Method for producing laminated film, laminated film, and packaging container

Abstract

To provide a method for producing a laminated film (30), a laminated film (30), and a packaging container, which are capable of reducing an environmental load and suppressing generation of air bubbles in an adhesive layer (36, 37). In the method for producing a laminated film (30), a solventless adhesive has a viscosity at 50°C of from 700 to 2000 mPa·s. The coating device (20) further includes a coating unit (21), the coating unit (21) including: a pair of rolls, a plurality of transfer rolls configured to sequentially transfer and supply the solventless adhesive, and an application roll (21e) disposed on the opposite side of a fine clearance from a doctor roll (21d), the doctor roll (21d) being one of the plurality of transfer rolls and positioned at an end on a side where supply of the solventless adhesive starts. A peripheral speed of the doctor roll (21d) is from 1.0 to 10.0 rn / min. FIG. 1

Description

Manufacturing method of laminated film, laminated film and packaging container

[0001] The present invention relates to a method for producing a laminated film in which raw material films are bonded together using a solventless adhesive to obtain a laminated film, a laminated film obtained by the method, and a packaging container formed from the laminated film.

[0002] Pouch packaging containers used for food packaging and flexible packaging containers used as cup lids have traditionally been made of laminated films in which multiple raw material films, such as resin films, are laminated together. In such packaging containers, when resin films with different properties are laminated together, such as a combination of a nylon film and a polyethylene film, the adhesion between the two films is poor, so they are generally attached using a laminating adhesive.

[0003] From the viewpoint of reducing the burden on the global environment, it is desirable to use solvent-free adhesives that do not contain organic solvents and can be applied by heating the adhesive to reduce its viscosity. For example, a laminate film using a conventional solvent-free adhesive is known, which has an adhesive layer made of a solvent-free adhesive that is composed of a base agent made of a polyester polyol and a curing agent made of an aliphatic diisocyanate compound and an alicyclic diisocyanate, and has a viscosity of 300 to 900 mPa·s at 70°C (see Patent Document 1).

[0004] Patent No. 5397584

[0005] However, laminated films using solvent-free adhesives are prone to large air bubbles in the adhesive layer, resulting in the laminated film's poor appearance, characterized by numerous small, speckled irregularities known as "yuzu peel." This problem is particularly pronounced when the laminated film is heat-treated. Meanwhile, packaging containers used in the food industry that use laminated films are often heat-treated for sterilization and other food preservation purposes. As a result, food packaging containers that have undergone heat treatment suffer from the appearance problem of yuzu peel. Furthermore, since the yuzu peel phenomenon is caused by air bubbles in the adhesive layer, as described above, it is possible that gaps have formed in the adhesive layer, raising concerns about the shelf life of the food contained therein.

[0006] The present invention has been made based on the above circumstances, and its object is to provide a method for producing a laminated film, a laminated film, and a packaging container that can reduce the environmental load and prevent air bubbles from forming in the adhesive layer.

[0007] The method for manufacturing a laminated film of the present invention includes a coating device having a pair of opposing rolls, in which a solvent-free adhesive is applied to one film passing between the rolls, and the other film is laminated while being superimposed with an adhesive coating layer made of the solvent-free adhesive interposed therebetween, wherein the solvent-free adhesive contains a base agent made of a polyester resin and a curing agent made of an aliphatic isocyanate, and the viscosity of the solvent-free adhesive is 700 to 2000 mPa·s at 50°C, and the coating device further includes a coating unit having the pair of rolls, a plurality of transfer rolls that sequentially transfer and supply the solvent-free adhesive to one of the pair of rolls, and an application roll arranged opposite, via a small clearance, a doctor roll that is located at the end of the plurality of transfer rolls where the supply of the solvent-free adhesive starts, and wherein the peripheral speed of the doctor roll is 1.0 to 10.0 m / min.

[0008] The laminate film of the present invention is characterized by being produced by the above-mentioned production method. Furthermore, the packaging container of the present invention is characterized by being formed from the above-mentioned laminate film.

[0009] According to the laminate film manufacturing method of the present invention, an adhesive layer is formed using a solventless adhesive with specific ingredients and viscosity in a coating device with a specific coating unit. This allows for clearance between the doctor roll and application roll of the coating unit, and the doctor roll operates at a low speed, preventing excessive mixing of the solventless adhesive accumulated between these rolls. This significantly reduces air entrainment in the solventless adhesive, thereby preventing the formation of air bubbles in the adhesive coating layer transferred to the film. This prevents the resulting laminate film and packaging container from exhibiting poor appearance, such as an orange peel appearance, and ensures stable storage of the contents in the packaging container. Furthermore, because the solventless adhesive does not use organic solvents, environmental impact is reduced.

[0010] 1 is an explanatory diagram showing the configuration of an example of a laminator for producing the laminated film of the present invention. 2 is an explanatory cross-sectional view showing the configuration of an example of the laminated film of the present invention.

[0011]

[0023] The laminate film manufacturing method of the present invention is a method for manufacturing a laminate film by using a laminator 10 to bond a pair of long films W1 and W2 together with a solvent-free adhesive while conveying them at high speed, as shown in Fig. 1, and includes the steps of applying a solvent-free adhesive, which is a mixture of two liquid components (a base agent and a curing agent) premixed, to one film W1 using a coating device 20, and then laminating the other film W2 while superimposing them together with an adhesive-coated layer of the solvent-free adhesive interposed therebetween.

[0012] The laminator 10 includes a coating device 20 that applies a solvent-free adhesive to one film W1, an unwinding roll 11 that supplies the one film W1 to be coated with the solvent-free adhesive to the coating device 20, a laminating section 12 having a pair of pressure rolls 12a, 12b that laminates the other film W2 onto the film W1 on which the adhesive coating layer has been formed and which has been sent out from the coating device 20, an unwinding roll 13 that supplies the other film W2, and a winding roll 14 that winds up the laminate of the films W1 and W2. The coating device 20 includes a coating unit 21 that sequentially transfers the mixed solvent-free adhesive onto one film W1 using multiple rolls and applies it while thinly spreading it, and a supply unit 25 that supplies the solvent-free adhesive to the coating unit 21.

[0013] The coating unit 21 includes a plurality of rolls 21a-21e (five in the illustrated example) rotatably supported and arranged in series with their axes parallel to each other. Specifically, the coating unit 21 includes a pair of rolls, namely, a backup roll 21a and a coating roll 21b, which face each other and allow the film W1 to pass between them; a metering roll 21c and a doctor roll 21d, which are transfer rolls that sequentially transfer and supply the solventless adhesive to one of the pair of rolls (the coating roll 21b); and an application roll 21e, which is arranged adjacent to the doctor roll 21d, which is located at the end of the transfer roll where the solventless adhesive supply starts, with a small clearance (gap) between them. The backup roll 21a, the coating roll 21b, the metering roll 21c, and the doctor roll 21d are arranged in series in this order with their outer circumferential surfaces in contact with each other. The film W1 to be coated with the solventless adhesive is sandwiched between the coating roll 21b, which is located at the end where the solventless adhesive supply ends, and the backup roll 21a, which presses against it. Between the doctor roll 21d and the application roll 21e, which are located at the supply start end of the solventless adhesive, there is formed a reservoir 22 for temporarily storing the mixed base agent and curing agent in the upper part of the clearance between the two rolls 21d and 21e. The reservoir 22 is formed by dividing the space having a generally V-shaped cross section caused by the clearance with a pair of barrier plates (not shown) spaced apart in the longitudinal direction of the rolls 21d and 21e.

[0014] The coating roll 21b, doctor roll 21d, and application roll 21e are metal rolls whose outer circumferential surfaces are made of metal, while the backup roll 21a and metering roll 21c are elastic rolls whose outer circumferential surfaces are made of an elastic material such as rubber. In other words, in the coating unit 21, the backup roll 21a through the doctor roll 21d are arranged in sequence, with the elastic rolls and metal rolls alternately arranged, allowing two adjacent elastic rolls and metal rolls to be pressed against each other. The backup roll 21a through the doctor roll 21d are rotated in sequence so that the outer circumferential surfaces of the adjacent rolls move in the same direction at the pressed-together position, i.e., so that they rotate in opposite directions. The doctor roll 21d is rotated so that the outer circumferential surface forming the storage section 22 moves downward.

[0015] The application roll 21e and the doctor roll 21d are provided with temperature regulators (not shown) for maintaining a constant temperature of the solventless adhesive stored in the reservoir 22. The coating roll 21b is also provided with a temperature regulator (not shown) for maintaining these at a constant temperature.

[0016] In the present invention, the peripheral speed of the doctor roll 21d is, for example, 1.0 to 10.0 m / min, and the application roll 21e is not rotated, or even if it is rotated, its peripheral speed is, for example, 0.1 m / min or less. The size of the clearance between the doctor roll 21d and the application roll 21e varies depending on the temperature of the solvent-free adhesive, i.e., the viscosity of the solvent-free adhesive stored in the storage section 22, but is preferably set in the range of 40 to 100 μm, more preferably 60 to 80 μm. If the clearance between the doctor roll 21d and the application roll 21e is excessively small, the amount of solvent-free adhesive applied in the roll width direction will vary greatly, potentially making it impossible to form a stable, uniform adhesive coating layer. If the clearance is excessively large, the solvent-free adhesive may drip from the storage section 22. Since the size of the clearance between the doctor roll 21d and the application roll 21e is within the above range, and since the doctor roll 21d is rotated at the above-mentioned peripheral speed while the application roll 21e is stopped from rotating, excessive mixing of the solvent-free adhesive in the storage section 22 is prevented, thereby extremely suppressing air entrainment due to air entrainment in the solvent-free adhesive and suppressing the formation of air bubbles in the adhesive coating layer transferred by the coating unit 21 and formed on the film W1.

[0017] In addition, the peripheral speeds of the backup roll 21a and the coating roll 21b (the speed at the pressed portion) are set to the same as the supply speed of the film W1, and the peripheral speed of the metering roll 21c is set to a value between the peripheral speeds of the adjacent coating roll 21b and the doctor roll 21d, since a large difference in peripheral speed between adjacent rolls would result in poor appearance.

[0018] As an example of the dimensions of the application roll 21e and the doctor roll 21d, the outer diameter may be 100 mm to 300 mm, and the width of the coating surface constituting the reservoir 22 may be approximately 600 mm to 1800 mm. The application roll 21e and the doctor roll 21d may have different outer diameters.

[0019] The supply unit 25 has a main agent tank 26 containing the main agent, a hardener tank 27 containing the hardener, and an adhesive supply section 28 that supplies the main agent and the hardener, and may further have a mixer (not shown) that stirs the solventless adhesive stored in the storage section 22.

[0020] In this laminator 10, one film W1 is transported at a predetermined speed from the unwinding roll 11 to between a pair of rolls 21a and 21b (between the backup roll 21a and the coating roll 21b) of the coating device 20. Meanwhile, in the supply unit 25, the base agent and curing agent are heated to predetermined temperatures in the base agent tank 26 and the curing agent tank 27. Predetermined amounts of the heated base agent and curing agent are supplied from the adhesive supply section 28 to the reservoir 22 between the doctor roll 21d and the application roll 21e after being mixed in a static mixer 29. The solventless adhesive is continuously supplied from the supply unit 25 to the reservoir 22 so that the liquid level in the reservoir 22 is maintained constant. The solventless adhesive is transferred from the doctor roll 21d, located at the supply start end of the coating unit 21, to the metering roll 21c, and then to the coating roll 21b, located at the supply end end. The adhesive is then applied from the coating roll 21b to the surface of one film W1 passing between the pair of rolls 21a and 21b, forming an adhesive coating layer. The film W1 with the adhesive coating layer formed thereon is then sent to the laminating section 12. Meanwhile, the other film W2 is supplied from the unwinding roll 13 to the laminating section 12. In the laminating section 12, the one film W1 and the other film W2 are superimposed on each other so that the other film W2 contacts the adhesive coating layer on the surface of the one film W1, and are then pressed together by the pair of pressure rolls 12a and 12b, thereby forming an intermediate laminate film comprising the pair of films W1 and W2. This intermediate laminate film is then taken up by the take-up roll 14. The intermediate laminate film wound up by the winding roll 14 is subjected to an aging treatment in which it is left standing at room temperature or under elevated temperature, whereby the adhesive coating layer hardens and an adhesive layer is formed, thereby obtaining a laminate film in which a pair of films W1, W2 are bonded together by the adhesive layer.When the laminated film is, for example, three or more films laminated together via an adhesive layer, the above-mentioned lamination process is carried out to bond two films together, and then a similar lamination process is repeated to obtain a laminated film in which three or more films are bonded together via an adhesive layer made of a solventless adhesive.

[0021] In the above, the heating temperatures of the base agent and curing agent and the temperature of the solventless adhesive in the reservoir 22 are preferably in the range of 40 to 80°C, with 40 to 50°C being particularly preferred. The coating temperature of the solventless adhesive on one film W1 is preferably in the range of 40 to 80°C, with 60 to 80°C being particularly preferred. These temperatures can be controlled by setting the temperatures of the rolls 21a to 21e of the coating unit 21 and the base agent tank 26 and the curing agent tank 27. A coating temperature within the above range minimizes heat damage to one film W1 while maintaining the viscosity of the solventless adhesive sufficiently low for practical use. The temperature of the pressure rolls 12a and 12b in the laminating unit 12 is, for example, 30 to 80°C. The feed speed of each film W1 and W2, i.e., the coating speed of the solventless adhesive, is preferably 100 to 200 m / min. The amount of solvent-free adhesive applied is 0.5 to 3.0 g / m 2 is preferably 1.2 to 2.6 g / m 2 If the amount of solvent-free adhesive applied is too small, sufficient adhesion cannot be obtained, while if the amount of solvent-free adhesive applied is too large, the laminated film may become misaligned or the solvent-free adhesive may leak from the edge of the laminated film, resulting in poor quality. The temperature for the aging treatment of the intermediate laminated film taken up by the take-up roll 14 is, for example, 30 to 70°C, and the treatment time is, for example, 48 to 96 hours. Other coating conditions in the laminator 10 can be set as appropriate.

[0022] [Laminate Film] The laminate film of the present invention is obtained by the above-described manufacturing method and, for example, as shown in FIG. 2 , has an outer layer resin film 31, an inner layer resin film 32, and an intermediate layer resin film 33 provided between the inner layer resin film 32 and the outer layer resin film 31. A vapor deposition layer 35 and an ink layer 34 are formed in this order on the inner surface of the outer layer resin film 31 (the surface on the intermediate layer resin film 33 side). An adhesive layer 36 formed with a solventless adhesive by the above-described laminator 10 is formed between the ink layer 34 and the intermediate layer resin film 33, and an adhesive layer 37 formed with a solventless adhesive by the above-described laminator 10 is formed between the inner layer resin film 32 and the intermediate layer resin film 33. That is, this laminate film 30 is obtained by repeating the above-described manufacturing method twice using three raw material films: the outer layer resin film 31 on which the vapor deposition layer 35 and ink layer 34 are formed, the intermediate layer resin film 33, and the inner layer resin film 32.

[0023] The outer layer resin film 31 is preferably a film with excellent thermal dimensional stability. By using such an outer layer resin film 31, it is possible to perform a baking process at a temperature of about 80° C. after, for example, gravure printing on the outer layer resin film 31, and therefore it is easy to form an ink layer. Furthermore, it is preferable to use a biaxially stretched film as the outer layer resin film 31, since this provides high tensile strength.

[0024] The outer layer resin film 31 is preferably made of a polyamide resin or a polyester resin. Examples of polyamide resins that can be used include nylon 6, nylon 8, nylon 6,6, nylon 6 / 6,6 copolymer, nylon 6,10, metaxylylene adipamide (MXD6), nylon 11, and nylon 12. Examples of polyester resins that can be used include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Copolyesters containing other polyester units can also be used as long as they do not impair the properties of these resins. Among the copolymerization components used to form such copolyesters, dicarboxylic acid components include isophthalic acid, p-β-oxyethoxybenzoic acid, naphthalene 2,6-dicarboxylic acid, diphenoxyethane-4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid, sebacic acid, and alkyl ester derivatives thereof. As the glycol component, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene glycol, cyclohexanedimethanol, an ethylene oxide adduct of bisphenol A, diethylene glycol, triethylene glycol, etc. These compounds can be used alone or in combination of two or more as the copolymerization component.

[0025] The thickness of the outer layer resin film 31 is selected appropriately depending on the type of resin that constitutes the outer layer resin film 31 and the use of the laminated film, etc., but if the outer layer resin film 31 is made of nylon, for example, the thickness is preferably 10 to 30 μm, and if the outer layer resin film 31 is made of polyethylene terephthalate (PET), the thickness is preferably 6 to 28 μm.

[0026] Furthermore, it is preferable that the surface of the outer resin film 31 that comes into contact with the adjacent layer be subjected to a surface modification treatment such as a corona treatment in order to improve adhesion to the adjacent layer.

[0027] As a material for forming the inner layer resin film 32, a resin with excellent heat-sealing properties is preferably used in order to form a pouch packaging bag or a heat-sealed lid. Examples of such resins include polyolefin resins such as polyethylene (PE) and polypropylene (PP).

[0028] The thickness of the inner layer resin film 32 is not particularly limited, but is preferably 50 to 200 μm when the inner layer resin film 32 is made of polyethylene, and is preferably 30 to 150 μm when the inner layer resin film 32 is made of polypropylene. It is also preferable to use a non-stretched film as the inner layer resin film 32.

[0029] The material constituting the intermediate layer resin film 33 can be a resin having gas barrier properties, and specific examples thereof include nylon resins such as aliphatic nylons such as nylon 6, nylon 8, nylon 11, nylon 12, nylon 6,6, nylon 6,10, nylon 10,6, and nylon 6 / 6,6 copolymer, partially aromatic nylons such as polymetaxylylene adipamide, and polyglycolic acid resin. Furthermore, the material constituting the intermediate layer resin film 33 can also be an olefin-based resin, such as polyethylene (PE) such as low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and linear very low-density polyethylene (LVLDPE), polypropylene (PP), ethylene-propylene copolymer, polybutene-1, ethylene-butene-1 copolymer, propylene-butene-1 copolymer, ethylene-propylene-butene-1 copolymer, ethylene-vinyl acetate copolymer (EVA), ionically cross-linked olefin copolymer (ionomer), or a mixture thereof. The thickness of the intermediate resin film 33 is not particularly limited, but is preferably 5 to 100 μm.

[0030] The ink layer 34 is formed by, for example, gravure printing on the vapor deposition layer 35 formed on the outer resin film 31. The thickness of such an ink layer 34 is preferably 1 to 8 μm.

[0031] The material that can be used to form the vapor deposition layer 35 includes a metal material such as aluminum, a non-metallic inorganic material such as silica, and the like.

[0032] The adhesive layers 36, 37 are formed of a specific solvent-free adhesive, which will be described in detail below. This solvent-free adhesive is a two-part, reaction-curing adhesive consisting of a base agent and a curing agent. The thickness of the adhesive layers 36, 37 is preferably 0.5 to 3 μm.

[0033] [Solvent-free adhesive] As the main component of the solvent-free adhesive, it is preferable to use a polyester-based resin, which has good adhesion to the inner layer resin film 32, the intermediate layer resin film 33, and the ink layer 34, and is also excellent in lamination strength and impact resistance, and polyester polyol resin is particularly preferable.

[0034] The polyester polyol resin may be one produced by an esterification reaction between a polybasic acid such as succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, or terephthalic acid and a polyhydric alcohol such as ethylene glycol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 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.

[0035] Specific examples of polyester polyol resins include: (1) adipate-based polyester glycols such as poly(ethylene adipate), poly(diethylene adipate), poly(propylene adipate), poly(tetramethylene adipate), poly(hexamethylene adipate), and poly(neopentylene adipate); (2) polycaprolactone-based polyester glycols such as poly-ε-caprolactone; and (3) other polyester polyol resins such as poly(hexamethylene sebacate) and poly(hexamethylene carbonate).

[0036] The base resin may contain, for example, a polyurethane compound in addition to the polyester resin. By using such a base resin, adhesion to the ink layer 34 can be ensured because the ink layer 34 usually contains a urethane component.

[0037] The number-average molecular weight of the resin constituting the base resin is preferably 400 to 1500, more preferably 500 to 1000. If the number-average molecular weight of the resin constituting the base resin is less than 400, the viscosity of the solvent-free adhesive decreases, which can lead to poor suitability for continuous lamination during the production of laminated films. Furthermore, the number of reactive terminal groups increases, necessitating the use of a larger amount of curing agent. As a result, the resulting adhesive layers 36, 37 have a high degree of crosslinking, increasing their hardness and potentially reducing their impact resistance. On the other hand, if the number-average molecular weight of the resin constituting the base resin exceeds 1500, the impact resistance of the resulting adhesive layers 36, 37 improves, but the viscosity of the solvent-free adhesive increases, resulting in poor wetting during application, which can lead to poor appearance and reduced lamination strength in the resulting laminated film 30.

[0038] The viscosity of the base agent is preferably 600 to 1800 mPa·s at 50°C, more preferably 1000 to 1400 mPa·s. If the viscosity of the base agent is less than 600 mPa·s, uneven transfer of the roll occurs, making film formation of the adhesive layers 36, 37 unstable, which may result in poor appearance of the resulting laminate film 30 and a significant decrease in laminate strength. On the other hand, if the viscosity of the base agent exceeds 1800 mPa·s, poor wetting is likely to occur when the solventless adhesive is applied, which may result in poor appearance of the resulting laminate film 30 and a decrease in laminate strength.

[0039] As the curing agent for the solventless adhesive, an isocyanate compound, particularly a mixture of an aliphatic isocyanate and an araliphatic diisocyanate, is preferably used. Examples of aliphatic isocyanates that constitute the curing agent include butane-1,4-diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isopropylene diisocyanate, methylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, m-tetramethylxylylene diisocyanate, lysine diisocyanate, and dimer diisocyanate, which is obtained by converting the carboxyl group of a dimer acid to an isocyanate group. These can be used alone or in combination of two or more. Of these, 1,6-hexamethylene diisocyanate (HDI) is preferred. Examples of the aromatic aliphatic diisocyanate constituting the curing agent include 1,3-xylylene diisocyanate or 1,4-xylylene diisocyanate or a mixture thereof (XDI), 1,3-tetramethylxylylene diisocyanate or 1,4-tetramethylxylylene diisocyanate or a mixture thereof (TMXDI), ω,ω'-diisocyanato-1,4-diethylbenzene, and the like.

[0040] The number-average molecular weight of the resin constituting the curing agent is preferably 400 to 1500, more preferably 500 to 1000. If the number-average molecular weight of the resin constituting the curing agent is less than 400, the viscosity of the solventless adhesive decreases, which can lead to poor suitability for continuous lamination during the production of laminated films. Furthermore, the number of terminal reactive groups increases, necessitating a larger amount of base resin. As a result, the resulting adhesive layers 36, 37 have a high degree of crosslinking, increasing their hardness and potentially reducing their impact resistance. On the other hand, if the number-average molecular weight of the resin constituting the curing agent exceeds 1500, the impact resistance of the resulting adhesive layers 36, 37 improves, but the viscosity of the solventless adhesive increases, resulting in poor wetting during application of the solventless adhesive, which can lead to poor appearance and reduced laminate strength in the resulting laminated film 30.

[0041] The viscosity of the curing agent constituting the solventless adhesive is preferably 150 to 1300 mPa·s at 50°C, and more preferably 450 to 850 mPa·s. If the viscosity of the curing agent is less than 150 mPa·s, the resulting adhesive layers 36, 37 will be soft, which may result in reduced laminate strength. On the other hand, if the viscosity of the curing agent exceeds 1300 mPa·s, the resulting adhesive layers 36, 37 will be hard, which may result in reduced impact resistance.

[0042] In solventless adhesives, the curing agent is preferably contained in an amount of 30 to 200 parts by weight, particularly 30 to 70 parts by weight, per 100 parts by weight of the base agent. If the curing agent content is too low, the resulting adhesive layers 36, 37 will be insufficiently crosslinked, which may reduce the laminate strength of the resulting laminate film 30. On the other hand, if the curing agent content is too high, the base agent and the curing agent will not be sufficiently mixed, resulting in the resulting adhesive layers 36, 37 containing a mixture of insufficiently crosslinked and over-crosslinked portions, which may reduce the laminate strength and impact resistance of the resulting laminate film 30.

[0043] In the present invention, the viscosity of the solvent-free adhesive at 50°C is 700 to 2000 mPa·s, more preferably 1000 to 1600 mPa·s. If the viscosity of the solvent-free adhesive is less than 700 mPa·s, the solvent-free adhesive may drip from the reservoir 22, or transfer between the rolls may be poor during application, resulting in "uneven transfer." Furthermore, the solvent-free adhesive may not be applied uniformly and may be partially thin, resulting in reduced laminate strength and impact resistance. On the other hand, if the viscosity of the solvent-free adhesive exceeds 2000 mPa·s, "poor wetting" may occur during application, resulting in partially thin adhesive layers 36, 37. Thinner portions of the adhesive layers 36, 37 may result in reduced laminate strength and impact resistance.

[0044] The solvent-free adhesive may contain a polyurethane compound in addition to the above-mentioned base agent and curing agent. By containing a polyurethane compound, adhesion to the ink layer 34 can be ensured, since the ink layer 34 usually contains a urethane component. The solvent-free adhesive may also contain various additives, such as fillers, softeners, antioxidants, stabilizers, adhesion promoters, leveling agents, antifoaming agents, plasticizers, inorganic fillers, tackifying resins, fibers, colorants such as pigments, and pot life extenders.

[0045] Furthermore, the solventless adhesive may contain an adhesion promoter, such as a silane coupling agent, a titanate coupling agent, an aluminum coupling agent, or an epoxy resin.

[0046] 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 vinyltris(β-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane; hexamethyldisilazane, γ-mercaptopropyltrimethoxysilane, and the like.

[0047] Specific examples of titanate coupling agents include tetraisopropoxytitanium, tetra-n-butoxytitanium, butyl titanate dimer, tetrastearyl titanate, titanium acetylacetonate, titanium lactate, tetraoctylene glycol titanate, titanium lactate, and tetrastearoxytitanium.

[0048] Specific examples of aluminum-based coupling agents include acetoalkoxyaluminum diisopropylate.

[0049] Specific examples of epoxy resins include various epoxy resins that are generally commercially available, such as epibis type, novolak type, β-methylepicro 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.

[0050] [Packaging Container] The packaging container of the present invention is formed from the above-mentioned laminated film, and is particularly suitable for use as a food packaging container such as a retort pouch, which contains food and undergoes a heat treatment while sealed. Heat treatment for food packaging containers is, for example, a treatment in which the food is heated to 100°C or higher, and examples thereof include sterilization treatments involving heat that are performed on ordinary food packaging containers, such as retort sterilization treatments that enable distribution at room temperature and heat treatments at 120°C for less than 4 minutes that enable chilled distribution, but are not limited to these, and refers to various known heat treatments for food. Retort sterilization refers to a pressurized heat treatment, in which, for example, a product filled in a heat-resistant container is heated with steam or hot water at about 110°C to 130°C for several tens of minutes while pressurizing the product so that the container is not damaged by the internal pressure of the product as the product temperature rises, and a F equivalent to at least 4 minutes at 120°C. 0 Heat sterilization that allows chilled distribution refers to, for example, heat treatment equivalent to 90°C for 10 minutes or longer, which is commonly used.

[0051] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and various modifications can be made. For example, the layer structure of the laminated film is not limited to the structure shown in Figure 2, and it may consist of two resin films, an outer layer resin film and an inner layer resin film, or may have multiple intermediate layer resin films. Furthermore, the ink layer and the vapor deposition layer are provided as needed and are not essential to the present invention.

[0052] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0053] Example 1 Solvent-free adhesive Table 1 shows the composition of the solvent-free adhesive used in Example 1. In Table 1, the viscosities of the base agent, curing agent, and solvent-free adhesive were measured using a B8L viscometer manufactured by TOKIMEC Corporation in accordance with a method in accordance with JIS K7117-2.

[0054] [Resin Film] The outer layer resin film was a 12 μm-thick biaxially oriented polyethylene terephthalate (PET) film with an alumina vapor deposition film formed on one side. The middle layer resin film was a 15 μm-thick biaxially oriented nylon film. The inner layer film was a 70 μm-thick unstretched polypropylene (CPP) film.

[0055] [Production of Laminated Film] A laminated film was produced as follows using a laminator configured as shown in Figure 1. The base agent and curing agent shown in Table 1 below were placed in a base agent tank and a curing agent tank, respectively, and heated to 50°C. The base agent and curing agent were then supplied to the adhesive coating section by the adhesive supply section in the mass blending ratio shown in Table 1 below, and mixed to prepare a solvent-free adhesive. Then, in the adhesive coating section, the solvent-free adhesive was applied at 80°C to one side of the outer layer resin film supplied from the unwinding roll, thereby forming an adhesive coating layer. The amount of solvent-free adhesive applied was 1.7 g / m 2 The coating speed was 150 m / min. The outer layer resin film with the adhesive coating layer formed thereon was then transported to a laminating section, where the outer layer resin film and an intermediate layer resin film with a vapor-deposited layer formed thereon, supplied from a winding roll, were laminated under pressure at 50°C to produce a first intermediate laminate film. The laminating speed was 150 m / min. The resulting first intermediate laminate film was wound onto a roll, and an adhesive coating layer was formed on the other side of the intermediate layer resin film in the first intermediate laminate film under the same conditions as above. This intermediate layer resin film was then laminated to an inner layer resin film to produce an intermediate laminate film. The resulting intermediate laminate film was subjected to an aging treatment by holding it at 40°C for 3 days, thereby producing a laminate film.

[0056] [Production of packaging container (pouch)] Two sheets of 130 mm wide and 175 mm high were cut out from the obtained laminated film, and the two laminated films with the inner surface layers joined together were heat-sealed at 200 ° C. to seal the bottom and three sides, producing a packaging container (pouch) with a width of 130 mm, a height of 175 mm, and a capacity of 200 ml. This pouch was filled with water (total content: 180 g), sealed by heat sealing, and then subjected to hot water pressure sterilization and shower cooling (sterilization temperature: 127 ° C., sterilization time: 30 minutes, sterilization pressure: 0.3 MPa).

[0057] [Evaluation of poor appearance] The appearance of the packaging container before and after hot water pressure sterilization shower cooling (heat sterilization treatment) was visually observed over an area of ​​1 m wide and 1 m long, and the presence or absence of a spotted minute uneven pattern (citrus peel) was checked. The case where no spotted minute uneven pattern was observed was evaluated as ◯, and the case where an uneven pattern was observed was evaluated as ×. The results are shown in Table 1 below.

[0058]

[0059] As is clear from the results in Table 1, the packaging container of Example 1 had a good appearance without any air bubbles forming in the adhesive layer either before or after the heat sterilization treatment, and therefore was confirmed to be useful as a packaging container for food.

[0060] REFERENCE SIGNS LIST 10 Laminator 11 Unwinding roll 12 Laminating section 12a, 12b Pressure roll 13 Unwinding roll 14 Winding roll 20 Coating device 21 Coating unit 21a Backup roll 21b Coating roll 21c Metering roll 21d Doctor roll 21e Application roll 22 Storage section 25 Supply unit 26 Base agent tank 27 Hardener tank 28 Adhesive supply section 29 Static mixer 30 Laminated film 31 Outer layer resin film 32 Inner layer resin film 33 Intermediate layer resin film 34 Ink layer 35 Vapor deposition layer 36, 37 Adhesive layer W1, W2 Film

Claims

1. A method for manufacturing a laminated film, comprising the steps of: applying a solvent-free adhesive to one film passing between a pair of opposing rolls in a coating device; and laminating the other film while superimposing the other film with an adhesive coating layer made of the solvent-free adhesive interposed therebetween; the solvent-free adhesive contains a base agent made of a polyester resin and a curing agent made of an aliphatic isocyanate; the viscosity of the solvent-free adhesive is 700 to 2000 mPa·s at 50°C; the coating device further comprises a coating unit having the pair of rolls, a plurality of transfer rolls that sequentially transfer and supply the solvent-free adhesive to one of the pair of rolls, and an application roll positioned opposite, with a small clearance between them, a doctor roll that is located at the end of the plurality of transfer rolls where the supply of the solvent-free adhesive starts; and the peripheral speed of the doctor roll is 1.0 to 10.0 m / min.

2. The method for producing a laminated film according to claim 1, wherein the size of the clearance is 40 to 100 μm.

3. The method for producing a laminated film according to claim 1 or 2, characterized in that the peripheral speed of the application roll is 0 to 0.1 m / min.

4. The method for producing a laminated film according to any one of claims 1 to 3, characterized in that the viscosity of the main agent of the solvent-free adhesive is 600 to 1800 mPa·s at 50°C.

5. In the adhesive coating layer, the coating amount of the solvent-free adhesive is 0.5 to 3.0 g / m 2 5. The method for producing a laminated film according to claim 1, wherein 6. A laminated film produced by the method of any one of claims 1 to 5.

7. A packaging container formed from the laminated film according to claim 6.

8. The packaging container according to claim 7, which is a food packaging container that contains food therein and undergoes a heat treatment in a sealed state.