Easy-to-bond polyamide film

Abstract

To provide an easily adhesive polyamide film which is excellent in impact resistance, bending pinhole resistance, and friction pinhole resistance, has a reduced amount of deteriorated matter attached to a die slip outlet during production, also has reduced thickness spots, and is excellent in water-resistant adhesive strength to a sealant film.SOLUTION: An easily adhesive polyamide film has an adhesive modified layer (C layer) composed of any one resin of a polyester resin, a polyurethane resin and / or a polyacrylic resin as solid contents in a coating amount of 0.01-3 g / m2, on at least one surface of a laminated and stretched polyamide film formed by stacking surface layers (B layers) composed of a polyamide resin composition containing 99-100 mass% of a polyamide 6 resin as a polyamide-based resin and less than 1 mass% of a polyamide-based elastomer on both surfaces of a base material layer (A layer) composed of a polyamide resin composition containing a mixed resin of 97.5-80 mass% of a polyamide 6 resin and 2.5-20 mass% of a polyamide-based elastomer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laminated biaxially stretched polyamide film that is excellent in impact resistance, bending pinhole resistance, and friction pinhole resistance, has few thickness irregularities, and also has excellent water-resistant adhesion strength to a sealant film. The easily adhesive polyamide film of the present invention is suitably used for films for food packaging and the like.

Background Art

[0002] Conventionally, biaxially stretched films made of aliphatic polyamides typified by nylon 6 have been excellent in impact resistance and pinhole resistance and have been widely used as various packaging material films.

[0003] Also, for liquid-filled packaging such as soups and seasonings, in order to further improve pinhole resistance and impact resistance, biaxially stretched polyamide films in which various elastomers (rubber components) are mixed with aliphatic polyamides to make them more flexible and improve pinhole resistance have been widely used.

[0004] As a means for improving the above-mentioned pinhole resistance, a film in which a polyamide-based elastomer is mixed with an aliphatic polyamide is known (see, for example, Patent Document 1). This film has good pinhole resistance and impact resistance in a low-temperature environment, and pinholes due to bending fatigue are less likely to occur even in a low-temperature environment.

[0005] However, pinholes are generated not only by bending but also by friction (rubbing). In many cases, the methods for improving pinholes due to bending and pinholes due to friction are contradictory. For example, when the flexibility of the film is increased, bending pinholes are less likely to occur, but the tendency is that pinholes due to friction are more likely to occur as the film becomes softer. On the other hand, by providing a surface coating agent on the outer surface of the biaxially stretched polyamide film, a laminate for packaging excellent in bending resistance and friction pinhole resistance has been proposed (see, for example, Patent Document 2). However, this method has little effect of preventing the generation of friction pinholes. In addition, a coating process is required. Furthermore, in the case of a film obtained by mixing an aliphatic polyamide with a polyamide-based elastomer, since the polyamide-based elastomer added during film production undergoes thermal degradation, it is likely to generate a deteriorated product called "eye lacquer" at the die lip outlet. And it has been found that the deteriorated product causes deterioration of the film thickness accuracy. In addition, the deteriorated product itself falls to produce defective products, and there is a problem of reducing the production efficiency during continuous film production.

[0006] In addition, when a film obtained by laminating a polyamide film with a sealant film is used for a liquid soup bag or a bag for pickled foods, it is required that the adhesive strength between the laminated films (also referred to as the lamination strength) is sufficiently high.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide an easily adhesive polyamide film that is excellent in impact resistance, flexural pinhole resistance, and friction pinhole resistance, and also excellent in water-resistant adhesive strength with a sealant film. Further, an easily adhesive polyamide film is provided that generates less "eye lacquer" (deteriorated product generated at the die lip outlet) during film production, has excellent operability, and further has less film thickness unevenness.

Means for Solving the Problems

[0009] That is, the present invention has the following configuration. (1) A base material layer (layer A) made of a polyamide resin composition containing a mixed resin of 97.5 to 80% by mass of polyamide 6 resin and 2.5 to 20% by mass of a polyamide-based elastomer, on both surfaces of which there is laminated a surface layer (layer B) made of a polyamide resin composition containing 100 to 80% by mass of polyamide 6 resin, less than 1% by mass of a polyamide-based elastomer, and 0 to 20% by mass of a polyamide resin other than polyamide 6 and the polyamide-based elastomer. At least one side of the laminated and stretched polyamide film has an adhesion-improving layer (layer C) made of any one of a polyester resin, a polyurethane resin, and / or a polyacrylic resin, with a coating amount of 0.01 to 3 g / m² as a solid content. 2 An easily adherable polyamide film, characterized by having the above. (2) The easily adherable polyamide film according to (1), characterized in that the impact strength is 0.75 J / 15 μm or more, the number of gelbo pinholes when a torsional bending test using a gelbo flex tester is carried out 1000 times at a temperature of 1°C is 5 or less, and the distance until pinholes occur in the friction resistance pinhole test is 3000 cm or more. (3) The easily adherable polyamide film according to (1) or (2), characterized in that the thickness of the layer B is at least 0.5 μm or more. (4) The easily adherable polyamide film according to any one of (1) to (3), characterized in that the polyamide resin composition constituting the layer B contains 0.01 to 0.3% by mass of an antioxidant.

Advantages of the Invention

[0010] The easily adherable polyamide film of the present invention exhibits impact resistance, puncture resistance, and pinhole resistance by dispersing a polyamide-based elastomer in a polyamide 6 resin with the polyamide 6 resin as the main component in the base material layer (layer A). In particular, it gives excellent flexural pinhole resistance in a low-temperature environment. And a surface layer (layer B) made of a polyamide resin composition containing 100 to 80% by mass or more of polyamide 6 resin, less than 1% of a polyamide-based elastomer, and 0 to 20% by mass of a polyamide resin other than polyamide 6 and the polyamide-based elastomer has friction resistance pinholes. By improving the lubricity and avoiding the contact of the polyamide - based elastomer with the die surface inside the die, the adhesion of deteriorated substances to the inner surface of the die and the adhesion of eye varnish to the die lip outlet can be suppressed over a long period of time. Thereby, the deterioration of the film thickness unevenness can be prevented. Also, when the film thickness unevenness deteriorates due to the adhesion of deteriorated substances to the inner surface of the die or the adhesion of eye varnish to the die lip outlet, it is necessary to stop production and clean the die lip. The easily - adherable polyamide film of the present invention can enable continuous production over a long period of time. Further, on at least one side of a laminated and stretched polyamide film composed of a base material layer (A layer) and a surface layer (B layer), an adhesion - modified layer (C layer) composed of any one of a polyester resin, a polyurethane resin, and / or a polyacrylic resin with a solid content coating amount of 0.01 - 3 g / m 2 is laminated. When used for a liquid soup bag or a bag for pickled foods by laminating with a sealant film, since the adhesive strength between the laminated films (also referred to as the lamination strength) is high, a packaging bag with less bag breakage can be provided.

Brief Description of the Drawings

[0011]

Figure 1

Explanation of Reference Numerals

[0012] 1: Head part of the fastness tester 2: Corrugated cardboard 3: Mounting board for sample holding 4: Four - folded film sample 5: Rubbing amplitude direction

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the easily - adherable polyamide film of the present invention will be described in detail. The easily - adherable polyamide film of the present invention is formed by laminating an adhesion - modified layer (C layer) on at least one side of a laminated and stretched polyamide film in which a surface layer (B layer) made of a specific polyamide resin composition is laminated on both surfaces of a base material layer (A layer) made of a specific polyamide resin composition.

[0014] <Base material layer (A layer)> The base material layer (A layer) in the present invention is a polyamide resin composition containing 97.5 to 80% by mass of polyamide 6 resin and 2.5 to 20% by mass of a polyamide-based elastomer. By containing 2.5 to 20% by mass of the polyamide-based elastomer in the base material layer (A layer) in the present invention, it has a structure in which the polyamide-based elastomer as a pinhole-resistant material is dispersed, and a laminated and stretched polyamide film with excellent flexural pinhole resistance, particularly excellent flexural pinhole resistance under low-temperature environments, can be obtained. By the content of the polyamide 6 resin in the base material layer (A layer) in the present invention being 97.5 to 80% by mass, a laminated and stretched polyamide film with good mechanical strength such as impact strength can be obtained.

[0015] Examples of the polyamide-based elastomer used for the base material layer (A layer) in the present invention include polyamide-based block copolymers composed of a hard segment composed of a polyamide component and a soft segment composed of a polyoxyalkylene glycol component. The polyamide component of the hard segment is selected from the group consisting of (1) lactam, (2) aminoaliphatic carboxylic acid, (3) aliphatic diamine and aliphatic dicarboxylic acid, or (4) aliphatic diamine and aromatic dicarboxylic acid. Specifically, examples thereof include (1) ω-lauryl lactam, ε-caprolactam, (2) aminoheptanoic acid, (3) hexamethylenediamine, nonanediamine and adipic acid, sebacic acid, (4) hexamethylenediamine, nonanediamine and terephthalic acid, isophthalic acid. In addition, examples of the polyoxyalkylene glycol constituting the soft segment of the polyamide-based block copolymer include polyoxytetramethylene glycol, polyoxyethylene glycol, polyoxy-1,2-propylene glycol, etc. Particularly, a polyamide elastomer in which the hard segment is polyamide 6 or polyamide 12 and the soft segment is polyoxytetramethylene glycol is preferable because it has a high effect of improving flexural pinhole resistance.

[0016] The melting point of the polyamide-based elastomer in the present invention is determined by the types and ratios of the hard segment composed of the polyamide component and the soft segment composed of the polyoxyalkylene glycol component. Usually, those in the range of 120°C to 180°C are used.

[0017] In the present invention, by using the polyamide-based elastomer as a constituent component of the base material layer of the laminated stretched polyamide film, the bending pinhole resistance of the laminated stretched polyamide film, particularly the bending pinhole resistance in a low-temperature environment, can be improved. The lower limit of the content of the polyamide-based elastomer in the polyamide resin composition of the base material layer is 2.5% by mass. Thereby, a laminated stretched polyamide film with good bending pinhole resistance can be obtained. The upper limit of the content of the polyamide-based elastomer in the polyamide resin composition of the base material layer is 20% by mass. Thereby, a laminated stretched polyamide film with good bending pinhole resistance can be obtained while maintaining other mechanical properties and transparency.

[0018] In the polyamide resin composition constituting the A layer in the present invention, other thermoplastic resins, for example, polyester-based polymers such as polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, and polyolefin-based polymers such as polyethylene and polypropylene may be contained within a range that does not impair their properties.

[0019] The polyamide resin composition constituting the A layer preferably contains 0.01 to 0.3% by mass of an antioxidant. When the content of the antioxidant exceeds the above range, whitening due to precipitation on the surface of the laminated stretched polyamide film, and poor adhesiveness during lamination with polyethylene and polypropylene sealants occur. When it is below the above range, when using recycled raw materials such as scrap materials and recycled resin as the polyamide resin composition of the A layer, poor film-forming operability may occur due to thermal deterioration of the recycled raw materials.

[0020] As the antioxidant, a phenolic antioxidant is preferred. As the phenolic antioxidant, a fully hindered phenolic compound or a partially hindered phenolic compound is preferred. For example, tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane, stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 3,9-bis[1,1-dimethyl-2-[β-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]2,4,8,10-tetraoxaspiro[5,5]undecane and the like can be mentioned.

[0021] By incorporating the above phenolic antioxidant into the polyamide resin composition of the A layer, the film-forming operability of the laminated and stretched polyamide film is improved. In particular, in a recycled raw material mixture system using film scraps, recycled resin, etc., thermal degradation due to the recycling of thermoplastic elastomers is likely to occur, and film-forming operation failures caused by this occur, leading to an increase in production costs due to a decrease in operation efficiency, and an increase in the amount of virgin raw material used due to a decrease in the amount of recycled raw material used, tending to increase production costs. In contrast, by incorporating an antioxidant into the polyamide resin composition of the A layer of a polyamide-based stretched film containing recycled raw materials, thermal degradation of various polymers including thermoplastic elastomers is suppressed, and stable film-forming operability is realized. From this, according to the present invention, by improving operability and reducing raw material costs due to an increase in the amount of recycled raw material used, it is possible to reduce production costs. Reduction enables the reduction of production costs.

[0022] The polyamide resin composition constituting the A layer may be a mixture of virgin polyamide 6 and a polyamide-based elastomer, or may be a composition obtained by adding virgin raw material to off-specification films or cut end materials (ear trimmings) generated during the production of laminated and stretched polyamide films as recycled resin.

[0023] <Surface layer (B layer)> In the present invention, the surface layer (B layer) is composed of 100 to 80% by mass of polyamide 6 resin, less than 1% by mass of polyamide-based elastomer, and 0 to 20% by mass of polyamide resin other than polyamide 6 resin and polyamide-based elastomer. By setting the content of the polyamide-based elastomer, which is a major cause of resin deterioration, to less than 1% by mass, it is possible to suppress the deterioration of the resin inside the die during film production, and to suppress the adhesion of deteriorated products to the inner surface of the die and the adhesion of eye lacquer to the die outlet. As a result, deterioration of film thickness unevenness can be prevented. Also, continuous production for a long time can be enabled. Also, by setting the content of the polyamide-based elastomer to less than 1% by mass, the friction-resistant pinhole property can be improved, and the pinhole generation distance in the friction test can be made 3000 cm or more.

[0024] The surface layer (B layer) in the present invention is configured to be laminated on both surfaces of the base material layer, but as long as it is a resin composition that satisfies the above composition, resin compositions different from each other on both surfaces may be used. For example, within the range that satisfies the above composition, a polyamide resin composition containing fine particles or fatty acid amide on one surface of the A layer to improve slipperiness is laminated, and a polyamide resin composition containing a copolymerized polyamide resin on the other surface to improve adhesiveness can be laminated.

[0025] As the polyamide 6 resin constituting the B layer in the present invention, the same one as the polyamide 6 resin of the A layer described above can be used. As the polyamide-based elastomer constituting the B layer in the present invention, similar to the one used in the above-described A layer, it is a polyamide-based block copolymer composed of a hard segment composed of a polyamide component and a soft segment composed of a polyoxyalkylene glycol component. It is most preferable that the B layer does not contain a polyamide-based elastomer.

[0026] The polyamide resin composition of the B layer in the present invention may contain a polyamide resin other than polyamide 6 and polyamide-based elastomer in a range not exceeding 20% by mass. Examples of the polyamide resin other than polyamide 6 and polyamide-based elastomer include polyamide 11 resin, polyamide 12 resin, polyamide 66 resin, polyamide 6·12 copolymer resin, polyamide 6·66 copolymer resin, and polyamide MXD6 resin.

[0027] The polyamide resin composition constituting the B layer in the present invention may contain, if necessary, other thermoplastic resins, for example, polyester-based polymers such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, and polyolefin-based polymers such as polyethylene and polypropylene, within a range that does not impair their properties.

[0028] It is preferable to contain fine particles in the polyamide resin compositions constituting the A layer and the B layer of the laminated and stretched polyamide film in the present invention in order to improve the slipperiness and make it easier to handle. The fine particles can be appropriately selected and used from among inorganic lubricants such as silica, kaolin, and zeolite, and polymer-based organic lubricants such as acrylic and polystyrene. In terms of transparency and slipperiness, it is preferable to use silica fine particles.

[0029] The preferable average particle diameter of the fine particles is 0.5 to 5.0 μm, more preferably 1.0 to 3.0 μm. If the average particle diameter is less than 0.5 μm, a large amount of addition is required to obtain good slipperiness. If it exceeds 5.0 μm, the surface roughness of the film becomes too large and it does not satisfy the practical properties, which is not preferable.

[0030] The range of the pore volume of the fine particles is preferably 0.5 to 2.0 ml / g, more preferably 0.8 to 1.6 ml / g. If the pore volume is less than 0.5 ml / g, voids are likely to occur and the transparency of the film deteriorates. If the pore volume exceeds 2.0 ml / g, protrusions on the surface due to the fine particles are less likely to form and the slipperiness of the film deteriorates, which is not preferable.

[0031] In the polyamide resin composition constituting the A layer and the B layer of the laminated and stretched polyamide film in the present invention, fatty acid amide and / or fatty acid bisamide can be contained for the purpose of improving the slipperiness. Examples of the fatty acid amide and / or fatty acid bisamide include erucic acid amide, stearic acid amide, ethylene bisstearic acid amide, ethylene bisbehenic acid amide, ethylene bisoleic acid amide and the like.

[0032] In this case, the content of the fatty acid amide and / or fatty acid bisamide in the polyamide polymer is preferably 0.01 to 0.40% by mass, more preferably 0.05 to 0.30% by mass. When the content of the fatty acid amide and / or fatty acid bisamide is less than the above range, the slipperiness is poor and the processability in printing, lamination, etc. is poor. When it exceeds the above range, bleeding to the film surface over time may cause spots on the surface, which is not preferable in terms of quality.

[0033] When the laminated and stretched polyamide-based film in the present invention is processed into a packaging material (bagged product), the B layer surface often becomes the outermost surface of the bagged product in a laminate structure. Therefore, when friction occurs with a transport package such as cardboard during the transport of the bagged product, the film may be scratched by the friction and the bag may be torn, or the bags may pierce each other due to contact, and the bending fatigue, etc. may increase and the bag may be torn. In the configuration of the present invention, by improving the slipperiness of the B layer, the factor causing bag tearing due to friction is reduced, and high bag tearing prevention performance is exhibited.

[0034] In the polyamide resin composition constituting the A layer and the B layer of the laminated and stretched polyamide film in the present invention, various additives such as an antistatic agent, an antifogging agent, an ultraviolet absorber, a dye, a pigment, etc. can be contained in one or both of the A layer and / or the B layer as needed.

[0035] As a method of addition, it can be carried out by known methods such as adding during resin polymerization or adding during melt extrusion with an extruder to form a masterbatch, and then adding this masterbatch to the polyamide polymer during film production for use.

[0036] There are no particular restrictions on the method of mixing various polyamide resins, polyamide-based elastomers, lubricants, etc. that make up the A layer and the B layer. However, a method is used in which the chip-shaped polymer is mixed using a blender or the like and then melted and molded.

[0037] The total thickness of the laminated and stretched polyamide film in the present invention is not particularly limited. However, when used as a packaging material, it is usually 100 μm or less, and generally, those with a thickness of 5 to 50 μm are used, and particularly those with a thickness of 8 to 30 μm are used.

[0038] In the laminated and stretched polyamide film of the present invention, when the thickness of the B layer occupies most of the total film thickness, the flexure-resistant pinhole resistance deteriorates. On the contrary, when the thickness of the A layer occupies almost the total film thickness, although the flexure-resistant pinhole resistance is excellent, the friction-resistant pinhole resistance is poor, and the deterioration of thickness unevenness cannot be suppressed. Therefore, in the present invention, it is preferable that the thickness of the A layer is 70 to 93%, particularly 80 to 93%, of the total thickness of the A layer and the B layer. Also, by setting the thickness of the B layer to at least 0.5 μm or more, preferably 1 μm or more, it is possible to achieve both flexure-resistant pinhole resistance and friction-resistant pinhole resistance and suppression of thickness unevenness.

[0039] The laminated and stretched polyamide film in the present invention preferably has an impact strength of 0.75 J / 15 μm or more. A more preferable impact strength is 1.0 J / 15 μm or more. Further, in the laminated and stretched polyamide film in the present invention, the number of gelbo pinholes when a torsional bending test using a gelbo flex tester is performed 1000 times at a temperature of 1°C is preferably 10 or less. More preferably, it is 5 or less. Furthermore, in the laminated and stretched polyamide film in the present invention, the distance until pinholes are generated in the friction-resistant pinhole test is preferably 2900 cm or more. More preferably, it is 3000 cm or more, and even more preferably 3100 cm or more. The laminated and stretched polyamide film of the present invention preferably satisfies these characteristics simultaneously. The stretched polyamide film having these characteristics is useful as a packaging film in which pinholes are less likely to occur during transportation. <Adhesion-modified layer (C layer)> The easily adhesive polyamide film of the present invention has an adhesion-modified layer composed of at least one of a polyester resin, a polyurethane resin, and / or a polyacrylic resin with a coating amount of 0.01 to 3 g / m as a solid content on at least one side. 2 The adhesion-modified layer in the present invention is provided by applying and drying a coating solution before winding the film as a mill roll in the film manufacturing process. The application of the coating solution can be performed on an unstretched film, a uniaxially stretched film, and / or a biaxially stretched film. When the film is manufactured by the sequential biaxial stretching method, usually, the coating solution is applied to the uniaxially stretched film and dried. When the film is manufactured by simultaneous biaxial stretching, usually, the coating solution is applied to the unstretched film and dried.

[0040] Since the coating solution for providing the adhesion-modified layer in the present invention is applied and dried to provide a coating film before winding the film as a mill roll in the film manufacturing process, in order to ensure safety and hygiene in manufacturing, it is preferable to use an aqueous dispersion of the resin.

[0041] (Polyester resin used for the adhesion-modified layer) When a polyester resin is provided as the adhesion-modifying layer in the present invention, a copolymerized polyester resin can be selected as the polyester resin. The copolymerized polyester resin is a polycondensate of a dicarboxylic acid component, a diol component, and other ester-forming components. Examples of the dicarboxylic acid component contained as a constituent component in the copolymerized polyester resin include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and 5-sodium sulfoisophthalic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, and sebacic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid and 1,2-cyclohexanedicarboxylic acid; and unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and tetrahydrophthalic acid, etc.

[0042] In addition to the above dicarboxylic acid components, salts of 5-sulfoisophthalic acid, sulfoterephthalic acid, 4-sulfoisophthalic acid, 4-sulfonaphthalene-2,6-dicarboxylic acid, and 5(4-sulfophenoxy)isophthalic acid can be used to impart water dispersibility. Among them, it is preferable to use 5-sodium sulfoisophthalic acid in the range of 1 to 10 mol%.

[0043] Examples of the diol component contained in the copolymerized polyester resin include aliphatic diols such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, and polyethylene glycol; alicyclic diols such as 1,4-cyclohexanedimethanol; aromatic diols such as 4,4'-bis(hydroxyethyl)bisphenol A; and further bis(polyoxyethylene glycol)bisphenol ether, etc. The polyester resin is preferably used as a coating liquid of an aqueous dispersion.

[0044] (Polyurethane resin used for the adhesion-modifying layer) When a polyurethane resin is provided as the adhesion-modifying layer in the present invention, examples of the polyurethane resin include those obtained by reacting polyols having two or more active hydrogens with organic polyisocyanates. Examples of the polyols include saturated polyester polyols; polyether polyols (such as polyethylene glycol, polytetramethylene glycol, etc.); amino alcohols (such as ethanolamine, diethanolamine, triethanolamine, etc.); unsaturated polyester polyols (such as those obtained by polycondensing an unsaturated polyvalent carboxylic acid alone or a mixture thereof with a saturated polyvalent carboxylic acid, and a mixture of a saturated polyvalent alcohol and an unsaturated polyvalent alcohol); polybutadiene polyols (such as 1,2-polybutadiene polyol, 1,4-polybutadiene polyol, etc.); and polyols having an unsaturated double bond such as acrylic polyols (acrylic polyols having a hydroxyl group in the side chain obtained by copolymerizing various acrylic monomers and an acrylic acid monomer having a hydroxyl group). Examples of the organic polyisocyanates include aromatic polyisocyanates (such as diphenylmethane diisocyanate, toluene diisocyanate, etc.); aliphatic polyisocyanates (such as hexamethylene diisocyanate, etc.); alicyclic polyisocyanates (such as isophorone diisocyanate, etc.); aromatic-aliphatic polyisocyanates (such as xylylene diisocyanate); and further polyisocyanates obtained by previously reacting these isocyanates with a low molecular weight polyol.

[0045] The production of this polyurethane resin can be carried out by known methods. During the production, it is necessary to ensure that there are two or more unreacted isocyanate groups in the resulting prepolymer. It is preferable to block these isocyanate groups, and especially when preparing an aqueous coating solution, this blocking is essential. This blocking is well-known as the blocking of isocyanates and can regenerate free isocyanate groups by heating. Examples of blocking agents include bisulfites, alcohols, oximes, active methylene compounds, imidazoles, lactams, imine compounds, amide compounds, imide compounds, and the like.

[0046] The reaction between these blocking agents and the isocyanate groups in the polyurethane prepolymer can be carried out at a temperature of room temperature to 100 °C, and a urethanization catalyst can be used as required. Here, it is advisable to introduce a hydrophilic group into the molecule to impart stable water dispersibility and water solubility to the polyurethane prepolymer. Examples of the hydrophilic group include ─SO3M (where M is an alkali metal or alkaline earth metal), -OH, -COOR (where R is the residue of ammonia or a tertiary amine), and the like. Among these, a carboxyl group neutralized with ammonia or a tertiary amine is particularly preferred. To introduce a carboxyl group neutralized with ammonia or a tertiary amine into the polyurethane prepolymer, for example, there are methods such as using a polyhydroxy compound containing a carboxyl group as one of the reaction raw materials during the synthesis of the polyurethane prepolymer, reacting a hydroxyl group-containing carboxylic acid or an amino group-containing carboxylic acid with the isocyanate groups of a polyurethane prepolymer having unreacted isocyanate groups, and then adding the reaction product to an aqueous ammonia or tertiary amine aqueous solution under high-speed stirring for neutralization. The polyurethane resin is preferably used as an aqueous dispersion coating solution.

[0047] (Polyacrylic resin used for the adhesion modification layer) When a polyacrylic resin is provided as the adhesion modifying layer in the present invention, examples of the polyacrylic resin include acrylic polymers obtained by polymerizing acrylic acid or methacrylic acid, or their salts or esters. Examples of acrylic ester-based and methacrylic ester-based monomers include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, glycidyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, and the like. Examples of salts of acrylic acid and methacrylic acid include sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, ammonium acrylate, ammonium methacrylate, and the like. In addition to these essential components, acrylic acid-based monomers such as acrylamide, methacrylamide, aminoethyl methacrylate, aminomethyl methacrylate, N-methylolacrylamide, N-methoxymethylacrylamide, etc. may be added. In addition to this, monomers such as vinyl chloride, vinyl acetate, styrene, vinyl ether, butadiene, isoprene, sodium vinyl sulfonate, etc. can also be used as copolymerization components. It should be noted that for the acrylic polymer, it is preferable that hydrophilic components such as acrylate components, methacrylate components, acrylic acid components, acrylamide components, 2-hydroxyethyl acrylate components, N-methylolacrylamide components, etc. are included as copolymerization components to enhance the functionality of the coating film. Also, a copolymer having a functional group on the molecular side chain may be used. Further, this acrylic polymer can be obtained by using a hard component such as methyl methacrylate or ethyl methacrylate as the main component and copolymerizing a soft component such as an acrylic ester as the copolymerization component. The polyacrylic resin is preferably used as an aqueous dispersion coating solution.

[0048] (Acrylic graft copolymer polyester aqueous dispersion used for the adhesion modifying layer) As the coating liquid used for the adhesion - modified layer in the present invention, an aqueous dispersion of a copolymer polyester obtained by graft - polymerizing a polyacrylic resin onto a polyester resin is particularly preferable. The average particle diameter of the acrylic - graft - copolymerized polyester particles in the acrylic - graft - copolymerized polyester aqueous dispersion, measured by the laser light scattering method, is 500 nm or less, preferably 10 nm to 500 nm, and more preferably 10 nm to 300 nm. When the average particle diameter exceeds 500 nm, the strength of the coating film after coating may decrease.

[0049] The content of the acrylic - graft - copolymerized polyester particles in the acrylic - graft - copolymerized polyester aqueous dispersion is usually 1% by mass to 50% by mass, preferably 3% by mass to 30% by mass. The particles in the acrylic - graft - copolymerized polyester aqueous dispersion that can be used in the present invention have a core - shell structure with a polyester main chain as the core in an aqueous dispersion medium.

[0050] The coating film obtained from the above - mentioned acrylic - graft - copolymerized polyester aqueous dispersion has extremely excellent adhesiveness to a polyamide film. Furthermore, since its antiblocking property is extremely excellent, it can be used without problems even in a film substrate with a relatively low glass transition point. Also, when forming a laminate, its adhesiveness to the adhesive used when laminating a printing ink or a sealant layer is also very good. The obtained laminated film (also referred to as a laminate film) has significantly improved durability in retort treatment and boiling water treatment.

[0051] (Polyester main chain of acrylic - graft - copolymerized polyester) The polyester that can be used as the main chain of the grafted polyester in the present invention is preferably It is a saturated or unsaturated polyester synthesized from at least a dicarboxylic acid component and a diol component, and the resulting polyester can be a single polymer or a mixture of two or more polymers. And a polyester that is not inherently dispersible or soluble in water is preferred. The weight average molecular weight of the polyester that can be used in the present invention is 5,000 to 100,000, preferably 5,000 to 50,000. If the weight average molecular weight is less than 5,000, the physical properties of the coating film such as the post-processability of the dry coating film will deteriorate. Furthermore, if the weight average molecular weight is less than 5,000, the polyester itself that forms the main chain is likely to be solubilized in water, so the acrylic graft copolymer polyester does not form a core-shell structure. When the weight average molecular weight of the polyester exceeds 100,000, it becomes difficult to disperse in water. From the viewpoint of water dispersion, 100,000 or less is preferred. The glass transition temperature of the acrylic graft copolymer polyester is 30°C or lower, preferably 10°C or lower. When it is 30°C or lower, preferably 10°C or lower, the adhesiveness and durability with the ink layer and the sealant layer are improved.

[0052] As the above-mentioned dicarboxylic acid component, it is preferably a dicarboxylic acid mixture containing at least one aromatic dicarboxylic acid, at least one aliphatic and / or alicyclic dicarboxylic acid, and at least one dicarboxylic acid having a radically polymerizable unsaturated double bond. The aromatic dicarboxylic acid contained in this dicarboxylic acid mixture is 30 to 99.5 mol%, preferably 40 to 99.5 mol%, the aliphatic and / or alicyclic dicarboxylic acid is 0 to 70 mol%, preferably 0 to 60 mol%, and the dicarboxylic acid having a radically polymerizable unsaturated double bond is 0.5 to 10 mol%, preferably 2 to 7 mol%, more preferably 3 to 6 mol%. When the content of the dicarboxylic acid containing a radically polymerizable unsaturated double bond is less than 0.5 mol%, effective grafting of the radically polymerizable monomer to the polyester is difficult, the dispersed particle size in the aqueous medium tends to increase, and the dispersion stability tends to decrease.

[0053] As the aromatic dicarboxylic acid, terephthalic acid, isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, etc. can be used. Further, sodium 5-sulfoisophthalate can also be used as needed. As the aliphatic dicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid, acid anhydrides thereof, etc. can be used. As the alicyclic dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, acid anhydrides thereof, etc. can be used.

[0054] As the dicarboxylic acid containing a radically polymerizable unsaturated double bond, as α,β-unsaturated dicarboxylic acids, fumaric acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid, and as alicyclic dicarboxylic acids containing an unsaturated double bond, 2,5-norbornenedicarboxylic anhydride, tetrahydrophthalic anhydride, etc. can be used. Among these, fumaric acid, maleic acid, and 2,5-norbornenedicarboxylic acid (endo-bicyclo-(2,2,1)-5-heptene-2,3-dicarboxylic acid) are preferred.

[0055] The above diol component is composed of at least one of aliphatic glycols having 2 to 10 carbon atoms, alicyclic glycols having 6 to 12 carbon atoms, and glycols containing an ether bond. As the aliphatic glycol having 2 to 10 carbon atoms, ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 2-ethyl-2-butylpropanediol, etc. can be used. As the alicyclic glycol having 6 to 12 carbon atoms, 1,4-cyclohexanedimethanol, etc. can be used. As the ether bond-containing glycol, diethylene glycol, triethylene glycol, dipropylene glycol, and further glycols obtained by adding 1 to several moles of ethylene oxide or propylene oxide to two phenolic hydroxyl groups of bisphenols, such as 2,2-bis(4-hydroxyethoxyphenyl)propane, can be used. Polyethylene glycol, polypropylene glycol, and polytetramethylene glycol can also be used as needed.

[0056] In addition to the above dicarboxylic acid component and diol component, a polycarboxylic acid and / or polyol having a functionality of 3 or more can be copolymerized. As the polycarboxylic acid having a functionality of 3 or more, (anhydrous) trimellitic acid, (anhydrous) pyromellitic acid, (anhydrous) benzophenone tetracarboxylic acid, trimesic acid, ethylene glycol bis(anhydrotrimellitate), glycerol tris(anhydrotrimellitate), etc. can be used. As the polyol having a functionality of 3 or more, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, etc. can be used. The polycarboxylic acid and / or polyol having a functionality of 3 or more can be used in the range of 0 to 5 mol%, preferably 0 to 3 mol%, based on the total polycarboxylic acid component containing the above dicarboxylic acid component or the total polyol component containing the above diol component.

[0057] (Graft portion of the acrylic graft copolymer polyester) The graft portion of the acrylic graft copolymer polyester that can be used in the present invention is an acrylic polymer derived from a monomer mixture containing at least one radically polymerizable monomer having a hydrophilic group or a group that can be changed to a hydrophilic group later.

[0058] The weight average molecular weight of the polymer constituting the graft portion is 500 to 50,000, preferably 4,000 to 50,000. When the weight average molecular weight is less than 500, the grafting rate decreases, so that the imparting of hydrophilicity to the polyester is not sufficiently carried out, and generally it is difficult to control the weight average molecular weight of the graft portion to less than 500. The graft portion forms a hydration layer of dispersed particles. In order to give the particles a sufficiently thick hydration layer and obtain a stable dispersion, it is desirable that the weight average molecule of the graft portion derived from the radically polymerizable monomer is 500 or more. The upper limit of the weight average molecular weight of the graft portion of the radically polymerizable monomer is preferably 50,000 as described above in terms of polymerizability in solution polymerization. The control of the molecular weight within this range can be achieved by appropriately selecting the amount of polymerization initiator, monomer dropping time, polymerization time, reaction solvent, and monomer composition, and appropriately combining a chain transfer agent and a polymerization inhibitor as necessary. The glass transition point is 30°C or lower, preferably 10°C or lower.

[0059] As the hydrophilic group of the radically polymerizable monomer, a carboxyl group, a hydroxyl group, a sulfonic acid group, an amide group, a quaternary ammonium salt, a phosphoric acid group, etc. can be used. As the group that can be changed to a hydrophilic group, an acid anhydride, glycidyl, chlorine, etc. can be used. The dispersibility of the graft polyester in water can be controlled by the hydrophilic group introduced into the polyester by grafting. Among the above hydrophilic groups, the carboxyl group is preferable for controlling the dispersibility of the graft polyester in water because the introduction amount thereof into the graft polyester can be accurately determined using the acid value known in the art.

[0060] Examples of the carboxyl group-containing radically polymerizable monomer include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, etc., and further maleic anhydride, itaconic anhydride, methacrylic anhydride, etc. that easily generate carboxylic acid when in contact with water / amine can be used. Preferred carboxyl group-containing radically polymerizable monomers are acrylic anhydride, methacrylic anhydride, and maleic anhydride.

[0061] In addition to the above hydrophilic group-containing radically polymerizable monomer, it is preferable to copolymerize at least one radically polymerizable monomer that does not contain a hydrophilic group. In the case of only the hydrophilic group-containing monomer, grafting onto the polyester main chain does not occur smoothly, and it is difficult to obtain a good copolymerized polyester aqueous dispersion. Only by copolymerizing at least one radically polymerizable monomer that does not contain a hydrophilic group can efficient grafting be carried out for the first time.

[0062] As the radically polymerizable monomer that does not contain a hydrophilic group, one or more combinations of monomers having an ethylenically unsaturated bond and not containing the above hydrophilic group are used. Such monomers include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, etc. acrylate esters; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, hydroxyphenylpropyl methacrylate, etc. methacrylate esters; acrylic acid or methacrylic acid derivatives such as acrylamide, N-methylolacrylamide, diacetoneacrylamide; nitriles such as acrylonitrile, methacrylonitrile; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, methyl isopropenyl ketone; N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl pyrrolidone; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide, vinyl fluoride; aromatic vinyl compounds such as styrene, α-methylstyrene, t-butylstyrene, vinyltoluene, vinylnaphthalenes; These monomers can be used alone or in combination of two or more.

[0063] The use ratio of the hydrophilic group-containing monomer and the monomer not containing a hydrophilic group is determined in consideration of the amount of the hydrophilic group introduced into the graft polyester. Usually, the mass ratio (hydrophilic group-containing monomer: monomer not containing a hydrophilic group) is in the range of 95:5 to 5:95, preferably 90:10 to 10:90, and more preferably 80:20 to 40:60.

[0064] When a carboxyl group-containing monomer is used as the hydrophilic group-containing monomer, the total acid value of the graft polyester is 600 to 4000 eq. / 10 6 g, preferably 700 to 3000 eq. / 10 6 g, and most preferably 800 to 2500 eq. / 10 6 g. When the acid value is 600 eq. / 10 6 g or less, it is difficult to obtain a copolymerized polyester aqueous dispersion with a small particle size when the graft polyester is dispersed in water, and furthermore, the dispersion stability of the copolymerized polyester aqueous dispersion decreases. When the acid value is 4000 eq. / 10 6 g or more, the water resistance of the adhesive modification layer formed from the copolymerized polyester aqueous dispersion becomes low.

[0065] The mass ratio of the polyester main chain to the graft portion in the acrylic graft copolymerized polyester (polyester: radically polymerizable monomer) is in the range of 40:60 to 95:5, preferably 55:45 to 93:7, and more preferably 60:40 to 90:10.

[0066] When the mass ratio of the polyester main chain is 40% by mass or less, the excellent performance of the base polyester already described, namely, high processability, excellent water resistance, and excellent adhesion to various substrates, cannot be fully exhibited. Conversely, undesirable properties of the acrylic resin, namely, low processability, gloss, water resistance, etc., are added. When the mass ratio of the polyester is 95% by mass or more, the amount of the hydrophilic group in the graft portion that imparts hydrophilicity to the graft polyester is insufficient, and a good aqueous dispersion cannot be obtained.

[0067] (Solvent for the grafting reaction of acrylic graft copolymerized polyester) The solvent for the grafting reaction is preferably composed of an aqueous organic solvent having a boiling point of 50 to 250°C. Here, the aqueous organic solvent refers to an organic solvent having a solubility in water at 20°C of at least 10 g / L or more, preferably 20 g / L or more. An aqueous organic solvent having a boiling point exceeding 250°C is unsuitable because its evaporation rate is slow and it cannot be sufficiently removed even by high-temperature baking of the coating film after film formation. Also, for an aqueous organic solvent having a boiling point of 50°C or lower, when carrying out the grafting reaction using it as a solvent, an initiator that decomposes into radicals at a temperature of 50°C or lower must be used, which increases the handling risk and is not preferable.

[0068] Examples of the aqueous organic solvent (Group 1) that dissolves polyester well and dissolves the polymerizable monomer containing a hydrophilic group, particularly a carboxyl group-containing polymerizable monomer, and its polymer relatively well include esters such as ethyl acetate; ketones such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; cyclic ethers such as tetrahydrofuran, dioxane, and 1,3-dioxolane; glycol ethers such as ethylene glycol dimethyl ether, propylene glycol methyl ether, propylene glycol propyl ether, ethylene glycol ethyl ether, and ethylene glycol butyl ether; carbitols such as methyl carbitol, ethyl carbitol, and butyl carbitol; lower esters of glycols or glycol ethers such as ethylene glycol diacetate and ethylene glycol ethyl ether acetate; ketone alcohols such as diacetone alcohol; N-substituted amides such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and the like.

[0069] On the other hand, examples of the aqueous organic solvents (second group) that hardly dissolve polyester but relatively well dissolve polymerizable monomers containing hydrophilic groups, particularly polymerizable monomers containing carboxyl groups, and their polymers include water, lower alcohols, lower glycols, lower carboxylic acids, lower amines, etc. Preferred are alcohols and glycols having 1 to 4 carbon atoms.

[0070] When the grafting reaction is carried out in a single solvent, one kind of the aqueous organic solvents of the first group can be used. When carried out in a mixed solvent, a plurality of kinds of the aqueous organic solvents of the first group or at least one kind of the aqueous organic solvents of the first group and at least one kind of the aqueous organic solvents of the second group can be used.

[0071] The grafting reaction can be carried out either in a single solvent from the aqueous organic solvents of the first group or in a mixed solvent composed of one kind each of the aqueous organic solvents of the first group and the second group. However, from the viewpoints of the progress behavior of the grafting reaction, the appearance, properties, etc. of the grafting reaction product and the aqueous dispersion derived therefrom, it is preferable to use a mixed solvent composed of one kind each of the aqueous organic solvents of the first group and the second group. The reason is that in the grafting reaction of polyester, gelation of the system easily occurs due to cross-linking between polyester molecules, but gelation can be prevented by using a mixed solvent as follows.

[0072] In the first group of solvents, the polyester molecular chains are in a state of extended chains with a large spread. On the other hand, in the mixed solvent of the first group / second group, it was confirmed by measuring the viscosity of the polyester in these solutions that the polyester molecular chains are in a state of being intertwined in a thread-like form with a small spread. When the polyester molecular chains are in an extended state, since all the reaction points in the polyester main chain can contribute to the grafting reaction, the grafting rate of the polyester increases, but at the same time, the rate of intermolecular crosslinking also increases. On the other hand, when the polyester molecular chains are in a thread-like form, the reaction points inside the thread cannot contribute to the grafting reaction, and at the same time, the rate of intermolecular crosslinking also decreases. Therefore, by selecting the type of solvent, the state of the polyester molecules can be adjusted, and thereby the grafting rate and intermolecular crosslinking by the grafting reaction can be adjusted.

[0073] The coexistence of a high grafting rate and gelation suppression can be achieved in a mixed solvent system. The optimal mixing ratio of the mixed solvent of the first group / second group can vary depending on the solubility of the polyester used, etc., but usually, the mass ratio of the mixed solvent of the first group / second group is in the range of 95:5 to 10:90, preferably 90:10 to 20:80, and more preferably 85:15 to 30:70.

[0074] (Radical polymerization initiator and chain transfer agent for acrylic graft copolymerized polyester) As the radical polymerization initiator that can be used in the present invention, organic peroxides and organic azo compounds known to those skilled in the art can be used. Examples of the organic peroxide include benzoyl peroxide and t-butyl peroxypivalate, and examples of the organic azo compound include 2,2'-azobisisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile). The amount of the radical polymerization initiator used for the grafting reaction is at least 0.2% by mass or more, preferably 0.5% by mass or more, based on the radically polymerizable monomer. In addition to the polymerization initiator, a chain transfer agent for adjusting the chain length of the graft portion, such as octyl mercaptan, mercaptoethanol, 3-t-butyl-4-hydroxyanisole, etc., can be used as needed. In this case, it is preferably added in the range of 0 to 5% by mass based on the radically polymerizable monomer.

[0075] (Grafting reaction of acrylic graft copolymerized polyester) The formation of the graft portion proceeds by the polymerization of the radically polymerizable unsaturated double bond in the above polyester and the above radically polymerizable monomer and / or the reaction of the radically polymerizable unsaturated double bond with the active end of the polymer of the above radically polymerizable monomer. The reaction product after the completion of the grafting reaction contains, in addition to the target grafted polyester, a polyester having no graft portion and a polymer of a radically polymerizable monomer that has not been grafted to the polyester. When the production ratio of the grafted polyester in the reaction product is low and the ratios of the polyester having no graft portion and the polymer of the radically polymerizable monomer that has not been grafted are high, a dispersion with good stability cannot be obtained.

[0076] Generally, the grafting reaction can be carried out by adding the radically polymerizable monomer and the radical initiator to the solution containing the above polyester at one time under heating, or by separately dropping them over a certain period of time and then continuing to heat with stirring for a further certain period of time to allow the reaction to proceed. Alternatively, if necessary, a part of the radically polymerizable monomer is added first, and then the remaining radically polymerizable monomer and the polymerization initiator are separately dropped over a certain period of time, and then the grafting reaction can be carried out by continuing to heat with stirring for a further certain period of time.

[0077] The mass ratio of the polyester to the solvent is selected to be a mass ratio at which the reaction proceeds uniformly during the polymerization step, taking into account the reactivity between the polyester and the radically polymerizable monomer and the solvent solubility of the polyester. Generally, it is in the range of 70:30 to 10:90, preferably 50:50 to 15:85.

[0078] (Aqueous dispersion of acrylic graft copolymer polyester) The graft polyester that can be used in the present invention can be dispersed in water by being put into an aqueous medium in a solid state or by being dissolved in a hydrophilic solvent and then put into an aqueous medium. In particular, when a monomer having an acidic group such as a sulfonic acid group and a carboxyl group is used as a radically polymerizable monomer having a hydrophilic group, the graft polyester is neutralized with a basic compound, whereby the graft polyester can be easily dispersed in water as fine particles having an average particle diameter of 500 nm or less to prepare a copolymer polyester aqueous dispersion.

[0079] As the basic compound, a compound that volatilizes during film formation or baking when a curing agent described below is blended is desirable. Such basic compounds preferably include ammonia, organic amines, etc. Examples of organic amines include triethylamine, N,N - diethylethanolamine, N,N - dimethylethanolamine, aminoethanolamine, N - methyl - N,N - diethanolamine, isopropylamine, iminobispropylamine, ethylamine, diethylamine, 3 - ethoxypropylamine, 3 - diethylaminopropylamine, sec - butylamine, propylamine, methylaminopropylamine, dimethylaminopropylamine, methyliminobispropylamine, 3 - methoxypropylamine, monoethanolamine, diethanolamine, triethanolamine, etc. The amount of the basic compound used is preferably an amount that at least partially neutralizes or completely neutralizes the carboxyl groups contained in the graft portion to make the pH value of the aqueous dispersion in the range of 5.0 to 9.0.

[0080] ​As a method for preparing a copolymerized polyester aqueous dispersion neutralized with a basic compound, after the grafting reaction is completed, the solvent is removed from the reaction solution under reduced pressure using an extruder or the like to obtain a melt or solid state (pellets, powder, etc.), and then this is added to an aqueous basic compound solution and stirred under heating, or immediately after the grafting reaction is completed, an aqueous basic compound solution is added to the reaction solution and heating and stirring are continued (one-pot method) to prepare an aqueous dispersion. From the viewpoint of convenience, the one-pot method is preferred. In this case, if the boiling point of the solvent used in the grafting reaction is 100°C or lower, part or all of it can be easily removed by distillation.

[0081] (Crosslinking agent added to the coating solution) The above aqueous dispersion can be used as it is as a coating agent for forming an adhesion-modified layer. However, by further blending a crosslinking agent (curing resin) and performing curing, high water resistance can be imparted to the adhesion-modified layer. Examples of the crosslinking agent include phenolic resins which are condensates of alkylated phenols, cresols, etc. and formaldehyde; amino resins such as addition products of urea, melamine, benzoguanamine, etc. and formaldehyde, and alkyl ether compounds composed of this addition product and an alcohol having 1 to 6 carbon atoms; polyfunctional epoxy compounds; polyfunctional isocyanate compounds; blocked isocyanate compounds; polyfunctional aziridine compounds; oxazoline compounds, etc. These crosslinking agents can be used alone or in combination of two or more. As the blending amount of the crosslinking agent, 5% by mass to 40% by mass is preferred based on the grafted polyester.

[0082] As a method for blending the crosslinking agent, (1) when the crosslinking agent is water-soluble, a method of directly dissolving or dispersing it in the aqueous dispersion, or (2) when the crosslinking agent is oil-soluble, after the grafting reaction is completed, before or after the water dispersion, the crosslinking agent is added and allowed to coexist with the polyester in the core part can be used. These methods can be appropriately selected according to the type and properties of the crosslinking agent. Furthermore, a curing agent or accelerator can be used in combination with the crosslinking agent.

[0083] In the adhesion modification layer used in the present invention, additives such as antistatic agents, inorganic lubricants, and organic lubricants can be contained within a range that does not impair the effects of the present invention in order to impart antistatic properties and slipperiness. When applying an antistatic agent, an inorganic lubricant, an organic lubricant, etc. to the film surface, it is preferable to contain them in the adhesion modification layer to prevent the desorption of these additives.

[0084] <Manufacturing method> The laminated stretched polyamide film in the present invention can be manufactured by a known manufacturing method. For example, a sequential biaxial stretching method and a simultaneous biaxial stretching method can be mentioned. The sequential biaxial stretching method is preferable because the film forming speed can be increased, which is advantageous in terms of manufacturing cost. A uniaxially stretched film by a uniaxial stretching method may also be used.

[0085] Before stretching the film, an unstretched sheet in which layer A and layer B are laminated is obtained. As a method for this, a coextrusion method using a feed block, a multi-manifold, etc. is preferable. In addition to the coextrusion method, a dry lamination method, an extrusion lamination method, etc. can also be selected. When laminating by the coextrusion method, it is desirable to select the relative viscosities of the polyamides used for layer A and layer B so that the difference in the melt viscosities of layer A and layer B is reduced.

[0086] As the sequential biaxial stretching device, a normal device is used. As manufacturing conditions, the stretching temperature in the longitudinal direction is preferably in the range of 50 to 100°C, the stretching ratio in the longitudinal direction is 2 to 5 times, the stretching temperature in the width direction is 120 to 200°C, the stretching ratio in the width direction is 3 to 5 times, and the heat setting temperature is 200°C to 230°C. In order to increase the adhesion strength to a sealant film or a printing layer, a corona treatment, a flame treatment, etc. may be performed on the surface of the laminated stretched polyamide film and / or the surface of the adhesion modification layer (layer C). Also, in order to increase the adhesion strength between the laminated stretched polyamide film and the adhesion modification layer, a corona treatment, a flame treatment, etc. may be performed on the surface of the laminated stretched polyamide film on the side of the adhesion modification layer (layer C).

[0087] As a method for forming the adhesion-modifying layer (C layer) in the present invention, a coating agent containing any one of a polyester resin, a polyurethane resin, and / or a polyacrylic resin is applied to the laminated and stretched polyamide film by a known coating method such as a gravure method, a reverse method, a die method, a bar method, or a dip method.

[0088] The coating amount of the coating agent is preferably 0.01 to 3 g / m as a solid content with respect to the polyamide film after biaxial stretching. 2 More preferably, it is applied so as to be 0.04 to 0.5 g / m. 2 With the above coating amount, sufficient adhesion strength between the adhesion-modifying layer and other layers can be obtained, and the occurrence of blocking between films can be suppressed.

[0089] In the present invention, the adhesion-modifying layer can be prepared by applying a coating agent to a biaxially stretched polyamide film substrate, or applying a coating agent to an unstretched or uniaxially stretched polyamide film substrate, followed by drying, and if necessary, further performing uniaxial stretching or heat setting after biaxial stretching. As the drying temperature after coating the coating agent, drying and heat setting are performed at 150 °C or higher, preferably 200 °C or higher, so that the coating film becomes strong and the adhesiveness between the adhesion-modifying layer and the polyamide film substrate is improved.

[0090] When stretching is performed after coating, it is necessary to control the moisture content of the coated film within the range of 0.1 to 2% in order not to impair the stretchability of the coated film. After stretching, drying and heat setting are performed at 200 °C or higher, so that the coating film becomes strong and the adhesiveness between the adhesion-modifying layer and the polyamide film substrate is remarkably improved.

[0091] The easily adhesive polyamide film of the present invention thus obtained can suppress the occurrence of scratches on the film and bag breakage due to friction even when friction occurs with a transport package such as cardboard during the transportation of bagged products. In addition, it can suppress bag breakage due to bending fatigue caused by contact between bags. Also, since the water-resistant adhesion strength between the polyamide film and the sealant film is high, high bag breakage prevention performance is exhibited.

Example

[0092] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. The evaluation of the film was carried out by the following measurement methods. Unless otherwise specified, the measurement was carried out in a measurement room at an environment of 23°C and a relative humidity of 65%. (1) Haze value of the film Using a direct-reading haze meter manufactured by Toyo Seiki Seisaku-sho, Ltd., the measurement was carried out in accordance with JIS-K-7105. Haze (%) = [Td (diffuse transmittance %) / Tt (total light transmittance %)] × 100 (2) Impact strength of the film Using a film impact tester manufactured by Toyo Seiki Seisaku-sho, Ltd., the measurement was carried out. The measured value was expressed in J (joule) / 15 μm converted per 10 μm thickness.

[0093] (3-1) Flexure pinhole resistance of the film Using a gelbo flex tester manufactured by Rigaku Kogyo Co., Ltd., the number of flexure fatigue pinholes was measured by the following method. After applying a polyester-based adhesive to the film produced in the example, a linear low-density polyethylene film with a thickness of 40 μm (L-LDPE film: manufactured by Toyobo Co., Ltd., L4102) was dry laminated, and aging was performed for 3 days in an environment at 40 °C to obtain a laminated film. The obtained laminated film was cut into 12 inches × 8 inches, made into a cylindrical shape with a diameter of 3.5 inches, one end of the cylindrical film was fixed to the fixed head side of the gelbo flex tester, and the other end was fixed to the movable head side, with an initial gripping interval of 7 inches. A 440-degree twist was applied in the first 3.5 inches of the stroke, and then 2.5 inches was a straight horizontal movement to complete the full stroke. Bending fatigue was performed 1000 times at a speed of 40 times / min, and the number of pinholes generated in the laminated film was counted. The measurement was performed in an environment at 1 °C. The L-LDPE film side of the test film was placed on the lower surface on filter paper (Advantec, No. 50), and the four corners were fixed with cellophane tape (registered trademark). Ink (Pilot ink (product number INK-350 - blue) diluted 5 times with pure water) was applied onto the test film and spread over one surface using a rubber roller. After wiping off the unnecessary ink, the test film was removed, and the number of ink dots attached to the filter paper was measured.

[0094] (3-2) Pinhole resistance to friction of the film Using a fastness tester (manufactured by Toyo Seiki Seisaku-sho), a friction test was performed by the following method, and the pinhole generation distance was measured. A laminated film similar to that produced in the above flexural pinhole resistance evaluation was made into a test sample folded four times with sharp corners, and rubbed against the inner surface of corrugated cardboard with an amplitude of 25 cm, an amplitude speed of 30 times / min, and a load of 100 g using a fastness tester. The corrugated cardboard used was K280×P180×K210(AF)=(face material liner × core material × back material liner (type of flute)).

[0095] The pinhole generation distance was calculated according to the following procedure. The longer the pinhole generation distance, the better the pinhole resistance to friction. First, a friction test was conducted at an amplitude of 100 times and a distance of 2500 cm. If no pinhole opened, the friction test was carried out with the number of amplitude cycles increased by 20 times and the distance increased by 500 cm. Also, if no pinhole opened, the friction test was further carried out with the number of amplitude cycles increased by 20 times and the distance increased by 500 cm. This was repeated, and the distance at which the pinhole opened was marked with an "×" and designated as level 1. If a pinhole opened at an amplitude of 100 times and a distance of 2500 cm, the friction test was carried out with the number of amplitude cycles decreased by 20 times and the distance decreased by 500 cm. Also, if a pinhole opened, the friction test was further carried out with the number of amplitude cycles decreased by 20 times and the distance decreased by 500 cm. This was repeated, and the distance at which no pinhole opened was marked with an "○" and designated as level 1. Next, as level 2, if the last one at level 1 was "○", the friction test was carried out with the number of amplitude cycles increased by 20 times. If no pinhole opened, it was marked with an "○", and if a pinhole opened, it was marked with an "×". If the last one at level 1 was "×", the friction test was carried out with the number of amplitude cycles decreased by 20 times. If no pinhole opened, it was marked with an "○", and if a pinhole opened, it was marked with an "×". Furthermore, as levels 3 to 20, if the previous level was "○", the friction test was carried out with the number of amplitude cycles increased by 20 times. If no pinhole opened, it was marked with an "○", and if a pinhole opened, it was marked with an "×". If the previous level was "×", the friction test was carried out with the number of amplitude cycles decreased by 20 times. If no pinhole opened, it was marked with an "○", and if a pinhole opened, it was marked with an "×". This was repeated to mark "○" or "×" for levels 3 to 20.

[0096] For example, results as shown in Table 1 were obtained. Using Table 1 as an example, the method for obtaining the pinhole generation distance will be explained. Count the number of "○" and "×" tests for each distance. Take the distance with the most test times as the median and set the coefficient to zero. For distances longer than that, the coefficient is set to +1, +2, +3,... for every 500 cm, and for distances shorter than that, the coefficient is set to -1, -2, -3,... for every 500 cm. In all the tests from level 1 to 20, the number of tests where no hole opened and the number of tests where a hole opened were compared, and the friction pinhole generation distance was calculated using the respective formulas for the following cases A and B. A: When the number of tests where no hole opened is greater than or equal to the number of tests where a hole opened in all the tests Friction pinhole generation distance = Median + 500 × (Σ(Coefficient × Number of tests with no hole opening) / Number of tests with no hole opening) + 1 / 2) B: When, in all tests, the number of tests with no hole opening is less than the number of tests with a hole opening Friction pinhole generation distance = Median + 500 × (Σ(Coefficient × Number of tests with a hole opening) / Number of tests with a hole opening) - 1 / 2)

[0097]

Table 1

[0098] (4) Film thickness The film is divided into 10 equal parts in the width direction (for films with a narrow width, it is temporarily divided into a width that can ensure the measurement of the thickness), 10 films with a length of 100 mm in the longitudinal direction are stacked and cut out, and conditioned for 2 hours or more in an environment of 23°C and 65% relative humidity. The central thickness of each sample is measured with a thickness measuring instrument manufactured by Tester Industry, and the average value is taken as the thickness. The thicknesses of the base material layer (A layer) and the surface layer (B layer) were calculated by measuring the total thickness of the laminated and stretched polyamide film measured by the above method, measuring the discharge amounts of the A layer and the B layer, and calculating the thicknesses of the A layer and the B layer based on the ratio of the discharge amounts. (5) Thickness unevenness (TV%) after 15 hours The thickness of the film 15 hours after the start of film formation was measured in the same manner as above, and the value (%) obtained by dividing the difference between the maximum value and the minimum value of the central thickness of each sample by the average value was calculated as the thickness unevenness (TV%) after 15 hours.

[0099] (6) Generation cycle of eye varnish (degraded product generated at the die lip outlet) After cleaning the lip of the die, film formation was started, and the time until eye varnish occurred on the lip of the die was observed.

[0100] (7) Coating amount of the adhesion modification layer The biaxially oriented polyamide film was cut into an area of 10 cm × 10 cm, and the adhesive-modified layer surface of the film was wiped with a cloth impregnated with a mixed organic solvent of methyl ethyl ketone / toluene = 1 / 1. The weights before and after wiping were measured using an analytical balance (AUW120D manufactured by Shimadzu Corporation). The weight difference measured was converted to per square meter to calculate the coating amount (g / m 2 ).

[0101] (8) Water-resistant laminating strength (laminating strength under water adhesion conditions) A polyester-based adhesive [a mixture of TM-569 (product name) and CAT-10L (product name) manufactured by Toyo Morton Co., Ltd. at a mass ratio of 7.2 / 1 (solid content concentration 23%)] was applied to the film so that the resin solid content after drying was 3.2 g / m 2 . After that, a 40-μm linear low-density polyethylene film (L-LDPE film: manufactured by Toyobo Co., Ltd., Lix (registered trademark) L4102) was dry-laminated, and aging was performed for 2 days in an environment at 40°C to obtain a laminated film. The produced laminated film was cut into strips with a width of 15 mm and a length of 200 mm. One end of the laminated film was peeled at the interface between the biaxially oriented polyamide film and the linear low-density polyethylene film. Using an autograph (manufactured by Shimadzu Corporation), under the conditions of a temperature of 23°C, a relative humidity of 50%, a tensile speed of 200 mm / min, and a peeling angle of 90°, water was dripped onto the peeling interface of the strip-shaped laminated film with a dropper, and the laminating strength was measured 3 times and evaluated by its average value.

[0102] (9) Relative viscosity of the raw polyamide The relative viscosity of a polyamide solution in which 0.25 g of polyamide was dissolved in a 25-ml volumetric flask with 96% sulfuric acid to a concentration of 1.0 g / dl was measured at 20°C. (10) Melting point of the raw polyamide In accordance with JIS K7121, using a differential scanning calorimeter model SSC5200 manufactured by Seiko Instruments Inc., in a nitrogen atmosphere, the sample weight was 10 mg, the starting temperature for temperature increase was 30°C, and the temperature increase rate was 20°C / min. The endothermic peak temperature (Tmp) was determined as the melting point. <Adjustment of Acrylic Graft Copolymer Polyester Coating Liquid for Modified Layer> 466 parts by mass of dimethyl terephthalate, 466 parts by mass of dimethyl isophthalate, 401 parts by mass of neopentyl glycol, 443 parts by mass of ethylene glycol, and 0.52 parts by mass of tetra-n-butyl titanate were charged into a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, and a transesterification reaction was carried out at 160 to 220 °C for 4 hours. Then, 23 parts by mass of fumaric acid was added, and the temperature was raised from 200 °C to 220 °C over 1 hour to carry out an esterification reaction. Then, the temperature was raised to 255 °C, the reaction system was gradually depressurized, and then reacted under a reduced pressure of 0.2 mmHg with stirring for 1 hour and 30 minutes to obtain a polyester. The obtained polyester was pale yellow and transparent, had a glass transition temperature of 60 °C, and a weight average molecular weight of 12,000. The composition obtained by NMR measurement and the like was as follows. ·Dicarboxylic Acid Component Terephthalic Acid 48 mol% Isophthalic Acid 48 mol% Fumaric Acid 4 mol% ·Diol Component Neopentyl Glycol 50 mol% Ethylene Glycol 50 mol%

[0103] Into a reactor equipped with a stirrer, a thermometer, a reflux device, and a metering dropping device, 75 parts by mass of the above polyester resin, 56 parts by mass of methyl ethyl ketone, and 19 parts by mass of isopropyl alcohol were placed, heated at 65 °C, and stirred to dissolve the resin. After the resin was completely dissolved, a solution prepared by dissolving a mixture of 17.5 parts by mass of methacrylic acid and 7.5 parts by mass of ethyl acrylate, and 1.2 parts by mass of azobis(dimethylvaleronitrile) in 25 parts by mass of methyl ethyl ketone was dropped into the polyester solution at a rate of 0.2 ml / min. After the dropping was completed, stirring was continued for another 2 hours. After sampling (5 g) for analysis was performed from the reaction solution, 300 parts by mass of water and 25 parts by mass of triethylamine were added to the reaction solution, and stirred for 1 hour to prepare a dispersion of the graft copolymerized polyester. Then, the temperature of the obtained dispersion was raised to 100 °C, and methyl ethyl ketone, isopropyl alcohol, and excess triethylamine were distilled off to obtain a copolymerized polyester aqueous dispersion. The obtained dispersion was diluted with water to a solid content concentration of 5% to obtain a coating solution AEG for the adhesion modifying layer. The parts by mass are values as solid content.

[0104] <Preparation of Polyester Coating Solution for Adhesion Modifying Layer> 100 parts by mass of a water-dispersible polyester resin (manufactured by Toyobo Co., Ltd., Vyloner MD1930) and 43 parts by mass of a reactive aqueous urethane resin (Elastron BN11 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were mixed and then diluted with water to a solid content concentration of 5% to obtain a coating solution PES for the adhesion modifying layer. The parts by mass are values as solid content. <Preparation of Polyurethane Coating Solution for Adhesion Modifying Layer> To 100 parts by mass of a water-dispersible polyurethane resin (Hydran KU400SF manufactured by DIC Corporation), 20 parts by mass of a trimethylol melamine resin (Beckamin APM manufactured by DIC Corporation) was mixed and then diluted with water to a solid content concentration of 5% to obtain a coating solution PU for the adhesion modifying layer. The parts by mass are values as solid content.

[0105] (Example 1) An apparatus consisting of two extruders and a co-extrusion T-die with a width of 380 mm was used. The molten resin was extruded in a sheet form from the T-die by laminating it in a B layer / A layer / B layer configuration, and was adhered to a cooling roll maintained at 20 °C to obtain a laminated unstretched sheet with a thickness of 200 μm. The resin compositions of the A layer and the B layer are as follows. Resin composition constituting the A layer: 97 parts by mass of nylon 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220 °C), and 3.0 parts by mass of a polyamide-based elastomer (manufactured by Arkema, PEBAX4033SA02) in which nylon 12 is the hard segment and polytetramethylene glycol is the soft segment, forming a polyamide resin composition. Resin composition constituting the B layer: A resin composition consisting of 100 parts by mass of nylon 6 (manufactured by Toyobo Co., Ltd., relative viscosity 2.8, melting point 220 °C), 0.54 parts by mass of silica fine particles, and 0.15 parts by mass of fatty acid amide. Note that the thickness of the laminated and stretched polyamide film was adjusted by configuring the feed block and the discharge amount of the extruder so that the total thickness was 15 μm, the thickness of the base material layer (A layer) was 12 μm, and the thicknesses of the front and back surface layers (B layer) were each 1.5 μm.

[0106] The obtained laminated unstretched sheet was guided to a roll-type stretching machine and stretched 1.7 times in the longitudinal direction at 80 °C using the peripheral speed difference of the rolls, and then further stretched 1.85 times at 70 °C. Next, an aqueous dispersion coating solution of an acrylic graft copolymerized polyester was applied to this longitudinally stretched film by a roll coater method and dried with hot air at 70 °C. Subsequently, this uniaxially stretched film was continuously guided to a tenter-type stretching machine, preheated at 110 °C, and then stretched 1.2 times at 120 °C, 1.7 times at 130 °C, and 2.0 times at 160 °C in the transverse direction. After heat setting treatment at 210 °C, relaxation treatments of 3% at 210 °C and 2% at 185 °C were performed. Then, the surface on the side to be dry laminated with a linear low-density polyethylene film was subjected to corona discharge treatment to obtain a two-layer three-layer laminated biaxially stretched polyamide film laminated in the order of B layer / A layer / B layer. The coating amount of the acrylic graft copolymerized polyester on the obtained biaxially stretched polyamide film was 0.3 g / m as the solid content.2 It was. The film property evaluation results are shown in Table 2.

[0107] (Examples 2 to 6 and Comparative Examples 1 to 4) Biaxially stretched films were obtained in the same manner as in Example 1, except that the resin compositions and thickness configurations of the A layer and the B layer were changed as shown in Table 2. The film property evaluation results of the obtained biaxially stretched films are shown in Table 2. In Comparative Examples 1 to 3, the adhesion modification layer was not applied.

[0108]

Table 2

[0109] The abbreviations for the types of the adhesion modification layer in Table 2 are as follows. AGE: Acrylic graft copolymer polyester coating layer for adhesion modification layer. PES: Polyester coating layer for adhesion modification layer. PU: Polyurethane coating layer for adhesion modification layer.

[0110] As shown in Table 2, in Comparative Examples 1 to 3 in which the surface layer (B layer) contained 1% by mass or more of the polyamide-based elastomer, the friction pinhole generation distance was shorter than 2900 cm and the friction pinhole resistance was insufficient. Also, as the content of the polyamide-based elastomer in the surface layer (B layer) increased, the thickness unevenness became worse. The time until the appearance of streaks on the die lip surface was also short. On the other hand, in Examples 1 to 6 in which the content of the polyamide-based elastomer in the surface layer (B layer) was less than 1% by mass, the friction pinhole resistance was good. Also, the deterioration of the film thickness unevenness could be suppressed. The time until the appearance of streaks on the die lip surface was 24 hours or more, enabling efficient production. In Examples 1 to 6, since the base material layer (A layer) contained 2.5% by mass or more of the polyamide-based elastomer, a film with good flexure pinhole resistance was obtained. Also, due to the presence of the adhesion modification layer, a film with sufficiently strong water-resistant laminating strength was obtained.

Industrial Applicability

[0111] The easily adherable polyamide film of the present invention is excellent in impact resistance, flexing pinhole resistance, and friction pinhole resistance, and has high quality with little thickness unevenness. Furthermore, since the water-resistant laminating strength of the film laminated with a sealant is high, it can be suitably used for applications such as packaging materials for foods.

Claims

1. A base material layer (layer A) made of a polyamide resin composition containing a mixed resin of 97.5 to 80% by mass of polyamide 6 resin and 2.5 to 20% by mass of a polyamide-based elastomer, on both surfaces of which a surface layer (layer B) made of a polyamide resin composition containing only 100% by mass of polyamide 6 resin as a polyamide-based resin and not containing a polyamide-based elastomer is laminated. On at least one side of the laminated and stretched polyamide film, an adhesion-modifying layer (layer C) made of any one of a polyester resin, a polyurethane resin, and / or a polyacrylic resin having a coating amount of 0.01 to 3 g / m as a solid content ２ is provided. The easy-adhesion polyamide film is characterized in that the thickness of layer A is 80 to 93% of the total thickness of layer A and layer B.

2. The impact strength is 0.75 J / 15 μm or more, the number of gelbo pinholes when the torsional bending test using a gelbo flex tester is carried out 1000 times at a temperature of 1°C is 5 or less, and the distance until pinholes are generated in the friction resistance pinhole test is 3000 cm or more. The easily adhesive polyamide film according to Claim 1, characterized by the above.

3. The easily adhesive polyamide film according to Claim 1 or 2, characterized in that the thickness of the B layer is at least 0.5 μm or more.

4. The easily adhesive polyamide film according to any one of Claims 1 to 3, characterized in that the polyamide resin composition constituting the B layer contains 0.01 to 0.3% by mass of an antioxidant.

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