Adhesive electrode for biosignal acquisition, electrode segment, and biosensor

Abstract

An adhesive electrode for biosignal acquisition according to the present invention has a conductive polymer and an aqueous emulsion adhesive. The aqueous emulsion adhesive contains a (meth)acrylic acid alkyl ester and a carboxy group-containing monomer. The carboxy group-containing monomer contains an acrylic acid and a monomer having higher hydrophobicity than the acrylic acid.

Description

Adhesive electrode for acquiring biological signals, electrode piece, and biological sensor

[0001] The present invention relates to an adhesive electrode, an electrode piece, and a biosensor for acquiring a biological signal.

[0002] Wearable biosensors that acquire bioinformation such as electrocardiogram waveforms, pulse waves, electroencephalograms, and electromyography are used in medical institutions such as hospitals and clinics, nursing homes, homes, etc. The biosensor is equipped with adhesive electrodes (bioelectrodes) for acquiring biosignals that come into contact with a living body to acquire the subject's bioinformation. When measuring the bioinformation, the biosensor is attached to the subject's skin and electrical signals related to the bioinformation are acquired by the bioelectrodes, thereby measuring the bioinformation.

[0003] As a bioelectrode for such a biosensor, for example, an adhesive sheet has been disclosed which has an adhesive layer containing a conductive organic polymer compound and an adhesive material, uses PEDOT:PSS as the conductive organic polymer compound and an aqueous emulsion as the adhesive material, and is attached to the skin surface of a wiring board (see, for example, Patent Document 1).

[0004] Japanese Patent Application Publication No. 2020-147659

[0005] However, the water-based emulsion used in the adhesive material has a tendency to easily absorb moisture, and therefore, when the adhesive sheet of Patent Document 1 absorbs sweat or external moisture while attached to the skin, its adhesive strength decreases and it becomes more likely to peel off from the skin, making it impossible to stably measure biological signals.

[0006] One aspect of the present invention aims to provide an adhesive electrode for acquiring biological signals that does not absorb more moisture than necessary even when moisture penetrates from the outside during use, improves skin contact impedance, and has excellent adhesion properties.

[0007] One aspect of the adhesive electrode for acquiring a biological signal according to the present invention is an adhesive electrode for acquiring a biological signal having a conductive polymer and an aqueous emulsion adhesive, wherein the aqueous emulsion adhesive contains a (meth)acrylic acid alkyl ester and a carboxy group-containing monomer, and the carboxy group-containing monomer contains acrylic acid and a monomer having higher hydrophobicity than the acrylic acid.

[0008] One aspect of the adhesive electrode for acquiring biological signals according to the present invention does not absorb more moisture than necessary even if moisture penetrates from the outside during use, improves skin contact impedance, and has excellent adhesion.

[0009] 1 is a diagram showing an example of a cross section of the configuration of an adhesive electrode for acquiring a biological signal according to an embodiment of the present invention; FIG. 2 is a diagram illustrating an example of acid-base interaction between polymers in an acrylic polymer; FIG. 3 is a diagram illustrating another example of acid-base interaction between polymers in an acrylic polymer; and FIG. 4 is an explanatory diagram showing a method for measuring the holding power of examples and comparative examples.

[0010] Hereinafter, embodiments of the present invention will be described in detail. In this specification, unless otherwise specified, the term "to" indicating a range of values ​​means that the range includes the values ​​before and after it as the lower and upper limits.

[0011] <Adhesive electrode for acquiring biological signals> An adhesive electrode for acquiring biological signals according to this embodiment will be described. Note that a living body refers to the human body (person) and animals such as cows, horses, pigs, chickens, dogs, and cats. The biosensor according to this embodiment can be suitably used for living bodies, particularly for the human body. In this embodiment, a case where the living body is a human will be described as an example.

[0012] The adhesive electrode for acquiring a biological signal according to this embodiment is a biological electrode that is attached to a part of a living body (for example, the skin, scalp, or forehead) to detect biological information. The adhesive electrode for acquiring a biological signal is attached to the surface of a living body and brought into contact with the surface, thereby measuring the potential difference (polarization voltage) between the living body and the adhesive electrode for acquiring a biological signal, and can be used to detect an electrical signal related to biological information (biosignal). In this embodiment, a case will be described in which the adhesive electrode for acquiring a biological signal is attached to human skin to acquire an electrical signal related to the human biological information (biosignal). The biosignal is, for example, an electrical signal representing an electrocardiogram waveform, an electroencephalogram, a pulse, or the like.

[0013] The adhesive electrode for acquiring a biological signal according to this embodiment may have a shape such as a sheet or a rod. The shape of the adhesive electrode for acquiring a biological signal in a plan view may be formed into any appropriate shape depending on the application, etc., such as a substantially rectangular, substantially polygonal, substantially circular, substantially elliptical, or a combination thereof. For example, one end of the adhesive electrode for acquiring a biological signal in the longitudinal direction thereof (one end) may be formed into a substantially rectangular shape, and the other end (the other end) in the longitudinal direction may be formed into a substantially arc shape.

[0014] The thickness of the adhesive electrode for acquiring a biological signal according to the present embodiment may be any appropriate thickness depending on the application, size, etc., as long as it can ensure strength, flexibility, low resistance, and conductivity. The thickness of the adhesive electrode for acquiring a biological signal refers to the length in a direction perpendicular to the surface of the adhesive electrode for acquiring a biological signal. The thickness of the adhesive electrode for acquiring a biological signal is, for example, the thickness measured at an arbitrary location on the cross section of the adhesive electrode for acquiring a biological signal. When measurements are taken at multiple locations at the same location, the thickness may be the average value of the thicknesses measured at these locations.

[0015] The adhesive electrode for acquiring a biological signal according to this embodiment is an electrode having adhesive properties (adhesive electrode), and contains a conductive polymer and an aqueous emulsion adhesive as adhesive materials, and may also contain other components.

[0016] An example of a cross section of the configuration of the adhesive electrode for acquiring a biological signal according to this embodiment is shown in Fig. 1. As shown in Fig. 1, in the adhesive electrode for acquiring a biological signal 1, conductive polymers 11 are dispersed in a particulate aqueous emulsion adhesive 12, and the plurality of conductive polymers 11 dispersed in the aqueous emulsion adhesive 12 are linked to each other.

[0017] The adhesive electrode for acquiring biological signals according to this embodiment comprises a conductive polymer and an aqueous emulsion adhesive, and the aqueous emulsion adhesive contains an acrylic polymer having a specific monomer composition, which enhances water resistance, suppresses absorption of external moisture even when moisture penetrates from the outside, improves skin contact impedance with the skin, and exhibits excellent adhesion.

[0018] [Conductive Polymer] Examples of the conductive polymer contained in the adhesive electrode for acquiring a biological signal include polythiophene-based conductive polymers, polyaniline-based conductive polymers, polypyrrole-based conductive polymers, polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, and derivatives thereof, and complexes thereof, etc. These may be used alone or in combination of two or more.

[0019] Examples of polythiophene-based conductive polymers include polythiophene, poly3-methylthiophene, poly3-ethylthiophene, poly3-propylthiophene, poly3-butylthiophene, poly3-hexylthiophene, poly3-heptylthiophene, poly3-octylthiophene, poly3-decylthiophene, poly3-dodecylthiophene, poly3-octadecylthiophene, poly3-bromothiophene, poly3-chlorothiophene, poly3-iodothiophene, poly3-cyanothiophene, poly3-phenylthiophene, poly3,4-dimethylthiophene, poly3,4-dibutylthiophene, poly3-hydroxythiophene, poly3-methoxythiophene, poly3-ethoxythiophene, poly3-butoxythiophene, poly3-hexyloxythiophene, poly3-heptyloxythiophene, poly3-octyloxythiophene, poly3-decyloxythiophene, poly3-dodecyloxythiophene, poly3 -octadecyloxythiophene, poly3,4-dihydroxythiophene, poly3,4-dimethoxythiophene, poly3,4-diethoxythiophene, poly3,4-dipropoxythiophene, poly3,4-dibutoxythiophene, poly3,4-dihexyloxythiophene, poly3,4-diheptyloxythiophene, poly3,4-dioctyloxythiophene, poly3,4-didecyloxythiophene, poly3,4-didodecyloxythiophene, poly3,4-ethylenedioxythiophene (also referred to as "PEDOT"), poly3,4-propylenedioxythiophene, poly3,4-butenedioxythiophene, poly3-methyl-4-methoxythiophene, poly3-methyl-4-ethoxythiophene, poly3-carboxythiophene, poly3-methyl-4-carboxythiophene, poly3-methyl-4-carboxyethylthiophene, and poly3-methyl-4-carboxybutylthiophene.

[0020] Examples of polyanionic conductive polymers include polymers having sulfonic acid groups such as polystyrene sulfonic acid (also referred to as "PSS"), polyvinyl sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polysulfoethyl methacrylate, poly(4-sulfobutyl methacrylate), and polymethacryloxybenzenesulfonic acid, and polymers having carboxylic acid groups such as polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacrylic carboxylic acid, polymethacrylic carboxylic acid, poly(2-acrylamido-2-methylpropanecarboxylic acid), polyisoprene carboxylic acid, and polyacrylic acid. These may be used as homopolymers obtained by polymerizing one type alone, or as copolymers of two or more types. Among these polyanions, polymers having sulfonic acid groups are preferred because they can achieve higher conductivity, and polystyrene sulfonic acid is more preferred.

[0021] Examples of polypyrrole-based conductive polymers include polypyrrole, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-ethylpyrrole), poly(3-n-propylpyrrole), poly(3-butylpyrrole), poly(3-octylpyrrole), poly(3-decylpyrrole), poly(3-dodecylpyrrole), poly(3,4-dimethylpyrrole), poly(3,4-dibutylpyrrole), poly(3-carboxypyrrole), poly(3-methyl-4-carboxypyrrole), poly(3-methyl-4-carboxyethylpyrrole), poly(3-methyl-4-carboxybutylpyrrole), poly(3-hydroxypyrrole), poly(3-methoxypyrrole), poly(3-ethoxypyrrole), poly(3-butoxypyrrole), poly(3-hexyloxypyrrole), and poly(3-methyl-4-hexyloxypyrrole).

[0022] Examples of polyacetylene-based conductive polymers include polyacetylenes having polar groups, such as polyphenylacetylene monoesters having an ester at the para-position of phenylacetylene, and polyphenylacetylene monoamides having an amide at the para-position of phenylacetylene.

[0023] Examples of polyphenylene-based conductive polymers include polyphenylene vinylene.

[0024] As these composites, a composite in which polythiophene is doped with polyaniline as a dopant is preferred, etc. Among composites of polythiophene and polyaniline, it is more preferred to use PEDOT / PSS in which PEDOT is doped with PSS, because it has a lower contact impedance with a living body and high conductivity.

[0025] The content of the conductive polymer is preferably 0.20 parts by mass to 20 parts by mass, more preferably 2.5 parts by mass to 15 parts by mass, and even more preferably 3.0 parts by mass to 12 parts by mass, relative to 100 parts by mass of the adhesive electrode for acquiring a biological signal. When the content is within the above preferred range relative to 100 parts by mass of the adhesive electrode for acquiring a biological signal, the adhesive electrode for acquiring a biological signal can have excellent conductivity, toughness, and flexibility.

[0026] The conductive polymer may be used as an aqueous solution dissolved in a solvent. In this case, the solvent may be an organic solvent or an aqueous solvent. Examples of organic solvents include ketones such as acetone and methyl ethyl ketone (MEK); esters such as ethyl acetate; ethers such as propylene glycol monomethyl ether; and amides such as N,N-dimethylformamide. Examples of aqueous solvents include water; and alcohols such as methanol, ethanol, propanol, and isopropanol. Of these, it is preferable to use an aqueous solvent.

[0027] [Water-based emulsion adhesive] The water-based emulsion adhesive contained in the adhesive electrode for acquiring a biological signal is used as a base material of the adhesive electrode for acquiring a biological signal, and has the function of improving the adhesiveness and flexibility of the adhesive electrode for acquiring a biological signal. Therefore, by including the water-based emulsion adhesive in the adhesive electrode for acquiring a biological signal, the adhesive electrode for acquiring a biological signal has low elasticity, improves its ability to conform to the irregularities of the surface of a living body, and can exhibit good adhesion to the skin.

[0028] The aqueous emulsion PSA is an acrylic emulsion PSA. The aqueous emulsion PSA can be formed from a water-dispersed pressure-sensitive adhesive composition containing an acrylic polymer, and may be formed from a water-dispersed pressure-sensitive adhesive composition containing, in addition to the acrylic polymer, a crosslinking agent, a tackifying resin, additives, and the like as optional components.

[0029] The content of the aqueous emulsion adhesive is not particularly limited and may be any appropriate amount, but is preferably 35% to 90% by mass, relative to 100% by mass of the adhesive electrode for acquiring a biological signal. The content of the aqueous emulsion adhesive is more preferably 40% by mass or more, even more preferably 50% by mass or more, more preferably 85% by mass or less, and even more preferably 80% by mass or less. When the content of the aqueous emulsion adhesive is within the above preferred range, adhesive strength and flexibility can be imparted to the adhesive electrode for acquiring a biological signal, and a decrease in conductivity can be suppressed.

[0030] The mass ratio of the conductive polymer to the aqueous emulsion adhesive (conductive polymer / aqueous emulsion adhesive) is preferably 8 to 18, more preferably 10 to 16, and even more preferably 12 to 14. When the mass ratio is within the above preferred range, the adhesive electrode for acquiring biological signals can maintain adhesive strength while exhibiting conductivity.

[0031] (Water-dispersed pressure-sensitive adhesive composition) A water-dispersed pressure-sensitive adhesive composition has at least some of its components dispersed in an aqueous medium. The water-dispersed type includes suspended and emulsified states. The aqueous medium refers to water or a mixed solvent (aqueous solvent) containing water as the main component as the solvent constituting the aqueous medium. A water-dispersed pressure-sensitive adhesive composition typically has an emulsion form in which an acrylic polymer is dispersed in water.

[0032] The acrylic polymer contained in the water-dispersible pressure-sensitive adhesive composition is contained as a base polymer in the water-dispersible pressure-sensitive adhesive composition.

[0033] The base polymer refers to the main component of the polymer contained in the water-dispersible pressure-sensitive adhesive composition.

[0034] The main component refers to the component that is contained in the largest proportion by mass of the components contained in the aqueous dispersion-type pressure-sensitive adhesive composition. The content of the acrylic polymer in the aqueous dispersion-type pressure-sensitive adhesive composition is 34 mass% or more, and may be more than 50 mass%, more than 60 mass%, or more than 80 mass%.

[0035] In this embodiment, the acrylic polymer refers to a polymer derived from a monomer component containing more than 50% by mass of an acrylic monomer. The acrylic monomer refers to a monomer having at least one (meth)acryloyl group in one molecule.

[0036] "(Meth)acryloyl" refers to acryloyl and methacryloyl inclusively. "(Meth)acrylate" refers to acrylate and methacrylate inclusively. "(Meth)acrylic" refers to acrylic and methacrylic inclusively.

[0037] The acrylic polymer is a polymer of monomer components containing an alkyl (meth)acrylate ester (m1) as a main component and a carboxyl group-containing monomer (m2) as a secondary component. The acrylic polymer preferably contains, as a secondary component, a nitrogen atom-containing monomer (m3) in which no hydrogen atom is bonded to the nitrogen atom (hereinafter, sometimes simply referred to as "nitrogen atom-containing monomer (m3)") in addition to the carboxyl group-containing monomer (m2).

[0038] The acrylic polymer has the above-mentioned monomer composition, so that the aqueous emulsion pressure-sensitive adhesive containing the acrylic polymer can function as a pressure-sensitive adhesive that has flexibility, high adhesive strength, and good water resistance. Furthermore, the flexibility of the aqueous emulsion pressure-sensitive adhesive containing the acrylic polymer makes it easy to deform, so that it can easily follow deformations of the skin, etc.

[0039] The acrylic polymer preferably contains, as a base polymer, an acrylic polymer constituted from a monomer component containing an alkyl (meth)acrylate (m1).

[0040] The (meth)acrylic acid alkyl ester (m1) may be, for example, a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having 1 to 20 carbon atoms at the ester terminal.

[0041] In addition, (meth)acrylic acid alkyl ester having an alkyl group with the number of carbon atoms of X to Y (X and Y are integers, and Y is an integer greater than X) at the ester terminal is referred to as "(meth)acrylic acid C Ｘ－Ｙ The (meth)acrylic acid alkyl ester (m1) may be used alone or in combination of two or more.

[0042] In order to obtain the desired adhesive properties (e.g., adhesive strength, cohesive strength, etc.), the proportion of the (meth)acrylic acid alkyl ester (m1) in the entire monomer components of the acrylic polymer is more than 50% by mass, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 92% by mass or more, and most preferably 94% by mass or more. In addition, in order to obtain the effect based on the copolymerization of the carboxy group-containing monomer (m2) and the nitrogen atom-containing monomer (m3) described below, the proportion of the (meth)acrylic acid alkyl ester in the entire monomer components is, for example, 99.4% by mass or less, preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less.

[0043] (Meth)acrylic acid C Ｘ－Ｙ Examples of alkyl esters include (meth)acrylic acid C １－２０ Alkyl esters and the like.

[0044] (Meth)acrylic acid C １－２０ Examples of alkyl esters include 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, and isooctyl (meth)acrylate. Examples of suitable acrylates include acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0045] (Meth)acrylic acid C１－２０ Among alkyl esters, (meth)acrylic acid C ４－２０ It is preferable to use alkyl esters, and (meth)acrylic acid C ４－１８ It is more preferable to use alkyl esters, and (meth)acrylic acid C ４－１２ It is more preferable to use alkyl esters, and (meth)acrylic acid C ４－１０ It is particularly preferred to use alkyl esters.

[0046] By using the above alkyl (meth)acrylate as the main component, the acrylic polymer tends to have good adhesive properties.

[0047] Among the monomer components constituting the acrylic polymer, (meth)acrylic acid C １－２０ (Meth)acrylic acid C in alkyl esters ４－１８ Alkyl ester (preferably (meth)acrylic acid C ４－１２ Alkyl esters, more preferably (meth)acrylic acid C ４－１０ The proportion of the alkyl ester) is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, and may be 95% by mass or more, 98% by mass or more, or 100% by mass.

[0048] (Meth)acrylic acid C １－２０ The alkyl ester is (meth)acrylic acid C ４－１０ Among alkyl esters, acrylic acid C ７－９ It is preferable to use an alkyl ester. ７－９ By using an alkyl ester, the acrylic polymer can have good adhesive strength and exhibit excellent flexibility.

[0049] Among the monomer components constituting the acrylic polymer, (meth)acrylic acid C １－２０ Acrylic acid C in alkyl esters ７－９The proportion of the alkyl ester is, for example, preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 98% by mass. １－２０ Acrylic acid C in alkyl esters ７－９ The proportion of alkyl esters may be 100% by weight.

[0050] Acrylic Acid C ７－９ Examples of alkyl esters include 2-ethylhexyl acrylate (2-EHA), heptyl acrylate, octyl acrylate, isooctyl acrylate, isononyl acrylate, etc. Among these, 2-EHA is preferred.

[0051] The carboxyl group-containing monomer (m2) used as a monomer component constituting the acrylic polymer contains acrylic acid (m2a) and a monomer (m2b) that is more hydrophobic than acrylic acid (m2a) (hereinafter also referred to as "relatively hydrophobic monomer (m2b)").

[0052] The combined use of acrylic acid (m2a) and a relatively hydrophobic monomer (m2b) as the carboxyl group-containing monomer (m2) can improve the adhesive strength and water resistance of aqueous emulsion pressure-sensitive adhesives. The reason for this is that, in the synthesis of a water-dispersible acrylic polymer, as shown in Figure 2, in polymer particles containing a (meth)acrylic acid alkyl ester (m1) and a carboxyl group-containing monomer (m2) in a dispersion containing these, the relatively polar acrylic acid (m2a) is present on the surface side of the polymer particles containing the (meth)acrylic acid alkyl ester (m1) and the carboxyl group-containing monomer (m2), which is thought to contribute to the dispersion stability of the polymer particles of the carboxyl group-containing monomer (m2) and the ease of dispersion preparation. On the other hand, the relatively hydrophobic monomer (m2b), due to its hydrophobicity, is present in large amounts inside the polymer particles of the carboxyl group-containing monomer (m2), which is thought to improve the cohesion inside the polymer particles containing the (meth)acrylic acid alkyl ester (m1) and the carboxyl group-containing monomer (m2). As a result, even after the polymer particles fuse together during subsequent drying to form an aqueous emulsion PSA, the aqueous emulsion PSA retains high cohesive strength as a bulk, which is thought to improve adhesive strength and water resistance. Note that the effects of combining acrylic acid (m2a) with a relatively hydrophobic monomer (m2b) are not limited to the above considerations.

[0053] The acrylic acid (m2a) is a polymerizable compound containing a carboxyl group copolymerizable with a (meth)acrylic acid alkyl ester in its structure. In addition to the acrylic acid (m2a), a polymerizable compound containing a carboxyl group copolymerizable with a (meth)acrylic acid alkyl ester in its structure may be included, or a polymerizable compound containing a carboxyl group copolymerizable with a (meth)acrylic acid alkyl ester in its structure may be used instead of the acrylic acid (m2a).

[0054] Examples of the polymerizable compound having a carboxyl group copolymerizable with a (meth)acrylic acid alkyl ester in its structure include, in addition to acrylic acid (m2a), itaconic acid, maleic acid, maleic anhydride, and 2-methacryloyloxyethyl succinic acid.

[0055] The acrylic acid (m2a) is preferably contained in an amount of 0.1 to 10% by mass relative to 100% by mass of the acrylic polymer, from the viewpoint of adjusting the hydrolysis of the silane-based monomer or the adhesiveness of the resulting aqueous emulsion adhesive.

[0056] Whether or not the relatively hydrophobic monomer (m2b) has higher hydrophobicity than acrylic acid can be determined from its chemical structure, and can also be determined from its water solubility at 20° C., which will be described later.

[0057] Examples of the relatively hydrophobic monomer (m2b) include ethylenically unsaturated monocarboxylic acids such as methacrylic acid (MAA), carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl phthalic acid, 2-(meth)acryloyloxyethiacryloxyethyl tetrahydrophthalic acid, crotonic acid, and isocrotonic acid. The above monomers can be used alone or in combination of two or more. Among these, MAA is preferred from the viewpoint of being effective in small amounts due to its low molecular weight.

[0058] The relatively hydrophobic monomer (m2b) is preferably a monomer having a water solubility (solubility in water) of 15.0 g / 100 mL or less at 20° C. By using the relatively hydrophobic monomer (m2b) having a water solubility of a predetermined value or less in combination with acrylic acid (m2a), the relatively hydrophobic monomer (m2b) is appropriately present inside the polymer particles containing the carboxy group-containing monomer (m2b), which is thought to contribute to improving the cohesive force inside the polymer particles.

[0059] The water solubility of the relatively hydrophobic monomer (m2b) is preferably 12.0 g / 100 mL or less, or may be 10.0 g / 100 mL or less, 8.0 g / 100 mL or less, or 5.0 g / 100 mL or less, from the viewpoint of improving the cohesion strength inside the polymer particles containing the carboxy group-containing monomer (m2b). Furthermore, from the viewpoint of emulsion polymerization property, the water solubility of the relatively hydrophobic monomer (m2b) is preferably 2.0 g / 100 mL or more, more preferably 6.0 g / 100 mL or more, and even more preferably 8.0 g / 100 mL or more.

[0060] The water solubility of the monomer material at 20°C can be determined based on the value measured in Techniques of Chemistry 4th Ed. Vol. II Organic Solvents (1985): New York, NY. John Wiley and Sons, Inc. ICSC(J) 1997. The same applies to the examples described below.

[0061] The combined content of acrylic acid (m2a) and the relatively hydrophobic monomer (m2b) is preferably 3 parts by mass or less, more preferably 2.7 parts by mass or less, and even more preferably 2.5 parts by mass or less, per 100 parts by mass of the aqueous dispersion-type pressure-sensitive adhesive composition. A combined content of 3 parts by mass or less, per 100 parts by mass of the aqueous dispersion-type pressure-sensitive adhesive composition, can enhance the water resistance of the aqueous emulsion PSA.

[0062] The ratio of the acrylic acid (m2a) to the relatively hydrophobic monomer (m2b) used is not particularly limited, and an appropriate ratio can be adopted depending on the dispersion stability, polymer preparation properties, the type of the relatively hydrophobic monomer (m2b) used, and the like.

[0063] The mass ratio ((m2a) / (m2b)) of the amount of acrylic acid (m2a) used to the amount of relatively hydrophobic monomer (m2b) used may be, for example, 0.1 or more, 0.5 or more, 1.0 or more (e.g., greater than 1.0), 1.5 or more, or 1.8 or more, from the viewpoints of dispersion stability, dispersion preparation ease, etc. Furthermore, the ratio ((m2a) / (m2b)) may be, for example, 10 or less, 5 or less, 3 or less, or 2 or less, from the viewpoints of improving adhesive strength and water resistance.

[0064] The amount of acrylic acid (m2a) used (the copolymerization ratio of acrylic acid (m2a) in the acrylic polymer) may be, for example, 0.1% by mass or more of the total monomer components, preferably 0.5% by mass or more, and more preferably 1.0% by mass or more (e.g., 1.5% by mass or more). By using a predetermined amount or more of acrylic acid, the adhesive properties (adhesive strength, cohesive strength, etc.) of the aqueous emulsion pressure-sensitive adhesive are improved, and the dispersion stability of the monomer components contained in the aqueous emulsion pressure-sensitive adhesive and the ease of dispersion preparation are also improved. Furthermore, from the viewpoint of the water resistance and flexibility of the aqueous emulsion pressure-sensitive adhesive, the amount of acrylic acid (m2a) used is, for example, preferably less than 10% by mass of the total monomer components, more preferably less than 5.0% by mass, and even more preferably less than 3.0% by mass.

[0065] The amount of the relatively hydrophobic monomer (m2b) used (the copolymerization ratio of the relatively hydrophobic monomer (m2b) in the acrylic polymer) may be, for example, 0.1% by mass or more of the total monomer components, preferably 0.3% by mass or more, more preferably 0.7% by mass or more, and may be more than 1.0% by mass (e.g., 1.5% by mass or more). By setting the amount of the relatively hydrophobic monomer (m2b) used within a predetermined range, the adhesive strength, cohesive strength, and water resistance of the aqueous emulsion PSA can be improved. Furthermore, from the viewpoints of water resistance, flexibility, etc., the amount of the relatively hydrophobic monomer (m2b) used is, for example, preferably less than 10% by mass of the total monomer components, more preferably less than 5.0% by mass, and even more preferably less than 3.0% by mass, and may be 1.5% by mass or less.

[0066] The amount of the carboxy group-containing monomer (m2) used (the copolymerization ratio of the carboxy group-containing monomer (m2) in the acrylic polymer) is not particularly limited and may be, for example, 0.1% by mass or more of the total monomer components, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 2.0% by mass or more, particularly preferably 2.5% by mass or more, and most preferably 3.0% by mass or more. By increasing the amount of the carboxy group-containing monomer (m2) used within a predetermined range, the adhesive strength, cohesive strength, and water resistance of the aqueous emulsion pressure-sensitive adhesive can be improved. Furthermore, from the viewpoint of the water resistance and flexibility of the aqueous emulsion pressure-sensitive adhesive, the amount of the carboxy group-containing monomer (m2) used is suitably, for example, less than 10% by mass of the total monomer components, preferably 5.0% by mass or less, or alternatively 4.5% by mass or less, or even 3.5% by mass or less.

[0067] As described above, the acrylic polymer preferably contains a nitrogen-containing monomer (m3) in addition to the carboxyl group-containing monomer (m2) as a constituent monomer component. The acrylic polymer can improve the adhesive strength and water resistance of an aqueous emulsion pressure-sensitive adhesive by using the carboxyl group-containing monomer (m2) and the nitrogen-containing monomer (m3) in combination. This is thought to be because, as shown in Figure 3, the coexistence of the carboxyl group-containing monomer (m2) and the nitrogen-containing monomer (m3) in the acrylic polymer improves the cohesive strength due to the acid-base interaction between the relatively hydrophobic monomer (m2b) of the carboxyl group-containing monomer (m2) and the nitrogen-containing monomer (m3), and this cohesive strength contributes to improving the adhesive strength and water resistance of the aqueous emulsion pressure-sensitive adhesive. The effects of using the carboxyl group-containing monomer (m2) in combination with the nitrogen-containing monomer (m3) are not limited to those discussed above. By utilizing the effect of the combined use of the carboxy group-containing monomer (m2) and the nitrogen atom-containing monomer (m3), for example, by employing a highly flexible material as the main monomer, the (meth)acrylic acid alkyl ester (m1), the aqueous emulsion pressure-sensitive adhesive can achieve flexibility, adhesive strength, and water resistance all at the same time.

[0068] As the nitrogen atom-containing monomer (m3), a monomer having a structure in which no hydrogen atom is bonded to the nitrogen atom is used. By using the nitrogen atom-containing monomer (m3) having the above structure in combination with a carboxy group-containing monomer (m2), the adhesive strength and water resistance of the aqueous emulsion pressure-sensitive adhesive can be improved. The nitrogen atom-containing monomer (m3) in which no hydrogen atom is bonded to the nitrogen atom exhibits a stronger acid-base interaction with carboxylic acids, including acrylic acid, than a nitrogen atom-containing monomer in which a hydrogen atom is bonded to the nitrogen atom. This acid-base interaction is thought to improve the cohesive strength, thereby improving the adhesive strength and water resistance of the aqueous emulsion pressure-sensitive adhesive. The effects of using the nitrogen atom-containing monomer (m3) in combination with a carboxy group-containing monomer (m2) are not limited to those discussed above.

[0069] As the nitrogen atom-containing monomer (m3), it is preferable to use a nitrogen atom-containing monomer having a small acid dissociation constant (pKa). It is believed that the smaller the pKa, the stronger the acid-base interaction with carboxylic acid, making it easier to obtain excellent cohesive strength. The pKa of the nitrogen atom-containing monomer (m3) may be, for example, 7 or less, 5 or less, or 3 or less. From the viewpoint of obtaining better adhesive strength and water resistance, a nitrogen atom-containing monomer (m3) having a pKa of 1 or less is used. The pKa may be 0.5 or less, 0 or less, or lower than 0, or -0.5 or less. The lower limit of the pKa of the nitrogen atom-containing monomer (m3) is -2 or more, -1.5 or more, or -1 or more. It is believed that by using a nitrogen atom-containing monomer (m3) having a pKa within the above range, good acid-base interaction can be obtained due to its basicity.

[0070] The pKa can be calculated from the concentration of the substance to be measured and the hydrogen ion concentration by measuring the hydrogen ion concentration of the substance using a pH meter.

[0071] As the nitrogen atom-containing monomer (m3), any monomer having a structure in which no hydrogen atom is bonded to the nitrogen atom can be used without any particular limitation, and examples thereof include a monomer having a nitrogen atom-containing ring, an amide group-containing monomer, and an amino group-containing monomer. The nitrogen atom-containing monomer (m3) can be used alone or in combination of two or more.

[0072] Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylmorpholine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and N-vinylpyridazine.

[0073] Examples of the amide group-containing monomer include N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-di(n-butyl)(meth)acrylamide, and N,N-di(t-butyl)(meth)acrylamide.

[0074] Examples of amino group-containing monomers include N,N-dialkylaminoalkyl(meth)acrylates such as N,N-dimethylaminoethyl(meth)acrylate.

[0075] As the nitrogen atom-containing monomer (m3), for example, a monomer having a cyclic structure containing a nitrogen atom in the ring (monomer having a nitrogen atom-containing ring) is used. By using a monomer having a nitrogen atom-containing ring, the aqueous emulsion pressure-sensitive adhesive can exhibit better adhesive strength and water resistance. It is thought that the structure having a nitrogen atom-containing ring provides a distance that makes it easy for the acid and base to interact with each other, making it easier to achieve a better cohesive strength improvement effect.

[0076] Suitable examples of the monomer having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone (NVP) and N-(meth)acryloylmorpholine. Among them, NVP has good biocompatibility and is suitable for use in adhesive electrodes for acquiring biological signals. The monomer having a nitrogen atom-containing ring can be used alone or in combination of two or more.

[0077] When a monomer having a nitrogen atom-containing ring is used as the nitrogen atom-containing monomer (m3), the proportion of the monomer having a nitrogen atom-containing ring in the entire nitrogen atom-containing monomer (m3) is not particularly limited and may be set appropriately. For example, from the viewpoint of effectively exhibiting the effects of using the monomer having a nitrogen atom-containing ring, the proportion of the monomer having a nitrogen atom-containing ring in the entire nitrogen atom-containing monomer (m3) may be, for example, 10% by mass or more, preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and most preferably 95% by mass or more. The proportion of the monomer having a nitrogen atom-containing ring in the entire nitrogen atom-containing monomer (m3) may be 100% by mass or less.

[0078] The amount of the nitrogen atom-containing monomer (m3), i.e., the copolymerization ratio of the nitrogen atom-containing monomer (m3) in the acrylic polymer, is not particularly limited and may be, for example, 0.1 mass% or more of the total monomer components, preferably 0.3 mass% or more, more preferably 0.5 mass% or more, even more preferably 0.8 mass% or more, particularly preferably 1.0 mass% or more, and most preferably 1.5 mass% or more. By increasing the amount of the nitrogen atom-containing monomer (m3) used within a predetermined range, the adhesive strength, cohesive strength, and water resistance of the aqueous emulsion pressure-sensitive adhesive can be improved.

[0079] From the viewpoint of the water resistance and flexibility of the aqueous emulsion pressure-sensitive adhesive, the amount of the nitrogen atom-containing monomer (m3) used is, for example, suitably less than 10 mass% of the total monomer components, preferably 5.0 mass% or less, more preferably 3.0 mass% or less, and even more preferably 2.5 mass% or less, and may be 2.0 mass% or less, 1.5 mass% or less, or 1.2 mass% or less.

[0080] The ratio of the carboxy group-containing monomer (m2) to the nitrogen atom-containing monomer (m3) is not particularly limited and is appropriately set so as to exhibit the desired adhesive strength and water resistance. The mass ratio (m2 / m3) of the amount of the carboxy group-containing monomer (m2) to the amount of the nitrogen atom-containing monomer (m3) may be, for example, 0.1 or more, suitably 0.5 or more, preferably 1.0 or more, more preferably 1.5 or more, and even more preferably 2.0 or more. The ratio (m2 / m3) may be 2.5 or more, 3.0 or more, or even 3.5 or more. The ratio (m2 / m3) may be, for example, 10 or less, suitably 7 or less, preferably 5 or less, and more preferably 4 or less. The ratio (m2 / m3) may be 3 or less, or 2.5 or less.

[0081] The monomer components constituting the acrylic polymer may further contain a silane-based monomer (also referred to as a silane coupling agent). By using an acrylic polymer containing a silane-based monomer as a monomer unit, a crosslinked structure can be introduced between polymer particles in the aqueous dispersion-type pressure-sensitive adhesive composition through a condensation reaction of silanol groups (silanol condensation). This crosslinking between polymer particles improves the cohesive strength of the polymer particles, thereby improving the adhesive strength and water resistance of the aqueous emulsion pressure-sensitive adhesive.

[0082] As the silane-based monomer, an alkoxysilyl group-containing monomer is preferably used. The alkoxysilyl group-containing monomer is typically an ethylenically unsaturated monomer having at least one, and preferably two or more (e.g., two or three) alkoxysilyl groups in one molecule.

[0083] Examples of the silane-based monomer include 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane. The silane-based monomers can be used alone or in combination of two or more.

[0084] In the embodiment in which the monomer component contains a silane-based monomer, the proportion of the alkoxysilyl group-containing monomer in the total monomer component is, for example, suitably 0.001% by mass or more, preferably 0.01% by mass or more.Furthermore, from the viewpoint of improving adhesion to the skin, the proportion of the silane-based monomer is, for example, suitably 0.5% by mass or less, preferably 0.2% by mass or less, and may be 0.1% by mass or less, or may be 0.05% by mass or less.

[0085] The monomer components constituting the acrylic polymer may, as necessary, contain another monomer (another copolymerizable monomer) copolymerizable with the (meth)acrylic acid alkyl ester, which is different from the carboxy group-containing monomer (m2), the nitrogen atom-containing monomer (m3), and the silane-based monomer.

[0086] Suitable examples of the other copolymerizable monomer include a monomer having a functional group such as a hydroxyl group and a monomer having a relatively high glass transition temperature of the homopolymer (for example, 10° C. or higher). The other copolymerizable monomers can be used alone or in combination of two or more.

[0087] Other copolymerizable monomers include, for example, acid anhydride group-containing monomers, hydroxyl group-containing monomers (e.g., 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate), monomers containing a sulfonic acid group or a phosphoric acid group, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, alkoxy group-containing monomers, vinyl esters, vinyl ethers, aromatic vinyl compounds, olefins, (meth)acrylic acid esters having an alicyclic hydrocarbon group, (meth)acrylic acid esters having an aromatic hydrocarbon group, and other heterocycle-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogen atom-containing (meth)acrylates such as vinyl chloride and fluorine atom-containing (meth)acrylates, silicon atom-containing (meth)acrylates such as silicone (meth)acrylate, (meth)acrylic acid esters obtained from terpene compound derivative alcohols, and polyfunctional monomers (monomers having at least two polymerizable functional groups having an unsaturated double bond such as (meth)acryloyl groups and vinyl groups).

[0088] Furthermore, as the other copolymerizable monomer, a carboxy group-containing monomer different from the acrylic acid (m2a) and the relatively hydrophobic monomer (m2b), or a nitrogen atom-containing monomer in which a hydrogen atom is bonded to a nitrogen atom (for example, an amide group-containing monomer or an amino group-containing monomer having a structure in which a hydrogen atom is bonded to a nitrogen atom) may be used.

[0089] The content of the other copolymerizable monomer is not particularly limited and may be set arbitrarily. When the monomer component of the acrylic polymer contains the other copolymerizable monomer, the proportion of the other copolymerizable monomer in the entire monomer component is suitably 30% by mass or less, may be 10% by mass or less, may be 3% by mass or less, or may be less than 1% by mass. The monomer component may be substantially free of the other copolymerizable monomer.

[0090] Furthermore, since the aqueous emulsion pressure-sensitive adhesive can achieve high cohesive strength by using a carboxy group-containing monomer (m2) in combination with a nitrogen atom-containing monomer (m3), it is not necessary to include a hydroxyl group-containing monomer used for purposes such as crosslinking reactions or improving cohesive strength. Therefore, the content of the hydroxyl group-containing monomer in the monomer component of the acrylic polymer may be, for example, less than 3 mass%, less than 1 mass%, or less than 0.1 mass%. Furthermore, the aqueous emulsion pressure-sensitive adhesive does not necessarily need to be substantially free of a hydroxyl group-containing monomer in its monomer component.

[0091] The acrylic polymer can be synthesized by emulsion polymerization. The mode of emulsion polymerization is not particularly limited, and the same monomer supply method, polymerization conditions, materials used, etc. as those used in general emulsion polymerization can be appropriately used.

[0092] The monomer supply method may be, for example, a batch charging method in which all the monomer raw materials are supplied at once, a continuous supply (dropping) method, or a divided supply (dropping) method.

[0093] The monomer raw materials are preferably supplied as a dispersion (emulsion) in which they are partly or entirely emulsified in water. For example, when the monomer raw materials are supplied by a dropwise addition method, the monomer raw materials are preferably added dropwise in the form of an emulsion.

[0094] The polymerization temperature may be, for example, 30°C or higher, 50°C or higher, 100°C or lower, or 80°C or lower.

[0095] The initiator used in the polymerization can be appropriately selected from commonly used polymerization initiators depending on the type of polymerization method, such as azo polymerization initiators, peroxide initiators, redox initiators formed by combining peroxides with reducing agents, and substituted ethane initiators.

[0096] When emulsion polymerization is used, it is preferable to use a water-soluble polymerization initiator. The polymerization initiator may be used alone or in combination of two or more. The amount of the polymerization initiator used may be selected, for example, from the range of 0.005 to 1 part by mass per 100 parts by mass of the monomer components.

[0097] The emulsifier used in emulsion polymerization is not particularly limited, and commonly used anionic surfactants, nonionic surfactants, etc. can be used. Furthermore, from the viewpoint of improving water resistance, it is preferable to use a surfactant having a radically polymerizable functional group (reactive emulsifier) ​​as the emulsifier used in emulsion polymerization. The emulsifier may be used alone or in combination of two or more.

[0098] As the reactive emulsifier, for example, one having a structure in which a radically polymerizable functional group is introduced into an anionic surfactant or a nonionic surfactant may be used.

[0099] Examples of radically polymerizable functional groups include vinyl groups, propenyl groups, isopropenyl groups, vinyl ether groups (vinyloxy groups), and allyl ether groups (allyloxy groups). The concept of a propenyl group here includes a 1-propenyl group (CH ３ -CH=CH and 2-propenyl group (CH ２ =CH-CH ２ -; sometimes referred to as an allyl group.

[0100] From the viewpoint of emulsifying properties such as polymerization stability during emulsion polymerization, it is preferable to use an anionic reactive emulsifier having a structure in which a radically polymerizable functional group is introduced into an anionic surfactant.

[0101] Examples of the anionic reactive emulsifier include polyoxyethylene (allyloxymethyl) alkyl ether sulfates (e.g., ammonium salts), polyoxyethylene nonylpropenyl phenyl ether sulfates (e.g., ammonium salts), alkyl allyl sulfosuccinates (e.g., sodium salts), methacryloxypolyoxypropylene sulfates (e.g., sodium salts), and polyoxyalkylene alkenyl ether sulfates (e.g., ammonium salts in which the alkenyl group terminates with an isopropenyl group).

[0102] When the anionic reactive emulsifier forms a salt, the salt may be, for example, a metal salt such as a sodium salt, or a non-metal salt such as an ammonium salt or an amine salt.

[0103] Examples of nonionic reactive emulsifiers having a structure in which a radically polymerizable functional group is introduced into a nonionic surfactant include polyoxyethylene nonylpropenyl phenyl ether.

[0104] By emulsion polymerizing a monomer raw material in the presence of a reactive emulsifier having a radically polymerizable functional group, the reactive emulsifier can react and be incorporated into an acrylic polymer. The reactive emulsifier incorporated into the acrylic polymer is restricted in its movement within the aqueous emulsion adhesive, making it less likely to migrate to the surface of an adhesive electrode for acquiring a biological signal containing the aqueous emulsion adhesive. Therefore, the use of a reactive emulsifier can inhibit migration of the emulsifier to the surface of the adhesive electrode for acquiring a biological signal. This is advantageous in terms of inhibiting a decrease in water-resistant adhesive strength when water is generated on the surface of the adhesive electrode for acquiring a biological signal, and is particularly preferable because it can improve sweat resistance.

[0105] The amount of the emulsifier used in emulsion polymerization may be, for example, 0.2 parts by mass or more, 0.5 parts by mass or more, 1.0 parts by mass or more, or 1.5 parts by mass or more, relative to 100 parts by mass of the monomer components. From the viewpoint of improving water resistance, the amount of the emulsifier used is suitably less than 10 parts by mass, preferably 5 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.5 parts by mass or less, relative to 100 parts by mass of the monomer components.

[0106] In the polymerization, various commonly used chain transfer agents can be used as needed. The chain transfer agent can also be understood as a molecular weight regulator or a polymerization degree regulator. Mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, thioglycolic acid, and α-thioglycerol can be used as the chain transfer agent. Alternatively, a chain transfer agent that does not contain a sulfur atom (non-sulfur chain transfer agent) can be used. The chain transfer agent may be used alone or in combination of two or more. When a chain transfer agent is used, the content thereof may be, for example, 0.01 to 1 part by mass per 100 parts by mass of the monomer components.

[0107] Emulsion polymerization can prepare a polymerization liquid (acrylic polymer emulsion) in the form of an emulsion in which an acrylic polymer is dispersed in water. A water-dispersible pressure-sensitive adhesive composition can be produced by using the polymerization liquid or a polymerization liquid that has been subjected to an appropriate post-treatment.

[0108] (Crosslinking Agent) The aqueous dispersion type pressure-sensitive adhesive composition may contain a crosslinking agent as needed. The type of crosslinking agent is not particularly limited, and can be appropriately selected from conventionally known crosslinking agents. Examples of such crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, and metal chelate-based crosslinking agents. The crosslinking agents can be used alone or in combination of two or more.

[0109] The amount of crosslinking agent used is not particularly limited, and may be, for example, 0.001 parts by mass or more, or 0.01 parts by mass, per 100 parts by mass of the acrylic polymer. The amount of crosslinking agent used may be, for example, 10 parts by mass or less, 5 parts by mass or less, less than 1 part by mass, less than 0.5 parts by mass, or less than 0.1 parts by mass, per 100 parts by mass of the acrylic polymer. The pressure-sensitive adhesive composition may be substantially free of a crosslinking agent. The aqueous dispersion pressure-sensitive adhesive composition can exhibit high cohesive strength with the use of a small amount of crosslinking agent, or substantially no crosslinking agent, depending on the monomer composition of the acrylic polymer.

[0110] (Tackifying Resin) The aqueous dispersion pressure-sensitive adhesive composition may optionally contain a tackifying resin for purposes such as improving adhesive strength. Examples of tackifying resins that can be used include phenolic tackifying resins, terpene tackifying resins, modified terpene tackifying resins, rosin tackifying resins, hydrocarbon tackifying resins, epoxy tackifying resins, polyamide tackifying resins, elastomer tackifying resins, and ketone tackifying resins. These may be used alone or in combination of two or more. The amount of tackifying resin used is suitably in the range of, for example, about 1 to 30 parts by mass per 100 parts by mass of the acrylic polymer, and may be 10 parts by mass or less, or the composition may be substantially free of tackifying resin.

[0111] (Additives) As described above, the aqueous dispersion pressure-sensitive adhesive composition may contain, as optional components, various commonly used additives such as leveling agents, crosslinking aids, plasticizers, softeners, fillers, colorants (dyes, pigments), antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, and dispersants, in any appropriate amounts. The various additives may be conventionally known and used in the usual manner. Detailed description of the various additives will be omitted.

[0112] When the adhesive electrode for acquiring a biological signal is used by adhering it to the skin, the water-dispersible pressure-sensitive adhesive composition may contain a component that reduces skin irritation, such as a carboxylic acid ester or a fatty acid ester.

[0113] The aqueous dispersion type pressure-sensitive adhesive composition can limit the amount of components other than the acrylic polymer. A pressure-sensitive adhesive containing fewer components other than the acrylic polymer can reduce the impact of these components on an adherend such as the skin. For example, when the adherend is the skin, the content of skin-irritating components can be suppressed. Therefore, the content of components other than the acrylic polymer (specifically, non-volatile components) in the aqueous dispersion type pressure-sensitive adhesive composition is not particularly limited, but may be, for example, 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably less than 1.0% by mass.

[0114] The change in mass of the adhesive electrode for acquiring a biological signal upon absorbing water is preferably less than 30%, more preferably 28% or less, and even more preferably 25% or less, of the mass of the adhesive electrode for acquiring a biological signal before absorbing water. If the change in mass of the adhesive electrode for acquiring a biological signal after absorbing water is less than 30% of the mass of the adhesive electrode for acquiring a biological signal before absorbing water, it can be said that the aqueous emulsion adhesive exhibits sufficient water resistance.

[0115] The method for measuring the mass of the adhesive electrode for acquiring a biosignal before and after absorbing water is not particularly limited, and any method may be used as long as it can measure the mass of the adhesive electrode for acquiring a biosignal before and after absorbing water. For example, the mass of the adhesive electrode for acquiring a biosignal before immersion in water is measured. The adhesive electrode for acquiring a biosignal is then immersed in water for 1 minute, pulled out, excess water is removed, and the mass of the adhesive electrode for acquiring a biosignal after absorbing water is measured. According to the following formula (1), the change in mass of the adhesive electrode for acquiring a biosignal before and after absorbing water is calculated by dividing the calculated mass after immersion by the mass before immersion (mass 1) and multiplying the result by 100. Mass change [%] of adhesive electrode for acquiring a biosignal = (mass after immersion / mass before immersion) × 100

[0116] The method for manufacturing the adhesive electrode for acquiring a biological signal according to this embodiment is not particularly limited, but an example of the method for manufacturing the adhesive electrode for acquiring a biological signal will be described below.

[0117] First, a conductive polymer and water are mixed to prepare a conductive polymer-containing aqueous solution (a step of preparing a conductive polymer-containing aqueous solution).

[0118] The conductive polymer and water may be mixed while stirring using a commonly used stirrer or the like so that the conductive polymer is mixed as uniformly as possible in the conductive polymer-containing solution.

[0119] The mixing ratio of the conductive polymer to water, mixing conditions such as mixing time, stirring speed of the conductive polymer-containing solution, temperature, etc. are not particularly limited, and may be set arbitrarily as appropriate as long as the conductive polymer can be sufficiently mixed into the conductive polymer-containing solution, although this may vary depending on the size of the stirring tank used, etc.

[0120] Next, the aqueous solution containing the conductive polymer is mixed with the water-dispersible pressure-sensitive adhesive composition prepared by adjusting the composition as described above, and optionally with a crosslinker, additives, etc., to prepare an aqueous solution containing the conductive composition (mixing step). The aqueous solution containing the conductive composition is used as a composition for forming an adhesive electrode.

[0121] The water-dispersible pressure-sensitive adhesive composition may be mixed with the conductive composition-containing aqueous solution while stirring using a commonly used stirrer or the like so that the composition is mixed as uniformly as possible.

[0122] The mixing ratio, mixing time, etc. of the conductive polymer-containing aqueous solution and the water-dispersible pressure-sensitive adhesive composition, etc., and the mixing conditions, such as the stirring speed and temperature of the conductive composition-containing aqueous solution, are not particularly limited and may be set arbitrarily as appropriate as long as the water-dispersible pressure-sensitive adhesive composition, etc. can be sufficiently mixed with the conductive polymer-containing aqueous solution, although this will depend on factors such as the size of the stirring tank used.

[0123] Next, the aqueous solution containing the conductive composition is applied to the surface (coating surface) of the release substrate and dried to evaporate the water contained in the aqueous solution containing the conductive composition (coating and drying step).

[0124] By applying an aqueous solution containing the conductive composition to the coating surface of the release substrate and drying it, the adhesive materials bond and fuse together while containing the conductive polymer and moisturizer inside, and a coating film is formed which is a hardened product of the adhesive electrode-forming composition.

[0125] When the coating film is heated, some of the moisture contained therein evaporates and is removed, thereby thinning the thickness of the coating film accordingly. The shape of the adhesive electrode for acquiring biosignals depends on the shape of the coating film, and it may be in the form of a sheet or the like. Therefore, the coating film is formed taking into consideration the fact that the thickness of the coating film will be thinned by heating and the desired thickness of the adhesive electrode for acquiring biosignals.

[0126] The release substrate may be a release liner, a core material, or the like. The release liner may be a resin film such as a polyethylene terephthalate (PET) film, a polyethylene (PE) film, a polypropylene (PP) film, a polyamide (PA) film, a polyimide (PI) film, or a fluororesin film. The core material may be a resin film such as a PET film or a PI film; a ceramic sheet; a metal film such as aluminum foil; a resin substrate reinforced with glass fiber or plastic nonwoven fiber; a silicone substrate, a glass substrate, or the like.

[0127] The method for applying the aqueous solution containing the conductive composition to the application surface of the release substrate is not particularly limited as long as it is possible to apply the aqueous solution containing the conductive composition to the release substrate, and a general application method may be used.

[0128] Examples of the coating method include roll coating, screen coating, gravure coating, spin coating, reverse coating, bar coating, blade coating, spray coating, air knife coating, dipping, dispensing, etc., as well as a method of dropping a small amount of an aqueous solution containing the conductive composition onto the surface to be coated of the substrate and spreading it with a doctor blade, etc. By these coating methods, the aqueous solution containing the conductive composition can be uniformly applied onto the surface to be coated.

[0129] The drying conditions for the aqueous solution containing the conductive composition applied to the coating surface of the release substrate are not particularly limited as long as they are conditions that allow the aqueous solution containing the conductive composition applied to the release substrate to be dried, and general drying conditions may be used.

[0130] The drying may be performed at room temperature or by heating using a dryer. Examples of the dryer that can be used include common dryers such as a drying oven, a vacuum oven, an air circulation oven, a hot air dryer, a far-infrared dryer, a microwave reduced pressure dryer, and a high-frequency dryer. The aqueous solution containing the conductive composition applied to the surface of the substrate using these dryers may be dried by a method of heating the interior of the dryer to a high temperature, a method of heating the substrate, a method of blowing hot air onto the aqueous solution containing the conductive composition, or a method of irradiating the aqueous solution containing the conductive composition with far-infrared rays, microwaves, or high frequencies.

[0131] The heating temperature (drying temperature) and heating time (drying time) when heating the aqueous solution containing the conductive composition using a dryer are set to a temperature and time that can evaporate the water contained in the aqueous solution containing the conductive composition.

[0132] The heating temperature may be, for example, 100° C. to 200° C. When the conductive composition contains a crosslinking agent, a heating temperature within the range of 100° C. to 200° C. can promote evaporation of water contained in the aqueous solution containing the conductive composition.

[0133] The heating time of the aqueous solution containing the conductive composition may be, for example, 0.5 to 300 minutes. If the heating time is 0.5 to 300 minutes, the water contained in the aqueous solution containing the conductive composition can be sufficiently evaporated.

[0134] When the coating film is formed by drying a release substrate coated with an aqueous solution containing a conductive composition while transporting it, the line speed (transport speed) of the release substrate coated with the aqueous solution containing a conductive composition may be set so as to obtain an adhesive electrode for acquiring a biological signal having the desired thickness, taking into consideration the heating temperature of the aqueous solution containing the conductive composition, the thickness of the adhesive electrode for acquiring a biological signal, etc.

[0135] Next, the obtained cured product is punched (pressed) using a press or the like as needed to form the outer shape of the cured product into a predetermined shape (forming step), thereby obtaining an adhesive electrode for acquiring a biological signal, which is a molded product having the outer shape of the predetermined shape.

[0136] It should be noted that molding may be performed using a laser processing machine instead of a press. Furthermore, the obtained cured product may be molded into a predetermined shape only in terms of its outer shape. Furthermore, when the cured product can be used as an adhesive electrode for acquiring a biological signal as is, the cured product may be used as an adhesive electrode for acquiring a biological signal without being molded or otherwise processed.

[0137] As described above, the adhesive electrode for acquiring a biological signal according to this embodiment includes a conductive polymer and an aqueous emulsion adhesive. The aqueous emulsion adhesive includes a (meth)acrylic acid alkyl ester (m1) and a carboxyl group-containing monomer (m2). The carboxyl group-containing monomer (m2) includes acrylic acid (m2a) and a relatively hydrophobic monomer (m2b). The conductive polymer allows the adhesive electrode for acquiring a biological signal to exhibit conductivity. The aqueous emulsion adhesive allows the electrode for acquiring a biological signal to exhibit adhesive strength and self-adhesion, while also improving flexibility, thereby enhancing adhesion to the skin and conformability to the skin surface. The aqueous emulsion adhesive is formed from an aqueous dispersion-type pressure-sensitive adhesive composition containing an acrylic polymer having the above-described monomer components, allowing the adhesive electrode to function as a pressure-sensitive adhesive that is flexible, has high adhesive strength, and is excellent in water resistance. Therefore, the aqueous emulsion adhesive allows the adhesive electrode for acquiring a biological signal to exhibit flexibility, while improving adhesion to the skin and water resistance. In addition, the adhesive electrode for acquiring biological signals is flexible and has improved adhesive strength, which allows it to easily conform to the surface of the skin.Therefore, even if the surface of the skin is deformed due to body movement, the electrode remains attached to the skin and is less likely to peel off from the skin, thereby keeping the contact impedance low.

[0138] Therefore, the adhesive electrode for acquiring biological signals does not absorb more moisture than necessary even if moisture penetrates from the outside during use, improving skin contact impedance due to the presence of moisture at the interface with the skin, and suppressing the absorption of more moisture than necessary, thereby providing excellent adhesion.

[0139] Furthermore, the adhesive electrode for acquiring biological signals contains a water-dispersible adhesive, which makes it easier to deform, allowing it to adhere tightly to the skin even if the skin is uneven, and it can follow any deformation of the skin surface while maintaining its adhesion, allowing for stable acquisition of biological signals.

[0140] The method for measuring the adhesive strength of the adhesive electrode for acquiring a biological signal is not particularly limited, and can be determined by any suitable method. For example, the adhesive strength of the adhesive electrode for acquiring a biological signal may be determined by performing a 180° peel test and measuring the 180° peel strength. For example, the adhesive strength of the adhesive electrode for acquiring a biological signal may be determined by measuring the 180° peel strength of an area of ​​a predetermined size (for example, 10 cm ２ ) is prepared as a test piece, and the electrode sheet is attached to a support substrate (e.g., a PET film, etc.) to form a backing, to prepare a measurement sample. The measurement sample is cut to a predetermined size (e.g., 1 cm x 1 cm) and attached to an adherend (e.g., a stainless steel plate, a Bakelite plate, etc.) and fixed. Thereafter, using a tensile tester, the load when the measurement sample is peeled from the adherend under peel conditions of a peel angle of 180° and a predetermined peel rate (e.g., 300 mm / min) is measured, and the adhesive strength (unit: N / 10 mm) is measured.

[0141] The method for measuring the contact impedance of the adhesive electrode for acquiring a biological signal is not particularly limited, and any appropriate method can be used. For example, ２ ) is prepared as a test piece, and the end of a copper plate having a predetermined size (e.g., 15 mm wide x 3 cm long) is attached to the end of the electrode, and the electrode surfaces are then attached, and the surface of the copper plate opposite to the surface attached to the electrode is fixed with a clip connected to a cable. The clip on the other side of the cable is connected to an impedance analyzer, and skin contact impedance is measured for a predetermined time (e.g., 1 minute).

[0142] In the adhesive electrode for acquiring a biological signal according to this embodiment, the aqueous emulsion adhesive preferably further contains a nitrogen atom-containing monomer (m3). The aqueous emulsion adhesive can achieve flexibility, adhesive strength, and water resistance by using acrylic acid (m2a), a carboxy group-containing monomer (m2), and a nitrogen atom-containing monomer (m3) in combination. Therefore, the adhesive electrode for acquiring a biological signal can exhibit adhesive strength and water resistance while also increasing flexibility, and can easily change shape to follow the movement of the skin during use, thereby enabling stable acquisition of biological signals even when the skin deforms due to body movement.

[0143] In the adhesive electrode for acquiring a biological signal according to this embodiment, the content of the acrylic acid (m2a) and the relatively hydrophobic monomer (m2b) is preferably 3 parts by mass or less per 100 parts by mass of the aqueous emulsion adhesive, thereby ensuring improved adhesive strength and water resistance of the adhesive electrode for acquiring a biological signal and enabling stable measurement of the biological signal.

[0144] In the adhesive electrode for acquiring a biological signal according to this embodiment, the mass ratio of the conductive polymer to the aqueous emulsion adhesive (conductive polymer / aqueous emulsion adhesive) is preferably 8 to 18. This allows the adhesive electrode for acquiring a biological signal to exhibit conductivity and also have adhesive strength, allowing for more stable measurement of the biological signal.

[0145] The adhesive electrode for acquiring a biological signal according to this embodiment preferably changes in mass upon absorbing water by less than 30% of the mass before absorbing water. By suppressing the change in mass of the adhesive electrode for acquiring a biological signal upon absorbing water, deformation due to expansion or the like can be suppressed, thereby suppressing a decrease in adhesive strength and enabling more stable measurement of biological signals.

[0146] The adhesive electrode for acquiring a biological signal according to this embodiment preferably uses at least one conductive polymer selected from the group consisting of a polythiophene-based conductive polymer, a polyaniline-based conductive polymer, and a polyacetylene-based conductive polymer, thereby ensuring that the adhesive electrode for acquiring a biological signal exhibits electrical conductivity.

[0147] <Electrode Piece> As described above, the adhesive electrode for acquiring a biological signal according to this embodiment can be formed into a film, and therefore can be used as an electrode piece in which the adhesive electrode for acquiring a biological signal is provided on a substrate. The electrode piece has higher rigidity than when the adhesive electrode for acquiring a biological signal is used alone, and therefore can be easier to handle.

[0148] The substrate used for the electrode piece can be formed using any appropriate material. Examples of the substrate used for the electrode piece include polyolefin resins such as polyethylene (PE) and polyethylene naphthalate (PEN), polyester resins such as polyethylene terephthalate (PET), acrylic resins, polyurethane resins, polystyrene resins, silicone resins, acrylic resins, vinyl chloride resins, plastic substrates such as polyimide (PI) and polycarbonate (PC), metal plates, and glass substrates. The substrate used for the electrode piece may be a substrate without a porous structure or a substrate (porous body) with a porous structure such as a nonwoven fabric sheet.

[0149] As described above, the adhesive electrode for acquiring a biological signal according to this embodiment has excellent water resistance and can stably measure a biological signal while having high adhesion to the skin. Therefore, the adhesive electrode for acquiring a biological signal can be effectively used as an electrode (biological electrode) for a biological sensor, in particular, a stick-on type biological sensor that requires stable acquisition of a biological signal, adhesion to the living body, and a long service life.

[0150] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, or modifications can be made without departing from the spirit of the invention. The above embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0151] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to these examples.

[0152] <Synthesis of Water-Based Emulsion Pressure-Sensitive Adhesive> [Synthesis of Water-Based Emulsion Pressure-Sensitive Adhesive A] To a flask equipped with a reflux condenser, a thermometer, and a dropping funnel were added 85 g of water and 10 g of reactive emulsifier A (product name "Aqualon KH-1025", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., solids concentration 25%). Separately, 350 g of 2-ethylhexyl acrylate (hereinafter abbreviated as 2-EHA), 7.3 g of acrylic acid (hereinafter abbreviated as AA), 3.7 g of N-vinylpyrrolidone (also NVP), and 3.7 g of methacrylic acid (hereinafter abbreviated as MAA) were added as monomer components, and 0.18 g of a silane monomer ("KBM-503", Shin-Etsu Chemical Co., Ltd., 3-methacryloxypropyltrimethoxysilane), 0.18 g of t-lauryl mercaptan as a chain transfer agent, 25 g of reactive emulsifier A ("Aqualon KH-1025"), and 140 g of water were added and emulsified using a high-pressure homogenizer to obtain an emulsion. 40 g of this emulsion was added to the flask and nitrogen substitution was performed for 1 hour. The temperature was then raised to 60°C, and 0.1 g of a water-soluble polymerization initiator (product name "VA-057", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to initiate polymerization. After 1 hour, 0.1 g of a water-soluble polymerization initiator (product name "VA-057") was added, and 364 g of the emulsion obtained above was added dropwise over 3 hours to carry out an emulsion polymerization reaction. The temperature was then raised to 70°C and maintained for a further 3 hours. The mixture was then cooled to room temperature to prepare aqueous emulsion pressure-sensitive adhesive A.

[0153] In the aqueous emulsion PSA A, of the monomer components of the acrylic polymer contained in the aqueous dispersion-type pressure-sensitive adhesive composition described in the above embodiment, 2-EHA was used as the "(meth)acrylic acid alkyl ester (m1)", AA as the "acrylic acid (m2a)", MAA as the "relatively highly hydrophobic monomer (m2b)", and NVP as the "nitrogen atom-containing monomer (m3)".

[0154] [Synthesis of Water-Based Emulsion Pressure-Sensitive Adhesive B] Using the same equipment as above, 0.33 g of KH-1025 and 108 g of water were added to a flask. As monomer components, 310 g of 2-EHA, 47.4 g of methyl acrylate (hereinafter abbreviated as MA), 4.6 g of AA, 2.73 g of MAA, 0.09 g of KBM-503, 0.09 g of t-lauryl mercaptan, 7 g of KH-1025, and 239 g of water were added and emulsified using a high-pressure homogenizer to obtain an emulsion. The flask was purged with nitrogen for 1 hour. The temperature was then raised to 60°C, 0.2 g of a water-soluble polymerization initiator (product name "VA-057", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, and 470 g of the emulsion was added dropwise over 3 hours to polymerize. Thereafter, 0.1 g of VA-057 was added, the temperature was raised to 70° C. and maintained at this temperature for 3 hours, and then the mixture was cooled to room temperature to prepare a water-based emulsion pressure-sensitive adhesive B.

[0155] In the aqueous emulsion PSA B, of the acrylic polymer monomer components contained in the aqueous dispersion-type pressure-sensitive adhesive composition described in the above embodiment, 2-EHA and MA were used as "(meth)acrylic acid alkyl ester (m1)", AA was used as "acrylic acid (m2a)", and MAA was used as "relatively highly hydrophobic monomer (m2b)".

[0156] [Synthesis of Water-Based Emulsion Pressure-Sensitive Adhesive C] Water-based emulsion pressure-sensitive adhesive C was obtained by the same process as in the synthesis of water-based emulsion pressure-sensitive adhesive A, except that the emulsification monomer composition was changed to 341 g of 2-EHA, 6.8 g of AA, and 3.4 g of MAA.

[0157] In the aqueous emulsion PSA C, of ​​the acrylic polymer monomer components contained in the aqueous dispersion-type pressure-sensitive adhesive composition described in the above embodiment, 2-EHA was used as the "(meth)acrylic acid alkyl ester (m1)," AA was used as the "acrylic acid (m2a)," and MAA was used as the "relatively highly hydrophobic monomer (m2b)."

[0158] [Synthesis of Water-Based Emulsion Pressure-Sensitive Adhesive D] Water-based emulsion pressure-sensitive adhesive D was obtained by the same process as in the synthesis of water-based emulsion pressure-sensitive adhesive A, except that the emulsifying monomer composition was changed to 341 g of 2-EHA, 6.8 g of AA, 1.75 g of MAA, and 1.75 g of NVP.

[0159] In the aqueous emulsion PSA D, of the monomer components of the acrylic polymer contained in the aqueous dispersion-type pressure-sensitive adhesive composition described in the above embodiment, 2-EHA was used as the "(meth)acrylic acid alkyl ester (m1)", AA as the "acrylic acid (m2a)", MAA as the "relatively highly hydrophobic monomer (m2b)", and NVP as the "nitrogen atom-containing monomer (m3)".

[0160] [Synthesis of aqueous emulsion pressure-sensitive adhesive E] The monomer composition for emulsification was changed to 304 g of 2-EHA, 6.8 g of AA, and 27.1 g of methyl methacrylate (MMA), and the emulsifier was changed to Hitenol LA16 (Dai-ichi Kogyo Seiyaku Co., Ltd., used after dilution to a solids concentration of 25%) as emulsifier B. Except for these, the same treatment as in the synthesis of aqueous emulsion pressure-sensitive adhesive A was carried out, to obtain aqueous emulsion pressure-sensitive adhesive E.

[0161] In the aqueous emulsion pressure-sensitive adhesive E, of the acrylic polymer monomer components contained in the aqueous dispersion-type pressure-sensitive adhesive composition described in the above embodiment, 2-EHA was used as the "(meth)acrylic acid alkyl ester (m1)," AA was used as the "acrylic acid (m2a)," and MMA was used as the "relatively highly hydrophobic monomer (m2b)."

[0162] [Synthesis of Water-Based Emulsion Pressure-Sensitive Adhesive F] Water-based emulsion pressure-sensitive adhesive F was obtained in the same manner as in the synthesis of Pressure-Sensitive Adhesive A, except that the emulsifying monomer composition was changed to 324 g of 2-EHA and 13.5 g of AA.

[0163] In the aqueous emulsion pressure-sensitive adhesive F, of the monomer components of the acrylic polymer contained in the aqueous dispersion-type pressure-sensitive adhesive composition described in the above embodiment, 2-EHA was used as "(meth)acrylic acid alkyl ester (m1)" and AA was used as "acrylic acid (m2a)".

[0164] Table 1 shows the acrylic polymer and emulsifier components contained in the aqueous emulsion pressure sensitive adhesives A to F, as well as the amounts of these components added.

[0165]

[0166] <Preparation of Electrode> [Example 1] (Preparation of Aqueous Solution of Conductive Composition) 1.0 g of PEDOT / PSS pellets ("Orgacon DRY", manufactured by Agfa Materials Japan, Inc.) as a conductive polymer and 18 g of water were added to a cup and stirred for 10 minutes at a rotation speed of 2000 rpm using a stirring mixer (Thinky Mixer, Awatori Mixer). Next, 12.0 g of an aqueous emulsion adhesive and 2.0 g of glycerin were added as binder resins, and the mixture was stirred, mixed, and degassed for 10 minutes using the Awatori Mixer at 2200 rpm to prepare an aqueous solution of conductive composition.

[0167] (Preparation of Electrode Sheet) The prepared aqueous conductive composition solution was applied using an applicator to a (additional) polyethylene terephthalate (PET) film (PET-50-SCA1, manufactured by Fujiko Co., Ltd., thickness 50 μm) that had been surface-treated with a silicone-based release agent. The PET film coated with the aqueous conductive composition solution was then transported to a drying oven (SPHH-201, manufactured by ESPEC Corporation), and the aqueous conductive composition solution was heated and dried at 130°C for 3 minutes to prepare a cured product of the conductive composition. The cured product was punched (pressed) into a desired shape to form a sheet, and an electrode was prepared as an electrode sheet (bioelectrode) having a thickness of 30 μm. The mass ratio of the conductive polymer to the aqueous emulsion adhesive (conductive polymer / aqueous emulsion adhesive) contained in the electrode sheet was 12.5.

[0168] [Examples 2 to 4, Comparative Examples 1 and 2] Electrode sheets were produced in the same manner as in Example 1, except that the type of aqueous emulsion adhesive in Example 1 was changed to the type shown in Table 2. In each of the Examples and Comparative Examples, the mass ratio of the conductive polymer to the aqueous emulsion adhesive (conductive polymer / aqueous emulsion adhesive) was 12.5.

[0169] [Comparative Example 3] An electrode sheet was produced in the same manner as in Example 1, except that the amount of PEDOT / PSS pellets was changed to 0.5 g. The mass ratio of the conductive polymer to the aqueous emulsion adhesive (conductive polymer / aqueous emulsion adhesive) in the electrode sheet was 6.5.

[0170] [Comparative Example 4] An electrode sheet was produced in the same manner as in Example 1, except that the amount of PEDOT / PSS pellets was changed to 1.6 g. The mass ratio of the conductive polymer to the aqueous emulsion adhesive (conductive polymer / aqueous emulsion adhesive) in the electrode sheet was 18.2.

[0171] Table 2 shows the type of aqueous emulsion adhesive used to prepare the electrode sheets in the above examples and comparative examples, and the mass ratio of the conductive polymer to the aqueous emulsion adhesive.

[0172] <Evaluation of electrode sheets> The electrode adhesive strength, adhesive strength during water supply, sheet resistance, contact impedance, holding power, and mass change of the obtained electrode sheets of each example and comparative example were measured. The measurement results are shown in Table 2. Note that the parts shown with a "gray background" in Table 2 indicate values ​​that do not satisfy the present embodiment or are unfavorable.

[0173] [Adhesive Strength Measurement] (Before Water Absorption) The electrode sheet was cut to a length of 5 cm and a width of 1 cm and bonded to a PET film (Lumirror S10, thickness 25 μm). Next, this film was bonded to a bakelite and fixed by rolling it back and forth with a 2 kg roller. The adhesive strength was measured by peeling it off at a speed of 300 mm / min using a tensile tester (AGS-J, manufactured by Shimadzu Corporation). An adhesive strength of 5 N / 10 mm or more was rated "good," and an adhesive strength of less than 5 N / 10 mm was rated "poor." (After Water Absorption) The electrode sheet bonded to the PET film was immersed in water for 3 seconds to absorb water. This was bonded to a bakelite and fixed by rolling it back and forth with a 2 kg roller. Excess water that had spilled out was wiped off with a cloth, and then the adhesive strength was measured. An adhesive strength of 2 N / 10 mm or more was rated "good," and an adhesive strength of less than 2 N / 10 mm was rated "poor."

[0174] [Measurement of Sheet Resistance] Using a non-contact resistance measuring instrument (NC-80NC, manufactured by Napson Corporation), the sheet resistance was measured as the surface resistance of the electrode sheet by an eddy current measurement method in accordance with JIS Z 2316-1: 2014. The measurement range was 0.5 mm to 150 mm from the main surface of the electrode sheet.

[0175] [Skin contact impedance measurement] Area 4 cm ２ A biosensor was fabricated using electrodes cut to 10 cm. The end of a copper foil tape cut to a width of 5 mm and a length of 10 cm was attached to the end of the electrode, and the other side was secured with a cable equipped with an alligator clip. The opposite clip was connected to an impedance analyzer (product name: IM3570, manufactured by Hioki E.E. Corporation), and the biosensor was attached to the subject's inner arm. Skin contact impedance was measured for 1 minute and evaluated based on the following criteria. (Dry Condition) In the dry condition, a skin contact impedance of 7 kΩ or less was rated "good," and a skin contact impedance of more than 7 kΩ was rated "poor." (Wet Condition) The skin was rubbed with a damp cloth until a few droplets were visible, and then the skin contact impedance was measured. This condition was considered wet. In the wet condition, a skin contact impedance of 4 kΩ or less was rated "good," and a skin contact impedance of more than 4 kΩ was rated "poor." Note that if the biosensor was prone to peeling when wet, measurements were performed while the subject was lightly pressed down with their hand.

[0176] [Measurement of Holding Power] (Dry State) An electrode was cut into a 1 cm x 1 cm piece, and the release liner on the light release side of the electrode was peeled off. The electrode was then bonded to a PET film (Lumirror S10, thickness: 25 μm) as shown in FIG. 4 . The release liner on the heavy release side was peeled off and the electrode was bonded to a Bakelite plate for measurement. Next, a 200 g weight was hung from the bottom end of the electrode in a 25°C atmosphere to apply a load to the electrode. The time until the electrode fell from the Bakelite plate was measured to measure the holding power of the electrode in a dry state. If the electrode did not fall from the Bakelite plate within 25 minutes, the result was rated "good." If the electrode fell from the Bakelite plate in less than 25 minutes, the result was rated "poor." Note that the holding power test can be used to evaluate the resistance of the electrode to tearing or peeling due to the force applied in the X and Y directions when a person moves. (Wet state) After immersing the electrode in water for 3 seconds, the time until the electrode fell off the Bakelite plate was measured in the same manner as in the (dry state) above to measure the electrode's holding power in the wet state. If the electrode did not fall off the Bakelite plate within 20 minutes, it was rated as "good," and if the electrode fell off the Bakelite plate in less than 20 minutes, it was rated as "poor."

[0177] [Measurement of Mass Change] The electrode was cut into a 1 cm x 1 cm piece, the release liner on the light release side was peeled off, and the mass was measured (mass before immersion). The electrode was then immersed in water for 1 minute. The electrode surface was attached to a release liner, lightly rubbed with a roller to remove excess water, and the mass was measured (mass 1). The electrode was peeled off from the heavy release liner, and the mass of the heavy release liner was measured (mass 2). The mass after immersion was calculated by subtracting mass 2 from mass 1. The mass change of the electrode was calculated by dividing the calculated mass after immersion by the mass before immersion (mass 1) and multiplying the result by 100, according to the following formula (1): Mass change of electrode [%] = (mass after immersion / mass before immersion) x 100

[0178]

[0179] As can be seen from Table 2, in each Example, the rate of decrease in adhesive strength after water supply was kept low. Furthermore, the sheet resistance and skin contact impedance were low, and the rate of decrease in skin contact impedance after water supply was also kept low. Furthermore, the holding power was long, the rate of decrease in holding power after water supply was also kept low, and the change in mass before and after water supply was also kept low. On the other hand, in each Comparative Example, among the evaluations of each Example above, at least the holding power was short, the rate of decrease in holding power after water supply was large, and the change in mass before and after water supply was also large.

[0180] Therefore, it was confirmed that the electrode sheets of the above examples contain a conductive polymer and an aqueous emulsion adhesive, and that if the aqueous emulsion adhesive contains a (meth)acrylic acid alkyl ester (m1) and a carboxyl group-containing monomer (m2) containing both acrylic acid (m2a) and a relatively hydrophobic monomer (m2b), the water resistance can be further increased and the adhesive strength and skin contact impedance of the adhesive electrode for acquiring a biological signal can be improved. Furthermore, it was confirmed that if the aqueous emulsion adhesive further contains a nitrogen atom-containing monomer (m3), the water resistance can be further increased and the adhesive strength and skin contact impedance of the adhesive electrode for acquiring a biological signal can be further improved.

[0181] Therefore, the adhesive electrode for acquiring biological signals according to this embodiment can be effectively used to measure biological information by adhering it to the skin of a subject, as it reduces absorption of moisture from the outside during use, improves skin contact impedance, and exhibits excellent adhesion.

[0182] The embodiments of the present invention are specified by, for example, the following aspects. [1] An adhesive electrode for acquiring a biological signal, comprising a conductive polymer and an aqueous emulsion adhesive, wherein the aqueous emulsion adhesive contains a (meth)acrylic acid alkyl ester and a carboxy group-containing monomer, and the carboxy group-containing monomer contains acrylic acid and a monomer having a higher hydrophobicity than the acrylic acid. [2] The adhesive electrode for acquiring a biological signal according to [1], wherein the carboxy group-containing monomer further contains a nitrogen atom-containing monomer in which no hydrogen atom is bonded to the nitrogen atom. [3] The adhesive electrode for acquiring a biological signal according to [1] or [2], wherein the content of the acrylic acid and the monomer having a higher hydrophobicity than the acrylic acid is 3 parts by mass or less per 100 parts by mass of the aqueous emulsion adhesive. [4] The adhesive electrode for acquiring a biological signal according to any one of [1] to [3], wherein the mass ratio of the conductive polymer to the aqueous emulsion adhesive is 8 to 18. [5] The adhesive electrode for acquiring a biological signal according to any one of [1] to [4], wherein a change in mass of the adhesive electrode for acquiring a biological signal when the adhesive electrode for acquiring a biological signal absorbs water is less than 30% of the mass of the adhesive electrode for acquiring a biological signal before absorbing water. [6] An electrode piece comprising the adhesive electrode for acquiring a biological signal according to any one of [1] to [5] on a substrate. [7] A biosensor comprising the adhesive electrode for acquiring a biological signal according to any one of [1] to [5].

[0183] This application claims priority based on Japanese Patent Application No. 2024-52607, filed with the Japan Patent Office on March 28, 2024, and incorporates the entire contents of said application by reference.

[0184] 11 Conductive polymer 12 Water-based emulsion adhesive

Claims

1. An adhesive electrode for acquiring biological signals, comprising a conductive polymer and an aqueous emulsion adhesive, wherein the aqueous emulsion adhesive contains a (meth)acrylic acid alkyl ester and a carboxy group-containing monomer, and the carboxy group-containing monomer contains acrylic acid and a monomer having higher hydrophobicity than the acrylic acid.

2. An adhesive electrode for acquiring biological signals as described in claim 1, wherein the carboxy group-containing monomer further includes a nitrogen atom-containing monomer in which no hydrogen atom is bonded to the nitrogen atom.

3. An adhesive electrode for acquiring biological signals as described in claim 1, wherein the content of the acrylic acid and the monomer more hydrophobic than the acrylic acid is 3 parts by mass or less per 100 parts by mass of the aqueous emulsion adhesive.

4. The adhesive electrode for acquiring biological signals according to claim 1, wherein the mass ratio of the conductive polymer to the aqueous emulsion adhesive is 8 to 18.

5. An adhesive electrode for acquiring biological signals as described in claim 1, wherein the change in mass of the adhesive electrode for acquiring biological signals when it absorbs water is less than 30% of the mass of the adhesive electrode for acquiring biological signals before absorbing water.

6. An electrode piece having the adhesive electrode for acquiring biosignals according to claim 1 attached to a substrate.

7. A biosensor comprising the adhesive electrode for acquiring biosignals according to claim 1.

Images