Adhesives and adhesive sheets

Abstract

To provide an adhesive which uses a biodegradable raw material, is excellent in adhesion force, cohesion force, and transparency of a coated film, dispenses with aging, and is suitable for bonding adhesive surfaces.SOLUTION: An adhesive contains an urethane resin (X) that is a reactant of polyol (A) having two hydroxyl groups and polyisocyanate (B), wherein the polyol (A) having the two hydroxyl groups contains polyol (Ax) which is composed of a copolymer of a mixture containing lactide (a1), a monomer (a2) having a lactone unit, and diol (a3) having a molecular weight of less than 200, and has a number average molecular weight of 2,000-40,000, a ratio (NCO / ON ratio) of a mol number of the isocyanate group in the polyisocyanate (B) to a mol number of the hydroxyl group in the polyol (A) having the two hydroxyl groups is 0.6 to 0.98, and a glass transition temperature of the urethane resin (X) is -20°C to 30°C.SELECTED DRAWING: None

Description

Technical Field

[0001] Embodiments of the present invention relate to adhesives and adhesive sheets using the same.

Background Art

[0002] Adhesive sheets having an adhesive layer formed from an adhesive are easy to handle and are thus used in a wide range of fields such as labels, tapes, and bonding applications. Among these, two-component curable acrylic adhesives composed of a main agent and a curing agent are widely used because they are excellent in adhesiveness, weather resistance, durability, etc. However, when using a curing agent, there are problems such as the pot life of the adhesive occurring and the painting work and process management becoming complicated. Further, for example, tapes for binding vegetables and fruits may be discarded or composted in the soil while being attached to the vegetables and fruits. However, since the decomposition rate of the acrylic adhesive constituting the adhesive label is extremely slow, the adhesive may remain in the soil semi-permanently and cause destruction of the ecosystem. For these reasons, in recent years, adhesives using biodegradable raw materials have begun to be recommended.

[0003] Therefore, Patent Document 1 discloses a one-component acrylic adhesive obtained by dissolving a complex compound of an acrylic resin, a keto-enol tautomer, and a polyvalent metal in a solvent containing an alcohol-based solvent.

[0004] Further, Patent Document 2 discloses an adhesive characterized by containing polylactic acid, a glass transition temperature lowering agent having a biodegradable material and / or a bio-derived material, and an adhesiveness-imparting agent.

[0005] [[ID= [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2-91178 [Patent Document 2] Japanese Patent Publication No. 2006-70091 [Patent Document 3] Japanese Patent Publication No. 2006-131705 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, while the pot life problem can be solved when using the adhesive described in Patent Document 1, there is a problem in that a certain period of aging (curing) is required after coating in order to harden the adhesive. In addition, because the acrylic resin is crosslinked by the hardener, there is a problem in that the adhesion between adhesive surfaces (self-adhesive surface adhesion strength) required for fastening tape is low.

[0008] Furthermore, the adhesives described in Patent Documents 2 and 3 contain tackifying resins such as rosin resin, and while they exhibit adhesive strength, they suffer from low cohesive strength. In addition, the poor compatibility between lactic acid-based resins and tackifying resins causes the coating film to whiten, making them unsuitable for applications requiring transparency.

[0009] Therefore, embodiments of the present invention provide an adhesive that uses biodegradable raw materials, exhibits excellent tackiness, cohesiveness, and transparency of the coating film, and furthermore, does not require aging, making it suitable for bonding adhesive surfaces together. [Means for solving the problem]

[0010] The inventors of this invention have diligently studied and completed the present invention in order to solve the above problems. Specifically, embodiments of the present invention relate to the following. However, the present invention is not limited to the embodiments described below and includes various embodiments.

[0011] One embodiment of the present invention is an adhesive comprising a urethane resin (X) which is a reaction product of a polyol (A) having two hydroxyl groups and a polyisocyanate (B), The polyol (A) having two hydroxyl groups includes a polyol (Ax) having two hydroxyl groups with a number average molecular weight of 2,000 to 40,000, which is a copolymer of a mixture containing lactide (a1), a monomer having lactone units (a2), and a diol (a3) ​​with a molecular weight of less than 200. The ratio (NCO / OH ratio) of the number of moles of isocyanate groups in polyisocyanate (B) to the number of moles of hydroxyl groups in polyol (A) having two hydroxyl groups is 0.6 to 0.98. The glass transition temperature of the urethane resin (X) is -20°C to 30°C. Regarding adhesives.

[0012] Another embodiment of the present invention relates to an adhesive sheet having a substrate and an adhesive layer formed from the adhesive of the above embodiment on at least one surface of the substrate. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide an adhesive that uses a high proportion of biodegradable raw materials, fully satisfies adhesive properties, exhibits excellent transparency, and does not require aging. Furthermore, it is possible to provide an adhesive sheet using the above adhesive. [Modes for carrying out the invention]

[0014] Before describing the present invention, terms are defined. As used herein, "adhesive sheet" means having a base material and an adhesive layer comprising the adhesive of the present invention.

[0015] In this specification, a numerical range specified using "~" means that the numbers written before and after "~" are included as the lower and upper limits. Unless otherwise noted, each of the components described herein may be used independently, individually, or in combination of two or more.

[0016] In this specification, the polyol (A) having two hydroxyl groups, the monomer (a2) having a lactone unit, the diol (a3) having a molecular weight of less than 200, the polyol (Ax) having a number average molecular weight of 2,000 to 40,000, and the diol (Ay) having a molecular weight of less than 1,500 may be abbreviated as polyol (A), monomer (a2), diol (a3), polyol (Ax), and diol (Ay), respectively.

[0017] In this specification, the "weight average molecular weight (Mw)" is a polystyrene conversion value determined by gel permeation chromatography (GPC) measurement. The "number average molecular weight (Mn)" is a polystyrene conversion value determined by GPC measurement. These can be measured by the methods described in the Examples section.

[0018] Hereinafter, embodiments of the present invention will be described in detail. However, the following description is an example (representative example) of the embodiments of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist thereof.

[0019] <1> Adhesive The adhesive, which is one embodiment of the present invention, contains a urethane resin (X). By containing the urethane resin (X), sufficient adhesive properties can be exhibited without using a curing agent, and furthermore, aging is unnecessary. Also, it is preferably a one-component adhesive that does not contain a curing agent. Since the urethane resins (X) are not crosslinked by covalent bonds without containing a curing agent, the adhesion between the adhesive surfaces can be enhanced.

[0020] <Urethane resin (X)> The urethane resin (X) is a reaction product of a polyol (A) and a polyisocyanate (B), and has a glass transition temperature of -20°C to 30°C.

[0021] The above-mentioned "reactant" means the reaction product of polyol (A) and polyisocyanate (B). The polyol (A) has two hydroxyl groups in one molecule. The polyisocyanate (B) is preferably a bifunctional isocyanate (also referred to as diisocyanate) having two isocyanate groups in one molecule.

[0022] The above-mentioned polyol (A) contains a polyol (Ax) having a number average molecular weight of 2,000 to 40,000, which is composed of a copolymer of a mixture containing lactide (a1), monomer (a2), and diol (a3). By the polyol (Ax) containing lactide (a1), monomer (a2), and diol (a3), the adhesive strength and cohesive strength of the adhesive containing the urethane resin (X) can be achieved simultaneously. The polyol (A) may further contain a diol (Ay) having a molecular weight of less than 1,500.

[0023] The number average molecular weight (Mn) of the above-mentioned polyol (Ax) is 2,000 to 40,000. When Mn is within the above range, urethane bonds are appropriately introduced into the urethane resin (X), and the adhesive strength and cohesive strength are improved.

[0024] The molecular weight of the above-mentioned diol (Ay) is less than 1,500. When the molecular weight is less than 1,500, the urethane bonds in the urethane resin (X) become dense, and the cohesive strength is improved.

[0025] The glass transition temperature (Tg) of the above-mentioned urethane resin (X) is -20°C to 30°C. Tg is more preferably -15°C or higher, and even more preferably -10°C or higher. Also, it is more preferably 20°C or lower, and even more preferably 10°C or lower. When Tg is within the above range, it is possible to achieve both adhesive strength and cohesive strength, and sufficient adhesive properties can be obtained. Specifically, when Tg is adjusted to -20°C or higher, sufficient cohesive strength can be obtained, and the holding power can be easily increased. Also, when Tg is adjusted to 30°C or lower, the adhesion to the adherend can be enhanced.

[0026] As described above, if a polyol (A) containing a polyol (Ax) with a number-average molecular weight (Mn) of 2,000 to 40,000 is used, and the urethane resin (X) has a glass transition temperature of -20 to 30°C, then an adhesive with excellent tackiness can be easily constructed even when large amounts of biodegradable raw materials such as lactide (a1), monomer (a2), and diol (a3) ​​are used to increase the proportion of biodegradable raw materials used.

[0027] The weight-average molecular weight (Mw) of the urethane resin (X) is preferably 30,000 to 180,000, more preferably 40,000 or more, and even more preferably 50,000 or more. Furthermore, it is more preferably 160,000 or less, and even more preferably 140,000 or less. When the Mw of the urethane resin (X) is adjusted within the above range, cohesive force can be imparted through the entanglement of polymer chains, making it easy to increase adhesive strength. In addition, it becomes possible to improve cohesive force through urethane bonds formed by urethane formation.

[0028] The following provides a more detailed explanation of the components of the adhesive. [Polyol (A)] Polyol (A) is obtained by including a polyol (Ax) which is a copolymer of a mixture containing lactide (a1), a monomer having lactone units (a2), and a diol (a3) ​​having a molecular weight of less than 200. The polyol (A) may further contain a diol (Ay) having a molecular weight of less than 1,500, if necessary. By including the diol (Ay), it is possible to control the concentration and density of urethane bonds in the urethane resin (X), thereby improving the tackiness.

[0029] <Polyol (Ax)> Polyol (Ax) is a polyol composed of a copolymer of a mixture containing lactide (a1), a monomer having lactone units (a2), and a diol (a3) ​​with a molecular weight of less than 200. Because polyol (Ax) has two hydroxyl groups in its molecule, it can react with polyisocyanate (B) to suppress gelation while preparing a urethane resin (X) with a desired weight-average molecular weight (Mw).

[0030] When increasing the proportion of biodegradable raw materials used, it is particularly preferable that lactide (a1), monomer (a2), and diol (a3) ​​are all biodegradable raw materials.

[0031] The number-average molecular weight (Mn) of the polyol (Ax) is 2,000 to 40,000, preferably 3,000 or more, and more preferably 4,000 or more. It is also preferably 35,000 or less, more preferably 30,000 or less, and even more preferably 25,000. When Mn is adjusted within the above range, urethane bonds are appropriately introduced into the urethane resin (X), improving adhesion and cohesiveness. Specifically, when Mn is adjusted to 2,000 or more, it is possible to suppress the number of urethane bonds in the urethane resin (X) obtained by urethane formation from becoming too large, and thus ensure adhesion. Furthermore, when Mn is adjusted to 40,000 or less, the number of urethane bonds becomes sufficient, and a decrease in cohesiveness can be suppressed.

[0032] In one embodiment, the content of diol (Ax) is preferably 40% by mass, and more preferably 50% by mass or more, based on the total mass of polyol (A). When the content is within the above range, a urethane resin (X) that exhibits excellent adhesive properties can be obtained.

[0033] From the viewpoint of obtaining sufficient reactivity in urethane formation, it is preferable that the mixture constituting the polyol (Ax) does not contain compounds having active hydrogen such as hydroxyl groups at only one end, and compounds in which acidic groups such as sulfonates form salts. Therefore, in one embodiment, it is preferable that the monomer mixture constituting the polyol (Ax) consists only of lactide (a1), monomer (a2), and diol (a3).

[0034] (Lactide (a1)) Lactide (a1) is used to increase the Tg of urethane resin (X) and impart cohesive force. Lactide (a1) is a cyclic compound having two ester bonds in a molecule formed by the dehydration condensation of the hydroxyl and carboxyl groups of two hydroxy acid molecules. Examples include glycolide, 3,6-dimethyl-1,4-dioxane-2,5-dione (derived from 2-hydroxypropionic acid (lactic acid)), and 1,6-dioxacyclodecane-2,7-dione (derived from 4-hydroxybutanoic acid). Among these, so-called lactides derived from lactic acid may also be optically active substances, and include L-lactide, D-lactide, DL-lactide, and meso-lactide. Among these, L-lactide and meso-lactide are preferred because they are readily available, biodegradable, and derived from plant materials, allowing for a high biomass content. Meso-lactide is even more preferred because it increases adhesive strength. The lactide (a1) described above may be used individually or in combination of two or more types. Here, DL-lactide means an equimolar mixture of L-lactide and D-lactide.

[0035] By copolymerizing lactide (a1) with monomer (a2) and diol (a3), described later, a urethane resin (X) with desired properties can be obtained. Crystalline L-lactide and D-lactide can have their crystallinity reduced by copolymerizing them with monomer (a2), thereby increasing their tackiness and transparency.

[0036] In one embodiment, the content of lactide (a1) is preferably 25 to 90% by mass, more preferably 40% by mass or more, and even more preferably 55% by mass or more, based on the total mass of the mixture constituting the polyol (Ax). Furthermore, it is more preferably 80% by mass or less, and even more preferably 75% by mass or less. The amount of crystalline L-lactide and D-lactide used is preferably 70% by mass or less. When the above content is within the above range, the glass transition temperature of the urethane resin (X) can be easily adjusted to an appropriate range, which is preferable because it allows for easy improvement of the adhesive properties.

[0037] (monomer (a2)) Monomer (a2) is a monomer having lactone units. By copolymerizing monomer (a2) with lactide (a1) and diol (a3), the glass transition temperature of the urethane resin (X) can be adjusted to an appropriate range. As a result, a urethane resin (X) can be obtained that can achieve excellent properties such as tackiness in adhesives. Monomer (a2) may be used as one type or a combination of two or more monomers.

[0038] Examples of monomers (a2) include lactones having 3 to 12 carbon atoms. Examples include β-propiolactone, β-butyrolactone, δ-valerolactone, ε-caprolactone, enanthractone, caprylolactone, and laurolactone. Among these, δ-valerolactone and ε-caprolactone are preferred because they are biodegradable raw materials.

[0039] In one embodiment, the monomer (a2) content is preferably 4 to 60% by mass, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the mixture constituting the polyol (Ax). Furthermore, it is more preferably 50% by mass or less, and even more preferably 40% by mass or less. When the content is within the above range, it is preferable in that the glass transition temperature of the urethane resin (X) can be appropriately adjusted and the adhesive properties can be easily improved.

[0040] (Diol (a3)) Diol (a3) ​​is a compound with two hydroxyl groups in its molecule and a molecular weight of less than 200. The two hydroxyl groups in diol (a3) ​​serve as starting points for copolymerization of polyol (Ax), and lactide (a1) and monomer (a2) are added in two directions to form a polymer chain with two terminal hydroxyl groups. Lactide (a1) has the function of increasing the Tg of polyol (Ax) and imparting cohesive force, but because the molecular weight of diol (a3) ​​is less than 200, the distance between lactide (a1) attached to one hydroxyl group and lactide (a1) attached to the other hydroxyl group becomes shorter. This effect strengthens the interaction between lactide (a1) and further improves the cohesive force of the urethane resin (X).

[0041] Diol (a3) ​​can be an aliphatic glycol, an alicyclic glycol, etc., but in order to increase the content of biodegradable raw materials, it is preferable that diol (a3) ​​is also a biodegradable raw material. Diol (a3) ​​may be used alone or in combination of two or more types.

[0042] Aliphatic glycols that can be used as diol (a3) ​​include, for example, ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,5-pentanediol, 2-butyl-2-ethylpropanediol, 1,9-nonanediol, 2-methyloctanediol, and 1,10-decanediol. Alicyclic glycols include, for example, 1,4-cyclohexanedimethanol and 1,2-cyclohexanedimethanol. Among these, ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, and 1,4-butanediol are preferred because they are biodegradable raw materials.

[0043] The molecular weight of the diol (a3) ​​is less than 200, more preferably 150 or less, and even more preferably 100 or less. Having a molecular weight of less than 200 improves the cohesive strength of the urethane resin (X).

[0044] In one embodiment, the content of diol (a3) ​​is preferably 0.1 to 10% by mass, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more, based on the total mass of the mixture constituting the polyol (Ax). Furthermore, it is more preferably 5% by mass or less, and even more preferably 3% by mass or less. When the content is within the above range, it is preferable in that the number-average molecular weight (Mn) of the polyol (Ax) can be appropriately adjusted.

[0045] [catalyst] In the production of polyols (Ax), one or more catalysts may be used as needed. Known compounds can be used as catalysts. Examples of usable catalysts include tertiary amine compounds and organometallic compounds.

[0046] Examples of tertiary amine compounds include triethylamine, triethylenediamine, and 1,8-diazabicyclo(5,4,0)-undecene-7(DBU).

[0047] Examples of organometallic compounds include tin compounds and non-tin compounds. Examples of tin compounds include dibutyltin dichloride, dibutyltin oxide, dibutyltin dibromide, dibutyltin dimaleate, dibutyltin dilaurate (DBTDL), dibutyltin diacetate, dibutyltin sulfide, dioctyltin dilaurate, tributyltin sulfide, tributyltin oxide, tributyltin acetate, triethyltin ethoxide, tributyltin ethoxide, dioctyltin oxide, tributyltin chloride, tributyltin trichloroacetate, tin 2-ethyloctoylate, and tin 2-ethylhexanoate.

[0048] Examples of non-tin compounds include titanium-based compounds such as dibutyltitanium dichloride, tetrabutyltitanate, and butoxytitanium trichloride; lead-based compounds such as lead oleate, lead 2-ethylhexanoate, lead benzoate, and lead naphthenate; iron-based compounds such as iron 2-ethylhexanoate and iron acetylacetonate; cobalt-based compounds such as cobalt benzoate and cobalt 2-ethylhexanoate; zinc-based compounds such as zinc naphthenate and zinc 2-ethylhexanoate; zirconium-based compounds such as zirconium naphthenate; and aluminum-based compounds such as aluminum trisacetylacetonate and aluminum acetate. The type and amount of catalyst added can be appropriately adjusted within a range that allows the reaction to proceed smoothly.

[0049] The amount of catalyst used is preferably 0.0001 to 1.0 parts by mass per 100 parts by mass of the total components of the polyol (Ax). More preferably, the above amount is 0.001 to 0.5 parts by mass, even more preferably 0.005 to 0.3 parts by mass, and still more preferably 0.01 to 0.3 parts by mass.

[0050] When a catalyst is used in the production of polyol (Ax), the catalyst may be deactivated. Examples of deactivators include acetylacetone or phosphoric acid compounds. The deactivator may be used alone or in combination of two or more.

[0051] [solvent] In the production of polyol (Ax), one or more solvents may be used as needed. Examples of usable solvents include ketone solvents such as acetone and methyl ethyl ketone, ester solvents such as ethyl acetate, hydrocarbon solvents such as toluene and xylene, and ether solvents such as diphenyl ether. In one embodiment, the adhesive may contain the solvent used in the production of polyol (Ax).

[0052] (Method for producing polyol (Ax)) The method for producing polyol (Ax) is not particularly limited. Polyol (Ax) can be produced by known polymerization methods such as bulk polymerization and solution polymerization, but bulk polymerization without solvents is more preferred. As a production method, for example, a method of ring-opening polymerization of lactide (a1) and monomer (a2) using the hydroxyl group of diol (a3) ​​as a starting point is preferred because the reaction is simple and high molecular weight can be easily achieved.

[0053] <Diol (Ay)> Diol (Ay) has a molecular weight of less than 1,500. Furthermore, if diol (Ay) is a polymer, its number-average molecular weight (Mn) is less than 1,500. The inclusion of diol (Ay) makes it possible to control the concentration and density of urethane bonds in the urethane resin (X), thereby improving its adhesive properties. In particular, the effect of hydrogen bonding derived from the urethane bonds enhances the interaction between adhesive surfaces, improving adhesion. Because diol (Ay) has two hydroxyl groups in its molecule, it can suppress gelation when reacting with polyisocyanate (B) while preparing a urethane resin (X) with a desired weight-average molecular weight (Mw).

[0054] For diol (Ay), the aforementioned diol (a3) ​​with a molecular weight of less than 200 can be used. Other compounds that can be used include polyester polyols, polyether polyols, polycarbonate polyols, and polybutadiene polyols. Among these, aliphatic diols and aliphatic polyester polyols are particularly preferred because many enzymes capable of degrading them exist in nature.

[0055] Since the aliphatic glycols that can be used as diols (Ay) are biodegradable raw materials, ethylene glycol, 1,3-propanediol, and 1,4-butanediol are preferred.

[0056] Diol (Ay) can also be a commercially available product. For example, Kuraray Polyol P-510 manufactured by Kuraray Co., Ltd. is a polyester polyol having two hydroxyl groups in its molecule, which is a copolymer of 3-methyl-1,5-pentanediol and adipic acid. Another example is Praxel L212AL manufactured by Daicel Corporation. This is a polyester polyol having two hydroxyl groups in its molecule, which is a polymer of a bifunctional hydroxyl group-containing compound and ε-caprolactone. Among these, the polymer of a bifunctional hydroxyl group-containing compound and ε-caprolactone is preferred because it is a biodegradable raw material.

[0057] The molecular weight or number-average molecular weight (Mn) of the diol (Ay) is less than 1,500. More preferably, it is less than 1,400, and even more preferably, less than 1,300. Being within this range makes it possible to effectively introduce urethane bonds into the urethane resin (X), thereby improving the adhesive properties.

[0058] In one embodiment, the content of diol (Ay) is preferably 0.5 to 60% by mass, more preferably 1% by mass or more, based on the total mass of polyol (A). Furthermore, it is more preferably 50% by mass or less. When the content is within the above range, a urethane resin (X) that exhibits excellent adhesive properties can be obtained.

[0059] [Polyisocyanate (B)] Any known compound can be used as polyisocyanate (B). Examples include aromatic polyisocyanates, aliphatic polyisocyanates, and alicyclic polyisocyanates. Polyisocyanate (B) is preferably a bifunctional isocyanate (also called a diisocyanate) having two isocyanate groups in one molecule. By using a diisocyanate, a urethane resin (X) with a desired weight-average molecular weight (Mw) can be prepared while suppressing gelation during reaction with polyol (A).

[0060] Examples of aromatic polyisocyanates include 1,3-phenylenediisocyanate, 4,4'-diphenyldiisocyanate, 1,4-phenylenediisocyanate, 4,4'-diphenylmethanediisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 4,4'-toluidinediisocyanate, 2,4,6-triisocyanatetoluene, 1,3,5-triisocyanatebenzene, and dianisidinedi. Examples include socianates, 4,4'-diphenyl ether diisocyanate, and 4,4',4”-triphenylmethane triisocyanate, ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylene diisocyanate, and 1,3-tetramethylxylylene diisocyanate.

[0061] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0062] Examples of alicyclic polyisocyanates include isophorone diisocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanate methyl)cyclohexane.

[0063] Other polyisocyanates include, for example, the trimethylolpropane adduct, biuret, allophanate, and isocyanurate derivatives of the above-mentioned polyisocyanates.

[0064] As polyisocyanate (B), 4,4'-diphenylmethane diisocyanate and 2,4'-diphenylmethane diisocyanate are preferred. When at least one of these is used, appropriate cohesive force can be imparted through urethane bonding, and sufficient adhesive properties can be easily obtained.

[0065] In the production of urethane resin (X), the ratio (NCO / OH) of the number of moles of isocyanate groups in polyisocyanate (B) to the number of moles of hydroxyl groups in polyol (A) having two hydroxyl groups is 0.6 to 0.98. More preferably, it is 0.7 or higher, and even more preferably, 0.8 or higher. By keeping the NCO / OH value within the above range, a urethane resin (X) with a desired weight-average molecular weight (Mw) can be prepared. If the NCO / OH value is greater than 0.98, gelation may occur during the manufacturing of the urethane resin (X), or isocyanate groups may remain, making it easier for gels or aggregates to form over time. If the NCO / OH value is less than 0.6, the molecular weight of the resulting urethane resin (X) will be small, and sufficient cohesive force may not be obtained.

[0066] The polyisocyanate (B) content is preferably 0.2 to 25% by mass, more preferably 0.5% by mass or more, and even more preferably 0.8% by mass or more, based on the total mass of the urethane resin (X). Furthermore, it is more preferably 20% by mass or less, and even more preferably 15% by mass or less. High adhesive strength and transparency can be obtained by having the polyisocyanate (B) content within the above range.

[0067] In the production of the urethane resin (X), catalysts and solvents may be used as needed. The catalysts and solvents may be the same as those exemplified in the production of the polyol (Ax) described above. In one embodiment, the adhesive may contain the solvent used in the production of the urethane resin (X).

[0068] [Method for manufacturing urethane resin (X)] The method for producing the urethane resin (X) is not particularly limited. The urethane resin (X) can be produced by known polymerization methods such as bulk polymerization and solution polymerization, but bulk polymerization without the use of solvents is more preferred. An adhesive using the urethane resin (X) produced by bulk polymerization can be used as a hot-melt type adhesive, and can also be used as a solvent-type adhesive by dissolving it in a solvent. An example of a production method is a procedure in which one or more polyols (A), one or more polyisocyanates (B), one or more catalysts if necessary, and one or more solvents are used, and these are charged together in a flask.

[0069] When a catalyst is used, the reaction temperature is preferably below 100°C, and more preferably between 80 and 95°C. When no catalyst is used, the temperature is preferably 120°C or higher, and more preferably 140°C or higher.

[0070] <Other ingredients> An adhesive according to one embodiment of the present invention may further contain general curing agents, tackifying resins, and additives in addition to the above components, as long as the properties as an adhesive and biodegradability are not impaired. Examples of usable curing agents include isocyanate curing agents, epoxy curing agents, melamine curing agents, carbodiimide curing agents, oxazoline curing agents, and aziridine curing agents. Examples of usable tackifying resins include rosin resins, terpene resins, alicyclic hydrocarbon resins, aliphatic petroleum resins, and aromatic petroleum resins. Examples of usable additives include ultraviolet absorbers, light stabilizers, leveling agents, antistatic agents, release modifiers, fillers, colorants, anti-aging agents, plasticizers, and surfactants.

[0071] <2> Adhesive sheet Another embodiment of the present invention relates to an adhesive sheet. The adhesive sheet has an adhesive layer formed from the adhesive of the above embodiment on at least one surface of a substrate. That is, the adhesive sheet has a substrate and an adhesive layer made of the adhesive of the above embodiment provided on one surface of the substrate. In one embodiment, a release sheet may be provided on the other surface of the adhesive layer that is not in contact with the substrate to prevent the adhesion of foreign matter. Typically, the adhesive layer is protected by the release sheet until immediately before use.

[0072] The substrate can be any flexible sheet or plate material and can be used without limitation. Examples of substrates include plastics, paper, metal foils, and laminates composed of one or more of these materials. The surface of the substrate in contact with the adhesive layer may be subjected to a simple bonding treatment to improve adhesion. For example, dry treatments such as corona discharge treatment or wet treatments such as anchor coating can be applied.

[0073] In one embodiment, examples of plastic materials constituting the base material include ester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); olefin resins such as polyethylene (PE), polypropylene (PP), and cycloolefin polymer (COP); vinyl resins such as polyvinyl chloride (PVC); amide resins such as nylon 66; and urethane resins (including foams).

[0074] In one embodiment, the resin used as the raw material for the base material is preferably biodegradable, for example, cellulose (CE) resin (Nippon Paper Chemicals Co., Ltd.'s Dissolving Pulp), polyvinyl alcohol resin (Mitsubishi Chemical Corporation's Nichigo G Polymer), polyethylene terephthalate succinate (PETS) resin (Dupon's Apexa 4026 / 6926), polybutylene adipate terephthalate (PBAT) resin (BASF's Ecoflex, Chemdo's TH801T), polybutylene succinate (PBS) resin (PTT MCC Biochem's BioPBS FZ71, FZ91, FZ78), polybutylene succinate adipate (PBSA) resin (PTT MCC Biochem's BioPBS FD92), polylactic acid (PLA) resin (NaturteWorks' 3000-7000 series, Total Corbion's L series, LX series, and D series; poly(3-hydroxybutyrate) (P3HB) resin (PHB Industrial's BIOCYCLE 1000); poly(4-hydroxybutyrate) (P4HB) resin (Tepha Medical Devices' TephaFLEX); poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) resin (Kaneka's AONILEX); poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) resin (TianAn Biopolymer's ENMAT Y1000); poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB-P4HB) resin (CJ Examples include polyhydroxyalkanoate resins such as Yield10 from CheilJedang, polycaprolactone resins (Praxel H1P, H5C, H8C from Daicel Corporation), and cellulose acetate (CA) resins (L-series from Daicel Corporation). The above biodegradable resins may be used individually or in combination of two or more types.

[0075] In addition to the above-mentioned substrates, resins treated with a decomposition solution containing fatty acid metal salts that promote biodegradation can also be used. For example, commercially available products include P-LIFE GREEN 20 (PE resin, decomposition solution containing 20% ​​of the company's SMC2360) and P-LIFE GREEN 20 (PP resin, decomposition solution containing 20% ​​of the company's SMC2360) from P-LIFE Japan Inc.

[0076] Suitable methods for molding the above-mentioned resin into a base material (sheet) include extrusion molding, in which the sheet extruded using a T-die in an extruder is cooled and solidified with a cast roll, and molding using an inflation molding machine.

[0077] The thickness of the substrate may generally be 10 to 300 μm. When using a polyurethane sheet (including foam) as the substrate, the thickness of the substrate (sheet) may generally be 20 to 50,000 μm. Paper can also be used as the substrate. Examples include plain paper, coated paper, and art paper. Metal foil can also be used as the substrate. Examples of metal foil include aluminum foil and copper foil.

[0078] The release sheet may be a release sheet having a known configuration. For example, a release sheet can be used that has been treated with a known release agent, such as a silicone-based release agent, on the surface of a sheet-like material such as plastic or paper.

[0079] One method for manufacturing an adhesive sheet is to apply the adhesive according to the above embodiment to the surface or both sides of a substrate to form a coating layer, and then, if necessary, dry and cure the coating layer to form an adhesive layer. The adhesive may be dissolved in an organic solvent and applied, or it may be applied by thermal melting without a solvent. The heating and drying temperature may generally be 60 to 200°C. The thickness of the adhesive layer may generally be 0.1 to 200 μm.

[0080] Methods of coating by dissolving in an organic solvent include applicators, gravure coaters, die coaters, lip coaters, comma coaters, knife coaters, reverse coaters, and spin coaters, while methods of coating by thermal melting include applicators, gravure coaters, roll coaters, die coaters, and slit coaters.

[0081] Another method, separate from the above, involves applying the adhesive of the above embodiment to the surface of a release sheet to form a coating layer, then drying and curing the coating layer as needed to form an adhesive layer, and finally bonding the substrate to the exposed surface of the adhesive layer. In this method, if a release sheet is bonded to the adhesive layer instead of the substrate, a cast adhesive sheet having a release sheet / adhesive layer / release sheet configuration is obtained.

[0082] The adhesive layer of the adhesive sheet of the present invention preferably has a gel fraction of less than 10% by mass, and more preferably less than 5% by mass. A gel fraction of less than 10% by mass allows for high adhesion between adhesive surfaces. In this invention, the gel fraction is calculated using the following formula (1) after attaching an adhesive sheet of a predetermined size to a SUS mesh (mesh opening: 0.077 mm, wire diameter: 0.05 mm), immersing it in ethyl acetate, extracting it at 50°C for 24 hours, drying it at 100°C for 30 minutes, and then attaching it to the SUS mesh (mesh opening: 0.077 mm, wire diameter: 0.05 mm), extracting it at 50°C for 24 hours, and then drying it at 100°C for 30 minutes. Formula (1) Gel fraction (mass%) = (G2 / G1) × 100 G1: Weight of the adhesive layer before extraction with ethyl acetate G2: Weight of the adhesive layer after extraction with ethyl acetate and drying. [Examples]

[0083] Embodiments of the present invention will be described below with reference to examples. It goes without saying that the embodiments of the present invention are not limited to these examples. In the following, "parts" means "parts by mass," and "%" means "percent mass." Furthermore, the amounts of raw materials (excluding solvents) listed in the examples and tables below are calculated on a non-volatile content basis.

[0084] Furthermore, the Mw, Mn, and Tg values ​​listed below were measured as follows. [Measurement of weight-average molecular weight (Mw) and number-average molecular weight (Mn)] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) were measured by gel permeation chromatography (GPC). The measurement conditions were as follows. Note that both Mw and Mn are polystyrene equivalent values. (Measurement conditions) Equipment: SHIMADZUProminence (manufactured by Shimadzu Corporation) Columns: Three SHODEXLF-804 (manufactured by Showa Denko) connected in series. Detector: Differential refractive index detector Solvent: Tetrahydrofuran (THF) Flow rate: 0.5mL / min Solvent temperature: 40℃ Sample concentration: 0.2% Sample injection volume: 100 μL

[0085] [Glass transition temperature (Tg)] A robotic DSC (Differential Scanning Calorimeter, Seiko Instruments "RDC220") was connected to an "SSC5200 Disk Station" (Seiko Instruments) and used for the measurements. Approximately 5 mg of the sample was placed in an aluminum pan, weighed, and set in the differential scanning calorimeter. An empty aluminum pan of the same type was used as a reference, and the pan was held at 150°C for 5 minutes, after which it was rapidly cooled to -80°C using liquid nitrogen. Subsequently, the temperature was increased at a rate of 10°C / min, and the glass transition temperature (Tg, unit: °C) was determined from the obtained DSC chart.

[0086] The materials listed in Tables 1-4 are as follows: <Polyol (Ax)> [Lactide (a1)] L-lactide (100% biodegradable) D-lactide (100% biodegradable) meso-lactide (100% biodegradable) [Monomer (a2)] ε-Caprolactone (100% biodegradable) δ-Valerolactone (100% biodegradable) [Diol (a3)] EG: Ethylene glycol, molecular weight 62.1 (biodegradability 100%) 1,4-BG: 1,4-butanediol, molecular weight 90.1 (biodegradability 100%) BEPG: 2-Butyl-2-ethylpropanediol, molecular weight 160.3 (biodegradability 0%) [Other ingredients] P-2010: Kuraray Polyol P-2010, Mn 2,000, manufactured by Kuraray Co., Ltd. (biodegradability 0%)

[0087] <Polyol (Ay)> EG: Ethylene glycol, molecular weight 62.1 (biodegradability 100%) L212AL: Praxel L212AL, Mn 1,250, manufactured by Daicel Corporation (100% biodegradable) P-510: Kuraray Polyol P-510, Mn500, manufactured by Kuraray Co., Ltd. (biodegradability 0%)

[0088] <Polyisocyanate (B)> 4,4'-MDI: 4,4'-diphenylmethane diisocyanate (biodegradability 0%) 2,4'-MDI: 2,4'-diphenylmethane diisocyanate (biodegradability 0%) HDI: Hexamethylene diisocyanate (biodegradability 0%)

[0089] The biodegradability of the above materials was determined based on ISO 17556, ISO 14851, ISO 14852, ISO 15985, ISO 13975, ISO 14853, ISO 14855-1, ISO 14855-2, ISO 18830, ISO 19679, ASTM D7081, and ASTM D6691, as well as JIS standards corresponding to the ISO standards. When biodegradability was confirmed, the biodegradability of the raw material was set to 100%.

[0090] [Example of polyol (Ax) production] (Polyol (Ax-1)) In a reaction vessel equipped with a stirrer, nitrogen inlet tube, thermometer, and outlet cooler, 80 parts of L-lactide, 19.4 parts of ε-caprolactone, 0.6 parts of EG, and 0.2 parts of aluminum trisacetylacetonate as a catalyst were charged. These materials were heated to 190°C under atmospheric pressure and a nitrogen atmosphere, and reacted for 10 hours to carry out the polymerization reaction. Subsequently, the remaining unreacted monomers were removed over 1 hour while the pressure was reduced to 10 mmHg to obtain polyol (Ax-1). The number-average molecular weight (Mn) of this polyol (Ax-1) was 10,500.

[0091] (Polyols (Ax-2 to Ax-14, Az-1 to Az-3)) Except for changing the blending amounts (parts by mass) as shown in Table 1, polyols (Ax-2 to Ax-14, Az-1 to Az-3) were obtained in the same manner as the production of polyol (Ax-1). The number-average molecular weight (Mn) of the obtained polyols is shown in Table 1.

[0092] [Table 1]

[0093] [Example of urethane resin (X) manufacturing] (Urethane resin (X-1)) 100 parts of polyol (Ax-1) and 2.2 parts of 4,4'-MDI were charged into a reaction vessel equipped with a stirrer, nitrogen inlet tube, thermometer, and reflux condenser. The reaction was carried out for 5 hours by gradually raising the temperature to 150°C. The reaction was terminated after confirming that the NCO characteristic absorption (2,270 cm-1) on the IR chart had disappeared. The weight-average molecular weight (Mw) of the urethane resin (X-1) obtained in this way was 98,000, and the glass transition temperature (Tg) was 26°C.

[0094] (Urethane resin (X-2~X-15, Z-1~Z-5)) Except for changing the materials and proportions (parts by mass) of urethane resin (X-1) as shown in Table 2, the same procedure as for the production of urethane resin (X-1) was followed to obtain urethane resins (X-2 to X-15, Z-1 to Z-5). The weight-average molecular weight (Mw) and glass transition temperature (Tg) of the obtained urethane resins are shown in Tables 2 to 4.

[0095] In Tables 2 and 3, the value of "NCO / OH" represents the ratio of the number of moles of isocyanate groups in the polyisocyanate (B) to the number of moles of hydroxyl groups in the polyol (A) having two hydroxyl groups when producing urethane resin (X).

[0096] [Examples of adhesive and adhesive sheet manufacturing] (Example 1) 100 parts of urethane resin (X-1) were dissolved in 150 parts of ethyl acetate to obtain an adhesive solution with a non-volatile content of 40%. The adhesive solution prepared earlier was applied to a 50 μm thick polyethylene terephthalate (PET) sheet using an applicator to a dry thickness of 20 μm, and the adhesive layer was dried in a hot air oven at 100°C for 2 minutes to produce an adhesive layer. After drying, it was laminated to a 38 μm thick release sheet (made of polyethylene terephthalate) to obtain an adhesive sheet.

[0097] (Examples 2-14, Comparative Examples 1-5) The materials and proportions (parts by mass) of Example 1 were changed as shown in Tables 2 and 3, and otherwise the procedure was the same as in Example 1 to obtain the adhesives and adhesive sheets of Examples 2 to 14 and Comparative Examples 1 to 5, respectively.

[0098] (Example 15) An adhesive layer was prepared by applying an adhesive made of urethane resin (X-15) heated to 180°C to a polyethylene terephthalate (PET) sheet with a thickness of 20 μm using an applicator. This layer was then laminated onto a 38 μm thick release sheet (made of polyethylene terephthalate) to obtain an adhesive sheet.

[0099] (Example 16) The materials and compounding amounts (parts by mass) of Example 1 were changed as shown in Table 4, and the same procedure as in Example 1 was followed except that the PET with a thickness of 50 μm was changed to a cellophane (CE) film with a thickness of 50 μm as the base material, to obtain the adhesive and the adhesive sheet of Example 16.

[0100] (Example 17) The materials and compounding amounts (parts by mass) of Example 1 were changed as shown in Table 4, and the same procedure as in Example 1 was followed except that the PET with a thickness of 50 μm was changed to a base material made of the following polylactic acid (PLA), to obtain the adhesive and the adhesive sheet of Example 17. [Base material made of PLA] Polylactic acid (LX175 manufactured by Total Corbion) resin was extruded at a temperature of 180 °C using a 30 mmΦ inflation extruder (manufactured by Tokusoku Seimitsu Kogyo Co., Ltd.) to obtain a film base material with a thickness of 50 μm.

[0101] [Gel fraction] The adhesive sheets manufactured using the adhesives obtained in Examples 1 to 17 and Comparative Examples 1 to 5 were cut into pieces with a width of 30 mm and a length of 100 mm. Then, in an environment of 23 °C and a relative humidity of 50% (50%RH), a measurement sample was prepared by peeling off the release sheet from the adhesive sheet and pasting the exposed adhesive layer onto a SUS mesh cut into a size of 40 mm in width and 110 mm in length. This measurement sample was immersed in ethyl acetate, extracted at 50 °C for 24 hours, dried at 100 °C for 30 minutes, and then calculated according to the above-mentioned calculation formula (1).

[0102] [Usage ratio of biodegradable raw materials in the adhesive] Regarding the adhesives obtained in Examples 1 to 17 and Comparative Examples 1 to 5, the usage ratio of biodegradable raw materials was calculated according to the following method. The usage ratio of biodegradable raw materials in the adhesive is the mass ratio of the biodegradable raw materials used in the production of the adhesive to the total mass of the adhesive, and was calculated by rounding to the first decimal place according to the following calculation formula (2). Note that each mass is in terms of non-volatile content. The usage ratio is preferably 60% or more, more preferably 80% or more, and even more preferably 90% or more. Calculation formula (2) The ratio of biodegradable raw materials used in the adhesive = [percentage of biodegradable raw materials used] / [percentage of adhesive by mass] × 100

[0103] [Evaluation of the physical properties of adhesive sheets] For adhesive sheets manufactured using the adhesives obtained in Examples 1-17 and Comparative Examples 1-5, measurement samples were prepared within one hour of coating according to the following method, and various physical properties were evaluated. The results are shown in Tables 2-4.

[0104] (1) SUS adhesive strength The obtained adhesive sheet was cut to a size of 25 mm in width and 150 mm in length. Next, under conditions of 23°C and 50% relative humidity (50% RH), the release sheet was peeled off the adhesive sheet, and the exposed adhesive layer was attached to a stainless steel (SUS) plate. A measurement sample was prepared by passing it back and forth once using a 5 kg roll. After storing this measurement sample under conditions of 23°C and 50% RH for 24 hours, the peel strength was measured using a tensile testing machine (Orientec Co., Ltd. "Tensilon") under conditions of a peel speed of 300 mm / min and a peel angle of 180°. The evaluation was performed based on the following criteria. Evaluation Criteria AA: Peel strength of 20N / 25mm or higher (Excellent) A: Peel strength of 17N / 25mm or more and less than 20N / 25mm (good) B: Peel strength of 13N / 25mm or more and less than 17N / 25mm (usable) C: Peel strength less than 13N / 25mm (Not usable)

[0105] (2) Self-adhesive surface adhesive strength Two adhesive sheets were prepared. Under conditions of 23°C and 50% RH, the release sheet was peeled off one adhesive sheet, and the exposed adhesive surface was laminated to the exposed adhesive surface of the other adhesive sheet. The laminated adhesive sheets were then cut to a size of 25 mm in width and 150 mm in length, and a measurement sample was prepared by passing it back and forth once on a 5 kg roll. After storing this measurement sample under conditions of 23°C and 50% RH for 24 hours, the T-shaped peel strength between the laminated adhesive sheets was measured using a tensile testing machine (Orientec Co., Ltd. "Tensilon") at a peeling speed of 300 mm / min. The evaluation was performed based on the following criteria. Evaluation Criteria AA: Peel strength of 20N / 25mm or higher (Excellent) A: Peel strength of 17N / 25mm or more and less than 20N / 25mm (good) B: Peel strength of 13N / 25mm or more and less than 17N / 25mm (usable) C: Peel strength less than 13N / 25mm (Not usable)

[0106] (3) Holding power The obtained adhesive sheet was cut to a size of 25 mm in width and 150 mm in length. The release sheet was peeled off the cut adhesive sheet, and the exposed adhesive layer was attached to a 25 mm wide and 25 mm long portion of the lower end of a 30 mm wide and 150 mm long stainless steel plate. A measurement sample was prepared by rolling it back and forth once with a 5 kg roller. After storing this measurement sample in a 40°C environment for 20 minutes, a 1 kg load was applied to the lower end of the adhesive sheet and left for 70,000 seconds to measure the holding force. The evaluation was performed by measuring the length by which the upper end of the adhesive surface of the adhesive sheet shifted downward from its original position. Evaluation Criteria A: The misalignment is less than 2 mm (good) B: The misalignment is between 2mm and 10mm (usable). C: The misalignment is 10mm or more (unusable).

[0107] (4) Transparency The transparency of the adhesive layer of the obtained adhesive sheets was visually inspected. The evaluation was based on the following criteria. Evaluation Criteria A: The adhesive layer is transparent (good). B: The adhesive layer is slightly cloudy (usable). C: The adhesive layer has turned white (unusable).

[0108] [Table 2]

[0109] [Table 3]

[0110] [Table 4]

[0111] As shown in Tables 2-4, the adhesive of the present invention (example) contains a specific urethane resin (X), resulting in a high proportion of biodegradable raw materials used in the adhesive. It was confirmed that it satisfies adhesive properties without the need for a curing agent and also exhibits excellent transparency.

[0112] On the other hand, it was difficult to obtain the desired adhesive properties with the adhesives of the comparative examples. In Comparative Example 1, the NCO / OH value was outside the range specified in the present invention, and in Comparative Example 2, the glass transition temperature (Tg) was outside the range specified in the present invention. Furthermore, in Comparative Examples 3, 4, and 5, none of lactide (a1), monomer (a2), or diol (a3) ​​were used when preparing the polyol (Ax). From the above, it can be seen that the adhesive of the present invention can achieve the desired adhesive properties and transparency by using a specific urethane resin (X).

Claims

1. An adhesive comprising a urethane resin (X) which is a reaction product of a polyol (A) having two hydroxyl groups and a polyisocyanate (B), The polyol (A) having two hydroxyl groups includes a polyol (Ax) having two hydroxyl groups with a number average molecular weight of 2,000 to 40,000, which is a copolymer of a mixture containing lactide (a1), a monomer having lactone units (a2), and a diol (a3) ​​having a molecular weight of less than 200, and the ratio of the number of moles of isocyanate groups in polyisocyanate (B) to the number of moles of hydroxyl groups in polyol (A) having two hydroxyl groups (NCO / OH ratio) is 0.6 to 0.

98. An adhesive in which the glass transition temperature of the urethane resin (X) is -1°C to 30°C.

2. The adhesive according to claim 1, wherein the gel fraction is less than 10% by mass.

3. The adhesive according to claim 1, wherein the content of lactide (a1) is 25 to 90% by mass, based on the total mass of the mixture constituting the polyol (Ax).

4. The adhesive according to claim 1, wherein the polyol (A) having the two hydroxyl groups further comprises a diol (Ay) having a molecular weight or number average molecular weight of less than 1,500.

5. An adhesive sheet having a base material and an adhesive layer formed from an adhesive according to any one of claims 1 to 4, provided on at least one surface of the base material.

6. The adhesive sheet according to claim 5, wherein the base material is biodegradable.

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