Double-sided adhesive sheet for skin application

Abstract

This invention provides a double-sided adhesive sheet for skin adhesion with excellent adhesion to the object being adhered to. The double-sided adhesive sheet 1 for skin adhesion of this invention comprises a substrate layer 2 and adhesive layers 3 and 4 disposed on both sides of the substrate layer 2. One adhesive surface 3a has a surface free energy of less than 20 mJ / m² at a temperature of 23°C and a relative humidity of 50%. The other adhesive surface 4a is attached to the skin side. The double-sided adhesive sheet 1 for skin adhesion preferably has a breaking stress of 0.8 N / mm² or higher in at least one direction.

Description

Technical Field

[0001] This invention relates to a double-sided adhesive sheet for use when attached to the skin. Prior Technology

[0002] Adhesive sheets for skin adhesion are sometimes used in medical, sports, and beauty fields. These sheets require excellent adhesion to the skin and superior safety. Examples of adhesive sheets for skin adhesion include those disclosed in references 1-3. For instance, reference 3 discloses a colloidal sheet for use in brainwave measurement. [Previous Technical Documents] [Patent Literature]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-128453 [Patent Document 2] Japanese Patent Application Publication No. 2020-128454 [Patent Document 3] Japanese Patent Application Publication No. 2021-24907 Summary of the Invention

[0004] [The problem the invention aims to solve]

[0005] In recent years, for purposes such as monitoring human health status and other health care applications, various measuring instruments and other electronic devices are sometimes used by applying them to the skin. When applying these electronic devices to the skin, the use of double-sided adhesive sheets has been considered. For double-sided adhesive sheets used to apply such devices to the skin, excellent adhesion to the adhesive material is required.

[0006] The present invention was conceived under such circumstances, and its purpose is to provide a double-sided adhesive sheet for skin adhesion with excellent adhesion to the object being adhered to. [Technical means to solve the problem]

[0007] To achieve the aforementioned objectives, the inventors conducted intensive research and discovered that a double-sided adhesive sheet for skin application, having a substrate layer and a surface free energy of the adhesive surface on the patch side within a specific range, exhibits excellent adhesion to the patch. This invention is based on these insights.

[0008] That is, the present invention provides a double-sided adhesive sheet for skin application, which has a substrate layer and an adhesive layer disposed on both sides of the substrate layer, wherein the surface free energy of one adhesive surface at a temperature of 23°C and a relative humidity of 50% is less than 20 mJ / m2, and the other adhesive surface is attached to the side of the skin.

[0009] The aforementioned double-sided adhesive sheet for skin adhesion preferably has a breaking stress of 0.8 N / mm² or higher in at least one direction.

[0010] The aforementioned double-sided adhesive sheet for skin adhesion preferably has a Young's modulus of 50 MPa or less in at least one direction.

[0011] The peel strength of the adhesive surface at 23°C and 50 mm / min relative to the silicone resin substrate at 180° is preferably 2 N / 20 mm or more.

[0012] The aforementioned double-sided adhesive sheet for skin adhesion preferably has an average transmittance of 40% or more in the wavelength range of 400-700 nm, as measured according to JIS K7136-1, and an average transmittance of 40% or more in the wavelength range of 2000-2500 nm.

[0013] The surface free energy of the other adhesive surface mentioned above is preferably 20~50 mJ / m2.

[0014] The total thickness of the above-mentioned double-sided adhesive sheet for skin adhesion is preferably less than 1000 μm.

[0015] The adhesive layer providing one adhesive surface and the adhesive layer providing the other adhesive surface are preferably composed of different types of base polymers.

[0016] The adhesive layer provided for the other adhesive surface is preferably an acrylic adhesive layer containing an acrylic polymer as the base polymer.

[0017] The aforementioned double-sided adhesive sheet for skin application is preferably used for attaching electronic devices to human skin.

[0018] The aforementioned electronic device is preferably a flexible device.

[0019] Furthermore, the present invention provides an electronic device having the above-mentioned double-sided adhesive sheet for skin application. [Effects of the Invention]

[0020] The double-sided adhesive sheet for skin application of the present invention provides excellent adhesion to the applied object. Simple Explanation of the Diagram

[0021] Figure 1 is a cross-sectional schematic diagram of a double-sided adhesive sheet for skin application according to one embodiment of the present invention. Implementation

[0022] [Double-sided adhesive sheet for skin adhesion] The double-sided adhesive sheet for skin application of the present invention is a double-sided adhesive sheet used to attach one adhesive side to an object and the other adhesive side to the skin. Furthermore, in this specification, the adhesive side attached to the object is sometimes referred to as "adhesive side A" and the adhesive side attached to the skin is sometimes referred to as "adhesive side B". Also, the adhesive layer providing adhesive side A is sometimes referred to as "adhesive layer A" and the adhesive layer providing adhesive side B is sometimes referred to as "adhesive layer B".

[0023] In the aforementioned double-sided adhesive sheet for skin adhesion, the surface free energy of the aforementioned adhesive surface (adhesive surface A) at a temperature of 23°C and a relative humidity of 50% is less than 20 mJ / m², preferably less than 18 mJ / m². By ensuring that the surface free energy is less than 20 mJ / m², adhesive surface A exhibits excellent adhesion to the substrate (especially substrates with low surface free energy).

[0024] The surface free energy of the other adhesive surface (adhesive surface B) at a temperature of 23°C and a relative humidity of 50% is preferably 20~50 mJ / m², more preferably 20.5~40 mJ / m². If the surface free energy is within the above range, then adhesive surface B has better adhesion to the skin.

[0025] The surface free energy γ of the adhesive surface is expressed by the following formula: γ = γd + γp + γh. Here, γd, γp, and γh in the above formula represent the dispersion component, polar component, and hydrogen bond component of the surface free energy, respectively. The surface free energy γ of the adhesive surface can be obtained by using water, diiodomethane, and 1-bromonaphthalene as probe solutions, and by using the Kitazaki-Hatake formula (Japan Adhesion Association Journal, Vol. 8, No. 3, 1972, pp. 131-141) based on the contact angle of each probe solution. The contact angle can be measured using a commercially available contact angle meter. As a contact angle meter, the product name "DMo-701" manufactured by Kyowa Interface Science Co., Ltd. can be used. The measurement is performed using the droplet method, and the contact angle is determined based on the shape of the droplet after 1000 ms. The same method is also used in the following examples.

[0026] The peel strength of adhesive surface A relative to the silicone resin substrate at a temperature of 23°C and a peel speed of 50 mm / min is preferably 2 N / 20 mm or more, more preferably 2.5 N / 20 mm or more, and even more preferably 4 N / 20 mm or more. If the peel strength is 2 N / 20 mm or more, then adhesive surface A exhibits excellent adhesion to the attached material.

[0027] The aforementioned double-sided adhesive sheet for skin adhesion comprises at least a substrate layer and adhesive layers disposed on both sides of the substrate layer. Specifically, it comprises at least a substrate layer, an adhesive layer providing adhesive surface A, and an adhesive layer providing adhesive surface B.

[0028] The adhesive layer disposed on the side providing adhesive surface A and the adhesive layer disposed on the side providing adhesive surface B can each be a single layer or multiple layers. The plurality of adhesive layers provided by the above-mentioned double-sided adhesive sheet for skin adhesion can be the same adhesive layer or adhesive layers with different compositions, thicknesses, physical properties, etc.

[0029] Adhesive layer A and adhesive layer B can be identical adhesive layers, or they can be adhesive layers with different thicknesses, physical properties, or compositions. Preferably, adhesive layer A and adhesive layer B have different compositions. Specific examples of different compositions include differences in the type of base polymer, the composition of monomer components constituting the base polymer (such as the type or ratio of structural units), and the composition of components other than the base polymer.

[0030] Figure 1 is a cross-sectional schematic diagram showing one embodiment of the double-sided adhesive sheet of the present invention. As shown in Figure 1, the double-sided adhesive sheet 1 for skin adhesion includes: a substrate layer 2, an adhesive layer (adhesive layer A) 3 disposed on one side of the substrate layer 2, and an adhesive layer (adhesive layer B) 4 disposed on the other side of the substrate layer 2. The adhesive layer 3 has an adhesive surface A (3a) for adhering to the object being adhered to, and the adhesive layer 4 has an adhesive surface B (4a) for adhering to the skin. Adhesive layers 3 and 4 are adhesive layers with different compositions.

[0031] (Substrate layer) The aforementioned substrate layer is a component that functions as a support in the double-sided adhesive sheet for skin adhesion. By including this substrate layer, the double-sided adhesive sheet for skin exhibits excellent operability; for example, it can be easily peeled off when removing the adhesive from the skin. The substrate layer can be a single layer or a laminate of the same or different substrates.

[0032] Examples of resins constituting the aforementioned substrate layer include: polyethylene resins (e.g., low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-low-density polyethylene), polypropylene resins (e.g., random copolymer polypropylene, block copolymer polypropylene, homopolymer polypropylene), polybutene, polymethylpentene, ethylene-vinyl acetate copolymer (EVA), ionomers, ethylene-(meth)acrylate copolymers, ethylene-(meth)acrylate (random, alternating) copolymers, ethylene-butene copolymers, ethylene-hexene copolymers, and other polyolefin resins; ether-based resins. Polyurethanes, including polyurethane-based, ester-based, and carbonate-based polyurethanes; polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PET), and polybutylene terephthalate (PBT); polycarbonate; polyimide; polyetheretherketone; polyetherimide; aromatic polyamides and fully aromatic polyamides; polyphenylene sulfide; fluoropolymers; polyvinyl chloride; polyvinylidene chloride; cellulose resins such as triacetin cellulose (TAC); silicone resins; acrylic resins such as polymethyl methacrylate (PMMA); polyvinyl acetate; polyurethane; and polyarylates. Only one of the above resins may be used, or two or more may be used. Furthermore, in this specification, the above-mentioned substrate layer does not include the release liner (release film) that is peeled off during the use (attachment) of the double-sided adhesive sheet.

[0033] Examples of substrate layers include: plastic substrates (e.g., plastic films), porous materials such as paper, cloth, and non-woven fabrics, meshes, and foamed sheets. More specifically, examples of substrate layers include: thermoplastic elastomer films based on polystyrene, or plastic films such as nylon, polyester, polyethylene, polypropylene, and polyurethane; woven or non-woven fabrics, braided fabrics, and paper containing synthetic or natural organic polymers such as cellulose; and laminates of two or more of these (laminates of fabric or paper, laminates of film and fabric, laminates of plastic films, etc.).

[0034] Of the aforementioned substrate layers, non-woven fabric or plastic substrates are preferred from the viewpoint of excellent transparency. Among the aforementioned plastic substrates, polyurethane-based substrates, polypropylene-based substrates, polyethylene-based substrates, ethylene-vinyl acetate-based substrates, and silicone-based substrates are more preferred. Especially from the viewpoints of softness (skin conformability), moderate moisture permeability, and tensile strength, polyurethane-based films are preferred, particularly polyester-based or polyether-based polyurethane films. Excellent softness results in excellent conformability to skin movements when the flexible device, as an adhesive, is attached to the skin.

[0035] The aforementioned substrate layer may also be formulated with various additives such as fillers (inorganic fillers, organic fillers, etc.), colorants (pigments or dyes), dispersants (surfactants, etc.), anti-aging agents, antioxidants, ultraviolet absorbers, antistatic agents, lubricants, and plasticizers. The formulation ratio of each additive relative to the total mass of the aforementioned substrate layer is approximately 30% by weight (e.g., less than 20% by weight, typically less than 10% by weight).

[0036] The aforementioned substrate layer may also include auxiliary layers. Examples of such auxiliary layers include: a coloring layer, a primer layer, and an antistatic layer disposed on the surface of the aforementioned substrate layer.

[0037] To improve adhesion and retention with the adhesive layer, the surface of the substrate layer may undergo physical treatments such as corona discharge treatment, plasma treatment, sanding treatment, ozone exposure treatment, flame exposure treatment, high voltage electric shock exposure treatment, and ionization radiation treatment; chemical treatments such as chromic acid treatment; and surface treatments utilizing the adhesion-enhancing properties of the coating agent (primer). Surface treatments to improve adhesion are preferably applied to the entire surface of the substrate layer.

[0038] From the viewpoint of superior flexibility, the thickness of the aforementioned substrate layer is preferably 500 μm or less, more preferably 250 μm or less, and even more preferably 50 μm or less. Furthermore, from the viewpoint of superior function and operability as a support, the thickness of the aforementioned substrate layer is preferably 1 μm or more, and more preferably 5 μm or more.

[0039] When using woven or non-woven fabrics or paper as the base layer, it is preferable to use a base weight of around 8 to 200 g / m².

[0040] (Adhesive layer) The aforementioned double-sided adhesive sheet for skin adhesion has at least an adhesive layer A and an adhesive layer B. Alternatively, the aforementioned double-sided adhesive sheet for skin adhesion may have other adhesive layers besides adhesive layers A and B between the substrate layer and adhesive layer A or adhesive layer B.

[0041] The adhesives used in the various adhesive layers constituting the aforementioned double-sided adhesive sheet for skin adhesion are not particularly limited. Examples include: acrylic adhesives, rubber adhesives (natural rubber, synthetic rubber, and mixtures thereof), silicone adhesives, polyester adhesives, urethane adhesives, polyether adhesives, polyamide adhesives, and fluorinated adhesives. Only one type of adhesive may be used, or two or more types may be used.

[0042] <Adhesive layer A> From the viewpoint that it is easy to design an adhesive layer with low surface free energy as the adhesive constituting adhesive layer A, a silicone-based adhesive is preferred. That is, adhesive layer A is preferably a silicone-based adhesive layer composed of a silicone-based adhesive.

[0043] The aforementioned silicone adhesives are not particularly limited, and can be appropriately selected from well-known or commonly used silicone adhesives. Examples of such silicone adhesives include: peroxide cross-linking silicone adhesives (peroxide-curing silicone adhesives), addition-type silicone adhesives, and condensation-type silicone adhesives. Addition-reaction silicone adhesives are preferred. The aforementioned silicone adhesives can be either one-component or two-component. Only one type of silicone adhesive can be used, or two or more types can be used.

[0044] The aforementioned addition-type silicone adhesives are generally produced by using platinum compounds such as chloroplatinic acid as catalysts to induce an addition reaction (hydrosiliconization) between organopolysiloxanes with vinyl or other alkenyl groups on their silicon atoms and organopolysiloxanes with hydrosilyl groups, thus generating silicone polymer adhesives. Peroxide-cured silicone adhesives are generally produced by using peroxides to harden (crosslink) organopolysiloxanes, thus generating silicone polymer adhesives. Furthermore, condensation-type silicone adhesives are generally produced by the dehydration or de-alcoholization reaction between polyorganosiloxanes with hydrolyzable silanol or alkoxysilyl groups at the ends, thus generating silicone polymer adhesives.

[0045] Examples of silicone-based adhesives include silicone rubber and silicone resin compositions. These silicone-based adhesives may also contain additives such as crosslinking agents, catalysts (hardeners), fillers, plasticizers, anti-aging agents, antistatic agents, and colorants (pigments or dyes, etc.), as needed.

[0046] As for the aforementioned silicone rubber, there are no particular limitations as long as it is a silicone-based rubber component. For example, organic polysiloxanes with dimethylsiloxane, methylphenylsiloxane, etc., as the main structural units can be used. Furthermore, depending on the type of reaction, examples include: silicone-based rubbers with alkenyl groups bonded to silicon atoms (organopolysiloxanes containing alkenyl groups, addition reaction type), silicone-based rubbers with at least methyl groups (peroxide curing type), and silicone-based rubbers with silanol groups or hydrolyzable alkoxysilyl groups at the ends (condensation type). Moreover, the weight average molecular weight of the organic polysiloxane in the silicone rubber is, for example, 150,000 or more, preferably 280,000 to 1,000,000, and more preferably 500,000 to 900,000.

[0047] The aforementioned silicone resin is not particularly limited as long as it is a silicone-based resin used in silicone adhesives. Examples include silicone resins comprising organopolysiloxanes, wherein the organopolysiloxane comprises a (co)polymer having at least one unit selected from the group consisting of an M unit containing the structural unit "R 3Si 1 / 2", a Q unit containing the structural unit "SiO 2", a T unit containing the structural unit "RSiO 3 / 2", and a D unit containing the structural unit "R 2SiO". Furthermore, R in the aforementioned structural unit represents a hydrocarbon group or a hydroxyl group. Examples of such hydrocarbon groups include: aliphatic hydrocarbon groups (alkyl groups such as methyl and ethyl), alicyclic hydrocarbon groups (cyclohexyl and cycloalkyl groups), and aromatic hydrocarbon groups (aryl groups such as phenyl and naphthyl). The ratio of the aforementioned M unit to at least one unit selected from Q, T, and D units is, for example, preferably, a molar ratio of approximately 0.3 / 1 to 1.5 / 1 (preferably 0.5 / 1 to 1.3 / 1). Various functional groups, such as vinyl groups, may also be introduced into the organopolysiloxane in this silicone resin as needed. Furthermore, the introduced functional groups can also be functional groups capable of undergoing cross-linking reactions. The silicone resin is preferably an MQ resin containing both M and Q units. The weight-average molecular weight of the organopolysiloxane in the silicone resin is, for example, 1000 or more, preferably 1000 to 20000, and more preferably 1500 to 10000.

[0048] There is no particular limitation on the mixing ratio of silicone rubber and silicone resin. For example, relative to 100 parts by mass of silicone rubber, the silicone resin is preferably 100 to 220 parts by mass, and more preferably 120 to 180 parts by mass.

[0049] Furthermore, silicone rubber and silicone resin in a silicone adhesive composition containing such materials can be in a simple mixed state, or they can react with each other to become condensates (especially partial condensates), crosslinking reactants, addition reaction products, etc.

[0050] Furthermore, in silicone-based adhesive compositions containing silicone rubber and silicone resin, a crosslinking agent is typically included to form a crosslinked structure. This crosslinking agent is not particularly limited, but examples include: siloxane-based crosslinking agents (silicone-based crosslinking agents) and peroxide-based crosslinking agents. Only one type of crosslinking agent may be used, or two or more may be used.

[0051] As a siloxane-based crosslinking agent, polyorganohydrosiloxanes having two or more hydrogen atoms bonded to silicon atoms in the molecule are preferably used, for example. In such polyorganohydrosiloxanes, various organic groups other than hydrogen atoms may be bonded to the silicon atoms bonded to hydrogen atoms. Examples of such organic groups include alkyl groups such as methyl and ethyl, or aryl groups such as phenyl, as well as halogenated alkyl groups. From a synthetic or operational point of view, alkyl groups are preferred, and methyl groups are particularly preferred. Furthermore, the skeletal structure of the polyorganohydrosiloxane can have any of the following: linear, branched, or cyclic skeletal structures, with a linear structure being preferred.

[0052] Examples of peroxide-based crosslinking agents include: diacetyl peroxide, alkyl peroxide esters, dicarbonate peroxide, monocarbonate peroxide, peroxy ketal, dialkyl peroxide, hydrogen peroxide, and ketone peroxide. More specifically, examples include: benzoyl peroxide, tributyl benzoate peroxide, diisopropylphenyl peroxide, tributylisopropylphenyl peroxide, di-tributyl peroxide, 2,5-dimethyl-2,5-di-tributylhexane peroxide, 2,4-dichlorobenzoyl peroxide, di-tributylperoxy-diisopropylbenzene, 1,1-bis(tributylperoxy)-3,3,5-trimethylcyclohexane, and 2,5-dimethyl-2,5-di-tributylhexyne-peroxide.

[0053] Examples of commercially available addition-curing silicone adhesives include: "KR-3700", "KR-3701", "X-40-3237-1", "X-40-3240", and "X-40-3291-1" (all manufactured by Shin-Etsu Chemical Industry Co., Ltd.). Similarly, examples of commercially available peroxide-curing silicone adhesives include: "KR-100", "KR-101-10", and "KR-130" (all manufactured by Shin-Etsu Chemical Industry Co., Ltd.).

[0054] The aforementioned silicone-based adhesive layer can be manufactured by, for example, by coating (applying) the adhesive composition used to form adhesive layer A onto the aforementioned substrate layer or release liner, allowing the obtained adhesive composition layer to dry and harden, or by coating (applying) the aforementioned adhesive composition onto the aforementioned substrate layer or release liner, and irradiating the obtained adhesive composition layer with active energy lines to harden it. Alternatively, heating and drying can be performed as needed.

[0055] Examples of active energy rays include ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, or ultraviolet radiation, with ultraviolet radiation being particularly preferred. Furthermore, there are no particular limitations on the irradiation energy, irradiation time, or irradiation method of the active energy rays.

[0056] Furthermore, the coating (application) of the above-mentioned adhesive composition can be performed using known coating methods. For example, gravure roller coating machines, reverse roller coating machines, contact roller coating machines, dip roller coating machines, rod coating machines, doctor blade coating machines, spray coating machines, corner wheel coating machines, direct coating machines, and other coating machines can be used.

[0057] The thickness of adhesive layer A is, for example, 5 to 500 μm, preferably 50 to 200 μm. If the thickness is 5 μm or more, the adhesion to the attached material is better. If the thickness is 500 μm or less (especially 200 μm or less), the thickness of the double-sided adhesive sheet can be reduced.

[0058] <Adhesive layer B> From the viewpoint of skin adhesion and safety, an acrylic adhesive is preferred as the adhesive constituting adhesive layer B. That is, the aforementioned adhesive layer is preferably an acrylic adhesive layer composed of an acrylic adhesive.

[0059] The aforementioned acrylic adhesive layer contains an acrylic polymer as its base polymer. This acrylic polymer is a polymer that includes acrylic monomers (monomers having a (meth)acrylic group in their molecule) as monomeric components of the polymer. That is, the aforementioned acrylic polymer contains structural units derived from acrylic monomers. Furthermore, only one type of acrylic polymer may be used, or two or more types may be used.

[0060] Furthermore, in this specification, the base polymer refers to the main component of the polymer composition used in the adhesive layer, for example, containing more than 50% by mass of the polymer composition. The content ratio of the acrylic polymer in the aforementioned acrylic adhesive layer relative to 100% by mass of the total acrylic adhesive layer is preferably 60% by mass or more, and more preferably 70% by mass or more.

[0061] The aforementioned acrylic polymers are preferably polymers composed (formed) of alkyl (meth)acrylate as an essential monomer component. That is, the aforementioned acrylic polymers preferably contain alkyl (meth)acrylate as a structural unit. Furthermore, in this specification, "(meth)acrylate" means "acrylic acid" and / or "methacrylic acid" (either or both of "acrylic acid" and "methacrylic acid"), and so on.

[0062] Regarding the aforementioned alkyl (meth)acrylates as essential monomeric components, alkyl (meth)acrylates having straight-chain or branched alkyl groups are preferably examples. Furthermore, only one of the aforementioned alkyl (meth)acrylates may be used, or two or more may be used.

[0063] There is no particular limitation as to alkyl methacrylates having straight-chain or branched alkyl groups, and examples include: methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, dibutyl methacrylate, terbutyl methacrylate, pentyl methacrylate, isoamyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, nonyl methacrylate, and iso... Nonyl acrylate, decyl acrylate, isodecyl acrylate, undecyl acrylate, dodecyl acrylate (lauryl acrylate), tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecanyl acrylate, stearyl acrylate, isostearyl acrylate, nonadecanyl acrylate, eicosyl acrylate, and other alkyl acrylates having straight or branched alkyl groups with 1 to 20 carbon atoms.

[0064] As an alkyl methacrylate having a straight-chain or branched alkyl group, it is preferred to be an alkyl methacrylate having a straight-chain or branched alkyl group having 6 or more carbon atoms (preferably 6 to 18). If the number of carbon atoms is 6 or more (especially 6 to 18), it is less irritating to the skin and is less likely to cause a decrease in adhesion even with prolonged use.

[0065] The aforementioned acrylic polymers may also contain other monomers (copolymeric monomers) capable of copolymerizing with the aforementioned (meth)acrylate, which have linear or branched alkyl groups, as monomeric components constituting the polymer. That is, the aforementioned acrylic polymers may also contain copolymeric monomers as structural units. Only one type of copolymeric monomer may be used, or two or more types may be used.

[0066] Examples of the aforementioned comonomers include: monomers containing carboxyl groups, monomers containing hydroxyl groups, monomers containing epoxy groups, monomers containing ketone groups, monomers containing alkoxy groups, monomers containing sulfonic acid groups, monomers containing phosphate groups, vinyl ester monomers, vinyl ether monomers, monomers containing isocyanate groups, aromatic vinyl compounds, alicyclic monomers, (meth)acrylates containing aromatic rings, chlorinated monomers, nitrogen-containing monomers, etc.

[0067] Adhesive layer B may also contain, as needed and without compromising the effects of the present invention, additives such as adhesive-improving resin, fillers, crosslinking agents, crosslinking accelerators, anti-aging agents, antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, foils, rust inhibitors, and colorants (pigments or dyes). Only one of the above additives may be used, or two or more may be used.

[0068] The adhesive layer B can be in any form, such as emulsion type, solvent type (solution type), active energy line curing type, heat-melting type (heat-melting type), etc. Among these, solvent type and active energy line curing type adhesive compositions are preferred in terms of ease of obtaining an adhesive layer with excellent production performance.

[0069] Examples of the aforementioned active energy lines include ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, or ultraviolet radiation, with ultraviolet radiation being particularly preferred. That is, the aforementioned active energy line-cured adhesive layer is preferably an ultraviolet-cured adhesive layer.

[0070] There are no particular limitations on the method for preparing the acrylic adhesive layer. For example, one could apply an adhesive (adhesive composition) containing the aforementioned acrylic polymer to the aforementioned substrate layer or release liner, and allow the resulting adhesive composition layer to dry and harden. Alternatively, one could apply the aforementioned adhesive composition to the substrate or release liner and irradiate the resulting adhesive composition layer with active energy lines to harden it. Furthermore, heating and drying may be performed as needed.

[0071] The above-described adhesive compositions can be prepared by known or conventional methods. For example, solvent-based adhesive compositions can be prepared by adding additives as needed to a solution containing the above-described acrylic polymer. For example, active energy line curing adhesive compositions can be prepared by adding additives as needed to a mixture of monomer components constituting the above-described acrylic polymer or a portion thereof.

[0072] Furthermore, the coating (application) of the above-mentioned adhesive composition can be performed using known coating methods. For example, gravure roller coating machines, reverse roller coating machines, contact roller coating machines, dip roller coating machines, rod coating machines, doctor blade coating machines, spray coating machines, corner wheel coating machines, direct coating machines, and other coating machines can be used.

[0073] The preferred heating and drying temperature for the solvent-based adhesive composition is 40-200°C, more preferably 50-180°C, and even more preferably 70-170°C. The drying time can be appropriately set, for example, 5 seconds to 20 minutes, preferably 5 seconds to 10 minutes, and more preferably 10 seconds to 5 minutes.

[0074] When adhesive layer B is formed by irradiation with active energy rays, the aforementioned acrylic polymer can be manufactured from the monomer components described above, and the adhesive layer can be formed. The monomer components described above can be partially polymerized and prepared into a slurry before irradiation with active energy rays. High-pressure mercury lamps, low-pressure mercury lamps, metal halide lamps, etc., can be used for ultraviolet irradiation.

[0075] The thickness of adhesive layer B is, for example, 10-200 μm, preferably 20-60 μm. If the thickness is 10 μm or more (especially 20 μm or more), the skin conformability and adhesion are superior. If the thickness is 200 μm or less (especially 60 μm or less), the thickness of the double-sided adhesive sheet can be reduced.

[0076] (Double-sided adhesive sheet for skin adhesion) The thickness (total thickness) of the aforementioned double-sided adhesive sheet for skin adhesion is preferably less than 1000 μm, more preferably less than 500 μm, and even more preferably less than 400 μm. If the thickness is less than 1000 μm, the flexibility is excellent, and the ability to follow skin movements is even better. Furthermore, the thickness of the double-sided adhesive sheet can be reduced. The thickness is preferably 40 μm or more, more preferably 80 μm or more, even more preferably 100 μm or more, and particularly preferably 130 μm or more. If the thickness is 40 μm or more (especially 80 μm or more), the adhesion between the adhesive and the skin is even better. Moreover, the thickness of the aforementioned double-sided adhesive sheet for skin adhesion refers to the thickness from adhesive surface A to adhesive surface B, i.e., the thickness of the adhesive body, excluding the release liner. Furthermore, in this specification, the structure comprising adhesive layer A, the aforementioned substrate layer and adhesive layer B, in which both adhesive surface A and adhesive surface B are adhesive surfaces, is sometimes referred to as an "adhesive body".

[0077] The fracture stress of the double-sided adhesive sheet for skin adhesion (the adhesive) in at least one direction is preferably 0.8 N / mm² or more, more preferably 1.0 N / mm² or more, further preferably 2.0 N / mm² or more, and even more preferably 5.0 N / mm² or more. If the fracture stress is 0.8 N / mm² or more, the adhesive layer is less prone to fracture during stretching, resulting in excellent skin-responsiveness when the flexible device, as an adhesive, is attached to the skin. The fracture stress was measured with a sample shaped like a dumbbell (size 3), at a clamping distance of 50 mm, a stretching speed of 50 mm / min, and at 23°C and 50% RH (relative humidity). In particular, it is preferable that the fracture stress of the substrate layer in at least one direction, either the MD direction (Machine direction) or the TD direction (Transverse direction), is within the aforementioned range, and more preferably that both directions' fracture stresses are within the aforementioned range.

[0078] The Young's modulus of the aforementioned double-sided adhesive sheet for skin adhesion (the aforementioned adhesive) in at least one direction is preferably 50 MPa or less, more preferably 15 MPa or less, and even more preferably 5 MPa or less. If the Young's modulus is 50 MPa or less, the skin's movement is well-followed when the flexible device used as the adhesive is attached to the skin. The Young's modulus of the aforementioned double-sided adhesive sheet for skin adhesion (the aforementioned adhesive) in at least one direction is, for example, 0.5 MPa or more. The aforementioned Young's modulus is a value measured with the sample shape set to dumbbell type 3, and under conditions of a clamping distance of 50 mm, a stretching speed of 50 mm / min, at 23°C and 50%RH. In particular, it is preferable that the Young's modulus of the aforementioned substrate layer in at least one of the MD and TD directions is within the aforementioned range, and more preferably that both Young's moduli are within the aforementioned range.

[0079] The elongation at break of the aforementioned double-sided adhesive sheet for skin adhesion (the aforementioned adhesive) in at least one direction is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more. If the elongation at break is 50% or more, the adhesive layer is less prone to breakage during stretching, resulting in excellent skin-responsiveness when the flexible device, as an adhesive, is attached to the skin. The aforementioned elongation at break is measured with the sample shaped as a dumbbell (size 3), at a clamping distance of 50 mm, a stretching speed of 50 mm / min, and at 23°C and 50% RH. In particular, it is preferable that the elongation at break of the aforementioned substrate layer in at least one of the MD and TD directions is within the aforementioned range, and more preferably that both directions are within the aforementioned range.

[0080] The average transmittance of the aforementioned double-sided adhesive sheet for skin adhesion (the aforementioned adhesive) measured according to JIS K7136-1, at wavelengths of 400-700 nm, is preferably 40% or more, more preferably 50% or more, and even more preferably 80% or more. If the average transmittance is 40% or more, the transmittance of visible light is high, the transparency of the double-sided adhesive sheet is excellent, and the visibility when adhered to the skin is excellent.

[0081] The average transmittance of the aforementioned double-sided adhesive sheet for skin adhesion (the aforementioned adhesive) at wavelengths of 2000-2500 nm, as measured according to JIS K7136-1, is preferably 40% or more, more preferably 50% or more, and even more preferably 80% or more. If the average transmittance is 40% or more, the infrared transmittance is high, and the photosensing function is excellent.

[0082] The aforementioned double-sided adhesive sheet for skin adhesion can have a release liner attached to the surface of the adhesive layer (adhesive side) before use. Furthermore, each adhesive side of the aforementioned double-sided adhesive sheet for skin adhesion can be protected by two release liners, or by a single release liner with release surfaces on both sides, wound into a roll (wound body). The release liner serves as a protective material for the adhesive layer and is peeled off when adhered to the substrate. Alternatively, the release liner may not be necessary.

[0083] The release liner described above can use conventional release paper or the like, and is not particularly limited. Examples include: a substrate with a release treatment layer, a low-adhesion substrate containing a fluoropolymer, or a low-adhesion substrate containing a non-polar polymer. Examples of substrates with a release treatment layer include plastic films or papers that have undergone surface treatment with silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide release agents. Examples of fluoropolymers in the low-adhesion substrate containing a fluoropolymer include: polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and chlorofluoroethylene-vinylidene fluoride copolymer. Examples of non-polar polymers include: olefin resins (e.g., polyethylene, polypropylene). Furthermore, the release liner can be formed by known or conventional methods. The thickness of the release liner is also not particularly limited.

[0084] The aforementioned double-sided adhesive sheet for skin adhesion exhibits excellent adhesion to the applied material and is used for attaching the applied material to the skin. The applied material is not particularly limited, but electronic devices can be cited as examples. From the viewpoint that the adhesive surface A of the aforementioned double-sided adhesive sheet for skin adhesion exhibits particularly excellent adhesion to materials containing silicon atoms, such as silicon oxide or silicone resin, electronic devices are especially preferred as the applied material. By attaching the aforementioned double-sided adhesive sheet for skin to an electronic device, an electronic device incorporating the aforementioned double-sided adhesive sheet for skin can be manufactured.

[0085] Furthermore, when the aforementioned double-sided adhesive sheet for skin exhibits excellent adhesion to both the skin and the attached object, as well as excellent softness, it also demonstrates excellent tracking ability of skin movements and is less prone to peeling off. Therefore, the attached object can be any of a rigid device, a semi-flexible device, or a flexible device, preferably a flexible device. Moreover, the aforementioned skin is particularly preferably human skin. Furthermore, the aforementioned double-sided adhesive sheet for skin attachment exhibits excellent photosensing function due to its excellent transparency. [Example]

[0086] The following examples illustrate the present invention in more detail, but the present invention is not limited to these examples.

[0087] Example 1 (Preparation of silicone adhesive layer) An addition-type silicone adhesive (trade name "KR-3700", manufactured by Shin-Etsu Chemical Co., Ltd.) was diluted with toluene and coated onto the release-treated surface of a 50 μm thick polyester film (trade name "DIAFOIL MRS", manufactured by Mitsubishi Chemical Co., Ltd.) that had undergone release treatment with a silicone-based release agent on one side. The film was then dried at 140°C for 8 minutes to form and produce an adhesive layer (silicone adhesive layer) with a thickness of 100 μm.

[0088] (Double-sided adhesive sheet) A silicone-based adhesive layer is bonded to the surface of a skin-adhesive tape (trade name "ST-276", manufactured by Nitto Denko Corporation) with a release liner layer on the surface of the adhesive layer, one side of which has an adhesive layer formed. Thus, a double-sided adhesive sheet is formed by laminating an adhesive layer and a silicone-based adhesive layer on both sides of the substrate layer, and then laminating a release liner layer on each of the adhesive layers.

[0089] Example 2 The double-sided adhesive sheet was prepared in the same manner as in Example 1, except that a skin-adhesive tape (trade name "ST-279", manufactured by Nitto Denko Co., Ltd.) was used instead of a skin-adhesive tape (trade name "ST-276", manufactured by Nitto Denko Co., Ltd.).

[0090] Example 3 The double-sided adhesive sheet was prepared in the same manner as in Example 1, except that a skin-adhesive tape (trade name "ST-245", manufactured by Nitto Denko Co., Ltd.) was used instead of a skin-adhesive tape (trade name "ST-276", manufactured by Nitto Denko Co., Ltd.).

[0091] Example 4 The double-sided adhesive sheet was prepared in the same manner as in Example 1, except that a skin-adhesive tape (trade name "ST-2410", manufactured by Nitto Denko Co., Ltd.) was used instead of a skin-adhesive tape (trade name "ST-276", manufactured by Nitto Denko Co., Ltd.).

[0092] Comparative Example 1 (Rubber-based adhesive layer) Hydrogenated styrene-isoprene-styrene block copolymer (trade name "2563NS", manufactured by Zongyan Chemical Co., Ltd.), which serves as the base polymer, was dissolved in toluene, and the solid content concentration was adjusted to 25% by mass to prepare an adhesive composition. This adhesive composition was coated onto the release-treated surface of a 38 μm thick polyester film (trade name "DIAFOIL MRF", manufactured by Mitsubishi Chemical Co., Ltd.), which had been treated with a silicone-based release agent on one side. The film was then dried at 120°C for 3 minutes to form and produce an adhesive layer (rubber-based adhesive layer) with a thickness of 50 μm.

[0093] (Double-sided adhesive sheet) The double-sided adhesive sheet was prepared in the same manner as in Example 1, except that the rubber-based adhesive layer described above was used instead of the silicone-based adhesive layer.

[0094] Comparative Example 2 The double-sided adhesive sheet prepared in Example 1 was used. However, in the following evaluation, the adhesive layer and silicone-based adhesive layer of the skin-adhesive tape were applied in the opposite manner to those in Example 1.

[0095] Comparative Example 3 (Acrylic adhesive layer) 40 parts by weight of butyl acrylate (BA), 40 parts by weight of cyclohexyl acrylate (CHA), 20 parts by weight of 4-hydroxybutyl acrylate (4-HBA), 0.05 parts by weight of 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name "Ominrad 651", manufactured by IGM Resins BV) as a photopolymerization initiator, and 0.05 parts by weight of 1-hydroxycyclohexylphenyl ketone (trade name "Ominrad 184", manufactured by IGM Resins BV) were mixed and irradiated with ultraviolet light under a nitrogen atmosphere to prepare a partial polymer (monomer slurry). 0.1 parts by weight of dipentaerythritol hexaacrylate (DPHA) (trade name "KAYARAD DPHA", manufactured by Nippon Kayaku Co., Ltd.) was added to the obtained monomer slurry and mixed uniformly to prepare an adhesive composition.

[0096] A coating layer was formed by applying the prepared adhesive composition to the release-treated side of a 38 μm thick polyester film (trade name "DIAFOIL MRF", manufactured by Mitsubishi Chemical Co., Ltd.) that had undergone release treatment with a silicone-based release agent on one side. Then, a 38 μm thick polyester film (trade name "DIAFOIL MRE", manufactured by Mitsubishi Chemical Co., Ltd.) that had undergone release treatment with silicone on one side was placed over the surface of the coating layer, with the release-treated side of the film becoming the coating layer side. This blocked oxygen, protecting the coating layer from its effects. The coated sheet obtained in this manner was then irradiated with ultraviolet light at an illuminance of 5 mW / cm² for 360 seconds using a chemical lamp (manufactured by Toshiba Corporation), thereby hardening the coating layer to form and produce a 50 μm thick adhesive layer (acrylic adhesive layer). Furthermore, the above illuminance values ​​were measured using an industrial UV detector (trade name "UVR-T1", manufactured by TOPCON Co., Ltd., light-receiving part model UD-T36) with a peak sensitivity wavelength of approximately 350 nm.

[0097] (Double-sided adhesive sheet) The acrylic adhesive layer described above is used instead of the silicone adhesive layer. Otherwise, the double-sided adhesive sheet is prepared in the same manner as in Example 1.

[0098] <Evaluation> The adhesive layers and double-sided adhesive sheets obtained in the examples and comparative examples were evaluated as follows. The results are shown in the table.

[0099] (1) Surface free energy For the two adhesive surfaces of the double-sided adhesive sheets prepared in the examples and comparative examples, the contact angles with water, diiodomethane, and 1-bromonaphthalene were measured using a contact angle meter (product name "DMo-701", manufactured by Kyowa Interface Science Co., Ltd.). Then, the surface free energy was calculated using the obtained contact angle values ​​and according to the Kitazaki-Hatake formula.

[0100] (2) Young's modulus and elongation at break The double-sided adhesive sheets obtained in the examples and comparative examples were punched into dumbbell No. 3 shapes (according to JIS K6251, width 5 mm). All release liner was peeled off to expose the adhesive sheet. Under conditions of 23°C and 50% RH, all release liner was peeled off again to expose the adhesive sheet. A tensile testing machine (product name "Autograph AG-10G tensile testing machine", manufactured by Shimadzu Corporation) was used to stretch the test piece until it broke at a clamping distance of 50 mm and a tensile speed of 50 mm / min. The Young's modulus was then calculated based on the obtained displacement and stress results. Furthermore, the initial clamping distance of the test piece was set to 0%, and the difference in elongation at break between the initial clamping distance and the initial clamping distance was divided as the elongation at break. Moreover, the tensile tests were performed in both the MD and TD directions of the substrate layer.

[0101] (3) Fracture stress The double-sided adhesive sheet obtained in the examples and comparative examples was punched into a dumbbell No. 3 shape (according to JIS K6251, width 5 mm). All release liner was peeled off to expose the adhesive sheet. It was placed in a tensile testing machine "Autograph AG-I" (manufactured by Shimadzu Corporation) with a clamping distance of 50 mm in the length direction and stretched at a tensile speed of 50 mm / min until it broke, thereby measuring the load (breakage stress).

[0102] (4) Transmission rate After completely peeling off the backing from the double-sided adhesive sheets obtained in the examples and comparative examples, the total light transmittance in the thickness direction of the double-sided adhesive sheets was measured using a UV-Vis-NIR spectrophotometer (device name "SolidSpec", manufactured by Shimadzu Corporation). Then, the average transmittance at wavelengths of 400~700 nm and the average transmittance at wavelengths of 2000~2500 nm were calculated respectively.

[0103] (5) Adhesion of the side surface of the adhesive to the attached object Under a testing environment of 23°C and 50%RH, a 25 μm thick PET film was attached to the skin-side adhesive surface (refer to Table 1) of the double-sided adhesive sheets obtained in the examples and comparative examples to serve as a substrate. The substrate was then cut into pieces with a width of 20 mm and a length of 100 mm to prepare test samples. For the prepared test samples, under a testing environment of 23°C and 50%RH, the adhesive surface (refer to Table 1) of the above-mentioned test samples was pressed onto a silicone rubber sheet (trade name "QP1-70", manufactured by Dow Toray Co., Ltd.) by passing a 2 kg roller back and forth once. After being placed in the same environment for 30 minutes, the 180° peel strength was measured using a 3-strand tensile testing machine (product name "AG-X plus", manufactured by Shimadzu Corporation) according to JIS Z0237:2000, at a tensile speed of 50 mm / min and a peel angle of 180°.

[0104] (6) Adhesion of the skin side surfaces The double-sided adhesive sheets obtained in the examples and comparative examples were cut into rectangles with a width of 50 mm and a length of 50 mm. A 5 μm thick PET film was attached to the adhesive side of the sheet to serve as a substrate. The adhesive side of the sheet was then attached to the forearm of five volunteers. The curling of the ends of the double-sided adhesive sheets after 3 hours at room temperature in this state was evaluated based on the following three stages. The results for Examples 1-4 were all 3. (The situation of curling up) 3: No curling; 2: Slight curling at the end; 1: More than half curled.

[0105] [Table 1] (Table 1) Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Double-sided adhesive sheet Adhesive side Adhesive side Adhesive side Adhesive side Adhesive side Adhesive side Adhesive side Silicone adhesive layer Silicone adhesive layer Silicone adhesive layer Silicone adhesive layer Rubber adhesive layer ST-276 acrylic adhesive layer ST-276 ST-279 ST-245 ST-2410 ST-276 Silicone adhesive layer ST-276 skin side skin side skin side skin side skin side skin side skin side Adhesion tightness of the side surface of the adhesive [N / 20 mm] 5.2 5.0 3.7 2.8 0.02 0.36 0.07 Young's modulus [MPa] MD direction 0.67 0.67 24.91 15.45 0.66 0.67 1.07 TD direction 0.63 0.71 2.46 0.91 1.05 0.63 0.96 Fracture stress [N / mm²] MD direction 7.14 5.07 8.32 6.57 5.37 7.14 5.87 TD direction 6.49 5.21 2.37 1.00 9.33 6.49 4.52 Elongation at break [%) MD direction 891 699 94 132 780 891 505 TD direction 875 674 262 697 813 875 444 Average transmittance [%] 400~700 nm 93.4 93.3 57.3 59.1 92.3 93.4 92.4 2000~2500 nm 79.9 83.6 51.7 50.6 78.3 79.9 79.8 Total thickness of the adhesive [μm] 160 130 410 440 110 160 110 Surface free energy of the adhesive side of the attached object [mJ / m²] 17.4 17.4 17.4 17.4 31.5 21.1 24.9 Surface free energy of the skin's side adhesion surface [mJ / m²] 21.1 21.1 28.2 21.3 21.1 17.4 21.1

[0106] As shown in Table 1, the double-sided adhesive sheet for skin application of the present invention demonstrates excellent adhesion to the object being applied and excellent adhesion to the skin. Furthermore, it is presumed that its adhesion to the skin and its softness are also excellent, as well as its ability to follow skin movements. On the other hand, when the surface free energy of the adhesive surface on the side that adheres to the object is relatively large (comparative example), the adhesion to the object is poorer.

[0107] 1: Double-sided adhesive sheet 2: Substrate layer 3: Adhesive layer 3a: Adhesive surface A 4: Adhesive layer 4a: Adhesive Surface B

Claims

1. A double-sided adhesive sheet for skin adhesion, comprising a substrate layer and adhesive layers disposed on both sides of the substrate layer, wherein the surface free energy of one adhesive surface at a temperature of 23°C and a relative humidity of 50% is less than 20 mJ / m2, and the other adhesive surface is attached to the skin, wherein the surface free energy of the other adhesive surface is 20 to 50 mJ / m2, and the adhesive layers providing the one adhesive surface and the adhesive layers providing the other adhesive surface comprise different types of base polymers.

2. The double-sided adhesive sheet for skin adhesion, as requested in item 1, has a fracture stress of 0.8 N / mm2 or higher in at least one direction.

3. The double-sided adhesive sheet for skin adhesion, as requested in item 1 or 2, has a Young's modulus of 50 MPa or less in at least one direction.

4. The double-sided adhesive sheet for skin application as claimed in claim 1 or 2, wherein the 180° peel strength of the adhesive surface relative to the silicone resin substrate, measured at a temperature of 23°C and a peel speed of 50 mm / min, is 2 N / 20 mm or more.

5. The double-sided adhesive sheet for skin application as requested in item 1 or 2, wherein the average transmittance of the total light transmitted according to JIS K7136-1 is 40% or more at wavelengths of 400 to 700 nm, and the average transmittance of the total light transmitted according to the wavelength range of 2000 to 2500 nm is 40% or more.

6. The total thickness of the double-sided adhesive sheet for skin application as requested in item 1 or 2 is less than 1000 μm.

7. The double-sided adhesive sheet for skin application as claimed in claim 1 or 2, wherein the adhesive layer providing the other adhesive side is an acrylic adhesive layer comprising an acrylic polymer as the base polymer.

8. The double-sided adhesive sheet for skin application as described in claim 1 or 2 is intended for attaching electronic devices to human skin.

9. The double-sided adhesive sheet for skin application as described in claim 8, wherein the aforementioned electronic device is a flexible device.

10. An electronic device comprising a double-sided adhesive sheet for skin application as claimed in claim 1 or 2.

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