JP7770802B2 - Double-sided adhesive sheet for application to the skin - Google Patents

Description

The present invention relates to a double-sided pressure-sensitive adhesive sheet that is applied to the skin.

Adhesive sheets for application to the skin are often used in fields such as medicine, sports, and beauty. Adhesive sheets for application to the skin are required to have excellent adhesion to the skin and be safe. Known examples of adhesive sheets for application to the skin include those disclosed in References 1 to 3. For example, Reference 3 discloses a gel sheet used for measuring electroencephalograms.

Japanese Patent Application Laid-Open No. 2020-128453 Japanese Patent Application Laid-Open No. 2020-128454 Japanese Patent Application Laid-Open No. 2021-24907

In recent years, for healthcare purposes, such as determining the health status of the human body, electronic devices such as various measuring instruments are sometimes attached to the skin of the human body. When attaching patches of electronic devices, etc. to the skin, it is thought that double-sided pressure-sensitive adhesive sheets can be used. The double-sided pressure-sensitive adhesive sheets used to attach such patches to the skin are required to have excellent adhesion to the patch.

The present invention was conceived in light of these circumstances, and its purpose is to provide a double-sided pressure-sensitive adhesive sheet for application to the skin that has excellent adhesion to the patch.

As a result of extensive research to achieve the above-mentioned objective, the inventors have discovered that a double-sided PSA sheet for application to skin, which is equipped with a base layer and in which the surface free energy of the adhesive surface facing the patch is within a specific range, exhibits excellent adhesion to the patch. The present invention was completed based on these findings.

That is, the present invention provides a double-sided pressure-sensitive adhesive sheet for application to the skin, comprising a base layer and pressure-sensitive adhesive layers provided on both sides of the base layer, one of the adhesive surfaces having a surface free energy of less than 20 mJ/ ^m2 at a temperature of 23°C and a relative humidity of 50%, and the other adhesive surface being the side that is applied to the skin.

The double-sided pressure-sensitive adhesive sheet for application to skin preferably has a breaking stress in at least one direction of 0.8 N/mm ² or more.

It is preferable that the above-mentioned double-sided pressure-sensitive adhesive sheet for application to the skin has a Young's modulus of 50 MPa or less in at least one direction.

It is preferable that the 180° peel strength of one of the adhesive surfaces against a silicone resin substrate, measured at a temperature of 23°C and a peel rate of 50 mm/min, is 2 N/20 mm or greater.

The above-mentioned double-sided pressure-sensitive adhesive sheet for application to skin preferably has an average total light transmittance of 40% or more in the wavelength range of 400 to 700 nm, and an average transmittance of 40% or more in the wavelength range of 2000 to 2500 nm, measured in accordance with JIS K7136-1.

The surface free energy of the other adhesive surface is preferably 20 to 50 mJ/m ² .

The total thickness of the above-mentioned double-sided adhesive sheet for application to the skin is preferably less than 1000 μm.

It is preferable that the adhesive layer providing one adhesive surface and the adhesive layer providing the other adhesive surface contain different types of base polymers.

The adhesive layer providing the other adhesive surface is preferably an acrylic adhesive layer containing an acrylic polymer as the base polymer.

The above-mentioned double-sided pressure-sensitive adhesive sheet for application to the skin is preferably used for attaching electronic devices to human skin.

It is preferable that the above electronic device is a flexible device.

The present invention also provides an electronic device equipped with the above-mentioned double-sided adhesive sheet for application to the skin.

The double-sided pressure-sensitive adhesive sheet for application to the skin of the present invention has excellent adhesion to the patch.

1 is a cross-sectional view of a double-sided pressure-sensitive adhesive sheet for application to skin according to one embodiment of the present invention.

[Double-sided adhesive sheet for skin application]
The double-sided pressure-sensitive adhesive sheet for application to skin of the present invention is a double-sided pressure-sensitive adhesive sheet that is used by applying one adhesive surface to a patch and the other adhesive surface to the skin. In this specification, the adhesive surface that is applied to the patch may be referred to as "adhesive surface A," and the adhesive surface that is applied to the skin may be referred to as "adhesive surface B." Furthermore, the adhesive layer that provides adhesive surface A may be referred to as "adhesive layer A," and the adhesive layer that provides adhesive surface B may be referred to as "adhesive layer B."

The surface free energy of one adhesive surface (adhesive surface A) of the double-sided pressure-sensitive adhesive sheet for application to skin at a temperature of 23°C and a relative humidity of 50% is less than 20 mJ/ ^m2 , and preferably ¹⁸ mJ/m2 or less. When the surface free energy is less than 20 mJ/ ^m2 , adhesive surface A has excellent adhesion to an article to be applied (particularly an article with low surface free energy).

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 to 50 mJ/ ^m2 , and more preferably 20.5 to 40 mJ/ ^m2 . When the surface free energy is within the above range, adhesive surface B has better adhesion to the skin.

The surface free energy γ of the adhesive surface is a value expressed by the following formula: γ = γ ^d + γ ^p + γ ^h . Here, γ ^d , γ ^p , and γ ^h in the 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 calculated from the contact angle of each probe liquid using water, diiodomethane, and 1-bromonaphthalene according to the Kitazaki-Hata method (Journal of the Japan Adhesion 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 with the product name "DMo-701" manufactured by Kyowa Interface Science Co., Ltd. can be used. The sessile drop method is used to measure the contact angle from the shape of the droplet 1,000 ms after the droplet has landed. A similar method is also used in the examples described below.

The 180° peel strength of adhesive surface A against a silicone resin substrate, measured at a temperature of 23°C and a peel rate 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. A peel strength of 2 N/20 mm or more indicates excellent adhesion of adhesive surface A to the object to be affixed.

The double-sided adhesive sheet for application to skin comprises at least a base layer and adhesive layers provided on both sides of the base layer. Specifically, it comprises at least a base layer, an adhesive layer providing adhesive surface A, and an adhesive layer providing adhesive surface B.

The adhesive layer provided on the side providing adhesive surface A and the adhesive layer provided on the side providing adhesive surface B may each be a single layer or multiple layers. The multiple adhesive layers provided on the double-sided adhesive sheet for application to skin may be the same adhesive layer, or may be adhesive layers with different compositions, thicknesses, physical properties, etc.

Adhesive layer A and adhesive layer B may be the same adhesive layer, or may be adhesive layers with different thicknesses, physical properties, component compositions, etc. In particular, adhesive layer A and adhesive layer B are preferably adhesive layers with different component compositions. Specific examples of different component compositions include differences in the type of base polymer, the composition of the monomer components that make up the base polymer (such as the type and proportion of structural units), and the composition of components other than the base polymer.

Figure 1 is a cross-sectional schematic diagram showing one embodiment of the double-sided pressure-sensitive adhesive sheet of the present invention. As shown in Figure 1, the double-sided pressure-sensitive adhesive sheet for application to skin 1 comprises a base layer 2, an adhesive layer (adhesive layer A) 3 provided on one side of the base layer 2, and an adhesive layer (adhesive layer B) 4 provided on the other side of the base layer 2. The adhesive layer 3 has an adhesive surface A (3a) that is attached to the patch, and the adhesive layer 4 has an adhesive surface B (4a) that is attached to the skin. The adhesive layers 3 and 4 have different component compositions.

(Base material layer)
The substrate layer is an element that functions as a support in the double-sided pressure-sensitive adhesive sheet for application to skin. By providing the substrate layer, the double-sided pressure-sensitive adhesive sheet for skin has excellent handleability, and for example, the patch can be easily peeled off from the skin. The substrate layer may be a single layer or a laminate of substrates of the same or different types.

Examples of resins constituting the substrate layer include polyethylene-based resins (e.g., low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and very low-density polyethylene), polypropylene-based resins (e.g., random copolymer polypropylene, block copolymer polypropylene, and homopolypropylene), polybutene, polymethylpentene, ethylene-vinyl acetate copolymer (EVA), ionomers, ethylene-(meth)acrylic acid copolymers, ethylene-(meth)acrylic acid ester (random and alternating) copolymers, ethylene-butene copolymers, and ethylene-hexene copolymers; and ether-based polyurethanes. Examples of suitable resins include polyurethanes such as tan, ester-based polyurethane, and carbonate-based polyurethane; polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate, and polybutylene terephthalate (PBT); polycarbonate; polyimide; polyether ether ketone; polyetherimide; polyamides such as aramid and wholly aromatic polyamide; polyphenyl sulfide; fluororesin; polyvinyl chloride; polyvinylidene chloride; cellulose resins such as triacetyl cellulose (TAC); silicone resins; acrylic resins such as polymethyl methacrylate (PMMA); polyvinyl acetate; polysulfone; and polyarylates. One or more of the above resins may be used. Note that, in this specification, the substrate layer does not include the release liner (separator) that is peeled off when the double-sided PSA sheet is used (applied).

Examples of the substrate layer include plastic substrates (e.g., plastic films), porous materials such as paper, cloth, and nonwoven fabrics, nets, and foam sheets. Specific examples of the substrate layer include polystyrene-based thermoplastic elastomer films, plastic films such as nylon, polyester, polyethylene, polypropylene, and polyurethane, woven or nonwoven fabrics, knitted fabrics, and paper made from synthetic or natural organic polymers such as cellulose, and laminates of two or more of these (e.g., laminates of fabrics or papers, laminates of films and fabrics, and laminates of plastic films).

Of these, nonwoven fabrics and plastic substrates are preferred as the substrate layer from the viewpoint of excellent transparency. As the plastic substrate, polyurethane-based substrates, polypropylene-based substrates, polyethylene-based substrates, ethylene-vinyl acetate-based substrates, and silicone-based substrates are more preferred. In particular, polyurethane-based films are preferred from the viewpoint of flexibility (skin conformability), appropriate moisture permeability, tensile strength, and the like, and polyester-based polyurethane films and polyether-based polyurethane films are particularly preferred. Excellent flexibility allows the flexible device to excellently conform to the movement of the skin when attached to the skin as a patch.

The substrate layer may contain various additives, such as fillers (inorganic fillers, organic fillers, etc.), colorants (pigments or dyes), dispersants (surfactants, etc.), antioxidants, antioxidants, UV absorbers, antistatic agents, lubricants, and plasticizers. The blending ratio of the various additives is approximately less than 30% by weight (e.g., less than 20% by weight, typically less than 10% by weight) relative to the total weight of the substrate layer (100% by weight).

The substrate layer may include an auxiliary layer. Examples of such an auxiliary layer include a colored layer, an undercoat layer, an antistatic layer, etc., provided on the surface of the substrate layer.

The surface of the substrate layer may be subjected to surface treatments such as physical treatments (corona discharge treatment, plasma treatment, sand matting treatment, ozone exposure treatment, flame exposure treatment, high-voltage shock exposure treatment, ionizing radiation treatment, etc.) or chemical treatments (chromate treatment, etc.) or treatments for enhancing adhesion using a coating agent (primer) in order to improve adhesion and retention with the adhesive layer. Surface treatments for enhancing adhesion are preferably applied to the entire surface of the substrate layer.

From the viewpoint of superior flexibility, the thickness of the 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 support function and superior handleability, the thickness of the substrate layer is preferably 1 μm or more, more preferably 5 μm or more.

When fabric such as woven fabric or nonwoven fabric, or paper is used as the substrate layer, it is preferable to use one having a basis weight of about 8 to 200 g/m ² .

(Adhesive layer)
The double-sided pressure-sensitive adhesive sheet for application to skin comprises at least a pressure-sensitive adhesive layer A and a pressure-sensitive adhesive layer B. The double-sided pressure-sensitive adhesive sheet for application to skin may comprise a pressure-sensitive adhesive layer other than the pressure-sensitive adhesive layer A and the pressure-sensitive adhesive layer B between the base layer and the pressure-sensitive adhesive layer A or the pressure-sensitive adhesive layer B.

The adhesives constituting each adhesive layer of the double-sided adhesive sheet for application to skin are not particularly limited, but examples include acrylic adhesives, rubber adhesives (natural rubber, synthetic rubber, mixtures of these, etc.), silicone adhesives, polyester adhesives, urethane adhesives, polyether adhesives, polyamide adhesives, and fluorine-based adhesives. Only one type of adhesive may be used, or two or more types may be used.

<Adhesive layer A>
A silicone-based pressure-sensitive adhesive is preferred as the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer A, from the viewpoint of easily designing a pressure-sensitive adhesive layer having low surface free energy. That is, the pressure-sensitive adhesive layer A is preferably a silicone-based pressure-sensitive adhesive layer composed of a silicone-based pressure-sensitive adhesive.

The silicone-based adhesive is not particularly limited and can be appropriately selected from known or commonly used silicone-based adhesives. Examples of the silicone-based adhesive include peroxide-crosslinked silicone-based adhesives (peroxide-cured silicone-based adhesives), addition-type silicone-based adhesives, and condensation-type silicone-based adhesives. Of these, addition reaction-type silicone-based adhesives are preferred. The silicone-based adhesive may be either a one-component type or a two-component type. One type of silicone-based adhesive may be used alone, or two or more types may be used.

The above-mentioned addition-type silicone-based pressure-sensitive adhesives are generally pressure-sensitive adhesives that produce a silicone-based polymer by subjecting an organopolysiloxane that has an alkenyl group, such as a vinyl group, on the silicon atom and an organopolysiloxane that has a hydrosilyl group to an addition reaction (hydrosilylation reaction) using a platinum compound catalyst, such as chloroplatinic acid. Peroxide-curing silicone-based pressure-sensitive adhesives are generally pressure-sensitive adhesives that produce a silicone-based polymer by curing (crosslinking) an organopolysiloxane with peroxide. Condensation-type silicone-based pressure-sensitive adhesives are generally pressure-sensitive adhesives that produce a silicone-based polymer by a dehydration or dealcoholization reaction between polyorganosiloxanes that have hydrolyzable silyl groups, such as silanol groups or alkoxysilyl groups, at the terminals.

The silicone-based adhesive may be, for example, a silicone-based adhesive composition containing silicone rubber and silicone resin. The silicone-based adhesive may further contain additives such as a crosslinking agent, a catalyst (curing agent), a filler, a plasticizer, an antioxidant, an antistatic agent, and a colorant (pigment, dye, etc.), as needed.

The silicone rubber is not particularly limited as long as it is a silicone-based rubber component. For example, organopolysiloxanes whose main structural units are dimethylsiloxane, methylphenylsiloxane, etc. can be used. Depending on the type of reaction, examples include silicone-based rubbers having alkenyl groups bonded to silicon atoms (alkenyl-group-containing organopolysiloxanes; in the case of addition reaction types), silicone-based rubbers having at least methyl groups (in the case of peroxide-curing types), and silicone-based rubbers having silanol groups or hydrolyzable alkoxysilyl groups at the terminals (in the case of condensation types). The weight-average molecular weight of the organopolysiloxane 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.

The silicone resin is not particularly limited as long as it is a silicone resin used in silicone-based pressure-sensitive adhesives, but examples include silicone resins containing organopolysiloxanes made of ( _{co )polymers} having at least one unit selected from the group consisting of M units made of the structural unit "R3Si1 _{/ 2} ", Q units made of the structural unit "SiO2", T units made of the structural unit "RSiO3/ ₂ ", and D units made of the structural unit "R2SiO". In the structural units, R represents a hydrocarbon group or a hydroxy group. Examples of the hydrocarbon group include aliphatic hydrocarbon groups (e.g., alkyl groups such as methyl and ethyl), alicyclic hydrocarbon groups (e.g., cycloalkyl groups such as cyclohexyl), and aromatic hydrocarbon groups (e.g., aryl groups such as phenyl and naphthyl). The ratio (ratio) of the M units to at least one unit selected from Q units, T units, and D units is, for example, a former/latter (molar ratio) of about 0.3/1 to 1.5/1 (preferably 0.5/1 to 1.3/1). Various functional groups, such as vinyl groups, may be introduced into the organopolysiloxane in such silicone resins as needed. The introduced functional groups may be functional groups capable of undergoing a crosslinking reaction. MQ resins composed of M units and Q units are preferred as silicone resins. The weight-average molecular weight of the organopolysiloxane in the silicone resin is, for example, 1,000 or more, preferably 1,000 to 20,000, and more preferably 1,500 to 10,000.

There are no particular limitations on the blending ratio of silicone rubber to silicone resin, but for example, it is preferable that the silicone resin be 100 to 220 parts by weight, and especially 120 to 180 parts by weight, per 100 parts by weight of silicone rubber.

The silicone rubber and silicone resin in the silicone-based pressure-sensitive adhesive composition containing them may be in a mixed state where they are simply mixed together, or they may react with each other to form a condensation product (particularly a partial condensation product), a crosslinked reaction product, an addition reaction product, etc.

Furthermore, silicone-based pressure-sensitive adhesive compositions containing silicone rubber and silicone resin typically contain a crosslinking agent to form a crosslinked structure. Examples of such crosslinking agents include, but are not limited to, siloxane-based crosslinking agents (silicone-based crosslinking agents) and peroxide-based crosslinking agents. A single crosslinking agent may be used, or two or more types may be used.

As the siloxane-based crosslinking agent, for example, a polyorganohydrogensiloxane having two or more hydrogen atoms bonded to silicon atoms in the molecule can be preferably used. In such polyorganohydrogensiloxanes, the silicon atoms to which hydrogen atoms are bonded may have various organic groups bonded in addition to the hydrogen atoms. Examples of such organic groups include alkyl groups such as methyl and ethyl groups, aryl groups such as phenyl groups, and halogenated alkyl groups. Among these, from the standpoint of synthesis and handling, alkyl groups, particularly methyl groups, are preferred. Furthermore, the skeletal structure of the polyorganohydrogensiloxane may be linear, branched, or cyclic, but a linear structure is preferred.

Examples of the peroxide-based crosslinking agent include diacyl peroxides, alkyl peroxy esters, peroxydicarbonates, monoperoxycarbonates, peroxyketals, dialkyl peroxides, hydroperoxides, and ketone peroxides. More specific examples include benzoyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, t-butylcumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, 2,4-dichloro-benzoyl peroxide, di-t-butylperoxy-diisopropylbenzene, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 2,5-dimethyl-2,5-di-t-butylperoxyhexyne-3.

Examples of the above-mentioned addition-type silicone-based adhesives available commercially include those under the trade names "KR-3700," "KR-3701," "X-40-3237-1," "X-40-3240," and "X-40-3291-1" (all manufactured by Shin-Etsu Chemical Co., Ltd.). Also, examples of the above-mentioned peroxide-curing silicone-based adhesives available commercially include those under the trade names "KR-100," "KR-101-10," and "KR-130" (all manufactured by Shin-Etsu Chemical Co., Ltd.).

The silicone-based pressure-sensitive adhesive layer can be produced, for example, by applying (coating) the pressure-sensitive adhesive composition for forming pressure-sensitive adhesive layer A onto the substrate layer or release liner and drying and curing the resulting pressure-sensitive adhesive composition layer, or by applying (coating) the pressure-sensitive adhesive composition onto the substrate layer or release liner and irradiating the resulting pressure-sensitive adhesive composition layer with active energy rays to cure it. If necessary, the resulting pressure-sensitive adhesive composition may be further dried by heating.

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

The adhesive composition may be applied (coated) using a known coating method. For example, a coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, or direct coater may be used.

The thickness of the adhesive layer A is, for example, 5 to 500 μm, and preferably 50 to 200 μm. A thickness of 5 μm or more provides superior adhesion to the application target. A thickness of 500 μm or less (particularly 200 μm or less) allows the thickness of the double-sided adhesive sheet to be reduced.

<Adhesive layer B>
From the viewpoints of adhesion to the skin and safety, an acrylic pressure-sensitive adhesive is preferred as the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer B. That is, the pressure-sensitive adhesive layer is preferably an acrylic pressure-sensitive adhesive layer composed of an acrylic pressure-sensitive adhesive.

The acrylic pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer. The acrylic polymer is a polymer that contains an acrylic monomer (a monomer having a (meth)acryloyl group in the molecule) as a monomer component that constitutes the polymer. In other words, the acrylic polymer contains structural units derived from the acrylic monomer. Note that only one type of acrylic polymer may be used, or two or more types may be used.

In this specification, the term "base polymer" refers to the main component of the polymer components used in the pressure-sensitive adhesive layer, for example, a polymer component contained in an amount of more than 50% by mass. The content of the acrylic polymer in the acrylic pressure-sensitive adhesive layer is preferably 60% by mass or more, and more preferably 70% by mass or more, relative to 100% by mass of the total amount of the acrylic pressure-sensitive adhesive layer.

The acrylic polymer is preferably a polymer constructed (formed) using a (meth)acrylic acid alkyl ester as an essential monomer component. In other words, the acrylic polymer preferably contains a (meth)acrylic acid alkyl ester as a structural unit. Note that, in this specification, "(meth)acrylic" refers to "acrylic" and/or "methacrylic" (either one or both of "acrylic" and "methacrylic"), and similarly applies to other terms.

Preferred examples of the (meth)acrylic acid alkyl ester as an essential monomer component include (meth)acrylic acid alkyl esters having a linear or branched alkyl group. Note that the (meth)acrylic acid alkyl esters may be used singly or in combination.

Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, and Examples of (meth)acrylic acid alkyl esters having a linear or branched alkyl group having 1 to 20 carbon atoms include isononyl acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate (lauryl (meth)acrylate), tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate (stearyl (meth)acrylate), isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

Among (meth)acrylic acid alkyl esters having a linear or branched alkyl group, (meth)acrylic acid alkyl esters having a linear or branched alkyl group with 6 or more carbon atoms (preferably 6 to 18) are preferred. A carbon atom number of 6 or more (particularly 6 to 18) results in relatively little skin irritation and is less likely to lose adhesive strength even with prolonged use.

The acrylic polymer may contain, as monomer components constituting the polymer, the alkyl (meth)acrylate ester having a linear or branched alkyl group, as well as other monomers (copolymerizable monomers) copolymerizable with the alkyl (meth)acrylate ester. That is, the acrylic polymer may contain a copolymerizable monomer as a structural unit. Only one type of copolymerizable monomer may be used, or two or more types may be used.

Examples of the copolymerizable monomer include carboxy group-containing monomers, hydroxy group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, alkoxy group-containing monomers, sulfonic acid group-containing monomers, phosphate group-containing monomers, vinyl ester monomers, vinyl ether monomers, isocyanate group-containing monomers, aromatic vinyl compounds, alicyclic monomers, aromatic ring-containing (meth)acrylates, chlorine-containing monomers, and nitrogen-containing monomers.

If necessary, adhesive layer B may further contain additives such as tackifying resins, fillers, crosslinking agents, crosslinking accelerators, antioxidants, antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, UV absorbers, polymerization inhibitors, foil-like materials, rust inhibitors, and colorants (pigments and dyes), to the extent that the effects of the present invention are not impaired. Only one of each of the above additives may be used, or two or more may be used.

The adhesive layer B may be in any form, such as an emulsion type, a solvent type (solution type), an active energy ray curable type, or a hot melt type. Among these, solvent-based and active energy ray curable adhesive compositions are preferred, as they allow for the production of adhesive layers with excellent productivity.

Examples of the active energy rays include ionizing radiation such as alpha rays, beta rays, gamma rays, neutron rays, and electron beams, as well as ultraviolet rays, with ultraviolet rays being particularly preferred. In other words, the active energy ray-curable adhesive layer is preferably an ultraviolet-curable adhesive layer.

The method for producing the acrylic pressure-sensitive adhesive layer is not particularly limited, but examples include coating (applying) a pressure-sensitive adhesive (pressure-sensitive adhesive composition) containing the acrylic polymer onto the substrate layer or release liner and drying and curing the resulting pressure-sensitive adhesive composition layer, or coating (applying) the pressure-sensitive adhesive composition onto a substrate or release liner and irradiating the resulting pressure-sensitive adhesive composition layer with active energy rays to cure it. If necessary, the resulting pressure-sensitive adhesive composition may be further dried by heating.

The above-mentioned pressure-sensitive adhesive composition can be prepared by known or conventional methods. For example, a solvent-based pressure-sensitive adhesive composition can be prepared by mixing additives, if necessary, into a solution containing the above-mentioned acrylic polymer. For example, an active energy ray-curable pressure-sensitive adhesive composition can be prepared by mixing additives, if necessary, into a mixture of monomer components constituting the above-mentioned acrylic polymer or a partially polymerized product thereof.

The adhesive composition may be applied (coated) using a known coating method. For example, a coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, comma coater, or direct coater may be used.

The heat drying temperature for solvent-based pressure-sensitive adhesive compositions is preferably 40 to 200°C, more preferably 50 to 180°C, and even more preferably 70 to 170°C. The drying time can be adjusted as needed, but is typically 5 seconds to 20 minutes, preferably 5 seconds to 10 minutes, and more preferably 10 seconds to 5 minutes.

When forming the adhesive layer B by irradiation with active energy rays, the acrylic polymer can be produced from the monomer component and the adhesive layer can be formed at the same time. The monomer component can be partially polymerized in advance to form a syrup before being irradiated with active energy rays. For ultraviolet irradiation, a high-pressure mercury lamp, a low-pressure mercury lamp, a metal halide lamp, or the like can be used.

The thickness of the adhesive layer B is, for example, 10 to 200 μm, and preferably 20 to 60 μm. A thickness of 10 μm or more (particularly 20 μm or more) provides superior conformability and adhesion to the skin. A thickness of 200 μm or less (particularly 60 μm or less) allows the thickness of the double-sided adhesive sheet to be reduced.

(Double-sided adhesive sheet for application to the skin)
The thickness (total thickness) of the double-sided pressure-sensitive adhesive sheet for application to skin is preferably less than 1000 μm, more preferably 500 μm or less, and even more preferably 400 μm or less. A thickness of less than 1000 μm provides excellent flexibility and superior ability to follow skin movements. Furthermore, the thickness of the double-sided pressure-sensitive 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. A thickness of 40 μm or more (particularly 80 μm or more) provides excellent adhesion to the patch and skin. The thickness of the double-sided pressure-sensitive adhesive sheet for application to skin refers to the thickness from adhesive surface A to adhesive surface B, i.e., the thickness of the adhesive body, and does not include the release liner. In this specification, a structure comprising adhesive layer A, the substrate layer, and adhesive layer B, with adhesive surface A and adhesive surface B as both adhesive surfaces, may be referred to as an "adhesive body."

The breaking stress in at least one direction of the double-sided pressure-sensitive adhesive sheet for application to skin (the pressure-sensitive adhesive body) is preferably 0.8 N/ ^mm² or ^more , more preferably 1.0 N/ ^mm² or more, even more preferably 2.0 N/ ^mm² or more, and particularly preferably 5.0 N/mm² or more. When the breaking stress is 0.8 N/ ^mm² or more, the pressure-sensitive adhesive layer is less likely to break when stretched, and the flexible device as a patch is excellent in its ability to follow the movement of the skin when attached to the skin. The breaking stress is a value measured in an environment of 23°C and 50% RH using a No. 3 dumbbell sample with a chuck distance of 50 mm and a pulling speed of 50 mm/min. In particular, it is preferable that the breaking stress in at least one of the MD and TD directions of the base layer is within the above range, and it is more preferable that the breaking stress in both directions is within the above range.

The Young's modulus in at least one direction of the double-sided pressure-sensitive adhesive sheet for application to skin (the pressure-sensitive adhesive body) is preferably 50 MPa or less, more preferably 15 MPa or less, and even more preferably 5 MPa or less. When the Young's modulus is 50 MPa or less, the flexible device as a patch will have excellent followability to skin movement when attached to the skin. The Young's modulus in at least one direction of the double-sided pressure-sensitive adhesive sheet for application to skin (the pressure-sensitive adhesive body) is, for example, 0.5 MPa or more. The Young's modulus is a value measured in an environment of 23°C and 50% RH using a No. 3 dumbbell sample with a chuck distance of 50 mm and a pulling speed of 50 mm/min. In particular, it is preferable that the Young's modulus in at least one direction of the MD and TD of the base layer is within the above range, and it is more preferable that the Young's modulus in both directions be within the above range.

The breaking elongation in at least one direction of the double-sided pressure-sensitive adhesive sheet for application to skin (the pressure-sensitive adhesive body) is preferably 50% or more, more preferably 70% or more, and even more preferably 90% or more. When the breaking elongation is 50% or more, the pressure-sensitive adhesive layer is less likely to break when stretched, and the flexible device as a patch has excellent followability to skin movement when attached to the skin. The breaking elongation is a value measured in an environment of 23°C and 50% RH using a No. 3 dumbbell sample with a chuck distance of 50 mm and a pulling rate of 50 mm/min. In particular, it is preferable that the breaking elongation in at least one of the MD and TD directions of the base layer is within the above range, and it is more preferable that the breaking elongation in both directions is within the above range.

The double-sided pressure-sensitive adhesive sheet for application to skin (the pressure-sensitive adhesive body) preferably has an average total light transmittance of 40% or more at wavelengths of 400 to 700 nm, measured in accordance with JIS K7136-1, more preferably 50% or more, and even more preferably 80% or more. An average transmittance of 40% or more means high visible light transmittance, excellent transparency of the double-sided pressure-sensitive adhesive sheet, and excellent visibility when applied to the skin.

The double-sided pressure-sensitive adhesive sheet for application to skin (the pressure-sensitive adhesive body) preferably has an average total light transmittance of 40% or more at wavelengths of 2000 to 2500 nm, measured in accordance with JIS K7136-1, more preferably 50% or more, and even more preferably 80% or more. An average transmittance of 40% or more results in high infrared transmittance and excellent light-sensing functionality.

The double-sided pressure-sensitive adhesive sheet for application to skin may have a release liner attached to the surface (adhesive surface) of the pressure-sensitive adhesive layer until use. Each adhesive surface of the double-sided pressure-sensitive adhesive sheet for application to skin may be protected by two release liners, or may be protected by a single release liner with release surfaces on both sides when wound into a roll (rolled body). The release liner is used as a protective material for the pressure-sensitive adhesive layer and is peeled off when the sheet is applied to the adherend. The release liner is not necessarily provided.

The release liner can be a conventional release paper, and is not particularly limited. Examples include substrates with a release treatment layer, low-adhesion substrates made of fluoropolymers, and low-adhesion substrates made of non-polar polymers. Examples of substrates with a release treatment layer include plastic films and papers surface-treated with release agents such as silicone-based, long-chain alkyl-based, fluorine-based, and molybdenum sulfide-based release agents. Examples of fluoropolymers used in the low-adhesion substrates made of fluoropolymers include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and chlorofluoroethylene-vinylidene fluoride copolymer. Examples of non-polar polymers include olefin-based resins (e.g., polyethylene, polypropylene, etc.). The release liner can be formed by known or conventional methods. The thickness of the release liner is also not particularly limited.

The double-sided pressure-sensitive adhesive sheet for application to skin has excellent adhesion to patches and is used in applications where patches are attached to the skin. Examples of such patches include, but are not limited to, electronic device devices. Because adhesive surface A of the double-sided pressure-sensitive adhesive sheet for application to skin has particularly excellent adhesion to silicon atom-containing substances such as silica and silicone resins, the adhesive is preferably an electronic device. By applying the double-sided pressure-sensitive adhesive sheet for application to an electronic device, the electronic device can be equipped with the double-sided pressure-sensitive adhesive sheet for application to skin.

Furthermore, the double-sided pressure-sensitive adhesive sheet for skin has excellent adhesion to the skin and the patch, and when it has excellent flexibility, it has excellent followability to the movement of the skin and is unlikely to peel off from the skin. For this reason, the patch may be a rigid device, semi-flexible device, or flexible device, with a flexible device being preferred. Furthermore, it is particularly preferable that the skin is human skin. Furthermore, the double-sided pressure-sensitive adhesive sheet for skin application can have excellent transparency, resulting in excellent light-sensing functionality.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples in any way.

Example 1
(Preparation of silicone-based adhesive layer)
An addition-type silicone-based pressure-sensitive adhesive (trade name "KR-3700", manufactured by Shin-Etsu Chemical Co., Ltd.) was diluted with toluene and applied to the release-treated surface of a 50 μm-thick polyester film (trade name "Diafoil MRS", manufactured by Mitsubishi Chemical Corporation), one side of which had been release-treated with a silicone-based release agent, and then heated and dried at 140°C for 8 minutes to form a 100 μm-thick pressure-sensitive adhesive layer (silicone-based pressure-sensitive adhesive layer).

(double-sided adhesive sheet)
The silicone-based pressure-sensitive adhesive layer was attached to the surface of a base layer of a skin patch tape (product name "ST-276", manufactured by Nitto Denko Corporation) which had a pressure-sensitive adhesive layer formed on one surface of the base layer and a release liner laminated on the surface of the pressure-sensitive adhesive layer. In this way, a double-sided pressure-sensitive adhesive sheet was produced in which a pressure-sensitive adhesive layer and a silicone-based pressure-sensitive adhesive layer were laminated on both sides of the base layer, and further release liners were laminated on both pressure-sensitive adhesive layers.

Example 2
A double-sided PSA sheet was prepared in the same manner as in Example 1, except that a skin patch tape (product name "ST-279", manufactured by Nitto Denko Corporation) was used instead of the skin patch tape (product name "ST-276", manufactured by Nitto Denko Corporation).

Example 3
A double-sided PSA sheet was prepared in the same manner as in Example 1, except that a skin patch tape (product name "ST-245", manufactured by Nitto Denko Corporation) was used instead of the skin patch tape (product name "ST-276", manufactured by Nitto Denko Corporation).

Example 4
A double-sided PSA sheet was prepared in the same manner as in Example 1, except that a skin patch tape (product name "ST-2410", manufactured by Nitto Denko Corporation) was used instead of the skin patch tape (product name "ST-276", manufactured by Nitto Denko Corporation).

Comparative Example 1
(Rubber-based adhesive layer)
A hydrogenated styrene-isoprene-styrene block copolymer (trade name "2563NS", manufactured by Soken Chemical & Engineering Co., Ltd.) serving as a base polymer was dissolved in toluene to adjust the solids concentration to 25% by mass, thereby preparing a pressure-sensitive adhesive composition. This pressure-sensitive adhesive composition was applied to the release-treated surface of a 38 μm-thick polyester film (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation), one side of which had been release-treated with a silicone-based release agent, and then heated and dried at 120°C for 3 minutes to form a 50 μm-thick pressure-sensitive adhesive layer (rubber-based pressure-sensitive adhesive layer).

(double-sided adhesive sheet)
A double-sided PSA sheet was prepared in the same manner as in Example 1, except that the above rubber-based PSA layer was used instead of the silicone-based PSA layer.

Comparative Example 2
The double-sided PSA sheet prepared in Example 1 was used, except that in the evaluation described below, the adhesive layers and silicone-based adhesive layers in the skin adhesive tape were used in the opposite directions to those in Example 1.

Comparative Example 3
(Acrylic adhesive layer)
40 parts by mass of butyl acrylate (BA), 40 parts by mass of cyclohexyl acrylate (CHA), 20 parts by mass of 4-hydroxybutyl acrylate (4-HBA), 0.05 parts by mass of 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name "Ominrad 651", manufactured by IGM Resins B.V.) as a photopolymerization initiator, and 0.05 parts by mass of 1-hydroxycyclohexyl-phenyl-ketone (trade name "Ominrad 184", manufactured by IGM Resins B.V.) were mixed together and irradiated with ultraviolet light under a nitrogen atmosphere to produce a partial polymer (monomer syrup). To the resulting monomer syrup, 0.1 parts by mass of dipentaerythritol hexaacrylate (DPHA) (trade name "KAYARAD DPHA", manufactured by Nippon Kayaku Co., Ltd.) was added and mixed uniformly to prepare a pressure-sensitive adhesive composition.

The pressure-sensitive adhesive composition prepared above was applied to the release-treated surface of a 38 μm-thick polyester film (trade name "Diafoil MRF", manufactured by Mitsubishi Chemical Corporation), one side of which had been treated with a silicone release agent, to form a coating layer. Next, a 38 μm-thick polyester film (trade name "Diafoil MRE", manufactured by Mitsubishi Chemical Corporation), one side of which had been treated with a silicone release agent, was placed on the surface of the coating layer, with the release-treated surface of the film facing the coating layer. This shielded the coating layer from oxygen. The sheet having the coating layer thus obtained was irradiated with ultraviolet light at an illuminance of 5 mW/cm ² using a chemical light lamp (manufactured by Toshiba Corporation) for 360 seconds, thereby curing the coating layer and forming a 50 μm-thick pressure-sensitive adhesive layer (acrylic pressure-sensitive adhesive layer). The illuminance values are values measured using an industrial UV checker (trade name "UVR-T1", manufactured by Topcon Corporation, photoreceptor model UD-T36) with a peak sensitivity wavelength of about 350 nm.

(double-sided adhesive sheet)
A double-sided PSA sheet was prepared in the same manner as in Example 1, except that the acrylic PSA layer was used instead of the silicone PSA layer.

<Evaluation>
The pressure-sensitive adhesive layers and double-sided pressure-sensitive adhesive sheets obtained in the examples and comparative examples were evaluated as follows, and the results are shown in the table below.

(1) Surface Free Energy For both adhesive surfaces of the double-sided PSA sheets produced in the Examples and Comparative Examples, the contact angles of water, diiodomethane, and 1-bromonaphthalene were measured using a contact angle meter (product name "DMo-701", manufactured by Kyowa Interface Science Co., Ltd.) The surface free energy was then calculated according to the Kitazaki-Hata equation using the obtained contact angle values.

(2) Young's Modulus and Elongation at Break Dumbbell No. 3 shapes (5 mm wide, conforming to JIS K6251) were punched out from the double-sided PSA sheets obtained in the Examples and Comparative Examples, and all release liners were peeled off to expose the PSA sheet. All release liners were peeled off to expose the PSA sheet in an environment of 23°C and 50% RH. A tensile test was then performed using a tensile tester (product name "Autograph AG-10G Tensile Tester", manufactured by Shimadzu Corporation) at a chuck distance of 50 mm and a tensile speed of 50 mm/min, stretching the test specimen until it broke. The Young's modulus was then calculated from the obtained displacement and stress results. The initial chuck distance of the test specimen was set to 0%, and the difference in elongation from the initial chuck distance at the time of test specimen breakage was divided by the initial chuck distance to obtain the elongation at break. The above-mentioned elongation test was performed in both the MD and TD directions of the substrate layer.

(3) Breaking Stress No. 3 dumbbell shapes (conforming to JIS K6251, width 5 mm) were punched out from the double-sided PSA sheets obtained in the Examples and Comparative Examples, all release liners were peeled off to expose the PSA sheets, and the sheets were set in a tensile testing machine "Autograph AG-I" (manufactured by Shimadzu Corporation) with a chuck distance of 50 mm in the longitudinal direction, and stretched at a tensile speed of 50 mm/min until breaking, and the load (breaking stress) was measured.

(4) Transmittance All release liners were peeled off from the double-sided PSA sheets obtained in the Examples and Comparative Examples, and the total light transmittance in the thickness direction of the double-sided PSA sheet was measured using an ultraviolet-visible-near-infrared spectrophotometer (device name "SolidSpec", manufactured by Shimadzu Corporation). The average transmittance in the wavelength range of 400 to 700 nm and the average transmittance in the wavelength range of 2000 to 2500 nm were then calculated.

(5) Adhesion of the adhesive surface on the patch side Under a measurement environment of 23°C and 50% RH, a 25 μm thick PET film was attached to the skin-facing adhesive surface (see Table 1) of the double-sided PSA sheets obtained in the Examples and Comparative Examples to form a backing, and the sheet was cut to a size of 20 mm wide and 100 mm long to prepare a measurement sample. For each measurement sample thus prepared, under an environment of 23°C and 50% RH, the adhesive surface (see Table 1) on the patch side of the measurement sample was pressed against a silicone rubber sheet (product name "QP1-70", manufactured by Dow-Toray Co., Ltd.) using a 2 kg roller, moving back and forth once. After leaving the sheet under the same environment for 30 minutes, the 180° peel strength was measured using a triple tensile tester (product name "AG-X plus", manufactured by Shimadzu Corporation) in accordance with JIS Z0237:2000, at a tensile speed of 50 mm/min and a peel angle of 180°.

(6) Adhesion of the Skin-Side Adhesive Surface The double-sided PSA sheets obtained in the Examples and Comparative Examples were cut into rectangles measuring 50 mm wide x 50 mm long, and the adhesive surface on the patch side was backed with a 5 μm-thick PET film. The skin-side adhesive surface was then applied to the forearms of five volunteers. After three hours at room temperature, the degree of lifting of the double-sided PSA sheet edge was evaluated using the following three-point scale. As a result, all of Examples 1 to 4 were given a score of 3.
(Floating condition)
3: No lifting, 2: Slight lifting at the edge, 1: More than half lifting

As shown in Table 1, the double-sided pressure-sensitive adhesive sheet for application to skin of the present invention was confirmed to have excellent adhesion to patches and to the skin. It is also presumed to have excellent adhesion to the skin and flexibility, and also excellent ability to follow the movement of the skin. On the other hand, when the surface free energy of the adhesive surface to which the patch is attached was high (Comparative Example), adhesion to the patch was poor.

1 double-sided adhesive sheet 2 base layer 3, 4 adhesive layer 3a adhesive surface A
4a Adhesive side B

Claims (10)

A substrate layer and a pressure-sensitive adhesive layer provided on both sides of the substrate layer,
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 ;
The other adhesive side is the side that is attached to the skin,
the surface free energy of the other adhesive surface at a temperature of 23°C and a relative humidity of 50% is 20 to 50 mJ/ ^m² ;
A double-sided pressure-sensitive adhesive sheet for application to skin, wherein the pressure-sensitive adhesive layer providing one of the pressure-sensitive adhesive surfaces and the pressure-sensitive adhesive layer providing the other of the pressure-sensitive adhesive surfaces contain different types of base polymers. 2. The double-sided pressure-sensitive adhesive sheet for application to skin according to claim 1, wherein the breaking stress in at least one direction is 0.8 N/mm ^<2> or more. The double-sided pressure-sensitive adhesive sheet for application to skin according to claim 1 or 2, wherein the Young's modulus in at least one direction is 50 MPa or less. The double-sided pressure-sensitive adhesive sheet for application to skin according to any one of claims 1 to 3, wherein the 180° peel strength of one of the adhesive surfaces against a silicone resin substrate, measured at a temperature of 23°C and a peel rate of 50 mm/min, is 2 N/20 mm or greater. The double-sided pressure-sensitive adhesive sheet for application to skin according to any one of claims 1 to 4, wherein the average total light transmittance measured in accordance with JIS K7136-1 is 40% or more in the wavelength range of 400 to 700 nm, and 40% or more in the wavelength range of 2000 to 2500 nm. The double-sided pressure-sensitive adhesive sheet for application to skin according to any one of claims 1 to 5 , which has a total thickness of less than 1000 µm. The double-sided pressure-sensitive adhesive sheet for application to skin according to any one of claims 1 to 6 , wherein the pressure-sensitive adhesive layer providing the other pressure-sensitive adhesive surface is an acrylic pressure-sensitive adhesive layer containing an acrylic polymer as a base polymer. The double-sided pressure-sensitive adhesive sheet for application to skin according to any one of claims 1 to 7 , which is used for applying an electronic device to human skin. The double-sided pressure-sensitive adhesive sheet for application to skin according to claim 8 , wherein the electronic device is a flexible device. An electronic device comprising the double-sided pressure-sensitive adhesive sheet for application to skin according to any one of claims 1 to 9 .