Method for producing multilayer film, and multilayer film

Abstract

Provided are: a method for producing a multilayer film in which a multilayer film having three or more layers including an aluminum foil as an intermediate layer can be laminated using a solvent-free adhesive; and a multilayer film. A method for producing a multilayer film in which three or more films are bonded together, the method comprising: a first lamination step in which a first intermediate is obtained by applying a solvent-free adhesive on a first film and laminating a second film while overlapping the first film with the second film; and a second lamination step in which a solvent-free adhesive is applied to the first intermediate and a third film is laminated while the third film is superimposed on the first intermediate, the first film and the second film being configured from an aluminum foil, said film being superimposed on the third film with the second adhesive applied layer interposed therebetween.

Description

Technical Field

[0001] The present invention relates to a method for producing a multilayer film in which a multilayer film of three or more layers is obtained by laminating raw material films using a solvent-free adhesive, and the multilayer film obtained thereby. Background Art

[0002] Bag packaging containers used for food packaging, medical product packaging, cosmetic packaging, etc., and soft packaging containers used for cup lids have conventionally been composed of a multilayer film in which a plurality of raw material films such as resin films and metal foils are laminated.

[0003] In such packaging containers, when resin films of different types having different characteristics are laminated, such as a combination of a nylon film and a polyethylene film, the adhesion between the two is insufficient, and therefore, the two are usually affixed using a lamination adhesive.

[0004] As such an adhesive, from the viewpoint of reducing the load on the global environment, it is desirable to use a solvent-free adhesive that does not contain an organic solvent and can be applied by heating the adhesive to reduce the viscosity. For example, as a conventional multilayer film using a solvent-free adhesive, a multilayer film having an adhesive layer formed of a solvent-free adhesive is known, wherein the solvent-free adhesive is composed of a main agent composed of a polyester polyol and a curing agent composed of an aliphatic diisocyanate compound and an alicyclic diisocyanate, and the viscosity of the solvent-free adhesive at 70° C. is 300 to 900 mPa·s (see Patent Document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent No. 5397584 Summary of the invention

[0008] Problems to be solved by the invention

[0009] On the other hand, in order to use a laminating adhesive to bond three or more raw material films together, usually, a coating device having a pair of coating rollers opposed to each other is used, the adhesive is coated on the first film passing between the coating rollers, and the second film is laminated while overlapping it with the adhesive coating layer formed by the adhesive to obtain an intermediate, the intermediate is temporarily wound up using a winding roller, and again in the same manner, the third film is laminated while overlapping it with the intermediate having the solidified adhesive layer.

[0010] However, when a solvent-free adhesive is used as the adhesive, it has been found that the raw material film of the third layer may not be laminated according to the above-mentioned production method.

[0011] Specifically, when the first film or the second film is aluminum foil, after the adhesive of the intermediate wound by the winding roll is solidified, it is sometimes impossible to unwind it into a mesh again. Even if it is forcibly stretched and unwound, it will result in unevenness and cracks on the resin film and aluminum foil.

[0012] The reason for this phenomenon is presumed to be as follows: the aluminum foil inevitably has tiny holes called pinholes, and the solvent-free adhesive is wound up by the winding roller in a low viscosity state, unlike the case of using the laminating adhesive containing an organic solvent used in the usual dry lamination. Therefore, while the prescribed film is attached to the surface side of the aluminum foil, the solvent-free adhesive seeps out to the opposite side through the pinholes of the aluminum foil, causing the surface of the film that is in contact with the back side of the aluminum foil due to the winding to also adhere, resulting in adhesion. In the case of the usual dry lamination, since the drying process is performed after the attachment and before the winding, the organic solvent volatilizes, and the viscosity of the adhesive is increased to a certain extent, and even if the aluminum foil is used in the first film or the second film, there will be no problem of seepage to the opposite side.

[0013] The present invention has been made based on the above circumstances, and an object of the present invention is to provide a method for producing a multilayer film and a multilayer film capable of laminating three or more multilayer films including an aluminum foil using a solvent-free adhesive.

[0014] Solutions for solving problems

[0015] The method for producing a multilayer film of the present invention is characterized in that it is a method for producing a multilayer film formed by laminating three or more films with an adhesive layer interposed therebetween, and the following steps are performed: a first lamination step, in a first coating device having a pair of coating rollers opposed to each other, an adhesive is applied to a first film passing between the coating rollers, and a second film is laminated while being overlapped with a first adhesive coating layer formed by the adhesive, to obtain a first intermediate; a second lamination step, in a second coating device having a pair of coating rollers opposed to each other, an adhesive is applied to the first intermediate, and a second film is laminated while being overlapped with a first adhesive coating layer formed by the adhesive, to obtain a first intermediate. The three films are laminated while overlapping each other via a second adhesive coating layer formed by the adhesive; then the following steps are performed: a aging step to solidify the first adhesive coating layer and the second adhesive coating layer to obtain adhesive layers respectively, wherein the first adhesive coating layer is formed of a solvent-free adhesive, and when provided to the second lamination step, the solvent-free adhesive of the first adhesive coating layer constituting the first intermediate has fluidity, and among the first film and the second film, the film overlapping the third film via the second adhesive coating layer is composed of aluminum foil.

[0016] Furthermore, the multilayer film of the present invention is characterized by being produced by the above-mentioned production method.

[0017] Effects of the Invention

[0018] According to the method for producing a multilayer film of the present invention, even when the film overlapping the third film with the second adhesive coating layer interposed therebetween is composed of aluminum foil and the first adhesive coating layer to be bonded is formed of a solvent-free adhesive, the aging step of solidifying the first adhesive coating layer to obtain the adhesive layer is performed after the second lamination step, that is, the first intermediate is supplied to the second lamination step without solidifying the first adhesive coating layer. Therefore, even when the solvent-free adhesive constituting the first adhesive coating layer is still fluid when supplied to the second lamination step, since the second adhesive coating layer is formed on the back side of the aluminum foil without any contact and opposition on the back side of the aluminum foil, and then the third film is overlapped, there is no undesirable adhesion (adhesion) to other films caused by the solvent-free adhesive passing through the pinholes, and as a result, a multilayer film of three or more layers including aluminum foil can be produced by lamination using a solvent-free adhesive. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an explanatory cross-sectional view showing the structure of an example of the multilayer film of the present invention.

[0020] Figure 2 This is an explanatory diagram showing the structure of an example of a laminator for producing the multilayer film of the present invention. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present invention will be described in detail.

[0022] 〔Multilayer film〕

[0023] The method for manufacturing a multilayer film of the present invention is a method for manufacturing a multilayer film of three or more layers by laminating three or more raw material films. Figure 1 As shown, the multilayer film 40 is composed of three films, namely, an outer layer film 42 made of resin, an inner layer film 43 made of resin, and an intermediate layer film 41 made of aluminum foil disposed between the inner layer film 43 and the outer layer film 42. The outer layer film 42 and the intermediate layer film 41 are bonded together by a first adhesive layer 46 formed by a solvent-free adhesive applied by a first coating device 10 of a laminator 1 described later, and the inner layer film 43 and the intermediate layer film 41 are bonded together by a second adhesive layer 47 formed by a solvent-free adhesive applied by a second coating device 20 of the laminator 1. The multilayer film 40 has no traces (pinhole traces) of the solvent-free adhesive on the outer surfaces of the outer layer film 42 and the inner layer film 43.

[0024] As a material constituting the outer layer film 42, polyamide-based resin or polyester-based resin is preferably used.

[0025] As the polyamide-based resin, for example, nylon 6, nylon 8, nylon 6,6, nylon 6 / 6,6 copolymer, nylon 6,10, poly(meta-xylylene adipamide) (MXD6), nylon 11, nylon 12, and the like can be used.

[0026] As polyester resins, for example, polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) can be used. In addition, copolyesters containing other polyester units can also be used within the range that does not damage the properties of these resins. Among the copolymer components used to form such copolyesters, as dicarboxylic acid components, the following can be used: isophthalic acid, p-β-oxyethoxybenzoic acid, 2,6-naphthalene dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfoisophthalate, adipic acid, sebacic acid or their alkyl ester derivatives. In addition, as diol components, the following can be used: propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, ethylene oxide adducts of bisphenol A, diethylene glycol, triethylene glycol, etc. These compounds can be used alone or in combination of two or more and used as copolymer components.

[0027] The thickness of the outer layer film 42 can be appropriately selected according to the type of resin constituting the outer layer film 42, the purpose of the multilayer film, etc. For example, when the outer layer film 42 is composed of nylon, the thickness is preferably 10 to 30 μm, and when the outer layer film 42 is composed of polyethylene terephthalate (PET), the thickness is preferably 6 to 28 μm.

[0028] Furthermore, it is preferable that the surface of the outer layer film 42 that is in contact with the adjacent layer is subjected to a surface modification treatment such as a corona treatment to improve the adhesion with the adjacent layer.

[0029] As a material constituting the inner layer film 43, a resin having excellent heat sealability is preferably used in order to form a sachet packaging bag or a heat seal lid. Examples of such a resin include polyolefin resins such as polyethylene (PE) and polypropylene (PP).

[0030] The thickness of the inner layer film 43 is not particularly limited, but is preferably 50 to 200 μm when the inner layer film 43 is made of polyethylene, and preferably 30 to 150 μm when the inner layer film 43 is made of polypropylene.

[0031] In addition, as the inner layer film 43, it is preferable to use a non-stretched film such as CPP.

[0032] The intermediate layer film 41 is made of aluminum foil, and its thickness is not particularly limited, but is preferably 5 to 100 μm.

[0033] There may be a tiny hole (pinhole) in the intermediate layer film 41. The pinhole is preferably 0.5 mm or less in diameter, for example.

[0034] The adhesive layers 46 and 47 are formed of a specific solvent-free adhesive described in detail below. The solvent-free adhesive is a two-component reaction-curing adhesive composed of a main agent and a curing agent.

[0035] The thickness of the adhesive layers 46 and 47 is preferably 0.5 to 3 μm.

[0036] [Method for producing multilayer film]

[0037] like Figure 2 As shown, a method for manufacturing a multilayer film according to an embodiment of the present invention is to use a laminator 1 to convey three long films W1, W2, and W3 at high speed while laminating them with solvent-free adhesives to manufacture the multilayer film. After the first lamination process and the second lamination process are performed in sequence, an aging process is performed: in the first lamination process, a solvent-free adhesive pre-mixed with two liquid components (a main agent and a curing agent) is coated on the first film W1 by a first coating device 10, and then the second film W2 is laminated with the first adhesive coating layer formed by the solvent-free adhesive. The first intermediate Wm1 is obtained by merging and laminating. In the second lamination process, the first intermediate Wm1 obtained by the first lamination process is transported to the second coating device 20 without being wound by a winding roller, and a solvent-free adhesive mixed with two liquid components (a main agent and a curing agent) in advance is applied by the second coating device 20, and then the third film W3 is overlapped and laminated through the second adhesive coating layer formed by the solvent-free adhesive in sequence; in the aging process, the first adhesive coating layer and the second adhesive coating layer are cured to obtain adhesive layers respectively.

[0038] In the formation Figure 1 In the case of the multilayer film 40 shown, a resin film such as PET is used as the first film W1 to become the outer layer film 42, an aluminum foil is used as the second film W2 to become the intermediate layer film 41, and a resin film such as CPP is used as the third film W3 to become the inner layer film 43.

[0039] The laminator 1 is a so-called tandem laminator, which includes: a first coating device 10, which coats a solvent-free adhesive on a first film W1; a take-up roller 31, which supplies the first film W1 to be coated with a solvent-free adhesive to the first coating device 10; a laminating section 32, which has a pair of pressure rollers 32a, 32b, which laminates a second film W2 on the first film W1 formed with an adhesive coating layer sent out from the first coating device 10; a take-up roller 33, which supplies the second film W2; a laminating section 34, which has a pair of pressure rollers 34a, 34b, which laminates a third film W3 on a first intermediate body Wm1 formed with a second adhesive coating layer sent out from the second coating device 20; a take-up roller 35, which supplies the third film W3; and a winding roller 36, which winds up the second intermediate body Wm2 which is a joint of the first film W1, the second film W2 and the third film W3.

[0040] The first coating device 10 includes: a coating unit 11, which sequentially transfers the mixed solvent-free adhesive onto one side of the conveyed first film W1 by using a plurality of rollers, and applies the adhesive while spreading it relatively thinly; and a supply unit 15, which supplies the solvent-free adhesive to the coating unit 11. The second coating device 20 includes: a coating unit 11, which sequentially transfers the mixed solvent-free adhesive onto the other side (the side opposite to the first film W1) of the second film W2 constituting the first intermediate body Wm1 by using a plurality of rollers, and applies the adhesive while spreading it relatively thinly; and a supply unit 15, which supplies the solvent-free adhesive to the coating unit 11. The first coating device 10 and the second coating device 20 basically have the same structure, so only the first coating device 10 will be described below. Figure 2 In the figure, the same structures as those of the first coating device 10 in the second coating device 20 are denoted by the same reference numerals.

[0041] The coating unit 11 has a plurality of (five in the example shown) rollers 11a to 11e that are supported to be rotatable and are arranged in series with their axes parallel to each other. Specifically, the coating unit 11 has: a pair of coating rollers 11a and 11b that face each other; and transfer rollers 11c, 11d, and 11e that transfer the solventless adhesive sequentially while supplying it to one of the pair of coating rollers 11a and 11b (coating roller 11b), two transfer rollers 11d and 11e located at the supply start side of the solventless adhesive are arranged adjacent to each other in the horizontal direction, and a storage portion 11f is formed on the upper side between the transfer rollers 11d and 11e, and the storage portion 11f mixes a main agent and a curing agent to prepare a solventless adhesive and temporarily stores the solventless adhesive. The storage portion 11f is formed by partitioning a space having a substantially V-shaped cross section between the transfer rollers 11d and 11e by a pair of weir plates (not shown) provided apart from each other in the longitudinal direction of the transfer rollers 11d and 11e.

[0042] The supply unit 15 includes a base tank containing a base, a curing agent tank containing a curing agent, and an adhesive supply portion for supplying the base and the curing agent, and may further include a mixer for stirring the solventless adhesive stored in the storage portion 11f.

[0043] In the laminator 1, the first film W1 is conveyed from the unwinding roller 31 to between a pair of coating rollers 11a and 11b of the first coating device 10 at a specified speed. On the other hand, in the supply unit 15, in the main agent tank and the curing agent tank, the main agent and the curing agent are heated to a specified temperature and melted. The main agent and the curing agent after heating and melting are supplied to the storage part 11f in a specified amount from the adhesive supply part. The solvent-free adhesive is continuously supplied from the supply unit 15 to the storage part 11f in such a manner that the liquid level of the storage part 11f is kept constant. Then, in the coating unit 11, the solvent-free adhesive is sequentially transferred to the coating roller 11b via the transfer rollers 11d and 11c, and is applied from the coating roller 11b to the surface of the first film W1 passing between the pair of coating rollers 11a and 11b, thereby forming a first adhesive coating layer.

[0044] Next, the first film W1 formed with the first adhesive coating layer is sent to the laminating section 32. On the other hand, the second film W2 is supplied from the unwinding roller 33 to the laminating section 32, and in the laminating section 32, the first film W1 and the second film W2 are overlapped in such a manner that the second film W2 contacts the first adhesive coating layer on the surface of the first film W1, and are pressed and bonded by a pair of pressure rollers 32a and 32b, thereby obtaining a first intermediate body Wm1 joined with a pair of films W1 and W2 (first laminating step).

[0045] When the first intermediate body Wm1 is not wound up, the first intermediate body Wm1 is provided to the second laminating step in a state where the solvent-free adhesive constituting the first adhesive coating layer of the first intermediate body Wm1 still has fluidity.

[0046] In the second lamination process, the first intermediate body Wm1 is conveyed at a predetermined speed between a pair of coating rollers 11a and 11b of the second coating device 20. On the other hand, in the second coating device 20, similarly to the first coating device 10 in the first lamination process, the second adhesive coating layer is formed by coating the surface of the second film W2 in the first intermediate body Wm1 passing between the pair of coating rollers 11a and 11b of the second coating device 20. Next, the first intermediate body Wm1 formed with the second adhesive coating layer is conveyed to the lamination unit 34. On the other hand, the third film W3 is supplied from the unwinding roller 35 to the laminating section 34. In the laminating section 34, the first intermediate Wm1 and the third film W3 are overlapped in such a way that the third film W3 contacts the second adhesive coating layer on the surface of the second film W2 of the first intermediate Wm1, and are pressed and bonded by a pair of pressure rollers 34a and 34b, thereby obtaining a second intermediate Wm2 in which the first film W1, the second film W2 and the third film W3 are sequentially stacked and bonded (second laminating process). The second intermediate Wm2 is wound up by the winding roller 36 and directly subjected to an aging treatment by being left to stand at room temperature or under heating, thereby curing the first adhesive coating layer and the second adhesive coating layer to form adhesive layers, respectively. Thus, a multilayer film 40 is obtained in which an intermediate film 41 (second film W2) composed of aluminum foil is bonded between a resin outer film 42 (first film W1) and a resin inner film 43 (third film W3) via a first adhesive layer 46 and a second adhesive layer 47 formed of a solvent-free adhesive, respectively. At the time of winding up on the winding roll 36, the solvent-free adhesive of the first adhesive coating layer and the second adhesive coating layer constituting the second intermediate body Wm2 still has fluidity, but since the first film W1 (resin outer film 42) and the third film W3 (resin inner film 43) do not have micropores through which the solvent-free adhesive passes, no adhesion occurs even if the second intermediate body Wm2 is subjected to an aging treatment in a wound state.

[0047] As described above, the heating temperature of the main agent and the curing agent, and the coating temperature of the solvent-free adhesive on the first film W1 and the first intermediate body Wm1 are both within the range of, for example, 40° C. to 80° C.

[0048] Furthermore, the temperature of the press rollers 32a and 32b in the laminating section 32 and the temperature of the press rollers 34a and 34b in the laminating section 34 are, for example, 30°C to 80°C.

[0049] Furthermore, the feeding speed of each of the films W1 , W2 , and W3 , that is, the coating speed of the solvent-free adhesive is preferably 100 to 200 m / min.

[0050] The coating amount of the solvent-free adhesive is preferably 0.5 to 3.0 g / m 2 , more preferably 1.2 to 2.1 g / m 2If the amount of the solvent-free adhesive applied is too small, sufficient adhesion cannot be obtained. On the other hand, if the amount of the solvent-free adhesive applied is too large, layer crossover may occur when the multilayer film is wound up, resulting in quality defects such as tunneling.

[0051] The temperature of the aging treatment of the second intermediate body Wm2 taken up by the take-up roll 36 is, for example, 30° C. to 70° C., and the treatment time is, for example, 48 hours to 96 hours.

[0052] In the laminator 1 , the time from the start of mixing of the main agent and the curing agent in the first coating device 10 to coating on the first film W1 is, for example, 0.5 to 20 minutes.

[0053] In the laminator 1, other coating conditions can be set appropriately.

[0054] 〔Solvent-free adhesive〕

[0055] The solvent-free adhesive used in the method for producing the multilayer film of the present invention contains a main agent formed of a polyester resin and a curing agent formed of an aliphatic isocyanate. As the main agent constituting the solvent-free adhesive, a polyester resin having good adhesion to the outer layer film 42, the intermediate layer film 41 and the inner layer film 43 and excellent lamination strength and impact resistance is preferably used, and a polyester polyol resin is particularly preferred.

[0056] The polyester polyol resin may be any one produced by an esterification reaction of a polybasic acid such as succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, or terephthalic acid with a polyhydric alcohol such as ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, 3,3-bis(hydroxymethyl)heptane, diethylene glycol, dipropylene glycol, glycerin, or trimethylolpropane.

[0057] Specific examples of polyester polyol resins include: (1) adipate-based polyester diols such as poly(ethylene adipate), poly(diethylene adipate), poly(propylene adipate), poly(tetramethylene adipate), poly(hexamethylene adipate), and poly(neopentyl adipate); (2) polycaprolactone-based polyester diols such as poly-ε-caprolactone; (3) other polyester polyol resins such as poly(hexamethylene sebacate) and poly(hexamethylene carbonate);

[0058] In addition, as a main agent, a polyurethane compound may be contained in addition to a polyester resin. By using such a main agent, when an ink layer containing ink is formed on the inner surface of the outer layer film 42 (the surface on the side of the intermediate layer film 41), since the ink generally contains a polyurethane component, adhesion to the ink layer can be ensured.

[0059] The number average molecular weight of the resin constituting the main agent is preferably 400 to 1500, and more preferably 500 to 1000. When the number average molecular weight of the resin constituting the main agent is less than 400, the viscosity of the solvent-free adhesive is reduced, so the continuous lamination adaptability is sometimes poor when manufacturing a multilayer film. In addition, since the number of terminal reactive groups increases, it is necessary to increase the amount of curing agent, as a result, in the obtained adhesive layers 46 and 47, there is a problem that the cross-linking amount is large and the hardness increases, and the impact resistance of the adhesive layers 46 and 47 is sometimes reduced. On the other hand, when the number average molecular weight of the resin constituting the main agent exceeds 1500, the impact resistance of the obtained adhesive layers 46 and 47 is improved, but the viscosity of the solvent-free adhesive increases, so poor wetting occurs when the solvent-free adhesive is applied, sometimes causing the appearance of the obtained multilayer film 40 to be poor and the reduction of lamination strength.

[0060] The viscosity of the main agent is preferably 600 to 1800 mPa·s at 50°C, and more preferably 1000 to 1400 mPa·s. When the viscosity of the main agent is less than 600 mPa·s, uneven transfer of the roller occurs, and the film formation of the adhesive layers 46 and 47 becomes unstable, which sometimes causes the appearance of the obtained multilayer film 40 to be poor and the lamination strength to be extremely reduced. On the other hand, when the viscosity of the main agent exceeds 1800 mPa·s, poor wetting is likely to occur during the application of the solvent-free adhesive, which sometimes causes the appearance of the obtained multilayer film 40 to be poor and the lamination strength to be reduced.

[0061] As the curing agent constituting the solvent-free adhesive, an isocyanate compound is preferably used, and a mixture of an aliphatic isocyanate and an aromatic aliphatic diisocyanate is particularly preferably used.

[0062] As the aliphatic isocyanate constituting the curing agent, butane-1,4-diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isopropylene diisocyanate, methylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, m-tetramethylxylylene diisocyanate, lysine diisocyanate, dimer diisocyanate obtained by converting the carboxyl group of dimer acid into an isocyanate group, etc. can be used alone, or two or more thereof can be used in combination. Among them, 1,6-hexamethylene diisocyanate (HDI) is preferred.

[0063] Examples of the aromatic aliphatic diisocyanate constituting the curing agent include 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate or a mixture thereof (XDI), 1,3-tetramethylxylylene diisocyanate, 1,4-tetramethylxylylene diisocyanate or a mixture thereof (TMXDI), and ω,ω′-diisocyanate-1,4-diethylbenzene.

[0064] The number average molecular weight of the resin constituting the curing agent is preferably 400 to 1500, more preferably 500 to 1000. When the number average molecular weight of the resin constituting the curing agent is less than 400, the viscosity of the solvent-free adhesive is reduced, so the continuous lamination adaptability is sometimes poor when manufacturing a multilayer film. In addition, since the number of terminal reactive groups increases, it is necessary to increase the amount of the main agent, as a result, in the obtained adhesive layers 46 and 47, there is a problem that the cross-linking amount is large and the hardness increases, and the impact resistance of the adhesive layers 46 and 47 is sometimes reduced. On the other hand, when the number average molecular weight of the resin constituting the curing agent exceeds 1500, the impact resistance of the obtained adhesive layers 46 and 47 is improved, but the viscosity of the solvent-free adhesive increases, so poor wetting occurs when the solvent-free adhesive is applied, sometimes causing the appearance of the obtained multilayer film 40 to be poor and the reduction of lamination strength.

[0065] The viscosity of the curing agent constituting the solvent-free adhesive is preferably 150 to 1300 mPa·s at 50°C, and more preferably 450 to 850 mPa·s. When the viscosity of the curing agent is less than 150 mPa·s, the viscosity of the curing agent is small, so the resulting adhesive layers 46 and 47 become soft, and as a result, the lamination strength may be reduced. On the other hand, when the viscosity of the curing agent exceeds 1300 mPa·s, the viscosity of the curing agent is large, so the resulting adhesive layers 46 and 47 become hard, and as a result, the impact resistance may be poor.

[0066] In the solvent-free adhesive, the curing agent is preferably contained in the range of 30 to 200 parts by mass, particularly 30 to 70 parts by mass, relative to 100 parts by mass of the main agent. When the proportion of the curing agent is too small, the crosslinking of the obtained adhesive layers 46 and 47 is insufficient, so the lamination strength of the obtained multilayer film 40 may be reduced. On the other hand, when the proportion of the curing agent is too large, the main agent and the curing agent are not fully mixed, and there are insufficient crosslinking parts and excessive crosslinking parts in the obtained adhesive layers 46 and 47, so the lamination strength and impact resistance of the obtained multilayer film 40 may be reduced.

[0067] In the present invention, the viscosity of the solvent-free adhesive is 700 to 2000 mPa·s at 50°C, and more preferably 1000 to 1600 mPa·s. When the viscosity of the solvent-free adhesive is less than 700 mPa·s, transfer between rollers becomes poor when the solvent-free adhesive is applied, and "uneven transfer" sometimes occurs. In addition, the solvent-free adhesive is not applied uniformly and becomes less locally, which sometimes causes a decrease in lamination strength and impact resistance. On the other hand, when the viscosity of the solvent-free adhesive exceeds 2000 mPa·s, "poor wetting" sometimes occurs when the solvent-free adhesive is applied, and the obtained adhesive layers 46 and 47 become locally thinner. If there are thin portions in the adhesive layers 46 and 47, it sometimes causes a decrease in lamination strength and impact resistance.

[0068] The solvent-free adhesive may contain a polyurethane compound in addition to the above-mentioned main agent and curing agent. When an ink layer containing ink is formed on the inner surface of the outer layer film 42, adhesion to the ink layer can be ensured by containing the polyurethane compound.

[0069] In addition, solvent-free adhesives may also contain various additives, such as fillers, softeners, antioxidants, stabilizers, adhesion promoters, leveling agents, defoamers, plasticizers, inorganic fillers, tackifying resins, fibers, colorants such as pigments, and shelf life extenders.

[0070] Furthermore, the solvent-free adhesive may contain an adhesion promoter. As the adhesion promoter, a silane coupling agent, a titanate coupling agent, an aluminum coupling agent, an epoxy resin, etc. can be used.

[0071] Specific examples of the silane coupling agent include aminosilanes such as γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β (aminoethyl)-γ-aminopropyltrimethoxysilane, N-β (aminoethyl)-γ-aminopropyltrimethyldimethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane; epoxysilanes such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-glycidoxypropyltriethoxysilane; vinylsilanes such as vinyltri(β-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane; hexamethyldisilazane, γ-mercaptopropyltrimethoxysilane, and the like.

[0072] Specific examples of the titanate coupling agent include tetraisopropoxytitanium, tetra-n-butoxytitanium, butyl titanate dimer, tetrastearyl titanate, titanium acetylacetonate, titanium lactate, tetraoctanediol titanate, titanium lactate, and tetrastearyl titanium.

[0073] Specific examples of the aluminum coupling agent include acetoalkoxyaluminum diisopropylate and the like.

[0074] Specific examples of epoxy resins include various epoxy resins that are generally commercially available, such as epi-bis (Epi-Bis) type, novolac type, β-methyl epichlorohydrin type, cyclic oxirane type, glycidyl ether type, glycidyl ester type, polyglycol ether type, glycol ether type, epoxidized fatty acid ester type, polycarboxylic acid ester type, aminoglycidyl type, and resorcinol type.

[0075] The packaging container formed of the multilayer film 40 is suitable as a packaging container such as a retort pouch or a refill pouch containing food (curry, sauce, etc.) or liquids such as drinks, detergents, softeners, bleaches, shampoos, conditioners, etc.

[0076] As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, Various changes are possible.

[0077] For example, the layer structure of the multilayer film is not limited to Figure 1 The structure shown may also be a structure formed by laminating four or more films, for example, a structure having a plurality of intermediate films. In this case, at least one of the intermediate films is an aluminum foil. In addition, the multilayer film may also form an ink layer, a vapor deposition layer, etc. on the inner surface of the outer film (the surface on the intermediate film side), the inner surface of the inner film (the surface on the intermediate film side), etc.

[0078] In addition, for example, the method for manufacturing a multilayer film of the present invention is not limited to the case where the intermediate layer film is composed of aluminum foil, but is also useful when a raw material film having through holes of a size that allows the solvent-free adhesive to pass through when the solvent-free adhesive is applied in the first lamination step is used as the intermediate layer film.

[0079] Furthermore, for example, the method for manufacturing a multilayer film of the present invention is not limited to the resin film being the first film coated with a solvent-free adhesive using a first coating device, and can also be configured as follows: the first film is an aluminum foil, and the second film is a resin film, and in the first intermediate, a second adhesive coating layer is formed on the first film (aluminum foil) using a second coating device, and a resin film is superimposed therebetween to form a third film.

[0080] Description of Reference Numerals

[0081] 1: Laminator;

[0082] 10: first coating device;

[0083] 11: coating unit;

[0084] 11a, 11b: coating rollers;

[0085] 11c, 11d, 11e: transfer rollers;

[0086] 11f: storage department;

[0087] 15: Supply unit;

[0088] 20: second coating device;

[0089] 31: unwinding roller;

[0090] 32: lamination section;

[0091] 32a, 32b: pressure rollers;

[0092] 33: unwinding roller;

[0093] 34: lamination section;

[0094] 34a, 34b: pressure rollers;

[0095] 35: unwinding roller;

[0096] 36: winding roller;

[0097] 40: Multilayer film;

[0098] 41: middle layer membrane;

[0099] 42: outer membrane;

[0100] 43: inner membrane;

[0101] 46: first adhesive layer;

[0102] 47: second adhesive layer;

[0103] W1: first membrane;

[0104] W2: second membrane;

[0105] W3: third membrane;

[0106] Wm1: first intermediate;

[0107] Wm2: second intermediate.

Claims

1. A method for manufacturing a multilayer film, characterized in that: This is a method for manufacturing a multilayer film by laminating three or more films with an adhesive layer interposed therebetween, and the following steps are performed: A first lamination step, in a first coating device having a pair of coating rollers facing each other, applying an adhesive to a first film passing between the coating rollers, laminating a second film while overlapping the first adhesive coating layer formed by the adhesive, to obtain a first intermediate; In a second laminating step, in a second coating device having a pair of coating rollers facing each other, an adhesive is applied to the first intermediate body, and a third film is laminated while being overlapped with a second adhesive coating layer formed by the adhesive; and then the following steps are performed: A aging step solidifies the first adhesive coating layer and the second adhesive coating layer to obtain adhesive layers, respectively, wherein: The first adhesive coating layer is formed of a solvent-free adhesive, and when subjected to the second lamination step, the solvent-free adhesive of the first adhesive coating layer constituting the first intermediate has fluidity. Of the first film and the second film, the film superimposed on the third film via the second adhesive coating layer is made of aluminum foil.

2. The method for producing a multilayer film according to claim 1, characterized in that: The first film is an outer layer film made of resin, the second film is an aluminum foil, and the third film is an inner layer film made of resin.

3. The method for producing a multilayer film according to claim 2, characterized in that: The outer layer film is formed of a polyamide resin or a polyester resin.

4. The method for producing a multilayer film according to claim 2, characterized in that: The inner layer film is formed of a polyolefin-based resin.

5. The method for producing a multilayer film according to claim 1, wherein: The second adhesive coating layer is formed of a solvent-free adhesive.

6. The method for producing a multilayer film according to claim 1, wherein: The solvent-free adhesive contains a main agent formed of a polyester resin and a curing agent formed of an aliphatic isocyanate, and the viscosity of the solvent-free adhesive is 700 to 2000 mPa·s at 50° C.

7. The method for producing a multilayer film according to claim 1, characterized in that: In the first adhesive coating layer, the coating amount of the adhesive is 0.5 to 3.0 g / m 2 .

8. A multilayer film, characterized in that It is manufactured by the manufacturing method as claimed in claim 1.

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