adhesive retention rate R A Typically, it is 100% or less. However, considering ease of balancing other properties (e.g., initial adhesion F0, water and solvent resistance), in some cases, it can be 98% or less, 95% or less, 90% or less, 85% or less, or 80% or less. Furthermore, in some cases, considering the reliability of the bond after impregnation with oil, the aforementioned adhesion F0 is... APreferably, the strength is 4.8 N / 10 mm or more (e.g., 5.0 N / 10 mm or more), more preferably 5.3 N / 10 mm or more (e.g., 5.5 N / 10 mm or more), and even more preferably 6.0 N / 10 mm or more. It can be 6.5 N / 10 mm or more, 7.0 N / 10 mm or more, or 7.5 N / 10 mm or more. The adhesive strength F after impregnation... A There is no particular upper limit. In some methods, considering the ease of balancing other properties (e.g., initial adhesion F0, water and solvent resistance), the adhesion F after impregnation is... A For example, it can be below 19N / 10mm, below 17N / 10mm, or below 15N / 10mm.

[0194] (Adhesion retention rate R) B )

[0195] In some of the methods of adhesive sheet disclosed herein, the adhesive sheet is of the following form:

[0196] Adhesion retention rate R B [%] = (Adhesive strength after impregnation F) B (initial adhesion force F0) × 100

[0197] The adhesive strength retention rate R is represented by B Preferably, it is 70% or higher. Here, the adhesive force F after impregnation in the above formula... B To measure the 180-degree peel strength after the adhesive sheet of the evaluation object is bonded to a stainless steel plate and immersed in a 50% isopropanol aqueous solution (a 1:1 volume ratio mixed solvent) for 2 weeks at 40°C and 90% RH, the initial adhesive force F0 in the above formula is the adhesive force to SUS as described above. The adhesive force F after immersion... B More specifically, the method described in the examples below is used for determination. Adhesive retention rate R B Based on the above-mentioned adhesive strength F after impregnation B The initial adhesive force F0 mentioned above is calculated using the above formula.

[0198] From the viewpoint of better suppressing the reduction in adhesive strength caused by contact with aqueous solvents (such as water, lower alcohols, or mixtures of water and lower alcohols), in some embodiments, the aforementioned adhesive strength retention rate R... B Preferably, it is 75% or more, more preferably 80% or more, even more preferably 84% or more (e.g., 85% or more), and can be 87% or more, or 90% or more. Adhesive retention rate R B There is no specific upper limit. Adhesive retention rate R BTypically, it is 100% or less. However, considering ease of achieving other properties (e.g., initial adhesion F0, oil resistance), in some cases it can be 99% or less, 98% or less, 96% or less, 95% or less, or 94% or less. Furthermore, in some cases, considering the bonding reliability after impregnation with aqueous solvents, the aforementioned adhesion F0 is... B Preferably, the strength is 6.0 N / 10 mm or more (e.g., 6.5 N / 10 mm or more), more preferably 7.0 N / 10 mm or more (e.g., 7.5 N / 10 mm or more), and even more preferably 8.0 N / 10 mm or more. It can be 8.2 N / 10 mm or more, 8.5 N / 10 mm or more, or 8.7 N / 10 mm or more. The adhesive strength F after impregnation... B There is no particular upper limit. In some methods, considering the ease of balancing other properties (e.g., initial adhesion F0, water and solvent resistance), the adhesion F after impregnation is... B For example, it can be below 19N / 10mm, below 18N / 10mm, below 17N / 10mm, or below 15N / 10mm.

[0199] In some embodiments, the adhesive sheet contains materials derived from biomass, and the biomass carbon ratio can be a specified value or higher. The biomass carbon ratio of the adhesive sheet is, for example, 1% or more, 10% or more, preferably 30% or more, and more preferably 50% or more. A high biomass carbon ratio of the adhesive sheet indicates a lower amount of fossil resources such as petroleum used. From this perspective, a higher biomass carbon ratio of the adhesive sheet is preferred. For example, the biomass carbon ratio of the adhesive sheet can be 55% or more, 60% or more, 70% or more, 75% or more, 80% or more, or greater than 80%. The upper limit of the biomass carbon ratio is defined as 100%, but it can be 99% or less. From the viewpoint of material availability, it can be 95% or less, or 90% or less. From the viewpoint of easily achieving good adhesive performance, in some embodiments, the biomass carbon ratio of the adhesive sheet can be, for example, 90% or less, 85% or less, or 80% or less.

[0200] <Applications>

[0201] The adhesive sheet disclosed herein has no particular limitation on its application and can be used for a variety of purposes. Utilizing its ability to balance high levels of adhesive strength, oil resistance, and water solvent resistance, the adhesive sheet disclosed herein is preferably used for fixing various components that may come into contact with one or both of oil and water-based solvents. As a representative example of such an application, its use in fixing parts in various portable devices can be cited. For example, it is suitable for fixing components in portable electronic devices. Non-limiting examples of portable electronic devices include: mobile phones, smartphones, tablet PCs, laptop PCs, various wearable devices (such as wrist-worn watches, modular devices worn on the body via clips or straps, including eyewear (monocular, binocular, and helmet-type), clothing-wearable devices (such as earpieces worn on shirts, socks, hats, etc.), and ear-wearable devices (such as headphones), digital cameras, digital camcorders, audio equipment (portable music players, voice recorders, etc.), calculators (desktop calculators, etc.), portable gaming devices, electronic dictionaries, electronic notebooks, e-books, in-vehicle 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 watches, pocket watches, flashlights, handheld mirrors, clips, etc. It should be noted that in this instruction manual, "portable" is not sufficient to mean merely being able to carry; in essence, it means being portable to a level that an individual (standard adult) can relatively easily move.

[0202] Figure 4 This is an example illustrating a portable electronic device (smartphone) using the adhesive sheet disclosed herein. For example... Figure 4 As shown, a battery (heating element) 540 is built into the housing 520 of the portable electronic device 500. Furthermore, the portable electronic device 500 is constructed including an adhesive sheet 550. In this configuration example, the adhesive sheet 550 has the form of a double-sided adhesive sheet (double-sided adhesive sheet) that secures the components constituting the portable electronic device 500. It should be noted that the portable electronic device 500 has a touch panel 570 that also functions as an input unit. The adhesive sheet disclosed herein can preferably be used as a component (component joining means) of the portable electronic device as described above.

[0203] Furthermore, the adhesive sheet disclosed herein may, in some embodiments, have an adhesive layer comprising an acrylic polymer with a high biomass carbon ratio. Therefore, by using it as a substitute for conventional acrylic adhesives (i.e., acrylic adhesives with a low biomass carbon ratio) in various applications, it can help reduce dependence on fossil-based materials. The adhesive sheet disclosed herein can preferably be used as an adhesive sheet that reduces dependence on fossil-based materials.

[0204] The matters disclosed in this specification include the following.

[0205] [1] An adhesive sheet, wherein the adhesive sheet has an adhesive layer comprising an acrylic polymer and a tackifying resin, the acrylic polymer being a polymer comprising a monomeric component of n-heptyl acrylate, the tackifying resin comprising more than 10 parts by weight relative to 100 parts by weight of the acrylic polymer, and the adhesive layer having a swelling degree of less than 100 for ethyl acetate.

[0206] [2] According to the adhesive sheet described in [1] above, wherein the monomer component contains 5.0% by weight or more of a carboxyl-containing monomer.

[0207] [3] According to the adhesive sheet described in [1] or [2] above, wherein the adhesive composition for forming the adhesive layer comprises an isocyanate crosslinking agent and an epoxy crosslinking agent in combination.

[0208] [4] The adhesive sheet according to any one of [1] to [3] above, wherein the adhesive layer comprises a phenolic tackifying resin as the tackifying resin.

[0209] [5] The adhesive sheet according to [4] above, wherein the terpene phenol resin is included as the phenolic tackifying resin, and the content of the terpene phenol resin is 20 parts by weight or more relative to 100 parts by weight of the acrylic polymer.

[0210] [6] The adhesive sheet according to any one of [1] to [5] above, wherein the weight-average molecular weight of the acrylic polymer is greater than 500,000.

[0211] [7] The adhesive sheet according to any one of [1] to [6] above, wherein the adhesive sheet has a 180-degree peel strength of 8.0 N / 10 mm or more against the stainless steel sheet.

[0212] [8] The adhesive sheet according to any one of [1] to [7] above, wherein the adhesive sheet is configured as a double-sided adhesive sheet.

[0213] [9] The adhesive sheet according to any one of [1] to [8] above is configured as a double-sided adhesive sheet having a resin film as a support substrate and an adhesive layer disposed on one surface and another surface of the support substrate.

[0214]

[10] The adhesive sheet according to any one of [1] to [9] above, wherein the adhesive sheet is used for fixing components in a portable device.

[0215]

[11] A portable device wherein an adhesive sheet is joined to a component constituting the electronic device, the adhesive sheet having an adhesive layer comprising an acrylic polymer and a tackifying resin, the acrylic polymer being a polymer comprising a monomeric component of n-heptyl acrylate, the tackifying resin having a content greater than 10 parts by weight relative to 100 parts by weight of the acrylic polymer, and the adhesive layer having a swelling degree of less than 100 for ethyl acetate.

[0216]

[12] The portable device described in

[11] above is a portable electronic device.

[0217]

[13] The portable device according to

[11] or

[12] above, wherein the monomer component of the acrylic polymer contains more than 5.0% by weight of carboxyl-containing monomers.

[0218]

[14] The portable device according to any one of

[11] to

[13] above, wherein the adhesive composition for forming the adhesive layer comprises an isocyanate crosslinking agent and an epoxy crosslinking agent.

[0219]

[15] The portable device according to any one of

[11] to

[14] above, wherein the adhesive layer comprises a phenolic tackifying resin as the tackifying resin.

[0220]

[16] The portable device according to

[15] above, wherein the terpene phenol resin is included as the phenolic tackifying resin, and the content of the terpene phenol resin is 20 parts by weight or more relative to 100 parts by weight of the acrylic polymer.

[0221]

[17] The portable device according to any one of

[11] to

[16] above, wherein the weight-average molecular weight of the acrylic polymer is greater than 500,000.

[0222]

[18] The portable device according to any one of

[11] to

[17] above, wherein the adhesive sheet has a 180-degree peel strength of 8.0 N / 10 mm or more against the stainless steel plate.

[0223]

[19] The portable device according to any one of

[11] to

[18] above, wherein it is configured as a double-sided adhesive sheet.

[0224]

[20] The portable device according to any one of

[11] to

[19] above, wherein the adhesive sheet is configured as a double-sided adhesive sheet having a resin film as a support substrate and the adhesive layer disposed on one surface and the other surface of the support substrate.

[0225] Example

[0226] The following describes some embodiments of the present invention, but it is not intended to limit the invention to the contents shown in these embodiments. It should be noted that, unless otherwise specified, "parts" and "%" are based on weight in the following description.

[0227] <Evaluation Methods>

[0228] (Initial adhesive force F0)

[0229] Under the test environment of 23℃ and 50%RH, a PET film with a thickness of 50μm was pasted on one adhesive side of the adhesive sheet (double-sided adhesive sheet) for lining, and then cut into a size of 10mm in width and 100mm in length to prepare the test sample.

[0230] At 23°C and 50%RH, a 2kg roller was used to press the other adhesive surface of the test sample onto the surface of a stainless steel sheet (SUS304 BA sheet) cleaned with ethyl acetate. The sample was left to stand in the same environment for 30 minutes, and then the peel strength (initial adhesive force F0) [N / 10mm] was determined using a tensile testing machine according to JIS Z0237:2000, at a tensile speed of 150mm / min and a peel angle of 180 degrees.

[0231] (Oil resistance)

[0232] Under the test environment of 23℃ and 50%RH, a PET film with a thickness of 50μm was pasted on one adhesive side of the adhesive sheet (double-sided adhesive sheet) for lining, and then cut into a size of 10mm in width and 100mm in length to prepare the test sample.

[0233] At 23°C and 50%RH, a 2kg roller was used to press the other adhesive surface of the test sample onto the surface of a stainless steel plate (SUS304 BA plate) cleaned with ethyl acetate in one pass. The sample was left in the same environment for 30 minutes, then immersed in an oleic acid bath and maintained at 40°C and 90%RH for 2 weeks. The test sample was then removed from the oleic acid bath, and the oleic acid adhering to it was gently wiped off. It was then left in the environment at 23°C and 50%RH for 30 minutes. Finally, using a tensile testing machine, according to JIS Z0237:2000, at a tensile speed of 150 mm / min and a peel angle of 180 degrees, the peel strength (adhesive force F after immersion) after oleic acid immersion was determined. A [N / 10mm].

[0234] Based on the measured values, the adhesion retention rate R is calculated using the following formula. A :

[0235] Adhesion retention rate R A [%] = (Adhesive strength after impregnation F) A / Initial adhesive force F0)×100.

[0236] (Water and solvent resistance)

[0237] In addition to immersing in a 50% (volume ratio) isopropanol aqueous solution instead of an oleic acid bath, the adhesion F after immersion... A Similarly, the peel strength (adhesive force F after impregnation) after immersion in an aqueous solvent was also measured. B [N / 10mm].

[0238] Based on the measured values, the adhesion retention rate R is calculated using the following formula. B :

[0239] Adhesion retention rate R B [%] = (Adhesive strength after impregnation F) B / Initial adhesive force F0)×100.

[0240] (Swelling degree)

[0241] Take approximately 0.1g of the adhesive sample (weight W) S1 A porous polytetrafluoroethylene membrane with an average pore size of 0.2 μm (weight W) was used. S2The package was wrapped into a pouch shape, and the opening was tied with kite string (weight Ws3). The porous polytetrafluoroethylene (PTFE) membrane used was NITOFLON NTF1122 (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent product, available from Nitto Denko Corporation. The package was immersed in 50 mL of ethyl acetate and kept at room temperature (approximately 23°C) for 7 days. Then, the package was removed, the ethyl acetate adhering to the outer surface was wiped off, and the weight (Ws3) of the package was measured. S4 Next, the package was dried at 130°C for 2 hours, and its weight (Wg5) was measured. The swelling degree of the adhesive layer was calculated by substituting the values ​​into the following formula.

[0242] Swelling degree = (W S4 -W S2 -W S3 ) / (W S5 -W S2 -W S3 )

[0243] <Example 1>

[0244] (Synthesis of acrylic polymers)

[0245] In a reaction vessel equipped with a stirrer, thermometer, nitrogen inlet, reflux condenser, and dropping funnel, 96 parts of n-heptyl acrylate (n-HpA) as a monomer, 4 parts of acrylic acid (AA), and ethyl acetate as a polymerization solvent were added, and the mixture was stirred for 2 hours while introducing nitrogen. This process removed oxygen from the polymerization system. Then, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator were added, and solution polymerization was carried out at 60°C–70°C for 8 hours to obtain a solution of an acrylic polymer (A1). The weight-average molecular weight (Mw) of the acrylic polymer (A1) was 900,000. It should be noted that the aforementioned n-HpA is a compound synthesized using heptanol derived from biomass, possessing a heptyl group at the ester terminus derived from biomass.

[0246] (Preparation of the adhesive composition)

[0247] The adhesive composition of this example was prepared by mixing 100 parts of the above-mentioned acrylic polymer (A1), 30 parts of tackifying resin B (trade name "YS Polystar S145", manufactured by Yasuhara Chemical Co., Ltd., terpene phenol resin, softening point 145℃, hydroxyl value 70mgKOH / g~110mgKOH / g), 3 parts of isocyanate crosslinking agent (solid component basis, the same below), and 0.03 parts of epoxy crosslinking agent. As the above-mentioned isocyanate crosslinking agent, "CORONATE L" (75% ethyl acetate solution of trimethylolpropane / toluene diisocyanate trimer adduct) manufactured by Tosoh Co., Ltd. was used, and as the above-mentioned epoxy crosslinking agent, "TETRAD-C" (1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) manufactured by Mitsubishi Gas Chemical Co., Ltd. was used.

[0248] (Making the adhesive sheet)

[0249] Two 38μm thick polyester release films (trade name "DIAFOIL MRF", 38μm thick, manufactured by Mitsubishi Chemical Corporation) were prepared. The aforementioned adhesive composition was applied to the release surfaces of these release films, and they were dried at 100°C for 2 minutes, thereby forming an adhesive layer with a thickness of 19μm. The adhesive layers formed on the two release films were then bonded to the first and second surfaces of a 12μm thick PET film (trade name "Lumirror", manufactured by Toray Industries, Inc.) serving as the substrate. The release films remained intact on the adhesive layers, serving to protect the surfaces (adhesive surfaces) of the adhesive layers. Through this process, a 50μm thick double-sided adhesive sheet with a substrate was obtained, with both adhesive surfaces protected by the two polyester release films.

[0250] <Example 2>

[0251] In the preparation of the adhesive composition in Example 1, tackifying resin A (trade name "YS Polystar T115", manufactured by Yasuhara Chemical Co., Ltd., a terpene phenolic resin with a softening point of 115°C and a hydroxyl value of 60 mg KOH / g) was used instead of tackifying resin B. Except for using the obtained adhesive composition, the double-sided adhesive sheet with a substrate of this example was prepared in the same manner as in Example 1.

[0252] <Examples 3 to Examples 9>

[0253] The monomer composition was changed to 94 parts n-HpA and 6 parts AA, and the concentration of monomer components during polymerization was adjusted. Otherwise, a solution of acrylic polymer (A2) was obtained in the same manner as the synthesis of acrylic polymer (A1). Using the above acrylic polymer (A2), the composition was changed to that shown in Table 1. Otherwise, the adhesive compositions of each example were prepared in the same manner as in Example 1, and double-sided adhesive sheets with substrates were made using the adhesive compositions of each example. As the tackifying resin C shown in Table 1, the trade name "PENSEL D125" (polypropylene rosin pentaerythritol ester, softening point 125°C, hydroxyl value 34 mg KOH / g) manufactured by Arakawa Chemical Industry Co., Ltd. was used.

[0254] <Examples 10-12>

[0255] The monomer composition was changed to 90 parts n-HpA and 10 parts AA, and the concentration of monomer components during polymerization was adjusted. Otherwise, a solution of acrylic polymer (A3) was obtained in the same manner as the synthesis of acrylic polymer (A1). Using the above acrylic polymer (A3), the composition was changed to that shown in Table 1. Otherwise, the adhesive compositions of each example were prepared in the same manner as in Example 1, and double-sided adhesive sheets with substrates were made using the adhesive compositions of each example.

[0256] <Comparative Examples 1 to 2>

[0257] Except that the amount of tackifying resin A used was set to 0 parts (Comparative Example 1) or 5 parts (Comparative Example 2), the adhesive composition of this example was prepared in the same manner as in Example 5, and the double-sided adhesive sheet with substrate of this example was made using the adhesive composition.

[0258] <Comparative Examples 3 to 4>

[0259] Except for changing the monomer composition to 90 parts of 2-ethylhexyl acrylate (2EHA) and 10 parts of AA, a solution of acrylic polymer (A4) was obtained in essentially the same manner as the synthesis of acrylic polymer (A1). Using the above acrylic polymer (A4), with the composition changed to that shown in Table 2, the adhesive compositions of each example were prepared in the same manner as in Example 1, and the double-sided adhesive sheets with substrates of each example were made using the adhesive compositions.

[0260] <Comparative Example 5>

[0261] Except for changing the monomer composition to 95 parts of n-butyl acrylate (BA) and 5 parts of AA, a solution of acrylic polymer (A5) was obtained in essentially the same manner as the synthesis of acrylic polymer (A1). Using the above acrylic polymer (A5), with the composition changed to that shown in Table 2, the adhesive composition of this example was prepared in the same manner as in Example 1, and the double-sided adhesive sheet with substrate of this example was made using the adhesive composition.

[0262] The summary and evaluation results of the adhesive sheets for each example are shown in Tables 1 and 2.

[0263]

[0264]

[0265] As shown in Table 1, the adhesive layers of Examples 1 to 12 contain an acrylic polymer comprising n-heptyl acrylate as a monomer component and a tackifying resin in an amount greater than 10 parts per 100 parts of the acrylic polymer, and the swelling degree to ethyl acetate is less than 100. The initial adhesive force F0 and the adhesion retention rate R to oil in these examples are... A and adhesion retention rate R to water-based solvents B All are good. That is, they achieve a high level of adhesion, oil resistance, and water and solvent resistance. It should be noted that the surface free energy γ of the adhesive layers in Examples 1 to 12 is all above 10 mJ / m. 2 ~35mJ / m 2 Within the range.

[0266] In contrast, as shown in Table 2, the adhesive sheets of Comparative Example 1 (which does not contain tackifying resin) and Comparative Example 2 (which has a low content of tackifying resin) have low initial adhesive strength F0. Comparative Examples 3 and 4 are examples of acrylic polymers that do not contain n-heptyl acrylate and use polymers with 2EHA as the main monomer component. Comparative Example 3 has a low initial adhesive strength F0. In Comparative Example 4, where the content of tackifying resin is increased, although the initial adhesive strength F0 increases, the swelling degree is much greater than 100, and the adhesion retention rate R to oil is low. A Significantly reduced. Comparative Example 5, an example of an acrylic polymer using a monomer component that does not contain n-heptyl acrylate and is mainly composed of BA, shows insufficient resistance to aqueous solvents.

[0267] The above provides a detailed description of specific examples of the present invention, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes any modifications or alterations made to the specific examples exemplified above.

[0268] Label Explanation

[0269] 1, 2, 3 adhesive sheets

[0270] 10 Supporting Substrates

[0271] 10A First Page

[0272] 10B Second Side (Back)

[0273] 21 Adhesive layer (first adhesive layer)

[0274] 21A Adhesive Surface (First Adhesive Surface)

[0275] 21B Second Adhesive Surface

[0276] 22 Adhesive layer (second adhesive layer)

[0277] 22A Adhesive Surface (Second Adhesive Surface)

[0278] 31, 32 Peeling gaskets

[0279] 100, 200, 300 adhesive sheets with release liner

Claims

1. An adhesive sheet, wherein, The adhesive sheet has an adhesive layer comprising an acrylic polymer and a tackifying resin. The acrylic polymer is a polymer containing more than 90% by weight of n-heptyl acrylate monomer. The monomer component contains more than 4.0% by weight of carboxyl-containing monomers. The content of the tackifying resin is 20 parts by weight or more and 100 parts by weight or less, relative to 100 parts by weight of the acrylic polymer. The swelling degree of the adhesive layer to ethyl acetate is less than 100. The adhesive composition used to form the adhesive layer comprises an isocyanate crosslinking agent. The thickness of the adhesive layer is less than 35 μm. The adhesive sheet has a peel strength of 8.0 N / 10 mm or more against the stainless steel plate at 180 degrees.

2. The adhesive sheet according to claim 1, wherein, The monomer component contains more than 5.0% by weight of carboxyl-containing monomers.

3. The adhesive sheet according to claim 1 or 2, wherein, The adhesive composition used to form the adhesive layer comprises, in combination, the isocyanate crosslinking agent and the epoxy crosslinking agent.

4. The adhesive sheet according to claim 1 or 2, wherein, The adhesive layer contains a phenolic tackifying resin as the tackifying resin.

5. The adhesive sheet according to claim 4, wherein, The resin contains terpene phenol resin as the phenolic tackifying resin. The content of the terpene phenol resin is 20 parts by weight or more relative to 100 parts by weight of the acrylic polymer.

6. The adhesive sheet according to claim 1 or 2, wherein, The weight-average molecular weight of the acrylic polymer is greater than 500,000.

7. The adhesive sheet according to claim 1 or 2, wherein, The degree of swelling of the adhesive layer is 30 or more and 90 or less.

8. The adhesive sheet according to claim 1 or 2, wherein, The adhesive sheet is configured as a double-sided adhesive sheet having a resin film as a support substrate and an adhesive layer disposed on one surface and the other surface of the support substrate.

9. The adhesive sheet according to claim 1 or 2, wherein, The adhesive pad is used to secure components in portable devices.

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