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

Abstract

To provide a manufacturing method of layer film, that can reduce an environmental load and prevent air bubbles from being formed in an adhesive layer, and to provide layer film and a packaging container.SOLUTION: In a manufacturing method of layer film, viscosity of a solventless type adhesive is 700-2000 mPa s at 50°C, and a coating apparatus includes: a pair of rolls; and a coating unit having a plurality of transfer rolls for sequentially transferring and supplying the solventless type adhesive, and an application roll which is arranged opposite to a doctor roll positioned at a supply start side end of the solventless type adhesive out of the plurality of transfer rolls, via a fine clearance. In the manufacturing method of layer film, circumferential speed of the doctor roll is 1.0-10.0 m / min.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a laminated film by laminating raw material films using a solvent-free adhesive to obtain a laminated film, the laminated film obtained thereby, and a packaging container formed by this laminated film.

Background Art

[0002] Pouch packaging containers used for food packaging and flexible packaging containers used for cup lids are conventionally composed of a laminated film in which a plurality of raw material films such as resin films are laminated. In such a packaging container, when resin films of different types with different properties are laminated, such as a combination of a nylon film and a polyethylene film, the adhesion between the two is poor, so they are generally attached with an adhesive for lamination.

[0003] From the perspective of reducing the environmental load on the earth, it is desired to use a solvent-free adhesive that does not contain an organic solvent and can be applied by heating the adhesive to lower its viscosity. For example, as a laminated film using a conventional solvent-free adhesive, there is known a laminated film having an adhesive layer composed of a main agent made of polyester polyol and a curing agent made of an aliphatic diisocyanate compound and an alicyclic diisocyanate, and having a viscosity at 70°C of 300 to 900 mPa·s (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in laminated films using solvent-free adhesives, large air bubbles tend to form in the adhesive layer, which causes a defect in appearance, resulting in numerous tiny, spot-like bumps and irregularities on the laminated film, often referred to as "orange peel." This orange peel is particularly pronounced when the laminated film is subjected to heat treatment. On the other hand, packaging containers used in the food sector that utilize laminated films are often heat-treated for sterilization and other purposes necessary for food preservation. As a result, there is an aesthetic problem in that heat-treated food packaging containers develop a pear-shaped surface. Furthermore, as mentioned above, since the cause of the pear-shaped surface is air bubbles in the adhesive layer, it can be assumed that there are gaps in the adhesive layer, which raises concerns about the shelf life of the food contained inside.

[0006] The present invention has been made based on the circumstances described above, and its purpose is to provide a method for manufacturing a laminated film, a laminated film, and a packaging container that can reduce the environmental burden and suppress the formation of air bubbles in the adhesive layer. [Means for solving the problem]

[0007] The present invention relates to a method for manufacturing a laminated film, comprising the steps of: applying a solvent-free adhesive to one film passing between the rolls in a coating apparatus equipped with a pair of opposing rolls; and laminating the other film by overlapping it with an adhesive coating layer made of the solvent-free adhesive, The aforementioned solvent-free adhesive comprises a main component made of a polyester resin and a curing agent consisting solely of a mixture of aliphatic isocyanates and aromatic aliphatic diisocyanates. The viscosity of the solvent-free adhesive is 700 to 2000 mPa·s at 50°C. The coating apparatus further comprises a coating unit having the pair of rolls, a plurality of transfer rolls that sequentially transfer and supply a solvent-free adhesive to one of the pair of rolls, and an application roll positioned opposite the doctor roll located at the starting end of the supply of the solvent-free adhesive among the plurality of transfer rolls, with a small clearance between them. A storage section for storing the solvent-free adhesive is formed in the upper part of the clearance between the doctor roll and the application roll. The temperature of the solvent-free adhesive in the storage section is in the range of 40 to 50°C. The doctor roll is characterized by having a peripheral speed of 1.0 to 10.0 m / min.

[0008] Furthermore, the laminated film of the present invention is characterized by being manufactured by the above-described manufacturing method. Furthermore, the packaging container of the present invention is characterized by being formed from the above-mentioned laminated film. [Effects of the Invention]

[0009] According to the method for manufacturing a laminated film of the present invention, by forming an adhesive layer using a solvent-free adhesive having specific components and viscosity in combination with a coating apparatus having a specific coating unit, a clearance is maintained between the doctor roll and the application roll of the coating unit, and because the doctor roll operates at a low speed, excessive mixing of the solvent-free adhesive stored between these rolls does not occur. As a result, air entrapment due to air encompass in the solvent-free adhesive can be suppressed, and therefore, the formation of air bubbles in the adhesive coating layer formed on the film by this transfer can be suppressed. Consequently, it is possible to prevent the occurrence of appearance defects such as orange peel on the resulting laminated film and packaging container, and to obtain stable storage of contents in the packaging container. Furthermore, since the solvent-free adhesive does not use organic solvents, it is possible to reduce the environmental impact. [Brief explanation of the drawing]

[0010] [Figure 1]This is an explanatory diagram showing the configuration of an example of a laminator for manufacturing the laminated film of the present invention. [Figure 2] This is an explanatory cross-sectional view showing the configuration of an example of the laminated film of the present invention. [Modes for carrying out the invention]

[0011] The embodiments of the present invention will be described in detail below. [Method for manufacturing laminated film] The present invention provides a method for manufacturing a laminated film, as shown in Figure 1, which involves laminating a pair of long films W1 and W2 together with a solvent-free adhesive while transporting them at high speed using a laminator 10. The method includes the step of applying a solvent-free adhesive, which has two liquid components (main agent and curing agent) pre-mixed, to one film W1 using a coating device 20, and then laminating the other film W2 over it with an adhesive coating layer made of the solvent-free adhesive.

[0012] The laminator 10 includes a coating device 20 for applying a solvent-free adhesive to one film W1, an unwinding roll 11 for supplying the 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 and 12b for laminating the other film W2 onto the film W1 with the adhesive coating layer formed on it, an unwinding roll 13 for supplying the other film W2, and a winding roll 14 for winding up the laminate of films W1 and W2. The coating apparatus 20 includes a coating unit 21 that sequentially transfers a mixed solvent-free adhesive onto one of the films W1 using multiple rolls, applying it while spreading it thinly, and a supply unit 25 that supplies the solvent-free adhesive to the coating unit 21.

[0013] The coating unit 21 has a plurality of rolls 21a to 21e (five in the illustrated example) that are rotatably supported and arranged in series parallel to each other by their axes. Specifically, the coating unit 21 has a backup roll 21a and a coating roll 21b, which are a pair of rolls that face each other and through which the film W1 passes; a metering roll 21c and a doctor roll 21d, which are transfer rolls that sequentially transfer and supply a solvent-free adhesive to one of the pair of rolls (the coating roll 21b); and an application roll 21e, which is positioned adjacent to and facing the doctor roll 21d, which is located at the beginning end of the transfer roll for supplying the solvent-free adhesive, with a small clearance (gap) between them along the horizontal direction. The backup roll 21a, coating roll 21b, metering roll 21c, and doctor roll 21d are arranged in series in this order with their outer surfaces in contact with each other. The film W1 to which the solvent-free adhesive is applied is sandwiched between the coating roll 21b, located at the end of the supply of the solvent-free adhesive, and the backup roll 21a, which presses against it. A storage section 22 is formed between the doctor roll 21d, located at the beginning of the supply of the solvent-free adhesive, and the application roll 21e, in the upper part of the clearance between the two rolls 21d and 21e, to temporarily store the mixed main agent and hardener. The storage section 22 is formed by partitioning a space with a roughly V-shaped cross-section due to the clearance by a pair of weir plates (not shown) that are 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 made of metal rolls, with at least their outer surfaces being made of metal, while the backup roll 21a and metering roll 21c are made of elastic rolls, with their outer surfaces being made of an elastic material such as rubber. In other words, in the coating unit 21, elastic rolls and metal rolls are arranged alternately from the backup roll 21a to the doctor roll 21d, thereby allowing two adjacent elastic rolls and metal rolls to be pressed against each other. The backup roll 21a, doctor roll 21d arranged in sequence are rotationally controlled such that the outer peripheral surfaces of each adjacent two rolls rotate in the same direction at the pressure contact part, that is, rotate in opposite directions to each other, with the two adjacent rolls being in pressure contact with each other. The doctor roll 21d is rotationally controlled such that the outer peripheral surface forming the storage part 22 moves downward.

[0015] The application roll 21e and the doctor roll 21d are provided with a temperature control device (not shown) for maintaining the solvent-free adhesive stored in the storage part 22 at a constant temperature. Also, the coating roll 21b is provided with a temperature control device (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, set to 1.0 to 10.0 m / min, and the application roll 21e is either not rotated or, even if rotated, its peripheral speed is, for example, 0.1 m / min or less. Also, 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, that is, the viscosity of the solvent-free adhesive stored in the storage part 22, but is preferably set within the range of 40 to 100 μm, more preferably 60 to 80 μm. When the clearance between the doctor roll 21d and the application roll 21e is excessively small, the variation in the coating amount of the solvent-free adhesive in the roll width direction becomes large, and there is a risk that a stable and uniform adhesive coating layer cannot be formed. When the clearance is excessively large, there is a risk that dripping of the solvent-free adhesive from the storage part 22 will occur. When the clearance between the doctor roll 21d and the application roll 21e is within the above range, and the doctor roll 21d rotates at the above circumferential speed while the application roll 21e is stopped from rotating, excessive mixing of the solvent-free adhesive in the storage portion 22 is suppressed. Therefore, entrainment of air due to air entrained in the solvent-free adhesive can be extremely suppressed, and generation of bubbles in the adhesive coating layer formed on the film W1 by being transferred by the coating unit 21 can be suppressed.

[0017] Also, the circumferential speeds (speeds of the pressure contact portions) of the backup roll 21a and the coating roll 21b are the same as the supply speed of the film W1, and the circumferential speed of the metering roll 21c is set to a value between the circumferential speed of the adjacent coating roll 21b and the circumferential speed of the doctor roll 21d because poor appearance occurs when the circumferential speeds between adjacent rolls are significantly different.

[0018] As an example of the dimensions of the application roll 21e and the doctor roll 21d, for example, the outer diameter can be 100 mm to 300 mm, and the width of the coating surface constituting the storage portion 22 can be about 600 mm to 1800 mm. The outer diameters of the application roll 21e and the doctor roll 21d may be different from each other.

[0019] The supply unit 25 includes a main agent tank 26 that stores the main agent, a curing agent tank 27 that stores the curing agent, and an adhesive supply unit 28 that supplies the main agent and the curing agent, and may further have a mixer (not shown) that stirs the solvent-free adhesive stored in the storage portion 22.

[0020] In this laminator 10, one film W1 is transported from the unwinding roll 11 at a predetermined speed between a pair of rolls 21a and 21b of the coating device 20 (between the backup roll 21a and the coating roll 21b). Meanwhile, in the supply unit 25, the main agent and hardener are heated to a predetermined temperature in the main agent tank 26 and the hardener tank 27. The heated main agent and hardener are then supplied from the adhesive supply unit 28 in predetermined amounts, mixed in the static mixer 29, to the storage unit 22 between the doctor roll 21d and the application roll 21e. Here, the solvent-free adhesive is continuously supplied from the supply unit 25 to the storage unit 22 so that the liquid level in the storage unit 22 is kept constant. Then, the solvent-free adhesive is sequentially transferred from the doctor roll 21d located at the supply start end of the coating unit 21, through the metering roll 21c, to the coating roll 21b located at the supply end end, and applied from the coating roll 21b to the surface of one of the films W1 passing between the pair of rolls 21a and 21b, thereby forming an adhesive coating layer. Next, the film W1 with the adhesive coating layer is sent to the laminating section 12. Meanwhile, the other film W2 is supplied to the laminating section 12 from the unwinding roll 13. In the laminating section 12, the two films W1 and W2 are overlapped so that the adhesive coating layer on the surface of the first film W1 is in contact with the adhesive coating layer of the second film W2, and are pressed together by a pair of pressure rolls 12a and 12b to bond them, thereby obtaining an intermediate laminated film in which the pair of films W1 and W2 are laminated. This intermediate laminated film is wound onto the winding roll 14. The intermediate laminated film wound onto the winding roll 14 is then subjected to an aging treatment in which it is left to stand at room temperature or under heating, causing the adhesive coating layer to harden and an adhesive layer to form, thereby obtaining a laminated film in which the pair of films W1 and W2 are bonded together by the adhesive layer. If the laminated film is, for example, made up of three or more films laminated with an adhesive layer in between, then by performing the above lamination process to bond two films together, and then repeating the same lamination process, a laminated film can be obtained in which three or more films are bonded together with an adhesive layer of solvent-free adhesive.

[0021] In the above, the heating temperature of the main agent and curing agent, and the temperature of the solvent-free adhesive in the storage section 22 are preferably in the range of 40 to 80°C, and particularly preferably in the range of 40 to 50°C. Furthermore, the coating temperature of the solvent-free adhesive on one of the films W1 is preferably in the range of 40 to 80°C, and particularly preferably in the range of 60 to 80°C. These temperatures can be controlled by setting the temperature of each roll 21a to 21e of the coating unit 21, and by setting the temperature of the main agent tank 26 and the curing agent tank 27. If the coating temperature is within the above range, the viscosity of the solvent-free adhesive can be kept sufficiently low for practical use while minimizing thermal damage to one of the films W1. Furthermore, the temperature of the pressure rolls 12a and 12b in the laminate section 12 is, for example, 30 to 80°C. Furthermore, the supply speed of each film W1 and W2, i.e., the application speed of the solvent-free adhesive, is preferably 100 to 200 m / min. The application rate for solvent-free adhesives is 0.5 to 3.0 g / m². 2 Preferably, it is 1.2 to 2.6 g / m². 2 If the amount of solvent-free adhesive applied is insufficient, adequate adhesion cannot be obtained. On the other hand, if the amount of solvent-free adhesive applied is excessive, there is a risk of misalignment of the laminated film during winding, or leakage of the solvent-free adhesive from the edges of the laminated film, resulting in poor quality. The aging temperature of the intermediate laminated film wound by the winding roll 14 is, for example, 30 to 70°C, and the processing time is, for example, 48 to 96 hours. In the laminator 10, other coating conditions can be set as appropriate.

[0022] [Laminated film] The laminated film of the present invention is obtained by the above manufacturing method, and for example, as shown in Figure 2, it 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-deposited 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 by the laminator 10 with a solvent-free adhesive is formed between the ink layer 34 and the intermediate layer resin film 33, and an adhesive layer 37 formed by the laminator 10 with a solvent-free adhesive is formed between the inner layer resin film 32 and the intermediate layer resin film 33. In other words, this laminated film 30 is obtained by repeating the above manufacturing method twice, using the outer layer resin film 31 with the vapor-deposited layer 35 and the ink layer 34, the intermediate layer resin film 33, and the inner layer resin film 32 as three raw material films.

[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 treatment at a temperature of about 80°C after, for example, gravure printing on the outer layer resin film 31, thus facilitating the formation of the ink layer. Furthermore, it is preferable to use a biaxially oriented film as the outer layer resin film 31 in order to obtain high tensile strength.

[0024] It is preferable to use a polyamide resin or a polyester resin as the material constituting the outer layer resin film 31. 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). Furthermore, copolyesters containing other polyester units can be used, provided that the properties of these resins are not impaired. Among the copolymerization components for forming such copolyesters, dicarboxylic acid components can include isophthalic acid, p-β-oxyethoxybenzoic acid, naphthalene 2,6-dicarboxylic acid, diphenoxyethane-4,4′-dicarboxylic acid, 5-sodium sulfisoisophthalic acid, adipic acid, sebacic acid, or alkyl ester derivatives thereof. Glycol components can include propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexylene glycol, cyclohexanedimethanol, ethylene oxide adducts of bisphenol A, diethylene glycol, and triethylene glycol. These compounds can be used individually or in combination of two or more as copolymerization components.

[0025] The thickness of the outer resin film 31 is appropriately selected depending on the type of resin constituting the outer resin film 31 and the application of the laminated film. For example, when the outer resin film 31 is made of nylon, it is preferably 10 to 30 μm thick, and when the outer resin film 31 is made of polyethylene terephthalate (PET), it is preferably 6 to 28 μm thick.

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

[0027] As the material constituting the inner layer resin film 32, it is preferable to use a resin with excellent heat-sealing properties for forming pouch packaging bags and heat-seal lids. Examples of such resins include polyolefin resins such as polyethylene (PE) and polypropylene (PP).

[0028] There are no particular restrictions on the thickness of the inner layer resin film 32, but for example, if the inner layer resin film 32 is made of polyethylene, it is preferably 50 to 200 μm thick, and if the inner layer resin film 32 is made of polypropylene, it is preferably 30 to 150 μm thick. Furthermore, it is preferable to use an unstretched film as the inner layer resin film 32.

[0029] As the material constituting the intermediate layer resin film 33, a resin having gas barrier properties can be used. Specific examples include 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 resins. Furthermore, the materials constituting the intermediate layer resin film 33 may include olefin resins such as polyethylene (PE) including low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), linear ultra-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), ion-crosslinked olefin copolymer (ionomer), or mixtures 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 a vapor-deposited layer 35 formed on an outer resin film 31. The thickness of such an ink layer 34 is preferably 1 to 8 μm.

[0031] The materials that make up the vapor-deposited layer 35 can be metallic materials such as aluminum, or non-metallic inorganic materials such as silica.

[0032] The adhesive layers 36 and 37 are formed with a specific solvent-free adhesive, which is detailed below. This solvent-free adhesive is a two-component, reaction-curing adhesive consisting of a main component and a curing agent. The thickness of the adhesive layers 36 and 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 resin that has good adhesion to the inner layer resin film 32, the intermediate layer resin film 33, and the ink layer 34, and also has excellent lamination strength and impact resistance, with polyester polyol resin being particularly preferred.

[0034] Polyester polyol resins can be produced by esterification reactions of polybasic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, and terephthalic acid with polyhydric alcohols 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, and 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] Furthermore, the main component may contain, for example, a polyurethane compound in addition to a polyester resin. By using such a main component, 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 main component is preferably 400 to 1500, and more preferably 500 to 1000. If the number-average molecular weight of the resin constituting the main component is less than 400, the viscosity of the solvent-free adhesive decreases, which can lead to poor continuous lamination suitability when manufacturing the laminated film. In addition, the number of terminal reactive groups increases, requiring a larger amount of curing agent. As a result, the resulting adhesive layers 36 and 37 may have a high crosslinking rate, increasing hardness and potentially reducing the impact resistance of the adhesive layers 36 and 37. On the other hand, if the number-average molecular weight of the resin constituting the main component exceeds 1500, the impact resistance of the resulting adhesive layers 36 and 37 improves, but the viscosity of the solvent-free adhesive increases, which can lead to poor wetting during the application of the solvent-free adhesive, resulting in poor appearance and reduced lamination strength of the resulting laminated film 30.

[0038] The viscosity of the main component is preferably 600 to 1800 mPa·s at 50°C, and more preferably 1000 to 1400 mPa·s. If the viscosity of the main component is less than 600 mPa·s, uneven transfer of the roll occurs, making the film formation of the adhesive layers 36 and 37 unstable, which can result in poor appearance of the resulting laminated film 30 and a drastic decrease in laminate strength. On the other hand, if the viscosity of the main component exceeds 1800 mPa·s, poor wetting is likely to occur during the application of the solvent-free adhesive, which can result in poor appearance of the resulting laminated film 30 and a decrease in laminate strength.

[0039] As a curing agent for solvent-free adhesives, it is preferable to use an isocyanate compound, particularly a mixture of aliphatic isocyanates and aromatic aliphatic diisocyanates. As the aliphatic isocyanates constituting the curing agent, butane-1,4-diisocyanate, 1,6-hexamethylene diisocyanate (HDI), isopropyl diisocyanate, methylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, m-tetramethylxylylene diisocyanate, lysine diisocyanate, and dimer isocyanate (in which the carboxyl group of a dimer acid is converted to an isocyanate group) can be used individually or in combination of two or more. Among these, 1,6-hexamethylene diisocyanate (HDI) is preferred. Examples of aromatic aliphatic diisocyanates that constitute the curing agent include 1,3-xylylenediisocyanate or 1,4-xylylenediisocyanate or a mixture thereof (XDI), 1,3-tetramethylxylylenediisocyanate or 1,4-tetramethylxylylenediisocyanate or a mixture thereof (TMXDI), and ω,ω′-diisocyanate-1,4-diethylbenzene.

[0040] The number-average molecular weight of the resin constituting the curing agent is preferably 400 to 1500, and 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 solvent-free adhesive decreases, which can lead to poor continuous lamination suitability when manufacturing the laminated film. In addition, the number of terminal reactive groups increases, requiring a larger amount of the main agent. As a result, the resulting adhesive layers 36 and 37 may have a high crosslinking rate, increasing hardness and potentially reducing the impact resistance of the adhesive layers 36 and 37. 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 and 37 improves, but the viscosity of the solvent-free adhesive increases, which can lead to poor wetting during the application of the solvent-free adhesive, resulting in poor appearance and reduced lamination strength of the resulting laminated film 30.

[0041] 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. If the viscosity of the curing agent is less than 150 mPa·s, the resulting adhesive layers 36 and 37 will be soft, resulting in low laminate strength. On the other hand, if the viscosity of the curing agent exceeds 1300 mPa·s, the resulting adhesive layers 36 and 37 will be hard, resulting in poor impact resistance.

[0042] In solvent-free adhesives, it is preferable that the curing agent is contained in an amount of 30 to 200 parts by mass, particularly 30 to 70 parts by mass, per 100 parts by mass of the main component. If the proportion of curing agent is too low, the resulting adhesive layers 36 and 37 will be under-crosslinked, which may reduce the lamination strength of the resulting laminated film 30. On the other hand, if the proportion of curing agent is too high, the main component and curing agent will not be sufficiently mixed, and the resulting adhesive layers 36 and 37 will contain areas with under-crosslinking and areas with excessive crosslinking, which may reduce the lamination strength and impact resistance of the resulting laminated film 30.

[0043] In the present invention, the viscosity of the solvent-free adhesive is 700 to 2000 mPa·s at 50°C, more preferably 1000 to 1600 mPa·s. If the viscosity of the solvent-free adhesive is less than 700 mPa·s, dripping of the solvent-free adhesive from the storage section 22 may occur, and transfer defects between rolls may occur during the application of the solvent-free adhesive, resulting in "uneven transfer." In addition, because the solvent-free adhesive is not applied uniformly and is partially reduced, a decrease in laminate strength and impact resistance may occur. On the other hand, if the viscosity of the solvent-free adhesive exceeds 2000 mPa·s, "poor wetting" may occur during the application of the solvent-free adhesive, and the resulting adhesive layers 36 and 37 may become partially thin. If thin areas exist in the adhesive layers 36 and 37, a decrease in laminate strength and impact resistance may occur.

[0044] In addition to the main agent and curing agent described above, solvent-free adhesives may also contain polyurethane compounds. The inclusion of polyurethane compounds ensures adhesion to the ink layer 34, as the ink layer 34 typically contains urethane components. Furthermore, solvent-free adhesives may 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 pot life extenders.

[0045] Furthermore, solvent-free adhesives may contain adhesion promoters. Examples of adhesion promoters include silane coupling agents, titanate coupling agents, aluminum-based coupling agents, epoxy resins, and the like.

[0046] Specific examples of silane coupling agents 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; and hexamethyldisilazane and γ-mercaptopropyltrimethoxysilane.

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

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

[0049] Specific examples of epoxy resins include various commercially available epoxy resins such as epibis type, novolac type, β-methylepiclo 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 can be suitably used as a food packaging container, such as a retort pouch, in which food is contained inside, sealed, and subjected to heat treatment. Heat treatment of food packaging containers refers to processes that involve heating to 100°C or higher, and includes sterilization processes that involve heating, which are commonly performed on food packaging containers. Examples include retort sterilization, which enables distribution at room temperature, and heat treatment at 120°C for less than 4 minutes, which enables chilled distribution. However, it is not limited to these and refers to various known heat treatments for food products. Retort sterilization refers to pressurized heat treatment, which involves heating products filled in heat-resistant containers with steam or hot water at around 110°C to 130°C for several tens of minutes while pressurizing the container to prevent damage from the internal pressure of the product as the temperature rises, so that the F0 value is 3.1 minutes or more, which is equivalent to at least 120°C for 4 minutes. Heat sterilization that enables chilled distribution refers to heat treatment equivalent to 90°C for 10 minutes or more, which is commonly used.

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

[0052] The following describes examples of the present invention, 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 viscosity of the main component, curing agent, and solvent-free adhesive was measured using a TOKIMEC B8L viscometer in accordance with JIS K7117-2.

[0054] [Resin film] As the outer layer resin film, a biaxially oriented polyethylene terephthalate (PET) film with a thickness of 12 μm and an alumina vapor-deposited film formed on one surface was used. A biaxially oriented nylon film with a thickness of 15 μm was used as the intermediate resin film. As the inner layer film, an unoriented polypropylene (CPP) film with a thickness of 70 μm was used.

[0055] [Manufacturing of laminated films] A laminated film was manufactured using a laminator with the configuration shown in Figure 1, as described below. The main component and hardener shown in Table 1 below were placed in the main component tank and hardener tank, respectively, and heated to 50°C. The main component and hardener were then supplied to the adhesive application section via the adhesive supply section in the mass mixing ratio shown in Table 1 below and mixed to prepare a solvent-free adhesive. Then, in the adhesive application section, the solvent-free adhesive was applied at 80°C to one side of the outer layer resin film supplied from the unwinding roll to form an adhesive coating layer. The amount of solvent-free adhesive applied was 1.7 g / m². 2The coating speed was 150 m / min. Subsequently, the outer layer resin film with the adhesive coating layer formed on it was transported to the laminating section, where the outer layer resin film and the intermediate layer resin film with the vapor-deposited layer formed on it, supplied from the unwinding roll, were laminated under pressure at 50°C to produce the first intermediate laminated film. The lamination speed was 150 m / min. The obtained first intermediate laminated film was wound onto a roll, and an adhesive coating layer was formed on the other side of the intermediate resin film of the first intermediate laminated film under the same conditions as above. An intermediate laminated film was then manufactured by laminating this intermediate resin film with the inner resin film. The obtained intermediate laminated film was subjected to an aging treatment by being held at 40°C for 3 days, thereby manufacturing a laminated film.

[0056] [Production of packaging containers (pouches)] Two pieces were cut from the obtained laminated film to a width of 130 mm and a height of 175 mm. The two laminated films, with their inner layers joined together, were heat-sealed at 200°C to seal the bottom and both sides, creating 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 contents 180g), sealed by heat sealing, and then subjected to hot water pressurized sterilization shower cooling (sterilization temperature 127°C, sterilization time 30 minutes, sterilization pressure 0.3MPa).

[0057] [Evaluation of cosmetic defects] The appearance of the packaging containers before and after hot water pressurized sterilization shower cooling (heat sterilization treatment) was visually observed in an area of ​​1 m in width and 1 m in length to check for the presence or absence of a spotted, minute uneven pattern (orange peel texture). The containers were evaluated as ○ if no spotted, minute uneven pattern was observed and × if it was observed. The results are shown in Table 1 below.

[0058] [Table 1]

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

[0060] 10 Laminators 11 unwinding roll 12 Laminated section 12a, 12b Pressure Roll 13 unwinding roll 14. Reel roll 20 Coating equipment 21 Coating Unit 21a Backup role 21b Coating Roll 21c Metaling Roll 21d Doctor Roll 21e Application Roles 22 Storage section 25 supply units 26 Main agent tank 27 Hardener Tank 28 Adhesive supply unit 29 Static Mixer 30-layer film 31 Outer layer resin film 32 Inner layer resin film 33 Intermediate layer resin film 34 Ink Layers 35 Deposited 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 the rolls in a coating apparatus having a pair of opposing rolls, and laminating the other film by overlapping it with an adhesive coating layer made of the solvent-free adhesive, The aforementioned solvent-free adhesive comprises a main component made of a polyester resin and a curing agent consisting solely of a mixture of aliphatic isocyanates and aromatic aliphatic diisocyanates. The viscosity of the solvent-free adhesive is 700 to 2000 mPa·s at 50°C. The coating apparatus further comprises a coating unit having the pair of rolls, a plurality of transfer rolls that sequentially transfer and supply a solvent-free adhesive to one of the pair of rolls, and an application roll positioned opposite the doctor roll located at the starting end of the supply of the solvent-free adhesive among the plurality of transfer rolls, with a small clearance between them. A storage section for storing the solvent-free adhesive is formed in the upper part of the clearance between the doctor roll and the application roll. The temperature of the solvent-free adhesive in the storage section is in the range of 40 to 50°C. A method for manufacturing a laminated film, characterized in that the peripheral speed of the doctor roll is 1.0 to 10.0 m / min.

2. The method for manufacturing a laminated film according to claim 1, characterized in that the size of the clearance is 40 to 100 μm.

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

5. In the adhesive coating layer, the amount of solvent-free adhesive applied is 0.5 to 3.0 g / m². 2 A method for manufacturing a laminated film according to any one of claims 1 to 4, characterized in that...

6. A laminated film characterized by being manufactured by the manufacturing method described in any one of claims 1 to 5.

7. A packaging container characterized by being formed by the laminated film described in claim 6.

8. The packaging container according to claim 7, characterized in that it is a food packaging container that contains food inside and is subjected to heat treatment in a sealed state.

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