Laminated film and packaging container using the same

Abstract

To provide a laminated film having a heat-seal layer that is environmentally friendly and possesses excellent adhesion to A-PET substrates, easy peelability, anti-fogging properties, blocking resistance, and transfer resistance. [Solution] A laminated film having at least two layers, a base layer and a heat-seal layer, wherein the base layer contains a polyester resin containing plant-derived ethylene glycol as a diol component, the heat-seal layer satisfies specific conditions with respect to thickness, two specific types of water-soluble polyester resins and inorganic particles, water contact angle and Tg, and the laminated film satisfies specific conditions with respect to haze value.

Description

Technical Field

[0001] The present invention relates to a laminated film that is environmentally friendly and has antifogging properties, and a packaging container using the same. More specifically, even when the contents are fresh foods such as cut vegetables, salads, and fruits, the visibility of the contents is good by suppressing fogging caused by water vapor generated from the contents, and moreover, it has good heat sealability and开封性 (it seems there is a typo here, perhaps "sealability") with respect to A-PET containers. The present invention relates to a laminated film containing a plant-derived raw material suitable for a packaging container, particularly a container lid material.

Background Art

[0002] Aromatic polyesters typified by polyethylene terephthalate (PET) are widely used as food containers and beverage containers. For example, in a container in which a fitting lid is attached to a formed container, it is used for packaging juices, salads, raw vegetables, etc. by utilizing its excellent transparency and airtightness. In recent years, for the purpose of reducing waste plastics, the lid material is becoming mainstream from the conventional fitting lid to the top seal type.

[0003] In recent years, a transformation to a recycling-oriented society is desired, and similarly in the material field, a shift away from fossil fuels is desired, and the use of biomass is attracting attention. Nowadays, the practical application of biomass plastics using these biomasses as raw materials is rapidly progressing, and attempts to produce polyester, which is a general-purpose polymer material, from these biomass raw materials are actively underway.

[0004] For example, biomass ethanol obtained by fermenting starch and sugars obtained from plants such as corn and sugarcane with microorganisms has been put into practical use, and it has also been successful in industrially producing ethylene glycol from this biomass ethanol via ethylene.

[0005] Furthermore, in recent years, in response to the trend toward monomaterialization, a structure in which a polyester film is coated with a heat-sealable polyester adhesive composition and laminated is being considered as a lid material for A-PET (amorphous polyethylene terephthalate) packaging containers. There is a need for a polyester coating composition that can be used for food applications and also possesses excellent adhesion, easy peelability, anti-fogging properties, and anti-blocking properties.

[0006] For example, Patent Document 1 proposes a composition in which an anti-fogging additive and an anti-blocking agent are added to a blend system of a semi-crystalline polyester resin with a Tg of -30 to 0°C and an amorphous polyester resin with a Tg of 45 to 110°C. Patent Document 2 also proposes an anti-fogging coating agent consisting of a polyester resin, a metal compound, and a surfactant.

[0007] However, while the resin composition in Patent Document 1 has anti-fogging properties and high adhesive strength, it is essential to add an anti-fogging additive other than polyester to impart anti-fogging properties, which presents challenges in terms of recyclability when applied to an A-PET substrate. Similarly, the anti-fogging coating agent in Patent Document 2 requires the separate addition of a surfactant to impart water dispersibility and anti-fogging properties, again presenting challenges in terms of recyclability when applied to an A-PET substrate. Furthermore, in the above-mentioned conventional technologies, anti-fogging properties are achieved by the bleed-out of low molecular weight surfactant components to the surface. This can lead to problems such as sticking to the back surface (blocking) or surfactant adhering to the back surface (transfer to the back) when unwinding a film wound on a roll, potentially causing printing defects or poor adhesion when performing post-processing such as printing or lamination on the opposite side of the sealed surface. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Patent No. 7280826 [Patent Document 2] Japanese Patent Publication No. 2023-51805 [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention was devised to solve the problems of the above-mentioned prior art, and aims to provide a laminated film having a heat-seal layer composed of a water-soluble polyester resin and inorganic particles that also possesses excellent adhesion to an A-PET substrate, easy peelability, anti-fogging properties, blocking resistance, and transfer resistance. It also aims to provide an environmentally friendly laminated film that contains plant-derived raw materials in the substrate layer. Furthermore, it aims to provide a packaging container that uses the laminated film as a lid material. [Means for solving the problem]

[0010] As a result of diligent research to achieve the above objectives, the inventors of the present invention have discovered that by using water-soluble polyester resins with different glass transition temperatures, which themselves possess excellent water dispersibility and anti-fogging properties, it is possible to achieve excellent adhesion to A-PET containers and exhibit anti-fogging properties without adding low molecular weight anti-fogging agents. Furthermore, by including plant-derived raw materials in the base layer, an environmentally friendly laminated film can be provided, leading to the completion of the present invention.

[0011] In other words, the present invention consists of the following configuration. (1) A laminated film having at least two layers, a base layer and a heat-seal layer, wherein the base layer contains a polyester resin containing plant-derived ethylene glycol as a diol component, the heat-seal layer satisfies the following conditions (i) to (iv), and the laminated 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 comprises a water-soluble polyester resin (A), a water-soluble polyester resin (B), and inorganic particles (C), wherein the glass transition temperature of the water-soluble polyester resin (A) is -15°C or higher and less than 20°C, the glass transition temperature of the water-soluble polyester resin (B) is 40°C or higher and 70°C or lower, the mass ratio of water-soluble polyester resin (A) to water-soluble polyester resin (B) is 90 / 10 to 48 / 52, and the content of inorganic particles (C) in the heat seal layer is 0.6 to 10% by mass; (iii) Under conditions of 23°C and 50% RH, 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 between 30° and 60°; (iv) The glass transition temperature of the heat seal layer, as measured by differential scanning calorimetry (DSC), is between 10°C and 25°C; (v) The haze value of the laminated film is 15% or less. (2) The laminated film described in (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) Of the polycarboxylic acid components constituting the water-soluble polyester resin (A), it contains 60 to 95 mol% of aromatic polycarboxylic acid components that do not have sulfonic acid groups, 5 to 20 mol% of aromatic polycarboxylic acid components that have sulfonic acid groups, and 3 to 25 mol% of aliphatic polycarboxylic acid components and / or alicyclic dicarboxylic acids; (vii) Of the polyhydric alcohol components constituting the water-soluble polyester resin (A), it contains more than 50 mol% of glycol containing an ether group; (viii) Of the polycarboxylic acid components constituting the water-soluble polyester resin (B), it contains 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 (1) or (2), wherein the average particle size of the inorganic particles (C) is 1 to 30 μm and the pore volume of the inorganic particles is 2 ml / g or less. (4) The laminated film according to (1) or (2), wherein the base layer is a biaxially oriented polyester film. (5) The laminated film according to (1) or (2), wherein the total biomass content of the polyester resin constituting the base layer is 10% or more and 20% or less. (6) A container lid material comprising the laminated film described in (1) or (2). (7) A packaging container formed by heat-sealing the laminated film described in (1) or (2) onto an A-PET container. [Effects of the Invention]

[0012] The laminated film of the present invention possesses anti-fogging properties, high adhesion to A-PET, and easy peelability, while also suppressing the occurrence of back-side transfer and blocking. Therefore, it can be suitably used as a heat-seal layer for recyclable food packaging containers and exhibits excellent processability. Furthermore, by including plant-derived raw materials in the base layer, an environmentally friendly laminated film can be provided. [Modes for carrying out the invention]

[0013] The embodiments of the present invention will be described in detail below.

[0014] The laminated film of the present invention has at least two layers, a base layer and a heat-seal layer, wherein the base layer contains a polyester resin containing plant-derived ethylene glycol as a diol component, and the heat-seal layer contains at least two types of water-soluble polyester resins (A) and water-soluble polyester resin (B), and inorganic particles (C). The laminated film of the present invention, by containing specific water-soluble polyester resins (A) and water-soluble polyester resin (B) in the heat-seal layer, can exhibit not only excellent easy-peel properties, a wide sealing temperature range, and blocking resistance, but also excellent anti-fogging properties without the addition of an anti-fogging agent.

[0015] <Water-soluble polyester resin (A)> The water-soluble polyester resin (A) has a chemical structure that can be obtained by polycondensation of a polyvalent carboxylic acid component and a polyhydric alcohol component. The polyvalent carboxylic acid component and the polyhydric alcohol component each consist of one or more selected components.

[0016] As the polyvalent carboxylic acid component constituting the water-soluble polyester resin (A), aromatic carboxylic acids, alicyclic polyvalent carboxylic acids, and / or aliphatic polyvalent carboxylic acids are used. Among them, aromatic dicarboxylic acids and aliphatic dicarboxylic acids are preferred.

[0017] It is preferable to contain 60 to 95 mol% of an aromatic polyvalent carboxylic acid component having no sulfonic acid group among the polyvalent carboxylic acid components. More preferably, it is 65 to 95 mol%, and even more preferably, it is 70 to 90 mol%. When the aromatic polyvalent carboxylic acid component having no sulfonic acid group is 60 mol% or more, the adhesion strength when formed into a coating film is good, and when it is 95 mol% or less, the easy-opening property when used as a lid material for a container is improved, which is preferable.

[0018] Examples of the aromatic polyvalent carboxylic acid component include aromatic polyvalent carboxylic acid components such as 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. One or more of these can be used, but it is preferable to use isophthalic acid from the viewpoint of water dispersibility. Also, in order to suppress gelation during synthesis, the content of the aromatic polyvalent carboxylic acid component having three or more functional groups is preferably 3 mol% or less.

[0019] Among the above polycarboxylic acid components, it is preferable to contain 5 to 20 mol% of an aromatic polycarboxylic acid component having a sulfonic acid group. More preferably, it is 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.

[0020] 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. One or more of these can be used.

[0021] Among the above polycarboxylic acid components, it is preferable to contain 3 to 25 mol% of an aliphatic and / or alicyclic polycarboxylic acid component. More preferably, it is 4 to 22 mol%, and even more preferably, it is 5 to 20 mol%. When the aliphatic and / or alicyclic polycarboxylic acid component is 25 mol% or less, the moisture resistance of the resin is maintained, which is preferable.

[0022] 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, citraconic acid, etc. Examples of the alicyclic polycarboxylic acid include 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, 1,2-cyclohexenedicarboxylic acid, 2,5-norbornanedicarboxylic acid, etc. One or more of these can be used.

[0023] Of the polyhydric alcohol components, it is preferable that the mixture contains more than 50 mol% of a glycol containing an ether group, such as diethylene glycol. Preferably, it is 55 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, and it may even be 100 mol%. It is preferable that the mixture contains more than 50 mol% of the above-mentioned glycol containing an ether group, as this improves the water dispersibility of the resin. It is preferable in terms of moisture resistance to have a blending amount of components other than the above-mentioned glycol containing an ether group of 50 mol% or less.

[0024] Examples of polyhydric alcohol components other than diethylene glycol include 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, 1,9-nonanediol, and other aliphatic glycols; 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. One or more of these can be used.

[0025] Furthermore, for purposes such as increasing the acid value, acid anhydrides such as trimellitic anhydride or pyromellitic anhydride may be added after 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 may be used. In the case of post-addition, the total amount of polycarboxylic acid components and polyol components may exceed 200 mol%. In this case, the total amount of the composition excluding the components to which the acid anhydrides were added shall be calculated as 200 mol%.

[0026] When producing a water-soluble polyester resin (A), various polymerization catalysts can be used, such as titanium compounds including tetra-n-butyl titanate, tetraisopropyl titanate, and titanium oxyacetyl cetonate; antimony compounds including antimony trioxide and tributoxyantimony; germanium compounds including germanium oxide and tetra-n-butoxygermanium; and acetates of magnesium, iron, zinc, manganese, cobalt, and aluminum. One or more of these catalysts can be used.

[0027] There are no particular limitations on the method for producing the water-soluble polyester resin (A), but examples include: 1) a method in which a polycarboxylic acid and a polyhydric alcohol are heated in the presence of any catalyst, followed by a dehydration esterification step, and then a depolyhydric alcohol-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 any catalyst, followed by a transesterification reaction, and then a depolyhydric alcohol-polycondensation reaction. In methods 1) and 2), some or all of the acid component may be substituted with an acid anhydride.

[0028] The glass transition temperature (Tg) of the water-soluble polyester resin (A) is preferably -15°C or higher and less than 20°C. More preferably -10°C or higher and less than 20°C. A Tg of less than 20°C for the water-soluble polyester resin (A) is preferable because it improves ease of opening when used as a lid material for containers. A Tg of -15°C or higher for the water-soluble polyester resin (A) is preferable because it reduces the likelihood of blocking during film roll unwinding, etc.

[0029] The reduced viscosity (ηsp / c) of the water-soluble polyester resin (A) is preferably 0.30 to 0.70 dl / g. Setting it above the lower limit of the above range results in good resin cohesiveness and easily exhibits excellent adhesion. Setting it below the upper limit of the above range easily improves water dispersibility. The reduced viscosity can be arbitrarily adjusted 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.

[0030] <Water-soluble polyester resin (B)> The water-soluble polyester resin (B), like the water-soluble polyester resin (A) described above, 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.

[0031] It is preferable that the water-soluble polyester resin (B) contains 1 to 30 mol% of an aromatic polycarboxylic acid component having sodium sulfonate among the polycarboxylic acid components constituting the resin. A content of 1 mol% or more of the aromatic polycarboxylic acid component having sodium sulfonate is preferable as it results in good water solubility. A content of 30 mol% or less is preferable as it results in good water resistance. 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.

[0032] The number average molecular weight of the water-soluble polyester resin (B) is preferably 10,000 to 30,000. More preferably, it is 12,000 to 25,000. If the number average molecular weight is less than the above range, the strength of the heat seal layer will decrease, which may reduce the heat seal strength and make blocking more likely. If it is more than the above range, the viscosity after water dispersion will increase, which may make unevenness more likely during coating.

[0033] The glass transition temperature (Tg) of the water-soluble polyester resin (B) is preferably 40°C to 70°C, and more preferably 45°C to 65°C. In the present invention, the heat seal layer achieves both heat sealability and blocking resistance by using water-soluble polyester resins with different glass transition temperatures in combination. Therefore, it is preferable that the Tg of the water-soluble polyester resin (B) is 40°C or higher, as this improves the blocking suppression effect when used in combination with the water-soluble polyester resin (A), which has a relatively low Tg. On the other hand, it is preferable that the Tg of the water-soluble polyester resin (B) is 70°C or lower, as this allows for high heat seal strength when used in combination with the water-soluble polyester resin (A).

[0034] The water-soluble polyester resin (B) is not particularly limited as long as it satisfies the above conditions, but specific examples include commercially available products such as Pluscoat Z-221 (manufactured by Go-o Chemical Co., Ltd.), Pluscoat Z-446 (manufactured by Go-o Chemical Co., Ltd.), Pluscoat Z-561 (manufactured by Go-o Chemical Co., Ltd.), and Byronal MD-1480 (manufactured by Toyobo Co., Ltd.).

[0035] <Inorganic particles (C)> The inorganic particles (C) are not particularly limited, but examples 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 can be any shape, such as powder, granules, flat plates, or needles.

[0036] 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 preferable because it exhibits an antiblocking effect. Furthermore, a particle size of 30 μm or less is preferable because it results in good adhesive strength when formed into a coating film.

[0037] The pore volume of the inorganic particles (C) is preferably 2 ml / g or less, and more preferably 1 ml / g or less. A pore volume of 2 ml / g or less is preferable because it prevents the particles from being destroyed during the preparation of the coating composition and provides a sufficient antiblocking effect.

[0038] The inorganic particles (C) are preferably 0.6% to 10% by mass of the heat seal layer. More preferably 0.7% to 9% by mass, and more preferably 0.8% to 8% by mass. By setting it to 10% by mass or less, antiblocking properties can be achieved without reducing adhesion.

[0039] 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. A thickness above this lower limit facilitates the development of anti-fogging and heat-sealing properties. 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. A thickness below this upper limit helps to suppress deterioration of thickness unevenness and blocking in the laminate.

[0040] The total content ratio of water-soluble polyester resin (A) and water-soluble polyester resin (B) in the heat seal layer is preferably 60% to 99% by mass of the heat seal layer. Furthermore, the mass ratio of water-soluble polyester resin (A) to 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 water-soluble polyester resin (A) is 90 parts by mass or less, the mass ratio of resins with low Tg is not too high, and a blocking suppression effect is obtained, which is preferable. On the other hand, when the mass ratio of water-soluble polyester resin (A) is 48 parts by mass or more (the mass ratio of water-soluble polyester resin (B) is 52 parts by mass or less), the Tg of the heat seal layer does not become too high, and good heat seal strength is obtained, which is preferable.

[0041] Under conditions of 23°C and 50% RH, when 1 μL of distilled water is dropped onto the surface of the heat-seal layer of the laminated film of the present invention, the water contact angle measured after 1 second is preferably 30° to 60°, more preferably 35° to 60°, and most preferably 40° to 60°. Generally, a smaller water contact angle on the surface of the heat-seal layer is thought to allow water droplets to spread easily and provide excellent anti-fogging properties. However, the heat-seal layer in the present invention provides sufficient anti-fogging properties even when the water contact angle on its back surface is within the above range. This is because, in the case of conventional low-molecular-weight anti-fogging agents, the anti-fogging agent dissolves into the attached water droplets, reducing the wettability of the heat-seal layer. As a result, it becomes necessary to add a large amount of anti-fogging agent in the initial stages, and consequently, sufficient anti-fogging properties cannot be obtained unless the water contact angle on the surface of the heat-seal layer is lowered more than necessary. In contrast, as in the present invention, the polyester resin itself has anti-fogging properties, so there is no dissolution into the attached water droplets, and the heat-seal surface can maintain a certain level of hydrophilicity even after water droplets have adhered, thus providing sufficient anti-fogging properties. Furthermore, as mentioned above, the fact that it is not necessary to excessively reduce the water contact angle (increase hydrophilicity) to obtain sufficient anti-fogging properties is also thought to contribute to the improved blocking performance.

[0042] 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 10°C or higher is preferable because it provides a blocking suppression effect. Furthermore, a Tg of 25°C or lower is preferable because it provides high heat seal strength.

[0043] The heat seal layer in the present invention can be formed by preparing an aqueous coating composition containing the essential components (A), (B), and (C) described above, and applying it to a substrate layer. Preferably, this coating composition contains substantially no curing agent; that is, it is preferable that the curing agent content is less than 1 part by mass (on a solids basis) per 100 parts by mass (on a solids basis) of the water-soluble polyester resin (A). By substantially omitting the curing agent, recycling of the coating film that forms the heat seal layer becomes easier.

[0044] Here, "curing agent" refers to a known curing agent that reacts with a water-soluble polyester resin to form a crosslinked structure. Examples of crosslinked structures include reactions that generate intermolecular carbon-carbon bonds by reacting unsaturated double bonds in the water-soluble polyester resin through radical addition, cationic addition, or anionic addition, or the formation of intermolecular bonds through condensation, polyaddition, or transesterification reactions with polycarboxylic acid groups or polyalcohol groups in the water-soluble polyester resin. Examples of curing agents include phenolic resins, amino resins, isocyanate compounds, epoxy compounds, or β-hydroxylamide compounds, and resins containing unsaturated bonds.

[0045] <Laminated film> The laminated film of the present invention has at least two layers: a base layer and a heat-seal layer. Specifically, the heat-seal layer is laminated on at least one side of a film that will serve as the base layer. The laminated film of the present invention can be obtained by applying an aqueous coating composition consisting of necessary components to a film that will serve as the base layer, and then performing a drying treatment. The thickness of the heat-seal layer is preferably 1 to 5 μm, and more preferably 2 to 4 μm. A thickness of 5 μm or less is preferable as it avoids blocking problems. The haze value of the laminated film is preferably 15% or less, and more preferably 12% or less. A haze value of 15% or less is preferable because it allows for good visibility of the contents when used as a lid for a container, etc.

[0046] The base layer preferably consists mainly of polyethylene terephthalate resin, with terephthalic acid as the dicarboxylic acid component and ethylene glycol as the diol component. Here, "main component" means that when the total amount of components is 100 mol%, it contains 50 mol% or more, preferably 80 mol% or more, and more preferably 90 mol% or more.

[0047] Other dicarboxylic acid components and diol components may be copolymerized as long as they do not hinder the objectives of the present invention. The upper limit of the copolymerization amount of other dicarboxylic acid components and diol components is preferably 15 mol% or less, more preferably 10 mol% or less, and particularly preferably 5 mol% or less, relative to the total dicarboxylic acid component or diol component. By keeping the copolymerization amount of dicarboxylic acid components and diol components below the above upper limit, thickness uniformity is improved, and blocking when stored in roll form is easily suppressed.

[0048] Other dicarboxylic acid components mentioned above include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,4'-dicarboxybiphenyl, and 5-sodium sulfisoisophthalic 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, undecanediic acid, dodecanediic acid, octadecanediic acid, fumaric acid, maleic acid, itaconic acid, mesaconic acid, citraconic acid, and dimer acid.

[0049] Other diol components mentioned above 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; ethylene oxide adducts or propylene oxide adducts of bisphenol A, bisphenol S, bisphenol C, bisphenol Z, bisphenol AP, and 4,4'-biphenol; and alicyclic diols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol.

[0050] The base layer is preferably composed of a polyester resin, and the polyester resin is preferably formed by polymerizing a dicarboxylic acid component and a diol component. The diol component constituting the polyester resin contained in the base layer is preferably plant-derived ethylene glycol. When the total diol component constituting the polyester resin contained in the base layer is 100 mol%, it is preferable that it contains 50 mol% or more of plant-derived ethylene glycol. Furthermore, when the total polyester resin constituting the base layer is 100% by mass, it is preferable that it contains 50 to 100% by mass of polyester resin containing such biomass-derived diol components.

[0051] For polyester raw materials containing plant-derived ethylene glycol as described above, it is preferable that the biomass-derived carbon content, as determined by radiocarbon (C14) measurement, is 10% to 20% of the total carbon in the polyester. Since atmospheric carbon dioxide contains a certain proportion of C14, it is known that the C14 content in plants that grow by taking in atmospheric carbon dioxide is about the same. On the other hand, it is safe to assume that petroleum-derived materials contain virtually no C14. Therefore, the proportion of biomass-derived carbon can be calculated by measuring the proportion of C14 contained in the total number of carbon atoms in the polyester. In this invention, the number of biomass-derived carbon atoms relative to the total number of carbon atoms in the polyester is defined as the biomass percentage (%).

[0052] Taking polyethylene terephthalate as an example, polyethylene terephthalate is a polymer of ethylene glycol containing 2 carbon atoms and terephthalic acid containing 8 carbon atoms in a molar ratio of 1:1. Therefore, if only biomass-derived ethylene glycol is used, the content of biomass-derived carbon relative to the total carbon in the polyester, i.e., the biomass content, will be 20%.

[0053] In the base layer of the present invention, the lower limit of the biomass content is preferably 10%, more preferably 12%, and particularly preferably 14%. On the other hand, in the base layer of the present invention, the upper limit of the biomass content may be 20%. When only ethylene glycol is used as a biomass-derived material, it will be 20% or less.

[0054] The base layer is preferably biaxially stretched to reduce thickness unevenness. Biaxial stretching can be performed by conventionally known methods, for example, by extruding an unstretched resin sheet onto a cooling drum, then heating it using roll heating, infrared heating, etc., and stretching it longitudinally to form a longitudinally stretched film. This stretching is preferably performed using the difference in peripheral speed of two or more rolls. Longitudinal stretching is usually performed in a temperature range of 50 to 120°C. Furthermore, the stretching ratio is preferably 3.0 to 4.0 times. By setting the stretching ratio to 3.0 times or higher, the thickness unevenness of the film is improved, blocking when stored in roll form can be suppressed, and the mechanical strength is sufficiently strong.

[0055] The layer structure of the base material is not particularly limited; it can be a single layer, a two-layer, three-layer, four-layer, or even a multi-layer structure with more layers. Furthermore, each layer may have a different composition.

[0056] The longitudinally stretched film is then subjected to sequential transverse stretching, heat setting, and heat relaxation processes to become a biaxially oriented film. Transverse stretching is usually performed in a temperature range of 60 to 130°C. The transverse stretching ratio is preferably 3.0 to 5.0 times. A stretching ratio of 3.0 times or higher results in good thickness uniformity of the film and sufficiently strong mechanical strength. Conversely, a stretching ratio of 5.0 times or lower can suppress breakage during film formation. After transverse stretching, heat setting is performed, with a preferred temperature range of 170°C to 240°C. The heat setting time is preferably 1 to 60 seconds. Furthermore, for applications where a reduction in thermal shrinkage rate is required, a relaxation treatment may be performed as needed.

[0057] The lower limit of the base layer thickness is preferably 5 μm, more preferably 10 μm, and particularly preferably 15 μm. A thickness of 5 μm or more maintains impact strength and tear strength. The upper limit of the base layer thickness is preferably 100 μm, more preferably 80 μm, and particularly preferably 50 μm. A thickness of 100 μm or less makes it suitable for use as a lid material for food containers, etc.

[0058] The thickness variation of the base material layer is preferably 15% or less, more preferably 10% or less, and particularly preferably 5% or less. By keeping it at 15% or less, it is possible to prevent localized winding stress from being applied to areas with poor thickness variation when stored in roll form, and as a result, blocking can be suppressed.

[0059] A printed layer may be laminated onto the substrate layer. Water-based and solvent-based resin-containing printing inks are preferred as the printing inks for forming the printed layer. Examples of resins used in printing inks include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. The printing inks may also contain known additives such as antistatic agents, light-blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoamers, crosslinking agents, anti-blocking agents, and antioxidants.

[0060] The method for creating the printed layer is not particularly limited, and known printing methods such as offset printing, gravure printing, and screen printing can be used. For drying the solvent after printing, known drying methods such as hot air drying, hot roll drying, and ultraviolet drying can be used.

[0061] The substrate 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 objectives of the present invention. The inorganic thin film layer is preferably made of a metal or an inorganic oxide. The material forming the inorganic thin film layer is not particularly limited as long as it can be formed into a thin film, but from the viewpoint of gas barrier properties, examples of inorganic oxides include aluminum, silicon dioxide (silica), aluminum oxide (alumina), and mixtures of silicon dioxide and aluminum oxide. A composite oxide of silicon dioxide and aluminum oxide is particularly preferred in terms of achieving both flexibility and density in the thin film layer. [Examples]

[0062] The effects of the present invention will be further illustrated below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" simply refers to parts by mass.

[0063] <Measurement of the composition of water-soluble polyester resin> The molar ratios of polycarboxylic acid and polyhydric alcohol components constituting the polyester resin were determined using a 400 MHz ¹H-nuclear magnetic resonance (¹H-NMR) spectrometer. Deuterated chloroform was used as the solvent.

[0064] <Measurement of glass transition temperature (Tg) of water-soluble polyester resin> Using a differential scanning calorimetry (DSC) DSC-220 manufactured by Seiko Instruments Inc., 5 mg of the sample (water-soluble polyester resin) was sealed in an aluminum-lidded container, and measurements were taken from -100°C to 250°C at a heating rate of 20°C / min. The temperature was determined by the intersection of the extension of the baseline below the glass transition temperature and the tangent line showing the maximum slope between the peak rise and the peak apex.

[0065] <Measurement of reduced viscosity (unit: dl / g)> A water-soluble polyester resin was dissolved at a sample concentration of 0.1 g / 25 ml in the measurement solvent phenol / tetrachloroethane (mass ratio 6 / 4), and measured using an Ubbelohde viscometer at a measurement temperature of 30°C.

[0066] <Water dispersibility> For water-soluble polyester resins A-1 to A-8, 210 parts by mass of the water-soluble polyester resin and 490 parts by mass of water were mixed and dissolved by stirring at 80°C. The dispersion state was then evaluated according to the following evaluation criteria. ◎: Disperse completely in water within 1 hour of stirring time without leaving any unemulsified material. In this context, "unemulsified material" refers to the components that settle when the aqueous dispersion is left to stand at 25°C for one day after preparation. ○: Disperse completely in water without leaving any unemulsified material within 1 to 3 hours of stirring. ×: Even after stirring for more than 3 hours, the mixture does not disperse in water, or unemulsified material remains.

[0067] <Average particle size of inorganic particles> The particle size was measured using a HORIBA LA-750 Particle Size Analyzer. The particle size corresponding to 50 mass percent was read, and this value was used as the average particle size.

[0068] <Pore volume of inorganic particles> The BET nitrogen adsorption isotherm was measured using a Cantachrome AS-1 to determine the pore volume. Specifically, the pore volume value used was that at a relative pressure P / P0 = 0.98.

[0069] <Preparation of laminated film for evaluation> Water-soluble polyester resin (A), water-soluble polyester resin (B), and inorganic particles (C) were mixed with water as the solvent in the ratios shown in Tables 2 and 3. This mixture was then coated onto a 25 μm thick biaxially oriented PET film (Toyobo Co., Ltd., Toyobo Ester E5102). The film was then dried at 100°C for 60 seconds to obtain a laminated film.

[0070] <Thickness of the heat seal layer> The thickness of the laminated film (base layer + heat seal layer) was measured using a Millitron 1202D electronic micrometer manufactured by Seiko EM Corporation. Afterward, the heat seal layer side of the laminated film was completely wiped with a solvent in which the heat seal layer is soluble. The thickness of the wiped sample was measured again in the same manner, and the thickness of the heat seal layer was calculated using the following formula. Heat seal layer thickness (μm) = Laminated film thickness (μm) - Sample thickness after wiping (μm)

[0071] <Water contact angle of the heat-sealed layer> Under conditions of 23°C and 50% RH, the water contact angle on the heat-seal layer side of the laminated film was measured using a contact angle meter (KRUSS, DSA100S). The amount of water dropped per measurement was 1 μL, and the angle between the heat-seal layer and the water droplet was read 1 second after dropping. The θ / 2 method was used to read the water contact angle, and 10 water contact angle measurements were taken for each sample. The average value of these measurements was used as the contact angle for that sample.

[0072] <Glass transition temperature (Tg) of the heat seal layer> The heat-seal layer of the laminated film obtained in the examples and comparative examples described later was scraped off with a razor blade, and only the heat-seal layer was isolated and used as a sample. Using a PerkinElmer differential scanning calorimetry (DSC) DSC8500, 5 mg of the sample obtained above was sealed in an aluminum-retaining lid container, and measured from -100°C to 250°C at a heating rate of 20°C / min. The temperature was determined by the temperature at the intersection of the extension of the baseline below the glass transition temperature and the tangent line showing the maximum slope between the rise of the peak and the peak apex.

[0073] <Hayes> In accordance with JIS K7136:2000, the haze of the laminated film was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., 300A). The measurement was performed twice, and the average value was calculated.

[0074] <Heat seal strength> The coated surface of the evaluation laminate film was heat-sealed to a 200 μm thick unstretched A-PET film at heat-seal temperatures of 110°C, 130°C, 150°C, or 180°C, at a pressure of 0.2 MPa, for 1 second. Subsequently, a 15 mm wide test piece was cut, and a 180° peel test was performed at 25°C using a Shimadzu Autograph AG-Xplus at a tensile speed of 200 mm / min to measure the heat seal strength.

[0075] <Easy to open> The heat-sealed side of the evaluation laminated film was placed on top of the A-PET container. The laminated film was then bonded to the container using heat sealing. The heat sealing conditions were a predetermined temperature, a pressure of 0.2 MPa, and a time of 1 second. Afterwards, the ease of peeling the laminated film by hand was judged according to the following criteria. ◎: It was firmly adhered and could be peeled off with light force by hand. ○: It was firmly attached, but could be peeled off by hand. △: The adhesive was insufficient, and it could be peeled off without applying much force. ×: The adhesive was too strong, making it impossible to peel off by hand, or the lid material was damaged.

[0076] <Water resistance> For the evaluation laminated films, after immersion in 23°C water for 24 hours, the heat-sealed layer was rubbed with a finger, and the degree of coating removal was visually evaluated and judged according to the following criteria. ○: No peeling of the heat-sealed layer. ×: The heat-sealed layer has peeled off.

[0077] <Anti-fogging properties> A 30cm x 30cm square sample was cut from the evaluation laminated film. 300mL of 50°C hot water was poured into a plastic container (capacity 500mL, opening diameter approximately 10cm), and the opening of the plastic container was covered with the sample so that the heat-sealed layer side faced the hot water side. The opening was sealed with a rubber band. After the evaluation sample was left to stand for 30 minutes at 5°C, the water droplets adhering to the lid material were visually evaluated and judged according to the following criteria. Rank 1: There was no fogging due to water droplets, and the entire surface was uniformly transparent. Rank 2: Fogging due to water droplets covers less than 20% of the total surface area of ​​the mouthpiece. Rank 3: Water droplets cover 20% to less than 50% of the total surface area of ​​the mouthpiece. Rank 4: Water droplets cover 50% to less than 70% of the total surface area of ​​the mouthpiece. Rank 5: More than 70% of the mouth area is fogged up by water droplets.

[0078] <Blocking properties> A 10cm square was cut from the evaluation laminated film, and the painted surface was heat-pressed against a 10cm square unprocessed surface of a 25μm thick A-PET film at 45°C and 1.5MPa for 30 seconds. Blocking was then evaluated by peeling by hand and judged according to the following criteria. ◎: Can be peeled off by hand without any resistance. ○: There is some resistance to peeling, but it can be peeled off by hand without damaging the material. △: It has peeling resistance, and slight material breakage may occur if peeled off by hand. ×: It has strong peel resistance, and attempting to peel it off will cause the entire material to break.

[0079] <bleed-through> Similar to the blocking evaluation described above, a 10cm square of the evaluation laminated film was cut, and its coated surface was heat-pressed against a 10cm square unprocessed surface of a 25μm thick A-PET film at 45°C and 1.5MPa for 30 seconds. After that, the overlapping laminated films were peeled apart, and the anti-fogging properties of the substrate layer surface that had been in contact with the heat-sealed layer were evaluated using the same procedure as described above for <anti-fogging properties>, and judged according to the following criteria. Note that for those that received a "×" in the blocking evaluation, evaluation was not performed because it was impossible to expose the substrate layer surface. ◎: The anti-fogging rank on the substrate layer side surface is 5 (no anti-fogging effect on the substrate layer side due to transfer to the back). ○: The anti-fogging rank on the substrate layer side surface is 4. △: The anti-fogging rank of the substrate layer side surface is 3-2. ×: The anti-fogging rank on the substrate layer side surface is 1 (anti-fogging properties on the substrate layer side are exhibited due to transfer to the back).

[0080] <Biomass content of the substrate layer> Biomass content was measured in accordance with ASTM D6866-22 Method B (AMS).

[0081] <Manufacturing example> Polyester resin (A-1) In a reaction vessel equipped with a stirrer, thermometer, heating element, cooling device, and distillation cooler, 373 parts by mass of dimethyl isophthalate, 71 parts by mass of dimethyl sodium 5-sulfoisophthalate, 458 parts by mass of diethylene glycol, and 0.2 parts by mass of tetrabutyl titanate were charged, and a transesterification reaction was carried out over 3 hours while raising the temperature to 220°C. After that, the temperature was lowered to 150°C, 49 parts by mass of sebaciate were added, and the esterification reaction was carried out over 4 hours while raising the temperature again to 220°C. After the esterification reaction was completed, the pressure in the system was reduced to 10 torr over 60 minutes while raising the temperature to 270°C, and then 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 desired 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 the measurement of resin properties are shown in Table 1.

[0082] Polyester resin (A-2)~(A-8) Similar to the synthesis of water-soluble polyester resin (A-1), water-soluble polyester resins (A-2) to (A-8) were obtained by changing the types of raw materials and their mixing ratios according to the information in Table 1. Note that water-soluble polyester resins (A-7) and (A-8), which exhibited poor water dispersibility, were not evaluated in laminated films due to the difficulty in preparing aqueous coating solutions.

[0083] Polyester resin (A-9) In an ester reaction vessel, 445 parts by mass of terephthalic acid, 74 parts by mass of isophthalic acid, 270 parts by mass of sebaciic 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 were charged, and the transesterification reaction was carried out over 4 hours while raising the temperature to 230°C. After the transesterification reaction was completed, the temperature in the system was raised to 250°C, and the pressure was reduced to 10 torr over 60 minutes, and the polycondensation reaction was carried out at 250°C for 60 minutes. Then, nitrogen was introduced into the system and the vacuum was broken to terminate the polycondensation reaction. After the reaction was completed, the polyester resin was removed and cooled to obtain polyester resin (A-9). The glass transition temperature of this resin was 7°C.

[0084] Table 1 shows the resin composition and properties of polyester resins (A-1) to (A-9).

[0085] [Table 1]

[0086] Polyester resin (B-1) As the water-soluble polyester resin (B-1), we used Pluscoat Z-221 (glass transition temperature 47°C, pH 4.5~6.5, molecular weight 14,000) manufactured by Go-O Chemical Co., Ltd.

[0087] Polyester resin (B-2) As the water-soluble polyester resin (B-2), we used Plascoat Z-561 (glass transition temperature 64°C, pH 5-7, molecular weight 27,000) manufactured by Go-O Chemical Co., Ltd.

[0088] Water-soluble polyester resin (B-3) Polyester resin (B-3) was obtained by the same method as for polyester resin (A-9), except that the raw materials 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.

[0089] As inorganic particles (C-1), silica particles SYLOBLOC S200 (manufactured by WRGrace and Co., in powder form, average particle size 3 μm, pore volume 0.6 ml / g) were used, and as inorganic particles (C-2), silica particles Silicea 780 (manufactured by Fuji Silicea Co., Ltd., in powder form, average particle size 11 μm, pore volume 0.4 ml / g) were used.

[0090] Polyester resin D: Biomass-derived polyester resin The ethylene glycol used as a raw material was produced by fermenting sugarcane to produce bioethanol, which was then dehydrated to produce bioethylene, and then monoethylene glycol was produced from the bioethylene. Dimethyl terephthalate was extracted from petroleum. A polyethylene terephthalate polyester resin D was obtained with a terephthalate / ethylene glycol ratio of 100 / 100 (mol%), an intrinsic viscosity of 0.69 dl / g, and a biomass content of 20%.

[0091] Polyester resin E: Petroleum-derived polyester resin Polyester resin E, which is polyethylene terephthalate derived from fossil fuels and has an intrinsic viscosity of 0.62 dl / g, was obtained by polymerization using a conventional method from terephthalic acid / ethylene glycol = 100 / 100 (mol%).

[0092] [Example 1] 100 parts by mass of polyester resin D and 0.1 parts by mass of porous silica particles with an average particle size of 2.7 μm and a pore volume of 1.60 ml / g were fed into an extruder. After melting the resin at 280°C in the extruder, it was cast from a T-die at 280°C and brought into contact with a cooling roll at 20°C to obtain a single-layer unstretched sheet. Next, the obtained unstretched sheet was stretched 3.5 times in the MD direction at a temperature of 115°C, and then passed through a tenter to stretch 4.0 times in the TD direction at a temperature of 115°C. Immediately after TD stretching, a heat setting treatment was performed at 220°C for 3 seconds, followed by a relaxation treatment of 7% for 1 second to obtain a biaxially oriented polyester film with a thickness of 25 μm.

[0093] 87% by mass of polyester resin (A-1), 11% by mass of polyester resin (B-1), and 2% by mass of inorganic particles (C-1) were charged, diluted with water to a solid content 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 seal layer. The coating composition obtained above was applied to a substrate layer by the wire bar coating method and dried at 100°C for 60 seconds to obtain a laminated film. The thickness of the coating layer was 3.2 μm.

[0094] [Example 2] to [Example 13], [Comparative Example 1] to [Comparative Example 10] Each laminated film was obtained in the same manner as in Example 1, except that the polyester resin (A), polyester resin (B), and inorganic particles (C) were as described in Tables 2 and 3.

[0095] [Example 14] A laminated film was obtained in the same manner as in Example 1, except that the resin fed into the extruder was changed to 50 parts by mass of polyester resin D, 50 parts by mass of polyester resin E, and 0.1 parts by mass of porous silica particles with an average particle size of 2.7 μm and a pore volume of 1.60 ml / g.

[0096] [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 (Rikemar L-71-D, manufactured by Riken Vitamin Co., Ltd., a nonionic surfactant, HLB 7.3) in an ethyl acetate solution (solid content concentration 10%). This coating composition was applied to the same biaxially oriented polyester film as in Example 1 using the wire bar coating method, and dried at 90°C for 20 seconds to obtain a laminated film. The thickness of the coated layer was 2.0 μm.

[0097] [Reference example 1] A laminated film was obtained in the same manner as in Example 1, except that the resin composition used for the base layer was changed to 100 parts by mass of polyester resin E and 0.1 parts by mass of porous silica particles with an average particle size of 2.7 μm and a pore volume of 1.60 ml / g.

[0098] The composition, physical properties, and evaluation results of various characteristics of the heat seal layers obtained in Examples 1-14, Comparative Examples 1-11, and Reference Example 1 are shown in Tables 2 and 3.

[0099] [Table 2]

[0100] [Table 3]

[0101] As is clear from Table 1, polyester resins A-1 to A-6 had a favorable ratio of polycarboxylic acid components, resulting in sufficient water dispersibility. However, A-7 did not have a favorable ratio of polycarboxylic acid components, resulting in poor water dispersibility. A-8 did not have a favorable ratio of glycol components, resulting in poor water dispersibility. A-9 did not contain aromatic polycarboxylic acid components with sulfonic acid groups and did not disperse in water.

[0102] Furthermore, as is clear from Table 2, all of the laminated films of Examples 1 to 14 possess excellent heat seal strength and anti-fogging properties, and also have easy opening, moisture resistance, and blocking resistance, as well as improved transfer-through. In addition, the base layer contains biomass-derived polyester raw materials, making it an environmentally friendly laminated film.

[0103] On the other hand, in Comparative Example 1, the heat seal strength was reduced because the thickness of the heat seal layer was thin. In Comparative Example 2, the heat seal strength was too high because the thickness of the heat seal layer was thick, resulting in poor ease of opening. In Comparative Examples 3 and 4, the low proportion of water-soluble polyester resin (B) resulted in a low Tg of the heat-seal layer, slightly worsening blocking resistance compared to the laminated film with the resin composition ratio of the present invention. In Comparative Examples 5 and 6, the high proportion of water-soluble polyester resin (B) resulted in an excessively high Tg of the heat-seal layer, leading to reduced heat-seal strength. In Comparative Example 7, the heat seal strength was reduced because the Tg of the water-soluble polyester resin A-5 used was high. In Comparative Example 8, the proportion of aromatic polycarboxylic acid components containing sulfonic acid groups in the water-soluble polyester resin A-6 used was high, resulting in excessive water solubility of the resin and consequently reduced water resistance. In Comparative Example 9, the low amount of inorganic particles added resulted in poor blocking resistance. In Comparative Example 10, the high amount of inorganic particles added resulted in high haze and poor transparency. In Comparative Example 11, instead of using a water-soluble polyester resin, an anti-fogging agent was added. However, due to the addition of a low molecular weight anti-fogging agent, sufficient performance in terms of blocking resistance and transfer resistance could not be obtained. In Reference Example 1, the laminated film had desirable properties such as heat seal strength and anti-fogging properties, but it did not use biomass-derived raw materials in the base layer, and no special measures were taken regarding environmental considerations. [Industrial applicability]

[0104] The laminated film of the present invention possesses anti-fogging properties, high adhesion to A-PET, and easy peelability, while also suppressing the occurrence of back-side transfer and blocking. Therefore, it can be suitably used as a heat-seal layer for recyclable food packaging containers and exhibits excellent processability. Furthermore, by including plant-derived raw materials in the base layer, an environmentally friendly laminated film can be provided.

Claims

1. A laminated film having at least two layers, a base layer and a heat-seal layer, wherein the base layer contains a polyester resin containing plant-derived ethylene glycol as a diol component, the heat-seal layer satisfies the following conditions (i) to (iv), and the laminated 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 comprises a water-soluble polyester resin (A), a water-soluble polyester resin (B), and inorganic particles (C), wherein the glass transition temperature of the water-soluble polyester resin (A) is -15°C or higher and less than 20°C, the glass transition temperature of the water-soluble polyester resin (B) is 40°C or higher and 70°C or lower, the mass ratio of water-soluble polyester resin (A) to water-soluble polyester resin (B) is 90 / 10 to 48 / 52, and the content of inorganic particles (C) in the heat seal layer is 0.6 to 10% by mass; (iii) Under conditions of 23°C and 50% R.H., 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 between 30° and 60°; (iv) The glass transition temperature of the heat seal layer, as measured by differential scanning calorimetry (DSC), is between 10°C and 25°C; (v) The haze value of the laminated film is 15% or less.

2. The laminated 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 (viiii) to (ix): (vi) The water-soluble polyester resin (A) contains 60 to 95 mol% of aromatic polycarboxylic acid components that do not have sulfonic acid groups, 5 to 20 mol% of aromatic polycarboxylic acid components that have sulfonic acid groups, and 3 to 25 mol% of aliphatic polycarboxylic acid components and / or alicyclic dicarboxylic acids; (vii) The water-soluble polyester resin (A) contains more than 50 mol% of the polyhydric alcohol component that comprises a glycol containing an ether group; (viiii) The water-soluble polyester resin (B) contains 1 to 30 mol% of an aromatic polycarboxylic acid component having sodium sulfonate among the polycarboxylic acid components that make up the resin; (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 average particle size of the inorganic particles (C) is 1 to 30 μm, and the pore volume of the inorganic particles is 2 ml / g or less.

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

5. The laminated film according to claim 1 or 2, wherein the total biomass content of the polyester resin constituting the base layer is 10% or more and 20% or less.

6. A container lid material comprising the laminated film described in claim 1 or 2 as a component.

7. A packaging container comprising a PET container heat-sealed with the laminated film described in claim 1 or 2.

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