Hot melt composition and remoistenable adhesive sheet

Abstract

A hot melt composition comprising: a polyvinyl alcohol polymer; a tackifying resin comprising an aromatic hydrocarbon resin; and a plasticizer, wherein the plasticizer comprises a trifunctional or higher polyether polyol or a polyalkylene glycol having a hydroxyl value of 500 to 1,058.

Description

Hot melt composition and remoistenable adhesive sheet

[0001] The present application claims priority to Japanese Patent Application No. 2024-109095, filed on July 5, 2024, and incorporates by reference the entire contents of said Japanese Patent Application.

[0002] Known water-dispersible hot melt adhesive compositions are those that combine a polyvinyl alcohol (hereinafter sometimes abbreviated as PVA)-based resin with a tackifier resin. Patent Document 1 discloses a hot melt adhesive composition of this type, whose main component is a PVA-based resin having an average degree of polymerization of 50 to 600 and a degree of saponification of 20 to 80 mol %, blended with a tackifier resin having an acid value of 50 or more. Patent Document 1 discloses that by combining a PVA-based resin having the aforementioned degree of polymerization and degree of saponification with a tackifier resin, the compatibility between the PVA-based resin and the tackifier resin is improved, resulting in a hot melt adhesive that has excellent melt stability and water dispersibility and allows the adherend paper to be recycled.

[0003] Patent Document 2 discloses an invention aimed at providing a hot melt composition that has both adhesiveness in a dry state and adhesiveness in a wet state. Patent Document 2 discloses a hot melt composition containing a PVA-based polymer, a crosslinking agent, and a plasticizer. The examples of Patent Document 2 describe a composition that contains a PVA-based polymer, a crosslinking agent such as a polycarboxylic acid, boric acid, or isocyanate, a trifunctional polypropylene glycol, and glycerin, but does not contain a tackifying resin.

[0004] JP 5-320603 Publication WO2021 / 132625 Publication

[0005] As mentioned above, hot melt adhesives containing PVA-based polymers are known to have rewettable adhesive properties. Hot melt adhesives with rewettable adhesive properties are used as adhesives applied to paper products such as books, paper bags, and paper tubes, and have adhesive properties to paper. However, these adhesives do not necessarily have sufficient adhesive properties to plastics. From the perspective of the SDGs, there is a high demand for rewettable labels that do not require release paper. For example, rewettable labels that have high adhesive properties even to plastic substrates such as plastic containers and can be attached using only water are desired. Furthermore, if labels affixed to plastic substrates could be peeled off using only water, it would be easier to separate plastic from paper, and it is expected that the recycling of plastic containers would be promoted.

[0006] An object of the present invention is to provide a hot melt composition that constitutes a hot melt adhesive that has rewet adhesion and adhesion to paper and plastics, and that can be peeled off by immersion in water.

[0007] A hot melt composition according to the present disclosure includes a polyvinyl alcohol-based polymer, a tackifier resin containing an aromatic hydrocarbon resin, and a plasticizer, the plasticizer including a tri- or higher functional polyether polyol or a polyalkylene glycol having a hydroxyl value of 500 to 1,058.

[0008] A hot melt composition is provided that forms an adhesive that has rewet adhesion, adhesion to paper and plastics, and that can be peeled off by immersion in water.

[0009] [Outline of the embodiment] First, embodiments of the hot melt composition and remoistenable adhesive sheet according to the present disclosure will be listed and explained. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less."

[0010] A hot melt composition according to the present disclosure includes a polyvinyl alcohol-based polymer, a tackifier resin containing an aromatic hydrocarbon resin, and a plasticizer, the plasticizer including a tri- or higher functional polyether polyol or a polyalkylene glycol having a hydroxyl value of 500 to 1,058.

[0011] The hot melt composition according to the present disclosure has rewettable adhesion, good adhesion to plastic substrates, and can form an adhesive layer that can be peeled off with water. Without being bound by theory, it is believed that the combination of a PVA-based resin and a tackifying resin, which are the base polymers of the hot melt composition, with an appropriate plasticizer has resulted in a hot melt composition that can adhere to plastics, has high compatibility with water, and is peelable.

[0012] In the hot melt composition, the content of the polyvinyl alcohol polymer may be 30 to 80% by mass, the content of the aromatic hydrocarbon resin may be 1 to 30% by mass, and the total content of the polyether polyol and the polyalkylene glycol may be 1 to 55% by mass. Within these ranges, the effects of the present disclosure can be obtained, and the physical properties and stability required for a hot melt adhesive can be achieved. Here, when the hot melt composition contains only one of the polyether polyol and the polyalkylene glycol, the content of the contained component is the total content of the polyether polyol and the polyalkylene glycol.

[0013] In the hot melt composition, the tackifier resin may contain an aromatic hydrocarbon resin and a resin other than the aromatic hydrocarbon resin, and the aromatic hydrocarbon resin content in the tackifier resin may be 40 mass% or more. With this configuration, the effects of the present disclosure can be reliably obtained.

[0014] In the hot melt composition, the polyvinyl alcohol polymer may have a degree of saponification of 15 to 70 mol % and a degree of polymerization of 200 to 1500. This configuration makes it easy to form a hot melt composition that has bleeding resistance and coatability suitable for a hot melt adhesive.

[0015] In the hot melt composition, the tri- or higher functional polyether polyol may have a hydroxyl value of 50 to 1500. This configuration makes it easier to achieve the effects of the present disclosure.

[0016] The hot melt composition according to the present disclosure may be a hot melt composition for a rewettable adhesive label. The hot melt composition according to the present disclosure is suitable for use as a hot melt adhesive for forming an adhesive layer in a rewettable label. Labels using the hot melt composition according to the present disclosure have rewettable adhesive properties and therefore do not require release paper. Furthermore, the label can be attached to plastic containers such as PET bottles and can be easily peeled off by immersion in water. This facilitates the recycling of plastic containers.

[0017] The remoistenable adhesive sheet according to the present disclosure may have an adhesive layer containing the above-described hot melt composition on a paper or resin substrate, and is suitable for use as a sheet for providing remoistenable adhesive labels and the like that do not require release paper.

[0018] [Specific Example of Embodiment] The hot melt composition according to the present disclosure will be described more specifically.

[0019] [Hot Melt Composition] The hot melt composition according to the present disclosure comprises a polyvinyl alcohol polymer, a tackifying resin containing an aromatic hydrocarbon resin, and a plasticizer. The hot melt composition according to the present disclosure can be used alone or in combination with other materials as a hot melt adhesive. A hot melt adhesive comprising the hot melt composition according to the present disclosure can be melted by heating and applied to a paper substrate or a resin substrate. The hot melt composition according to the present disclosure can form a rewettable adhesive layer. This adhesive layer becomes tacky when wetted with water and can adhere to substrates such as paper and plastic. Furthermore, once the hot melt composition according to the present disclosure is adhered to a substrate, it can be cleanly removed without leaving any adhesive residue by simply immersing it in water.

[0020] The melt viscosity (160°C) of the hot melt composition according to the present disclosure is not particularly limited, but is preferably 500 to 100,000 mPa·s. When it is in this range, it can be handled in the same way as conventional hot melt adhesives, and an adhesive layer can be formed on a substrate using existing techniques and equipment. The lower limit of the melt viscosity is preferably 800 mPa·s or more, more preferably 1,000 mPa·s or more. The upper limit of the melt viscosity is preferably 50,000 mPa·s or less, more preferably 10,000 mPa·s or less. The melt viscosity (160°C) was measured in accordance with JIS K6862.

[0021] The softening point (hereinafter sometimes referred to as SP) of the hot melt composition according to the present disclosure is not particularly limited, but is 50 to 160°C, preferably 70 to 140°C, and more preferably 80 to 120°C. When it is within this range, it can be handled in the same way as conventional hot melt adhesives, and an adhesive layer can be formed on a substrate using existing equipment and known conditions. The softening point is a value measured in accordance with JIS K6863.

[0022] [Polyvinyl Alcohol-Based Polymer] The hot melt composition according to the present disclosure contains a polyvinyl alcohol (PVA)-based polymer. The PVA-based polymer is the base polymer in the hot melt composition. Specifically, the PVA-based polymer may be polyvinyl alcohol produced by saponifying a vinyl acetate homopolymer. Examples of the PVA-based polymer include ordinary (unmodified) polyvinyl alcohol, hydrophilic-group-modified polyvinyl alcohol, and hydrophobic-group-modified polyvinyl alcohol. Only one type of PVA-based polymer may be used, or two or more types of PVA-based polymers may be used in combination.

[0023] The hydrophilic group-modified polyvinyl alcohol may be, for example, a saponified polymer of vinyl acetate and another vinyl monomer capable of imparting hydrophilicity, or a PVA-based polymer modified with a hydrophilic compound. Examples of the vinyl monomer that imparts hydrophilicity include unsaturated acids such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid, or salts thereof; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallylsulfonic acid, and salts thereof; and amines such as polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, and polyoxypropylene vinylamine.

[0024] The hydrophobic-group-modified polyvinyl alcohol may be, for example, a saponified polymer of vinyl acetate and an unsaturated monomer capable of imparting hydrophobicity, or a PVA-based polymer modified with a hydrophobic compound. Examples of the monomer that imparts hydrophobicity include olefins such as ethylene, propylene, butylene, α-octene, α-dodecene, and α-octadecene.

[0025] The degree of saponification of the PVA-based polymer is not limited as long as the hot melt composition has the effects of the present disclosure, but is preferably 15 to 70 mol%. When a PVA-based polymer with a saponification degree of 15 mol% or more is used, the hot melt composition exhibits water peelability. When a PVA-based polymer with a saponification degree of 70 mol% or less is used, it melts when heated to a temperature range commonly used for hot melt adhesives, making it suitable as a hot melt adhesive. In addition, it has good thermal stability and is easy to use as a hot melt adhesive. The lower limit of the saponification degree is more preferably 20 mol% or more, 23 mol% or more, or 30 mol% or more. The upper limit of the saponification degree is more preferably 65 mol% or less, or 60 mol% or less.

[0026] The degree of polymerization of the PVA-based polymer is not limited as long as the hot melt composition has the effects of the present disclosure, but is preferably 200 to 1500. Using a PVA-based polymer with a degree of polymerization of 200 or more suppresses the occurrence of oil stains (bleeding). Using a PVA polymer with a degree of polymerization of 1500 or less suppresses the viscosity of the hot melt composition from becoming excessively high, thereby achieving appropriate coatability as a hot melt adhesive. The lower limit of the degree of polymerization is more preferably 250 or more, or 300 or more. The upper limit of the degree of polymerization is more preferably 1300 or less, 1000 or less, or 700 or less.

[0027] Two or more PVA polymers having different degrees of saponification and / or degrees of polymerization may be used in combination. When two or more PVA polymers are used, the average values ​​of the degrees of saponification and polymerization are preferably within the above ranges. The degrees of saponification and average degrees of polymerization of the PVA polymers can be determined by measuring them in accordance with JIS K6726.

[0028] The content of the PVA-based polymer in the entire hot-melt composition is not limited as long as the effects of the present disclosure are achieved, but is preferably 30 to 80% by mass. When the proportion of the PVA-based polymer in the hot-melt composition is 30% by mass or more, the occurrence of oil stains (bleeding) is suppressed. When the proportion is 80% by mass or less, it is easy to obtain appropriate coatability as a hot-melt adhesive. The lower limit of the content of the PVA-based polymer in the entire hot-melt composition is more preferably 35% by mass or more, 40% by mass or more, and 45% by mass or less. The upper limit of the content of the PVA-based polymer in the entire hot-melt composition is more preferably 75% by mass or less, 70% by mass or less, or 65% by mass or less.

[0029] The hot melt composition according to the present disclosure may contain a resin other than a PVA-based polymer as a base polymer. The content of the resin other than a PVA-based polymer in the hot melt composition is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the content of the PVA-based polymer. It is more preferable that the base polymer consists solely of a PVA-based polymer.

[0030] The resin other than the PVA-based polymer used in combination with the PVA-based polymer may be a thermoplastic resin typically used as a component of a hot melt adhesive, such as an elastomer-based, polyolefin-based, ethylene vinyl acetate copolymer (EVA)-based, polyacrylate-based, polyester-based, polyamide-based, or polylactic acid-based thermoplastic resin.

[0031] Examples of elastomer-based thermoplastic resins include conjugated diene polymers, which are polymers having structural units based on conjugated diene compounds, and acrylic block copolymers. The conjugated diene polymers may be hydrogenated conjugated diene copolymers or non-hydrogenated conjugated diene copolymers. Specific examples of conjugated diene polymers include thermoplastic block copolymers, which are copolymers of conjugated diene compounds and vinyl aromatic hydrocarbons.

[0032] Examples of conjugated diene polymers include styrene-butadiene block copolymers, styrene-isoprene block copolymers, and hydrogenated products thereof. The elastomeric thermoplastic block copolymer may be an ABA triblock copolymer. Examples of ABA triblock copolymers include styrene-butadiene-styrene block copolymer (SBS) and styrene-isoprene-styrene block copolymer (SIS). Examples of hydrogenated products thereof include styrene-ethylene-butylene-styrene block copolymer (SEBS) and styrene-ethylene-propylene-styrene block copolymer (SEPS).

[0033] Examples of acrylic block copolymers include copolymers of a block mainly composed of methacrylic acid ester units and a block mainly composed of acrylic acid ester units. Examples of acrylic block copolymers include methyl methacrylate-n-butyl acrylate block copolymer, methyl methacrylate-2-ethylhexyl acrylate block copolymer, etc. Examples of ABA triblock copolymers of acrylic block copolymers include methyl methacrylate-n-butyl acrylate-methyl methacrylate block copolymer, methyl methacrylate-2-ethylhexyl acrylate-methyl methacrylate block copolymer, etc.

[0034] Examples of polyolefin-based thermoplastic resins include polyolefin homopolymers and copolymers, polyα-olefins based on ethylene, propene and / or butene, amorphous polyα-olefins (APAOs), and ethylene / α-olefin and propylene / α-olefin copolymers.

[0035] Examples of EVA-based thermoplastic resins include copolymers synthesized from ethylene and vinyl acetate. Examples of polyacrylate-based thermoplastic polymers include block copolymers of polymeryl methacrylate and polybutyl acrylate. Examples of polyester-based thermoplastic polymers include polyesters, which are polymers of dimer acid. Examples of polyamide-based thermoplastic polymers include nylon. Examples of polylactic acid thermoplastic polymers include polylactide homopolymers. The above-mentioned base polymers can be used alone or in combination of two or more together with the PVA-based polymer.

[0036] [Tackifying Resin] The hot melt composition according to the present disclosure includes a tackifying resin, which includes an aromatic hydrocarbon resin. The aromatic hydrocarbon resin is a resin having a monomer (aromatic monomer) having an aromatic ring as a constituent unit, and may be a hydrogenated derivative, mainly composed of a monomer having an aromatic ring. The aromatic hydrocarbon resin may be a resin obtained by copolymerizing a monomer having an aromatic ring with a monomer (non-aromatic monomer) not having an aromatic ring. The aromatic hydrocarbon resin is preferably a resin obtained by polymerizing only aromatic monomers. Examples of monomers having an aromatic ring include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, and vinylanthracene. Examples of non-aromatic monomers include non-aromatic conjugated diene compounds. Specific examples of non-aromatic conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene.

[0037] Examples of aromatic hydrocarbon resins include styrene-based resins such as styrene oligomer, polystyrene, poly-α-methylstyrene, and modified poly-α-methylstyrene. As the styrene oligomer, it is preferable to use one having a softening point of about 70 to 150°C and a weight average molecular weight (Mw) of about 800 to 7000. The modified poly-α-methylstyrene may be, for example, phenol-modified poly-α-methylstyrene, and it is preferable to use one having an SP of about 75 to 95°C.

[0038] The hot melt composition according to the present disclosure may contain a tackifying resin other than an aromatic hydrocarbon resin, as long as it contains a predetermined proportion of an aromatic hydrocarbon resin. Tackifying resins other than aromatic hydrocarbon resins can be those known for use in hot melt adhesives. Examples include aliphatic tackifying resins, alicyclic tackifying resins, natural product tackifying resins, non-aromatic petroleum-based tackifying resins, and their hydrogenated and acid-modified derivatives. Specific examples include rosin resins, terpene resins, and DCPD-based resins. Examples of rosin resins include natural rosin, modified rosin, hydrogenated rosin, glycerol esters thereof (including rosin esters), pentaerythritol esters thereof, and acid-modified derivatives thereof. Examples of terpene resins include homopolymers of terpene monomers, terpene copolymers, polyterpene resins, phenol-modified terpene resins (terpene phenolic resins), hydrogenated derivatives thereof, and acid-modified derivatives thereof.

[0039] Of the above, in the tackifier resin of the hot melt composition according to the present disclosure, the resin to be combined with the aromatic hydrocarbon resin is preferably a rosin ester resin or a terpene phenol resin.

[0040] The softening point of the tackifier resin contained in the hot melt composition according to the present disclosure is not particularly limited, but may be 75 to 150° C. When the softening point of the tackifier resin is within this range, it is easy to configure and manufacture a hot melt composition that has physical properties that make it easy to handle as a hot melt adhesive.

[0041] The tackifying resin may be synthesized or commercially available, such as Sylvares SA100 (Kraton) for α-methylstyrene, FTR8100 and FTR8120 (both manufactured by Mitsui Chemicals, Inc.), YS Resin SX-100 (Yasuhara Chemical Co., Ltd.), and Piccolastic A75 (Eastman Chemical Company) for styrene oligomers, Sylvares 520 and Sylvares 525 (both manufactured by Kraton) for phenol-modified α-methylstyrene, and Sylvalite RE100L (Kraton) for rosin esters.

[0042] The proportion of the aromatic hydrocarbon resin serving as a tackifier resin relative to the entire hot melt composition is preferably 1 to 30% by mass. When the aromatic hydrocarbon resin is 1% by mass or more, adhesion to plastic substrates (particularly polypropylene) is exhibited. When the aromatic hydrocarbon resin is 30% by mass or less, compatibility with the base polymer is good, and a hot melt composition with excellent stability is obtained. The lower limit of the aromatic hydrocarbon resin content is preferably 3% by mass or more, 5% by mass or more, 7% by mass or more, or 10% by mass or more relative to the entire hot melt composition. The upper limit of the aromatic hydrocarbon resin content is preferably 25% by mass or less, 20% by mass or less, or 15% by mass or less relative to the entire hot melt composition. The lower limit of the tackifier resin content relative to the entire hot melt composition is preferably 1% by mass or more, 5% by mass or more, 7% by mass or more, or 10% by mass or more. The upper limit of the content is preferably 30% by mass or less, 25% by mass or less, 20% by mass or less, or 15% by mass or less. As long as the contents of the aromatic hydrocarbon resin and the tackifier resin are within the above ranges, a tackifier resin agent other than the aromatic hydrocarbon resin may be contained. The proportion of the aromatic hydrocarbon resin relative to the total tackifier resin is preferably 40% by mass or more, 50% by mass or more, or 60% by mass or more, and may even be 100% by mass.

[0043] [Plasticizer] The hot melt composition according to the present disclosure contains a tri- or higher functional polyether polyol or a polyalkylene glycol having a hydroxyl value of 500 to 1058 as a plasticizer (hereinafter, "tri- or higher functional polyether polyol, polyalkylene glycol having a hydroxyl value of 500 to 1058" may be referred to as a "specific plasticizer"). In other words, the plasticizer contains a polyether polyol, and the effects of the present disclosure can be obtained when the polyether polyol is tri- or higher functional, or when the polyalkylene glycol (corresponding to a bifunctional polyether polyol) has a hydroxyl value of 500 to 1058. Note that "tri- or higher functionality" means that the polyether polyol has three or more hydroxyl groups. The hydroxyl groups are preferably alcoholic hydroxyl groups. The plasticizer is also called a softener.

[0044] The tri- or higher functional polyether polyol is preferably a reaction product of a tri- or higher functional polyol with a polyalkylene glycol, a polymer of a tri- or higher functional polyol, or a reaction product of a polymer of a tri- or higher functional polyol (e.g., diglycerol) with a polyalkylene glycol. Examples of tri- or higher functional polyols include glycerin, trimethylolethane, trimethylolpropane, sorbitol, pentaerythritol, and adamantanetriol, and these may be modified with ethylene oxide or propylene oxide. The tri- or higher functional polyol is preferably a linear or branched hydrocarbon compound. Examples of alkylene glycols include glycols having 2 to 10 carbon atoms, such as ethylene glycol, propylene glycol, and butylene glycol.

[0045] Suitable examples of tri- or higher functional polyether polyols include polyoxyalkylene glyceryl ether, polyoxyalkylene pentaerythritol ether, polyglycerin, diglycerin, triglycerin, ditrimethylolpropane, dipentaerythritol, and tripentaerythritol. The alkylene preferably has 2 to 10 carbon atoms. Among these, polyoxyethylene glyceryl ether, polyoxypropylene glyceryl ether, polyoxyethylene polyoxypropylene glyceryl ether, polyoxyethylene pentaerythritol ether, polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene pentaerythritol ether, and polyglycerin are more preferred.

[0046] The hydroxyl value of the trifunctional or higher polyether polyol is not limited as long as it can constitute a hot melt composition having the effects of the present disclosure, but is preferably 50 to 1500. Within this range, both good adhesion to polypropylene substrates and good water releasability can be achieved. Furthermore, if the upper limit of the hydroxyl value is 1500 or less, adhesive strength with the plastic adherend is easily obtained. Furthermore, a hot melt composition with excellent thermal stability is easily obtained. The hydroxyl value is more preferably 60 or more, and even more preferably 80 or more, 100 or more, 400 or more, or 500 or more. The hydroxyl value is more preferably 1300 or less, and even more preferably 1200 or less, 1000 or less, or 800 or less. Note that the hydroxyl value in this specification is a value provided by the manufacturer or an average value calculated from the compound name and degree of polymerization or molecular weight disclosed by the manufacturer.

[0047] The number average molecular weight (Mn) of the tri- or higher functional polyether polyol is not limited as long as it can constitute a hot melt composition having the effects of the present disclosure, but may be 200 or more, preferably 220 or more, and more preferably 240 or more. If Mn is 200 or more, a hot melt composition in which the occurrence of oil stains (bleeding) is suppressed can be constituted. Mn is preferably 2000 or less. When the Mn of the polyether polyol is 2000 or less, adhesion to plastic substrates can be exhibited.

[0048] When the tri- or higher functional polyether polyol is polyoxyethylene glyceryl ether or polyoxypropylene glyceryl ether, the hydroxyl value may be about 80 to 700. When the tri- or higher functional polyether polyol is polyglycerin, the hydroxyl value of the polyglycerin may be about 1,000 to 1,500.

[0049] When the plasticizer is a polyalkylene glycol (i.e., a polyether polyol having two hydroxyl groups in the molecule), one with a hydroxyl value of 500 to 1058 is used. A hot melt composition using a polyalkylene glycol with a hydroxyl value within this range as a plasticizer can achieve the effects of the present disclosure. Examples of polyalkylene glycols include polyethylene glycol, polypropylene glycol, polyethylene polypropylene glycol, polybutylene glycol, and copolymers thereof, which are polymers of glycols having 2 to 10 carbon atoms. Among these, polyethylene glycol or polypropylene glycol is preferred. The hydroxyl value of 1058 is the hydroxyl value of polyethylene glycol, which has the smallest molecular weight (degree of polymerization: 2).

[0050] The hydroxyl value of the polyalkylene glycol is preferably 500 or more, more preferably 550 or more, or 600 or more. The hydroxyl value is preferably 1000 or less, more preferably 900 to 800. When the hydroxyl value is within this range, both good adhesion to polypropylene substrates and good water removability can be achieved.

[0051] The total content of the tri- or higher functional polyether polyol and the alkylene glycol having a hydroxyl value of 500 to 1058 relative to the total hot melt composition may be 1 to 55% by mass. When the total content of the specific plasticizer is 1% by mass or more, adhesion to plastic substrates and releasability (releasability when immersed in water) are exhibited. When the total content is 55% by mass or less, a hot melt composition compatible with other components and exhibiting bleed resistance is obtained. The lower limit of the total content of the specific plasticizer is preferably 2% by mass or more, 10% by mass or more, 20% by mass or more, or 25% by mass or more. The upper limit of the content is preferably 50% by mass or less, or 45% by mass or less. The content of the specific plasticizer relative to the total hot melt composition is preferably 15% by mass or more, 20% by mass or more, or 25% by mass or more. The content of the plasticizer is preferably 55% by mass or less, 50% by mass or less, or 45% by mass or less.

[0052] The plasticizer may be one of the above-mentioned plasticizers, or a combination of two or more of them. That is, the hot melt composition according to the present disclosure contains one or more plasticizers selected from the group consisting of tri- or higher functional polyether polyols and polyalkylene glycols having a hydroxyl value of 500 to 1058. Furthermore, the plasticizer may contain a plasticizer other than the specific plasticizer, as long as the effects of the present disclosure are not impaired. Examples of plasticizers other than the specific plasticizer include polyalkylene glycols having a hydroxyl value other than 500 to 1058, fatty acids, polysaccharides, polyesters, etc.

[0053] When a specific plasticizer and a plasticizer other than the specific plasticizer are contained, the content of the plasticizer (the total of the specific plasticizer and the plasticizer other than the specific plasticizer) relative to the entire hot melt composition is preferably 1% by mass or more, 15% by mass or more, 20% by mass or more, or 25% by mass or more. The plasticizer content is preferably 55% by mass or less, 50% by mass or less, or 45% by mass or less. When a specific plasticizer is combined with a plasticizer other than the specific plasticizer, the total amount of tri- or higher functional polyether polyol and alkylene glycol having a hydroxyl value of 500 to 1058 relative to the plasticizer is preferably 27% by mass or more, more preferably 50% by mass or more, and may even be 100% by mass. When the total amount is 30% by mass or more, a hot melt composition with good adhesion and water releasability is easily obtained.

[0054] It is also possible to combine a specific plasticizer with a polyalkylene glycol having a hydroxyl value other than 500 to 1,058, and a polyalkylene glycol having a hydroxyl value of 500 to 1,058 may be combined with a tri- or higher functional polyether polyol.

[0055] Furthermore, from the viewpoint of blocking resistance, the plasticizer is preferably a combination of a specific plasticizer and a polyalkylene glycol having a hydroxyl value of 60 or less (preferably a hydroxyl value of 40 or less, more preferably a hydroxyl value of 10 or less). In this case, the content of the specific plasticizer is preferably 1 to 10% by mass, more preferably 1 to 5% by mass, based on the total amount of the hot-melt composition. The proportion of the specific plasticizer relative to the total amount of the polyalkylene glycol having a hydroxyl value of 60 or less and the specific plasticizer is preferably 1 to 40% by mass, 1 to 20% by mass or less, or 1 to 10% by mass.

[0056] [Other Components] The hot melt composition according to the present disclosure may contain other components (additives) as long as the effects of the present disclosure are not substantially impaired. Examples of other components include antioxidants, ultraviolet absorbers, particulate fillers, fluorescent agents, surfactants, etc. The content of other components is 10% by mass or less of the total amount of the hot melt composition.

[0057] Examples of antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(4'-hydroxy-3',5'-di-t-butylphenyl)propionate, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 2,4-bis(octylthiomethyl)-o-cresol, 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2,4-di-t-amyl-6-[1-(3,5-di-t-amyl-2-hydroxyphenyl]-2-methyl-2-propanol] ... )ethyl]phenyl acrylate, 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)]acrylate, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, etc.; sulfur-based antioxidants such as dilauryl thiodipropionate, lauryl stearyl thiodipropionate, pentaerythritol tetrakis(3-laurylthiopropionate); phosphorus-based antioxidants such as tris(nonylphenyl)phosphite, tris(2,4-di-t-butylphenyl)phosphite, etc. The antioxidants may be used alone or in combination of two or more.

[0058] Examples of the ultraviolet absorber include benzotriazole-based ultraviolet absorbers such as 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-t-butylphenyl)benzotriazole, and 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole; benzophenone-based ultraviolet absorbers such as 2-hydroxy-4-methoxybenzophenone; salicylic acid ester-based ultraviolet absorbers; cyanoacrylate-based ultraviolet absorbers; and hindered amine-based light stabilizers. The ultraviolet absorbers may be used alone or in combination of two or more.

[0059] The particulate filler is not particularly limited, and examples thereof include calcium carbonate, kaolin, talc, titanium oxide, mica, styrene beads, etc. The particulate filler may be used alone or in combination of two or more. The surfactant is not particularly limited, and examples thereof include ionic surfactants and nonionic surfactants.

[0060] [Production Method] The method for producing the hot melt composition according to the present disclosure is not particularly limited, and any known method for producing a hot melt composition can be selected and used. For example, the materials constituting the hot melt composition can be mixed by heating and kneading using a melting tank, roll, Banbury mixer, kneader, extruder, or the like to produce the hot melt composition. The heating temperature is not limited as long as it is a temperature at which the raw materials are melted and denaturation is suppressed, but may be, for example, 170 to 200°C, preferably 165 to 170°C, and typically 170°C.

[0061] [Applications] The hot melt composition according to the present disclosure is suitable for use as a hot melt adhesive having rewettable adhesive properties. The application of the hot melt adhesive is not particularly limited, but it is suitable for use, for example, in constructing rewettable adhesive sheets for use as labels, stickers, wallpaper, and the like. The hot melt composition according to the present disclosure has high adhesive strength even when the substrate to which it is applied is a resin, particularly a low-polarity polypropylene resin, and therefore can be used in a wide range of applications. In such labels, stickers, and the like, an adhesive layer coated with the hot melt composition according to the present disclosure is formed on the adhesive surface behind the display surface (printed surface) of a substrate such as paper. The substrate on which the adhesive layer is formed is typically paper, but may also be a resin substrate. The substrate may also be a laminate composed of paper and resin, a nonwoven fabric, or the like. Labels obtained by cutting the rewettable adhesive sheet according to the present disclosure to a desired size and shape are suitable for use as labels to be attached to plastic containers such as PET bottles and polyethylene bottles.

[0062] EXAMPLES The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0063] [Preparation of Hot Melt Compositions] Hot melt compositions of Examples 1 to 24 and Comparative Examples 1 to 5 were prepared using the following materials. [Materials] PVA resins JMR-20L: manufactured by Japan Vinyl Acetate & Poval Co., Ltd., saponification degree 35 mol%, polymerization degree 400 JMR-10M: manufactured by Japan Vinyl Acetate & Poval Co., Ltd., saponification degree 65 mol%, polymerization degree 250 JMR-10L: manufactured by Japan Vinyl Acetate & Poval Co., Ltd., saponification degree 35 mol%, polymerization degree 250 JMR-150L: manufactured by Japan Vinyl Acetate & Poval Co., Ltd., saponification degree 23 mol%, polymerization degree 1480 LM-10HD: manufactured by Kuraray Co., Ltd., saponification degree 40 mol%, polymerization degree 500 LM-20: manufactured by Kuraray Co., Ltd., saponification degree 35 mol%, polymerization degree 350 Tackifying resins Sylvares SA100: α-methylstyrene, manufactured by Kraton, softening point 100°C, Mw 1700 FTR8100: Styrene oligomer, manufactured by Mitsui Chemicals, Inc., softening point 100°C, Mw 1130 FTR8120: Styrene oligomer, manufactured by Mitsui Chemicals, Inc., softening point 120°C, Mw 1650 YS Resin SX-100: Styrene oligomer, manufactured by Yasuhara Chemical Co., Ltd., softening point 100°C, Mw 2500 Piccolastic A75: Styrene oligomer, manufactured by Eastman Chemical Company, softening point 73°C, Mw 1380 Sylvares 520: Phenol-modified α-methylstyrene, manufactured by Kraton, softening point 75°C, Mw 845 Sylvares 525: Phenol-modified α-methylstyrene, manufactured by Kraton, softening point 94°C, Mw 1860 Sylvalite RE100L: Rosin ester, manufactured by Kraton, softening point 100°C, Mw 1250 Marquid No.31: Rosin ester, manufactured by Arakawa Chemical Industries, Ltd., softening point 140°C, Mw 298 Plasticizers Sannix GP-250: Polyoxypropylene glyceryl ether, manufactured by Sanyo Chemical Industries, Ltd., hydroxyl value 670 Braunon GL-26: Polyoxyethylene glyceryl ether, manufactured by Aoki Oil & Fat Industries, Ltd., hydroxyl value 100 Sannix GP-400: Polyoxypropylene glyceryl ether, manufactured by Sanyo Chemical Industries, Ltd., hydroxyl value 400 Braunon GL-3: Polyoxyethylene glyceryl ether, manufactured by Aoki Oil & Fat Industries, Ltd., hydroxyl value 633 Braunon PE-4: Polyoxyethylene pentaerythritol ether, manufactured by Aoki Oil & Fat Industries, Ltd., hydroxyl value 720 R-PG: Polyglycerin, manufactured by Sakamoto Pharmaceutical Industry Co., Ltd., hydroxyl value 1240 BRAWNON PEG-200: Polyethylene glycol, manufactured by Aoki Oil Industries Co., Ltd., hydroxyl value 565; EXCENOL 750ED: Polypropylene glycol, manufactured by AGC Inc., hydroxyl value 760; BRAWNON PEG-400: Polyethylene glycol, manufactured by Aoki Oil Industries Co., Ltd., hydroxyl value 280, molecular weight 400; Food additive glycerin: Glycerin, manufactured by Sakamoto Pharmaceutical Co., Ltd., hydroxyl value 1827; Triacetin: Glyceryl triacetate, manufactured by Daihachi Chemical Industry Co., Ltd., hydroxyl value 0; PEG6000S: Polyethylene glycol, manufactured by Sanyo Chemical Industries, Ltd., hydroxyl value 13; PEG20000: Polyethylene glycol, manufactured by Sanyo Chemical Industries, Ltd., hydroxyl value 5.6.

[0064] The above-mentioned materials were charged into a heat kneader in the blending amounts (wt%) shown in Tables 1, 3, and 5. Hot melt compositions were produced by kneading while heating at 170°C. Blank cells in the tables indicate that the component was not included.

[0065] [Evaluation] <Viscosity> The melt viscosity of each prepared composition was measured at 160°C. The measurement was carried out in accordance with JIS K6862. <SP (Softening Point)> The softening point of each prepared composition was measured in accordance with JIS K6863.

[0066] <Evaluation of Adhesive Layer> <Preparation of Evaluation Samples> In order to evaluate the adhesive strength, water peelability, and bleeding resistance to various plastics and paper, evaluation samples were prepared by applying each heated composition to the surface of a substrate to form an adhesive layer. Specifically, the hot melt composition was applied to a film thickness of 20 μm on a substrate of fine paper (60N fine paper without glue <55>, manufactured by Marusho Chemical Industry Co., Ltd.) using a slot coater (manufactured by Suntool Co., Ltd.).

[0067] <Evaluation of Adhesion Strength> The adhesive strength of the composition was measured and evaluated according to the following procedures (1) to (4). (1) An evaluation sample was cut into a size of 100 mm x 25 mm, and water was applied to the surface coated with the hot melt composition using a stamp moistener. (2) The evaluation sample was bonded to a substrate (PP, PET, PE, or high-quality paper) and pressed back and forth with a 2 kg roller. The resulting mixture was then left to stand for 24 hours in a 20°C environment. (3) In a 20°C environment, the evaluation sample was peeled from the substrate in a 180° direction at a peel rate of 300 mm / min using an Autograph (registered trademark) (Shimadzu Corporation: AGS-J). The peel strength was calculated based on the average test force (N / 2.5 cm). (4) The adhesive strength of the hot melt composition was evaluated based on the following criteria. The peeling state between the evaluation sample and the substrate was also visually observed. In the table, "material failure" means adherend failure, "interface" means interfacial failure, and "cohesion" means cohesive failure (JIS K 6800 (2006)). Adhesion strength evaluation criteria: Adherend failure or peel strength is 2.5 N / 25 mm or more; ◯ Peel strength is less than 2.5 N / 25 mm; ×

[0068] <Evaluation of Water-Releasability> Water-releasability was evaluated by measuring the water-releasability time according to the following procedures (1) to (4). (1) A sample for evaluation was cut into a size of 20 mm x 15 mm, and water was applied to the surface coated with the hot melt composition using a stamp moistening machine. (2) The sample for evaluation and a substrate (PP, PET, PE) were bonded together, and the sample was pressed and attached by rolling a 2 kg roller back and forth once, and then allowed to stand for 24 hours in an environment of 20°C. (3) The sample for evaluation was immersed in a 100 mL beaker filled with water at room temperature, and the time until the sample for evaluation peeled off was measured. (4) The water-releasability of the hot melt composition was evaluated based on the following criteria. Criteria for water-releasability: Peeled within 30 minutes; ◯ Peeled in 30 to 60 minutes; △ Not peeled within 60 minutes; ×

[0069] <Evaluation of Bleeding Resistance> Bleeding resistance was measured and evaluated according to the following procedures (1) to (4). (1) A sample for evaluation was cut into a size of 50 mm x 50 mm. (2) The surface of the evaluation sample coated with the hot melt composition was attached to a piece of wood-free paper. (3) A weight of 2 kg was applied and the sample was left standing for one week in a 60°C environment. (4) After leaving the sample for one week, the occurrence of oil stains on the substrate was visually confirmed and evaluated based on the following criteria. Criteria for bleed resistance: No oil stains on the substrate were visually confirmed (no oil stains); ○ Oil stains on the substrate were visually confirmed (oil stains); ×

[0070] <Evaluation of Blocking Resistance> Blocking resistance was measured and evaluated according to the following procedures (1) to (4). (1) A sample for evaluation was cut into a size of 100 mm x 25 mm. (2) The surface of the evaluation sample coated with the hot melt composition was attached to a piece of wood-free paper. (3) A weight of 2 kg was applied and the sample was left standing for 3 days in a 40°C environment. (4) After leaving the sample for 3 days, the sample was returned to room temperature, and then peeled off by hand, and evaluated based on the following criteria. Criteria for evaluation of blocking resistance: The wood-free paper or the sample was not torn; ◯ The wood-free paper or the sample was torn; ×

[0071] [Example Series 1] Tables 1 and 2 show the compositions and evaluation results comparing the types of tackifier resins.

[0072]

[0073]

[0074] As shown in Tables 1 and 2, all of the compositions of Examples 1 to 8 according to the present disclosure had good adhesive strength not only to paper but also to PP, PET, and PE. It was also confirmed that after adhering to the PP, PET, and PE substrates, the compositions could be peeled off with water. Furthermore, the peeled high-quality paper retained its shape without being shredded, making it easy to recover. In particular, the hot-melt compositions of Examples 1 to 7 exhibited good water-removal properties. On the other hand, Comparative Example 1, which did not contain an aromatic hydrocarbon resin as a tackifier resin, exhibited insufficient water-removal properties.

[0075] [Example Series 2] Tables 3 and 4 show the compositions and evaluation results comparing the types of plasticizers.

[0076]

[0077]

[0078] As shown in Tables 3 and 4, Examples 1 and 9 to 15, which are compositions according to the present disclosure, all exhibited good adhesion not only to paper but also to PP, PET, and PE. Furthermore, it was confirmed that after adhering to each of the PP, PET, and PE substrates, they could be peeled off with water. Furthermore, the peeled high-quality paper retained its shape without being shredded, making it easy to recover. On the other hand, Comparative Example 2, which used polyethylene glycol with a hydroxyl value of less than 500 as the plasticizer, exhibited insufficient adhesion to PP. Comparative Example 3, which used glycerin with a hydroxyl value of more than 1058 as the plasticizer, exhibited good adhesion to high-quality paper, but insufficient adhesion to PP and PET, as well as insufficient water-removal properties and bleed resistance. Furthermore, Comparative Example 4, which used glyceryl triacetate as the plasticizer, exhibited insufficient adhesion to PP, PET, and PE, and also insufficient water-removal properties from PP and PE.

[0079] [Example Series 3] Tables 5 to 7 show the compositions and evaluation results of hot melt compositions in which the blending amounts of each component were adjusted.

[0080]

[0081]

[0082]

[0083] As shown in Tables 5 to 7, all of the compositions of Examples 16 to 24 according to the present disclosure had good adhesion not only to paper but also to PP, PET, and PE. Furthermore, it was confirmed that after adhering to each of the PP, PET, and PE substrates, they could be peeled off with water. Furthermore, the peeled high-quality paper retained its shape without being shredded, making it easy to recover. Hot-melt compositions containing 1% by mass or more of a specific plasticizer exhibited good adhesion, water-removal properties, and good blocking resistance. On the other hand, Comparative Example 5, which used polyethylene glycol with a hydroxyl value of less than 500 as a plasticizer, exhibited good adhesion to high-quality paper, but insufficient adhesion to PP and PET, and insufficient water-removal properties. These results demonstrate that the inclusion of a small amount of a specific plasticizer in a hot-melt composition improves adhesion and water-removal properties.

[0084] This specification discloses the following configurations. [1] A hot melt composition comprising a polyvinyl alcohol-based polymer, a tackifier resin containing an aromatic hydrocarbon resin, and a plasticizer, wherein the plasticizer contains a tri- or higher functional polyether polyol or a polyalkylene glycol having a hydroxyl value of 500 to 1,058. [2] The hot melt composition according to [1], wherein the content of the polyvinyl alcohol-based polymer is 30 to 80 mass% of the hot melt composition, the content of the aromatic hydrocarbon resin is 1 to 30 mass% of the hot melt composition, and the total content of the polyether polyol and the polyalkylene glycol is 1 to 55 mass%. [3] The hot melt composition according to [1] or [2], wherein the tackifier resin contains an aromatic hydrocarbon resin and a resin other than the aromatic hydrocarbon resin, and the content of the aromatic hydrocarbon resin in the tackifier resin is 40 mass% or more. [4] The hot melt composition according to any one of [1] to [3], wherein the polyvinyl alcohol polymer has a degree of saponification of 15 to 70 mol % and a degree of polymerization of 200 to 1500. [5] The hot melt composition according to any one of [1] to [4], wherein the tri- or higher functional polyether polyol has a hydroxyl value of 50 to 1500. [6] The hot melt composition according to any one of [1] to [5], which is a hot melt composition for use in a remoistenable adhesive label. [7] A remoistenable adhesive sheet having, on a paper substrate or a resin substrate, an adhesive layer comprising the hot melt composition according to any one of [1] to [6].

[0085] The present invention is intended to cover a wide range of applications, including those related to the present invention, including those related to the present invention.

Claims

1. A hot melt composition comprising: a polyvinyl alcohol polymer; a tackifying resin containing an aromatic hydrocarbon resin; and a plasticizer, wherein the plasticizer comprises a tri- or higher functional polyether polyol or a polyalkylene glycol having a hydroxyl value of 500 to 1,058.

2. The hot melt composition according to claim 1, wherein the content of said polyvinyl alcohol polymer is 30 to 80% by mass, the content of said aromatic hydrocarbon resin is 1 to 30% by mass, and the total content of said polyether polyol and said polyalkylene glycol is 1 to 55% by mass, relative to the hot melt composition.

3. A hot melt composition according to claim 1 or claim 2, wherein the tackifier resin contains an aromatic hydrocarbon resin and a resin other than an aromatic hydrocarbon resin, and the content of the aromatic hydrocarbon resin in the tackifier resin is 40 mass% or more.

4. The hot melt composition according to claim 1 or 2, wherein the polyvinyl alcohol polymer has a degree of saponification of 15 to 70 mol % and a degree of polymerization of 200 to 1500.

5. The hot melt composition according to claim 1 or 2, wherein the tri- or higher functional polyether polyol has a hydroxyl value of 50 to 1,500.

6. The hot melt composition according to claim 1 or 2, which is a hot melt composition for rewettable adhesive labels.

7. A remoistenable adhesive sheet having an adhesive layer containing the hot melt composition according to claim 1 or 2 on a paper substrate or a resin substrate.

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