Freshness preservation packaging containers

Abstract

The present invention provides a packaging container that is particularly suitable for maintaining the freshness of fruits and vegetables, and that has good anti-fogging properties and is easy to open. [Solution] A food freshness preservation packaging container comprising a heat-sealable lid material and a container mainly composed of polyethylene terephthalate, wherein the heat-sealable lid material is composed of two or more layers including a base layer mainly composed of polyethylene terephthalate and a heat-seal layer containing at least two types of polyester resin and an anti-fogging agent, the heat seal strength between the heat-sealable lid material and the container is 1.0 N / 15 mm or more and 15 N / 15 mm or less, the oxygen permeability of the heat-sealable lid material measured at a temperature of 23°C and a relative humidity of 65% RH is 200 [cc / (m2·d·atm)] or less, and the water vapor permeability of the heat-sealable lid material measured at a temperature of 40°C and a relative humidity of 90% RH is 100 [g / (m2·d)] or less, a freshness preservation packaging container.

Description

[Technical Field]

[0001] This invention relates to food packaging containers. [Background technology]

[0002] Aromatic polyesters, such as polyethylene terephthalate (PET), are widely used as food and beverage containers. For example, in containers with fitted lids, their excellent transparency and airtightness make them suitable for packaging soups, salads, and fresh vegetables. In particular, when packaging foods such as salads and fresh vegetables, anti-fogging properties are required because moisture released from the vegetables can cause fogging inside the container.

[0003] Patent Document 1 discloses a packaging container manufactured by heat-forming the container body and a lid coated with an anti-fogging agent using vacuum pressure forming, and then bonding the container body and lid together using heat sealing.

[0004] In recent years, there has been a trend towards using top-seal lids to facilitate easy opening, standardize lid materials (monomaterial), and reduce waste by decreasing thickness. Top-seal lids, like those with interlocking lids, require transparency, airtightness, anti-fogging properties, as well as ease of opening. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-14295 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a packaging container that is particularly suitable for maintaining the freshness of fruits and vegetables, can extend shelf life (expiration date), enhances product value (appearance), and has good anti-fogging and easy-to-open properties. [Means for solving the problem]

[0007] As a result of diligent research by the present inventors, we have discovered that a food packaging container comprising a heat-sealable lid material including a base layer mainly composed of polyethylene terephthalate and a heat-seal layer containing an anti-fogging agent, and a container mainly composed of polyethylene terephthalate, has an excellent effect in maintaining the freshness of fruits and vegetables, and have completed the inventions represented below.

[0008] (Section 1) A food freshness preservation packaging container comprising a heat-sealable lid material and a container whose main component is polyethylene terephthalate, The heat-sealable lid material is composed of two or more layers, including a base layer mainly composed of polyethylene terephthalate and a heat-seal layer containing an anti-fogging agent. The heat seal strength between the heat-sealable lid material and the container is 1.0 N / 15 mm or more and 15 N / 15 mm or less. The oxygen permeability of the heat-sealable lid material, measured under conditions of 23°C and 65% RH relative humidity, is 200 cc / (m²·d·atm) or less. A freshness-preserving packaging container having a heat-sealable lid material whose water vapor permeability under conditions of 40°C and 90% RH is 100 g / (m²·d) or less. (Section 2) The freshness-preserving packaging container according to item 1, wherein the heat-seal layer of the heat-sealable lid material contains a polyester resin and an anti-fogging agent, and the mass ratio of the polyester resin to the anti-fogging agent in the heat-seal layer is 99:1 to 80:20. (Section 3) The freshness-preserving packaging container according to item 1 or 2, wherein the heat-sealable lid material has a breaking strength of 180 MPa or more and 260 MPa or less in either the longitudinal or widthwise direction. (Section 4) A freshness-preserving packaging container according to any one of claims 1 to 3, wherein the elongation at break of the heat-sealable lid material in either the longitudinal or widthwise direction is 80% or more and 170% or less. (Section 5) The freshness-preserving packaging container according to any one of claims 1 to 4, wherein the heat-sealable lid material has a heat-sealing layer, a base material layer, and a printing layer in this order.

Effect of the Invention

[0009] The heat-sealable lid material of the packaging container of the present invention has a low oxygen permeability and a water vapor permeability within a predetermined range, and an antifogging agent is contained in the antifogging heat-sealing layer of the heat-sealable lid material. By setting the heat-sealing strength between the container body and the heat-sealable lid material to be 1 N / mm or more and 15 N / mm or less, it is possible to contribute to extending the shelf life of contents such as fruits and vegetables and improving the commercial value, and a packaging container with good antifogging properties and easy opening properties can be obtained.

Brief Description of the Drawings

[0010] [Figure 1] It is a schematic view of the shape of the A-PET container used in the examples.

Modes for Carrying Out the Invention

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

[0012] (Heat-sealable lid material) The base material layer in the heat-sealable lid material of the present invention mainly uses a polyethylene terephthalate-based resin as a constituent component, uses terephthalic acid as a dicarboxylic acid component, and uses ethylene glycol as a diol component. Here, "mainly used as a constituent component" means that when the total amount of constituent components is 100 mol%, it contains 50 mol% or more, preferably 80% or more, and more preferably 90% or more.

[0013] 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 setting the copolymerization amount of dicarboxylic acid components and diol components to 15 mol% or less, thickness uniformity is improved, and the reduction in antifogging performance due to transfer of the antifogging agent to the back when stored in roll form can be suppressed.

[0014] 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.

[0015] 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.

[0016] In order to reduce thickness variations, the base material layer in the heat-sealable lid material of the present invention is preferably biaxially stretched. Biaxial stretching can be performed by conventionally known methods. For example, an unstretched resin sheet extruded onto a cooling drum is subsequently heated by roll heating, infrared heating, etc., and stretched in the longitudinal direction 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 more, the thickness variations of the resulting biaxially oriented film are improved, which not only suppresses the reduction in anti-fogging performance due to transfer of the anti-fogging agent to the back when stored in roll form, but also results in sufficiently strong mechanical strength.

[0017] 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. By stretching the ratio to 3.0 times or more, the resulting biaxially oriented film has good thickness uniformity, which not only suppresses the reduction in antifogging performance due to transfer of the antifogging agent to the back when stored in roll form, but also results in sufficiently strong mechanical strength. Furthermore, by stretching the ratio to 5.0 times or less, breakage during film formation can be suppressed. 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. For applications where further reduction of thermal shrinkage is required, a relaxation treatment may be performed as needed.

[0018] The base layer in the heat-sealable lid material of the present invention preferably has a lower limit of thickness of 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 allows for suitable use as a lid material.

[0019] The upper limit of thickness unevenness in the base material layer of the heat-sealable lid material of the present invention is preferably 15%, more preferably 10%, and particularly preferably 5%. By keeping it at 15% or less, it is possible to prevent localized winding stress from being applied to areas with poor thickness unevenness when stored in roll form, and as a result, it is possible to suppress the reduction in anti-fogging performance due to the transfer of the anti-fogging agent to the non-anti-fogging surface.

[0020] A printed layer may be laminated on the base layer of the heat-sealable lid material of the present invention. Water-based and solvent-based resin-containing printing inks are preferably used as the printing ink for forming the printed layer. Examples of resins used in the printing ink 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, defoaming agents, crosslinking agents, anti-blocking agents, and antioxidants.

[0021] The printing 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.

[0022] In the heat-sealable lid material of the present invention, the base material layer may be provided with a gas barrier layer, such as an inorganic thin film layer or a metal layer, as long as the objectives of the present invention are not impaired.

[0023] When an inorganic thin film layer is used as a gas barrier layer, the inorganic thin film layer is a thin film 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 made into a thin film, but from the viewpoint of gas barrier properties, inorganic oxides such as aluminum, silicon dioxide (silica), aluminum oxide (alumina), and mixtures of silicon dioxide and aluminum oxide are preferred. In particular, a composite oxide of silicon dioxide and aluminum oxide is preferred because it can achieve both flexibility and density in the thin film layer.

[0024] In this composite oxide, the mixing ratio of silicon oxide and aluminum oxide is preferably in the range of 20-70% Al by mass ratio of the metal content. On the other hand, if it is 70% or less, the inorganic thin film layer can be made softer, which can suppress the destruction of the thin film and the reduction of gas barrier properties during secondary processing such as printing and lamination. Here, silicon oxide refers to various silicon oxides such as SiO and SiO2 or mixtures thereof, and aluminum oxide refers to various aluminum oxides such as AlO and Al2O3 or mixtures thereof.

[0025] The thickness of the inorganic thin film layer is typically 1 to 100 nm, preferably 5 to 50 nm. A thickness of 1 nm or less makes it easier to obtain satisfactory gas barrier properties. On the other hand, a thickness of 100 nm or less offers advantages in terms of flexibility and manufacturing cost.

[0026] There are no particular restrictions on the method for forming an inorganic thin film layer; for example, any known deposition method such as vacuum deposition, sputtering, ion plating (physical vapor deposition methods (PVD)), or chemical vapor deposition (CVD) can be used as appropriate. Below, a typical method for forming an inorganic thin film layer will be described using a silicon oxide / aluminum oxide thin film as an example. For example, when using vacuum deposition, a mixture of SiO2 and Al2O3, or a mixture of SiO2 and Al, is preferably used as the deposition raw material. These deposition raw materials are usually particles, and it is desirable that the size of each particle is such that the pressure during deposition does not change, with a preferred particle size of 1 to 5 mm. For heating, methods such as resistance heating, high-frequency induction heating, electron beam heating, and laser heating can be used. It is also possible to use reactive deposition by introducing oxygen, nitrogen, hydrogen, argon, carbon dioxide, water vapor, etc. as a reaction gas, or by using means such as ozone addition or ion assistance. Furthermore, the film formation conditions can be arbitrarily changed, such as by applying a bias to the substrate (laminated film to be deposited) or by heating or cooling the substrate. Such deposition materials, reaction gases, bias of the deposition target, heating and cooling, etc., can be similarly modified when using sputtering or CVD methods. Furthermore, a printed layer may be laminated on the above inorganic thin film layer.

[0027] (Heat-sealed layer containing anti-fogging agent) The heat-seal layer containing the antifogging agent in the heat-sealable lid material of the present invention preferably comprises a polyester resin having a chemical structure obtained by polycondensation of a carboxylic acid component consisting of a divalent or higher polyhydric carboxylic acid compound and an alcohol component consisting of a divalent or higher polyhydric alcohol compound. Since the heat-seal layer containing the antifogging agent needs to exhibit antifogging properties when used as a lid material, it is desirable that it be located in the outermost layer of the heat-sealable lid material.

[0028] As the polycarboxylic acid component, aromatic dicarboxylic acids or aliphatic carboxylic acids are preferred, with aromatic dicarboxylic acids being more preferred. The lower limit of the copolymerization amount of the dicarboxylic acid component is preferably 40 mol% or more, more preferably 45 mol% or more, and particularly preferably 50 mol% or more, relative to the total amount of the carboxylic acid component. By setting it to 40 mol% or more, sufficient heat seal strength with the polyester container can be obtained. The upper limit of the copolymerization amount of the dicarboxylic acid component is preferably 80 mol% or more, more preferably 75 mol% or more, and particularly preferably 70 mol% or more, relative to the total amount of the carboxylic acid component. By setting it to 80 mol% or less, it is possible to prevent the heat seal strength with the polyester container from being too strong, which would result in poor ease of opening.

[0029] Examples of dicarboxylic acid components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and naltalenedicarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and dodecanedicarboxylic acid; p-oxybenzoic acid, p-(hydroxyethoxy)benzoic acid, fumaric acid, maleic acid, itaconic acid, hexahydrophthalic acid, tetrahydrophthalic acid, 1,4-cyclohexanedicarboxylic acid, trimellitic acid, trimesic acid, and pyromellitic acid.

[0030] Aliphatic diols are preferred as the polyhydric alcohol component. The lower limit of the copolymerization amount of the diol component is preferably 70 mol%, more preferably 75 mol%, and particularly preferably 80 mol%. A value of 70 mol% or more ensures sufficient heat seal strength with the polyester container.

[0031] Examples of diol components include, but are not limited to, ethylene glycol, propylene glycol, 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0032] The heat-seal layer containing the anti-fogging agent in the heat-sealable lid material of the present invention may contain at least two different polyester resins (A) and polyester resin (B). In particular, by using at least two polyester resins with different glass transition temperatures, cohesive failure can be selectively induced in the heat-seal layer, thereby enabling easy opening over a wide temperature range.

[0033] The glass transition temperature of the polyester resin (A) is preferably in the range of 0°C to 40°C, more preferably in the range of 5°C to 35°C, and particularly preferably in the range of 10°C to 30°C. Being within this range provides easy opening while maintaining the heat seal strength necessary for content retention.

[0034] The lower limit of the reduced viscosity (ηsp / c) of the polyester resin (A) is preferably 0.2 dl / g, more preferably 0.4 dl / g, and particularly preferably 0.6 dl / g. A viscosity of 0.2 dl / g or higher allows the resin to cohesive and develop heat seal strength.

[0035] The lower limit of the number-average molecular weight (Mn) of the polyester resin (A) is preferably 5000, more preferably 10000, and particularly preferably 15000. Setting it to 5000 or higher allows the resin to cohesive and develop heat-seal strength.

[0036] The glass transition temperature of the polyester resin (B) is preferably in the range of 41°C to 80°C, more preferably in the range of 46°C to 75°C, and particularly preferably in the range of 51°C to 60°C. Being within this range provides easy opening while maintaining the heat seal strength necessary for content retention.

[0037] The lower limit of the reduced viscosity (ηsp / c) of the polyester resin (B) is preferably 0.1 dl / g, more preferably 0.2 dl / g, and particularly preferably 0.3 dl / g. A viscosity of 0.1 dl / g or higher allows for resin cohesive force and thus heat seal strength.

[0038] The lower limit of the number-average molecular weight (Mn) of the polyester resin (B) is preferably 2000, more preferably 5000, and particularly preferably 10000. A value of 2000 or higher allows for resin cohesive force and thus improves heat seal strength.

[0039] The lower limit of the mass ratio of polyester resin (A) to polyester resin (B) is preferably polyester resin (A):polyester resin (B) = 50:50 mass%, more preferably 45:55 mass%, and particularly preferably 60:40 mass%. By setting it to 50:50 mass% or higher, the anti-fogging layer can be made brittle, allowing the heat seal strength to be within the range described in the claim over a wide temperature range, and easy opening can be achieved. The upper limit of the mass ratio of polyester resin (A) to polyester resin (B) is preferably polyester resin (A):polyester resin (B) = 90:10 mass%, more preferably 85:15 mass%, and particularly preferably 80:20 mass%. By setting it to 90:10 mass% or less, the seal strength of the seal surface can be increased, the heat seal strength can be within the range described in the claim over a wide temperature range, and easy opening can be achieved.

[0040] The heat-seal layer of the heat-sealable lid material of the present invention preferably contains an anti-fogging agent. The anti-fogging agent is not particularly limited as long as it provides anti-fogging properties, and for example, anionic surfactants, nonionic surfactants, cationic surfactants, or amphoteric surfactants can be used. Among these, the use of a nonionic surfactant is preferred. Here, anti-fogging properties refer to the ability to prevent fogging of the inner surface of the packaging material due to evaporating moisture when water is placed in the packaging container and sealed with the lid material. In particular, lid materials for packaging containers of fresh foods such as vegetables and fruits may require excellent anti-fogging performance because the contents may become difficult to see due to the evaporation of moisture, which can reduce the value of the product.

[0041] For example, anionic surfactants include sulfate salts of higher alcohols, higher alkyl sulfonates, higher carboxylates, alkylbenzene sulfonates, polyoxyethylene alkyl sulfates, polyoxyethylene alkylphenyl ether sulfates, and vinyl sulfosuccinates. Nonionic surfactants include compounds having a polyoxyethylene structure such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyethylene glycol fatty acid esters, ethylene oxide-propylene oxide block copolymers, polyoxyethylene fatty acid amides, and ethylene oxide-propylene oxide copolymers, as well as sorbitan derivatives. Cationic surfactants include alkylamine salts, dialkylamine salts, trialkylamine salts, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, and alkylbenzalkonium chloride. Amphoteric surfactants include lauryl betaine and lauryldimethylamine oxide.

[0042] Nonionic surfactants include, specifically, sorbitan-based surfactants such as sorbitan monostearate, sorbitan distearate, sorbitan monopalmitate, sorbitan dipalmitate, sorbitan monobehenate, sorbitan dibehenate, sorbitan monolaurate, and sorbitan dilaurate; glycerin-based surfactants such as glycerin monolaurate, glycerin dilaurate, diglycerin monopalmitate, diglycerin dipalmitate, glycerin monostearate, glycerin distearate, diglycerin monostearate, diglycerin distearate, diglycerin monolaurate, and diglycerin dilaurate; polyethylene glycol monostearate, polyethylene glycol Examples include polyethylene glycol-based surfactants such as licole monopalminate, trimethylolpropane-based surfactants such as trimethylolpropane monostearate, diethanolalkylamine-based and diethanolalkylamide-based surfactants such as lauryldiethanolamine, oleyldiethanolamine, stearyldiethanolamine, lauryldiethanolamide, oleyldiethanolamide, and stearyldiethanolamide, pentaerythritol-based surfactants such as pentaerythritol monopalmitate, and polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan distearate, and mono and distearates of sorbitan-diglycerin condensates. These can be used individually or in combination of two or more types.

[0043] Examples of cationic surfactants include amine salts such as laurylamine acetate, triethanolamine monoformate, and stearamidoethyldiethylamine acetate, and quaternary ammonium salts such as lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, dilauryldimethylammonium chloride, distearyldimethylammonium chloride, lauryldimethylbenzylammonium chloride, and stearyldimethylbenzylammonium chloride. These can be used alone or in combination of two or more.

[0044] The lower limit of the antifogging agent content in the heat-seal layer containing the antifogging agent in the heat-sealable lid material of the present invention is a mass ratio of polyester resin (A or A+B) to antifogging agent that is preferably 99:1, more preferably 97:3, and particularly preferably 94:6. Antifogging properties are achieved when the ratio is 99:1 or higher. The upper limit of the antifogging agent content is a mass ratio of polyester resin (A or A+B) to antifogging agent that is preferably 80:20, more preferably 83:17, and particularly preferably 86:14. Sufficient heat-seal strength with polyester containers is obtained when the ratio is 80:20 or higher.

[0045] The heat-seal layer containing the anti-fogging agent in the heat-sealable lid material may contain an anti-blocking agent for the purpose of providing blocking resistance. Examples of anti-blocking agents include inorganic particles, organic particles, waxes, etc., and can be included in an amount that does not reduce the heat-seal strength. These anti-blocking agents can be used alone or in combination of two or more types. The lower limit of the anti-blocking agent content, calculated as the solid content concentration of the anti-fogging layer, is preferably 0.1% by mass or more, more preferably 0.3% by mass, and particularly preferably 0.5% by mass. Blocking resistance is exhibited when the content is 0.1% by mass or more. The upper limit of the anti-blocking agent content, calculated as the solid content concentration of the anti-fogging layer, is preferably 5.0% by mass or less, more preferably 4.5% by mass, and particularly preferably 4.0% by mass. When the content is 5.0% by mass or less, the heat-seal strength is not inhibited.

[0046] The lower limit of the thickness of the heat-seal layer containing the anti-fogging agent in the heat-sealable lid material of the present invention is preferably 0.1 μm, more preferably 0.2 μm, and particularly preferably 0.4 μm. A thickness of 0.1 μm or more enables 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 3 μm, and particularly preferably 1 μm. A thickness of 5 μm or less prevents deterioration of thickness unevenness in the laminate, and consequently suppresses the reduction in anti-fogging properties due to transfer of the anti-fogging agent to the back.

[0047] The upper limit of thickness variation in the heat-sealable lid material of the present invention is preferably 15%, more preferably 10%, and particularly preferably 5%. 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, it is possible to suppress the reduction in anti-fogging performance due to the transfer of the anti-fogging agent to the non-anti-fogging surface.

[0048] (Physical properties of heat-sealable lid material) The heat-sealable lid material of the present invention preferably has a haze of 1% to 15%. If the haze exceeds 10%, the transparency of the film deteriorates, resulting in poor visibility of the contents when used in packaging. The upper limit of the haze is more preferably 13% or less, and particularly preferably 11% or less. The lower the haze, the higher the transparency, which is desirable, but with the current state of technology, 1% is the lower limit, and even 2% or more is sufficiently preferable for practical purposes.

[0049] The lower limit of the longitudinal or widthwise breaking strength of the heat-sealable lid material of the present invention is preferably 180 MPa, more preferably 185 MPa, and particularly preferably 190 MPa. A breaking strength of 180 MPa or higher provides sufficient mechanical strength when used as a container lid material. The upper limit of the breaking strength is not particularly limited, but is preferably 260 MPa, more preferably 255 MPa, and particularly preferably 250 MPa. A breaking strength of 260 MPa or lower substantially suppresses fracture caused by foreign matter during the stretching process, resulting in good film-forming properties.

[0050] The lower limit of the elongation at break in the longitudinal or widthwise direction of the heat-sealable lid material of the present invention is preferably 80%, more preferably 90%, and particularly preferably 100%. If it is 80% or higher, fracture caused by foreign matter during the stretching process can be substantially suppressed, and good film-forming properties can be obtained. The upper limit of the elongation at break is not particularly limited, but is preferably 170%, more preferably 160%, and particularly preferably 150%. If it is 170% or lower, sufficient mechanical strength can be obtained when used as a lid material for a container.

[0051] The heat-sealable lid material of the present invention has an oxygen permeability of 200 [cc / (m³) at a temperature of 23°C and a relative humidity of 65%RH. 2 The oxygen permeability of the film is less than or equal to 200 [cc / (m³). This is because the oxygen concentration inside the container changes when fresh produce is placed inside. Inside the container, oxygen is consumed and carbon dioxide is produced by the respiration of the fresh produce. By setting the oxygen permeability of the film to the above range, the exchange of oxygen with the outside is reduced, making it easier to create a low-oxygen state favorable for MA packaging, and as a result, the respiration of fresh produce is suppressed, leading to an extension of shelf life. Oxygen permeability of 200 [cc / (m³) 2 If the oxygen permeability exceeds 150 [cc / (m³)], the respiration rate of fruits and vegetables increases, which can easily lead to discoloration and other problems, so this is undesirable. 2 Preferably it is less than or equal to 100 [cc / (m)], and 100 [cc / (m 2 It is more preferable if it is less than or equal to (d·atm)

[0052] The heat-sealable lid material of the present invention has a water vapor transmission rate of 100 [g / (m³)] under conditions of 40°C and 90% RH relative humidity. 2 ·d) or less. Water vapor transmission rate is 100 [g / (m³] 2 If the water vapor permeability exceeds (d), when fresh produce is placed in the packaging, moisture inside the packaging is more easily released to the outside, increasing the amount of moisture transpiration from the fresh produce, which is undesirable. The water vapor permeability should be 80 [g / (m³]. 2 It is preferable that it is less than or equal to d), and 60[g / (m 2 It is more preferable if it is less than or equal to (d) below.

[0053] (container) The packaging container of the present invention includes a molded container made of a polyester resin whose main component is polyethylene terephthalate (PET). Here, "main component" means that when the total amount of components is taken as 100 mol%, it contains 50 mol% or more, preferably 80% or more, and more preferably 90% or more. Because the container is made of a polyester resin, monomaterialization can be achieved, in which the lid material is also made of the same resin, resulting in an environmental benefit. The container of the present invention is not particularly limited in its layer structure, and may have a single layer structure, or a structure in which two, three, four or more layers are laminated.

[0054] The above polyester resin may be in either a crystalline or amorphous state. From the viewpoint of moldability, an amorphous polyester resin is preferred, and amorphous PET is more preferred. Note that the amorphous state includes PET in a state that has not crystallized, such as A-PET, and PET in a state that has not completely crystallized, such as PET-G.

[0055] (Contents) The contents to be placed in the container of this invention include broccoli, komatsuna, rapeseed, pea sprouts, green onions, tomatoes, snow peas, green beans, spinach, komatsuna, garland chrysanthemum, perilla leaves, chestnuts, chives, green onions, parsley, mizuna, bell peppers, cucumbers, bitter melon, eggplant, green asparagus, white asparagus, myoga ginger, bean sprouts, radish sprouts, Chinese cabbage, cabbage, carrots, pumpkins, lettuce, bell peppers, onions, yams, radishes, turnips, corn, potatoes and other legumes, grains, herbs and all kinds of vegetables, shiitake mushrooms, button mushrooms, nameko mushrooms, shimeji mushrooms, enoki mushrooms, king oyster mushrooms, Examples include mushrooms such as maitake, matsutake, and edamame; fruits such as sudachi, kabosu, grapes, melons, cherries, strawberries, persimmons, kiwifruit, cherries, green plums, pears, apples, bananas, peaches, loquats, blueberries, and watermelons; flowers such as roses, carnations, chrysanthemums, calla lilies, cherries, peaches, plums, freesias, armerias, sweet peas, hydrangeas, petunias, and dahlias; fish such as salmon, flounder, sole, yellowtail, saury, sardines, mackerel, octopus, squid, sea bream, golden snapper, tuna, needlefish, hairtail, flying fish, conger eel, and eel; shellfish such as ark shells, clams, Manila clams, mussels, scallops, and surf clams; and meats such as pork, beef, chicken, and lamb. Among these contents, it is preferable to use it for vegetables and fruits, and more preferably for packaging broccoli, lettuce, green onions, cabbage, shiitake mushrooms, and shimeji mushrooms. Furthermore, these contents may be placed in the packaging with inedible parts such as peels and stems attached, or with the inedible parts removed and the edible parts cut, or with the inedible parts attached and the edible parts cut. [Examples]

[0056] (Example of polyester synthesis for lid material) The ester reaction vessel was heated to 200°C, at which point a slurry consisting of terephthalic acid [86.4 parts by mass] and ethylene glycol [64.4 parts by mass] was added. While stirring, antimony trioxide [0.017 parts by mass] and triethylamine [0.16 parts by mass] were added as catalysts. The temperature was then increased, and the pressurized esterification reaction was carried out under conditions of a gauge pressure of 0.34 MPa and 240°C.

[0057] Subsequently, the pressure inside the esterification reaction vessel was returned to atmospheric pressure, and magnesium acetate tetrahydrate [0.071 parts by mass], followed by trimethyl phosphate [0.014 parts by mass], was added. Furthermore, after raising the temperature to 260°C over 15 minutes, trimethyl phosphate [0.012 parts by mass], followed by sodium acetate [0.0036 parts by mass] was added. After 15 minutes, the mixture was dispersed using a high-pressure disperser, and then 0.10 parts by mass of silica particles with an average particle size of 2.5 μm were added to the total composition. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction vessel, and a polycondensation reaction was carried out under reduced pressure at 280°C to obtain polyester for lid material.

[0058] (Example of polyester synthesis for heat-seal layer containing anti-fogging agent) (Polyester A-1) In an ester reaction vessel, terephthalic acid [445 parts by mass], isophthalic acid [74 parts by mass], sebadic acid [270 parts by mass], ethylene glycol [277 parts by mass], 2,2-dimethyl-1,3-propanediol [465 parts by mass], and tetrabutyl titanate [0.5 parts by mass] 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 PolySL A-1. The glass transition temperature was 7°C.

[0059] (Polyester B-1) Polyester B-1 was obtained by the same method as for polyester A-1, except that the raw materials were changed to dimethyl terephthalate [455 parts by mass], dimethyl isophthalate [455 parts by mass], ethylene glycol [291 parts by mass], 2,2-dimethyl-1,3-propanediol [488 parts by mass], and tetrabutyl titanate [0.5 parts by mass]. The glass transition temperature was 67°C.

[0060] (Example of container manufacturing) The polyester used for the container body was prepared in the same manner as the polyester used for the lid, except that silica particles were not added. The A-PET sheet prepared using the above-mentioned polyester was softened at 130°C, and an A-PET container with the shape shown in Figure 1 was fabricated by vacuum and pressure molding using a mold. The bottom was 100 mm x 100 mm, the height was 80 mm, the lid seal portion was 8 mm wide, and the thickness was approximately 300 μm.

[0061] Each physical property was measured using the following method.

[0062] [Oxygen permeability] Oxygen permeability was measured according to the JIS K7126-2 method. For the lid material, oxygen permeability was measured by allowing oxygen to pass through it using an oxygen permeability measuring device (MOCON, OX-TRAN 2 / 20) under conditions of 23°C and 65% RH humidity. Prior to measurement, the sample was left at 23°C and 65% RH humidity for 4 hours to allow it to adjust to humidity.

[0063] [Water vapor transmission rate] Water vapor transmission was measured according to JIS K7126 Method B. For the lid material, a water vapor transmission rate measuring device (MOCON, PERMATRAN-W3 / 33MG) was used to measure the water vapor transmission rate by passing a humidifying gas through it under conditions of 40°C and 90% RH. Prior to measurement, the sample was conditioned by leaving it at 23°C and 65% RH for 4 hours.

[0064] [Hayes] Measurements were taken in accordance with JIS K7136. For the lid material, a haze meter (NDH8000, manufactured by Nippon Denshoku Industries Co., Ltd.) was used for measurement. Two measurements were taken, and the average value was calculated.

[0065] [Breaking strength] Measurements were taken in accordance with JIS K7113. For the lid material, one strip of film sample was cut out with a length of 140 mm in the measurement direction (film longitudinal direction, width direction) and a length of 20 mm in the direction perpendicular to the measurement direction. Using a tensile testing machine (Shimadzu Corporation, Autograph AG-Xplus), the sample was gripped at both ends by 20 mm on each side with chucks (chuck distance 100 mm), and a tensile test was performed under conditions of ambient temperature 23°C and tensile speed 200 mm / min. The strength at fracture (MPa) was measured, and the average value was calculated.

[0066] [Elongation at break] Measurements were taken in accordance with JIS K7113. For the lid material, one strip of film sample was cut, with a length of 140 mm in the measurement direction (film longitudinal direction, width direction) and a length of 20 mm in the direction perpendicular to the measurement direction. Using a tensile testing machine (Shimadzu Corporation, Autograph AG-Xplus), the sample was gripped at both ends by 20 mm on each side with chucks (chuck distance 100 mm), and a tensile test was performed under conditions of ambient temperature 23°C and tensile speed 200 mm / min, and the elongation (%) at the time of fracture was measured. The measurement was performed twice, and the average value was calculated.

[0067] [Heat seal strength] A PET container piece and the heat-sealed side of the lid material containing the anti-fogging agent were placed on top of each other. This sample was bonded using a heat sealer. The heat sealing conditions were: upper bar temperature 170°C, lower bar 30°C, pressure 0.2 MPa, and time 2 seconds. The heat-sealed sample was cut to have a seal width of 15 mm. The heat seal strength was measured using a tensile testing machine "AGS-KNX" (manufactured by Shimadzu Corporation) at a tensile speed of 200 mm / min. The heat seal strength is expressed as strength per 15 mm (N / 15 mm).

[0068] [Easy to open] The lid seal portion of a PET container and the heat-sealed layer containing the anti-fogging agent of the lid were placed on top of each other. The lid was then heat-sealed from above. The heat-sealing conditions were 120°C, 0.2 MPa pressure, and 2 seconds time. Afterwards, the ease of peeling the lid by hand was evaluated by the following tactile sensation. Judgment ○: Adequately adhered and can be easily peeled off by hand Judgment △: Inadequate adhesion and can be peeled off without applying force Judgment ×: Adhesion is too strong and cannot be peeled off by hand or the lid material is damaged

[0069] [Freshness retention performance] Broccoli was placed in a packaging container sealed with a container and a lid material, and the freshness retention performance was evaluated by the color value change and odor after leaving it for 3 days in an environment of 30°C and 85% RH. The detailed method is shown below.

[0070] First, cut a single flower bud (about 5 cm) from commercially available broccoli, and measure the L * value and b * value with a colorimeter (Konica Minolta, Color Leader CR-20). For the measurement of the color L * value and b * value, the measurement was performed 3 times, and the average value of each was used.

[0071] Next, place the broccoli for which the color L * value and b * value were measured into the container, and overlap the seal part of the container lid material and the heat-sealing layer side containing the anti-fogging agent of the lid material. It was sealed with a cup sealer (E-Pack Industry Co., Ltd., EPK-Hand Sealer NO) from above the lid material.

[0072] The container in which the broccoli was sealed by the above method was placed in a thermo-hygrostat (Espec, LHU124) set at a temperature of 30°C and a humidity of 85% RH and left for 3 days. Then, take out the broccoli from the container and measure the color value. The method for measuring the color value is the same as the method before leaving the broccoli. For each of the color L * value and b * value, the color value change after leaving was calculated by the following formula. Color value change = (Color value after leaving) - (Color value before leaving)

[0073] The color value change was evaluated according to the following criteria. ○: Color L* value, b * The change in value is 5 or less for both. △: Color L * value, b * Any change in any one of the values ​​is 5 or less. ×: Color L * value, b * The change in value is greater than 5 for both.

[0074] [Anti-fog evaluation] The amount of water droplets on the inner surface of the packaging (the surface in contact with the produce) after the broccoli had been left out was visually evaluated according to the following criteria. ○: No water droplets are present on the inner surface of the lid of the packaging container (less than 1 / 5 of the surface area of ​​the lid). ×: Water droplets are present on the inner surface of the lid of the packaging container (more than 1 / 5 of the surface area of ​​the lid).

[0075] [Odor evaluation] The odor of broccoli after being left out of its packaging was evaluated according to the following criteria. ○: No odor when the packaging is opened. ×: There is an odor (like pickles) when the packaging is opened.

[0076] [Example 1] The polyester material for the lid was fed into the extruder. After the resin was melted at 280°C in the extruder, it was cast from a T-die at 280°C and adhered to a cooling roll at 10°C by electrostatic adhesion to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched 3.2 times in the longitudinal direction at a temperature of 115°C, then passed through a tenter and stretched 4.0 times in the width direction at 110°C, and then subjected to a heat setting treatment at 220°C for 3 seconds and a relaxation treatment of 5% for 1 second to obtain a biaxially oriented polyester film (substrate layer) with a thickness of 25 μm.

[0077] Coating agent A was obtained by heating and stirring polyester A-1 [75.8% by mass], polyester B-2 [19.3% by mass], and an anti-fogging agent (Rikemar L-71-D, manufactured by Riken Vitamin Co., Ltd., a nonionic surfactant, HLB 7.3) [4.9% by mass] in an ethyl acetate solution (solid content concentration 10%). Coating agent A was applied to this biaxially oriented polyester film by the wire bar coating method, and dried at 90°C for 20 seconds to laminate an anti-fogging layer and obtain a heat-sealable lid material. The thickness of the coated layer was 1.5 μm.

[0078] [Example 2] A heat-sealable lid material was obtained in the same manner as in Example 1, except that the base layer was changed to a biaxially oriented inorganic binary vapor-deposited barrier film (manufactured by Toyobo Co., Ltd., EcoSeal® VE100-12μm).

[0079] [Comparative Example 1] Polyester A-1 [79.7% by mass] and polyester B-2 [20.3% by mass] were heated and stirred in an ethyl acetate solution (solid content concentration 10%) to obtain coating agent B. This coating agent B was applied to the biaxially oriented polyester film prepared in Example 1 using the wire bar coating method, and dried at 90°C for 20 seconds to obtain a heat-sealable lid material. The thickness of the coated layer was 1.5 μm.

[0080] [Comparative Example 2] An unstretched, linear low-density polyethylene film (L4102-40μm, manufactured by Toyobo Co., Ltd., registered trademark) was used as the base layer, and a heat-sealable lid material was created.

[0081] Table 1 shows the physical properties of the heat-sealable lid material and the evaluation results of the packaging container for Examples 1-2 and Comparative Examples 1-2.

[0082] [Table 1]

[0083] The packaging materials of Examples 1 and 2 all exhibited excellent characteristics, resulting in favorable evaluation results. The packaging container of Comparative Example 1 showed good freshness preservation performance due to minimal change in color value and lack of odor. However, the anti-fogging layer of the laminated film did not exhibit anti-fogging properties, resulting in poor performance. The packaging container of Comparative Example 2 had high oxygen permeability and low water vapor permeability, preventing moisture released from vegetables from escaping, resulting in poor freshness preservation performance. Furthermore, it did not exhibit anti-fogging properties, resulting in poor performance. In addition, the adhesive strength between the seal layer of the base layer and the PET container was too weak, resulting in poor ease of opening.

Claims

1. A food freshness preservation packaging container comprising a heat-sealable lid material and a container whose main component is polyethylene terephthalate, The heat-sealable lid material is composed of two or more layers, including a base layer mainly composed of polyethylene terephthalate and a heat-seal layer containing an anti-fogging agent. The substrate layer is provided with an inorganic thin film layer. The heat-seal layer comprises a polyester resin and an anti-fogging agent. The polyester resin is at least two different polyester resins, polyester resin (A) and polyester resin (B). The glass transition temperature of the polyester resin (A) is in the range of 0°C to 40°C. The glass transition temperature of the polyester resin (B) is in the range of 41°C to 67°C. The heat seal strength between the heat-sealable lid material and the container is 1.0 N / 15 mm or more and 15 N / 15 mm or less. The oxygen permeability of the heat-sealable lid material, measured at a temperature of 23°C and a relative humidity of 65% RH, was 200 cc / (m³). ２ ・d・atm) is less than or equal to, The water vapor permeability of the heat-sealable lid material is 100 g / m² under conditions of 40°C and 90% RH relative humidity. ２ d) A freshness-preserving packaging container that is as follows:

2. The freshness-preserving packaging container according to Claim 1, wherein the mass ratio of polyester resin to anti-fogging agent in the heat-seal layer is 99:1 to 80:

20.

3. The freshness-preserving packaging container according to claim 1, wherein the heat-sealable lid material has a breaking strength of 180 MPa or more and 260 MPa or less in either the longitudinal or widthwise direction.

4. The freshness-preserving packaging container according to claim 1, wherein the elongation at break of the heat-sealable lid material in either the longitudinal or widthwise direction is 80% or more and 170% or less.

5. The freshness-preserving packaging container according to claim 1, wherein the heat-sealable lid material has a heat-seal layer, a base material layer, and a printed layer in that order.

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