Hot melt adhesive, method for producing same, and coating method

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

Hot melt adhesive, and manufacturing and application methods thereof

[0001] The present invention relates to a hot melt adhesive and to a method for producing and applying the same.

[0002] Conventionally, when imparting antibacterial properties to hot melt adhesives, inorganic silver-based antibacterial agents (see, for example, Patent Document 1), triclosan (see, for example, Patent Document 2), quaternary ammonium salts (see, for example, Patent Document 3), etc. have been used as antibacterial agents. Parahydroxybenzoic acid esters (parabens) are also known as antibacterial agents, but their use conditions are limited.

[0003] Chinese Patent Application Publication No. 115873558 Specification Japanese Patent Publication "JP-T-2004-525996A" Japanese Patent Publication "JP-A-2007-51281A" Japanese Patent Publication "JP-A-2020-117567A"

[0004] However, the above-mentioned conventional techniques for imparting antibacterial properties to hot melt adhesives have room for improvement in terms of providing antibacterial hot melt adhesives that do not undergo phase separation even when heated for long periods of time, are highly safe for the human body, and can maintain stable antibacterial properties even when heated for long periods of time.

[0005] Specifically, the technology of adding an inorganic silver-based antibacterial agent described in Patent Document 1 requires particle stabilizers, dispersants, etc. because phase separation and precipitation occur in the usage environment. Furthermore, triclosan used in the technology described in Patent Document 2 is said to exhibit endocrine disrupting effects and affect thyroid function and thyroid homeostasis, raising safety concerns. Furthermore, the quaternary ammonium salt used in the technology described in Patent Document 3 has poor long-term heat resistance, raising concerns about phase separation when heated for a long period of time.

[0006] Patent Document 4 discloses an antibacterial resin composition obtained by melt-kneading paraben with a thermoplastic resin having a low melting point of 65° C. to 110° C., but this is not a hot-melt adhesive. Therefore, when this antibacterial resin composition is applied to a substrate, it is not heated in an open state for a long period of time, as is the case with hot-melt adhesives.

[0007] An object of the present invention is to provide an antibacterial hot melt adhesive that does not undergo phase separation even when heated for a long period of time, is highly safe for the human body, and can maintain stable antibacterial properties even when heated for a long period of time.

[0008] In order to solve the above-mentioned problems, a hot melt adhesive according to one embodiment of the present invention is a hot melt adhesive comprising a base polymer, a tackifier, and an antibacterial agent having a paraben structure whose 10% weight loss temperature in thermogravimetry is 200°C or higher, and whose melt viscosity at 140°C is 20,000 mPa s or lower.

[0009] In order to solve the above-mentioned problems, a method for producing a hot melt adhesive according to one embodiment of the present invention includes a step of kneading an antibacterial agent having a paraben structure, whose 10% weight loss temperature in thermogravimetry is 200°C or higher, with a composition containing a base polymer and a tackifier, while maintaining the temperature at 140°C or lower.

[0010] In order to solve the above-mentioned problems, a method for applying a hot melt adhesive according to one embodiment of the present invention includes a coating step of melting a hot melt adhesive at 140°C or less, the hot melt adhesive including an antibacterial agent having a paraben structure and having a 10% weight loss temperature of 200°C or higher in thermogravimetry, a base polymer, and a tackifier, and coating the molten hot melt adhesive onto a substrate.

[0011] According to one aspect of the present invention, it is possible to provide an antibacterial hot melt adhesive that does not undergo phase separation even when heated for a long period of time, is highly safe for the human body, and can maintain stable antibacterial properties even when heated for a long period of time.

[0012] The following describes in detail the embodiments of the present invention. However, the present invention is not limited to these, and various modifications are possible within the scope of the description. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in different embodiments. Unless otherwise specified in this specification, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B."

[0013] [1. Hot Melt Adhesive] A hot melt adhesive according to one embodiment of the present invention is a hot melt adhesive comprising a base polymer, a tackifier, and an antibacterial agent having a paraben structure whose 10% weight loss temperature in thermogravimetry is 200°C or higher, and whose melt viscosity at 140°C is 20,000 mPa s or lower.

[0014] [1.1] Base Polymer The base polymer contained in the hot melt adhesive according to one embodiment of the present invention is not particularly limited. Examples of the base polymer include styrene-based block copolymers, olefin-based polymers, olefin-vinyl acetate copolymers, olefin-unsaturated carboxylic acid copolymers, acrylic polymers, olefin-acrylate copolymers, polyester-based polymers, polyamide-based polymers, and combinations of two or more of these. Among these, styrene-based block copolymers, olefin-based polymers, olefin-vinyl acetate copolymers, olefin-unsaturated carboxylic acid copolymers, acrylic polymers, and combinations of two or more of these are preferred due to their excellent processability and ease of availability. The hot melt adhesive may contain only one type of base polymer, or may contain two or more types.

[0015] Examples of styrene-based block copolymers include non-hydrogenated styrene-based block copolymers such as styrene-butadiene-styrene block copolymer (SBS) and styrene-isoprene-styrene block copolymer (SIS), and hydrogenated styrene-based block copolymers (e.g., hydrogenated products of the above-mentioned non-hydrogenated styrene-based block copolymers) such as styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-butene-butylene-styrene (SBBS). Among these, from the viewpoint of adhesive strength, it is more preferable that the styrene-based block copolymer is a non-hydrogenated (unhydrogenated) styrene-based block copolymer.

[0016] Examples of olefin-based polymers include homopolymers and copolymers of olefin monomers (olefins having 2 to 10 carbon atoms, such as ethylene, propylene, butene, and isobutylene). More specific examples of olefin-based polymers include poly-α-olefins, amorphous poly-α-olefins (APAOs), ethylene / α-olefin copolymers, propylene / α-olefin copolymers, styrene-ethylene-butylene-olefin crystalline block copolymers, random polypropylenes, block polypropylenes, polypropylenes, ethylene / propylene copolymers, ethylene / 1-butene copolymers, ethylene / 1-hexene copolymers, ethylene / 1-octene copolymers, propylene / ethylene copolymers, propylene / ethylene / α-butene copolymers, polybutenes, 1-butene / ethylene copolymers, 1-butene / propylene copolymers, and propylene / 1-butene copolymers.

[0017] Examples of olefin-vinyl acetate copolymers include ethylene-vinyl acetate copolymers.

[0018] Examples of the olefin-unsaturated carboxylic acid copolymer include ethylene-methacrylic acid copolymer, ethylene-acrylic acid copolymer, and the like.

[0019] Examples of olefin-acrylate copolymers include ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, and the like.

[0020] Examples of acrylic polymers include acrylic block copolymers (such as methyl methacrylate-n-butyl acrylate-methyl methacrylate block copolymer, methyl methacrylate-2-ethylhexyl acrylate-methyl methacrylate block copolymer, etc.), polyacrylic esters, and polymethacrylic esters.

[0021] The base polymer in the hot melt adhesive is more preferably a styrene-based block copolymer, an olefin-based polymer, an olefin-vinyl acetate copolymer, or an acrylic block copolymer, even more preferably a styrene-based block copolymer, an olefin-based polymer, or an olefin-vinyl acetate copolymer, and even more preferably a styrene-based block copolymer.

[0022] The lower limit of the content of the base polymer in the hot melt adhesive may be 5 wt% or more, 10 wt% or more, 15 wt% or more, or 20 wt% or more, relative to 100 wt% of the hot melt adhesive. The upper limit of the content of the base polymer in the hot melt adhesive may be 90 wt% or less, 60 wt% or less, 50 wt% or less, 40 wt% or less, or 30 wt% or less, relative to 100 wt% of the hot melt adhesive. If the content of the base polymer is 5 wt% or more, the adhesive properties of the adhesive are improved.

[0023] When the base polymer is a styrene-based block copolymer, the lower limit of the content of the base polymer in the hot melt adhesive is more preferably 5 wt% or more, even more preferably 10 wt% or more, and even more preferably 15 wt% or more, based on 100 wt% of the hot melt adhesive. When the base polymer is a styrene-based block copolymer, the upper limit of the content of the base polymer in the hot melt adhesive is more preferably 50 wt% or less, even more preferably 40 wt% or less, and even more preferably 30 wt% or less, based on 100 wt% of the hot melt adhesive.

[0024] When the base polymer is an olefin-based polymer, the lower limit of the content of the base polymer in the hot melt adhesive is more preferably 15% by weight or more, even more preferably 20% by weight or more, and even more preferably 25% by weight or more, relative to 100% by weight of the hot melt adhesive. When the base polymer is an olefin-based polymer, the upper limit of the content of the base polymer in the hot melt adhesive is more preferably 90% by weight or less, even more preferably 80% by weight or less, and even more preferably 70% by weight or less, relative to 100% by weight of the hot melt adhesive.

[0025] When the base polymer is an olefin-vinyl acetate copolymer, the lower limit of the content of the base polymer in the hot melt adhesive is more preferably 15% by weight or more, even more preferably 20% by weight or more, and even more preferably 25% by weight or more, based on 100% by weight of the hot melt adhesive. When the base polymer is an olefin-vinyl acetate copolymer, the upper limit of the content of the base polymer in the hot melt adhesive is more preferably 70% by weight or less, even more preferably 60% by weight or less, and even more preferably 50% by weight or less, based on 100% by weight of the hot melt adhesive.

[0026] When the base polymer is an acrylic polymer, the lower limit of the content of the base polymer in the hot melt adhesive is more preferably 5 wt% or more, even more preferably 10 wt% or more, and even more preferably 15 wt% or more, relative to 100 wt% of the hot melt adhesive. When the base polymer is an acrylic polymer, the upper limit of the content of the base polymer in the hot melt adhesive is more preferably 70 wt% or less, even more preferably 60 wt% or less, and even more preferably 50 wt% or less, relative to 100 wt% of the hot melt adhesive.

[0027] [1.2] Tackifier The hot melt adhesive according to one embodiment of the present invention contains a tackifier. The tackifier is not particularly limited, but examples thereof include petroleum-based resins and natural resins.

[0028] Examples of petroleum-based resins include aliphatic petroleum resins, alicyclic petroleum resins, aromatic petroleum resins, and styrene-based resins. Hydrogenated petroleum resins (hydrogenated petroleum resins) are also used. Examples of hydrogenated petroleum resins include hydrogenated C9 petroleum resins and hydrogenated dicyclopentadiene-based petroleum resins (hydrogenated DCPD resins, etc.). Examples of styrene-based resins include homopolymers of styrene, methylstyrene, vinyltoluene, methoxystyrene, tertiary butylstyrene, and chlorostyrene. Hydrogenated styrene-based resins (hydrogenated styrene-based resins, etc.) are also used.

[0029] Examples of natural resins include rosin-based resins and terpene-based resins. Examples of rosin-based resins include natural rosins (gum rosin, tall rosin, wood rosin, etc.), disproportionated rosin, polymerized rosin, glycerin esters of these rosins, and pentaerythritol esters of these rosins. Hydrogenated rosin-based resins (e.g., hydrogenated rosin-based resins) are also used. Examples of terpene-based resins include terpene resins, hydrocarbon-modified terpene resins, aromatic-modified terpene resins, and phenol-modified terpene resins. Hydrogenated terpene-based resins (e.g., hydrogenated terpene-based resins) are also used.

[0030] Hydrogenated resins are more preferred as tackifiers. Tackifiers before hydrogenation may have an odor, but hydrogenating them can suppress this odor. Furthermore, hydrogenation increases the saturated hydrocarbon ratio of the hot melt adhesive, thereby reducing the overall polarity. This reduces the affinity with paraben-based antibacterial agents, making it easier for antibacterial properties to be expressed on the adhesive surface. The hydrogenation rate of the tackifier is preferably 50% or higher, and the higher the hydrogenation rate, the more preferable it is (e.g., 70% or higher, 80% or higher, 90% or higher).

[0031] A hot melt adhesive according to one embodiment of the present invention may contain only one type of tackifier, or may contain two or more types of tackifier.

[0032] The lower limit of the tackifier content in the hot melt adhesive can be greater than 0 wt%, 5 wt% or more, 10 wt% or more, 15 wt% or more, or 20 wt% or more, relative to 100 wt% of the hot melt adhesive. The upper limit of the tackifier content in the hot melt adhesive can be 80 wt% or less, 70 wt% or less, 60 wt% or less, or 50 wt% or less, relative to 100 wt% of the hot melt adhesive. When the tackifier content exceeds 0 wt%, the hot melt adhesive is imparted with sufficient tack. Furthermore, a tackifier content of 80 wt% or less is preferred because it increases the flexibility of the hot melt adhesive and improves its wettability.

[0033] When the base polymer is a styrene-based block copolymer, the lower limit of the tackifier content in the hot melt adhesive is more preferably 20% by weight or more, even more preferably 30% by weight or more, and even more preferably 40% by weight or more, based on 100% by weight of the hot melt adhesive. When the base polymer is a styrene-based block copolymer, the upper limit of the tackifier content in the hot melt adhesive is more preferably 80% by weight or less, even more preferably 75% by weight or less, and even more preferably 70% by weight or less, based on 100% by weight of the hot melt adhesive.

[0034] When the base polymer is an olefin-based polymer or an olefin-vinyl acetate copolymer, the lower limit of the tackifier content in the hot melt adhesive is more preferably 5 wt% or more, even more preferably 10 wt% or more, and even more preferably 15 wt% or more, based on 100 wt% of the hot melt adhesive. When the base polymer is an olefin-based polymer or an olefin-vinyl acetate copolymer, the upper limit of the tackifier content in the hot melt adhesive is more preferably 80 wt% or less, even more preferably 70 wt% or less, and even more preferably 60 wt% or less, based on 100 wt% of the hot melt adhesive.

[0035] When the base polymer is an acrylic block copolymer, the lower limit of the tackifier content in the hot melt adhesive is more preferably 20% by weight or more, even more preferably 25% by weight or more, and even more preferably 30% by weight or more, based on 100% by weight of the hot melt adhesive. When the base polymer is an acrylic block copolymer, the upper limit of the tackifier content in the hot melt adhesive is more preferably 80% by weight or less, even more preferably 70% by weight or less, and even more preferably 60% by weight or less, based on 100% by weight of the hot melt adhesive.

[0036] [1.3] Antibacterial Agent The hot melt adhesive according to one embodiment of the present invention contains an antibacterial agent having a paraben structure and having a 10% weight loss temperature of 200°C or higher as measured by thermogravimetry (TG measurement).

[0037] Here, the 10% weight loss temperature in TG measurement means the temperature at which the weight of an antibacterial agent having a paraben structure has decreased by 10% by weight compared to the weight before heating, when the temperature is increased at 10°C / min (i.e., the weight of the antibacterial agent having a paraben structure has reached 90% of the weight before heating). Hereinafter, in this specification, the 10% weight loss temperature in TG measurement may be referred to as "T10".

[0038] The T10 of the antibacterial agent having a paraben structure may be 200°C or higher, more preferably 205°C or higher, and even more preferably 210°C or higher. If the T10 of the antibacterial agent having a paraben structure is 200°C or higher, the antibacterial agent can remain even after heating for a long period of time. Therefore, a hot melt adhesive having antibacterial properties can be provided. The upper limit of the T10 of the antibacterial agent having a paraben structure is preferably as high as possible from the viewpoint of allowing the antibacterial agent to remain even after heating for a long period of time, but is, for example, 300°C or lower. From the viewpoint of antibacterial activity, the T10 of the antibacterial agent is more preferably 250°C or lower, even more preferably 245°C or lower, and particularly preferably 240°C or lower.

[0039] The antibacterial agent having a paraben structure with a T10 of 200°C or more may be a parahydroxybenzoic acid ester with a T10 of 200°C or more.

[0040] The parahydroxybenzoic acid ester is preferably, for example, an ester of parahydroxybenzoic acid and a hydrocarbon group having 4 to 15 carbon atoms (however, when the hydrocarbon group has 4 carbon atoms, a straight-chain saturated hydrocarbon group is excluded), more specifically, an ester of parahydroxybenzoic acid and a hydrocarbon group having 4 to 15 carbon atoms (however, when the hydrocarbon group is an alkyl group having 4 carbon atoms, an n-butyl group is excluded). More preferred are parahydroxybenzoic acid alkyl esters and parahydroxybenzoic acid benzyl esters, each having an alkyl group with 6 to 14 carbon atoms. The alkyl group of the alkyl ester may be linear, branched, or cyclic, and examples thereof include an isobutyl group (2-methylpropyl group), an n-pentyl group, a 2-methylbutyl group, an isopentyl group (3-methylbutyl group), a neopentyl group, an n-hexyl group, an isohexyl group, a cyclohexyl group, an n-heptyl group, an n-octyl group, a 2-ethylhexyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, and an n-hexadecyl group. Among these, from the viewpoints of antibacterial activity and stability under heat, the antibacterial agent having a paraben structure used in one embodiment of the present invention is preferably n-hexyl parahydroxybenzoate (NHPB), 2-ethylhexyl parahydroxybenzoate (EHPB), n-hexadecyl parahydroxybenzoate (CEPB), benzyl parahydroxybenzoate (POB-Bz), etc., and more preferably n-hexyl parahydroxybenzoate and / or benzyl parahydroxybenzoate. The parahydroxybenzoic acid esters may be used alone or in combination of two or more. When two or more parahydroxybenzoic acid esters are mixed, it is sufficient that the T10 of the entire mixture of parahydroxybenzoic acid esters is 200°C or higher, but it is more preferable that each of the T10 is 200°C or higher.

[0041] The lower limit of the content of the antibacterial agent in the hot melt adhesive is preferably 0.5 wt% or more, more preferably 1 wt% or more, even more preferably 1.5 wt% or more, and may be 2 wt% or more, based on 100 wt% of the hot melt adhesive. A content of 0.5 wt% or more of the antibacterial agent is preferable because sufficient antibacterial properties are imparted. The upper limit of the content of the antibacterial agent in the hot melt adhesive may be 20 wt% or less, or 10 wt% or less, based on 100 wt% of the hot melt adhesive. A content of 20 wt% or less of the antibacterial agent suppresses softening of the hot melt adhesive, making it suitable as a hot melt adhesive. The hot melt adhesive according to one embodiment of the present invention may contain an antibacterial agent other than the antibacterial agent described above, provided that the content does not impair performance. The content of the antibacterial agent other than the antibacterial agent is preferably 1 wt% or less, more preferably 0.5 wt% or less, based on 100 wt% of the hot melt adhesive.

[0042] [1.4] Plasticizer The plasticizer is not particularly limited, but examples thereof include oils such as mineral oil, synthetic oil, and vegetable oil.

[0043] Examples of the mineral oil include paraffinic oil, naphthenic oil, and liquid paraffin. Examples of paraffins contained in paraffinic oil include n-paraffin, isoparaffin, and derivatives of these saturated hydrocarbons. Examples of naphthenes contained in naphthenic oil include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, and cyclooctane. Paraffinic oil is oil that contains a relatively large amount of paraffin, and naphthenic oil is oil that contains a relatively large amount of naphthene.

[0044] Specific examples of synthetic oils include ether oils, ester oils, phosphate esters, chlorinated paraffins, ethylene-α-olefin oligomers, polybutene, low-molecular-weight polybutadiene, polyisoprene, and hydrogenated versions thereof, all of which are liquid at 25°C. Specific examples of ester oils include fatty acid esters. Specific examples of fatty acid esters include isopropyl myristate, octyldodecyl myristate, glycerin triisooctanoate, diisopropyl adipate, diethyl sebacate, dibutyl sebacate, dioctyl sebacate, dodecyl sebacate, cetyl ethylhexanoate, cetyl palmitate, ethylhexyl palmitate, isopropyl palmitate, tributyl acetylcitrate, medium-chain fatty acid triglycerides, ethylene glycol salicylate, and glycol distearate.

[0045] Specific examples of vegetable oils include olive oil, rice germ oil, corn oil, camellia oil, castor oil, jojoba seed oil, eucalyptus leaf oil, and derivatives thereof (including hydrogenated oils).

[0046] The lower limit of the plasticizer content in the hot melt adhesive may be 0 wt% or more, 5 wt% or more, 7 wt% or more, or 10 wt% or more, based on 100 wt% of the weight of the hot melt adhesive. The upper limit of the plasticizer content in the hot melt adhesive may be 60 wt% or less, 40 wt% or less, 25 wt% or less, 15 wt% or less, or 10 wt% or less, based on 100 wt% of the weight of the hot melt adhesive. A plasticizer content of 10 wt% or more of the hot melt adhesive is preferred because it allows the melt viscosity of the hot melt adhesive to be adjusted within an appropriate range. Furthermore, a plasticizer content of 60 wt% or less can provide the hot melt adhesive with sufficient cohesive strength. A hot melt adhesive according to one embodiment of the present invention may contain only one type of plasticizer, or two or more types. The hot melt adhesive may not contain a plasticizer.

[0047] When the base polymer is a styrene-based block copolymer, the lower limit of the plasticizer content in the hot melt adhesive is more preferably 5 wt% or more, even more preferably 10 wt% or more, and even more preferably 15 wt% or more, based on 100 wt% of the hot melt adhesive. When the base polymer is a styrene-based block copolymer, the upper limit of the plasticizer content in the hot melt adhesive is more preferably 30 wt% or less, even more preferably 25 wt% or less, and even more preferably 20 wt% or less, based on 100 wt% of the hot melt adhesive.

[0048] When the base polymer is an olefin-based polymer and / or an olefin-vinyl acetate copolymer, the hot melt adhesive does not need to contain a plasticizer. When the base polymer is an olefin-based polymer and / or an olefin-vinyl acetate copolymer, the upper limit of the plasticizer content in the hot melt adhesive is more preferably 55% by weight or less, even more preferably 50% by weight or less, and even more preferably 45% by weight or less, based on 100% by weight of the hot melt adhesive.

[0049] When the base polymer is an acrylic block copolymer, the lower limit of the plasticizer content in the hot melt adhesive is more preferably 5 wt% or more, even more preferably 10 wt% or more, and even more preferably 15 wt% or more, relative to 100 wt% of the hot melt adhesive. When the base polymer is an acrylic block copolymer, the upper limit of the plasticizer content in the hot melt adhesive is more preferably 50 wt% or less, even more preferably 40 wt% or less, and even more preferably 30 wt% or less, relative to 100 wt% of the hot melt adhesive.

[0050] [1.5] Wax Examples of the wax include animal waxes, plant waxes, polyolefin waxes, mineral waxes, and synthetic waxes. Wax is an organic substance that is solid at room temperature and becomes liquid when heated, and has a weight-average molecular weight of less than 10,000, and is generally referred to as "wax." The wax is not particularly limited as long as it has wax-like properties and can be used to obtain the hot melt adhesive of the present invention.

[0051] Examples of animal-based waxes include shellac wax and beeswax. Examples of plant-based waxes include carnauba wax, rice wax, and oat wax. Examples of polyolefin-based waxes include polyethylene wax, polypropylene wax, and ethylene-vinyl acetate copolymer-based wax. Examples of mineral-based waxes include paraffin wax and microcrystalline wax. Examples of synthetic waxes include Fischer-Tropsch wax (FT wax). As the wax, an aliphatic hydrocarbon-based wax is preferred. Of the waxes mentioned above, polyolefin-based wax, paraffin wax, microcrystalline wax, and Fischer-Tropsch wax are examples of aliphatic hydrocarbon-based waxes. Only one type of wax may be used, or two or more types may be used in combination.

[0052] The lower limit of the wax content in the hot melt adhesive may be 0 wt% or more, 0.1 wt% or more, 0.3 wt% or more, or 0.5 wt% or more, based on 100 wt% of the weight of the hot melt adhesive. The upper limit of the wax content in the hot melt adhesive may be 80 wt% or less, 75 wt% or less, 70 wt% or less, or 65 wt% or less, based on 100 wt% of the weight of the hot melt adhesive. If the wax content is within the above range, it is advantageous in that it is easy to achieve both adhesive strength and antibacterial properties. The hot melt adhesive does not need to contain wax.

[0053] [1.6] Other Components The hot melt adhesive according to one embodiment of the present invention may contain components other than the base polymer, tackifier, antibacterial agent, plasticizer, and wax. Such components include antioxidants, stabilizers, fillers, colorants, UV absorbers, surfactants, antistatic agents, flame retardants, fragrances, coupling agents, etc. These other components are also referred to as additives. The content of these other components is 10% by weight or less relative to 100% by weight of the hot melt adhesive.

[0054] (Antioxidant) Examples of the antioxidant include phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants. Examples of phenol-based antioxidants include 2,6-di-tert-butyl-4-methylphenol, n-octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenylacrylate, and tetrakis[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane. Examples of phosphorus-based antioxidants include tris(2,4-di-t-butylphenyl)phosphite and bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite. Examples of sulfur-based antioxidants include dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, and pentaerythrityl tetrakis(3-laurylthiopropionate). These antioxidants may be used alone or in combination of two or more. Alternatively, a phenol-based antioxidant, which is a primary antioxidant, may be used in combination with a phosphorus-based antioxidant or a sulfur-based antioxidant, which is a secondary antioxidant.

[0055] (Others) Examples of the stabilizer include 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, pentaerythrityl tetrakis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and pentaerythritol tetrakis(3-laurylthiodipropionate).

[0056] Examples of the filler include talc, calcium carbonate, clay silica, mica, wollastonite, feldspar, and aluminum silicate.

[0057] Examples of the colorant include pigments and dyes.

[0058] [1.7] Hot Melt Adhesives Hot melt adhesives are adhesives that are solid at room temperature and can be applied to an adherend by heating to melt the resin. Because hot melt adhesives are solvent-free, there is no risk of solvent remaining in the adhesive layer. Therefore, adverse effects such as skin irritation caused by solvents can be suppressed, making them suitable for use in applications involving contact with living organisms such as the skin. Furthermore, when forming an adhesive layer using a hot melt adhesive, a drying process for volatilizing the solvent is not required, making them suitable for improving productivity.

[0059] The melt viscosity of the hot melt adhesive according to one embodiment of the present invention at 140°C may be 20,000 mPa·s or less, more preferably 15,000 mPa·s or less, and even more preferably 10,000 mPa·s or less. Typically, hot melt adhesives are melted and applied at approximately 160°C, but a melt viscosity of 20,000 mPa·s or less at 140°C is preferable because the low viscosity provides excellent applicability even when maintained at a low temperature of 140°C, allowing the molten hot melt adhesive to be stably applied to the adherend. The lower limit of the melt viscosity of the hot melt adhesive according to one embodiment of the present invention at 140°C is not particularly limited, but is preferably 500 mPa·s or more, and more preferably 600 mPa·s or more. A melt viscosity of 500 mPa·s or more at 140°C has the advantage of suppressing equipment contamination due to seepage from the substrate during application.

[0060] In a hot melt adhesive according to one embodiment of the present invention, the saturated hydrocarbon ratio (saturated hydrocarbon ratio), as defined by the following formula (1), is preferably 25% by weight or more, more preferably 40% by weight or more, and even more preferably 50% by weight. The upper limit of the saturated hydrocarbon ratio is not particularly limited and may be 100% by weight or less, or 90% by weight or less. A hot melt adhesive with a saturated hydrocarbon ratio of 25% by weight or more is likely to exhibit antibacterial properties. Saturated hydrocarbon ratio of hot melt adhesive [wt %] = [Saturated hydrocarbon ratio of specified components × (parts by weight of the specified components / total parts by weight of the hot melt adhesive)] × 100 ... (1) The term "specified components" as used herein refers to the base polymer and tackifier that constitute the hot melt adhesive, as well as, if a plasticizer and / or wax is included, the plasticizer and / or wax. The term "saturated hydrocarbon ratio of specified components" refers to the ratio of the saturated hydrocarbon moieties (a) and (b) below contained in these "specified components." The saturated hydrocarbon portion may have a straight-chain, branched, or cyclic structure.

[0061] (a) The saturated hydrocarbon ratio of a base polymer is the ratio (wt%) of repeating units in the base polymer that consist only of saturated hydrocarbons. (b) The saturated hydrocarbon ratio of a tackifier, plasticizer, and wax is the ratio (wt%) of saturated hydrocarbon portions in hydrocarbon compounds consisting only of carbon and hydrogen atoms. The saturated hydrocarbon ratio of a tackifier, plasticizer, and wax is calculated by counting only the saturated hydrocarbon ratio of hydrocarbon compounds consisting of carbon and hydrogen atoms. If the tackifier, plasticizer, or wax is a compound containing atoms other than carbon and hydrogen atoms, the saturated hydrocarbon ratio is not counted. The hydrocarbon compound consisting of carbon and hydrogen atoms may have a linear, branched, or cyclic structure, such as an alkane, alkene, or alkyne. Hydrocarbon compounds with 20 or more carbon atoms are preferred.

[0062] For example, when the base polymer is an ethylene-vinyl acetate copolymer, the content of ethylene units corresponds to the saturated hydrocarbon ratio. When the base polymer is SIS, both styrene units and isoprene units are unsaturated hydrocarbons, so the saturated hydrocarbon ratio is 0% by weight.

[0063] For example, when the plasticizer is a mineral oil, the proportions of paraffinic carbon, naphthenic carbon, and aromatic carbon contained in the mineral oil are calculated by ring analysis (ndM method) as %CP, %CN, and %CA, respectively, and the sum of %CP and %CN corresponds to the saturated hydrocarbon proportion. When the plasticizer is dioctyl sebacate, the saturated hydrocarbon proportion is 0% by weight because the molecule contains an oxygen atom.

[0064] For example, when the tackifier is a partially hydrogenated petroleum resin, the saturated hydrocarbon ratio corresponds to the proportion of saturated hydrocarbons contained in the resin calculated by GPC measurement (described later). When the tackifier is a rosin ester resin, the saturated hydrocarbon ratio is 0% by weight because the compound contains oxygen atoms. In other words, when the compound contains atoms other than carbon and hydrogen atoms, the saturated hydrocarbon ratio is not counted, and the saturated hydrocarbon portion is 0% by weight.

[0065] When the tackifier is a partially hydrogenated petroleum resin, the saturated hydrocarbon ratio is calculated from the hydrogenation degree. The hydrogenation degree is obtained by GPC measurement and is known as an index correlated with the content of hydrocarbons with multiple bonds (unsaturated hydrocarbons). The hydrogenation degree is calculated by the formula: [(area of ​​ultraviolet light (wavelength 265 nm) absorption of the material) / (peak area detected by a differential refractometer)]. For example, when the hydrogenation degree of the unhydrogenated resin is 15 and the hydrogenation degree of the fully hydrogenated resin is 0, the saturated hydrocarbon ratio of the partially hydrogenated resin can be calculated using formula (2): Saturated hydrocarbon ratio of partially hydrogenated resin = -6.6667 × (hydrogenation degree) + 100 ... (2) The hydrogenation degree in this specification was determined as a standard polystyrene equivalent value by gel permeation chromatography (GPC) analysis under the following conditions. UV absorption was measured using a 265 nm light source. Apparatus: LC-20AD (Shimadzu Corporation) Differential Refractometer: RID-20A (Shimadzu Corporation) Ultraviolet Absorption Detector: SPD-M20A (Shimadzu Corporation) Column: ResiPore (Agilent Technologies, Inc.) Solvent: Chloroform (Kishida Chemical Co., Ltd., for GPC analysis) Sample Concentration: 20.0 mg / ml Flow Rate: 1.0 ml / min Measurement Temperature: 40°C The present inventors have discovered that when an adhesive layer is formed using a hot melt adhesive with a saturated hydrocarbon ratio of 25% by weight or more, the antibacterial agent tends to bleed out to the adhesive layer surface more easily than when a hot melt adhesive with a saturated hydrocarbon ratio of less than 25% by weight is used. This is presumably due to a decrease in the polarity of the hot melt adhesive, which reduces its affinity with paraben-based antibacterial agents and makes it easier for antibacterial properties to be expressed on the adhesive layer surface. This effect is also presumably associated with a tendency for the sustained release of the antibacterial agent to be enhanced. Therefore, it is believed that the antibacterial properties of the hot melt adhesive are improved when the saturated hydrocarbon ratio of the hot melt adhesive is within the above-mentioned range.

[0066] As described above, the hot melt adhesive according to one embodiment of the present invention is substantially free of solvent. Here, "substantially free of solvent" means that the upper limit of the solvent content is preferably less than 0.5 wt %, and more preferably less than 0.1 wt %, based on 100 wt % of the weight of the hot melt adhesive.

[0067] [1.8] Use of Hot Melt Adhesives The uses of the hot melt adhesive according to one embodiment of the present invention are not particularly limited. For example, the hot melt adhesive can be used in the production of sanitary products (such as disposable diapers, sanitary napkins, pet sheets, urine absorption pads, and nursing pads), industrial filters for air conditioners and air purifiers, and bath mats. The hot melt adhesive can be used as a general-purpose hot melt adhesive in, for example, the production of disposable nonwoven-containing sanitary products; paper processing; flexible packaging; woodworking; carton and case sealing; labeling; and other assembly applications. In particular, the adhesive can be suitably used for bonding nonwoven fabrics in disposable diapers and sanitary napkins containing nonwoven fabrics as constituent materials; bonding elastic accessories in diapers and adult incontinence briefs; stabilizing the core of diapers and napkins; bonding diaper backsheet laminates; processing industrial filter materials; assembling surgical gowns and surgical drapes; and processing bath mats. In the case of a disposable diaper, the hot melt adhesive composition can be used, for example, to bond a top sheet to an absorbent body (pulp, tissue, etc.).

[0068] [2. Method for Producing Hot Melt Adhesive] A method for producing a hot melt adhesive according to one embodiment of the present invention includes a step of kneading an antibacterial agent having a paraben structure, which has a 10% weight loss temperature of 200°C or higher in thermogravimetry, with a composition containing a base polymer and a tackifier, while maintaining a temperature of 140°C or lower. Note that "kneading while maintaining a temperature of 140°C or lower" here refers to kneading the materials to be kneaded at a temperature of 140°C or lower, and does not include passing through a temperature range of 140°C or lower during the process of heating to a temperature of 140°C or higher. Kneading the antibacterial agent having a paraben structure with the composition containing a base polymer and a tackifier while maintaining a temperature of 140°C or lower is preferable because it can prevent the antibacterial agent having a paraben structure from evaporating during kneading. In fact, when an antibacterial agent having a paraben structure (e.g., NHPB) was kneaded at 160°C for 1 hour, evaporation was observed, but when kneaded at 140°C, no evaporation was observed, confirming that evaporation can be suppressed.

[0069] The antibacterial agent having a paraben structure, the base polymer, and the tackifier are as described in Section 1. Hot Melt Adhesive. If the melt viscosity of the hot melt adhesive at 140°C is 20,000 mPa·s or less, it can be easily stirred and uniformly melt-mixed even when maintained at a temperature of 140°C or less. Furthermore, as described above, the composition containing the base polymer and the tackifier may contain a plasticizer, wax, and / or other components.

[0070] The method for kneading while maintaining a temperature of 140°C or less is not particularly limited, but examples thereof include a method in which the components are mixed by heating and kneading using a stirring kneader, roll, Banbury mixer, kneader, extruder, or the like.

[0071] In a method for producing a hot melt adhesive according to one embodiment of the present invention, the temperature at which an antibacterial agent having a paraben structure and a 10% weight loss temperature of 200°C or higher in thermogravimetry is kneaded may be 140°C or lower. Therefore, (1) the antibacterial agent and a composition containing a base polymer and a tackifier may all be mixed simultaneously and kneaded at 140°C or lower, or (2) a composition containing components other than the antibacterial agent, such as the base polymer and tackifier, may be mixed and kneaded first, and then the antibacterial agent may be added and kneaded at 140°C or lower. When using method (2), the composition containing the base polymer and tackifier may be mixed first and kneaded at a temperature above 140°C, as long as the temperature of the kneaded mixture after adding the antibacterial agent is maintained at 140°C or lower. Mixing components that are less susceptible to temperature effects at a high temperature can shorten the time required for mixing. Furthermore, when a composition containing a base polymer and a tackifier is mixed first, the order of addition of the base polymer, the tackifier, and other components used as needed is not particularly limited, and all components of the composition may be mixed at the same time, or the components of the composition other than the base polymer may be mixed and then the base polymer may be mixed, or vice versa. Alternatively, other components may be added and kneaded after the antibacterial agent, as long as the kneading is performed while maintaining a temperature of 140°C or less.

[0072] In one embodiment of the present invention, an example of a method for producing a hot melt adhesive includes a step of mixing and melting each component of the hot melt adhesive, excluding the antibacterial agent, and a step of adding the antibacterial agent to the molten composition obtained in the step and kneading and dispersing the antibacterial agent at 140°C or less. In the method, the step of mixing and melting each component of the hot melt adhesive, excluding the antibacterial agent, is carried out, for example, by stirring the components in a heated state. The heating temperature at this time is, but is not limited to, for example, 100°C to 200°C, and the heating time is, for example, 30 minutes to 10 hours. The step of adding the antibacterial agent to the molten composition obtained and kneading and dispersing the antibacterial agent is usually carried out by lowering the temperature and then adding the antibacterial agent to the molten composition obtained and kneading it in a heated state. The heating temperature in the dispersion step needs only to be maintained at 140°C or less, and the lower limit of the heating temperature is not particularly limited, but is, for example, 80°C. The dispersion step time is, for example, 15 minutes to 6 hours.

[0073] Furthermore, a method for producing a hot melt adhesive according to one embodiment of the present invention may include the steps of mixing and melting each component of the hot melt adhesive except for the base polymer and the antibacterial agent, mixing the base polymer with the resulting melt to melt the base polymer, and adding the antibacterial agent to the melt of the composition obtained in the steps above, and kneading and dispersing the antibacterial agent at 140°C or less.

[0074] [3. Method for Applying Hot Melt Adhesive] A method for applying a hot melt adhesive according to one embodiment of the present invention includes a coating step of melting a hot melt adhesive, the hot melt adhesive including an antibacterial agent having a paraben structure, whose 10% weight loss temperature in thermogravimetry is 200°C or higher, a base polymer, and a tackifier, while maintaining the temperature at 140°C or lower, and applying the molten hot melt adhesive to a substrate.

[0075] Here, the hot melt adhesive containing the antibacterial agent having a paraben structure, the base polymer, and the tackifier is as described above.

[0076] Typically, the application process is continued in an open state for a long period of time, from several hours to several tens of hours. Therefore, the hot melt adhesive is heated for a long period of time by melting a large amount of hot melt adhesive at once or by adding hot melt adhesive during application. Furthermore, when heated in an open state, the components in the hot melt adhesive are prone to vaporization. The application process can maintain stable antibacterial properties even when heated for a long period of time by preventing the hot melt adhesive from exceeding 140°C. In particular, when the hot melt adhesive is heated in an open state for a long period of time, the effect of suppressing the decrease in antibacterial activity due to the vaporization of the antibacterial agent is significantly observed.

[0077] The application step is a step of applying a molten hot melt adhesive to a substrate (adherend). In the application step, for example, the hot melt adhesive in a molten state is applied to a first adherend. Next, a second adherend is brought into contact with the first adherend with the hot melt adhesive applied. By leaving the first adherend in this state, the hot melt adhesive cools and solidifies. This causes the first adherend and the second adherend to be bonded to each other.

[0078] The method for applying the molten hot melt adhesive to the adherend is not particularly limited. Examples include contact application and non-contact application. Contact application refers to an application method in which the device used for application (such as a coater) is in contact with the adherend when applying the hot melt adhesive composition. Specific contact application methods include slot coating and roll coater coating. Non-contact application refers to an application method in which the device used for application is not in contact with the adherend when applying the hot melt adhesive. Specific non-contact application methods include spiral coating, spray coating, and bead coating. Spiral coating is suitable for use with the hot melt adhesive according to one embodiment of the present invention. Spiral coating is a method in which the adhesive is applied in a spiral pattern using air intermittently or continuously.

[0079] <Summary> One embodiment of the present invention includes the following configuration.

[0080] [1] A hot melt adhesive comprising a base polymer, a tackifier, and an antibacterial agent having a paraben structure whose 10% weight loss temperature in thermogravimetry is 200°C or higher, wherein the hot melt adhesive has a melt viscosity of 20,000 mPa s or lower at 140°C.

[0081] [2] The hot melt adhesive according to [1], wherein the saturated hydrocarbon ratio defined by formula (1) is 25% by weight or more: saturated hydrocarbon ratio [% by weight] = sum of [saturated hydrocarbon ratio of a predetermined component × (parts by weight of the component / total parts by weight of the hot melt adhesive)] × 100 ... (1) In formula (1), the predetermined component refers to the base polymer and tackifier that constitute the hot melt adhesive, and, if a plasticizer and / or wax is included, the plasticizer and / or wax, and in formula (1), the saturated hydrocarbon ratio of a predetermined component refers to the ratio of the saturated hydrocarbon moieties of the following (a) and (b) contained in the predetermined component.

[0082] (a) The saturated hydrocarbon ratio of the base polymer is the ratio (wt%) of repeating units in the base polymer that consist only of saturated hydrocarbons. (b) The saturated hydrocarbon ratio of the tackifier, plasticizer, and wax is the ratio (wt%) of saturated hydrocarbon portions in hydrocarbon compounds that consist only of carbon atoms and hydrogen atoms. [3] The hot melt adhesive according to [1] or [2], wherein the amount of the antibacterial agent added is 1 wt% or more relative to the hot melt adhesive.

[0083] [4] A hygiene product comprising the hot melt adhesive according to any one of [1] to [3].

[0084] [5] A method for producing a hot melt adhesive, comprising a step of kneading an antibacterial agent having a paraben structure whose 10% weight loss temperature in thermogravimetry is 200°C or higher with a composition containing a base polymer and a tackifier, while maintaining a temperature of 140°C or lower.

[0085] [6] A method for applying a hot melt adhesive, comprising a coating step of melting a hot melt adhesive at 140°C or less, the hot melt adhesive comprising an antibacterial agent having a paraben structure whose 10% weight loss temperature in thermogravimetry is 200°C or higher, a base polymer, and a tackifier, and applying the molten hot melt adhesive to a substrate.

[0086] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0087] The hot melt adhesives obtained in the examples and comparative examples were evaluated by the following methods.

[0088] [Compatibility Test] <Test Method> 50 g of the hot melt adhesive obtained in the Examples and Comparative Examples was placed in a glass bottle, and the glass bottle was left to stand for 24 hours in a thermostatic chamber at 180° C. Before and after the test, the presence or absence of phase separation and precipitation was observed.

[0089] <Evaluation criteria for compatibility> Compatibility was evaluated according to the following criteria: A: Neither phase separation nor precipitation occurred B: At least one of phase separation and precipitation occurred [Antibacterial test] <Preparation of test specimen> The hot melt adhesives obtained in the examples and comparative examples were formed into films with a thickness of 10 mm, and cut into squares of 50 mm x 50 mm to prepare test specimens.

[0090] <Test Method> The antibacterial test was carried out in accordance with JIS Z2801.

[0091] <Evaluation Criteria for Antibacterial Property> Antibacterial property was evaluated according to the following criteria: The antibacterial activity value R was calculated in accordance with JIS Z2801 and is shown as a reference value, and the presence or absence of antibacterial property was evaluated based on the antibacterial property (%) below.

[0092] (Antibacterial Activity (%)) Antibacterial activity (%) is an index that focuses on the bacterial suppression effect on an untreated test piece after the test, and is expressed by the following formula: Antibacterial activity (%) = [1 - (number of viable bacteria (cells / cm) on an antibacterial-treated test piece after 24 hours] ２ ) / Number of live bacteria on untreated test piece after 24 hours (pieces / cm ２ )) × 100 If the antibacterial activity against any one of Escherichia coli, Staphylococcus aureus, and Candida was 40% or more, the sample was evaluated as having antibacterial activity.

[0093] [Confirmation of evaporation during preparation of hot melt adhesive] In the examples and comparative examples, the antibacterial agent was added to a composition containing components of the hot melt adhesive other than the antibacterial agent, and the mixture was placed in a sealed container and kneaded at 140°C for 1 hour. After that, the presence or absence of any deposits on the top plate of the container where the kneading had been performed was visually confirmed.

[0094] If any adhesions were found on the top plate of the container, they were collected and the FT-IR spectrum was measured. If an absorption peak derived from the antibacterial agent was detected in the FT-IR spectrum, it was judged that vaporization had occurred, and if no absorption peak derived from the antibacterial agent was detected, it was judged that vaporization had not occurred.

[0095] [Evaluation of Coatability] The hot melt adhesive was melted at 140° C. and checked for its ability to be applied with a coater. If the hot melt adhesive could be melted at 140° C. and applied with a coater, the coatability was rated as "good", and if the hot melt adhesive did not melt at 140° C. or if a decrease in coatability occurred due to poor discharge or the like, the coatability was rated as "poor".

[0096] [Measurement of Melt Viscosity of Hot Melt Adhesive] In accordance with the measurement method described in JIS K 6682, the viscosity of the molten hot melt adhesive was measured at 160°C, 140°C, and 120°C using a Brookfield viscometer (spindle No. 27 rotor).

[0097] [Evaluation of sustained release] The test piece of Example 6 that had been subjected to the antibacterial test described above was removed from the petri dish, and the surface (upper surface) of the test piece that had not been in contact with the petri dish was washed with 30 mL of acetone. Thereafter, the unwashed surface (lower surface) of the test piece was placed in contact with a clean petri dish and left to stand for 3 days, after which the antibacterial test described above was carried out again. If the test piece was evaluated as having antibacterial properties, it was evaluated as having sustained release properties.

[0098] [Preparation of Hot Melt Adhesive: Example 1] The materials were kneaded together to prepare a hot melt adhesive of Example 1 according to the composition (unit: parts by weight) shown in Tables 1 and 2. The specific procedure is as follows.

[0099] (1) A tackifier, an antioxidant, and a plasticizer were placed in a kneader in the composition shown in Table 1. These were heated and kneaded at 170 to 180°C until they were fully melted.

[0100] (2) A base polymer was added to the resulting melt in the composition shown in Table 1. The resulting mixture was heated and kneaded at 170 to 180°C, thereby uniformly dispersing the base polymer in the melt. In this way, Composition 1 was obtained.

[0101] (3) The set temperature of the kneader was lowered to 140° C. After the temperature inside the kneader reached 140° C., the antibacterial agent was added in the amount (unit: parts by weight) shown in Table 2, where the weight of Composition 1 was taken as 100 parts by weight, and the mixture was kneaded at 140° C. and a rotation speed of 120 rpm for 1 hour to obtain a hot melt adhesive.

[0102] The resulting hot melt adhesives were evaluated for melt viscosity, compatibility, vaporization during preparation of the hot melt adhesive, coatability, and antibacterial properties. The results and the saturated hydrocarbon ratios of the hot melt adhesives are shown in Table 2. In Table 2, diagonal lines indicate that no measurements were performed.

[0103] [Preparation of Hot Melt Adhesives: Examples 2 to 14, Comparative Examples 1 to 5] Hot melt adhesives were obtained by the same procedure as in Example 1, except that the materials and compositions were changed to those shown in Tables 1 to 3.

[0104] When a wax was included in the components shown in Table 1, the wax was added to the kneader together with the tackifier, antioxidant, and plasticizer in the above-mentioned step (1), and heated and kneaded at 170 to 180°C until it was fully melted.

[0105] The resulting hot melt adhesives were evaluated for melt viscosity, compatibility, vaporization during hot melt adhesive preparation, coatability, and antibacterial properties. The results, along with the saturated hydrocarbon ratio of the hot melt adhesive, are shown in Table 2. Although antibacterial properties were not evaluated in Example 2, the hot melt adhesive was measured using FT-IR, and antibacterial peaks were confirmed. Based on the results of Examples 1 and 3, it is believed that the adhesive has antibacterial properties against Escherichia coli and Staphylococcus aureus. In Table 2, "-" indicates a negative antibacterial value. Phase separation and precipitation were observed in Comparative Example 2, and vaporization of the antibacterial agent was observed in Comparative Examples 3 and 4 during hot melt adhesive preparation, so antibacterial properties were not evaluated.

[0106] [Summary] The hot melt adhesives of Comparative Examples 1 and 2, which contained 1 part by weight and 1.5 parts by weight of an inorganic antibacterial agent per 100 parts by weight of Composition 1, respectively, exhibited phase separation and precipitation. This is believed to be due to poor compatibility between the antibacterial agent and the other components of the hot melt adhesive. In contrast, the hot melt adhesives of Examples 1 and 3, which had the same composition but contained a similar amount of an antibacterial agent with a paraben structure and a T10 of 200°C or higher instead of the inorganic or ionic antibacterial agent, exhibited good compatibility.

[0107] The hot melt adhesives of Examples 3 and 12 to 14, each containing 1.5 parts by weight of an antibacterial agent having a paraben structure and a T10 of 200°C or higher per 100 parts by weight of Composition 1, did not exhibit any antibacterial agent vaporization during preparation, confirming their antibacterial properties. On the other hand, the hot melt adhesives of Comparative Examples 3 and 4, which have the same composition except that an antibacterial agent having a paraben structure and a T10 of less than 200°C was blended in the same blending amount instead of the antibacterial agent having a T10 of 200°C or higher, exhibited antibacterial agent vaporization during preparation. Because the hot melt adhesives of Comparative Examples 3 and 4 are heated in an open state for a long period of time when applied to a substrate, it is considered that the hot melt adhesives of Comparative Examples 3 and 4 have difficulty in exhibiting stable antibacterial properties and are therefore unsuitable for use.

[0108] Furthermore, from the results of Examples 1 and 6 to 11, in which the compositions of the base polymer, tackifier, etc. were changed, it was confirmed that hot melt adhesives containing an antibacterial agent having a paraben structure and having a T10 of 200°C or higher have antibacterial properties even if the compositions of the base polymer, tackifier, etc. are different.

[0109] Comparing Example 11 with the other Examples, it can be seen that hot melt adhesives with a higher saturated hydrocarbon ratio as defined by formula (1) have higher antibacterial properties and are more likely to exhibit the effects of the antibacterial agent.

[0110] A sustained release evaluation was carried out after the antibacterial test using test pieces prepared using the hot melt adhesive of Example 6. As a result, the test pieces still had antibacterial properties when the sustained release evaluation was carried out after the surfaces of the test pieces were washed, which indicated that the hot melt adhesive of Example 6 had sustained release properties.

[0111] According to one aspect of the present invention, it is possible to provide an antibacterial hot melt adhesive that does not undergo phase separation even when heated for a long period of time, is highly safe for the human body, and can stably maintain antibacterial properties even when heated for a long period of time. Therefore, one aspect of the present invention can be used in the production of sanitary products (such as disposable diapers, sanitary napkins, pet sheets, urine absorption pads, and breast pads), industrial filters for air conditioners and air purifiers, and bath mats.

Claims

1. A hot-melt adhesive comprising a base polymer, a tackifier, and an antibacterial agent having a parabene structure with a 10% weight loss temperature in thermogravimetric measurement of 200°C or higher, wherein the melt viscosity at 140°C is 20,000 mPa·s or less.

2. The hot-melt adhesive according to claim 1, wherein the saturated hydrocarbon ratio defined by formula (1) is 25% by weight or more: Saturated hydrocarbon ratio [% by weight] = [Sum of (saturated hydrocarbon ratio of a predetermined component × (parts by weight of the component / total parts by weight of the hot-melt adhesive))] × 100... (1) In formula (1), the predetermined components are the base polymer and the tackifier constituting the hot-melt adhesive, and when a plasticizer and / or wax is included, the plasticizer and / or wax. In formula (1), the saturated hydrocarbon ratio of the predetermined component is the ratio of the saturated hydrocarbon moieties of the following (a) and (b) contained in the predetermined component. (a) The saturated hydrocarbon ratio of the base polymer is the ratio (% by weight) of the repeating units consisting only of saturated hydrocarbons in the base polymer. (b) The saturated hydrocarbon ratios of the tackifier, plasticizer, and wax are the ratios (% by weight) of the saturated hydrocarbon moieties in hydrocarbon compounds consisting only of carbon atoms and hydrogen atoms.

3. The hot-melt adhesive according to claim 1, wherein the addition amount of the antibacterial agent is 1% by weight or more based on the hot-melt adhesive.

4. A sanitary article comprising the hot-melt adhesive according to any one of claims 1 to 3.

5. A method for producing a hot-melt adhesive, comprising a step of kneading an antibacterial agent having a parabene structure with a 10% weight loss temperature in thermogravimetric measurement of 200°C or higher, a base polymer, and a tackifier while maintaining a temperature of 140°C or lower.

6. A method for applying a hot-melt adhesive, comprising a step of melting a hot-melt adhesive comprising an antibacterial agent having a parabene structure with a 10% weight loss temperature in thermogravimetric measurement of 200°C or higher, a base polymer, and a tackifier at 140°C or lower, and applying the melted hot-melt adhesive to a substrate.