Manufacturing method of laminate

Abstract

To provide a method for manufacturing a laminate which can continuously perform a second lamination step without aging after a first lamination step, and prevents delamination and telescope.SOLUTION: The above problem is solved by a method for manufacturing a laminate which includes: a first step of coating a first substrate with a first solventless type adhesive which contains polyol (A1) and polyisocyanate (B1) and has viscosity at 60°C of 50-6,000 mPa s, then pressure-bonding the first substrate to an intermediate substrate, and obtaining an intermediate laminate; and a second step of coating the intermediate substrate with a second solventless type adhesive which contains polyol (A2) and polyisocyanate (B2) and has viscosity at 40°C of 50-5,000 mPa s, then pressure-bonding the intermediate substrate to a second substrate, and obtaining a laminate, wherein a difference in viscosity at 40°C between the first solventless type adhesive and the second solventless type adhesive is 2,000 mPa s or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a laminate suitable for flexible packaging materials used for packaging foods, medicines, cosmetics, detergents, miscellaneous goods, etc. [Background technology]

[0002] Two-component curing urethane adhesives used in flexible packaging materials for foods, pharmaceuticals, cosmetics, detergents, miscellaneous goods, etc. have traditionally been available in solvent-based and solventless types, with solventless adhesives being preferred from the standpoint of environmental considerations such as eliminating the use of organic solvents and improving work efficiency by eliminating the need for a drying process. Solvent-free adhesives do not contain solvents and must have low viscosity in order to exhibit coatability, and typically contain low molecular weight polyols and polyisocyanates.

[0003] On the other hand, the structure of flexible packaging materials varies depending on the contents and the desired physical properties. In addition to two-layer structures in which two substrates are bonded together with an adhesive, multi-layer structures in which multiple substrates are bonded together with an adhesive are also commonly used. However, when a solventless adhesive is used to produce a composite film with a multilayer structure (e.g., a three-layer structure) by successively performing the first and second lamination processes, the laminated film formed in the first lamination process can peel off (hereinafter also referred to as delamination) when the adhesive is applied in the second lamination process, resulting in a defect in which air gets mixed in. Furthermore, in the second lamination process, slight misalignment occurs in the laminated film formed in the first lamination process, and this misalignment accumulates, resulting in a defect known as telescoping, in which the end of the roll becomes deformed into a bamboo shoot shape when the film is wound up in the second lamination process. This is presumably because, as mentioned above, the molecular weights of the polyol and polyisocyanate contained in the solventless adhesive are low, resulting in a low initial cohesive strength of the adhesive layer that is formed. Therefore, when manufacturing a three-layer laminate film using a solvent-free adhesive, it was necessary to carry out aging for a certain period of time or more between the first lamination process and the second lamination process to improve the cohesive strength of the adhesive layer formed in the first lamination process.

[0004] One possible way to solve this problem is to increase the curing speed of the adhesive to shorten the aging time. However, since solventless adhesives are generally produced by retaining a mixed solution of polyol and polyisocyanate on a roll and applying it to a substrate using a roll coater, if the curing speed is increased by adding a catalyst or the like to shorten the aging time, there are problems in that the pot life is significantly shortened and the adhesive thickens on the roll, causing a deterioration in appearance. To address the above-mentioned problems, for example, Patent Document 1 discloses a technique in which a polyol and a polyisocyanate are applied to separate substrates and then bonded together. By applying the polyol and the polyisocyanate separately, the curing speed can be freely adjusted using additives and the like without having to consider the pot life issue. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 082683 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method described in Patent Document 1 cannot be applied to existing coating machines, requiring modification or the introduction of new equipment. Furthermore, while the method described in Patent Document 1 shortens the aging time, it does not solve the aforementioned problems of the laminated film formed in the first lamination step peeling off and air being mixed in when applying the adhesive in the second lamination step (also known as delamination), and the occurrence of telescoping, in which the end of the roll is deformed into a bamboo shoot shape when winding in the second lamination step. Therefore, it is currently difficult to produce a three-layer laminate by consecutively performing the first lamination step and the second lamination step. Therefore, an object of the present invention is to provide a method for manufacturing a laminate that can perform a second lamination step consecutively after the first lamination step without aging, and that is free from delamination and telescoping. [Means for solving the problem]

[0007] As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by the following embodiments, and have thus completed the present invention.

[0008] An embodiment of the present invention is a method for producing a laminate having a first substrate layer, a first adhesive layer, an intermediate substrate layer, a second adhesive layer, and a second substrate layer in this order, the method comprising: a first step of applying a first solvent-free adhesive containing a polyol (A1) and a polyisocyanate (B1) and having a viscosity of 50 to 6,000 mPa·s at 60°C onto the first substrate; and then pressing the first solvent-free adhesive onto the first substrate to obtain an intermediate laminate having the first substrate layer, the first adhesive layer, and the intermediate substrate layer in this order; and a second step of applying a second solvent-free adhesive containing a polyol (A2) and a polyisocyanate (B2) and having a viscosity of 50 to 5,000 mPa·s at 40°C to the intermediate substrate of the intermediate laminate obtained in the first step 1, and then pressing the applied second solvent-free adhesive to a second substrate to obtain a laminate, wherein the difference in viscosity at 40°C between the first solvent-free adhesive and the second solvent-free adhesive is 2,000 mPa·s or more.

[0009] Another embodiment of the present invention relates to a method for producing the above-mentioned laminate, wherein the difference in viscosity between the first solvent-free adhesive and the second solvent-free adhesive at 60°C is 1,000 mPa·s or more.

[0010] Another embodiment of the present invention relates to the method for producing the laminate, wherein the polyol (A1) and the polyol (A2) are each independently a polyester polyol or a polyether polyol.

[0011] Another embodiment of the present invention relates to the method for producing the laminate, wherein the polyisocyanate (B1) and the polyisocyanate (B2) are each independently an aromatic isocyanate compound, an araliphatic isocyanate compound, an aliphatic isocyanate compound, an alicyclic polyisocyanate compound, or a modified product thereof.

[0012] Another embodiment of the present invention relates to the method for producing the laminate, wherein the first adhesive layer has a thickness of 2.5 μm or less.

[0013] Another embodiment of the present invention relates to a method for producing the above laminate, wherein when the roll coating temperature when applying the first solventless adhesive is T1°C, T1 is in the range of 50 to 90°C.

[0014] Another embodiment of the present invention relates to the method for producing the laminate, wherein, when the roll coating temperature when applying the second solventless adhesive is T2°C, T2 is in the range of 30 to 70°C. [Effects of the Invention]

[0015] According to the present invention, it is possible to carry out the second lamination step consecutively after the first lamination step without carrying out aging, and it is possible to provide a method for producing a laminate without delamination or telescoping. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention relates to a method for producing a laminate having a first substrate layer, a first adhesive layer, an intermediate substrate layer, a second adhesive layer, and a second substrate layer in this order, the method comprising: applying a first solventless adhesive containing a polyol (A1) and a polyisocyanate (B1) and having a viscosity of 50 to 6,000 mPa·s at 60°C onto the first substrate; and then pressing the first solventless adhesive onto the intermediate substrate to obtain an intermediate laminate having the first substrate layer, the first adhesive layer, and the intermediate substrate layer in this order. The method comprises a first step, and a second step of applying a second solvent-free adhesive containing a polyol (A2) and a polyisocyanate (B2) and having a viscosity of 50 to 5,000 mPa·s at 40°C to the intermediate substrate of the intermediate laminate obtained in the first step 1, followed by pressing the applied adhesive to a second substrate to obtain a laminate, wherein the difference in viscosity at 40°C between the first solvent-free adhesive and the second solvent-free adhesive is 2,000 mPa·s or more.

[0017] The present invention can solve the above problem by providing a first solvent-free adhesive having a viscosity of 50 to 6,000 mPa·s at 60°C, a second solvent-free adhesive having a viscosity of 50 to 5,000 mPa·s at 40°C, and a viscosity difference between the first and second solvent-free adhesives of 2,000 mPa·s or more.

[0018] First, the first solvent-free adhesive applied in the first step has a high viscosity of 50 to 6,000 mPa·s at 60°C, so it has a certain initial cohesive strength even in an uncured state. Therefore, if the second step is carried out without aging, it is possible to prevent the formed laminate film from peeling off and air from getting mixed in. On the other hand, if the second solvent-free adhesive is also as viscous and tacky as the first, when the second adhesive is applied using a roll coater and pressed onto the intermediate laminate, the intermediate laminate film will be momentarily removed from the coating roll, the initial cohesive force of the first adhesive layer will be lost, and the first substrate will peel away from the intermediate substrate, inducing air intrusion. Therefore, by making the viscosity of the second solvent-free adhesive 50 to 5,000 mPa·s at 40°C and by making the viscosity difference from the first solvent-free adhesive 2,000 mPa·s or more, it is possible to reduce tack on the coating roll and prevent the film from being removed. In addition, the initial cohesive force of the first adhesive is overcome by the tack of the second solvent-free adhesive on the roll, and the film is momentarily taken up onto the coating roll, causing slight misalignment in the intermediate laminate, even if it does not result in air being mixed in. If winding continues with this slight misalignment, telescoping problems will gradually occur. However, by making the difference in viscosity between the first and second solvent-free adhesives 2,000 mPa·s or more, slight misalignment in the intermediate laminate can be prevented, and telescoping can be suppressed. The present invention will be described in detail below.

[0019] <First and second solvent-free adhesives> The first solventless adhesive used in the present invention contains a polyol (A1) and a polyisocyanate (B1). It is important that the viscosity at 60°C is 50 to 6,000 mPa·s. Having a viscosity at 60°C within this range ensures that the adhesive has a certain initial cohesive strength even in an uncured state, and when the second step is carried out without aging, it is possible to prevent the first substrate and intermediate substrate in the formed laminated film from peeling off and air from being mixed in. The second solventless adhesive used in the present invention contains a polyol (A2) and a polyisocyanate (B2). Furthermore, it is important that the viscosity at 40°C is 50 to 5,000 mPa·s. Having a viscosity at 40°C within this range reduces tackiness on the coating roll, and when the second adhesive is applied by roll coating and pressure-bonded to the intermediate laminate, the intermediate laminate film is not momentarily removed from the coating roll. As a result, peeling between the first substrate and the intermediate substrate and air intrusion can be prevented.

[0020] The viscosity of the solventless adhesive in this specification refers to the viscosity measured within 10 minutes after mixing the polyol and polyisocyanate and heating the adhesive to 60°C or 40°C. The viscosity can be measured using a cone and plate viscometer in accordance with JIS K 5600-2-3:2014. The viscosity of the first solventless adhesive at 60°C is preferably in the range of 500 to 6,000 mPa·s, more preferably 1,000 to 5,500 mPa·s, and even more preferably 1,500 to 5,000 mPa·s. The viscosity of the second solventless adhesive at 40°C is preferably in the range of 300 to 3,000 mPa·s, and more preferably 500 to 2,000 mPa·s.

[0021] As mentioned above, it is important that the first solventless adhesive has a viscosity at 40°C that is at least 2,000 mPa·s higher than that of the second solventless adhesive. The difference in viscosity at 40°C is preferably 2,000 mPa·s or more and 25,000 mPa·s or less, and more preferably 4,500 to 20,000 mPa·s. The difference in viscosity between the first solvent-free adhesive at 60°C and the second solvent-free adhesive at 60°C is preferably 1,000 mPa·s or more. The difference in viscosity at 60°C is preferably 1,000 mPa·s or more and 6,000 mPa·s or less, more preferably 1,000 to 5,000 mPa·s. Such a difference in viscosity at 40°C and 60°C prevents film removal and prevents the first substrate from peeling off from the intermediate substrate, resulting in air getting mixed in. It also prevents slight misalignment of the intermediate laminate and suppresses telescoping. The viscosity of the first solventless adhesive at 40°C is preferably in the range of 4,000 to 25,000 mPa·s, and more preferably 6,000 to 22,000 mPa·s. The viscosity of the second solventless adhesive at 60°C is preferably in the range of 100 to 1000 mPa·s, and more preferably 100 to 600 mPa·s.

[0022] [Polyols (A1), (A2)] The polyols (A1) and (A2) may be compounds having two or more hydroxyl groups, and each may be independently selected from known polyols, such as polyester polyols, polycarbonate polyols, polycaprolactone polyols, polyvalerolactone polyols, polyether polyols, polyolefin polyols, polyurethane polyols, acrylic polyols, silicone polyols, castor oil-based polyols, fluorine-based polyols, and polyhydroxyalkanes. Furthermore, examples of the polyol that can be used include glycols such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-5-pentanediol, 1,6-hexanediol, neopentyl glycol, methylpentane glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, bishydroxyethoxybenzene, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, and triethylene glycol; polyalkylene glycols having a number average molecular weight of 200 to 3,000; trifunctional or tetrafunctional aliphatic alcohols such as glycerin, trimethylolpropane, and pentaerythritol; and polyols in which the above-mentioned glycols or polyols are added to the above-mentioned trifunctional or tetrafunctional aliphatic alcohols. The polyols may be used singly or in combination of two or more. From the viewpoints of leveling ability and adhesive performance to a substrate, the polyols (A1) and (A2) are preferably polyester polyols or polyether polyols.

[0023] (polyester polyol) Examples of polyester polyols include polyester polyols obtained by reacting a carboxyl group component with a hydroxyl group component; and polyester polyols obtained by ring-opening polymerization of lactones such as polycaprolactone, polyvalerolactone, and poly(β-methyl-γ-valerolactone). Examples of the carboxyl group component include dibasic acids such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, phthalic anhydride, adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride, and itaconic anhydride, or dialkyl esters thereof, or mixtures thereof. Examples of the hydroxyl group component include diols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, butylene glycol, neopentyl glycol, dineopentyl glycol, trimethylolpropane, glycerin, 1,6-hexanediol, 1,4-butanediol, 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolheptane, 1,9-nonanediol, polyoxyethylene glycol, polyoxypropylene glycol, polytetramethylene ether glycol, polyether polyol, polycarbonate polyol, polyolefin polyol, acrylic polyol, polyurethane polyol, and mixtures thereof. The above carboxyl group components and hydroxyl group components may be used singly or in combination of two or more.

[0024] The polyester polyol preferably has a number average molecular weight in the range of 100 to 5,000, more preferably 500 to 4,000. When the number average molecular weight is in the above range, fluidity is achieved at room temperature or by heating, which is preferable. The polyester polyol preferably has an acid value in the range of 0 to 5.0 mgKOH / g, more preferably 0 to 3.0 mgKOH / g, which is preferable because a rapid increase in viscosity after mixing the two liquids can be suppressed if the acid value is in the above range. The polyester polyol preferably has a hydroxyl group concentration in the range of 10 to 300 mgKOH / g, more preferably 30 to 200 mgKOH / g, since this range allows the number average molecular weight to be adjusted to a range suitable for use in solventless adhesives.

[0025] (Polyether polyol) Polyether polyols are compounds that contain two or more hydroxyl groups and two or more ether bonds in the molecule, including polyalkylene glycols such as polyethylene glycol, polytrimethylene glycol, polypropylene glycol, polytetramethylene glycol, and polybutylene glycol; polyethylene glycol / polypropylene glycol block copolymers; and propylene oxide / ethylene oxide random polyethers. Alternatively, an addition polymer obtained by addition polymerization of an oxirane compound such as ethylene oxide, propylene oxide, butylene oxide, or tetrahydrofuran to a low molecular weight polyol such as water, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, or sucrose may be used as the polyether polyol. Examples of the addition polymer include propylene glycol propylene oxide adducts, glycerin propylene oxide adducts, sorbitol-based propylene oxide adducts, and sucrose-based propylene oxide adducts.

[0026] These polyols may be acid-modified polyols in which some of the hydroxyl groups in the polyol have been acid-modified, or may be polyols in which carboxyl groups have been introduced by reacting with an acid anhydride, or polyols in which urethane bonds have been introduced by reacting with a diisocyanate. Examples of the acid anhydrides include pyromellitic anhydride, mellitic anhydride, trimellitic anhydride, and trimellitic ester anhydrides. Examples of the trimellitic ester anhydrides include ethylene glycol bisanhydrotrimellitate and propylene glycol bisanhydrotrimellitate. Examples of the diisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, hexamethylene diisocyanate, and hydrogenated diphenylmethane diisocyanate.

[0027] The viscosity of the polyols (A1) and (A2) is not particularly limited, as long as it is adjusted so that the viscosity of the first and second solventless adhesives obtained by mixing them with the polyisocyanates (B1) and (B2) described below falls within a predetermined range. To achieve the above ranges, the viscosity of polyol (A1) at 60°C may be in the range of 100 to 5,000 mPa·s or 500 to 4,000 mPa·s, and the viscosity of polyol (A2) at 40°C may be in the range of 50 to 3,000 mPa·s or 500 to 2,000 mPa·s.

[0028] [Polyisocyanates (B1), (B2)] The polyisocyanates (B1) and (B2) react with the polyols (A1) and (A2) to cure the adhesive. Examples of such polyisocyanates include, independently, aromatic isocyanate compounds, araliphatic isocyanate compounds, aliphatic isocyanate compounds, alicyclic polyisocyanate compounds, and modified products thereof. These polyisocyanates may be used singly or in combination of two or more.

[0029] Examples of the aromatic isocyanate compound include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, or a mixture thereof, 4,4'-toluene diisocyanate, dianisidine diisocyanate, 4,4'-diphenyl ether diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, or a mixture thereof, ω,ω'-diisocyanate, aromatic diisocyanates such as 1,4-diethylbenzene, 1,3-bis(1-isocyanato-1-methylethyl)benzene, or 1,4-bis(1-isocyanato-1-methylethyl)benzene or mixtures thereof; aromatic triisocyanates such as triphenylmethane-4,4',4'-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; aromatic polyisocyanates such as 4,4'-diphenyldimethylmethane-2,2'-5,5'-tetraisocyanate and polymethylene polyphenyl polyisocyanate; or modified products thereof.

[0030] Examples of the araliphatic isocyanate compound include araliphatic diisocyanates such as 1,3- or 1,4-xylylene diisocyanate or a mixture thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene or a mixture thereof, and modified products thereof. Examples of the aliphatic isocyanate compound include aliphatic diisocyanates such as trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanatomethyl caproate, lysine diisocyanate, and dimer acid diisocyanate; and modified products thereof. Examples of alicyclic isocyanate compounds include alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, isophorone diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methyl 2,4-cyclohexane diisocyanate, methyl 2,6-cyclohexane diisocyanate, 1,4-bis(isocyanatemethyl)cyclohexane, 1,3-bis(isocyanatemethyl)cyclohexane, and norbornene diisocyanate; or modified products thereof.

[0031] Examples of the modified isocyanate compound include allophanate-type modified compounds, isocyanurate-type modified compounds, biuret-type modified compounds, and adduct-type modified compounds, as well as reaction products having an isocyanate group and a urethane bond, which are obtained by reacting the isocyanate compound with a polyol under conditions of an excess of isocyanate groups. The polyol that forms the isocyanate-modified product is not particularly limited and can be selected from known polyols, such as low-molecular-weight polyols with a molecular weight of less than 200, such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 3,3'-dimethylolpropane, cyclohexanedimethanol, diethylene glycol, triethylene glycol, dipropylene glycol, glycerol, trimethylolpropane, pentaerythritol, and sorbitol; and polyols such as polypropylene glycol, polyester polyols, polyetherester polyols, polyesteramide polyols, polycaprolactone polyols, polyvalerolactone polyols, acrylic polyols, polycarbonate polyols, polyhydroxyalkanes, castor oil, and polyurethane polyols. These known polyols may be used alone or in combination of two or more. The molar ratio of isocyanate groups to hydroxyl groups (number of moles of NCO / number of moles of OH) during the reaction of an isocyanate compound with a known polyol is preferably 2 or more.

[0032] The viscosities of the polyisocyanates (B1) and (B2) are not particularly limited, as long as they are adjusted so that the viscosities of the first and second solventless adhesives fall within a predetermined range. To achieve the above ranges, the viscosity of the polyisocyanate (B1) at 60°C may be in the range of 100 to 5,000 mPa·s or 500 to 4,000 mPa·s, and the viscosity of the polyisocyanate (B2) at 40°C may be in the range of 100 to 5,000 mPa·s or 500 to 4,000 mPa·s.

[0033] The solventless adhesive of the present invention is obtained by mixing the polyol and polyisocyanate described above. The blending ratio of the polyol and polyisocyanate (polyol / polyisocyanate) is generally within the range of 10 / 100 to 100 / 10 by mass ratio.

[0034] [Other ingredients] The first solvent-free adhesive and the second solvent-free adhesive may contain components other than the polyol and the polyisocyanate to satisfy various physical properties required for the package. Such other components may be blended with either the polyol or the polyisocyanate, or may be added when blending the polyol and the polyisocyanate. These other components may be used alone or in combination of two or more.

[0035] (Silane coupling agent) The first and second solventless adhesives may contain a silane coupling agent to improve adhesive strength to the substrate. Examples of the silane coupling agent include trialkoxysilanes having a vinyl group, such as vinyltriethoxysilane and vinyltriethoxysilane; trialkoxysilanes having an amino group, such as 3-aminopropyltriethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; and trialkoxysilanes having a glycidyl group, such as 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane. The content of the silane coupling agent is preferably 0.1 to 5 mass %, more preferably 0.2 to 3 mass %, based on the polyol (A1) or (A2). By setting it within this range, the adhesive strength to metal can be improved.

[0036] (phosphoric acid or phosphoric acid derivatives) The first and second solventless adhesives may contain phosphoric acid or a phosphoric acid derivative to improve adhesive strength to the substrate. The phosphoric acid may be any phosphoric acid having at least one free oxygen acid, such as hypophosphorous acid, phosphorous acid, orthophosphoric acid, or hypophosphoric acid; or condensed phosphoric acids such as metaphosphoric acid, pyrophosphoric acid, tripolyphosphoric acid, polyphosphoric acid, or ultraphosphoric acid. Phosphoric acid derivatives include, for example, phosphoric acids obtained by partially esterifying the above-mentioned phosphoric acids with alcohols while leaving at least one free oxygen acid. Examples of such alcohols include aliphatic alcohols such as methanol, ethanol, ethylene glycol, and glycerin; and aromatic alcohols such as phenol, xylenol, hydroquinone, catechol, and phloroglucinol. The content of phosphoric acid or a derivative thereof is preferably 0.001 to 10 mass %, more preferably 0.005 to 5 mass %, and particularly preferably 0.01 to 1 mass %, based on the mass of the first and second solventless adhesives.

[0037] (Leveling agent or defoaming agent) The first and second solventless adhesives may further contain a leveling agent or antifoaming agent to improve the appearance of the laminate. Examples of leveling agents include polyether-modified polydimethylsiloxane, polyester-modified polydimethylsiloxane, aralkyl-modified polymethylalkylsiloxane, polyester-modified hydroxyl-containing polydimethylsiloxane, polyetherester-modified hydroxyl-containing polydimethylsiloxane, acrylic copolymer, methacrylic copolymer, polyether-modified polymethylalkylsiloxane, acrylic acid alkyl ester copolymer, methacrylic acid alkyl ester copolymer, and lecithin. Examples of antifoaming agents include silicone resin, silicone solution, and copolymers of alkyl vinyl ether, acrylic acid alkyl ester, and methacrylic acid alkyl ester.

[0038] (Other additives) The first and second solventless adhesives may contain various additives within the scope of the present invention, such as inorganic fillers such as silica, alumina, mica, talc, aluminum flakes, and glass flakes, layered inorganic compounds, stabilizers (antioxidants, heat stabilizers, UV absorbers, hydrolysis inhibitors, etc.), rust inhibitors, thickeners, plasticizers, antistatic agents, lubricants, antiblocking agents, colorants, fillers, and nucleating agents.

[0039] <Production of laminate> The method for producing a laminate of the present invention includes the following steps. First step: A step of applying the first solvent-free adhesive described above onto a first substrate, and then pressing it with an intermediate substrate to obtain an intermediate laminate having a first substrate layer, a first adhesive layer, and an intermediate substrate layer in that order. Second step: A step of applying the second solventless adhesive described above to the intermediate substrate of the intermediate laminate obtained in the first step 1, and then pressing it with a second substrate to obtain a laminate.

[0040] The method for applying the first or second solvent-free adhesive layer and pressing it onto another substrate is not particularly limited and can be appropriately selected from conventionally known lamination methods. However, since solvent-free adhesives have high viscosity, roll coating is generally the preferred application method. The thickness of the first adhesive layer and the second adhesive layer is not particularly limited, but each independently is preferably in the range of 0.5 to 3.5 μm, more preferably 1.0 to 2.5 μm. In particular, by setting the thickness of the first adhesive layer in the range of 1.0 to 2.5 μm, delamination and telescoping can be further suppressed.

[0041] The first and second steps may be carried out continuously in-line, or the second step may be carried out after a winding step. In either case, the manufacturing method of the present invention allows a multilayer laminate to be obtained without carrying out an aging step between the first and second steps.

[0042] Furthermore, if the roll coating temperature when applying the first solvent-free adhesive is T1° C. and the roll coating temperature when applying the second solvent-free adhesive is T2° C., then temperature T1 is preferably 50 to 90° C., more preferably 50 to 80° C., and even more preferably 60 to 80° C. By setting temperature T1 within the above range, the leveling properties of the adhesive are excellent and the cohesive force of the first adhesive is maintained, resulting in better telescoping prevention. The temperature T2 is preferably 30 to 70° C., more preferably 35 to 65° C., and even more preferably 40 to 60° C. By setting the temperature T2 within the above range, the leveling properties of the adhesive are excellent and the cohesive force of the second adhesive is maintained, resulting in better suppression of telescoping. T1 and T2 can be adjusted appropriately depending on the viscosity of the adhesive, the amount of application, etc., but are usually used such that T1>T2.

[0043] [First substrate] The first substrate may be a conventional plastic film commonly used for packaging materials. Examples of such plastic films include polyester resin films such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polylactic acid (PLA); polyolefin resin films such as polyethylene (PE) and polypropylene (PP); polystyrene resin films; polyamide resin films such as nylon (NY) 6 and poly-p-xylylene adipamide (MXD6 nylon); polycarbonate resin films; polyacrylonitrile resin films; polyimide resin films; and composites or mixtures thereof (e.g., nylon 6 / MXD6 / nylon 6, nylon 6 / ethylene-vinyl alcohol copolymer / nylon 6). The thickness of the plastic film is preferably 5 to 50 μm. The first substrate may be a laminate of multiple such plastic films, or may be a vapor-deposited film having a vapor-deposited layer of a metal oxide such as silica or alumina, or may have a printed layer on the substrate.

[0044] The printed layer is a layer on which any desired printed pattern such as letters, numbers, pictures, figures, symbols, or designs is formed for decoration, indication of contents, expiration date, manufacturer, seller, or other indication or aesthetic purposes, and includes solid printed layers. The printed layer is generally formed using printing ink containing a colorant such as a pigment or dye. The method for forming the printed layer is not particularly limited, and examples include gravure coating, flexo coating, roll coating, bar coating, die coating, curtain coating, spin coating, and inkjet coating. The thickness of the printed layer is preferably 0.1 to 10 μm.

[0045] [Intermediate substrate] As the intermediate substrate, in addition to the plastic films listed above as the first substrate, metallized films, metal foils, etc. can be used. Examples of metallized films include aluminum-deposited films, and examples of metal foils include aluminum foils.

[0046] [Second substrate] As the second substrate, in addition to the substrates exemplified above as the first substrate and intermediate substrate, a sealant substrate can also be used. Examples of sealant base materials include polyethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE), acid-modified polyethylene, solid polypropylene (CPP), acid-modified polypropylene, copolymerized polypropylene, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid ester copolymer, ethylene-(meth)acrylic acid copolymer, and ionomer. The thickness of the sealant substrate is preferably 10 to 150 μm, taking into consideration processability into packaging materials, heat sealing properties, and the like. The first substrate, intermediate substrate, and second substrate may be a single layer or a laminate in which multiple layers are laminated. [Example]

[0047] The present invention will be specifically described below with reference to examples and comparative examples. In the examples and comparative examples, "parts" and "%" mean "parts by mass" and "% by mass" unless otherwise specified.

[0048] [Method for measuring acid value (AV)] Approximately 1 g of sample was precisely weighed into a stoppered Erlenmeyer flask and dissolved in 100 mL of a toluene / ethanol (volume ratio: toluene / ethanol = 2 / 1). Phenolphthalein test solution was added as an indicator and allowed to stand for 30 seconds. The solution was then titrated with 0.1 N alcoholic potassium hydroxide solution until it turned a pale pink color. The acid value was calculated using the following formula (1) (unit: mgKOH / g). (Equation 1) Acid value (mgKOH / g) = [{(ba) × F × 28.25} / S] S: Amount of sample collected (g) a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (mL) b: Amount of 0.1N alcoholic potassium hydroxide solution consumed in the blank experiment (mL) F: Potency of 0.1N alcoholic potassium hydroxide solution

[0049] [Method for measuring hydroxyl value (OHV)] Approximately 1 g of sample was precisely weighed into a stoppered Erlenmeyer flask and dissolved in 100 mL of a toluene / ethanol (volume ratio: toluene / ethanol = 2 / 1). Exactly 5 mL of an acetylating agent (25 g of acetic anhydride dissolved in pyridine to a volume of 100 mL) was then added and stirred for approximately 1 hour. Phenolphthalein test solution was added as an indicator and allowed to stand for 30 seconds. The solution was then titrated with 0.1 N alcoholic potassium hydroxide solution until it turned a pale pink color. The hydroxyl value was calculated using the following formula (2). The hydroxyl value was the value for the resin in its dry state (unit: mgKOH / g). (Equation 2) Hydroxyl value (mgKOH / g) = [{(ba) × F × 28.25} / S] / (non-volatile content / 100) + D S: Amount of sample collected (g) a: Amount of 0.1N alcoholic potassium hydroxide solution consumed (mL) b: Amount of 0.1N alcoholic potassium hydroxide solution consumed in the blank experiment (mL) F: Potency of 0.1N alcoholic potassium hydroxide solution D: Acid value (mgKOH / g)

[0050] [Method for measuring number average molecular weight (Mn)] The number average molecular weight (Mn) was measured using a GPC (gel permeation chromatography) "Shodex GPC System-21" manufactured by Showa Denko Co., Ltd. GPC is a liquid chromatography that separates and quantifies substances dissolved in a solvent based on differences in their molecular size. Tetrahydrofuran was used as the solvent, and the molecular weight was determined in polystyrene equivalent.

[0051] [Method for measuring NCO content (mass%)] Approximately 1 g of sample was weighed into a 200 mL Erlenmeyer flask and dissolved in 10 mL of 0.5 N di-n-butylamine toluene solution and 10 mL of toluene. Next, phenolphthalein test solution was added as an indicator, and after 30 seconds, the solution was titrated with 0.25 N hydrochloric acid until it turned pale pink. The NCO content (mass%) was calculated using the following formula (3). (Formula 3):NCO(mass%)={(ba)×4.202×F×0.25} / S Where S: sample amount (g) a: Consumption of 0.25N hydrochloric acid solution (ml) b: Amount of 0.25N hydrochloric acid solution consumed in the blank experiment (ml) F: Potency of 0.25N hydrochloric acid solution

[0052] [Method for measuring ICI viscosity (mPa·s)] The viscosity at each temperature was measured using a cone-plate viscometer "CV-1S" manufactured by Toa Kogyo Co., Ltd. The displayed value when the value stabilized was taken as the ICI viscosity.

[0053] <Synthesis of polyester polyol> (Synthesis Example 1) Polyester polyol-1 A reaction vessel equipped with a stirrer, temperature control system, reflux condenser, dropping tank, and nitrogen gas inlet tube was charged with 212 parts of isophthalic acid, 346 parts of adipic acid, 74 parts of ethylene glycol, and 368 parts of neopentyl glycol, and the mixture was heated to 235°C with stirring under a nitrogen stream. The reaction was continued until the acid value reached 10.0 mgKOH / g or less, after which the reaction temperature was increased to 200°C, and the pressure inside the reaction vessel was gradually reduced to 1.3 kPa or less to produce polyester polyol-1 with an acid value of 0.4 mgKOH / g, a hydroxyl value of 127 mgKOH / g, and a number average molecular weight of approximately 890.

[0054] (Synthesis Examples 2 to 6) Polyester Polyols 2 to 6 Polyester polyols-2 to 6 were obtained in the same manner as in Synthesis Example 1, except that the compositions were changed as shown in Table 1.

[0055] [Table 1]

[0056] The abbreviations in Table 1 are as follows: IPA: Isophthalic acid ADA: Adipic acid BA:benzoic acid EG: Ethylene glycol DEG: Diethylene glycol NPG: Neopentyl glycol PG: 1,2-propanediol

[0057] <Production of Polyol (A1)> (A1-1, A1-2) As the polyol (A1-1) and the polyol (A1-2), polyester polyol-1 and polyester polyol-2 obtained in Synthesis Examples 1 and 2 were used, respectively.

[0058] (A1-3) 90 parts of polyester polyol-3 obtained in Synthesis Example 3 and 4 parts of tolylene diisocyanate were charged into a reaction vessel and heated at 80 to 90°C for 5 hours while stirring under a nitrogen gas flow to carry out a urethane reaction, and the disappearance of the isocyanate groups was confirmed by IR. Next, 6 parts of diethylene glycol was charged and stirred until the solution became homogeneous, yielding polyol (A1-3), which was a mixture of polyester urethane polyol and DEG.

[0059] (A1-4) 55 parts of polyester polyol-4 obtained in Synthesis Example 4, 35 parts of a triol having a number average molecular weight of approximately 400, in which polypropylene glycol was added to glycerin, and 10 parts of DEG were mixed and stirred until the solution became homogeneous, thereby obtaining polyol (A1-4), which is a mixture of polyester polyol, triol, and DEG.

[0060] The polyols obtained are shown in Table 2 together with their viscosity measurements.

[0061] [Table 2]

[0062] The abbreviations in Table 2 are as follows: PPG-400-3 functional group: A triol with a number average molecular weight of approximately 400, obtained by adding polypropylene glycol to glycerin. TDI: Tolylene diisocyanate

[0063] <Production of Polyisocyanate (B1)> (B1-1) 25 parts of hexamethylene diisocyanate biuret, 50 parts of hexamethylene diisocyanate nurate, and 25 parts of isophorone diisocyanate nurate were charged into a reaction vessel, heated to 50°C to 60°C under a nitrogen gas flow, dissolved, and stirred to obtain a polyisocyanate mixture (B1-1) with an isocyanate group content of 20.4%.

[0064] (B1-2) A polyisocyanate mixture (B1-2) having an isocyanate group content of 25.1% was obtained in the same manner as (B1-1), except that the composition was changed to that shown in Table 3.

[0065] (B1-3) 11 parts of polypropylene glycol having a number average molecular weight of approximately 400, 53 parts of polypropylene glycol having a number average molecular weight of approximately 2,000, and 35 parts of 4,4'-diphenylmethane diisocyanate were charged into a reaction vessel, and the mixture was heated at 80-90°C for 3 hours while stirring under a nitrogen gas flow to carry out a urethane reaction, yielding a polyisocyanate reaction product (B1-3) having an isocyanate group content of 7.9%.

[0066] (B1-4) A reaction vessel was charged with 37 parts of PPG-2000, 7 parts of the polyester polyol-5 obtained in Synthesis Example 5, and 27 parts of tolylene diisocyanate, and the mixture was heated at 80 to 90°C for 3 hours while stirring under a nitrogen gas stream to carry out a urethane reaction, yielding a polyurethane polyisocyanate. Next, unreacted tolylene diisocyanate was removed using a thin-film distillation apparatus, and finally, 29 parts of a mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate was added, and the mixture was stirred at 70°C or below until the solution became homogeneous, yielding a polyisocyanate reaction product (B1-4) with an isocyanate group content of 10.9%.

[0067] The polyisocyanates obtained are shown in Table 3 together with their viscosity measurements.

[0068] [Table 3]

[0069] The abbreviations in Table 3 are as follows: PPG-400: Polypropylene glycol with a number average molecular weight of approximately 400 PPG-2000: Polypropylene glycol with a number average molecular weight of approximately 2,000 4,4'-MDI: 4,4'-diphenylmethane diisocyanate TDI: Tolylene diisocyanate HDI biuret: Biuret of hexamethylene diisocyanate HDI Nurate: Nurate form of hexamethylene diisocyanate IPDI nurate: nurate form of isophorone diisocyanate IPDI: Isophorone diisocyanate monomer Liquid MDI: A mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate

[0070] <Production of the first solvent-free adhesive> First solventless adhesives 1-1 to 1-5 were obtained by mixing polyol (A1) and polyisocyanate (B1) in the amounts shown in Table 4. The viscosity of the resulting adhesives was measured immediately after mixing, and the results are shown in Table 4.

[0071] [Table 4]

[0072] <Production of Polyol (A2)> (A2-1) 30 parts of polyester polyol-3 obtained in Synthesis Example 3, 50 parts of polyester polyol-6 obtained in Synthesis Example 6, 15 parts of PPG-400, and 5 parts of DEG were blended and stirred until the solution became homogeneous, yielding polyol (A2-1), which was a mixture of polyester polyol, polypropylene glycol, and DEG.

[0073] (A2-2, A2-4) Polyols (A2-2) and (A2-4) were obtained in the same manner as (A2-1), except that the compositions were changed as shown in Table 5.

[0074] (A2-3) 35 parts of PPG-400, 19 parts of PPG-2000, 33 parts of PPG-400-3 functional, and 13 parts of 4,4'-MDI were charged into a reaction vessel, and the mixture was heated at 80-90°C for 4 hours while stirring under a nitrogen gas flow to carry out a urethane reaction. Disappearance of the isocyanate groups was confirmed by IR, yielding polyol (A2-3), a polyether urethane polyol.

[0075] The polyols obtained are shown in Table 5 along with their viscosity measurements.

[0076] [Table 5]

[0077] The abbreviations in Table 5 are as follows: PPG-400: Polypropylene glycol with a number average molecular weight of approximately 400 PPG-2000: Polypropylene glycol with a number average molecular weight of approximately 2,000 PPG-400-3 functional group: A triol with a number average molecular weight of approximately 400, obtained by adding polypropylene glycol to glycerin. DEG: Diethylene glycol 4,4'-MDI: 4,4'-diphenylmethane diisocyanate

[0078] <Production of Polyisocyanate (B2)> (B2-1) A reaction vessel was charged with 5 parts of PPG-400, 28 parts of PPG-2000, 4 parts of PPG-400-trifunctional copolymer, and 25 parts of 4,4'-MDI. The mixture was heated at 80-90°C for 3 hours with stirring under a nitrogen gas flow to carry out a urethane reaction, yielding a polyurethane polyisocyanate. Next, 13 parts of HDI biuret, 13 parts of liquid MDI, and 12 parts of a mixture of polymeric diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate were added, and the mixture was stirred at 70°C or below until the solution became homogeneous, yielding polyisocyanate (B2-1) with an isocyanate group content of 16.5%.

[0079] (B2-2, B2-4) A polyisocyanate (B2-2) having an isocyanate group content of 21.5% and a polyisocyanate (B2-4) having an isocyanate group content of 10.7% were obtained in the same manner as (B2-1), except that the compositions were changed to those shown in Table 6.

[0080] (B2-3, B2-5) As shown in Table 6, (B1-1) was used for (B2-3), and (B1-4) was used for (B2-5).

[0081] The polyisocyanates obtained are shown in Table 6 together with their viscosity measurements.

[0082] [Table 6]

[0083] The abbreviations in Table 6 are as follows: PPG-400: Polypropylene glycol with a number average molecular weight of approximately 400 PPG-2000: Polypropylene glycol with a number average molecular weight of approximately 2,000 PPG-400-3 functional group: A triol with a number average molecular weight of approximately 400, obtained by adding polypropylene glycol to glycerin. 4,4'-MDI: 4,4'-diphenylmethane diisocyanate HDI biuret: Biuret of hexamethylene diisocyanate Liquid MDI: A mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate Crude MDI: A mixture of polymeric diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate

[0084] <Production of the second solvent-free adhesive> Second solventless adhesives 2-1 to 2-5 were obtained by mixing polyol (A2) and polyisocyanate (B2) in the amounts shown in Table 7. The viscosity of the obtained adhesives was measured immediately after mixing, and the results are shown in Table 7.

[0085] [Table 7]

[0086] <Preparation of laminate> [Example 1] Using a solventless adhesive laminator with the coating roll temperature set to 60°C, adhesive 1-1 was applied at a rate of 1.5 g / m onto a 12 μm thick, 600 mm wide polyethylene terephthalate film ("Ester Film E5102" manufactured by Toyobo Co., Ltd.). 2 The adhesive was applied at a coating speed of 150 m / min. Thereafter, the adhesive-coated surface was bonded to an aluminum foil having a thickness of 7 μm and a width of 600 mm (first step). Next, using a solventless adhesive laminator with the coating roll temperature set to 40°C, adhesive 2-1 was applied to the aluminum foil of the obtained laminate in an amount of 2.0 g / m 2 The adhesive was applied at a coating speed of 150 m / min. Thereafter, a 70 μm thick, 600 mm wide unstretched polypropylene film (Toray Industries, Inc., "Torayfan ZK207") was bonded to the adhesive-coated surface (second process). Approximately 4000 m of the laminate was produced by the above steps. The difference in viscosity between adhesive 1-1 and adhesive 2-1 at 40°C was 5,230 mPa·s, and the difference in viscosity at 60°C was 1,250 mPa·s.

[0087] [Example 2~ 8、10~ 17. Comparative Example 1] A laminate was obtained in the same manner as in Example 1, except that the adhesive, substrate, and coating conditions were changed as shown in Table 8. A 15 μm-thick nylon film ("Emblem ONBC" manufactured by Unitika Ltd.) was used as the intermediate substrate in Examples 11 to 15 and the first substrate in Example 17. A 100 μm-thick linear low-density polyethylene film ("TUX-FCD" manufactured by Mitsui Chemicals Tohcello Inc.) was used as the second substrate in Examples 15 to 17. A 12 μm-thick aluminum-deposited PET ("Diallaster H27" manufactured by Reiko Co., Ltd., VMPET) was used as the intermediate substrate in Example 17.

[0088] <Evaluation of laminate> obtained The following evaluations were carried out on the phenomena occurring during processing in step 2. The results are shown in Tables 8 and 9.

[0089] Delamination between the first substrate and the intermediate substrate The second process was divided into four steps: the first step, in which the coating speed was increased to 150 m / min; the second step, from 150 m / min until the coating volume stabilized; the third step, in which the laminate continued to form after the coating volume stabilized; and the fourth step, in which the processing stop button was pressed to decelerate. At each step, the film of the intermediate laminate formed in the first step was removed, and it was checked whether delamination had occurred between the first substrate and the intermediate substrate. Delamination results in the incorporation of air. If the film of the intermediate laminate was removed to the extent that delamination occurred between the first substrate and the intermediate substrate, abnormal noise was generated in the coating area, and the presence or absence of abnormal noise was used to determine whether delamination had occurred. Evaluation was based on the following criteria. A: No delamination occurs in any process (good) B: Delamination does not occur in the second and third steps, but delamination occurs in the first and fourth steps (usable) C: Delamination does not occur in the third step, but occurs in the first, second, and fourth steps. Or, delamination occurs in all steps (unusable).

[0090] [Telescope] In the second step, the stage at which telescoping occurred in the wound roll of the approximately 4000 m laminate was visually observed, and the results were evaluated according to the following criteria. A: No telescope (good) B: No telescope below 2000m, telescope occurs above 2000m (usable) C: Telescope occurs below 2000m (unusable)

[0091] [Table 8]

[0092] According to the evaluation results, by setting the difference in viscosity between the first adhesive and the second adhesive at 40°C to 2,000 mPa·s or more, delamination between the first substrate and the intermediate laminate and telescoping due to misalignment of the intermediate laminate did not occur, and a good three-layer laminate could be produced. In particular, as in Examples 1 to 4, even when an adhesive containing an aliphatic polyisocyanate with a slow curing rate was used as the first solvent-free adhesive, by increasing the difference in viscosity with the second solvent-free adhesive, it was possible to produce a good three-layer laminate without performing aging between the first and second steps, demonstrating the usefulness of this manufacturing method. On the other hand, the comparative example 1 is However, because the difference in viscosity between the first adhesive and the second adhesive at 40°C was small, less than 2,000 mPa·s, it was not possible to solve the delamination between the first substrate and the intermediate laminate, or the telescoping due to misalignment of the intermediate laminate.

Claims

1. A method for producing a laminate including, in this order, a first substrate layer, a first adhesive layer, an intermediate substrate layer, a second adhesive layer, and a second substrate layer, the method comprising: a first step of applying a first solventless adhesive containing a polyol (A1) and a polyisocyanate (B1) and having a viscosity of 50 to 6,000 mPa s at 60°C onto the first substrate, and then pressing the first solventless adhesive onto an intermediate substrate to obtain an intermediate laminate having a first substrate layer, a first adhesive layer, and an intermediate substrate layer in this order; and a second step of applying a second solventless adhesive containing a polyol (A2) and a polyisocyanate (B2) and having a viscosity of 50 to 5,000 mPa s at 40°C onto the intermediate substrate of the intermediate laminate obtained in the first step, and then pressing the applied adhesive onto a second substrate to obtain a laminate; When the roll coating temperature when applying the first solventless adhesive is T1°C, T1 is in the range of 50 to 90°C, When the roll coating temperature when applying the second solventless adhesive is T2°C, T2 is in the range of 30 to 70°C, A method for manufacturing a laminate, characterized in that the difference in viscosity between the first solvent-free adhesive and the second solvent-free adhesive at 40°C is 2,000 mPa·s or more, and the viscosity of the first solvent-free adhesive at 40°C is higher than the viscosity of the second solvent-free adhesive at 40°C.

2. 2. The method for producing a laminate according to claim 1, wherein the difference in viscosity at 60°C between the first solvent-free adhesive and the second solvent-free adhesive is 1,000 mPa·s or more.

3. The method for producing a laminate according to claim 1 or 2, wherein the polyol (A1) and the polyol (A2) are each independently a polyester polyol or a polyether polyol.

4. The method for producing a laminate according to any one of claims 1 to 3, wherein the polyisocyanate (B1) and the polyisocyanate (B2) are each independently an aromatic isocyanate compound, an araliphatic isocyanate compound, an aliphatic isocyanate compound, an alicyclic polyisocyanate compound, or a modified product thereof.

5. The method for producing a laminate according to any one of claims 1 to 4, wherein the first adhesive layer has a thickness of 2.5 µm or less.

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