Laminated film and packaging container using same

Abstract

Provided is a laminated film having a heat seal layer that exhibits, even with respect to an A-PET base material, adhesiveness and easy peelability, as well as antifogging properties, blocking resistance, and offset resistance. This laminated film has two layers of a base material layer and a heat seal layer, wherein: (i) the thickness of the heat seal layer is 1-5 μm; (ii) the heat seal layer contains a water-soluble polyester resin (A), a water-soluble polyester resin (B), and inorganic particles (C), wherein the Tg of (A) is -15°C or more and less than 20°C, the Tg of (B) is 40°C-70°C, the mass ratio of (A) / (B) is 90 / 10-50 / 50, and the content of (C) in the heat seal layer is 0.6%-10% by mass; (iii) when 1 μL of distilled water is dropped on a surface of the heat seal layer of the laminated film, the water contact angle measured after 1 second is 30°-60°; (iv) the Tg of the heat seal layer is 10°C-25°C; and (v) the haze value of the laminate film is 15% or less.

Description

Laminated film and packaging container using same

[0001] The present invention relates to an anti-fogging laminate film and a packaging container using the same. More specifically, the present invention relates to a laminate film suitable for packaging containers, particularly container lids, that can suppress fogging caused by water vapor generated from the contents, even when the contents include fresh foods such as cut vegetables, salads, and fruits, thereby improving visibility of the contents, and that also has good heat-sealing and opening properties for A-PET containers.

[0002] Aromatic polyesters, such as polyethylene terephthalate (PET), are widely used as food and beverage containers. For example, containers with snap-on lids on molded containers are used to package soups, salads, raw vegetables, and other foods, taking advantage of their excellent transparency and airtightness. In recent years, top-seal lids have become mainstream, replacing traditional snap-on lids, in order to reduce plastic waste.

[0003] Furthermore, in response to the recent trend toward mono-materials, lid materials for A-PET (amorphous polyethylene terephthalate) packaging containers have been considered in which a polyester film is coated with a heat-sealable polyester adhesive composition and then bonded together. There is a demand for polyester coating compositions that can be used for food applications and that combine excellent adhesion, easy peelability, anti-fogging properties, and blocking resistance.

[0004] For example, Patent Document 1 proposes a composition in which an anti-fog additive and an anti-blocking agent are added to a blend of a semi-crystalline polyester resin having a Tg of −30 to 0° C. and an amorphous polyester resin having a Tg of 45 to 110° C. Furthermore, Patent Document 2 proposes an anti-fog coating agent comprising a polyester resin, a metal compound, and a surfactant.

[0005] However, although the resin composition of Patent Document 1 has anti-fogging properties and high adhesive strength, it is necessary to add an anti-fogging additive other than polyester to impart anti-fogging properties, which poses a problem in recyclability when applied to an A-PET substrate. Furthermore, the anti-fogging coating agent of Patent Document 2 requires the separate addition of a surfactant to impart water dispersibility and anti-fogging properties, which also poses a problem in recyclability when applied to an A-PET substrate. Furthermore, in the above-mentioned conventional technology, anti-fogging properties are exhibited by bleeding out of a low-molecular-weight surfactant component to the surface, which causes problems such as sticking to the back surface (blocking) when unwinding a film wound around a roll, or adhesion of the surfactant to the back surface (offset), which may cause poor printing or poor adhesion when performing post-processing such as printing or lamination on the surface opposite the sealing surface.

[0006] Japanese Patent No. 7280826 Japanese Patent Application Laid-Open No. 2023-51805

[0007] The present invention has been devised to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a laminated film having a heat seal layer made of a water-soluble polyester resin and inorganic particles, which has excellent adhesion even to A-PET substrates, as well as easy peelability, anti-fogging properties, blocking resistance, and anti-offset properties, and a packaging container using the same.

[0008] As a result of extensive research to achieve the above object, the present inventors have found that by using a water-soluble polyester resin with a different glass transition temperature, which resin itself has both excellent water dispersibility and anti-fogging properties, in combination with the resin, it is possible to achieve excellent adhesion to A-PET containers and to exhibit anti-fogging properties without adding a low-molecular-weight anti-fogging agent, thereby completing the present invention.

[0009] That is, the present invention comprises the following configurations (1) to (6): (1) A laminate film having at least two layers, a base layer and a heat-sealing layer, wherein the heat-sealing layer satisfies the following conditions (i) to (iv), and the laminate film satisfies the following condition (v): (i) the thickness of the heat-sealing layer is 1 μm or more and 5 μm or less; (ii) the heat-sealing layer contains a water-soluble polyester resin (A), a water-soluble polyester resin (B), and inorganic particles (C), wherein the water-soluble polyester resin (A) has a glass transition temperature of −15° C. or more and less than 20° C., the water-soluble polyester resin (B) has a glass transition temperature of 40° C. or more and 70° C. or less, the mass ratio of the water-soluble polyester resin (A) / the water-soluble polyester resin (B) is 90 / 10 to 48 / 52, and the content of the inorganic particles (C) in the heat-sealing layer is 0.6 to 10 mass%; (iii) the heat-sealing layer can be heated at 23° C. and 50% RH. Under these conditions, 1 μL of distilled water is dropped onto the surface of the heat seal layer of the laminated film, and the water contact angle measured after 1 second is 30° or more and 60° or less; (iv) the glass transition temperature of the heat seal layer measured by differential scanning calorimetry (DSC) is 10° or more and 25°C or less; (v) the haze value of the laminated film is 15% or less. (2) The laminate film according to (1), characterized in that the water-soluble polyester resin (A) satisfies the following conditions (vi) to (vii), and the water-soluble polyester resin (B) satisfies the following conditions (viii) to (ix): (vi) Among the polycarboxylic acid components constituting the water-soluble polyester resin (A), 60 to 95 mol % of an aromatic polycarboxylic acid component having no sulfonic acid group is contained, 5 to 20 mol % of an aromatic polycarboxylic acid component having a sulfonic acid group is contained, and 3 to 25 mol % of an aliphatic polycarboxylic acid component and / or an alicyclic dicarboxylic acid is contained; (vii) Among the polyhydric alcohol components constituting the water-soluble polyester resin (A), more than 50 mol % of a glycol having an ether group is contained; (viii) Among the polycarboxylic acid components constituting the water-soluble polyester resin (B), 1 to 30 mol % of an aromatic polycarboxylic acid component having sodium sulfonate is contained; (ix) The number average molecular weight of the water-soluble polyester resin (B) is 10,000 to 30,000.(3) The laminate film according to (1) or (2), wherein the inorganic particles (C) have an average particle size of 1 to 30 μm and a pore volume of 2 ml / g or less. (4) The laminate film according to (1) or (2), wherein the substrate layer is a biaxially oriented polyester film. (5) A container closure material comprising the laminate film according to (1) or (2). (6) A packaging container obtained by heat-sealing the laminate film according to (1) or (2) to an A-PET container.

[0010] The laminated film of the present invention has anti-fogging properties, high adhesion to A-PET, and easy peelability, and also suppresses the occurrence of set-off and blocking. Therefore, it can be suitably used as a heat-seal layer for recyclable food packaging containers and has excellent processability.

[0011] Hereinafter, embodiments of the present invention will be described in detail.

[0012] The laminate film of the present invention has at least two layers, a substrate layer and a heat-sealing layer, and the heat-sealing layer contains at least two types of water-soluble polyester resin (A) and water-soluble polyester resin (B), and inorganic particles (C). Because the heat-sealing layer contains the specific water-soluble polyester resin (A) and water-soluble polyester resin (B), the laminate film of the present invention can not only exhibit excellent easy-peel properties, a wide sealing temperature range, and blocking resistance, but also exhibit excellent anti-fogging properties without the addition of an anti-fogging agent.

[0013] <Water-soluble polyester resin (A)> The water-soluble polyester resin (A) has a chemical structure that can be obtained by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component, and the polycarboxylic acid component and the polyhydric alcohol component each consist of one or more selected components.

[0014] The polycarboxylic acid component constituting the water-soluble polyester resin (A) may be an aromatic carboxylic acid, an alicyclic polycarboxylic acid, or an aliphatic polycarboxylic acid, with aromatic dicarboxylic acids and aliphatic dicarboxylic acids being preferred.

[0015] The polycarboxylic acid component preferably contains 60 to 95 mol % of an aromatic polycarboxylic acid component having no sulfonic acid groups, more preferably 65 to 95 mol %, and even more preferably 70 to 90 mol %. When the aromatic polycarboxylic acid component having no sulfonic acid groups is 60 mol % or more, the adhesive strength of the coating film becomes good, and when it is 95 mol % or less, the ease of opening when used as a container lid material is improved, which is preferable.

[0016] Examples of the aromatic polycarboxylic acid component include terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, phenylenedicarboxylic acid, trimellitic acid, pyromellitic acid, benzophenonetetracarboxylic acid, and alkali metal salts thereof. While one or more of these may be used, it is preferable to use isophthalic acid from the viewpoint of water dispersibility. Furthermore, in order to suppress gelation during synthesis, it is preferable that the content of the trifunctional or higher aromatic polycarboxylic acid component be 3 mol % or less.

[0017] The polycarboxylic acid component preferably contains 5 to 20 mol % of an aromatic polycarboxylic acid component having a sulfonic acid group, more preferably 8 to 20 mol %. When the aromatic polycarboxylic acid component having a sulfonic acid group is 5 mol % or more, the water dispersibility of the resin becomes good, which is preferable. When the aromatic polycarboxylic acid component having a sulfonic acid group is 20 mol % or less, the water resistance of the resin is maintained, which is preferable.

[0018] Examples of the aromatic polycarboxylic acid component having a sulfonic acid group include 5-sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, 5-[4-sulfophenoxy]isophthalic acid, and alkali metal salts thereof, and these can be used alone or in combination.

[0019] Of the polycarboxylic acid components, the aliphatic and / or alicyclic polycarboxylic acid component is preferably contained in an amount of 3 to 25 mol %, more preferably 4 to 22 mol %, and even more preferably 5 to 20 mol %. When the aliphatic and / or alicyclic polycarboxylic acid component is contained in an amount of 25 mol % or less, the moisture resistance of the resin is preferably maintained.

[0020] Examples of the aliphatic polycarboxylic acid component include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid, fumaric acid, maleic acid, itaconic acid, and citraconic acid, and examples of the alicyclic polycarboxylic acid include 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, 1,2-cyclohexenedicarboxylic acid, and 2,5-norbornanedicarboxylic acid. These may be used alone or in combination of two or more.

[0021] Among the polyhydric alcohol components, it is preferable to contain more than 50 mol% of an ether group-containing glycol, such as diethylene glycol. Preferably, it is 55 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and even more preferably 80 mol% or more, and it may even be 100 mol%. When the above-mentioned ether group-containing glycol is contained in an amount of more than 50 mol%, the water dispersibility of the resin becomes good, which is preferable. It is preferable to blend components other than the above-mentioned ether group-containing glycol in an amount of 50 mol% or less in terms of moisture resistance.

[0022] Examples of the polyhydric alcohol component other than diethylene glycol include aliphatic glycols such as ethylene glycol, 1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,4-butanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,8-octanediol, 3-methyl-1,6-hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-1,8-octanediol, and 1,9-nonanediol; alicyclic glycols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecane glycols, and hydrogenated bisphenols; and polyether glycols such as triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. These may be used alone or in combination of two or more.

[0023] In addition, for the purpose of increasing the acid value, acid anhydrides such as trimellitic anhydride and pyromellitic anhydride may be added (post-added) after the polymerization of the water-soluble polyester resin (A). Specific examples of acid anhydrides for imparting acid value include trimellitic anhydride, pyromellitic anhydride, and ethylene glycol bisanhydrotrimellitate, and one or more of these can be used. When added (post-added), the total amount of the polycarboxylic acid component and the polyhydric alcohol component may exceed 200 mol%. In this case, the total amount of the composition excluding the component to which the acid anhydride or the like is added (post-added) is calculated as 200 mol%.

[0024] When producing the water-soluble polyester resin (A), the following polymerization catalysts can be used: titanium compounds such as tetra-n-butyl titanate, tetraisopropyl titanate, and titanium oxyacetylcetonate; antimony compounds such as antimony trioxide and tributoxyantimony; germanium compounds such as germanium oxide and tetra-n-butoxygermanium; and acetates of magnesium, iron, zinc, manganese, cobalt, and aluminum. These catalysts can be used alone or in combination.

[0025] The method for producing the water-soluble polyester resin (A) is not particularly limited, and examples thereof include 1) a method in which a polycarboxylic acid and a polyhydric alcohol are heated in the presence of an arbitrary catalyst, followed by a dehydration esterification step, followed by a polyhydric alcohol removal / polycondensation reaction, and 2) a method in which an alcohol ester of a polycarboxylic acid and a polyhydric alcohol are heated in the presence of an arbitrary catalyst, followed by a transesterification reaction, followed by a polyhydric alcohol removal / polycondensation reaction, etc. In the methods 1) and 2), part or all of the acid component may be substituted with an acid anhydride.

[0026] The glass transition temperature (Tg) of the water-soluble polyester resin (A) is preferably -15°C or higher and lower than 20°C, and more preferably -10°C or higher and lower than 20°C. When the Tg of the water-soluble polyester resin (A) is lower than 20°C, the ease of opening is improved when used as a lid material for a container, which is preferable. When the Tg of the water-soluble polyester resin (A) is -15°C or higher, there is no risk of blocking occurring when preparing a coating composition for a heat seal layer, which is preferable.

[0027] The reduced viscosity (ηsp / c) of the water-soluble polyester resin (A) is preferably 0.30 to 0.70 dl / g. By setting the reduced viscosity at or above the lower limit of the above range, the resin cohesive force is improved and excellent adhesive properties are likely to be exhibited. Furthermore, by setting the reduced viscosity at or below the upper limit of the above range, water dispersibility is likely to be improved. The reduced viscosity can be adjusted as desired by changing the polymerization time, temperature, and degree of reduced pressure during polymerization (in the case of reduced-pressure polymerization) of the water-soluble polyester resin.

[0028] <Water-soluble polyester resin (B)> Similar to the water-soluble polyester resin (A) described above, the water-soluble polyester resin (B) has a chemical structure that can be obtained by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component, and the polycarboxylic acid component and the polyhydric alcohol component each consist of one or more selected components.

[0029] Among the polycarboxylic acid components constituting the water-soluble polyester resin (B), it is preferable to contain 1 to 30 mol % of an aromatic polycarboxylic acid component having sodium sulfonate. When the aromatic polycarboxylic acid component having sodium sulfonate is contained in an amount of 1 mol % or more, water solubility is improved, which is preferable. When the aromatic polycarboxylic acid component having sodium sulfonate is contained in an amount of 30 mol % or less, water resistance is improved, which is preferable. Examples of aromatic polycarboxylic acid components having sodium sulfonate include 5-sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, 5-[4-sulfophenoxy]isophthalic acid, and alkali metal salts thereof.

[0030] The number average molecular weight of the water-soluble polyester resin (B) is preferably 10,000 to 30,000, and more preferably 12,000 to 25,000. If the number average molecular weight is less than the above range, the strength of the heat seal layer decreases, which may result in a decrease in heat seal strength and may also make the resin more susceptible to blocking. If the number average molecular weight is greater than the above range, the viscosity after aqueous dispersion increases, which may make the resin more susceptible to unevenness during coating.

[0031] The glass transition temperature (Tg) of the water-soluble polyester resin (B) is preferably 40°C to 70°C, more preferably 45°C to 65°C. The heat seal layer in the present invention achieves both heat sealability and blocking resistance by using water-soluble polyester resins with different glass transition temperatures in combination. Therefore, if the Tg of the water-soluble polyester resin (B) is 40°C or higher, the blocking suppression effect is improved by using it in combination with the water-soluble polyester resin (A) with a relatively low Tg, which is preferable. On the other hand, if the Tg of the water-soluble polyester resin (B) is 70°C or lower, high heat seal strength can be obtained by using it in combination with the water-soluble polyester resin (A), which is preferable.

[0032] The water-soluble polyester resin (B) is not particularly limited as long as it satisfies the above conditions, but specific examples that can be used include commercially available products such as PLASCOAT Z-221 (manufactured by GOO Chemical Co., Ltd.), PLASCOAT Z-446 (manufactured by GOO Chemical Co., Ltd.), PLASCOAT Z-561 (manufactured by GOO Chemical Co., Ltd.), and Vylonal MD-1480 (manufactured by Toyobo Co., Ltd.).

[0033] <Inorganic particles (C)> Inorganic particles (C) are not particularly limited, but include inorganic particles containing oxides, hydroxides, sulfates, carbonates, or silicates of metals such as magnesium, calcium, barium, zinc, zirconium, molybdenum, silicon, antimony, or titanium.Among these inorganic particles, silica particles are particularly preferred.The shape of the particles is not particularly limited, and may be any shape such as powder, granules, granules, platelets, or needles.

[0034] The average particle size of the inorganic particles (C) is preferably 1 to 30 μm, more preferably 1 to 20 μm, and even more preferably 1 to 12 μm. A particle size of 1 μm or more is preferred because it can exhibit an anti-blocking effect. Furthermore, a particle size of 30 μm or less is preferred because it can improve the adhesive strength when formed into a coating film.

[0035] The pore volume of the inorganic particles (C) is preferably 2 ml / g or less, more preferably 1 ml / g or less. When the pore volume is 2 ml / g or less, there is no risk of the particles being destroyed during preparation of the coating composition, and a sufficient anti-blocking effect is exhibited, which is preferable.

[0036] The inorganic particles (C) are preferably present in the heat seal layer in an amount of 0.6% by mass or more and 10% by mass or less, more preferably 0.7% by mass or more and 9% by mass or less, and even more preferably 0.8% by mass or more and 8% by mass or less. By setting the amount to 10% by mass or less, antiblocking properties can be exhibited without reducing adhesiveness.

[0037] The lower limit of the thickness of the heat seal layer of the present invention is preferably 1 μm, more preferably 1.5 μm, and particularly preferably 2 μm. By making the thickness equal to or greater than the lower limit, anti-fogging properties and heat sealability are easily exhibited. The upper limit of the thickness of the heat seal layer is preferably 5 μm, more preferably 4 μm, and particularly preferably 3.5 μm. By making the thickness equal to or less than the upper limit, it is easy to suppress the thickness unevenness of the laminate and blocking.

[0038] The total content of the water-soluble polyester resin (A) and the water-soluble polyester resin (B) in the heat-seal layer is preferably 60% by mass or more and 99% by mass or less. The mass ratio of the water-soluble polyester resin (A) to the water-soluble polyester resin (B) in the heat-seal layer is preferably 90 / 10 to 48 / 52, more preferably 85 / 15 to 50 / 50, and most preferably 80 / 20 to 55 / 45. When the mass ratio of the water-soluble polyester resin (A) is 90 parts by mass or less, the mass ratio of the resin with a low Tg is not too high, which is preferable because blocking can be suppressed. On the other hand, when the mass ratio of the water-soluble polyester resin (A) is 48 parts by mass or more (the mass ratio of the water-soluble polyester resin (B) is 52 parts by mass or less), the Tg of the heat-seal layer is not too high, which is preferable because heat-seal strength is good.

[0039] The water contact angle measured after 1 second of dropping 1 μL of distilled water on the surface of the heat seal layer of the laminate film of the present invention under conditions of 23° C. and 50% RH is preferably 30° to 60°, more preferably 35° to 60°, and most preferably 40° to 60°. Generally, when the water contact angle on the surface of the heat seal layer is small, water droplets tend to wet and spread easily, resulting in excellent anti-fogging properties. However, the heat seal layer of the present invention can achieve sufficient anti-fogging properties even if the water contact angle on the back surface is within the above range. This is presumably because, when using conventional low molecular weight anti-fogging agents, the anti-fogging agent dissolves in the adhering water droplets, reducing the wettability of the heat-sealing layer side, so that it becomes necessary to add a large amount of anti-fogging agent at the initial stage, and as a result, the water contact angle of the heat-sealing layer surface must be lowered more than necessary in order to obtain sufficient anti-fogging properties, whereas, as in the present invention, the polyester resin itself has anti-fogging properties, so that it does not dissolve in the adhering water droplets, and the heat-sealing surface can maintain a certain degree of hydrophilicity even after the water droplets are attached, so that it can obtain sufficient anti-fogging properties.In addition, as mentioned above, it is not necessary to make the water contact angle too small (high hydrophilicity) to obtain sufficient anti-fogging properties, which is also thought to be one of the reasons for improving blocking properties.

[0040] The glass transition temperature (Tg) of the heat-seal layer in the present invention, as measured by differential scanning calorimetry (DSC), is preferably in the range of 10° C. to 25° C., more preferably 11° C. to 24° C., and most preferably 13° C. to 22° C. A Tg of the heat-seal layer of 10° C. or higher is preferred because it provides a blocking suppression effect. A Tg of the heat-seal layer of 25° C. or lower is preferred because it provides high heat-seal strength.

[0041] The heat seal layer in the present invention can be formed by preparing an aqueous coating composition containing the above essential components (A), (B), and (C) and coating this on a substrate layer.This coating composition preferably does not substantially contain a curing agent, that is, the curing agent content is preferably less than 1 part by mass (solid content equivalent) per 100 parts by mass (solid content equivalent) of the water-soluble polyester resin (A).By substantially not incorporating a curing agent, recycling is easy when the coating film that forms the heat seal layer is made.

[0042] Here, the curing agent refers to a known curing agent that reacts with the water-soluble polyester resin to form a crosslinked structure, and the form of the crosslinked structure can be, for example, a reaction in which an unsaturated double bond in the water-soluble polyester resin is reacted by a radical addition reaction, a cation addition reaction, an anion addition reaction, or the like to form an intermolecular carbon-carbon bond, or the formation of an intermolecular bond by a condensation reaction with a polycarboxylic acid group or a polyhydric alcohol group in the water-soluble polyester resin, a polyaddition reaction, an ester exchange reaction, or the like. Examples of the curing agent include a phenolic resin, an amino resin, an isocyanate compound, an epoxy compound, a β-hydroxylamide compound, an unsaturated bond-containing resin, and the like.

[0043] <Laminate Film> The laminate film of the present invention has at least two layers: a base layer and a heat-sealing layer. Specifically, the heat-sealing layer is laminated on at least one side of the base layer film. The laminate film of the present invention can be obtained by applying an aqueous coating composition containing the necessary components to the base layer film, followed by a drying treatment. The thickness of the heat-sealing layer is preferably 1 to 5 μm, more preferably 2 to 4 μm. A thickness of the heat-sealing layer of 5 μm or less is preferred because it avoids blocking problems. The haze value of the laminate film is preferably 15% or less, more preferably 12% or less. A haze value of 15% or less is preferred because it provides good visibility of the contents when used as a container lid or the like.

[0044] The base layer preferably contains a polyethylene terephthalate resin as a main component, terephthalic acid as a dicarboxylic acid component, and ethylene glycol as a diol component. Here, the term "main component" refers to a component that accounts for 50 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more, of the total amount of all components taken as 100 mol%.

[0045] Other dicarboxylic acid components and diol components may be copolymerized within a range that does not impair the object of the present invention. The upper limit of the copolymerization amount of the other dicarboxylic acid component and diol component is preferably 15 mol% or less, more preferably 10 mol% or less, and particularly preferably 5 mol% or less, based on the total dicarboxylic acid components or diol components. By setting the copolymerization amount of the dicarboxylic acid component and the diol component to the above upper limit or less, thickness unevenness is improved and blocking during storage in roll form is easily suppressed.

[0046] Examples of the other dicarboxylic acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,4'-dicarboxybiphenyl, and 5-sodium sulfoisophthalic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexadicarboxylic acid, 2,5-norbornenedicarboxylic acid, and tetrahydrophthalic acid; and aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, octadecanedioic acid, fumaric acid, maleic acid, itaconic acid, mesaconic acid, citraconic acid, and dimer acid.

[0047] Examples of the other diol component include aliphatic diols such as 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol, 1,10-decanediol, dimethyloltricyclodecane, and triethylene glycol; alicyclic diols such as bisphenol A, bisphenol S, bisphenol C, bisphenol Z, bisphenol AP, ethylene oxide adducts or propylene oxide adducts of 4,4'-biphenol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol.

[0048] The substrate layer is preferably biaxially stretched to reduce thickness unevenness. Biaxial stretching can be performed by a conventionally known method. For example, an unstretched resin sheet extruded onto a cooling drum is subsequently heated by roll heating, infrared heating, or the like, and stretched in the longitudinal direction to form a longitudinally stretched film. This stretching is preferably performed using the difference in peripheral speed between two or more rolls. Longitudinal stretching is usually performed in a temperature range of 50 to 120°C. The longitudinal stretching ratio is preferably 3.0 to 4.0 times. A stretching ratio of 3.0 times or more improves thickness unevenness of the film, suppresses blocking when stored in a rolled form, and provides sufficiently strong mechanical strength.

[0049] The longitudinally stretched film is then subjected to the sequential processes of transverse stretching, heat setting, and heat relaxation to produce a biaxially oriented film. Transverse stretching is typically performed at a temperature ranging from 60 to 130°C. The transverse stretching ratio is preferably 3.0 to 5.0 times. A stretching ratio of 3.0 times or more improves film thickness uniformity, suppresses the deterioration of anti-fogging properties due to offset of the anti-fogging agent when stored in roll form, and ensures sufficient mechanical strength. Furthermore, a stretching ratio of 5.0 times or less prevents breakage during film formation. After transverse stretching, a heat setting treatment is performed, preferably at a temperature ranging from 170 to 240°C. The heat setting time is preferably 1 to 60 seconds. Furthermore, for applications requiring reduced thermal shrinkage, a relaxation treatment may be performed as needed.

[0050] The lower limit of the thickness of the substrate layer is preferably 5 μm, more preferably 10 μm, and particularly preferably 15 μm. By making it 5 μm or more, impact strength and tear strength can be maintained. The upper limit of the thickness of the substrate layer is preferably 100 μm, more preferably 80 μm, and particularly preferably 50 μm. By making it 100 μm or less, it can be suitably used as a lid material for containers such as food products.

[0051] The thickness unevenness of the base material layer is preferably 15% or less, more preferably 10% or less, and particularly preferably 5% or less. By setting the thickness unevenness to 15% or less, when the base material layer is stored in a roll form, it is possible to prevent localized application of winding stress to areas with poor thickness unevenness, and as a result, it is possible to suppress blocking.

[0052] A printing layer may be laminated on the substrate layer. The printing ink for forming the printing layer is preferably a water-based or solvent-based resin-containing printing ink. Resins used in printing inks include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. The printing ink may contain known additives such as antistatic agents, light-blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, antifoaming agents, crosslinking agents, antiblocking agents, and antioxidants.

[0053] The method for providing the printed layer is not particularly limited, and known printing methods such as offset printing, gravure printing, screen printing, etc. can be used. To dry the solvent after printing, known drying methods such as hot air drying, heat roll drying, and ultraviolet drying can be used.

[0054] The base layer may be provided with a gas barrier layer such as an inorganic thin film layer or a metal layer, as long as it does not impair the object of the present invention. The inorganic thin film layer is preferably made of a metal or an inorganic oxide. There are no particular restrictions on the material that forms the inorganic thin film layer, as long as it can be formed into a thin film. From the viewpoint of gas barrier properties, inorganic oxides such as aluminum, silicon oxide (silica), aluminum oxide (alumina), and mixtures of silicon oxide and aluminum oxide are preferred. A composite oxide of silicon oxide and aluminum oxide is particularly preferred from the viewpoint of achieving both flexibility and density in the thin film layer.

[0055] The effects of the present invention will be further illustrated below with reference to examples, but the present invention is not limited to these. In the examples and comparative examples, parts simply refer to parts by mass.

[0056] <Measurement of composition of water-soluble polyester resin> Using a 400 MHz 1H-nuclear magnetic resonance spectrometer (1H-NMR), the molar ratios of the polycarboxylic acid component and polyhydric alcohol component constituting the polyester resin were determined. Deuterated chloroform was used as the solvent.

[0057] <Measurement of Glass Transition Temperature (Tg) of Water-Soluble Polyester Resin> Using a differential scanning calorimeter (DSC) DSC-220 manufactured by Seiko Instruments Inc., 5 mg of a sample (water-soluble polyester resin) was sealed in an aluminum lidded container, and measurement was performed from −100° C. to 250° C. at a temperature increase rate of 20° C. / min. The glass transition temperature (Tg) was determined as the temperature at the intersection of an extension of the baseline below the glass transition temperature and a tangent line showing the maximum slope between the rising part of the peak and the peak apex.

[0058] <Measurement of reduced viscosity (unit: dl / g)> A water-soluble polyester resin was dissolved in a measurement solvent of phenol / tetrachloroethane (mass ratio 6 / 4) at a sample concentration of 0.1 g / 25 ml, and the reduced viscosity was measured at a measurement temperature of 30° C. using an Ubbelohde viscometer.

[0059] <Water Dispersibility> For water-soluble polyester resins A-1 to A-8, 210 parts by mass of water-soluble polyester resin and 490 parts by mass of water were mixed and stirred to dissolve at 80°C, and the dispersion state was evaluated according to the following evaluation criteria. ⊚: Dispersed in water within 1 hour of stirring without leaving any unemulsified matter. The unemulsified matter referred to here refers to components that settle when the aqueous dispersion is left to stand for 1 day at 25°C after preparation. ◯: Dispersed in water within 1 to 3 hours of stirring without leaving any unemulsified matter. ×: Not dispersed in water or unemulsified matter remains even after stirring for more than 3 hours.

[0060] <Average particle size of inorganic particles> Measurement was performed using a HORIBA LA-750 Particle Size Analyzer. The particle size corresponding to 50 mass percent was read and this value was taken as the average particle size.

[0061] <Pore Volume of Inorganic Particles> The pore volume was determined by measuring the BET nitrogen adsorption isotherm using AS-1 manufactured by Quantachrome Co., Ltd. Specifically, the pore volume was determined when the relative pressure P / P0 was 0.98.

[0062] <Preparation of Laminated Film for Evaluation> The water-soluble polyester resin (A), the water-soluble polyester resin (B), and the inorganic particles (C) were mixed in the ratios shown in Tables 2 and 3 using water as a solvent, and this mixture was applied to a biaxially stretched PET film (Toyobo Ester E5102, manufactured by Toyobo Co., Ltd.) having a thickness of 25 μm. The film was then dried at 100° C. for 60 seconds to obtain a laminated film.

[0063] <Thickness of Heat Seal Layer> The thickness of the laminate film (base layer + heat seal layer) was measured using a Millitron 1202D electronic micrometer manufactured by Seiko EM Corporation. Then, the heat seal layer side of the laminate film was completely wiped off with a solvent in which the heat seal layer is soluble. The thickness of the sample after wiping was also measured in the same way, and the thickness of the heat seal layer was calculated using the following formula: Thickness of heat seal layer (μm) = Thickness of laminate film (μm) - Thickness of sample after wiping (μm)

[0064] <Water contact angle of heat seal layer> The water contact angle of the heat seal layer side of the laminated film was measured using a contact angle meter (DSA100S, manufactured by KRUSS) under conditions of 23°C and 50% RH. The amount of water dropped per measurement was 1 μL, and the angle between the heat seal layer and the water drop was read 1 second after the drop. The water contact angle was measured using the θ / 2 method, and water contact angles were measured at 10 locations per sample, and the average value was used as the contact angle of that sample.

[0065] <Haze> The haze of the laminated film was measured using a haze meter (300A, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136: 2000. The measurement was carried out twice, and the average value was calculated.

[0066] <Glass Transition Temperature (Tg) of Heat-Seal Layer> The heat-seal layer of the laminated film obtained in the Examples and Comparative Examples described below was scraped off with a razor blade, and only the heat-seal layer was isolated and used as a sample. 5 mg of the sample obtained above was sealed in an aluminum lidded container using a PerkinElmer DSC8500 differential scanning calorimeter (DSC), and measurement was performed from -100°C to 250°C at a heating rate of 20°C / min. The glass transition temperature (Tg) of the heat-seal layer was determined as the temperature at the intersection of an extension of the baseline below the glass transition temperature and a tangent line showing the maximum slope between the rising part of the peak and the peak apex.

[0067] <Heat seal strength> The coated surface of the laminate film for evaluation was heat-sealed to a 200 μm thick unstretched A-PET film at a heat seal temperature of 110° C., 130° C., 150° C., or 180° C. under a pressure of 0.2 MPa for 1 second. Thereafter, a 15 mm wide test piece was cut out and subjected to a 180° peel test at 25° C. using an Autograph AG-Xplus manufactured by Shimadzu Corporation at a tensile speed of 200 mm / min to measure the heat seal strength.

[0068] <Ease of opening> The heat seal layer side of the laminate film for evaluation was placed on an A-PET container. The laminate film was heat sealed from above. The heat sealing conditions were a specified temperature, a pressure of 0.2 MPa, and a time of 1 second. The laminate film was then peeled off by hand, and the ease of peeling was evaluated according to the following criteria: ◎: Sufficiently adhered and could be peeled off by hand with light force. ○: Sufficiently adhered but could be peeled off by hand. △: Adhesion was insufficient and could be peeled off without force. ×: Adhesion was too strong and could not be peeled off by hand, or the lid material was damaged.

[0069] <Water resistance> After immersing the laminated film for evaluation in water at 23°C for 24 hours, the heat seal layer was rubbed with a finger and the state of peeling of the coating film was visually evaluated and rated according to the following criteria: ◯: No peeling of the heat seal layer; ×: Peeling of the heat seal layer occurred.

[0070] <Anti-Fog Properties> A 30 cm x 30 cm square sample was cut from the laminate film for evaluation. 300 mL of 50°C hot water was poured into a plastic container (500 mL capacity, approximately 10 cm diameter of the mouth). The sample was used to cover the mouth of the plastic container with the heat seal layer facing the hot water, to prepare an evaluation sample. The mouth was sealed with a rubber band. The evaluation sample was left to stand for 30 minutes at 5°C, and then visually evaluated for water droplets adhering to the lid material, and rated according to the following criteria: Rank 1: No water droplet-induced fogging, and the entire surface was uniformly transparent. Rank 2: Water droplet-induced fogging was less than 20% of the total mouth area. Rank 3: Water droplet-induced fogging was 20% or more but less than 50% of the total mouth area. Rank 4: Water droplet-induced fogging was 50% or more but less than 70% of the total mouth area. Rank 5: Water droplet-induced fogging was 70% or more of the total mouth area.

[0071] <Blocking properties> The laminated film for evaluation was cut into a 10 cm square, and the coated surface was heat-pressed against a 10 cm square untreated surface of a 25 μm thick A-PET film at a temperature of 45°C and a pressure of 1.5 MPa for 30 seconds. Blocking was then evaluated by peeling it off by hand and rated according to the following criteria: ◎: Can be peeled off by hand with no peeling resistance. ○: There is some peeling resistance, but it can be peeled off by hand without breaking the material. △: There is peeling resistance, and some material breakage occurs when peeling by hand. ×: There is strong peeling resistance, and the material breaks all over when trying to peel it off.

[0072] <Set-off> As in the blocking evaluation described above, the evaluation laminate film was cut into a 10 cm square, and the coated surface was heat-pressed against a 10 cm square untreated surface of a 25 μm thick A-PET film at a temperature of 45° C. and a pressure of 1.5 MPa for 30 seconds. Thereafter, the laminated film was peeled off, and the anti-fogging property of the substrate layer side of the substrate layer surface that had been in contact with the heat seal layer was evaluated in the same manner as in the <Anti-fogging Property> described above, and rated according to the following criteria. For samples that were rated × in the blocking evaluation, the substrate layer surface could not be exposed, so no evaluation was performed. ⊚: Anti-fogging rank of the substrate layer side surface was 5 (anti-fogging property on the substrate layer side was not exhibited due to set-off). ○: Anti-fogging rank of the substrate layer side surface was 4. △: Anti-fogging rank of the substrate layer side surface was 3 to 2. ×: Anti-fogging rank of the substrate layer side surface was 1 (anti-fogging property on the substrate layer side was exhibited due to set-off).

[0073] Polyester Resin (A-1) 373 parts by mass of dimethyl isophthalate, 71 parts by mass of 5-dimethylsodium sulfoisophthalate, 458 parts by mass of diethylene glycol, and 0.2 parts by mass of tetrabutyl titanate were charged into a reactor equipped with a stirrer, thermometer, heater, cooling device, and distillation condenser. The mixture was heated to 220°C and subjected to a transesterification reaction over 3 hours. The temperature was then lowered to 150°C, 49 parts by mass of sebacic acid was added, and the mixture was heated again to 220°C and subjected to an esterification reaction over 4 hours. After the esterification reaction was completed, the pressure inside the system was increased to 270°C while reducing the pressure to 10 torr over 60 minutes, and the pressure was further reduced to a vacuum of 1 torr or less, and a polycondensation reaction was carried out at 270°C until the predetermined viscosity was reached. After the reaction was completed, the water-soluble polyester resin was removed and cooled to obtain water-soluble polyester resin (A-1). The resin composition and the results of measuring the resin's physical properties are shown in Table 1.

[0074] Polyester Resins (A-2) to (A-8) Water-soluble polyester resins (A-2) to (A-8) were obtained in the same manner as in the synthesis of water-soluble polyester resin (A-1), except that the types and blending ratios of raw materials were changed according to the descriptions in Table 1. Water-soluble polyester resins (A-7) and (A-8) had poor water dispersibility, and therefore were not evaluated in laminate films because it was difficult to prepare an aqueous coating solution for them.

[0075] Polyester Resin (A-9) An ester reactor was charged with 445 parts by mass of terephthalic acid, 74 parts by mass of isophthalic acid, 270 parts by mass of sebacic acid, 277 parts by mass of ethylene glycol, 465 parts by mass of 2,2-dimethyl-1,3-propanediol, and 0.5 parts by mass of tetrabutyl titanate, and the mixture was heated to 230°C while carrying out a transesterification reaction over 4 hours. After completion of the transesterification reaction, the system was heated to 250°C while the pressure was reduced to 10 torr over 60 minutes, and a polycondensation reaction was carried out at 250°C for 60 minutes. Nitrogen was then flowed into the system, and the polycondensation reaction was terminated by breaking the vacuum. After completion of the reaction, the polyester resin was removed and cooled to obtain polyester resin (A-9). The glass transition temperature of this resin was 7°C.

[0076] The resin compositions and physical properties of the polyester resins (A-1) to (A-9) are shown in Table 1.

[0077]

[0078] Polyester Resin (B-1) As the water-soluble polyester resin (B-1), PLASCOAT Z-221 (glass transition temperature 47° C., pH 4.5 to 6.5, molecular weight 14,000) manufactured by GOO Chemical Co., Ltd. was used.

[0079] Polyester Resin (B-2) As the water-soluble polyester resin (B-2), PLASCOAT Z-561 (glass transition temperature 64° C., pH 5 to 7, molecular weight 27,000) manufactured by GOO Chemical Co., Ltd. was used.

[0080] Water-soluble polyester resin (B-3)

[0063] Polyester resin (B-3) was obtained by the same method as for producing polyester resin (A-9), except that in the synthesis method for polyester resin (A-9), the raw materials used were changed to 455 parts by mass of dimethyl terephthalate, 455 parts by mass of dimethyl isophthalate, 291 parts by mass of ethylene glycol, 488 parts by mass of 2,2-dimethyl-1,3-propanediol, and 0.5 parts by mass of tetrabutyl titanate. The glass transition temperature of this resin was 67°C.

[0081] Silica particles SYLOBLOC S200 (manufactured by W.R. Grace and Co., powder form, average particle size 3 μm, pore volume 0.6 ml / g) were used as inorganic particles (C-1), and silica particles Sylysia 780 (manufactured by Fuji Silysia Ltd., powder form, average particle size 11 μm, pore volume 0.4 ml / g) were used as inorganic particles (C-2).

[0082] Example 1: 87% by weight of polyester resin (A-1), 11% by weight of polyester resin (B-1), and 2% by weight of inorganic particles (C-1) were charged, diluted with water to a solids ratio of 25%, and stirred at room temperature for 30 minutes. After cooling to room temperature, the mixture was removed from the container to obtain a coating composition for forming a heat-sealing layer. The coating composition obtained above was applied to a biaxially oriented polyester film (Toyobo Co., Ltd., Toyobo Ester E5202, thickness 25 μm) using a wire bar coating method, and dried at 100°C for 60 seconds to obtain a laminated film. The coating layer had a thickness of 3.2 μm.

[0083] [Examples 2 to 13], [Comparative Examples 1 to 10] Each laminate film was obtained in the same manner as in Example 1, except that the polyester resin (A), the polyester resin (B), and the inorganic particles (C) were changed as shown in Tables 2 and 3.

[0084] [Comparative Example 11] A coating composition was obtained by heating and stirring 65% by mass of polyester resin (A-9), 28% by mass of polyester resin (B-3), 2% by mass of inorganic particles (C), and 5% by mass of an anti-fogging agent (Rikemal L-71-D, nonionic surfactant, HLB 7.3, manufactured by Riken Vitamin Co., Ltd.) in an ethyl acetate solution (solids concentration 10%). This coating composition was applied to the same biaxially oriented polyester film as in Example 1 by wire bar coating and dried at 90°C for 20 seconds to obtain a laminated film. The thickness of the coating layer was 2.0 μm.

[0085] The compositions and physical properties of the heat seal layers of Examples 1 to 13 and Comparative Examples 1 to 11 obtained above, as well as the evaluation results of various characteristics, are shown in Tables 2 and 3.

[0086]

[0087]

[0088] As is clear from Table 1, in polyester resins A-1 to A-6, the ratio of the polycarboxylic acid component was within the preferred range, and sufficient water dispersibility was obtained, but in A-7, the ratio of the polycarboxylic acid component was not within the preferred range, resulting in poor water dispersibility. In A-8, the ratio of the glycol component was not within the preferred range, resulting in poor water dispersibility. In A-9, no aromatic polycarboxylic acid component having a sulfonic acid group was contained, and it was not dispersed in water.

[0089] Furthermore, as is clear from Table 2, all of the laminated films of Examples 1 to 13 have excellent heat seal strength and anti-fogging properties, and further have all of easy-open properties, moisture resistance, and blocking resistance, and further have improved set-off.

[0090] On the other hand, in Comparative Example 1, the heat seal layer was thin, resulting in reduced heat seal strength. In Comparative Example 2, the heat seal layer was thick, resulting in excessively high heat seal strength and poor ease of opening. In Comparative Examples 3 and 4, the composition ratio of the water-soluble polyester resin (B) was low, resulting in a low Tg of the heat seal layer, and blocking resistance was slightly worse than that of the laminate film of the present invention. In Comparative Examples 5 and 6, the composition ratio of the water-soluble polyester resin (B) was high, resulting in an excessively high Tg of the heat seal layer and reduced heat seal strength. In Comparative Example 7, the water-soluble polyester resin A-5 used had a high Tg, resulting in reduced heat seal strength. In Comparative Example 8, the water-soluble polyester resin A-6 used had a high proportion of an aromatic polycarboxylic acid component having sulfonic acid groups, resulting in excessively high water solubility of the resin and reduced water resistance. In Comparative Example 9, the amount of inorganic particles added was small, resulting in poor blocking resistance. In Comparative Example 10, the amount of inorganic particles added was large, resulting in increased haze and reduced transparency. In Comparative Example 11, a water-soluble polyester resin was not used as the polyester resin, but an anti-fogging agent was added instead. However, due to the addition of a low molecular weight anti-fogging agent, sufficient performance could not be obtained in terms of blocking resistance and offset resistance.

[0091] The laminate film of the present invention is a laminate film that combines excellent adhesion to A-PET substrates with easy-open properties, anti-fogging properties, anti-blocking properties, and anti-offset properties, and therefore can suppress fogging caused by water vapor generated from the contents, even when the contents are fresh foods such as cut vegetables, salads, and fruits, thereby improving the visibility of the contents, and has the potential for widespread industrial use. Furthermore, because it has excellent recyclability when applied to a PET substrate, it is expected that using packaging containers using the laminate film of the present invention as a lid material will contribute to reducing waste plastic and promoting mono-materialization.

Claims

1. A laminate film having at least two layers, a base layer and a heat seal layer, characterized in that the heat seal layer satisfies the following conditions (i) to (iv), and the laminate film satisfies the following condition (v): (i) the thickness of the heat seal layer is 1 μm or more and 5 μm or less; (ii) the heat seal layer contains a water-soluble polyester resin (A), a water-soluble polyester resin (B), and inorganic particles (C), the water-soluble polyester resin (A) has a glass transition temperature of -15°C or more and less than 20°C, the water-soluble polyester resin (B) has a glass transition temperature of 40°C or more and 70°C or less, the mass ratio of the water-soluble polyester resin (A) / the water-soluble polyester resin (B) is 90 / 10 to 48 / 52, and the content of the inorganic particles (C) in the heat seal layer is 0.6 to 10 mass%; (iii) the heat seal layer can be maintained at 23°C, 50% RH. Under these conditions, 1 μL of distilled water is dropped onto the surface of the heat seal layer of the laminated film, and the water contact angle measured after 1 second is 30° or more and 60° or less; (iv) the glass transition temperature of the heat seal layer measured by differential scanning calorimetry (DSC) is 10° or more and 25°C or less; (v) the haze value of the laminated film is 15% or less.

2. The laminate film according to claim 1, wherein the water-soluble polyester resin (A) satisfies the following conditions (vi) to (vii), and the water-soluble polyester resin (B) satisfies the following conditions (viii) to (ix): (vi) the polycarboxylic acid components constituting the water-soluble polyester resin (A) contain 60 to 95 mol % of an aromatic polycarboxylic acid component not having a sulfonic acid group, 5 to 20 mol % of an aromatic polycarboxylic acid component having a sulfonic acid group, and 3 to 25 mol % of an aliphatic polycarboxylic acid component and / or an alicyclic dicarboxylic acid; (vii) the polyhydric alcohol components constituting the water-soluble polyester resin (A) contain more than 50 mol % of a glycol containing an ether group; (viii) the polycarboxylic acid components constituting the water-soluble polyester resin (B) contain 1 to 30 mol % of an aromatic polycarboxylic acid component having sodium sulfonate; (ix) the number average molecular weight of the water-soluble polyester resin (B) is 10,000 to 30,000.

3. The laminated film according to claim 1 or 2, wherein the inorganic particles (C) have an average particle size of 1 to 30 μm and a pore volume of 2 ml / g or less.

4. The laminated film according to claim 1 or 2, wherein the substrate layer is a biaxially oriented polyester film.

5. A container lid material comprising the laminated film according to claim 1 or 2 as a constituent element.

6. A packaging container characterized by being formed by heat-sealing the laminated film according to claim 1 or 2 to an A-PET container.

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