Oxygen absorbing film

Abstract

The present invention provides an oxygen-absorbing film suitable as a packaging material that is excellent in regard to suppressing the oxidization of a packaging target and in terms of not adsorbing aroma components and having excellent tearability. An oxygen-absorbing film 1 comprises, from the outer layer side, at least a surface base material layer 2 having oxygen barrier property, an oxygen-absorbing resin layer 3, and an inner surface base material layer 4 containing a stretched PET base material and allowing for heat-sealing, which are layered in this order.

Description

[Technical Field]

[0001] The present invention relates to an oxygen-absorbing film. [Background technology]

[0002] Conventionally, so-called gas replacement packaging has been known in which the contents are filled and sealed while the air inside the package is replaced with an inert gas such as nitrogen to prevent deterioration of the contents. Gas replacement involves suctioning and evacuating the air from the package when filling the contents, or forcibly replacing the air inside the package with an inert gas. However, even with gas replacement packaging, it is difficult to completely remove oxygen from the package. For this reason, the present applicant has proposed, for example, in Patent Document 1, a packaging film with an oxygen absorption function. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-039475 [Patent Document 2] Japanese Patent Application Publication No. 11-302405 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-329077 [Patent Document 4] Japanese Patent Application Publication No. 6-220220 [Patent Document 5] Japanese Patent Application Laid-Open No. 2004-196951 Summary of the Invention [Problem to be solved by the invention]

[0004] By using such a packaging film with oxygen absorption function, it is possible to remove the oxygen remaining in the package after filling, thereby preventing deterioration of the packaged object due to oxidation and enabling long-term storage. However, when packaging luxury goods that also affect the sense of smell, such as coffee, it is important not only to prevent deterioration due to oxidation but also to maintain the aroma components, and there is a demand for packaging films that can prevent the aroma components from being sorbed into the packaging itself. Packaging films are used as various types of packaging bags, but tearability upon opening is also required. For example, polyester films are typically used as part of multilayer packaging for food and pharmaceutical products. Focusing on the issue of improving the tearability of this type of packaging, biaxially oriented polyester films have been proposed, including those made by blending polyethylene terephthalate with modified polybutylene terephthalate (PBT), those made by blending polyethylene terephthalate with polycarbonate (PC), and those made by blending polybutylene terephthalate with an acrylonitrile-styrene copolymer (see Patent Documents 2, 3, 4, and 5). While all of these films are expected to improve tearability, they involve incompatible blends of different thermoplastic resins, which can result in issues such as high haze in the film itself, reducing visibility of the contents, or the film being prone to breakage when stretched.

[0005] The present inventors have made this invention in consideration of the above-mentioned circumstances, and it is an object of the present invention to provide an oxygen-absorbing film that is suitable as a packaging material, has excellent properties for inhibiting oxidation of the packaged object, is excellent in non-sorption of aroma components, and also has excellent tearability. [Means for solving the problem]

[0006] The oxygen-absorbing film according to the present invention is formed by laminating, in this order from the outer layer side, at least a surface substrate layer having oxygen barrier properties, an oxygen-absorbing resin layer, and an inner substrate layer containing a biaxially oriented PET substrate, and the inner substrate layer contains the biaxially oriented PET substrate and a heat-sealable polyester-based resin layer laminated on the inner side of the biaxially oriented PET substrate. the thickness of the biaxially oriented PET substrate is 6 to 16 μm, the thickness of the heat-sealable polyester-based resin layer is 0.1 to 5.0 μm, and the heat-sealable polyester-based resin layer is made of either a copolymer polyester consisting of three components, terephthalic acid, ethylene glycol, and neopentyl glycol, a copolymer polyester consisting of four components, terephthalic acid, isophthalic acid, ethylene glycol, and neopentyl glycol, or a copolymer polyester consisting of four components, terephthalic acid, isophthalic acid, ethylene glycol, and diethylene glycol. It is composed of 。 [Effects of the Invention]

[0007] According to the present invention, an oxygen-absorbing film can be provided that is suitable as a packaging material, having excellent properties of inhibiting oxidation of the packaged object, non-sorption of aroma components, and excellent tearability. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram illustrating an example of an oxygen-absorbing film according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the oxygen-absorbing film according to the present invention will be described with reference to embodiments thereof.

[0010] The oxygen-absorbing film 1 in this embodiment is formed by laminating, in this order from the outer layer side, at least a surface base material layer 2 having oxygen barrier properties, an oxygen-absorbing resin layer 3, and an inner base material layer 4 that includes a stretched PET base material and is heat-sealable. The surface base material layer 2 is located on the outer layer side and the inner base material layer 4 is located on the inner layer side, and the film is made into a desired shape such as a gable pouch, a gusset pouch, a flat pouch, or a pillow shape depending on the object to be packaged, and is suitably used as a packaging material that enables long-term storage of the object to be packaged.

[0011] [Surface base material layer] From the viewpoint of scratch resistance and chemical resistance, the surface substrate layer 2 preferably uses, as the substrate film, a biaxially stretched film made of a polyester resin such as polyethylene terephthalate or a polyamide resin such as nylon, for example, and a coating layer mainly made of an oxygen barrier resin such as a polyvinyl alcohol resin, an ethylene-vinyl alcohol copolymer, a polyacrylic acid resin or a vinylidene chloride resin, a laminated film containing a vapor-deposited thin film of a metal oxide or metal such as silica or alumina, or a laminated film obtained by dry-laminating a metal foil such as aluminum foil to the above substrate film via a urethane adhesive, but is not limited to these. The surface substrate layer 2 preferably has an oxygen permeability of 50 cc / (m 2 ) in an environment of 25°C-90% RH. 2 ·day·atm), preferably less than 25cc / (m 2 Various substrates having an oxygen barrier property of less than 1000 kJ / day atm can be used as the surface substrate.

[0012] [Oxygen-absorbing resin layer] The oxygen-absorbing resin used in the oxygen-absorbing resin layer 3 is preferably an oxygen-absorbing polyester resin containing a functional group or bonding group reactive with oxygen in its structure. Examples of functional groups or bonding groups reactive with oxygen include carbon-carbon double bond groups, aldehyde groups, and phenolic hydroxyl groups. In particular, unsaturated polyester resins having a carbon-carbon double bond group are preferred, and polyester resins having an unsaturated alicyclic structure are more preferred. Polyester resins having an unsaturated alicyclic structure are advantageous because they suppress the generation of low-molecular-weight decomposition components, which are by-products in the autoxidation reaction of the resin.

[0013] Examples of polyester resins having an unsaturated alicyclic structure include polyesters obtained by polymerizing tetrahydrophthalic acid or a derivative thereof, or tetrahydrophthalic anhydride or a derivative thereof as an acid component with a diol component. When tetrahydrophthalic acid or a derivative thereof, or tetrahydrophthalic anhydride or a derivative thereof is used as the acid component, these may be esterified to methyl esters or the like.

[0014] Tetrahydrophthalic acid or its derivatives, or tetrahydrophthalic anhydride or its derivatives, include 4-methyl-Δ 3 -Tetrahydrophthalic acid or 4-methyl-Δ 3 -Tetrahydrophthalic anhydride, cis-3-methyl-Δ 4 -Tetrahydrophthalic acid or cis-3-methyl-Δ 4 Tetrahydrophthalic anhydride is particularly preferred. These tetrahydrophthalic acids or derivatives thereof, or tetrahydrophthalic anhydride or derivatives thereof, are highly reactive with oxygen and can therefore be suitably used as the acid component.

[0015] These tetrahydrophthalic acid or its derivatives, or tetrahydrophthalic anhydride or its derivatives, are 4-methyl-Δ 4 It can be obtained by structural isomerization of an isomer mixture containing 1-tetrahydrophthalic anhydride, and is produced industrially.

[0016] Examples of diol components include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, trimethylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 2-phenylpropanediol, 2-(4-hydroxyphenyl)ethyl alcohol, α,α-dihydroxy-1,3-diisopropylbenzene, o-xylene glycol, m-xylene glycol, p-xylene glycol, α,α-dihydroxy-1,4-diisopropylbenzene, hydroquinone, 4,4-dihydroxydiphenyl, naphthalenediol, and derivatives thereof. Preferably, an aliphatic diol, such as diethylene glycol, triethylene glycol, or 1,4-butanediol, is used, and more preferably, 1,4-butanediol. When 1,4-butanediol is used, an oxygen-absorbing polyester resin having high oxygen absorption performance and producing a small amount of decomposition products during the oxidation process can be obtained. These diol components can be used alone or in combination of two or more.

[0017] The oxygen-absorbing polyester resin may be a copolymer obtained by including other acid components or derivatives thereof, such as aromatic dicarboxylic acids, aliphatic dicarboxylic acids, or aliphatic hydroxycarboxylic acids, in the raw material monomers in addition to tetrahydrophthalic acid or a derivative thereof or tetrahydrophthalic anhydride or a derivative thereof, or the like.

[0018] Examples of aromatic dicarboxylic acids and derivatives thereof include phthalic acid, phthalic anhydride, benzene dicarboxylic acids such as isophthalic acid and terephthalic acid, naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, anthracene dicarboxylic acid, sulfoisophthalic acid, sodium sulfoisophthalate, and derivatives thereof. Among these, phthalic acid, phthalic anhydride, isophthalic acid, and terephthalic acid are preferred.

[0019] Examples of aliphatic dicarboxylic acids and their derivatives include oxalic acid, malonic acid, succinic acid, succinic anhydride, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, 3,3-dimethylpentanedioic acid, and derivatives thereof. Among these, succinic acid, succinic anhydride, adipic acid, and sebacic acid are preferred, with succinic acid being particularly preferred. Other examples include hexahydrophthalic acid having an alicyclic structure, dimer acid, and its derivatives.

[0020] Examples of the aliphatic hydroxycarboxylic acid and its derivatives include glycolic acid, lactic acid, hydroxypivalic acid, hydroxycaproic acid, hydroxyhexanoic acid, and derivatives thereof.

[0021] These other acid components may be esterified, such as dimethyl terephthalate or bis-2-hydroxydiethyl terephthalate, or may be acid anhydrides, such as phthalic anhydride or succinic anhydride. These other acid components may be used alone or in combination of two or more.

[0022] By copolymerizing other acid components, the glass transition temperature of the resulting oxygen-absorbing polyester resin can be easily controlled, and the oxygen-absorbing performance can be improved. Furthermore, by controlling the crystallinity of the oxygen-absorbing polyester resin, the solubility in organic solvents can be improved.

[0023] Furthermore, since tetrahydrophthalic acid or a derivative thereof, or tetrahydrophthalic anhydride or a derivative thereof is prone to undergo a radical crosslinking reaction due to heat during polymerization, by blending another acid component and reducing the composition ratio of tetrahydrophthalic acid or a derivative thereof, or tetrahydrophthalic anhydride or a derivative thereof, contained in the raw material monomers, gelation during polymerization can be suppressed and a high-molecular-weight oxygen-absorbing polyester resin can be stably obtained.

[0024] The oxygen-absorbing polyester resin may further contain structural units derived from polyhydric alcohols, polycarboxylic acids, or derivatives thereof, etc. By introducing polyhydric alcohols and polycarboxylic acids to control the branched structure, it is possible to adjust the melt viscosity characteristics and the solution viscosity characteristics of the polyester dissolved in a solvent.

[0025] Examples of polyhydric alcohols and derivatives thereof include 1,2,3-propanetriol, sorbitol, 1,3,5-pentanetriol, 1,5,8-heptanetriol, trimethylolpropane, pentaerythritol, 3,5-dihydroxybenzyl alcohol, glycerin, and derivatives thereof. Examples of polycarboxylic acids and derivatives thereof include 1,2,3-propanetricarboxylic acid, meso-butane-1,2,3,4-tetracarboxylic acid, citric acid, trimellitic acid, pyromellitic acid, and derivatives thereof. When a component having three or more functional groups, such as a polyhydric alcohol or a polycarboxylic acid, is copolymerized, the amount is preferably 5 mol % or less of the total acid components.

[0026] In this embodiment, it is preferable to use, as the oxygen-absorbing resin, an oxygen-absorbing polyester resin obtained by copolymerizing tetrahydrophthalic acid or a derivative thereof, or tetrahydrophthalic anhydride or a derivative thereof as an acid component, 1,4-butanediol as a diol component, and succinic acid or succinic anhydride as another acid component.

[0027] In this case, the structural units derived from tetrahydrophthalic acid or a derivative thereof, or tetrahydrophthalic anhydride or a derivative thereof contained in the oxygen-absorbing polyester resin preferably account for 70 to 95 mol %, more preferably 75 to 95 mol %, and even more preferably 80 to 95 mol %, of the total acid components. The proportion of structural units derived from succinic acid or succinic anhydride relative to the total acid components is preferably 0 to 15 mol %, more preferably 0 to 12.5 mol %, and even more preferably 0 to 10 mol %. By adjusting the composition ratio in this way, it is possible to obtain an oxygen absorbing resin that is excellent in oxygen absorbing performance and adhesiveness, and also excellent in solubility in organic solvents.

[0028] The oxygen-absorbing polyester resin can be synthesized by, for example, interfacial polycondensation, solution polycondensation, melt polycondensation, or solid-phase polycondensation. A polymerization catalyst is not necessarily required, but conventional polyester polymerization catalysts such as titanium-, germanium-, antimony-, tin-, and aluminum-based catalysts can be used. Known polymerization catalysts such as nitrogen-containing basic compounds, boric acid and boric acid esters, and organic sulfonic acid compounds can also be used. Furthermore, various additives such as coloring inhibitors (e.g., phosphorus compounds) and antioxidants can also be added during polymerization. Addition of an antioxidant can suppress oxygen absorption during polymerization and subsequent processing, thereby preventing performance degradation and gelation of the oxygen-absorbing resin.

[0029] In addition, the polymerization was carried out at a shear rate of 100 s under conditions of a temperature of 220°C. -1 It is preferable to appropriately adjust the polymerization conditions, such as the composition ratio and molecular weight of the raw material monomers, so that the melt viscosity at this temperature is less than 90 Pa·s, preferably less than 60 Pa·s, and more preferably less than 30 Pa·s. By keeping the melt viscosity low, good coatability can be achieved, and by adding a curing agent, the material strength can be adjusted as desired, making it suitable for use as a solvent-soluble dry lamination adhesive.

[0030] The number-average molecular weight of the oxygen-absorbing polyester resin is preferably 500 to 100,000, and more preferably 2,000 to 10,000. The weight-average molecular weight is preferably 5,000 to 200,000, more preferably 10,000 to 100,000, and even more preferably 20,000 to 70,000. If the molecular weight is lower than the above range, the cohesive strength, i.e., creep resistance, of the resin decreases, while if it is higher, the solubility in organic solvents decreases and the coatability decreases due to an increase in solution viscosity, which is undesirable. The glass transition temperature of the oxygen-absorbing polyester resin is preferably −20° C. to 10° C., more preferably −15° C. to 6° C., and even more preferably −12° C. to 2° C. By setting the glass transition temperature within this range, sufficient oxygen-absorbing performance can be obtained. In order to obtain sufficient oxygen absorption performance, the acid value of the oxygen-absorbing polyester resin is preferably 5 mgKOH / g or less, more preferably 1 mgKOH / g or less. If the acid value exceeds 5 mgKOH / g, a rapid autoxidation reaction may be hindered, and stable oxygen absorption performance may not be obtained. The acid value of the oxygen-absorbing polyester resin is measured in accordance with JIS K 0070.

[0031] Furthermore, when oxygen-absorbing polyester resins are used as solvent-soluble dry lamination adhesives, the internal stress generated during the oxygen absorption reaction (oxidative curing reaction) can reduce the laminate strength. To prevent this, a component with a low glass transition temperature, primarily composed of saturated polyester resin, can be added. Such a component can mitigate the internal stress generated during the oxidative curing reaction due to its flexibility.

[0032] The saturated polyester resin is a polyester resin that does not substantially contain carbon-carbon double bond groups, and can be obtained, for example, by polycondensation of a dicarboxylic acid component, a diol component, and a hydroxycarboxylic acid component. The saturated polyester resin is preferably a polyester having an iodine value of 3 g / 100 g or less, and particularly preferably a polyester having an iodine value of 1 g / 100 g or less. If the iodine value of the saturated polyester resin exceeds 3 g / 100 g, it is undesirable because low-molecular-weight decomposition components are likely to be generated during the oxygen absorption reaction of the oxygen-absorbing resin. The iodine value is measured in accordance with JIS K 0070.

[0033] Examples of the dicarboxylic acid component include the aromatic dicarboxylic acids and aliphatic dicarboxylic acids exemplified above as components of the oxygen-absorbing polyester resin, hexahydrophthalic acid, dimer acid, and derivatives thereof, which can be used alone or in combination of two or more. Examples of the diol component include the diols exemplified above as components of the oxygen-absorbing polyester resin, which can be used alone or in combination of two or more. Examples of the hydroxycarboxylic acid component include the aliphatic hydroxycarboxylic acids exemplified above as components of the oxygen-absorbing polyester resin.

[0034] The glass transition temperature of the saturated polyester resin is preferably −10° C. or lower, more preferably −70° C. to −15° C., and even more preferably −60° C. to −20° C. By setting the glass transition temperature within this range, it is possible to effectively alleviate internal stress caused by the oxidative curing reaction accompanying oxygen absorption.

[0035] The ratio A / B of the oxygen-absorbing polyester resin (A) to the saturated polyester resin (B) is preferably 0.6 to 9, more preferably 1 to 9, and even more preferably 2 to 9. By setting the ratio A / B within this range, it is possible to exhibit excellent oxygen-absorbing performance while maintaining high laminate strength before and after oxygen absorption.

[0036] A transition metal catalyst may be added to the oxygen-absorbing resin layer 3 formed using the oxygen-absorbing resin described above to promote the oxygen-absorbing reaction. Examples of the transition metal catalyst include inorganic salts, organic salts, and complex salts of transition metals such as manganese, iron, cobalt, nickel, copper, silver, tin, titanium, zirconium, vanadium, and chromium, with manganese, iron, cobalt, nickel, and copper being particularly preferred. More specifically, examples of the transition metal catalyst include transition metal salts composed of a transition metal selected from manganese, iron, cobalt, nickel, and copper and an organic acid. In particular, from the viewpoint of promoting the oxygen-absorbing reaction of the oxygen-absorbing resin and enhancing its oxygen absorption properties, the transition metal catalyst is preferably an organic acid salt of manganese, iron, or cobalt, and more preferably an organic acid salt of cobalt. The content of the transition metal catalyst in the oxygen-absorbing resin layer 3 is preferably 1 ppm to 1000 ppm, more preferably 10 ppm to 500 ppm, and even more preferably 20 ppm to 300 ppm, in terms of metal equivalent.

[0037] Furthermore, when forming the oxygen-absorbing resin layer 3, it is preferable to prepare the oxygen-absorbing resin so that it can be used as a dry laminating adhesive by dissolving it in an organic solvent. Examples of organic solvents include ethyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, isopropanol, etc. Ethyl acetate, in particular, is a common solvent for dry laminating adhesives for flexible packaging because it is relatively less likely to cause unpleasant odors caused by residual solvents. Considering industrial applications, it is preferable to use a single solvent of ethyl acetate that does not contain toluene, xylene, etc.

[0038] When using oxygen-absorbing polyester resins, they can be used as two-component curing adhesives by blending an isocyanate curing agent. Blending an isocyanate curing agent increases adhesive strength and cohesive force, and also enables curing at low temperatures around room temperature. Examples of isocyanate curing agents include aliphatic isocyanate curing agents such as xylylene diisocyanate (XDI), hexamethylene diisocyanate (HDI), lysine diisocyanate, lysine methyl ester diisocyanate, trimethylhexamethylene diisocyanate, and n-pentane-1,4-diisocyanate, and alicyclic isocyanate curing agents such as isophorone diisocyanate (IPDI), cyclohexane-1,4-diisocyanate, methylcyclohexyl diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate. Among these, XDI and HDI are preferred as aliphatic isocyanate curing agents, and IPDI is preferred as an alicyclic isocyanate curing agent. XDI is particularly preferred. The use of XDI exhibits the most excellent oxygen absorption performance. These aliphatic and / or alicyclic isocyanate curing agents are preferably used as polyisocyanate compounds with increased molecular weight, such as adducts, isocyanurates, and biuret forms. These aliphatic and / or alicyclic isocyanate curing agents may be used alone or in combination of two or more.

[0039] The isocyanate curing agent is preferably added in an amount of 3 to 30 phr, more preferably 3 to 20 phr, and even more preferably 3 to 15 phr, based on the oxygen-absorbing polyester resin as the main component, in terms of solid weight. If the amount added is too small, the adhesiveness and cohesive strength will be insufficient, while if the amount added is too large, the amount of oxygen-absorbing component contained in the resin composition per unit weight will be small, resulting in insufficient oxygen-absorbing performance. Furthermore, if the mobility of the resin is significantly reduced by curing, the oxygen-absorbing reaction will be less likely to proceed, and the oxygen-absorbing performance will be reduced.

[0040] [Inner base material layer] In order to improve tearability and non-sorption of aroma components, the inner substrate layer 4 is preferably made heat-sealable by laminating a heat-sealable polyester resin layer on the inner side of the stretched PET substrate, or by using a surface substrate made heat-sealable by amorphizing or low-crystallizing the entire thickness of the stretched PET substrate at least in the heat-sealing region of the stretched PET substrate. For example, a general-purpose heat-sealing agent made primarily of polyolefin resin can be applied in thin film form to one side of the stretched PET substrate to make it heat-sealable, but this is insufficient due to poor non-sorption properties. The inner surface of the stretched PET substrate refers to the surface opposite to the surface facing the oxygen-absorbing resin layer 3, and the heat-sealed area refers to the portion that is heat-sealed when forming the bag into the desired shape as described above.

[0041] Regarding such an inner surface base material layer 4, first, an embodiment including a stretched PET base material and a heat-sealable polyester-based resin layer laminated on the inner surface side of the stretched PET base material will be described.

[0042] As the stretched PET substrate, a stretched and oriented polyethylene terephthalate film is preferably used, and in particular, a biaxially stretched polyethylene terephthalate film is preferably used. The stretched PET substrate is made of a polyethylene terephthalate resin, and for reasons such as controlling film formability and crystallinity, it is preferably made of a polyethylene terephthalate resin in which approximately 0.1 to 3 mol % of the acid component, terephthalic acid, has been modified with isophthalic acid. The thickness of the stretched PET substrate is not particularly limited as long as it has a desired oxygen permeability so as not to inhibit the oxygen absorption function of the oxygen-absorbing resin layer 3. However, to maintain handleability while achieving high oxygen permeability, the thickness of the stretched PET substrate is preferably 6 to 20 μm, more preferably 6 to 16 μm, and even more preferably 7 to 14 μm.

[0043] The heat-sealable polyester resin layer is preferably formed using a heat-sealable copolymer polyester from the viewpoint of non-sorption of aroma components. In particular, it is preferably formed using a copolymer polyester obtained by copolymerizing at least one acid component selected from the group consisting of terephthalic acid, isophthalic acid, and adipic acid with at least one diol component selected from the group consisting of ethylene glycol, diethylene glycol, neopentyl glycol, propylene glycol, butanediol, and 1,4-cyclohexanedimethanol. In this case, polyesters copolymerized with terephthalic acid and isophthalic acid as acid components have a high glass transition temperature and are therefore excellent in non-sorption of aroma components. Furthermore, copolymerization allows the crystallinity of the resin to be controlled low, resulting in an amorphous structure, which also provides good heat-sealability, making them particularly preferred. Examples of heat-sealable copolymer polyesters include, but are not limited to, copolymer polyesters consisting of three components: terephthalic acid, ethylene glycol, and neopentyl glycol; copolymer polyesters consisting of three components: terephthalic acid, isophthalic acid, and ethylene glycol; copolymer polyesters consisting of three components: terephthalic acid, isophthalic acid, and propylene glycol; copolymer polyesters consisting of three components: terephthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol; copolymer polyesters consisting of four components: terephthalic acid, isophthalic acid, ethylene glycol, and neopentyl glycol; and copolymer polyesters consisting of four components: terephthalic acid, isophthalic acid, ethylene glycol, and diethylene glycol. Such copolymer polyesters are non-sorbent of aroma components and have heat-sealing properties, and also have appropriate oxygen permeability, so they do not inhibit the oxygen absorption function of the oxygen-absorbing resin layer 3. Furthermore, they have high adhesion to the stretched PET substrate, so that an adhesive layer between the stretched PET substrate and the heat-sealing polyester-based resin layer can be omitted, making them suitable as resins for forming the heat-sealing polyester-based resin layer in this embodiment.

[0044] The thickness of the heat-sealable polyester resin layer is preferably 0.1 to 5.0 μm, more preferably 0.5 to 4.0 μm, and even more preferably 0.5 to 3 μm. In this case, the thicker the heat-sealable polyester resin layer, the higher the heat-seal strength can be expected to be, but it is particularly preferred to make the heat-sealable polyester resin layer thinner than the thickness of the aforementioned stretched PET substrate, since this provides excellent tearability and non-sorption of aromatic components.

[0045] A heat-sealable polyester resin layer can be laminated on the inner surface of the stretched PET substrate by any known method, including, but not limited to, applying a coating agent containing the aforementioned resin dissolved therein to one surface of the stretched PET substrate and drying the coating, or preparing a two-layer film consisting of a PET resin and the aforementioned copolymer polyester resin by the T-die method, and then subjecting the film to a moderate uniaxial or biaxial stretching treatment so as not to impair the heat-sealability inherent to the copolymer polyester resin.

[0046] Next, an embodiment will be described in which the inner surface base material layer 4 includes a stretched PET base material, and the entire thickness of the stretched PET base material is amorphous or low-crystallized at least in the heat seal region of the stretched PET base material.

[0047] The stretched PET substrate can be the same as in the embodiment described above, and therefore a redundant description will be omitted. Stretched, oriented polyethylene terephthalate film is highly crystalline due to orientation crystallization and does not have heat-sealability. However, by preheating the film surface as necessary, then scanning and irradiating the film surface with an ultraviolet laser or infrared laser beam, and then rapidly cooling immediately after the scanning is completed, only a portion of the film can be selectively rendered amorphous or low-crystallized, thereby imparting heat-sealability. This allows the film to be used as an inner substrate that includes a stretched PET substrate and forms a heat-sealable inner substrate layer 4. This embodiment is particularly preferred due to the non-sorption properties of the polyethylene terephthalate resin itself.

[0048] The crystallinity of the untreated stretched PET region and the amorphous or low-crystallized PET region can be measured by known methods, such as a general density method (density measured by a density gradient tube method) or a method disclosed in Japanese Patent Publication No. 7-80502 in which density distribution is measured by a laser Raman method and the crystallinity is calculated from a conversion formula.

[0049] In this embodiment, when at least the heat-sealed region of the stretch-oriented polyethylene terephthalate film is amorphized or low-crystallized, only the portion necessary for heat sealing is treated, thereby shortening the treatment time, and the remaining untreated portion has excellent non-sorption properties derived from the stretched PET substrate, high crystallinity, and excellent tearability, which is preferable. To amorphize or low-crystallize at least the heat-sealed region of the stretch-oriented polyethylene terephthalate film, for example, the treatment methods described in JP-A-2016-000796 and JP-A-2020-189892 can be applied. Furthermore, when these treatment methods are applied to make at least the heat seal region of the stretched PET substrate amorphous or low-crystallization, the stretched PET substrate can be laminated with other layers as needed before the treatment is applied to the stretched PET substrate.

[0050] As described above, the inner substrate layer 4 in this embodiment can be either of the following: a stretched PET substrate and a heat-sealable polyester resin layer laminated on the inner side of the stretched PET substrate; or a stretched PET substrate in which the entire stretched PET substrate in the thickness direction is amorphous or low-crystallized at least in the heat-sealed region of the stretched PET substrate. In either case, the oxygen permeability of the inner substrate layer 4 is 50 cc / (m ) or less in an environment of 25°C-60% RH so as not to inhibit the oxygen absorption function of the oxygen-absorbing resin layer 3. 2 ·day·atm) or more, and more preferably 80cc / (m 2 ·day·atm) or more, more preferably 100cc / (m 2 ·day·atm) or more.

[0051] In this embodiment, the oxygen-absorbing film 1 can be produced by dry laminating the inner substrate for forming the inner substrate layer 4 onto the surface substrate for forming the surface substrate layer 2 using a dry laminating adhesive containing the oxygen-absorbing resin prepared as described above. A known dry laminator can be used for this process. For example, a series of laminating steps can be performed, in which the dry laminating adhesive containing the oxygen-absorbing resin is applied to the surface substrate, the substrate is passed through a drying oven to volatilize the organic solvent, and the inner substrate is bonded to the surface substrate using nip rolls heated to 50 to 120°C. This forms an oxygen-absorbing resin layer 3 made of the oxygen-absorbing adhesive resin contained in the dry laminating adhesive between the surface substrate and the inner substrate. This allows the production of an oxygen-absorbing film 1 comprising the surface substrate layer 2 having oxygen barrier properties, the oxygen-absorbing resin layer 3, and the inner substrate layer 4 laminated in this order.

[0052] In producing the oxygen-absorbing film 1 in this manner, the amount of dry lamination adhesive containing the oxygen-absorbing resin to be applied is 0.1 to 30 g / m in terms of solid content. 2 is preferable, and more preferably 1 to 15 g / m 2 , and more preferably 2 to 10 g / m 2 is.

[0053] The heat seal strength of the oxygen-absorbing film 1 is not particularly limited as long as the heat seal interface is melted and sufficiently sealed, but for example, the lower limit is preferably 1 N / 15 mm or more, and more preferably 2 N / 15 mm or more. In this case, the higher the heat seal strength, the better, and this film is suitable for use when packaging relatively lightweight foods or medicines. Furthermore, if the heat seal strength is too high, it becomes difficult to disassemble, so the upper limit of the heat seal strength is preferably 12 N / 15 mm or less, more preferably 9 N / 15 mm or less, and particularly preferably 7 N / 15 mm or less.

[0054] According to the present embodiment as described above, it is possible to provide an oxygen-absorbing film 1 suitable as a packaging material, which is excellent in suppressing oxidation of the packaged object, non-sorption of aroma components, and also has excellent tearability. Furthermore, as mentioned above, when an oxygen-absorbing polyester resin is used as the oxygen-absorbing resin and prepared as a dry lamination adhesive, the internal stress generated by the oxygen-absorbing reaction may reduce the laminate strength. If the laminate strength is reduced and delamination occurs during tearing, the film may become difficult to tear. However, by including a stretched PET substrate in the inner substrate layer 4, such a problem can be effectively avoided. [Example]

[0055] The present invention will be described in more detail below with reference to specific examples.

[0056] [Example 1] A 0.9 molar ratio of methyltetrahydrophthalic anhydride isomer mixture (Hitachi Chemical Co., Ltd.; HN-2200) was used as the acid component, a 0.1 molar ratio of succinic anhydride was used as the other acid component, 1,4-butanediol was used as the diol component, and 300 ppm of isopropyl titanate was used as the polymerization catalyst. The mixture was reacted in a nitrogen atmosphere at 150-200°C for approximately 6 hours while removing the generated water. Polymerization was then carried out under a reduced pressure of 0.1 kPa at 200-220°C for approximately 3 hours to obtain oxygen-absorbing polyester resin (A). The oxygen-absorbing polyester resin (A) had a number-average molecular weight (Mn) of 3400, a weight-average molecular weight (Mw) of 52600, and a glass transition temperature (Tg) of -5.0°C.

[0057] The resulting oxygen-absorbing polyester resin (A) was mixed with saturated polyester resin (B) (DIC Corporation; Polycizer W4010 / Mn: 3600, Mw: 9500) with a Tg of -26°C so that the solids weight ratio (A / B) was 4.0. An HDI / IPDI curing agent (DIC Graphics Corporation; KL-75) was added as an isocyanate curing agent to the solids of the mixture so that the solids amounted to 7 phr (parts per hundred resin). Furthermore, cobalt neodecanoate was added as a catalyst to a metal equivalent of 80 ppm relative to the total solids, and the mixture was dissolved in ethyl acetate to prepare a dry laminating adhesive containing the oxygen-absorbing resin at a solids concentration of 32 wt%.

[0058] Next, a surface substrate was prepared by dry-laminating a 7 μm thick aluminum foil to a 12 μm thick biaxially stretched PET film via a urethane adhesive, and an inner substrate was prepared by laminating a 1 μm thick heat-sealable polyester resin layer (oxygen permeability: 130 cc / (m) at 25°C-60%RH) on one side of the 12 μm thick biaxially stretched PET film (stretched PET substrate) and a copolymer polyester (copolymerization ratio: terephthalic acid 29 mol%, isophthalic acid 21 mol%, ethylene glycol 28 mol%, neopentyl glycol 22 mol%) whose acid components are terephthalic acid and isophthalic acid and whose diol components are ethylene glycol and neopentyl glycol) to a thickness of 1 μm. 2 ·day·atm)) and were set in the dry laminator. Then, the aforementioned dry lamination adhesive was applied to the aluminum foil side of the surface substrate at a rate of 5 g / m. 2 The resulting film was then dry-laminated to the stretched PET side of the inner substrate, and then stored at 35°C in a nitrogen atmosphere for 5 days to obtain oxygen-absorbing film 1 having a layer structure consisting of surface substrate layer (biaxially stretched PET film / urethane adhesive / aluminum foil) 2 / oxygen-absorbing resin layer 3 / inner substrate layer (biaxially stretched PET film / heat-sealable polyester resin layer) 4. The oxygen permeability of the inner substrate is measured by measuring the inner substrate at 50.2 cm 2The samples were cut to the size of 100 mm and attached to a mixed gas permeability tester (GTR Tech Co., Ltd.; flow-type water vapor permeability tester GTR-20XFTSK), and measurements were taken under the conditions of a temperature of 25°C, a humidity of 60% RH, an oxygen test gas flow rate of 40 ml / min, and a helium flow gas flow rate of 5 ml / min.

[0059] The obtained oxygen-absorbing film 1 was evaluated for (a) oxygen absorption performance, (b) tear strength, and (c) non-sorption as follows. The results are shown in Table 1.

[0060] (a) Oxygen absorption performance A test piece measuring 2 cm x 15 cm was cut out from the oxygen absorbing film 1 and placed in a container with an internal volume of 85 cm 3 The contents were placed in an oxygen-impermeable steel foil-laminated cup with a humidity-regulating liquid consisting of an aqueous glycerin solution, and the cup was heat-sealed with an aluminum foil-laminated film lid and stored in an atmosphere of 25°C. The humidity inside the cup was controlled to 60% RH using the humidity-regulating liquid, and the oxygen concentration inside the cup after 28 days of storage was measured using a micro gas chromatograph (3000MICRO GC manufactured by INFICON). 2 The oxygen absorption per unit volume was calculated, and the oxygen absorption after 28 days of storage was 0.030 ml / cm 2 Above 0.030ml / cm 2 Anything less than this was considered poor.

[0061] (b) Tear strength Test pieces measuring 150 mm x 50 mm were cut from the oxygen-absorbing film 1. According to JIS K 7128-1, rectangular test pieces were slit halfway along their length using the trouser method under an atmosphere of 23°C and 50% RH. The long legs of the trouser-shaped test pieces were attached to a tensile testing machine (Shimadzu Corporation; Precision Universal Testing Machine Autograph AG-IS) and the tear strength (unit: N) was measured at a tear rate of 200 mm / min. The tear strength was calculated by excluding the first 20 mm and the last 5 mm of the tear, and the average strength of the remaining 50 mm was used. A tear strength of less than 0.2 N in the MD (machine direction) and TD (transverse direction) was evaluated as good (○), and a tear strength of 0.2 N or greater was evaluated as poor (×).

[0062] (c) non-sorption A 5cm x 4cm test piece was cut from the oxygen-absorbing film 1, the heat-seal layer 5 side of which was placed in contact with Salonpas Ae (Hisamitsu Pharmaceutical Co., Ltd.), and the sample was returned to its original packaging, heat-sealed, and then left at 22°C for two weeks. The test piece was then removed, placed in a sealed glass vial, and heated at 80°C for 30 minutes. The volatilized sorbed components were quantitatively measured using a gas chromatograph equipped with a headspace sampler (Agilent Technologies; 6890 Series GC System, FID detector). The three components measured were dl-camphor, l-menthol, and methyl salicylate. The sorption amount of each sample was calculated relative to the adsorption amount of a commercially available 12 μm stretched PET film, with the sum of the sorption amounts of the three components being 1. A sum of the relative sorption amounts of the three components less than 10 was considered good (○), and a sum of 10 or more was considered poor (×).

[0063] (d) Heat seal strength Using a heat seal tester (manufactured by Tester Sangyo Co., Ltd.), the seal time was 1 second and the seal pressure was 2 kgf / cm. 2 The temperature was fixed at 110°C to 190°C, and test specimens were prepared while measuring the temperature at the seal interface. Heat seal strength was measured in accordance with JIS-Z1707 using a precision universal testing machine, Autograph AG-IS (Shimadzu Corporation), at 23°C and 50% RH. The film was pulled in the machine direction (MD) at a rate of 300 mm / min, and the maximum test force (N / 15 mm width) was measured as the heat seal strength. The maximum seal strength within the above sealing temperature range was also recorded as the heat seal strength.

[0064] [Table 1]

[0065] [Example 2] The inner substrate was a 9 μm-thick biaxially stretched PET film (stretched PET substrate) on one side of which was laminated a 3 μm-thick heat-sealable polyester resin layer made of a copolymer polyester (copolymerization ratio: terephthalic acid 41 mol%, isophthalic acid 9 mol%, ethylene glycol 48 mol%, diethylene glycol 2 mol%) whose acid components were terephthalic acid and isophthalic acid and whose diol components were ethylene glycol and diethylene glycol (oxygen permeability: 140 cc / (m) at 25°C-60% RH). 2 An oxygen-absorbing film 1 was obtained in the same manner as in Example 1, except that a 1000 kJ / kg sieve (1000 kJ / kg sieve) was used. The oxygen-absorbing film 1 obtained was evaluated for (a) oxygen absorption performance, (b) tear strength, and (c) non-sorption. The results are also shown in Table 1.

[0066] [Example 3] A carbon dioxide laser oscillator (wavelength 10.6 μm) was used on a 12 μm thick stretched PET substrate at an output of 35 W, a spot diameter on the irradiated surface of approximately 2.7 mm, a scanning line spacing of 1100 μm, and a scanning speed of 540 mm / sec. Except for using an inner substrate in which only the heat-sealed region of the stretched PET substrate was amorphized in the entire thickness direction, oxygen-absorbing film 1 was obtained in the same manner as in Example 1. The obtained oxygen-absorbing film was evaluated for (a) oxygen absorption performance, (b) tear strength, and (c) non-sorption. The results are also shown in Table 1. For the evaluation, test pieces were cut out from areas other than the heat-sealed area.

[0067] [Example 4] An oxygen-absorbing film 1 was obtained in the same manner as in Example 1, except that an HDI / IPDI curing agent (KL-75 manufactured by DIC Graphics Corporation) was mixed with the oxygen-absorbing polyester resin (A) as an isocyanate curing agent so that the solid content was 10 phr to prepare a dry lamination adhesive containing the oxygen-absorbing resin. The obtained oxygen-absorbing film 1 was evaluated for (a) oxygen absorption performance, (b) tear strength, and (c) non-sorption. The results are also shown in Table 1.

[0068] [Example 5] An oxygen-absorbing film 1 was obtained in the same manner as in Example 2, except that the dry laminating adhesive containing the oxygen-absorbing resin prepared in Example 4 was used. The obtained oxygen-absorbing film 1 was evaluated for (a) oxygen absorption performance, (b) tear strength, and (c) non-sorption. The results are also shown in Table 1.

[0069] [Example 6] An oxygen-absorbing film 1 was obtained in the same manner as in Example 3, except that the dry laminating adhesive containing the oxygen-absorbing resin prepared in Example 4 was used. The obtained oxygen-absorbing film 1 was evaluated for (a) oxygen absorption performance, (b) tear strength, and (c) non-sorption. The results are also shown in Table 1.

[0070] [Comparative Example 1] An oxygen-absorbing film 1 was obtained in the same manner as in Example 1, except that a 17 μm-thick unstretched isophthalic acid-modified PET film (Fine Cast Film, manufactured by Toyo Kohan Co., Ltd.) was used as the inner substrate. The obtained oxygen-absorbing film 1 was evaluated for (a) oxygen absorption performance, (b) tear strength, and (c) non-sorption. The results are also shown in Table 1.

[0071] Comparative Example 2 An oxygen-absorbing film 1 was obtained in the same manner as in Example 1, except that a 30 μm-thick amorphous PET film made of cyclohexanedimethanol-modified polyethylene terephthalate resin (Hytron PG, manufactured by Tamapoly Co., Ltd.) was used as the inner substrate. The obtained oxygen-absorbing film 1 was evaluated for (a) oxygen absorption performance and (c) non-sorption. The results are also shown in Table 1.

[0072] The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. [Explanation of symbols]

[0073] 1. Oxygen absorbing film 2 Surface base material layer 3. Oxygen-absorbing resin layer 4 Inner base material layer

Claims

1. The film is formed by laminating, in this order from the outer layer side, at least a surface substrate layer having oxygen barrier properties, an oxygen-absorbing resin layer, and an inner substrate layer containing a biaxially stretched PET substrate, the inner surface base material layer includes the biaxially oriented PET base material and a heat-sealable polyester-based resin layer laminated on the inner surface side of the biaxially oriented PET base material, The thickness of the biaxially stretched PET substrate is 6 to 16 μm, the thickness of the heat-sealable polyester resin layer is 0.1 to 5.0 μm; An oxygen-absorbing film, characterized in that the heat-sealable polyester resin layer is formed using a copolymer polyester consisting of three components, namely, terephthalic acid, ethylene glycol, and neopentyl glycol, a copolymer polyester consisting of four components, namely, terephthalic acid, isophthalic acid, ethylene glycol, and neopentyl glycol, or a copolymer polyester consisting of four components, namely, terephthalic acid, isophthalic acid, ethylene glycol, and diethylene glycol.

2. 2. The oxygen-absorbing film according to claim 1, wherein the oxygen permeability of the inner substrate layer is 50 cc / (m2·day·atm) or more in an environment of 25° C. and 60% RH.

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