Sticky and adhesive agent

Abstract

The present invention achieves a sticky and adhesive agent excellent in a peeling property and a dispersion property of a water-absorbing material at the time of thermal melting. The sticky and adhesive agent contains a sticky and adhesive agent of a hot-melting type, a water-absorbing material, and a surfactant. The water-absorbing material contains a cellulose-based compound.

Description

adhesive

[0001] The present invention relates to an adhesive.

[0002] In recent years, growing global awareness of the SDGs has led to increased attention being paid to recycling and reuse. Against this backdrop, there is a growing demand for labels that can be easily peeled off from substrates during recycling. One means of achieving such labels is a pressure-sensitive adhesive that becomes easier to peel off when it absorbs water. For example, Patent Document 1 discloses a peelable adhesive composition that contains 100 parts by weight of an adhesive base resin and 1 to 200 parts by weight of a water-absorbent crosslinked polymer, and whose adhesive strength decreases after absorbing water.

[0003] International Publication No. 2002 / 055626

[0004] The adhesive composition described in Patent Document 1 is heated during production and application to a substrate. However, the water-absorbing crosslinked polymer aggregates in the molten adhesive composition, leaving room for improvement in dispersibility.

[0005] An object of one aspect of the present invention is to provide an adhesive that is excellent in peelability and dispersibility of a water-absorbing substance when heated and melted.

[0006] The present invention includes the following aspects. <1> A pressure-sensitive adhesive comprising a hot-melt pressure-sensitive adhesive, a water-absorbing substance, and a surfactant, wherein the water-absorbing substance comprises a cellulose-based compound. <2> The pressure-sensitive adhesive according to <1>, wherein the surfactant comprises a nonionic surfactant. <3> The pressure-sensitive adhesive according to <2>, wherein the HLB of the surfactant is 18 or less. <4> The pressure-sensitive adhesive according to any one of <1> to <3>, wherein the content of the water-absorbing substance is 0.5 to 45 wt% relative to the weight of the pressure-sensitive adhesive (100 wt%). <5> The pressure-sensitive adhesive according to any one of <1> to <4>, wherein the content of the surfactant is 0.5 to 10 wt% relative to the weight of the pressure-sensitive adhesive (100 wt%). <6> The pressure-sensitive adhesive according to any one of <1> to <5>, wherein the content of the cellulose-based compound in the water-absorbing substance is 70 to 100 wt% relative to the weight of the water-absorbing substance (100 wt%). <7> The cellulose-based compound is D ５０is 30 μm or less, and D ９５ <8> An article in which a first adherend and a second adherend are bonded together via an adhesive layer, the adhesive layer comprising the adhesive according to any one of <1> to <7>.

[0007] According to one aspect of the present invention, it is possible to provide a pressure-sensitive adhesive having excellent peelability and excellent dispersibility of a water-absorbing substance when heated and melted.

[0008] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the specifically described embodiments. Those skilled in the art can make various modifications within the scope described in this specification. For example, embodiments obtained by appropriately combining technical means disclosed in different embodiments are included in the technical scope of the present invention.

[0009] 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." In this specification, the term "adhesive" includes both a pressure-sensitive adhesive and an adhesive. In one embodiment, the pressure-sensitive adhesive is a pressure-sensitive adhesive. In one embodiment, the pressure-sensitive adhesive is an adhesive.

[0010] [1. Pressure-sensitive adhesive] A pressure-sensitive adhesive according to one embodiment of the present invention comprises a hot-melt pressure-sensitive adhesive, a water-absorbing substance, and a surfactant. The water-absorbing substance comprises a cellulose-based compound. Such a composition improves the dispersibility of the water-absorbing substance during heat melting, thereby reducing problems caused by aggregation of the water-absorbing substance. Therefore, a pressure-sensitive adhesive having excellent coatability and capable of producing a good coated product can be provided. Examples of problems caused by aggregation of the water-absorbing substance include filter clogging and poor performance of the resulting coated product (variation in film thickness, localization of the water-absorbing substance, etc.).

[0011] According to the findings of the present inventors, the pressure-sensitive adhesive using the water-absorbing crosslinked polymer disclosed in Patent Document 1 has a drawback in that the dispersibility of the water-absorbing substance is low when heated and melted. Such pressure-sensitive adhesives sometimes have difficulties in industrial use (such as reduced coatability) due to the non-uniform dispersion of the water-absorbing substance when heated and melted. The pressure-sensitive adhesive according to one embodiment of the present invention solves the above problem by incorporating a cellulose compound as the water-absorbing substance.

[0012] Pressure-sensitive adhesives with excellent releasability can also contribute to the achievement of the Sustainable Development Goals (SDGs) advocated by the United Nations. For example, articles attached with pressure-sensitive adhesives with excellent releasability can be easily peeled off when recycled, and can therefore contribute to the achievement of Goal 12, "Ensure sustainable consumption and production patterns." The pressure-sensitive adhesive according to one embodiment of the present invention may be an easily peelable pressure-sensitive adhesive. Because the easily peelable pressure-sensitive adhesive has excellent releasability, it can contribute to the achievement of the above-mentioned SDGs.

[0013] [1.1. Hot-melt pressure-sensitive adhesive] A hot-melt pressure-sensitive adhesive is an adhesive that can be applied to an adherend by heating and melting it. A hot-melt pressure-sensitive adhesive usually contains a base polymer and a tackifying resin. The hot-melt pressure-sensitive adhesive may further contain a plasticizer and / or wax as an optional component. The pressure-sensitive adhesive may contain only one type of hot-melt pressure-sensitive adhesive, or may contain two or more types of hot-melt pressure-sensitive adhesive.

[0014] (Base Polymer) Examples of the base polymer include styrene-based block copolymers, acrylic polymers, olefin-based polymers, polyester-based polymers, polyamide-based polymers, and combinations thereof. Among these, styrene-based block copolymers, acrylic polymers, olefin-based polymers, and combinations thereof are preferred because they have excellent processability and are easily available. The hot-melt pressure-sensitive adhesive may contain only one type of base polymer, or may contain two or more types.

[0015] Examples of styrene-based block copolymers include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butylene-styrene block copolymer (SEBS), and styrene-ethylene-propylene-styrene block copolymer (SEPS). 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.). Examples of olefin-based polymers include homopolymers and copolymers of olefin monomers (such as ethylene, propylene, and butene). More specific examples of olefin-based polymers include poly-α-olefins, amorphous poly-α-olefins (APAOs), ethylene / α-olefin copolymers, propylene / α-olefin copolymers, ethylene-vinyl acetate copolymers, and ethylene-ethyl acrylate copolymers.

[0016] The lower limit of the content of the base polymer in the hot melt pressure-sensitive adhesive may be 25 wt % or more, 30 wt % or more, 35 wt % or more, or 39 wt % or more, relative to 100 wt % of the hot melt pressure-sensitive adhesive. The upper limit of the content of the base polymer in the hot melt pressure-sensitive adhesive may be 85 wt % or less, 80 wt % or less, 75 wt % or less, 70 wt % or less, or 65 wt % or less, relative to 100 wt % of the hot melt pressure-sensitive adhesive. When the content of the base polymer is within the above range, the pressure-sensitive adhesive properties of the pressure-sensitive adhesive are improved.

[0017] (Tackifying Resin) Examples of the tackifying resin include rosin-based resins, terpene-based resins, petroleum-based resins, and styrene-based resins. The hot-melt pressure-sensitive adhesive may contain only one type of tackifying resin, or may contain two or more types.

[0018] Examples of rosin-based resins include natural rosins (such as gum rosin, tall rosin, and wood rosin), disproportionated rosin, polymerized rosin, glycerin esters of these rosins, and pentaerythritol esters of these rosins. Hydrogenated rosin-based resins (such as the hydrogenated products of the above-mentioned rosin-based resins) can also be used.

[0019] Examples of terpene resins include terpene resins, hydrocarbon-modified terpene resins, aromatic-modified terpene resins, and phenol-modified terpene resins. Hydrogenated terpene resins (such as hydrogenated versions of the above-mentioned terpene resins) can also be used.

[0020] Examples of petroleum-based resins include aliphatic petroleum resins, alicyclic petroleum resins, and aromatic petroleum resins. Hydrogenated petroleum-based resins (such as hydrogenated products of the above-mentioned petroleum-based resins) can also be used.

[0021] Examples of styrene-based resins include polymers made of styrene-based monomers and copolymers of styrene-based monomers. Examples of styrene-based monomers include styrene, methylstyrene, vinyltoluene, methoxystyrene, tertiary butylstyrene, and chlorostyrene. More specific examples of styrene-based resins include styrene homopolymers and α-methylstyrene homopolymers. Hydrogenated styrene-based resins (such as the hydrogenated products of the above-mentioned styrene-based resins) can also be used.

[0022] The lower limit of the content of the tackifier resin in the hot melt pressure-sensitive adhesive may be more than 0 wt%, 5 wt% or more, 10 wt% or more, 15 wt% or more, or 20 wt% or more, based on 100 wt% of the weight of the hot melt pressure-sensitive adhesive. The upper limit of the content of the tackifier resin in the hot melt pressure-sensitive adhesive may be 70 wt% or less, 65 wt% or less, 60 wt% or less, 55 wt% or less, or 50 wt% or less, based on 100 wt% of the weight of the hot melt pressure-sensitive adhesive. When the content of the tackifier resin is within the above range, the adhesive properties of the pressure-sensitive adhesive are improved.

[0023] (Plasticizer) Examples of plasticizers include oils. Examples of oils include mineral oils, synthetic oils, vegetable oils, and fatty acid esters. The hot melt pressure-sensitive adhesive may contain only one type of plasticizer, or may contain two or more types of plasticizers, or may not contain any plasticizers.

[0024] Specific examples of mineral oils include process oils (paraffinic process oils, naphthenic process oils, aromatic process oils, etc.) and liquid paraffin. Examples of paraffins contained in paraffinic process oils include n-paraffins, isoparaffins, and derivatives of these saturated hydrocarbons. Examples of naphthenic process oils include cycloparaffinic hydrocarbons including cyclopentane, cyclohexane, etc., and derivatives thereof. Paraffinic process oils are process oils that contain a relatively large amount of paraffins, and naphthenic process oils are process oils that contain a relatively large amount of naphthenes. In addition to these, these process oils may further contain paraffins and / or naphthenes and / or aromatic compounds.

[0025] As these mineral oils, commercially available products may be used as long as the desired hot melt pressure-sensitive adhesive can be obtained. Commercially available paraffinic process oils include PS-32, Diana Fresia S32, and Diana Process Oil PW-90 (all manufactured by Idemitsu Kosan Co., Ltd.). Commercially available naphthenic process oils include Diana Fresia N90 (manufactured by Idemitsu Kosan Co., Ltd.), NYFLEX223A (manufactured by Japan Chemtech Co., Ltd.), and SNH68 (manufactured by Sankyo Yuka Kogyo Co., Ltd.).

[0026] Specific examples of synthetic oils include ether oil, ester oil, phosphate ester, chlorinated paraffin, ethylene-α-olefin oligomer, polybutene, low-molecular-weight polybutadiene, polyisoprene, and hydrogenated products thereof, all of which are liquid at 25°C.

[0027] 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).

[0028] 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 triglyceride, ethylene glycol salicylate, and glycol distearate.

[0029] The lower limit of the plasticizer content in the hot melt pressure-sensitive 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 pressure-sensitive adhesive. The upper limit of the plasticizer content in the hot melt pressure-sensitive adhesive may be 30 wt% or less, 25 wt% or less, 20 wt% or less, 15 wt% or less, or 10 wt% or less, based on 100 wt% of the weight of the hot melt pressure-sensitive adhesive. For example, a hot melt pressure-sensitive adhesive containing no plasticizer may be formed by blending wax or the like instead of a plasticizer. When the plasticizer content is within the above range, the adhesive properties of the pressure-sensitive adhesive are improved.

[0030] (Wax) Examples of waxes include animal waxes, vegetable waxes, polyolefin waxes, mineral waxes, and synthetic waxes. The hot melt pressure-sensitive adhesive may contain only one type of wax, or may contain two or more types of wax, or may not contain any wax.

[0031] 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. As the wax, aliphatic hydrocarbon-based waxes are preferred. Of the waxes mentioned above, polyolefin-based waxes, paraffin wax, microcrystalline wax, and Fischer-Tropsch wax are examples of aliphatic hydrocarbon-based waxes.

[0032] The lower limit of the wax content in the hot melt pressure-sensitive 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 pressure-sensitive adhesive. The upper limit of the wax content in the hot melt pressure-sensitive adhesive may be 20 wt% or less, 15 wt% or less, 10 wt% or less, or 5 wt% or less, based on 100 wt% of the weight of the hot melt pressure-sensitive adhesive. When the wax content is within the above range, it is easy to impart the desired function to the pressure-sensitive adhesive. The hot melt pressure-sensitive adhesive may not contain wax.

[0033] (Content of hot melt adhesive) The lower limit of the content of the hot melt adhesive in the adhesive is preferably 50 wt% or more, more preferably 55 wt% or more, even more preferably 60 wt% or more, and particularly preferably 65 wt% or more, based on 100 wt% of the weight of the adhesive. The upper limit of the content of the hot melt adhesive in the adhesive is preferably 99 wt% or less, more preferably 98 wt% or less, based on 100 wt% of the weight of the adhesive. When the content of the hot melt adhesive is within the above range, it is easy to obtain an adhesive having sufficient adhesive properties.

[0034] [1.2. Water-absorbing substance] The adhesive contains a water-absorbing substance. The water-absorbing substance contains a cellulose-based compound. An adhesive having such a composition improves the dispersibility of the water-absorbing substance when heated and melted. The adhesive may contain only one type of water-absorbing substance, or may contain two or more types. The water-absorbing substance may contain only one type of cellulose-based compound, or may contain two or more types.

[0035] Examples of cellulose-based compounds include cellulose and cellulose derivatives, with cellulose derivatives being preferred. Examples of cellulose derivatives include carboxyalkyl cellulose and hydroxyalkyl cellulose (the number of carbon atoms in the alkyl group is, for example, 1 to 4). More specific examples of cellulose derivatives include carboxymethyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methyl cellulose. The cellulose derivative may be in the form of a salt. Examples of the salt include sodium salt, potassium salt, calcium salt, and ammonium salt. More specific examples of cellulose derivatives in the form of a salt include sodium carboxymethyl cellulose, calcium carboxymethyl cellulose, potassium carboxymethyl cellulose, and ammonium carboxymethyl cellulose.

[0036] Among these, sodium carboxymethylcellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, and hydroxypropyl methylcellulose are preferred from the viewpoint of dispersibility of the water-absorbing substance during heat melting. Furthermore, sodium carboxymethylcellulose is more preferred from the viewpoint of water absorbency. In one embodiment, the cellulose compound is preferably a non-crosslinked cellulose compound (uncrosslinked cellulose compound).

[0037] When the cellulose compound is an ether-type cellulose derivative (such as sodium carboxymethylcellulose), the lower limit of the degree of etherification of the hydroxyl groups may be 0.1 or more, or 0.5 or more. The upper limit of the degree of etherification may be 1.6 or less, or 1.0 or less. The degree of etherification of the cellulose derivative is the average number of etherified hydroxyl groups per glucose unit, and takes a value of 0 to 3. The degree of etherification of the cellulose derivative may be appropriately selected by a person skilled in the art, taking into account the balance with other components contained in the adhesive.

[0038] The cellulose-based compound may be in the form of particles. ５０ The lower limit of the average particle diameter (D) of the cellulose-based compound may be 1 μm or more, and preferably 10 μm or more. ５０ The upper limit of the average particle diameter (D) may be 300 μm or less or 150 μm or less, and preferably 60 μm or less or 30 μm or less. ５０ When the average particle diameter (D ５０ When the average particle diameter (D) is equal to or less than the upper limit, good coating properties can be easily achieved and the adhesive layer can be made thin. ５０ ) is the value at which the cumulative volume based on the total volume is 50% in the particle size distribution measured by a laser diffraction / scattering method. ９５ ) is D ５０ Greater than. ９５ The upper limit of may be 500 μm or less, preferably 200 μm or less or 150 μm or less, and more preferably 100 μm or less. ９５ The lower limit of D is not particularly limited, but is, for example, 3 μm or more. ９５ When the value of D is within this range, good coating properties can be easily achieved and the adhesive layer can be made thin. ５０ and D ９５ is measured by the method described in the Examples. When it is difficult to measure by the laser diffraction / scattering method, the particle diameter of the primary particles shown in a scanning or transmission electron microscope image can be measured and the average value can be calculated.

[0039] In the case of a water-soluble cellulose compound such as sodium carboxymethylcellulose, the lower limit of the viscosity of the aqueous solution of the cellulose compound may be 5 mPa·s or more, more preferably 50 mPa·s or more. The upper limit of the viscosity of the aqueous solution of the cellulose compound may be 120,000 mPa·s or less, more preferably 50,000 mPa·s or less. Here, the viscosity is measured under conditions of a 1 to 5 wt % aqueous solution at 25°C. The viscosity of the cellulose compound can be appropriately selected by those skilled in the art, taking into account the balance with other components contained in the adhesive.

[0040] The lower limit of the content of the water-absorbing substance in the adhesive is preferably 0.5 wt% or more, more preferably 1 wt% or more, even more preferably 5 wt% or more, and particularly preferably 10 wt% or more, based on 100 wt% of the weight of the adhesive. The upper limit of the content of the water-absorbing substance in the adhesive is preferably 45 wt% or less, more preferably 40 wt% or less, and even more preferably 30 wt% or less, based on 100 wt% of the weight of the adhesive. If the content of the water-absorbing substance is 45 wt% or less, it is easy to obtain an adhesive that exhibits the desired adhesive properties. If the content of the water-absorbing substance is 0.5 wt% or more, it is easy to obtain an adhesive that exhibits the desired releasability.

[0041] The lower limit of the content of the cellulose-based compound in the water-absorbing substance is preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more, based on 100% by weight of the water-absorbing substance. The upper limit of the content of the cellulose-based compound in the water-absorbing substance may be 100% by weight or less, 97% by weight or less, or 95% by weight or less, based on 100% by weight of the water-absorbing substance. In one embodiment, the water-absorbing substance consists solely of cellulose-based compounds. If the content of the cellulose-based compound in the water-absorbing substance is within the above range, the dispersibility of the water-absorbing substance during heat melting is improved.

[0042] Examples of water-absorbing substances other than cellulose-based compounds include cross-linked synthetic polymers, polysaccharides other than cellulose-based compounds, and protein-based polymers. In one embodiment, the adhesive contains almost no cross-linked synthetic polymers as water-absorbing substances. The proportion of cross-linked synthetic polymers in the total weight of the water-absorbing substance may be 5 wt% or less, 3 wt% or less, 1 wt% or less, 0.1 wt% or less, or 0.01 wt% or less. The water-absorbing substance may not contain cross-linked synthetic polymers.

[0043] Crosslinked synthetic polymers are water-absorbing materials obtained by crosslinking a water-absorbent resin with a crosslinking agent. Examples of crosslinked water-absorbent resins include unsaturated carboxylic acids and their neutralized products. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, β-hydroxyacrylic acid, and β-acryloxypropionic acid. More specific examples of crosslinked synthetic polymers include a crosslinked product of a hydrolyzed starch-acrylonitrile graft polymer, a crosslinked product of a neutralized starch-acrylic acid graft polymer, a crosslinked product of a saponified vinyl acetate-acrylic acid ester copolymer, a crosslinked product of a hydrolyzed acrylonitrile copolymer, a crosslinked product of a hydrolyzed acrylamide copolymer, a crosslinked product of a partially neutralized polyacrylic acid, a carboxyl group-containing crosslinked polyvinyl alcohol modified product, a crosslinked isobutylene-maleic anhydride copolymer, a polyethylene oxide crosslinked product, and a crosslinked urethane modified product. Note that, in this specification, cellulose derivatives having crosslinks are not included in the crosslinked synthetic polymers.

[0044] Examples of polysaccharides other than cellulose compounds include guar gum, locust bean gum, xanthan gum, karaya gum, pectin, alginic acid, chitin, and chitosan. Examples of protein polymers include gelatin and collagen.

[0045] [1.3. Surfactant] The pressure-sensitive adhesive contains a surfactant. By including a surfactant, a pressure-sensitive adhesive exhibiting good releasability can be easily obtained. The surfactant may be a component contained in a hot-melt pressure-sensitive adhesive. The pressure-sensitive adhesive may contain only one type of surfactant, or may contain two or more types of surfactants.

[0046] Examples of surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants. From the viewpoint of compatibility, nonionic surfactants are preferred. Pressure-sensitive adhesives containing nonionic surfactants tend to exhibit good compatibility when heated and melted. Furthermore, such pressure-sensitive adhesives are less likely to bleed out when stored at room temperature.

[0047] Examples of nonionic surfactants include ether type, ester ether type, ester type, and alkanolamide type. Examples of ester type nonionic surfactants include polyoxyethylene alkyl ethers (polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene myristyl ether, polyoxyethylene octyldodecyl ether, polyoxyethylene hydrogenated castor oil, etc.). Examples of ester ether type nonionic surfactants include fatty acid polyoxyethylene sorbitan (polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan triisostearate, polyoxyethylene sorbitan tetraoleate, etc.), fatty acid polyethylene glycol (polyethylene glycol monolaurate, polyoxyethylene glycol monostearate, polyethylene glycol distearate). Examples of ester-type nonionic surfactants include sucrose fatty acid esters (sucrose stearate, sucrose palmitate, sucrose myristate, sucrose oleate, and sucrose laurate). Among these, polyoxyethylene alkyl ethers are preferred because of their excellent peeling and adhesive properties. Among polyoxyethylene alkyl ethers, polyoxyethylene lauryl ether is preferred.

[0048] The lower limit of the HLB of the nonionic surfactant is preferably 4 or more, more preferably 5 or more. The upper limit of the HLB of the surfactant is preferably 18 or less, more preferably 17 or less, and even more preferably 15 or less. The HLB of the surfactant is calculated by the Griffin method. If the HLB of the surfactant is within the above range, it is likely to exhibit good compatibility when heated and melted. When the pressure-sensitive adhesive contains two or more types of surfactants, the proportion of surfactants having an HLB of 18 or less is preferably 70 wt% or more, more preferably 80 wt% or more, and even more preferably 90 wt% or more, based on the total weight of the surfactants.

[0049] The lower limit of the surfactant content in the adhesive is preferably 0.5 wt% or more, more preferably 0.7 wt% or more, and even more preferably 1 wt% or more, based on 100 wt% of the weight of the adhesive. The upper limit of the surfactant content in the adhesive is preferably 13 wt% or less, more preferably 10 wt% or less, even more preferably 7 wt% or less, and particularly preferably 5 wt% or less, based on 100 wt% of the weight of the adhesive. Adhesives having a surfactant content of 13 wt% or less tend to exhibit good adhesive properties and compatibility. Adhesives having a surfactant content of 0.5 wt% or more tend to exhibit good releasability.

[0050] The lower limit of the content of the nonionic surfactant in the surfactant is preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more, based on 100% by weight of the surfactant. The upper limit of the content of the nonionic surfactant in the surfactant may be 100% by weight or less, 97% by weight or less, or 95% by weight or less, based on 100% by weight of the surfactant. In one embodiment, the surfactant consists solely of a nonionic surfactant. If the content of the nonionic surfactant in the surfactant is within the above range, good compatibility is likely to be exhibited during heat melting.

[0051] [1.4. Other Components] The pressure-sensitive adhesive may further contain components other than those described above. Examples of other components include water-soluble fillers, coupling agents, organic solvents, thixotropic agents, viscosity modifiers, colorants, weathering agents, discoloration inhibitors, curing agents, antioxidants, heat stabilizers, light stabilizers, UV absorbers, inorganic particles, carbon fibers, conductive particles, fillers, antistatic agents, flame retardants, antibacterial agents, and fragrances. The surfactant may be a component contained in the hot-melt pressure-sensitive adhesive. The pressure-sensitive adhesive may contain only one type of other component, or may contain two or more types. The pressure-sensitive adhesive may contain only one type of component (e.g., water-soluble filler) contained in the same category, or may contain two or more types.

[0052] Examples of antioxidants include phenolic antioxidants, organic sulfur antioxidants, and phosphorus antioxidants. Examples of phenolic antioxidants include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and 2,6-di-tert-butyl-4-ethylphenol. Examples of organic sulfur antioxidants include dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, and distearyl-3,3'-thiodipropionate. Examples of phosphorus antioxidants include tris(2,4-di-tert-butylphenyl)phosphite. These antioxidants may be used alone or in combination of two or more.

[0053] The lower limit of the content of other components in the adhesive may be 0 wt % or more, 1 wt % or more, or 3 wt % or more, based on 100 wt % of the weight of the adhesive. The upper limit of the content of other components in the adhesive may be 10 wt % or less, 7 wt % or less, or 5 wt % or less, based on 100 wt % of the weight of the adhesive. When the content of other components is within the above range, it is easy to impart the desired function to the adhesive. The adhesive may not contain any other components.

[0054] The lower limit of the viscosity of the adhesive at 180°C is usually 100 mPa s or more, and from the viewpoint of coatability, it is preferably 1,000 mPa s or more, and more preferably 3,000 mPa s or more. The upper limit of the viscosity of the adhesive at 180°C is usually 100,000 mPa s or less, and from the viewpoint of coatability, it is preferably 50,000 mPa s or less, and more preferably 30,000 mPa s or less. The viscosity at 180°C is measured in accordance with JIS K 6862.

[0055] The lower limit of the softening point of the adhesive is usually 70° C. or higher, and from the viewpoints of coatability and heat resistance (adhesive residue), it is preferably 80° C. or higher, and more preferably 90° C. or higher. The upper limit of the softening point of the adhesive is usually 150° C. or lower, and from the viewpoints of coatability and heat resistance (adhesive residue), it is preferably 140° C. or lower, and more preferably 130° C. or lower. The softening point is measured in accordance with JIS K 6863.

[0056] 2. Manufacturing method and uses of adhesives 2.1. Manufacturing method Adhesives can be manufactured in accordance with conventional methods. For example, adhesives can be manufactured by the following steps. 1. A tackifier resin and a plasticizer are heated and kneaded to fully melt them. 2. A base polymer is added to the obtained melt. The mixture is heated and kneaded to fully melt the base polymer. 3. A water-absorbing substance and a surfactant are further added to the melt obtained in step 2 and dispersed uniformly. In this way, the desired adhesive is obtained.

[0057] In one embodiment, the method for producing a pressure-sensitive adhesive may include a step of producing a hot-melt pressure-sensitive adhesive. For example, a hot-melt pressure-sensitive adhesive produced by the following steps may be cooled and then reheated, and a water-absorbing substance and a surfactant may be added to produce a pressure-sensitive adhesive. The surfactant and additives may be added when producing the hot-melt pressure-sensitive adhesive. 1. A tackifier resin and a plasticizer are heated and kneaded to thoroughly melt them. 2. A base polymer is further added and thoroughly melted.

[0058] [2.2. Use] In an article according to one aspect of the present invention, a first adherend and a second adherend are bonded via an adhesive layer. This adhesive layer contains an adhesive according to one embodiment of the present invention. In one embodiment, the adhesive layer consists solely of an adhesive. In another embodiment, the adhesive layer contains other components (such as a temperature indicator, a filler, an antioxidant, a heat stabilizer, a light stabilizer, an ultraviolet absorber, a surfactant, a colorant, an antistatic agent, a flame retardant, an antibacterial agent, or a fragrance).

[0059] In one embodiment, the adhesive is an easily peelable adhesive that can be easily peeled from an adherend when immersed in water. Therefore, when the article is immersed in water, the first adherend and the second adherend can be easily separated. Examples of articles include substrates (glass substrates, plastic substrates, metal substrates, paper substrates, etc.) to which a label is attached. The adhesive is particularly suitable for use as an easily peelable adhesive for labels.

[0060] [Measurement Method] (Preparation of Each Sample) The adhesive according to the Examples or Comparative Examples was applied to high-quality paper by heat pressing to obtain a sample. The adhesive was applied to a thickness of 320 μm.

[0061] (Attachment to glass plate) Samples were molded to the dimensions described below. Then, the samples were attached to glass plates using the following procedure. The ambient temperature during attachment was 23°C. Samples coated with adhesives containing hot melt 1 and hot melt 2: 1. The sample was attached to a glass plate with a load of 2 kgf applied using a roller. Samples coated with adhesives containing hot melt 3 and hot melt 4: 1. The surface of the sample was heated for 10 seconds using a hot plate at 90°C. 2. The sample was attached to a glass plate with a load of 2 kgf applied using a roller.

[0062] (Adhesion) Adhesion was evaluated according to the following procedure. 1. A sample measuring 20 mm in width and 25 mm in length was attached to a glass plate. 2. 20 minutes after attachment, the peel strength was measured when peeled in a 180-degree direction. The peel speed was 300 mm / min. Adhesion was evaluated based on the measured peel strength. The specific evaluation criteria are as follows: A: 2.0 N / 10 mm or more B: 1.0 N / 10 mm or more, less than 2.0 N / 10 mm C: Less than 1.0 N / mm (Removability) Removal was evaluated according to the following procedure. 1. A sample measuring 5 mm in width and 5 mm in length was attached to a glass plate. 2. 30 minutes after attachment, the glass plate was immersed in water at 23°C. The time until the sample peeled from the glass plate was measured to evaluate removability. The specific evaluation criteria are as follows. A: Less than 30 minutes B: 30 minutes or more but less than 120 minutes C: 120 minutes or more (Compatibility and Dispersibility) Compatibility and dispersibility were evaluated according to the following procedure. 1. 50 g of a sample was placed in a mayonnaise bottle (volume: 140 mL) and left to stand in a thermostatic bath at 160°C. 2. Phase separation of the adhesive and aggregation of the water-absorbing substance over time was visually confirmed. The time until phase separation of the adhesive was measured was measured to evaluate compatibility and dispersibility. Specific evaluation criteria are as follows: ● Evaluation of compatibility A: The adhesive did not phase separate even after 5 hours. B: The adhesive phase separated in 2 to 5 hours. C: The adhesive phase separated in less than 2 hours. ● Evaluation of dispersibility A: The water-absorbing substance did not aggregate even after 5 hours. B: The water-absorbing substance aggregated in 2 to 5 hours. C: The water-absorbing substance aggregated in less than 2 hours.

[0063] (Particle size) The volumetric particle size distribution of the water-absorbing substance was measured using an LA-960V2 manufactured by Horiba Ltd. The refractive index was set to 1.5. In the particle size distribution, the value at which the cumulative volume, counting from the smallest particle size, reaches 50% was defined as D ５０ In the particle size distribution, the value at which the cumulative volume, counting from the smallest particle diameter, reaches 95% is defined as D ９５ It was decided.

[0064] [Components] The following materials were used as components constituting the adhesive.

[0065] (Components of hot melt pressure-sensitive adhesive) Base polymer 1: SIS5403P (styrene-isoprene-styrene block copolymer, JSR Corporation) Base polymer 2A: LA3320 (acrylic polymer, Kuraray Co., Ltd.) Base polymer 2B: LA2114 (liquid acrylic polymer, Kuraray Co., Ltd.) Base polymer 3: VESTOPLAST 704 (amorphous poly-α-olefin, Evonik Corporation) Base polymer 4: Ultrathene 722 (ethylene-vinyl acetate copolymer, Tosoh Corporation) Wax 1: Petrothene 353 (polyethylene wax, Tosoh Corporation) Wax 2: Sarawax SX105 (Fischer-Tropsch wax, Shell) Tackifying resin 1: SYLVARES SA-100 (α-methylstyrene, Kraton Corporation) Tackifying resin 2: Arcon M-100 (hydrogenated petroleum resin, Arakawa Chemical Industries, Ltd.) Tackifying resin 3: Alcon P-115 (hydrogenated petroleum resin, Arakawa Chemical Industries, Ltd.) Tackifying resin 4: Imave P-100 (hydrogenated petroleum resin, Idemitsu Kosan Co., Ltd.) Plasticizer 1: DOS (di(2-ethylhexyl) sebacate, Toyokuni Oil Mills Co., Ltd.) Plasticizer 2: SP-52M (liquid paraffin, Cosmo Oil Lubricants Co., Ltd.) Antioxidant 1: Adekastab AO-60G (phenolic antioxidant, ADEKA Corporation) Antioxidant 2: Irgafos 168 (phosphorus-based antioxidant, BASF SE) (water-absorbing substance) Water-absorbing substance 1: Sunrose F10LC (sodium carboxymethylcellulose, viscosity in 1% aqueous solution: 90 to 130 mPa·s, degree of etherification: 0.55 to 0.65, D ５０ : 45 μm, D ９５ Water-absorbing material 2: Sunrose F10MC (carboxymethylcellulose sodium, viscosity in 1% aqueous solution: 50 to 150 mPa·s, degree of etherification: 0.65 to 0.75, D ５０ : 42 μm, D ９５Water-absorbing material 3: Sunrose F120MC (carboxymethylcellulose sodium, viscosity in 1% aqueous solution: 800 to 1200 mPa·s, degree of etherification: 0.65 to 0.75, D ５０ : 52 μm, D ９５ Water-absorbing material 4: Sunrose F350HC (carboxymethylcellulose sodium, viscosity in 1% aqueous solution: 2000 to 4000 mPa·s, degree of etherification: 0.8 to 1.0, D ５０ : 59 μm, D ９５ Water-absorbing material 5: L-HPC LH-31 (hydroxypropyl cellulose, insoluble in water, degree of etherification: 0.33, D ５０ : 19 μm, D ９５ : 133 μm, Shin-Etsu Chemical Co., Ltd.) Water-absorbing material 6: Daicel SP-200 (hydroxyethyl cellulose, viscosity in 5% aqueous solution: 80 to 170 mPa·s, degree of etherification: 1.0 to 1.3%, Daicel Miraize Co., Ltd.) Water-absorbing material 7: Metrose NE-4VF (hydroxypropyl methylcellulose, degree of etherification by methoxy group: 0.57 to 0.72, degree of etherification by hydroxypropoxy group: 0.12 to 0.36, D ５０ : 13 μm, D ９５ Water-absorbing material 8: Water-absorbing material (sodium carboxymethylcellulose, ground product of Sunrose F10LC (Nippon Paper Industries Co., Ltd.), D) prepared by the method described in the Production Examples. ５０ : 14 μm, D ９５ : 62 μm) Water-absorbing material 9: Junron PW-120 (crosslinked polyacrylic acid, D ５０ : 14 μm, D ９５: 77 μm, Toagosei Co., Ltd.) Water-absorbing material 10: AQUPEC SW-703ER (crosslinked acrylic acid-alkyl methacrylate copolymer, Sumitomo Seika Chemicals Co., Ltd.) (Surfactants) Surfactant 1: DKS NL-30 (polyoxyethylene lauryl ether, HLB: 8.1, Dai-ichi Kogyo Seiyaku Co., Ltd.) Surfactant 2: DKS NL-15 (polyoxyethylene lauryl ether, HLB: 5.0, Dai-ichi Kogyo Seiyaku Co., Ltd.) Surfactant 3: DKS NL-100 (polyoxyethylene lauryl ether, HLB: 13.8, Dai-ichi Kogyo Seiyaku Co., Ltd.) Surfactant 4: DKS NL-180 (polyoxyethylene lauryl ether, HLB: 16.1, Dai-ichi Kogyo Seiyaku Co., Ltd.) [Production Example] (Size adjustment of water-absorbing material) Sunrose F10LC (sodium carboxymethylcellulose, Nippon Paper Industries Co., Ltd.) was pulverized using a single track jet mill FS-4 (Seishin Enterprise Co., Ltd.) to obtain water-absorbing substance 8.

[0066] (Preparation of hot melt pressure-sensitive adhesive) Hot melt pressure-sensitive adhesives 1 to 4 were prepared by kneading the materials according to the compositions (unit: parts by weight) shown in Table 1 below. The specific procedure is as follows: 1. A tackifier resin, a plasticizer, a wax and an antioxidant were charged into a kneader. These were heated and kneaded at 150 to 190°C to be sufficiently melted. 2. A base polymer was charged into the obtained melt. By heating and kneading at 150 to 190°C, the base polymer was uniformly dispersed in the melt. In this way, hot melt pressure-sensitive adhesives 1 to 4 were obtained.

[0067] (Preparation of adhesive) Each material was kneaded according to the composition (unit: parts by weight) shown in Tables 2 to 4 below to prepare adhesives. The specific procedure is as follows: 1. The hot melt adhesive was placed in a kneader. These were heated and kneaded at 150 to 190°C to be fully melted. 2. A water-absorbing substance and a surfactant were added to the obtained melt to obtain an adhesive.

[0068] [Examples 1 to 8, Comparative Examples 1 and 2] See Table 2 below. In Examples 1 to 4, hot melt pressure-sensitive adhesives containing different types of base polymers were formulated. All of the obtained pressure-sensitive adhesives were excellent in pressure-sensitive adhesiveness, releasability, compatibility and dispersibility.

[0069] In Examples 5 to 8, the blending amounts of the hot melt pressure-sensitive adhesive, water-absorbing substance and surfactant were changed. All of the obtained pressure-sensitive adhesives were excellent in pressure-sensitive adhesive property, releasability, compatibility and dispersibility. In Comparative Examples 1 and 2, pressure-sensitive adhesives were prepared without blending a water-absorbing substance or surfactant. The obtained pressure-sensitive adhesives were inferior in releasability. From the viewpoint of pressure-sensitive adhesive property and releasability, more preferred blending amounts of the water-absorbing substance and surfactant are as follows (in all cases, the weight of the pressure-sensitive adhesive is taken as 100 wt%). - Lower limit of the blending amount of the water-absorbing substance: between 1 wt% and 25 wt% (e.g., 5 wt% or more or 10 wt% or more) - Upper limit of the blending amount of the water-absorbing substance: between 25 wt% and 40 wt% (e.g., 30 wt% or less) - Lower limit of the blending amount of the surfactant: between 0.5 wt% and 1 wt% (e.g., 0.7 wt% or more) - Upper limit of the blending amount of the surfactant: between 1 wt% and 10 wt% (e.g., 7 wt% or less or 5 wt% or less).

[0070] [Examples 9 to 15, Comparative Examples 3 to 6] See Table 3 below (for reference, the results of Example 1 are also shown in Table 3). In Examples 9 to 15 and Comparative Examples 3 to 6, the type of water-absorbing substance was changed. In Examples 9 to 15, a water-absorbing substance that was a cellulose-based compound was blended. All of the obtained adhesives were excellent in adhesiveness, releasability, compatibility, and dispersibility. In Comparative Examples 3 to 6, a water-absorbing substance that was not a cellulose-based compound was blended. All of the obtained adhesives were poor in dispersibility of the water-absorbing substance. These results show that if the water-absorbing substance is a cellulose-based compound, adhesives with excellent dispersibility of the water-absorbing substance, stable quality, and suitable for industrial applications can be obtained. Conversely, if the water-absorbing substance is not a cellulose-based compound, adhesives with poor dispersibility of the water-absorbing substance, and unsuitable for industrial applications can be obtained.

[0071] The adhesives of Examples 14 and 15 were D ５０ and D９５ A water-absorbing substance with a small water absorption coefficient was used. Therefore, compared with other Examples, the adhesive layer could be made thinner. Furthermore, when the pressure-sensitive adhesives of Examples 14 and 15 were applied using an application device having a filter, the application could be carried out without clogging the filter, and therefore it can be said that pressure-sensitive adhesives with excellent applicability were obtained.

[0072] [Examples 16 to 18] Table 4 is referenced below (for reference, the results of Example 1 are also shown in Table 4). In Examples 16 to 18, the HLB of the surfactant was changed. All of the obtained pressure-sensitive adhesives were excellent in pressure-sensitive adhesive properties, releasability, compatibility and dispersibility. From the viewpoint of compatibility, a more preferred upper limit of the HLB of the surfactant is between 13.8 and 16.1 (for example, 15.0 or less, preferably 13.8 or less).

[0073] The present invention can be used for adhesives, pressure sensitive adhesives, and the like.

Claims

1. A peelable adhesive containing a hot-melt type adhesive, a water-absorbing substance, and a surfactant, wherein the water-absorbing substance contains a cellulose-based compound.

2. The peelable adhesive according to Claim 1, wherein the surfactant contains a nonionic surfactant.

3. The peelable adhesive according to Claim 2, wherein the HLB of the surfactant is 8.1 to 13.

8.

4. The peelable adhesive according to Claim 1, wherein the content of the water-absorbing substance is 0.5 to 45% by weight based on 100% by weight of the peelable adhesive.

5. The peelable adhesive according to Claim 1, wherein the content of the surfactant is 0.7 to 10% by weight based on 100% by weight of the peelable adhesive.

6. The peelable adhesive according to Claim 1, wherein the content of the cellulose-based compound in the water-absorbing substance is 70 to 100% by weight based on 100% by weight of the water-absorbing substance.

7. The cellulose-based compound is D ５０ is 1 to 30 μm, D ９５ is 100 μm or less, the peelable adhesive according to Claim 1.

8. The peelable adhesive according to Claim 1, which is for a label.

9. An article in which a first adherend and a second adherend are adhered via an adhesive layer, wherein the adhesive layer contains the peelable adhesive according to any one of Claims 1 to 8.