Transparent gas barrier film

Abstract

[Problem] The purpose of the present invention is to provide an inexpensive transparent barrier film with excellent acid resistance in which the environment is taken into account and a plastic film created using a recycled resin from PET bottles is used. [Solution] A transparent gas barrier film having an aluminum oxide layer in which aluminum oxide is the main component on at least one surface of a substrate polyester film, wherein the transparent gas barrier film is characterized in that the absorption coefficient of the aluminum oxide layer immediately after vapor deposition is less than 0.03 nm-1, the vapor deposition film thickness is 6-10 nm, the substrate polyester film includes 50 wt% or more of a polyester resin recycled from PET bottles and is a polyester film obtained by biaxial stretching, and the isophthalic acid content, the limiting viscosity, the thermal shrinkage rate, the lamination strength, and the variation in thickness are within predetermined ranges.

Description

[Technical Field]

[0001] The present invention relates to a packaging material that is excellent in transparency, gas barrier properties, printability, and flexibility and that is required to be airtight for foods, medicines, electronic components, etc. More specifically, the present invention relates to a transparent barrier film that has excellent properties as a gas barrier material, and is formed by laminating an aluminum oxide layer on a plastic film made from polyester resin recycled from PET bottles. [Background technology]

[0002] In recent years, interest in environmental issues has increased, and concern about waste has grown, leading to calls to reduce the use of disposable plastic containers, etc. There has also been talk of reducing waste caused by expired food products.

[0003] For this reason, there has been a demand for the reduction, reuse, and recycling of plastic products. Various technologies have been implemented, including a technology that recycles the PET bottles that are used in large quantities and reuses them as packaging film.

[0004] A film technology has been disclosed that uses polyester resin recycled from PET bottles, has good dimensional stability under heat, has a uniform thickness, and has improved adhesive strength with other films (see, for example, Patent Document 1).

[0005] Furthermore, a technology is known that uses packaging materials with gas barrier properties (low oxygen permeability, low water vapor permeability) to extend the shelf life of food and prevent deterioration of the contents. For flexible packaging materials, a transparent barrier film technology is known in which a metal oxide layer is laminated on a plastic film (see, for example, Patent Document 2). Silicon oxide and aluminum oxide are often used as metal oxides because of their transparency. Metal oxide layers are typically laminated onto plastic films using vapor deposition or CVD methods. Among these, laminated films that use an aluminum oxide layer as a barrier layer, which is prepared by a reactive vapor deposition method in which aluminum is evaporated and oxygen is introduced, have become mainstream (see, for example, Patent Document 3).

[0006] Furthermore, there is a transparent barrier film in which a metal oxide layer is laminated onto a recycled plastic film as a substrate (see, for example, Patent Document 4).

[0007] The transparent barrier film with an aluminum oxide layer created by reactive vapor deposition used in Patent Document 3 uses aluminum, which is an inexpensive vapor deposition material, and because the evaporation temperature of aluminum is low, it can be produced using relatively inexpensive equipment with an induction heating or resistance heating vapor deposition source. Therefore, it can be provided as a packaging material at a lower cost than transparent barrier films using silicon oxide or silicon oxide and aluminum oxide as vapor deposition materials. However, a drawback is that when acidic contents are placed in a bag made using this transparent barrier film with an aluminum oxide layer, the barrier properties are reduced, causing the contents to deteriorate. To address this issue, a barrier layer made of silicon oxide, which is an expensive evaporation material, or a mixed layer of silicon oxide and aluminum oxide, which is produced using an expensive evaporation apparatus that uses an electron beam evaporation source, has been used. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. WO2014 / 050844 [Patent Document 2] Patent No. 2929609 [Patent Document 3] Patent No. 2638797 [Patent Document 4] International Publication No. WO2015 / 146496 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in view of the problems of the conventional technology. That is, an object of the present invention is to provide an inexpensive transparent barrier film that is excellent in acid resistance and takes environmental issues into consideration. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that the above problems can be solved by the following means, and have arrived at the present invention. That is, the present invention has the following configuration. A transparent gas barrier film having an aluminum oxide layer containing aluminum oxide as a main component on at least one side of a base polyester film, wherein the absorption coefficient of the aluminum oxide layer immediately after deposition is 0.03 nm -1 The transparent gas barrier film is characterized by having a thickness of less than 1000 nm, a vapor-deposited film thickness of 6 nm or more and 10 nm or less, the base polyester film being a biaxially stretched polyester film containing 50% by weight or more of polyester resin recycled from PET bottles, and satisfying the following requirements: (1) The content of isophthalic acid components relative to the total dicarboxylic acid components in the total polyester resin constituting the base polyester film is 0.5 mol % or more and 5.0 mol % or less (2) The intrinsic viscosity of the resin constituting the base polyester film is 0.58 dI / g or more and 0.70 dI / g or less. (3) The heat shrinkage rate of the base polyester film at 150°C in the longitudinal and transverse directions is 0.1% or more and 1.5% or less. (4) When a polyolefin film is laminated on the side opposite to the aluminum oxide layer of the base polyester film, the lamination strength is 4.0 N / 15 mm or more and 20.0 N / 15 mm or less. (5) Measure the thickness Tn (n = 1 to 200) (unit: μm) at 200 points every 5 mm along a 1 m length of film in both the longitudinal and transverse directions. The maximum thickness is Tmax, the minimum thickness is Tmin, and the average thickness is Tave. The thickness variation calculated using the following formula is 16% or less in both the longitudinal and transverse directions. Thickness variation = {(Tmax-Tmin) / Tave} x 100(%)

[0011] In addition, the absorption coefficient immediately after deposition is 0.02 nm -1 The transparent gas barrier film is characterized by the above.

[0012] In addition, the absorption coefficient is finally 0.002 nm -1 A transparent gas barrier film characterized by the following: [Effects of the Invention]

[0013] The present invention provides a transparent gas barrier film that is environmentally friendly, inexpensive, has excellent transparency, and maintains its barrier properties even when packaging acidic contents, allowing the contents to be stored for a long period of time. [Brief explanation of the drawings]

[0014] [Figure 1] Transmittance wavelength characteristics of the substrate plastic film and transparent gas barrier film measured with a spectrophotometer [Figure 2] Transmittance wavelength characteristics of the plastic film substrate, color matching functions for the D65 illuminant and the CIE standard colorimetric observer [Figure 3] Vapor deposition schematic diagram [Figure 4] Vapor deposition schematic diagram [Figure 5] Schematic diagram showing one aspect of the inside of an extruder in a film production facility [Figure 6] Vapor deposition equipment schematic diagram DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below. The transparent gas barrier film of the present invention is a plastic film having an aluminum oxide layer containing aluminum oxide as a main component on at least one side of the plastic film, characterized in that the absorption coefficient of the aluminum oxide layer immediately after deposition is less than 0.03 nm-1 and the film thickness is 6 nm or more and 10 nm or less.

[0016] In the present invention, an aluminum oxide layer containing aluminum oxide as a main component refers to a layer that essentially contains 99% or more aluminum oxide and contains other components as impurities. Furthermore, aluminum oxide includes not only stoichiometrically complete oxide but also aluminum oxide that is oxygen-deficient.

[0017] The absorption coefficient α in the present invention can be expressed by Equation 1, where the total light transmittance of the aluminum oxide layer is Tal % and the film thickness of the aluminum oxide layer is tal nm. α=-1 / tal ln(Tal / 100) Formula (1) The total light transmittance Tal % of the aluminum oxide layer can be expressed by formula (2), where the total light transmittance of the transparent gas barrier film having the aluminum oxide layer is T0 % and the total light transmittance of the plastic film substrate on which the aluminum oxide layer is laminated is Tb %. Tal=T0 / Tb×100...Equation (2)

[0018] The thickness of the aluminum oxide layer of the present invention is determined so that the density of the aluminum oxide thin film is equal to the bulk density (3.97 g / cm 3 ) times 0.74 (2.94 g / cm 3 ) was determined using a fluorescent X-ray analyzer. The reason for multiplying it by 0.74 is that it closely matches the actual film thickness determined by TEM, etc. To determine film thickness using an X-ray fluorescence spectrometer, it is necessary to first measure a sample of known film thickness using the X-ray fluorescence spectrometer, determine the amount of fluorescent X-rays emitted from the sample, and create a calibration curve of film thickness and fluorescent X-ray intensity.

[0019] The samples used to create the fluorescent X-ray calibration curve are those for which the amount of aluminum attached per unit area is identified by inductively coupled plasma optical emission spectroscopy, and the film thickness is measured by converting it into film thickness using the density of the aluminum oxide thin film.

[0020] The total light transmittance referred to in the present invention refers to the total light transmittance conforming to JIS K 7375. In addition, in an optical film thickness meter installed in a vapor deposition apparatus to measure film thickness, light is irradiated from one side of the object to be measured using a light source such as a fluorescent lamp, xenon lamp, or white LED, and the value measured for the amount of light emerging from the other side is also treated as the total light transmittance by measuring a sample whose total light transmittance has been measured in accordance with JIS K 7375 in advance using the optical film thickness meter and taking a correlation.

[0021] Figure 1 shows a graph of the light transmittance of the substrate plastic film and transparent barrier film measured using a spectrophotometer. Whereas the substrate plastic film has a light transmittance of 1, the transparent barrier film has a light transmittance of 2, and light is absorbed monotonically at all wavelengths, if we take into account the wavelength range of the D65 light source specified as the light source in JIS K 7375 and the transmittance function of the CIE standard colorimetric observer, the value converted from the optical film thickness meter value can also be treated as total light transmittance. The wavelength range is shown in Figure 2.

[0022] The transparent gas barrier film of the present invention is a plastic film having an aluminum oxide layer containing aluminum oxide as a main component on at least one side of the plastic film, and has an absorption coefficient of 0.03 nm immediately after deposition of the aluminum oxide layer. -1 is less than. The method for producing a transparent gas barrier film of the present invention is a method for producing a transparent gas barrier film made of a plastic film having an aluminum oxide layer containing aluminum oxide as a main component on at least one side of the plastic film, the method comprising the steps of: -1 The aluminum oxide layer is formed to have a thickness of less than 100 nm. In the present invention, "immediately after deposition" refers to the time point at which the optical thickness is measured for the purpose of controlling the film thickness immediately after an aluminum oxide layer is deposited on a plastic film in a vacuum chamber. When the deposited aluminum oxide layer comes into contact with oxygen, oxidation progresses further, causing a change in the total light transmittance. After the deposition is completed, the deposited plastic film is removed from the deposition apparatus and the total light transmittance is immediately measured, which coincides with the time when the optical thickness is measured.

[0023] The absorption coefficient immediately after deposition is 0.03 nm -1 If the film is exposed to the atmosphere and oxidation is accelerated, the barrier properties will deteriorate if a bag is made using this transparent barrier film to package acidic materials. In other words, the film will have poor acid resistance. The absorption coefficient immediately after deposition is 0.03 nm. -1 Less than is preferred. The structure of the material allows acid molecules to easily approach metal atoms, or it is unclear whether the oxidized metal atoms are in a state where they can easily react with acid, but deterioration by acid occurs. In the present invention, acid resistance refers to the state in which, when highly acidic contents are placed in a package using a transparent barrier film, the aluminum oxide layer, which is the barrier layer, does not lose its barrier properties due to chemical changes caused by the acid.

[0024] The absorption coefficient immediately after deposition is 0.02 nm -1 In the method for producing a transparent gas barrier film of the present invention, the absorption coefficient immediately after deposition is preferably 0.02 nm -1 It is preferable to adjust it to 0.02 nm or more. -1 If the temperature is less than this, the degree of oxidation of aluminum oxide is high and transparency is increased, but the water vapor permeability is decreased, which is not preferable as a barrier film. It is speculated that the density of the aluminum oxide layer decreases due to a large reaction with oxygen during deposition, but this is not certain.

[0025] The absorption coefficient in this invention is finally 0.002 nm -1 The term "less than" refers to a value that indicates an absorption coefficient of 0.002 nm or less when a transparent barrier film, in which an aluminum oxide layer is laminated by vapor deposition onto a plastic film substrate, is removed from a vacuum chamber, exposed to the atmosphere, and stored at room temperature between 10°C and 40°C for at least one week. -1 The following is true:

[0026] The transparent gas barrier film of the present invention has an inorganic oxide vapor-deposited layer having a thickness of 6 nm to 10 nm. The method for producing the transparent gas barrier film of the present invention also includes an aluminum oxide layer forming step for adjusting the thickness of the aluminum oxide layer to 6 nm to 10 nm. The final absorption coefficient is 0.002 nm. -1 If the thickness exceeds 10 nm, the light absorption of the thin film exceeds 1%, causing coloration to become a problem, even if the film thickness is 10 nm or less. Although coloration can be suppressed by reducing the film thickness, barrier properties become an issue when the film thickness is 5 nm.

[0027] The absorption coefficient immediately after deposition is 0.03 nm for films with a thickness of 10 nm or less -1 A suitable method for producing the transparent barrier film having the aluminum oxide layer described below is reactive vapor deposition. The reactive vapor deposition method involves heating and evaporating metallic aluminum, then introducing oxygen into the deposition chamber to cause the metallic aluminum to react with aluminum oxide, which is then deposited on the plastic film of the substrate.Methods that can be used to heat and evaporate metallic aluminum include resistance heating, induction heating, and electron beam heating.

[0028] One method for controlling the film thickness is to measure the aluminum oxide layer deposited on the plastic film with a film thickness gauge that uses fluorescent X-rays, compare it with the target film thickness, and adjust the heating accordingly. In this case, the absorption coefficient is set to 0.03 nm. -1 To achieve the following, a photometer is installed to irradiate light from one side of the plastic film and measure the light transmitted from the other side, and the amount of oxygen introduced is controlled by the total transmitted light dose.

[0029] Alternatively, metallic aluminum is first vapor-deposited onto a plastic film on the substrate. An optical film thickness meter is used to irradiate light from one side of the vapor-deposited plastic film, measure the light transmitted through the other side, and convert the result into film thickness. This controls the thickness of the deposited metallic aluminum to a constant film thickness. Oxygen is then introduced to deposit aluminum oxide. In this case, there is a manufacturing method in which the evaporation conditions are kept constant and the optical film thickness meter is used as a total light transmittance meter to control the amount of oxygen introduced to achieve the target total light transmittance. The latter manufacturing method is preferred because the equipment required is simple.

[0030] When using an optical film thickness gauge, a suitable method is a resistance heating method in which an aluminum wire is supplied to a boat-type heating element as the evaporation source. After oxygen is introduced, the film thickness cannot be calculated from the total light transmittance. With a boat-type evaporation source, the aluminum evaporation material is supplied by wire, so if the wire supply speed is maintained when the target evaporation amount is reached, if the evaporation slows down and the molten aluminum on the boat increases, it can be determined that the evaporation amount has decreased. If the evaporation amount increases, the wire supply cannot keep up, so it does not exceed a certain level. In this way, once the aluminum evaporation rate is determined, it becomes stable, which is preferable.

[0031] Figures 3 and 4 show schematic diagrams of the deposition apparatus. Aluminum evaporated from the deposition source (9) is deposited on the plastic film (5) of the substrate on the coating roll (6). A coating window (7) is installed near the coating roll (6) to limit the angle of incidence of the aluminum vapor onto the substrate and to prevent adhesion to unwanted areas. The oxygen inlet (8) is preferably installed close to the coating roll (6) as shown in FIG. 3, at a position where it does not interfere with the flow of aluminum vapor. It is thought that if the oxygen inlet (8) is placed close to the evaporation source as in Figure 4, the aluminum will oxidize in the evaporation source, causing the evaporation rate to become unstable. If oxygen is introduced at a position away from the flow of aluminum vapor as shown in Figure 4, the probability that the oxygen will encounter aluminum atoms decreases, and the oxygen will not be used effectively. Unconsumed oxygen increases the pressure inside the vacuum evaporation chamber. When evaporation is carried out under high pressure, the density of the formed film tends to decrease.

[0032] It is presumed that as the density of aluminum oxide decreases, its ability to block gas permeation decreases. Therefore, the pressure for vapor deposition is set at 1×10, which increases the density of aluminum oxide and improves the barrier properties. -2 Pa or less is preferred.

[0033] In Figure 4, placing the oxygen inlet (8) in the aluminum vapor can increase efficiency, but this reduces the efficiency of aluminum or aluminum oxide adhering to the oxygen inlet and depositing it on the plastic film of the substrate. Also, if the deposits adhering to the oxygen inlet (8) peel off and fall into the evaporation source, this is undesirable as it changes the amount of evaporation.

[0034] When producing transparent barrier film, it is preferable to use the roll-to-roll method for deposition. After deposition, the plastic film is removed in roll form, so the aluminum oxide layer is not exposed to the atmosphere. Therefore, it is necessary to rewind the rolled plastic film once in the atmosphere to trap air between the layers of the plastic film. The rewinding conditions should preferably be such that an air layer of 0.4µm or more is trapped. Furthermore, since rewinding at high temperatures and high humidity can cause condensation to block the deposited plastic film, a temperature of 40°C or less and a relative humidity of 70RH% or less is preferable. The amount of air entrapped can be expressed by equation (3). When the thickness of the rewound plastic film is t μm, the length is 1 m, the diameter of the paper tube used is 2 r mm, and the diameter of the wound rolled plastic film is 2 R mm, the thickness of the air layer entrapped between the plastic film, tair μm, can be expressed by equation (3). tair=π(R 2 -r 2 ) / lt...Equation (3)

[0035] The rewound roll of plastic film is preferably stored at room temperature between 10°C and 40°C for at least one week until it stabilizes, as oxidation of the aluminum oxide layer will gradually progress. It is believed that raising the temperature accelerates oxidation, but raising the temperature above 40°C is not desirable as it may affect the physical properties of the film. Also, lowering the temperature below 10°C is not desirable as it slows down the oxidation.

[0036] The gas barrier properties of the transparent gas barrier film of the present invention are such that the oxygen permeation amount under an atmosphere of a temperature of 23°C and a relative humidity of 65% RH is 1.0 ml / m2 both in the untreated state and after the acid resistance evaluation described below. 2 / day(24hr) / MPa or more 100ml / m 2 / day (24hr) / MPa or less. 2 If the gas barrier strength exceeds 1.0 ml / m / day / MPa, it may be difficult to use the composition in food, pharmaceuticals, industrial products, etc., which is not desirable. The lower the gas barrier strength, the better. However, at the current technological level, the gas barrier strength of this composition is 1.0 ml / m / day / MPa. 2 / day / MPa is the lower limit, and 1.0 ml / m 2 / day / MPa is sufficient for practical use. A more preferable range is 1.0 ml / m 2 / day / MPa or more 70ml / m 2 / day / MPa or less, and particularly preferably 1.0 ml / m 2 / day / MPa or more 30ml / m 2 / day / MPa or less.

[0037] The plastic film referred to in the present invention is a film obtained by melt-extruding polyester resin recycled from PET bottles and biaxially stretching it. The biaxial stretching method is not particularly limited, and a tubular method or a simultaneous biaxial stretching method can be used. In particular, a sequential biaxial stretching method is preferred.

[0038] The lower limit of the intrinsic viscosity of the resin constituting the plastic film obtained by measuring the plastic film is preferably 0.58 dI / g, more preferably 0.60 dI / g. If it is less than 0.58 dI / g, many recycled resins made from PET bottles have an intrinsic viscosity exceeding 0.68 dI / g, and reducing the viscosity when using such resin to produce a film can result in thickness unevenness, which is not preferred. It is also not preferred because the plastic film may become discolored. The upper limit is preferably 0.70 dI / g, more preferably 0.68 dI / g. If it exceeds 0.70 dI / g, it is not preferred because it can make it difficult for the resin to be discharged from the extruder, reducing productivity.

[0039] The lower limit of the thickness of the plastic film is preferably 8 μm, more preferably 10 μm, and even more preferably 12 μm. If it is less than 8 μm, the strength of the plastic film may be insufficient, which is not preferable. The upper limit is preferably 200 μm, more preferably 50 μm, and even more preferably 30 μm. If it exceeds 200 μm, it may become too thick and difficult to process.

[0040] The lower limit of the heat shrinkage rate of a plastic film in the machine direction (sometimes referred to as MD) and the transverse direction (sometimes referred to as TD) when treated at 150°C for 30 minutes is preferably 0.1%, more preferably 0.3%. If it is less than 0.1%, the improvement effect will saturate and the film may become mechanically brittle, which is not preferable. The upper limit is preferably 1.5%, more preferably 1.2%. If it exceeds 1.5%, dimensional changes during processing such as printing may cause pitch deviation, which is not preferable. Furthermore, if it exceeds 1.5%, dimensional changes during processing such as printing may cause shrinkage in the width direction, which is not preferable.

[0041] The lower limit of the refractive index in the thickness direction of the plastic film is preferably 1.4930, more preferably 1.4940. If it is less than 1.4930, the orientation may be insufficient, and the laminate strength may not be obtained. The upper limit is preferably 1.4995, more preferably 1.4980. If it exceeds 1.4995, the surface orientation may be disrupted, and the mechanical properties may be insufficient, which is not preferable.

[0042] A 1-meter length of plastic film is measured every 5 mm at 200 points up to a thickness Tn (n = 1 to 200) (unit: μm), and the maximum thickness is Tmax, the minimum thickness is Tmin, and the average thickness is Tave. The thickness unevenness calculated by the following formula (4) is preferably 16% or less, more preferably 12% or less, and even more preferably 10% or less in each of the longitudinal and transverse directions. A thickness unevenness exceeding 16% is not desirable because it can cause misalignment when rolled into a plastic film or cause poor appearance of the peeled surface when the laminated portion is peeled, reducing the commercial value. Thickness variation = {(Tmax - Tmin) / Tave} × 100 (%) Equation (4)

[0043] When a polyolefin film is laminated to the side of a plastic film opposite the aluminum oxide layer, the lower limit of the laminate strength is preferably 4.0 N / 15 mm, more preferably 4.5 N / 15 mm, and even more preferably 5.0 N / 15 mm. If it is less than 4.0 N / 15 mm, the laminated portion may easily peel when made into a bag, which is not preferred. The upper limit is preferably 20.0 N / 15 mm, more preferably 15.0 N / 15 mm, and even more preferably 10.0 N / 15 mm. If it exceeds 20.0 N / 15 mm, the plastic film may actually be destroyed when peeled, which is not preferred.

[0044] The appearance evaluation after lamination is performed by visually inspecting the sample after delamination. For easier visual inspection, it is preferable to dye the adhesive. The evaluation is as follows: A grade of ◯ means that there is no minute loss of adhesive on the surface after delamination; a grade of △ means that minute loss accounts for 10% or less of the total delamination area; and a grade of × means that minute loss exceeds 10% of the total delamination area. A grade of △ is preferable, and a grade of ◯ is more preferable. A grade of × is undesirable because it reduces the commercial value due to poor appearance of the laminated area after delamination. Note that if the lamination strength is less than 40 N / 15 mm, the plastic film does not satisfy the basic characteristics of the present invention, and therefore is not preferable even if it is graded as ◯.

[0045] As a raw material for plastic film, it is preferable to use recycled polyester resin made from PET bottles containing an isophthalic acid component as an acid component. The crystallinity of the polyester used in PET bottles is controlled to improve the bottle appearance, and as a result, polyester containing 10 mol% or less of isophthalic acid may be used. In order to utilize recycled resin, it may be necessary to use a material containing an isophthalic acid component.

[0046] The lower limit of the amount of terephthalic acid component of all dicarboxylic acid components constituting the polyester resin contained in the plastic film is preferably 95.0 mol%, more preferably 96.0 mol%, even more preferably 96.5 mol%, and particularly preferably 97.0 mol%. A content of less than 95.0 mol% is not preferred because crystallinity decreases and the heat shrinkage rate may increase. Furthermore, the upper limit of the amount of terephthalic acid component of the polyester resin contained in the plastic film is preferably 99.5 mol%, more preferably 99.0 mol%. Since recycled polyester resins made from PET bottles often contain dicarboxylic acid components other than terephthalic acid, such as isophthalic acid, it is not preferred for the terephthalic acid component constituting the polyester resin in the plastic film to exceed 99.5 mol%, as this makes it difficult to produce polyester films with a high proportion of recycled resin.

[0047] The lower limit of the amount of isophthalic acid component relative to the total dicarboxylic acid components constituting the polyester resin contained in the plastic film is preferably 0.5 mol%, more preferably 0.7 mol%, even more preferably 0.9 mol%, and particularly preferably 1.0 mol%. Because recycled polyester resins made from PET bottles contain a large amount of isophthalic acid component, it is not desirable for the isophthalic acid component constituting the polyester resin in the film to be less than 0.5 mol%, as this makes it difficult to produce polyester films with a high proportion of recycled resin. The upper limit of the amount of isophthalic acid component relative to the total dicarboxylic acid components constituting the polyester resin contained in the plastic film is preferably 5.0 mol%, more preferably 4.0 mol%, even more preferably 3.5 mol%, and particularly preferably 3.0 mol%. A content exceeding 5.0 mol% is not desirable because it reduces crystallinity and can increase the thermal shrinkage rate. Furthermore, keeping the isophthalic acid component content within the above range facilitates the production of plastic films with excellent lamination strength, shrinkage rate, and thickness uniformity, which is preferable.

[0048] The upper limit of the intrinsic viscosity of the recycled resin from PET bottles is preferably 0.90 dI / g, more preferably 0.80 dI / g, even more preferably 0.77 dI / g, and particularly preferably 0.75 dI / g. If the intrinsic viscosity exceeds 0.90 dI / g, the resin becomes difficult to extrude from the extruder, which may reduce productivity, and is therefore not preferred.

[0049] The lower limit of the content of polyester resin recycled from PET bottles in the plastic film is preferably 50% by weight, more preferably 65% ​​by weight, and even more preferably 75% by weight. A content of less than 50% by weight results in a poor content of recycled resin, which is undesirable in terms of contributing to environmental protection. The upper limit of the content of polyester resin recycled from PET bottles is preferably 95% by weight, more preferably 90% by weight, and even more preferably 85% by weight. A content of more than 95% by weight is undesirable because it may be difficult to add sufficient lubricants or additives such as inorganic particles to improve the functionality of the plastic film. Polyester resin recycled from PET bottles can also be used as a masterbatch (high-concentration resin) when adding lubricants or additives such as inorganic particles to improve the functionality of the plastic film.

[0050] As the lubricant type, inorganic lubricants such as silica, calcium carbonate, and alumina are preferred, as well as organic lubricants, with silica and calcium carbonate being more preferred, as these can provide transparency and lubricity. The lower limit of the lubricant content in the plastic film is preferably 0.01% by weight, more preferably 0.015% by weight, and even more preferably 0.02% by weight. If it is less than 0.01% by weight, the slipperiness may decrease. The upper limit is preferably 1% by weight, more preferably 0.2% by weight, and even more preferably 0.1% by weight. If it exceeds 1% by weight, the transparency may decrease, which is not preferable.

[0051] While the method for producing the plastic film used in the laminated film of the present invention is not particularly limited, the following production method is recommended. The temperature setting for melting and extruding the resin in the extruder is important. The basic concept is (1) to suppress degradation by extruding at as low a temperature as possible since the polyester resin used in PET bottles contains an isophthalic acid component, while (2) to ensure that the intrinsic viscosity and fine highly crystalline portions are sufficiently and uniformly melted at high temperatures and pressures, the inclusion of an isophthalic acid component reduces the stereoregularity of the polyester, leading to a lower melting point. Therefore, extrusion at high temperatures can significantly reduce or degrade the melt viscosity due to heat, resulting in reduced mechanical strength and an increase in the amount of degraded foreign matter. Furthermore, simply lowering the extrusion temperature may not achieve sufficient melt-kneading, resulting in problems such as increased thickness unevenness and the presence of foreign matter such as fisheyes. Based on the above, recommended production methods include, for example, using two extruders in tandem, increasing the pressure in the filter section, and using a screw with high shear force as part of the screw configuration. The following is an example of temperature control using one extruder.

[0052] Figure 5 shows one embodiment of the inside of an extruder in a film-forming facility according to the present invention. A screw 10 having flights 11 between barrels 12 is provided with a feed section 13, a compression section 14, and a metering section 15 extending from the base to the tip of the screw. The compression section 14 is the area where the space between the screw 10 and barrel 11 narrows. In the present invention, it is preferable to set the temperatures of the feed section 13 and metering section 15 as low as possible and the compression section 14 to a high temperature, thereby achieving sufficient melt-kneading in the high-shear compression section 14 and preventing thermal degradation in the feed section 13 and metering section 15.

[0053] The lower limit of the set temperature in the resin melting section in the extruder (excluding the highest set temperature in the compression section of the screw in the extruder) is preferably 270° C., and the upper limit is preferably 290° C. If the temperature is below 270° C., extrusion is difficult, and if the temperature is above 290° C., resin deterioration may occur, which is not preferable. The lower limit of the maximum set temperature of the compression section of the screw in the extruder is preferably 295°C. Polyester resins used in PET bottles often contain high-melting-point crystals (260°C to 290°C) for transparency reasons. Furthermore, additives and crystallization nucleating agents are added, which can cause variations in the fine melting behavior of the resin material. Temperatures below 295°C are not preferred, as it becomes difficult to sufficiently melt them. The upper limit of the maximum set temperature of the compression section of the screw in the extruder is preferably 310°C. Temperatures above 310°C can cause resin degradation, which is not preferred.

[0054] The lower limit of the time for the resin to pass through the highest set temperature zone of the compression section of the screw in the extruder is preferably 10 seconds, more preferably 15 seconds. If it is less than 10 seconds, the polyester resin used in the PET bottle will not be sufficiently melted, which is not preferred. The upper limit is preferably 60 seconds, more preferably 50 seconds. If it exceeds 60 seconds, the resin is more likely to deteriorate, which is not preferred. By setting the extruder within this range, it is possible to obtain a film with little thickness unevenness, foreign matter such as fisheyes, and coloration, while using a large amount of polyester resin recycled from PET bottles.

[0055] The molten resin is extruded onto a cooling roll in the form of a sheet and then biaxially stretched. Although simultaneous biaxial stretching may be used as the stretching method, sequential biaxial stretching is particularly preferred. This method makes it easier to achieve both the productivity and the quality required for the present invention.

[0056] In the present invention, the film stretching method is not particularly limited, but the following points are important. When stretching a resin having an intrinsic viscosity of 0.64 dI / g or more and containing an isophthalic acid component, the stretching ratio and temperature in the machine direction (MD) and transverse direction (TD) are important. If the MD stretching ratio and temperature are inappropriate, the stretching force will not be applied evenly, resulting in insufficient molecular orientation, which may increase thickness unevenness and insufficient mechanical properties. Furthermore, in the subsequent TD stretching step, the film may break or experience extreme thickness unevenness. If the TD stretching ratio and temperature are inappropriate, the film may not be stretched evenly, resulting in poor balance between the machine and transverse orientations and insufficient mechanical properties. Furthermore, if the film proceeds to the subsequent heat setting step with significant thickness unevenness or insufficient molecular chain orientation, uniform relaxation will not be achieved, further increasing thickness unevenness and insufficient mechanical properties will occur. Therefore, it is basically recommended that in MD stretching, the temperature be controlled as described below to perform stretching stepwise, and in TD stretching, stretching be performed at an appropriate temperature so as not to cause an extreme deterioration in the orientation balance. Although not limited to the following embodiment, an example will be described.

[0057] As a method for stretching in the machine direction (MD), a roll stretching method or an IR heating method is preferred.

[0058] The lower limit of the MD stretching temperature is preferably 100°C, more preferably 110°C, and even more preferably 120°C. If the temperature is less than 100°C, even if a polyester resin with an intrinsic viscosity of 0.64 dI / g or more is stretched and molecularly oriented in the machine direction, breakage of the plastic film or extreme thickness defects may occur in the subsequent transverse stretching step, which is not preferred. The upper limit is preferably 140°C, more preferably 135°C, and even more preferably 130°C. If the temperature exceeds 140°C, the orientation of the molecular chains may be insufficient, resulting in insufficient mechanical properties, which is not preferred.

[0059] The lower limit of the MD stretching ratio is preferably 2.5 times, more preferably 3.5 times, and even more preferably 4 times. If it is less than 2.5 times, even if a polyester resin with an intrinsic viscosity of 0.64 dI / g or more is stretched and molecularly oriented in the machine direction, film breakage or extreme thickness defects may occur in the subsequent transverse stretching step, which is not very preferable. The upper limit is preferably 5 times, more preferably 4.8 times, and even more preferably 4.5 times. If it exceeds 5 times, the effects of improving mechanical strength and thickness unevenness may saturate, making it less meaningful.

[0060] Although the MD stretching method may be the single-stage stretching described above, it is more preferable to divide the stretching into two or more stages, which allows for good stretching of polyester resins made from recycled resins containing isophthalic acid, which have a high intrinsic viscosity, and improves thickness unevenness, laminate strength, mechanical properties, etc.

[0061] The lower limit of the first-stage MD stretching temperature is preferably 110°C, more preferably 115°C. If the temperature is lower than 110°C, the film will not be sufficiently longitudinally stretched, resulting in poor flatness, which is undesirable. The upper limit of the first-stage MD stretching temperature is preferably 125°C, more preferably 120°C. If the temperature exceeds 125°C, the molecular chain orientation will be insufficient, which may result in a decrease in mechanical properties, which is undesirable.

[0062] The lower limit of the first-stage MD stretching ratio is preferably 1.1 times, more preferably 1.3 times. By using weak stretching in the first stage at 1.1 times or more, a polyester resin having an intrinsic viscosity of 0.64 dI / g or more can be finally stretched longitudinally sufficiently, thereby increasing productivity. The upper limit of the first-stage MD stretching ratio is preferably 2 times, more preferably 1.6 times. A ratio exceeding 2 times is not preferred because the orientation of molecular chains in the longitudinal direction becomes too high, making it difficult to stretch in the second and subsequent stages or resulting in a film with poor thickness unevenness.

[0063] The lower limit of the MD stretching temperature in the preferred second stage (or final stage) is preferably 10°C, more preferably 115°C. If the temperature is 110°C or higher, polyester resins with an intrinsic viscosity of 0.64 dI / g or higher can be sufficiently stretched longitudinally, making transverse stretching possible in the next step, and thickness unevenness in the longitudinal and transverse directions can be improved. The upper limit is preferably 130°C, more preferably 125°C. If the temperature exceeds 130°C, crystallization is promoted, making transverse stretching difficult or increasing thickness unevenness, which is not preferred.

[0064] The lower limit of the preferred second-stage (or final-stage) MD stretching ratio is preferably 2.1 times, more preferably 2.5 times. If it is less than 2.1 times, even if a polyester resin with an intrinsic viscosity of 0.64 dI / g or more is stretched and molecularly oriented in the machine direction, breakage of the plastic film may occur in the subsequent transverse stretching step, or extreme thickness defects may occur, which is not preferred. The upper limit is preferably 3.5 times, more preferably 3.1 times. If it exceeds 3.5 times, the machine orientation becomes too high, making it impossible to perform stretching in the second or subsequent stages, or the plastic film may have significant thickness unevenness, which is not preferred.

[0065] The lower limit of the TD stretching temperature is preferably 110°C, more preferably 120°C, and even more preferably 125°C. If the temperature is less than 110°C, the stretching stress in the transverse direction increases, which may cause the plastic film to break or the thickness unevenness to become extremely large, and this is not preferred. The upper limit is preferably 150°C, more preferably 145°C, and even more preferably 140°C. If the temperature exceeds 150°C, the orientation of the molecular chains does not increase, which may result in a decrease in mechanical properties, and this is not preferred.

[0066] The lower limit of the transverse direction (TD) stretching ratio is preferably 3.5 times, more preferably 3.9 times. If it is less than 3.5 times, the molecular orientation may be weak and the mechanical strength may be insufficient, which is not preferable. In addition, the orientation of the molecular chains in the machine direction is high, which results in a poor balance between the machine and machine directions, resulting in large thickness variations, which is not preferable. The upper limit is preferably 5.5 times, more preferably 4.5 times. If it exceeds 5.5 times, it may break, which is not preferable.

[0067] To obtain a plastic film for use in the transparent gas barrier film of the present invention, it is desirable to appropriately set the conditions for heat setting in a tenter following TD stretching and for subsequent cooling of the plastic film to room temperature. Compared to conventional polyethylene terephthalate films that do not contain isophthalic acid, polyester films containing recycled resins from PET bottles have lower crystallinity, are more susceptible to micro-melting, and have lower mechanical strength. Therefore, if the film is suddenly exposed to high temperatures under tension after stretching or if it is suddenly cooled under tension after high-temperature heat setting, the inevitable temperature difference across the film's width can disrupt the tension balance in the width direction, resulting in thickness unevenness and poor mechanical properties. On the other hand, attempting to address this phenomenon by lowering the heat setting temperature may result in insufficient laminate strength. In the present invention, it is recommended that the film be subjected to heat setting 1 at a slightly lower temperature, heat setting 2 at a sufficiently higher temperature (or heat setting 3, if necessary), followed by a slow cooling step to cool the film to room temperature. However, this method is not limited to this, and examples thereof include a method of controlling the film tension in accordance with the hot air speed in the tenter and the temperature of each zone, a method of performing heat treatment at a relatively low temperature in an oven with a sufficient length after the end of stretching, and a method of relaxing the film with a heated roll after the end of heat setting.

[0068] As an example, a method using temperature control of a tenter will be described below.

[0069] The lower limit of the temperature for heat setting 1 is preferably 160°C, more preferably 170°C. If the temperature is less than 160°C, the final heat shrinkage rate will be large, which may cause misalignment or shrinkage during processing, and this is not preferred. The upper limit is preferably 215°C, more preferably 210°C. If the temperature exceeds 215°C, the plastic film will be suddenly exposed to high temperatures, which may cause thickness unevenness or breakage, and this is not preferred.

[0070] The lower limit of the heat setting time 1 is preferably 0.5 seconds, more preferably 2 seconds. If it is less than 0.5 seconds, the temperature of the plastic film may not rise sufficiently. The upper limit is preferably 10 seconds, more preferably 8 seconds. If it exceeds 10 seconds, productivity may decrease, which is not preferable.

[0071] The lower limit of the temperature for heat setting 2 is preferably 220°C, more preferably 227°C. Temperatures below 220°C are undesirable because the thermal shrinkage rate increases, which can lead to misalignment or shrinkage during processing. The upper limit is preferably 240°C, more preferably 237°C. Temperatures above 240°C are undesirable because the film may melt or, even if it does not melt, it may become brittle.

[0072] The lower limit of the time for heat setting 2 is preferably 0.5 seconds, more preferably 3 seconds. If it is less than 0.5 seconds, breakage may occur during heat setting, which is not preferable. The upper limit is preferably 10 seconds, more preferably 8 seconds. If it exceeds 10 seconds, sagging may occur, resulting in thickness unevenness, which is not preferable.

[0073] If necessary, the lower limit of the temperature for heat setting 3 is preferably 205°C, more preferably 220°C. If the temperature is less than 205°C, the heat shrinkage rate increases, which may cause misalignment or shrinkage during processing, and is therefore not preferred. The upper limit is preferably 240°C, more preferably 237°C. If the temperature exceeds 240°C, the film may melt, or even if it does not melt, it may become brittle, which is also not preferred.

[0074] If necessary, the lower limit of the time for heat setting 3 is preferably 0.5 seconds, more preferably 3 seconds. If it is less than 0.5 seconds, breakage may occur easily during heat setting, which is not preferable. The upper limit is preferably 10 seconds, more preferably 8 seconds. If it exceeds 10 seconds, sagging may occur, resulting in thickness unevenness, which is not preferable.

[0075] TD relaxation can be performed at any point during heat setting. The lower limit is preferably 0.5%, more preferably 3%. If it is less than 0.5%, the thermal shrinkage rate, particularly in the lateral direction, becomes large, which may lead to misalignment or shrinkage during processing, which is not preferred. The upper limit is preferably 10%, more preferably 8%. If it exceeds 10%, sagging may occur, resulting in thickness unevenness, which is not preferred.

[0076] The lower limit of the annealing temperature after TD heat setting is preferably 90°C, more preferably 100°C. If the temperature is less than 90°C, the plastic film contains isophthalic acid, and therefore, shrinkage due to a sudden temperature change may cause thickness unevenness or breakage, which is not preferred. The upper limit of the annealing temperature is preferably 150°C, more preferably 140°C. If the temperature exceeds 150°C, a sufficient cooling effect may not be obtained, which is not preferred.

[0077] The lower limit of the annealing time after heat setting is preferably 2 seconds, more preferably 4 seconds. If it is less than 2 seconds, sufficient annealing effect may not be obtained, which is not preferable. The upper limit is preferably 20 seconds, more preferably 15 seconds. If it exceeds 20 seconds, it is likely to be disadvantageous in terms of productivity, which is not preferable.

[0078] In addition to the above-mentioned plastic film and aluminum oxide layer, the transparent barrier film of the present invention may be provided with various layers that are provided in known gas barrier films, if necessary. For example, when a transparent barrier film with an inorganic thin film layer is used as a packaging material, it is preferable to form a heat-sealable resin layer called a sealant. The heat-sealable resin layer is usually formed on the inorganic thin film layer, but it can also be formed on the outside of the plastic film (the side opposite the inorganic thin film layer). The heat-sealable resin layer is usually formed by extrusion lamination or dry lamination. The thermoplastic polymer that forms the heat-sealable resin layer can be any polymer that can sufficiently exhibit sealant adhesive properties, and examples of such polymers that can be used include polyethylene resins such as HDPE, LDPE, and LLDPE, polypropylene resins, ethylene-vinyl acetate copolymers, ethylene-α-olefin random copolymers, and ionomer resins.

[0079] Furthermore, a transparent gas barrier film having an inorganic thin film layer may have at least one printed layer or other plastic film and / or paper layer laminated between or on the outside of the inorganic thin film layer or plastic film and the heat-sealable resin layer.

[0080] As the printing ink for forming the printing layer, aqueous and solvent-based resin-containing printing inks are preferably used. Examples of resins used in printing inks include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. The printing ink may contain known additives such as antistatic agents, light-blocking agents, UV absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoamers, crosslinking agents, anti-blocking agents, and antioxidants. The printing method for forming the printing layer is not particularly limited, and known printing methods such as offset printing, gravure printing, and screen printing can be used. To dry the solvent after printing, known drying methods such as hot air drying, heat roll drying, and infrared drying can be used.

[0081] On the other hand, from the viewpoint of obtaining sufficient rigidity and strength of the laminate, other plastic substrates and paper substrates are preferably used, such as paper, polyester resin, polyamide resin, and biodegradable resin. In addition, in order to obtain a laminate having excellent mechanical strength, oriented films such as biaxially oriented polyester film and biaxially oriented nylon film are preferred.

[0082] In particular, when a transparent gas barrier film having an inorganic thin film layer is used as a packaging material, it is preferable to laminate a nylon film between the inorganic thin film layer and the heat-sealable resin layer to improve mechanical properties such as pinhole resistance and puncture resistance. Here, nylon types typically used include nylon 6, nylon 66, and metaxylene adipamide. The thickness of the nylon film is typically 10 to 30 μm, preferably 15 to 25 μm. If the nylon film is thinner than 10 μm, it may lack strength, while if it exceeds 30 μm, it may be too stiff and unsuitable for processing. As the nylon film, a biaxially oriented film with a stretch ratio in both the longitudinal and transverse directions of typically 2 times or more, preferably about 2.5 to 4 times, is preferred.

[0083] The transparent barrier film of the present invention also includes an embodiment having the above-mentioned layers other than the inorganic thin film layer. [Example]

[0084] The present invention will be specifically explained below by showing examples, but the present invention is not limited to these examples. A transparent barrier film was produced using a deposition apparatus with a roll-to-roll type film transport system and an evaporation source consisting of an array of boat-type resistance heating evaporation sources (9) as shown in the schematic diagram in Figure 6. The BN composite boat has a mechanism for feeding aluminum wire. An oxygen inlet (8) is installed in the coating window (7). The coating roll (6) was set at -5°C.

[0085] The plastic film (5) of the substrate is unwound from the unwinding roll (16), and the deposition surface is treated by a planar type plasma source (17) before being guided to the coating roll (6). The plasma source (17) was set to an input power of 10 kW, and plasma was generated by flowing argon gas at 400 sccm and oxygen gas at 100 sccm.

[0086] After surface treatment of the plastic film (5) on the substrate, it is guided to the coating window position by a coating roll (6) and vapor deposition is carried out. The deposited plastic film is moved to an optical film thickness meter (18) to measure the total light transmittance, after which the film is taken up on a take-up roll (19).

[0087] The evaluation method is shown below. (1) Total light transmittance The total light transmittance during deposition was obtained by converting the values ​​of the optical film thickness meter using a sample measured with a turbidity meter (NDH5000, Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7375 so that the values ​​of the optical film thickness meter could be converted. After deposition, the sample was taken out and measured with a turbidity meter.

[0088] (2)Oxygen transmission rate (OTR) The oxygen transmission rate (OTR) was measured in accordance with JIS K7126-2 using an oxygen transmission rate measuring device (OXTRAN-2 / 20 manufactured by MOCON, USA) under the measurement conditions of a temperature of 23°C and a humidity of 65% RH.

[0089] (3) Water vapor transmission rate (WVTR) The water vapor transmission rate (WVTR) was measured in accordance with JIS K7129 Method B using a water vapor transmission rate measuring device (PERMATRAN-W3 / 31 manufactured by MOCON, USA) under the measurement conditions of a temperature of 40°C and a humidity of 90% RH.

[0090] (4) Acid resistance A laminated film was created by dry laminating the transparent barrier film with a linear low density polyethylene film (LLDEP: L4102 40 μm manufactured by Toyobo Co., Ltd.) using an adhesive made by mixing TM569 and CAT-10L manufactured by Toyo-Morton Co., Ltd. Cut two pieces of laminated film to A5 size (148mm x 210mm), overlap the L4012 side, seal three sides and create a bag. The seal width is 10mm. Dilute vinegar (Mizukan Grain Vinegar) 50% with water and fill a bag with 100ml of water. Store the bag in a room at 40°C for one week. After one week, the contents are removed, washed with water, dried, and then the oxygen permeability is measured. Acid resistance is evaluated by oxygen permeability.

[0091] (5) Content of terephthalic acid and isophthalic acid components contained in the raw polyester and the polyester constituting the film A sample solution was prepared by dissolving the raw polyester resin or polyester film in a solvent containing a 10:1 (volume ratio) mixture of chloroform D (manufactured by Eurisop) and trifluoroacetic acid D1 (manufactured by Eurisop). The sample solution was then subjected to NMR measurement of the protons in the sample solution using an NMR device (Varian GEMINI-200 nuclear magnetic resonance analyzer) at a temperature of 23°C and an accumulation count of 64. In the NMR measurement, the peak intensity of a specific proton was calculated, and the content (mol%) of terephthalic acid and isophthalic acid components in 100 mol% of the acid component was calculated.

[0092] (6) Intrinsic viscosity (IV) of the raw resin and the resin that constitutes the film The sample was dried in a vacuum at 130°C overnight, then crushed or cut, and 80 mg of the crushed sample was precisely weighed and dissolved in a mixed solution of phenol / tetrachloroethane = 60 / 40 (volume ratio) at 80°C for 30 minutes by heating. After dissolving by heating at 80°C, the sample was cooled to room temperature, and the mixed solvent prepared in the above ratio was added to a measuring flask to make 20 ml, after which the viscosity was measured at 30°C (unit: dI / g). An Ostwald viscometer was used to measure the intrinsic viscosity.

[0093] (7) Thickness of plastic film Using a PEACOCK dial gauge (manufactured by Ozaki Seisakusho), the thickness Tn (n = 1 to 200) μm was measured at 200 points every 5 mm along a 1 m length of the film in the vertical and horizontal directions, and the average value was taken as the thickness of the base film.

[0094] (8) Thermal shrinkage rate of plastic film in the longitudinal and transverse directions A 10mm wide sample was taken, and lines were marked at 200mm intervals at room temperature (27°C). The distance between the lines was measured (L0). The plastic film was then sandwiched between papers and placed in a hot air oven controlled at 150°C for 30 minutes. After that, the film was removed and the distance between the lines was measured (L). The thermal shrinkage was calculated using the following formula. Samples were taken in both the machine and cross directions. Heat shrinkage rate (%) = {(L0-L) / L0} x 100

[0095] (9) Refractive index in the thickness direction of plastic film The refractive index in the thickness direction (Nz) was determined in accordance with JIS K7142 using an Abbe refractometer NAR-1T (manufactured by Atago Co., Ltd.) with sodium D line as the light source, a test piece with a refractive index of 1.74, and methylene iodide as the intermediate liquid.

[0096] (10) Lamination strength of plastic film The plastic film thus formed and a 40 μm-thick polyethylene film ("L4102" manufactured by Toyobo Co., Ltd.) were laminated to the side of the substrate film opposite the inorganic thin film layer by dry lamination using a urethane adhesive (TM569, CAT10L manufactured by Toyo-Morton Co., Ltd., ethyl acetate in a weight ratio of 33.6:4.0:62.4), and aged at 40°C for 4 days to obtain a laminate for evaluating laminate strength. The lamination conditions were a line speed of 20 m / min, a dryer temperature of 80°C, and a coating amount of 3 g / m after drying. 2 The laminate was cut into a test piece 15 mm wide and 200 mm long, and the peel strength (N / 15 mm) was measured at the bonding surface between the surface opposite the inorganic thin film layer laminated surface of the substrate film and the polyolefin resin layer using a Toyo Baldwin "Tensilon UMT-II-500" under conditions of a temperature of 23°C and a relative humidity of 65%. The pulling speed was 20 cm / min, and the peel angle was 180°.

[0097] (11) Evaluation of appearance after delamination of plastic film The sheet after the peeling treatment in (10) was treated with neocarmine solution at 50°C for 30 minutes, and the area ratio of the part that was not dyed pink was calculated to evaluate the appearance after peeling the plastic film laminate. A rating of 〇 means that there is no loss of adhesive on the surface after peeling, a rating of △ means that the loss of adhesive is 10% or less of the total peeled area, and a rating of × means that it exceeds 10%.

[0098] (12) Uneven thickness of plastic film Using a PEACOCK dial gauge (manufactured by Ozaki Seisakusho), the thickness Tn (n = 1 to 200) (μm) was measured at 200 points every 5 mm along a 1 m length of film in the longitudinal and transverse directions, and the maximum thickness was Tmax, the minimum thickness was Tmin, and the average thickness was Tave, which was calculated using the following formula (4). Thickness variation = {(Tmax - Tmin) / Tave} × 100 (%) Equation (4)

[0099] (13) Thickness of inorganic thin film layer The thickness of the aluminum oxide layer was measured using an X-ray fluorescence spectrometer (Supermini200, manufactured by Rigaku Corporation). A calibration curve was created by determining the thickness of a sample by measuring the amount of aluminum deposited on the sample using inductively coupled plasma atomic emission spectroscopy, and then measuring the X-ray fluorescence intensity of the sample.

[0100] Example 1 Preparation of polyester resin recycled from PET bottles After washing away any remaining beverages and other foreign matter from PET beverage bottles, the resulting flakes were crushed and melted in an extruder. The flakes were filtered twice using successively smaller mesh filters to remove even finer particles, and then filtered a third time using a filter with the smallest mesh size (50 μm) to obtain recycled polyester raw material. The resulting resin had a composition of terephthalic acid / isophthalic acid / ethylene glycol = 97.0 / 3.0 / / 100 (mol%), and the resin's intrinsic viscosity was 0.70 dl / g. This was designated Polyester A.

[0101] Preparation of plastic films Polyester B was a polyethylene terephthalate resin with an intrinsic viscosity of 0.62 dl / g, composed of 100% terephthalic acid / ethylene glycol (mol%), and polyester C was a masterbatch of polyester B containing 0.3% amorphous silica with an average particle size of 1.5 μm. The raw materials were dried at 125°C for 8 hours under a reduced pressure of 33 Pa. The resulting mixture was mixed in a weight ratio of 80 / 10 / 10 polyester A / B / C and fed into a single-screw extruder. The resin temperature was set to 280°C from the extruder through the melt line, filter, and T-die. However, the resin temperature was set to 305°C for 45 seconds from the start of the extruder screw compression section, after which it was returned to 280°C.

[0102] The molten material extruded from the T-die was pressed against a cooling roll to form an unstretched sheet. This was then stretched 1.41 times in the machine direction using rolls heated to 118°C with different peripheral speeds (MD1), and further stretched 2.92 times in the machine direction using rolls heated to 128°C with different peripheral speeds (MD2). The machine-stretched sheet was introduced into a tenter, preheated to 121°C, and then stretched 4.3 times transversely at 131°C. The sheet was subsequently heat-set at 180°C for 2.5 seconds without relaxation (0%) (TS1), followed by 231°C with 5% relaxation for 3.0 seconds (TS2), followed by 222°C with no relaxation for 2.5 seconds (TS3). The sheet was then cooled at 120°C for 6.0 seconds in the same tenter, and finally wound up on a winder to obtain a 12 μm-thick biaxially oriented polyester film (plastic film).

[0103] The plastic film contains 80% polyester A recycled from PET bottles. The content of isophthalic acid components relative to all dicarboxylic acid components in all polyester resins constituting the plastic film is 2.4 mol %, and the intrinsic viscosity of the constituting resin is 0.64 dL / g. The thermal shrinkage rate of the plastic film at 150°C is 0.8% in the longitudinal direction and 0.5% in the transverse direction. The thickness variation of the plastic film in the longitudinal direction is 7.6%, and the thickness variation in the transverse direction is 6.4%. When laminated with polyethylene film, the lamination strength was 6.1 N / 15 mm, and the appearance of the peeled surface was also at the standard of ◯. The total light transmittance of the plastic film is 84%.

[0104] This plastic film was set in a vapor deposition device. First, aluminum was vapor-deposited without oxygen, aiming for a total light transmittance of 18%. After the total light transmittance stabilized, oxygen was introduced and controlled so that the total light transmittance became 64%. The amount of oxygen introduced was 12,509 sccm. The pressure in the vapor deposition chamber after oxygen introduction was 1.4 x 10 -3 The pressure was Pa. Table 1 shows the conditions of Example 1. This transparent barrier film was rewound using a slitter at a speed of 333 m / min. Based on the diameter of the rewound roll of plastic film, it was estimated that the amount of air entrapped between the plastic film was approximately 0.4 μm thick. The rewound transparent barrier film was stored in a room at 23°C for three weeks, after which the total light transmittance was measured with a turbidity meter and the absorption coefficient was calculated. The results are shown in Table 2. Table 2 also shows the OTR and WVTR measured for a laminate film in which LLDEP was bonded to a transparent barrier film. Table 2 also shows the results of an acid resistance test.

[0105] Example 2 A sample was prepared in the same manner as in Example 1, except that the polyesters A, B, and C were mixed in a weight ratio of 60 / 30 / 10. The evaluation results of Example 2 are shown in Table 2. The content of isophthalic acid components relative to all dicarboxylic acid components in all polyester resins constituting the plastic film was 1.8 mol %. The intrinsic viscosity of the constituent resins was 0.63 dL / g. The thermal shrinkage rate of the plastic film at 150°C is 0.9% in the longitudinal direction and 0.5% in the transverse direction. The thickness variation of the plastic film in the longitudinal direction is 7.9%, and the thickness variation in the transverse direction is 6.4%. When laminated with polyethylene film, the lamination strength was 6.2 N / 15 mm, and the appearance of the peeled surface was also at the standard of ◯. The total light transmittance of the plastic film is 83%.

[0106] Example 3 In Example 1, a sample was prepared in the same manner as in Example 1, except that vapor deposition was carried out under the conditions shown in Table 1. The evaluation results of Example 2 are shown in Table 2. The content of isophthalic acid components relative to all dicarboxylic acid components in all polyester resins constituting the plastic film was 2.4 mol %. The intrinsic viscosity of the constituent resin was 0.64 dL / g. The thermal shrinkage rate of the plastic film at 150°C is 0.8% in the longitudinal direction and 0.5% in the transverse direction. The thickness variation of the plastic film in the longitudinal direction is 7.6%, and the thickness variation in the transverse direction is 6.4%. When laminated with polyethylene film, the lamination strength was 6.1 N / 15 mm, and the appearance of the peeled surface was also at the standard of ◯. The total light transmittance of the plastic film is 84%.

[0107] Comparative Example 1 Samples were prepared in the same manner as in Example 1, except that deposition was carried out under the conditions shown in Table 1. The evaluation results of the sample of Comparative Example 1 are shown in Table 2. The content of isophthalic acid components relative to all dicarboxylic acid components in all polyester resins constituting the plastic film was 2.4 mol %. The intrinsic viscosity of the constituent resin was 0.64 dL / g. The thermal shrinkage rate of the plastic film at 150°C is 0.8% in the longitudinal direction and 0.5% in the transverse direction. The thickness variation of the plastic film in the longitudinal direction is 7.6%, and the thickness variation in the transverse direction is 6.4%. When laminated with polyethylene film, the lamination strength was 6.1 N / 15 mm, and the appearance of the peeled surface was also at the standard of ◯. The total light transmittance of the plastic film is 84%.

[0108] [Table 1]

[0109] [Table 2] In contrast to Examples 1 to 3, in Comparative Example 1, the absorption coefficient immediately after deposition was higher than 0.03 nm −1 , and therefore the OTR value after the acid resistance test was high, and the barrier properties were impaired. [Industrial Applicability]

[0110] The present invention provides a transparent barrier film that is environmentally friendly by reusing PET bottles, has an aluminum oxide layer as a barrier layer that can be produced at low cost, has excellent acid resistance, and can be used to package a wide range of contents. [Explanation of symbols]

[0111] 1: Transmittance wavelength characteristics of the substrate plastic film (12µm thick PET film) 2: Transmittance wavelength characteristics of transparent gas barrier film laminated with aluminum oxide layer 3: Spectral power wavelength characteristics of D65 light source 4: y color matching function 5: Plastic film 6: Coating roll 7: Coating window 8: Oxygen inlet 9: Evaporation source (resistance heating boat) 10: Screw 11: Flight 12: Barrel 13: Supply section 14: Compression section 15:Measuring part 16: Unwinding roll 17: Plasma source 18: Optical film thickness gauge 19: Winding roll

Claims

1. A transparent gas barrier film having an aluminum oxide layer containing aluminum oxide as a main component on at least one side of a base polyester film, wherein the absorption coefficient of the aluminum oxide layer immediately after deposition is 0.03 nm －１ a transparent gas barrier film characterized in that the thickness of the vapor-deposited film is 6 nm or more and 10 nm or less, the base polyester film is a biaxially stretched polyester film containing 50 wt % or more of a polyester resin recycled from PET bottles and containing 10 mol % or less of an isophthalic acid component, and the transparent gas barrier film satisfies the following requirements: (1) The content of isophthalic acid components relative to the total dicarboxylic acid components in the total polyester resin constituting the base polyester film is 0.5 mol % or more and 5.0 mol % or less. (2) The intrinsic viscosity of the resin constituting the base polyester film is 0.58 dI / g or more and 0.70 dI / g or less. (3) The heat shrinkage rate of the base polyester film at 150°C in the longitudinal and transverse directions is 0.1% or more and 1.5% or less. (4) When a polyolefin film is laminated on the side of the base polyester film opposite to the aluminum oxide layer, the lamination strength is 4.0 N / 15 mm or more and 20.0 N / 15 mm or less. (5) Measure the thickness Tn (n = 1 to 200) (unit: μm) at 200 points every 5 mm along 1 m of film in both the longitudinal and transverse directions. The maximum thickness is Tmax, the minimum thickness is Tmin, and the average thickness is Tave. The thickness variation calculated by the following formula is 16% or less in both the longitudinal and transverse directions. Thickness variation = {(Tmax-Tmin) / Tave} x 100 (%)

2. The absorption coefficient immediately after deposition is 0.02 nm －１ The transparent gas barrier film according to claim 1, characterized in that

3. The final absorption coefficient is 0.002 nm -1 3. The transparent gas barrier film according to claim 1, wherein:

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