Transparent gas barrier film

Abstract

The objective of this invention is to provide an inexpensive, highly acid-resistant transparent barrier film made using a plastic film created from recycled PET bottle resin, in consideration of the environment. [Solution] In a transparent gas barrier film having an aluminum oxide layer mainly composed of aluminum oxide on at least one side of a polyethylene terephthalate base film, 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 film is less than 6 nm and has a vapor deposition film thickness of 6 nm or more and 10 nm or less, the base polyethylene terephthalate film contains 50% by weight or more of polyethylene terephthalate resin recycled from PET bottles, and is a polyethylene terephthalate film that is biaxially oriented, and the isophthalic acid content, intrinsic viscosity, heat shrinkage rate, laminate strength, and thickness uniformity are within a predetermined range.

Description

[Technical Field]

[0001] This invention relates to a packaging material for food, pharmaceuticals, electronic components, and other items requiring airtightness, which offers excellent transparency, gas barrier properties, printability, and flexibility. More specifically, it relates to a transparent barrier film with excellent gas-blocking properties, comprising a layer of aluminum oxide laminated onto a plastic film made from polyester resin recycled from PET bottles. [Background technology]

[0002] In recent years, with increasing concern for environmental issues and waste management, there has been a growing call for reducing the use of disposable plastic containers and other waste. Furthermore, there is also growing emphasis on reducing waste caused by expired food products.

[0003] For this reason, there has been a desire to reduce, reuse, and recycle plastic products. Various technologies have been implemented, but one of them is the recycling of PET bottles, which are used in large quantities, and reuse them as packaging film.

[0004] A technology has been disclosed for a film that uses recycled polyester resin from PET bottles, exhibiting good dimensional stability during heating, uniform thickness, and improved adhesion strength to other films. (See, for example, Patent Document 1.)

[0005] Furthermore, a technique is known for using packaging materials with gas barrier properties (low oxygen permeability, low water vapor permeability) to extend the shelf life of food products and prevent deterioration of the contents. In flexible packaging materials, a technique for transparent barrier films, in which a metal oxide layer is laminated on a plastic film, is known. (See, for example, Patent Document 2.) From a transparency standpoint, silicon dioxide and aluminum oxide are frequently used as metal oxides. The metal oxide layer is mainly laminated onto a plastic film using vapor deposition or CVD (Chemical Vapor Deposition) methods. Among these, laminated films using an aluminum oxide layer as a barrier layer, created by reactive vapor deposition methods that involve evaporating aluminum and introducing oxygen, have become mainstream (see, for example, Patent Document 3).

[0006] Furthermore, there are transparent barrier films made by laminating a metal oxide layer onto a recycled plastic film base. (See, for example, Patent Document 4.)

[0007] In the transparent barrier film with an aluminum oxide layer created by reactive vapor deposition used in Patent Document 3, the vapor deposition material is inexpensive aluminum, and since aluminum has a low evaporation temperature, it can be manufactured using relatively inexpensive equipment with induction heating or resistance heating type vapor deposition sources. For this reason, it can be provided as a packaging material at a lower cost compared to transparent barrier films that use 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 decrease and the contents deteriorate. Therefore, although the deposition material is expensive, measures have been taken to address this by using a silicon oxide barrier layer, or by using a layer made of a mixture of silicon oxide and aluminum oxide, which is produced using expensive deposition equipment that uses an electron beam deposition source. [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 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The present invention has been made against the background of such problems of the prior art. That is, an object of the present invention is to provide a transparent barrier film that is excellent in acid resistance, inexpensive, and takes environmental problems into consideration.

Means for Solving the Problems

[0010] As a result of intensive studies by the present inventors, it has been found that the above problems can be solved by the means shown below, and the present invention has been reached. That is, the present invention has the following configuration. In a transparent gas barrier film having an aluminum oxide layer mainly composed of aluminum oxide on at least one side of a base polyester film, the absorption coefficient immediately after deposition of the aluminum oxide layer is 0.03 nm -1 less than, and the deposition film thickness is 6 nm or more and 10 nm or less, and the base polyester film is a polyester film that contains 50% by weight or more of a polyester resin recycled from a PET bottle and is biaxially stretched, and satisfies the following requirements. It is a transparent gas barrier film characterized by that. (1) The content rate of the isophthalic acid component with respect to all dicarboxylic acid components in all polyester resins 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 150°C heat shrinkage rate in the longitudinal and transverse directions of the base polyester film is 0.1% or more and 1.5% or less (4) When a polyolefin film is laminated on the opposite side of the aluminum oxide layer lamination surface 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) When measuring 200 points of each thickness Tn (n = l to 200) (unit: μm) measured every 5 mm for 1 m lengths of the film in the longitudinal and transverse directions, and setting the maximum thickness at this time as Tmax, the minimum thickness as Tmin, and the average thickness as Tave, the thickness unevenness obtained by the following formula is 16% or less in each of the longitudinal and transverse directions Thickness unevenness = {(Tmax - Tmin) / Tave} × 100 (%)

[0011] Also, the absorption coefficient immediately after vapor deposition is 0.02 nm -1 or more, and it is a transparent gas barrier film characterized by the above.

[0012] Also, the absorption coefficient is finally 0.002 nm -1 or less, and it is a transparent gas barrier film characterized by the above.

Effect of the Invention

[0013] According to the present invention, it is possible to provide a transparent gas barrier film that takes environmental problems into consideration, is inexpensive, has excellent transparency, can maintain the barrier property even when packaging acidic contents, and enables long-term storage of the contents.

Brief Description of the Drawings

[0014] [Figure 1] Transmittance wavelength characteristics of the plastic film and the transparent gas barrier film of the substrate measured with a spectrophotometer [Figure 2] Transmittance wavelength characteristics of the plastic film of the substrate, equal-energy function of the D65 light source and the CIE colorimetric standard observer [Figure 3] Vapor deposition schematic diagram [Figure 4] Vapor deposition schematic diagram [Figure 5] Schematic diagram showing a state inside the extruder of the film-forming equipment [Figure 6] Vapor deposition apparatus schematic diagram

Embodiment for Carrying Out the Invention

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

[0016] In this invention, an aluminum oxide layer primarily composed of aluminum oxide refers to a layer that substantially contains 99% or more aluminum oxide, with other components present as impurities. Furthermore, aluminum oxide includes not only stoichiometrically complete oxides but also aluminum oxide that is deficient in oxygen.

[0017] In this invention, the absorption coefficient α can be expressed by Equation 1, where the total light transmittance of the aluminum oxide layer is Tal % and the 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 equation (2), where T0% is the total light transmittance of the transparent gas barrier film having the aluminum oxide layer, and Tb% is the total light transmittance of the plastic film substrate on which the aluminum oxide layer is laminated. Tal=T0 / Tb×100...Equation (2)

[0018] The thickness of the aluminum oxide layer in this invention is determined by the density of the aluminum oxide thin film being the bulk density (3.97 g / cm³). 3 ) 0.74 times (2.94 g / cm³) 3 This value was determined using an X-ray fluorescence spectrometer. 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 samples with known film thicknesses using the X-ray fluorescence spectrometer, determine the amount of X-ray fluorescence emitted from the samples, and create a calibration curve between film thickness and X-ray fluorescence intensity.

[0019] For creating the X-ray fluorescence calibration curve, samples are used in which the amount of aluminum deposited per unit area is identified by inductively coupled plasma emission spectroscopy, and the film thickness is measured by converting it to film thickness based on the density of the aluminum oxide thin film.

[0020] In this invention, total light transmittance refers to total light transmittance in accordance with JIS K 7375. Furthermore, the value obtained by measuring the amount of light emitted from one side of the object to be measured using an optical film thickness meter installed in the deposition apparatus to measure film thickness, using a light source such as a fluorescent lamp, xenon lamp, or white LED, is also treated as total light transmittance by first measuring a sample whose total light transmittance has been measured in accordance with JIS K 7375 using an optical film thickness meter and then correlating the results.

[0021] Figure 1 shows a graph of the light transmittance of the plastic film on the substrate and the transparent barrier film measured with a spectrophotometer. The transparent barrier film has a light transmittance of 2 compared to the plastic film on the substrate (light transmittance of 1), and since it monotonically absorbs light at all wavelengths, the value obtained from the optical film thickness meter can also be treated as the total light transmittance, considering the wavelength range of the D65 light source specified as the light source in JIS K 7375 and the CIE colorimetric standard observer's transparency function. Figure 2 shows the wavelength range.

[0022] The transparent gas barrier film of the present invention is a plastic film having an aluminum oxide layer mainly composed of aluminum oxide on at least one side of the plastic film, wherein the absorption coefficient of the aluminum oxide layer immediately after deposition is 0.03 nm -1 It is less than. The present invention relates to a method for manufacturing a transparent gas barrier film, in which a transparent gas barrier film is manufactured from a plastic film having an aluminum oxide layer mainly composed of aluminum oxide on at least one side of the plastic film, wherein the absorption coefficient of the aluminum oxide layer immediately after deposition is 0.03 nm -1 The process includes a step of forming an aluminum oxide layer to adjust the level to less than [amount missing]. In this invention, "immediately after deposition" refers to the point in time when the optical thickness is measured for film thickness control or the like, immediately after the aluminum oxide layer has been deposited onto the plastic film in a vacuum chamber. When the deposited aluminum oxide layer comes into contact with oxygen, further oxidation occurs, changing its total light transmittance. After the vapor deposition is completed, if the plastic film vapor-deposited from the vapor deposition apparatus is taken out and the total light transmittance is measured immediately, it will coincide with the time point when the optical thickness is measured.

[0023] If the absorption coefficient immediately after vapor deposition is 0.03 nm -1 or more, even if it is exposed to the atmosphere to promote oxidation, when a bag is made using this transparent barrier film and an acidic substance is packaged, the barrier property will deteriorate. That is, it becomes a barrier film with poor acid resistance. The absorption coefficient immediately after vapor deposition is preferably less than 0.03 nm. -1 Less than is preferable. It is unclear whether the acid molecules have a structure that makes them likely to approach the metal atoms. Or whether the metal oxide atoms are in a state where they easily react with the acid, but deterioration due to the acid occurs. In addition, the acid resistance referred to in the present invention means that when a highly acidic content is put into a package using a transparent barrier film, the aluminum oxide layer, which is the barrier layer, does not lose its barrier property due to chemical changes caused by the acid.

[0024] The absorption coefficient immediately after vapor deposition is 0.02 nm -1 or more is preferable. In the method for producing the transparent gas barrier film of the present invention, the absorption coefficient immediately after vapor deposition is preferably adjusted to 0.02 nm or more. -1 If it is less than 0.02 nm, the degree of oxidation of aluminum oxide is high and the transparency increases, but the water vapor transmission rate decreases, which is not preferable as a barrier film. -1 It is presumed that the density of the aluminum oxide layer decreases by reacting a lot with oxygen during vapor deposition, but it is not certain.

[0025] When the absorption coefficient referred to in the present invention is finally 0.002 nm -1 or less, it means that a transparent barrier film in which an aluminum oxide layer is laminated on a plastic film of a substrate by vapor deposition is taken out of the vacuum chamber, the aluminum oxide layer is exposed to the atmosphere, and after being stored at room temperature of at least 10°C to 40°C for one week or more, the absorption coefficient is determined to be 0.002 nm or less. -1 -1 or less.

[0026] The transparent gas barrier film of the present invention has an inorganic oxide deposition layer thickness of 6 nm to 10 nm. Furthermore, the method for manufacturing the transparent gas barrier film of the present invention includes an aluminum oxide layer formation step in which the thickness of the aluminum oxide layer is adjusted to 6 nm to 10 nm. The final absorption coefficient is 0.002 nm. -1 If the thickness exceeds 10 nm, even if the film thickness is 10 nm or less, the light absorption of the thin film will exceed 1%, causing discoloration problems. While it is possible to reduce discoloration by thinning the film thickness, barrier properties become an issue at 5 nm.

[0027] The absorption coefficient immediately after deposition is 0.03 nm for a film thickness of 10 nm or less. -1 The reactive vapor deposition method is suitable for creating a transparent barrier film having an aluminum oxide layer as described below. Reactive vapor deposition is a method in which metallic aluminum is heated to evaporate, and then oxygen is introduced into the deposition tank to react the metallic aluminum with aluminum oxide, thereby depositing it onto a plastic film substrate. Methods for heating and evaporating the metallic aluminum include resistance heating, induction heating, and electron beam heating.

[0028] One method for controlling film thickness involves measuring the aluminum oxide layer deposited on the plastic film using a film thickness gauge that utilizes fluorescent X-rays, comparing it to the target film thickness, and adjusting the heating accordingly. In this case, the absorption coefficient is set to 0.03 nm. -1 To achieve the following, a photometer is installed that measures the light transmitted through the other end of a plastic film when light is shone from one end, and the amount of oxygen introduced is controlled based on the total transmitted light dose.

[0029] Alternatively, metallic aluminum is first deposited onto a plastic film substrate. An optical film thickness meter is used to control the thickness of the deposited metallic aluminum by irradiating the plastic film with light from one side and measuring the light transmitted from the other side, converting it into film thickness. After that, oxygen is introduced to deposit aluminum oxide. In this method, 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 so that the target total light transmittance is achieved. The latter manufacturing method is preferred because the equipment is simpler.

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

[0031] Figures 3 and 4 show schematic diagrams of the vapor deposition apparatus. Aluminum evaporated from the vapor deposition source (9) accumulates on the plastic film substrate (5) on the coating roll (6). A coating window (7) is installed near the coating roll (6) to limit the angle of incidence of aluminum vapor to 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 Figure 3, in a position that does not obstruct the flow of aluminum vapor. As shown in Figure 4, if the oxygen inlet (8) is brought close to the evaporation source, it is thought that the aluminum will oxidize at the evaporation source, making the evaporation rate unstable. As shown in Figure 4, if oxygen is introduced at a position far from the flow of aluminum vapor, the probability of oxygen encountering aluminum atoms decreases, and the oxygen is not used effectively. Unconsumed oxygen increases the pressure inside the vacuum deposition chamber. When deposition is performed 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, considering that the pressure for deposition increases the density of aluminum oxide and improves barrier properties, we set it to 1 × 10⁻⁶. -2 Pa or less is preferable.

[0033] In Figure 4, placing the oxygen inlet (8) into the aluminum vapor can increase efficiency, but this reduces the efficiency of depositing aluminum or aluminum oxide onto the plastic film of the substrate due to adhesion of aluminum or aluminum oxide to the oxygen inlet. Furthermore, it is undesirable for the deposits attached to the oxygen inlet (8) to detach and fall into the evaporation source, which alters the evaporation rate.

[0034] In the production of transparent barrier films, it is preferable to use a roll-to-roll deposition method. Since the plastic film is removed in roll form after deposition, the aluminum oxide layer is not exposed to the atmosphere. Therefore, it is necessary to rewind the roll of plastic film in the atmosphere to enclose air between the layers of the plastic film. When rewinding, it is preferable to enclose an air layer of 0.4 μm or more. Furthermore, if rewinding is done at high temperature and high humidity, there is a risk that the deposited plastic film may block due to condensation, so it is preferable to rewind at 40°C or below and a relative humidity of 70 RH or below. 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, and the diameter of the paper tube used is 2 r mm, and the diameter of the wound roll of plastic film is 2 R mm, the thickness of the layer of air trapped between the plastic films, tair μm, can be expressed by equation (3). tair = π(R 2 -r 2 ) / lt...Equation (3)

[0035] Since the rolled-up plastic film undergoes gradual oxidation of the aluminum oxide layer, it is preferable to store it until it stabilizes. Storage at room temperature between 10°C and 40°C for at least one week is necessary. While it is presumed that oxidation is accelerated by increasing the temperature, raising it above 40°C is undesirable as it may affect the physical properties of the film. Conversely, lowering the temperature below 10°C is also undesirable as it slows down oxidation.

[0036] The gas barrier properties of the transparent gas barrier film of the present invention are such that the oxygen permeability under an atmosphere of 23°C and 65% RH is 1.0 ml / m², both in the untreated and acid-resistant evaluations described below. 2 / day(24hr) / MPa or more 100ml / m 2 It is preferable that the gas barrier strength is 100 ml / m² or less. 2 Gas barrier properties exceeding / day / MPa may make use in food, pharmaceuticals, and industrial products difficult, and are therefore undesirable. While lower gas barrier properties are generally better, the current technological level for this configuration provides a barrier property of 1.0 ml / m³. 2 The lower limit is / day / MPa, and 1.0 ml / m 2 Even at / day / MPa, it is practically sufficient. A more preferable range is 1.0 ml / m 2 / day / MPa or more 70ml / m 2 The pressure is less than or equal to / day / MPa, and is particularly preferably 1.0 ml / m 2 / day / MPa or more 30ml / m 2 It is within the range of / day / MPa or less.

[0037] The plastic film referred to in this invention is made by melt-extruding polyester resin recycled from PET bottles and then forming a film using a biaxial stretching method. The biaxial stretching method is not particularly limited, and methods such as the tubular stretching method and the simultaneous biaxial stretching method can be used. The sequential biaxial stretching method is particularly 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, and 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 when using them to make a film, reducing the viscosity can result in uneven thickness, which is undesirable. Also, the plastic film may become discolored, which is undesirable. The upper limit is preferably 0.70 dI / g, and more preferably 0.68 dI / g. If it exceeds 0.70 dI / g, the resin may become difficult to extrude from the extruder, which can reduce productivity, and is therefore undesirable.

[0039] The lower limit of the plastic film thickness is preferably 8 μm, more preferably 10 μm, and even more preferably 12 μm. A thickness of less than 8 μm is undesirable because it may result in insufficient strength as a plastic film. The upper limit is preferably 200 μm, more preferably 50 μm, and even more preferably 30 μm. A thickness exceeding 200 μm may make it too thick and difficult to process.

[0040] The lower limit of the thermal shrinkage rate of the plastic film after treatment at 150°C for 30 minutes in the longitudinal (sometimes referred to as MD) and transverse (sometimes referred to as TD) directions is preferably 0.1%, and more preferably 0.3%. A value less than 0.1% is undesirable because the improvement effect saturates and the film may become mechanically brittle. The upper limit is preferably 1.5%, and more preferably 1.2%. A value exceeding 1.5% is undesirable because dimensional changes during processing such as printing may cause pitch misalignment. Furthermore, a value exceeding 1.5% is undesirable because dimensional changes during processing such as printing may cause shrinkage in the width direction.

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

[0042] The thickness variation calculated using the following formula (4), where 200 measurements are taken at 5mm intervals along a 1m length of plastic film in both the longitudinal and transverse directions up to each thickness Tn (n=l~200) (unit: μm), and the maximum thickness at this time is Tmax, the minimum thickness is Tmin, and the average thickness is Tave, is preferably 16% or less, more preferably 12% or less, and even more preferably 10% or less in both the longitudinal and transverse directions. A variation exceeding 16% is undesirable because it can cause winding misalignment when the plastic film is rolled, or result in a poor appearance of the peeled surface when the laminated portion is peeled off, which can reduce the product's value. Thickness unevenness = {(Tmax-Tmin) / Tave} × 100(%) ... Equation (4)

[0043] When a polyolefin film is laminated to the side of a plastic film opposite to the aluminum oxide layer, the lower limit of the lamination strength is preferably 4.0 N / 15 mm, more preferably 4.5 N / 15 mm, and even more preferably 5.0 N / 15 mm. A strength of less than 4.0 N / 15 mm is undesirable because the laminated portion may easily peel off when the film is made into a bag. 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. A strength exceeding 20.0 N / 15 mm is undesirable because the plastic film may be substantially destroyed upon peeling.

[0044] The appearance evaluation after lamination is performed by visually inspecting the sample after peeling off the laminate. It is preferable to stain the adhesive to facilitate visual inspection. The evaluation is as follows: ○ level means there are no minute gaps in the adhesive on the peeled surface, △ level means that minute gaps cover 10% or less of the total peeled area, and × level means that minute gaps cover more than 10% of the total peeled area. Preferably it is △, and more preferably it is ○. × is undesirable because the appearance of the laminated part after peeling is poor and the commercial value is reduced. Note that if the lamination strength is less than 40N / 15mm, the basic characteristics of the present invention are not met, and therefore even if it is at the ○ level, it is an undesirable plastic film.

[0045] It is preferable to use recycled polyester resin made from PET bottles containing isophthalic acid as an acid component as a raw material for plastic film. The polyester used in PET bottles undergoes crystallinity control to improve the bottle's 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 materials containing isophthalic acid.

[0046] The lower limit of the amount of terephthalic acid component in the total 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%. If it is less than 95.0 mol%, the crystallinity decreases, which may lead to a higher thermal shrinkage rate, and is therefore undesirable. Furthermore, the upper limit of the amount of terephthalic acid component in the polyester resin contained in the plastic film is preferably 99.5 mol%, and more preferably 99.0 mol%. Since recycled polyester resin made from PET bottles often contains dicarboxylic acid components other than terephthalic acid, such as isophthalic acid, if the terephthalic acid component constituting the polyester resin in the plastic film exceeds 99.5 mol%, it becomes difficult to manufacture polyester films with a high proportion of recycled resin, and is therefore undesirable.

[0047] The lower limit of the amount of isophthalic acid component in 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%. Since recycled polyester resin made from PET bottles sometimes contains a large amount of isophthalic acid, having less than 0.5 mol% of isophthalic acid component in the polyester resin constituting the film is undesirable because it makes it difficult to manufacture polyester films with a high proportion of recycled resin. The upper limit of the amount of isophthalic acid component in 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%. If it exceeds 5.0 mol%, the crystallinity decreases, which may lead to a higher thermal shrinkage rate, and is therefore undesirable. Furthermore, setting the isophthalic acid component content within the above range makes it easier to create plastic films with excellent lamination strength, shrinkage rate, and thickness uniformity, which is preferable.

[0048] The upper limit of the intrinsic viscosity of recycled resin made 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 it exceeds 0.90 dI / g, the resin may become difficult to extrude from the extruder, which can reduce productivity and is therefore undesirable.

[0049] The lower limit of the content of recycled polyester resin from PET bottles in a plastic film is preferably 50% by weight, more preferably 65% ​​by weight, and even more preferably 75% by weight. If the content is less than 50% by weight, the utilization of recycled resin is insufficient and not very desirable in terms of contribution to environmental protection. The upper limit of the content of recycled polyester resin from PET bottles is preferably 95% by weight, more preferably 90% by weight, and even more preferably 85% by weight. If it exceeds 95% by weight, it may not be possible to sufficiently add lubricants and additives such as inorganic particles to improve the functionality of the plastic film, which is not very desirable. In addition, recycled polyester resin from PET bottles can also be used as a masterbatch (high-concentration content resin) when adding lubricants and additives such as inorganic particles to improve the functionality of the plastic film.

[0050] As for lubricants, inorganic lubricants such as silica, calcium carbonate, and alumina are preferred, as are organic lubricants, with silica and calcium carbonate being more preferred. These can be used to achieve 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 lubricity 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 undesirable.

[0051] The method for manufacturing the plastic film used in the laminated film of the present invention is not particularly limited, but the following manufacturing method is recommended, for example. The temperature setting for melting and extruding the resin in the extruder is important. The basic idea is that (1) since the polyester resin used in PET bottles contains isophthalic acid components, degradation is suppressed by extruding at the lowest possible temperature, and (2) there are parts that are melted at high temperature and high pressure in order to sufficiently and uniformly melt the intrinsic viscosity and fine highly crystalline parts. The inclusion of isophthalic acid components reduces the stereoregularity of polyester, leading to a decrease in the melting point. Therefore, extrusion at high temperatures results in a significant decrease in melt viscosity due to heat and degradation, leading to a decrease in mechanical strength and an increase in degraded foreign matter. Furthermore, simply lowering the extrusion temperature may not allow for sufficient melting and mixing, which can lead to problems such as increased thickness unevenness and foreign matter such as fish eyes. For the reasons above, recommended manufacturing methods include, for example, using two extruders in tandem, increasing the pressure in the filter section, and using a screw with strong shear force in part of the screw configuration. The following is an example of using a single extruder and controlling the temperature.

[0052] Figure 5 shows one aspect of the interior of the extruder in the film-forming equipment of the present invention. In the screw 10 having flights 11 between barrels 12, there is a supply section 13, a compression section 14, and a metering section 15 from the base to the tip of the screw. The compression section 14 is a region where the space between the screw 10 and the barrels 11 narrows. In the present invention, it is preferable to set the temperature of the supply section 13 and the metering section 15 as low as possible and the temperature of the compression section 14 high, so that sufficient melting and kneading occurs in the high-shear compression section 14, and thermal degradation is prevented in the supply section 13 and the metering section 15.

[0053] The lower limit of the set temperature for the resin melting section in the extruder (excluding the maximum set temperature for the compression section of the screw in the extruder) is preferably 270°C, and the upper limit is preferably 290°C. Below 270°C, extrusion is difficult, and above 290°C, resin degradation may occur, which is undesirable. The lower limit of the maximum set temperature in the compression section of the screw inside the extruder is preferably 295°C. Polyester resin used in PET bottles often contains high-melting-point crystals (260°C to 290°C) for transparency reasons. In addition, additives and crystallization nucleating agents are added, resulting in variations in the fine melting behavior within the resin material. Below 295°C, it becomes difficult to sufficiently melt these crystals, which is undesirable. The upper limit of the maximum set temperature in the compression section of the screw inside the extruder is preferably 310°C. Above 310°C, resin degradation may occur, which is undesirable.

[0054] The lower limit of the time the resin passes through the region of the highest set temperature in 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 for PET bottles cannot be sufficiently melted, which is undesirable. The upper limit is preferably 60 seconds, more preferably 50 seconds. If it exceeds 60 seconds, resin degradation is likely to occur, which is undesirable. By setting the extruder within this range, it is possible to obtain a film with less thickness unevenness, foreign matter such as fisheyes, and discoloration, while using a large amount of polyester resin recycled from PET bottles.

[0055] The resin, thus molten, is extruded into a sheet on a cooling roll and then biaxially stretched. While simultaneous biaxial stretching is acceptable, sequential biaxial stretching is particularly preferred. These methods facilitate achieving both productivity and the quality required for this invention.

[0056] In this invention, the method of stretching the film is not particularly limited, but the following points are important. When stretching a resin containing isophthalic acid with an intrinsic viscosity of 0.64 dI / g or higher, the ratios of stretching in the longitudinal (MD) direction and transverse (TD) direction, as well as the temperature, are important. If the MD stretching ratio or temperature is not appropriate, the stretching force will not be applied uniformly, the molecular orientation will be insufficient, and the thickness may become uneven or the mechanical properties may be insufficient. In addition, the film may break or the thickness may become extremely uneven in the subsequent TD stretching step. If the TD stretching ratio or temperature is not appropriate, the film will not be stretched uniformly, the balance of longitudinal and transverse orientation will be poor, and the mechanical properties may be insufficient. Furthermore, if the film proceeds to the next heat-setting step with large thickness variations or insufficient molecular chain orientation, uniform relaxation will not be possible, leading to problems such as further increases in thickness variations and insufficient mechanical properties. Therefore, it is generally recommended that MD stretching is performed in stages with the temperature control described below, and TD stretching is performed at an appropriate temperature to prevent the orientation balance from becoming extremely poor. The following examples illustrate the principle, although it is not limited to these embodiments.

[0057] For longitudinal (MD) stretching methods, roll stretching and IR heating methods are preferred.

[0058] The lower limit of the MD stretching temperature is preferably 100°C, more preferably 110°C, and even more preferably 120°C. Below 100°C, even if a polyester resin with an intrinsic viscosity of 0.64 dI / g or higher is stretched and the molecules are oriented in the longitudinal direction, the plastic film may break during the subsequent transverse stretching step, or extreme thickness defects may occur, which is undesirable. The upper limit is preferably 140°C, more preferably 135°C, and even more preferably 130°C. Above 140°C, the orientation of the molecular chains may become insufficient, resulting in insufficient mechanical properties, which is not very desirable.

[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 higher is stretched and molecular orientation is performed in the longitudinal direction, film breakage may occur in the next transverse stretching step, or extreme thickness defects may occur, which is not very desirable. 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 effect of improving mechanical strength and thickness uniformity may saturate, and it will not be very meaningful.

[0060] While the above single-stage stretching method is acceptable for MD stretching, it is more preferable to divide the stretching into two or more stages. Dividing the stretching into two or more stages makes it possible to effectively stretch polyester resin made from recycled resin containing isophthalic acid, which has high intrinsic viscosity, resulting in better thickness uniformity, laminate strength, and mechanical properties.

[0061] The preferred lower limit for the first-stage MD stretching temperature is 110°C, and more preferably 115°C. Below 110°C, there is insufficient heat, preventing sufficient longitudinal stretching and resulting in poor planarity, which is undesirable. The preferred upper limit for the first-stage MD stretching temperature is 125°C, and more preferably 120°C. Above 125°C, the orientation of the molecular chains becomes insufficient, which may lead to a decrease in mechanical properties, and is therefore undesirable.

[0062] The preferred lower limit for the first-stage MD stretching ratio is 1.1x, and more preferably 1.3x. A ratio of 1.1x or higher allows for sufficient longitudinal stretching of the polyester resin with an intrinsic viscosity of 0.64 dI / g or higher in the first stage, thereby increasing productivity. The preferred upper limit for the first-stage MD stretching ratio is 2x, and more preferably 1.6x. A ratio exceeding 2x is undesirable because the orientation of the molecular chains in the longitudinal direction becomes too high, making it difficult to stretch in subsequent stages and potentially resulting in a film with uneven thickness.

[0063] The preferred lower limit of the second (or final) MD stretching temperature is preferably 10°C, more preferably 115°C. Above 110°C, polyester resins with an intrinsic viscosity of 0.64 dI / g or higher can be sufficiently stretched longitudinally, enabling transverse stretching in the next step and resulting in good thickness uniformity in both the longitudinal and transverse directions. The preferred upper limit is preferably 130°C, more preferably 125°C. Above 130°C, crystallization is promoted, making transverse stretching difficult and potentially leading to greater thickness uniformity, which is undesirable.

[0064] The preferred lower limit of the MD stretching ratio for the second (or final) stage is preferably 2.1 times, and 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 higher is stretched and molecular orientation is achieved in the longitudinal direction, the plastic film may break in the next transverse stretching step or extreme thickness defects may occur, which is not desirable. The preferred upper limit is preferably 3.5 times, and more preferably 3.1 times. If it exceeds 3.5 times, the longitudinal orientation becomes too high, which may prevent stretching in the second and subsequent stages, or result in a plastic film with large thickness variations, which is not desirable.

[0065] The lower limit of the TD stretching temperature is preferably 110°C, more preferably 120°C, and even more preferably 125°C. Below 110°C, the lateral stretching stress increases, which may cause the plastic film to break or result in extremely large variations in thickness, which is undesirable. The upper limit is preferably 150°C, more preferably 145°C, and even more preferably 140°C. Above 150°C, the orientation of the molecular chains does not increase, which may lead to a decrease in mechanical properties, which is undesirable.

[0066] The lower limit of the transverse (TD) stretching ratio is preferably 3.5 times, and more preferably 3.9 times. If it is less than 3.5 times, the molecular orientation may be weak, resulting in insufficient mechanical strength, which is undesirable. Also, if the orientation of the molecular chains in the longitudinal direction is large, the balance between longitudinal and transverse directions will be poor, leading to greater thickness unevenness, which is also undesirable. The upper limit is preferably 5.5 times, and more preferably 4.5 times. If it exceeds 5.5 times, breakage may occur, which is undesirable.

[0067] To obtain the plastic film used in the transparent gas barrier film of the present invention, it is desirable to appropriately set the conditions for heat setting, which is performed in the tenter immediately after the completion of TD stretching, and for lowering the plastic film to room temperature thereafter. Polyester film containing recycled resin made from PET bottles containing isophthalic acid has lower crystallinity, is more prone to melting into very small particles, and has lower mechanical strength compared to ordinary polyethylene terephthalate film that does not contain isophthalic acid. Therefore, if the film is rapidly exposed to high temperatures under tension after the completion of stretching, or rapidly cooled under tension after the completion of high-temperature heat setting, the tension balance in the width direction is disrupted due to the unavoidable temperature difference in the width direction of the film, resulting in uneven thickness and poor mechanical properties. On the other hand, if one tries to address this phenomenon by lowering the heat setting temperature, sufficient laminate strength may not be obtained. In the present invention, it is recommended to perform a slightly low-temperature heat setting 1 and a sufficiently high-temperature heat setting 2 (heat setting 3 if necessary) after the completion of stretching, followed by a slow cooling process to lower the film to room temperature. However, this method is not the only one that can be used. Other methods include controlling the film tension according to the speed of the hot air in the tenter and the temperature of each zone, performing a relatively low-temperature heat treatment with sufficient furnace length after the stretching is complete, and using a heated roll to relax the film after heat setting is complete.

[0068] As an example, the method using temperature control of a tenter is shown below.

[0069] The lower limit of the temperature for heat fixing 1 is preferably 160°C, and more preferably 170°C. Below 160°C, the thermal shrinkage rate will ultimately be large, which may cause misalignment or shrinkage during processing, and is therefore undesirable. The upper limit is preferably 215°C, and more preferably 210°C. Above 215°C, the plastic film will be subjected to a rapid increase in temperature, which may result in uneven thickness or breakage, and is therefore undesirable.

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

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

[0072] The lower limit of the time for heat setting 2 is preferably 0.5 seconds, and more preferably 3 seconds. If it is less than 0.5 seconds, fracture may occur during heat setting, which is undesirable. The upper limit is preferably 10 seconds, and more preferably 8 seconds. If it exceeds 10 seconds, sagging may occur and thickness unevenness may occur, which is undesirable.

[0073] If necessary, the lower limit of the temperature when heat fixing 3 is provided is preferably 205°C, and more preferably 220°C. Below 205°C, the thermal shrinkage rate increases, which can lead to misalignment or shrinkage during processing, and is therefore undesirable. The upper limit is preferably 240°C, and more preferably 237°C. Above 240°C, the film may melt, or even if it does not melt, it may become brittle, which is therefore undesirable.

[0074] If necessary, the lower limit of the time for heat setting 3 is preferably 0.5 seconds, and more preferably 3 seconds. A time of less than 0.5 seconds may increase the likelihood of fracture during heat setting, which is undesirable. The upper limit is preferably 10 seconds, and more preferably 8 seconds. A time exceeding 10 seconds may cause sagging and uneven thickness, which is undesirable.

[0075] TD relaxation can be performed at any point during heat fixing. The lower limit is preferably 0.5%, and more preferably 3%. Below 0.5%, the thermal shrinkage rate, especially in the lateral direction, becomes large, which can lead to misalignment and shrinkage during processing, and is therefore undesirable. The upper limit is preferably 10%, and more preferably 8%. Above 10%, sagging and uneven thickness may occur, which is therefore undesirable.

[0076] The lower limit of the slow cooling temperature after TD heat fixation is preferably 90°C, and more preferably 100°C. Below 90°C, because it is a plastic film containing isophthalic acid, rapid temperature changes may cause shrinkage, leading to uneven thickness or breakage, which is undesirable. The upper limit of the slow cooling temperature is preferably 150°C, and more preferably 140°C. Above 150°C, sufficient cooling effect may not be obtained, which is undesirable.

[0077] The lower limit of the slow cooling time after heat setting is preferably 2 seconds, and more preferably 4 seconds. A time of less than 2 seconds may not provide sufficient slow cooling, so it is not very desirable. The upper limit is preferably 20 seconds, and more preferably 15 seconds. A time exceeding 20 seconds tends to be disadvantageous in terms of productivity, so it is not very desirable.

[0078] In addition to the plastic film and aluminum oxide layer mentioned above, the transparent barrier film of the present invention may optionally include various layers found in known gas barrier films. For example, when using a transparent barrier film with an inorganic thin film layer as a packaging material, it is preferable to form a heat-sealable resin layer called a sealant. The heat-sealable resin layer is usually provided on the inorganic thin film layer, but it may also be provided on the outside of the plastic film (the side opposite the side with the inorganic thin film layer). The heat-sealable resin layer is usually formed by extrusion lamination or dry lamination. Any thermoplastic polymer that can sufficiently exhibit sealant adhesion can be used to form the heat-sealable resin layer, and examples 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 laminated between or outside the inorganic thin film layer or plastic film and the heat-sealable resin layer.

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

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

[0082] In particular, when using a transparent gas barrier film equipped with an inorganic thin film layer 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 strength. Typical types of nylon 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 sufficient strength; on the other hand, if it exceeds 30 μm, it may be too stiff and unsuitable for processing. A biaxially oriented nylon film with a stretch ratio of typically 2 times or more in both the longitudinal and transverse directions, preferably around 2.5 to 4 times, is preferred.

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

[0084] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. A transparent barrier film was fabricated using a vapor deposition apparatus equipped with a vapor deposition source consisting of boat-type resistance heating vapor deposition sources (9) arranged in a schematic diagram shown in Figure 6, and a roll-to-roll type film transport system. Boats made by BN Composites have a mechanism that feeds aluminum wire into them. The oxygen inlet (8) is installed in the coated window (7). The coating roll (6) was set to -5°C.

[0085] The plastic film (5) of the substrate is unwound from the unwinding roll (16), the vapor-deposited surface is treated by a planer-type plasma source (17), and then 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 400 sccm of argon gas and 100 sccm of oxygen gas through it.

[0086] After surface treatment, the plastic film (5) of the substrate is guided to the coating window position by a coating roll (6) and vapor deposition is performed. The vapor-deposited plastic film is moved to an optical film thickness gauge (18) and its total light transmittance is measured. After the measurement, the film is wound onto a winding roll (19).

[0087] The evaluation method is as follows. (1) Total light transmittance The total light transmittance during vapor deposition was measured using a turbidimeter (NDH5000, Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7375. The values ​​obtained were then converted to those of an optical film thickness gauge using a conversion method based on the sample data. Furthermore, the samples removed after deposition were measured using a turbidimeter.

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

[0089] (3) Water vapor transmission rate (WVTR) 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 measurement conditions of 40°C and 90% RH.

[0090] (4) Acid resistance A laminated film was created by dry laminating a linear low-density polyethylene film (LLDEP: L4102, 40 μm, manufactured by Toyobo Co., Ltd.) onto the transparent barrier film that had been prepared. For dry lamination, an adhesive mixture of TM569 and CAT-10L, manufactured by Toyo Morton Co., Ltd., was used. Cut two sheets of laminated film to A5 size (148mm x 210mm), overlap the L4012 sides, and seal three sides to create a bag. The seal width is 10mm. Dilute vinegar (Mizukan Grain Vinegar Co., Ltd.) with water to 50%, put 100ml into a bag, and seal it. Store this bag in a room at 40°C for one week. After one week, remove the contents, wash them with water, dry them, and then measure the oxygen permeability. 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 prepared by mixing chloroform D (manufactured by Eurysop) and trifluoroacetic acid D1 (manufactured by Eurysop) in a 10:1 volume ratio. Subsequently, the proton NMR of the prepared sample solution was measured using an NMR spectrometer (Varian GEMINI-200) at a temperature of 23°C and with 64 integration cycles. In the NMR measurement, the peak intensity of a predetermined proton was calculated to determine the content (mol%) of terephthalic acid and isophthalic acid components in 100 mol% of the acid component.

[0092] (6) Intrinsic viscosity of the raw material resin and the resin constituting the film (IV) The sample was vacuum-dried at 130°C overnight, then pulverized or cut. 80 mg was accurately weighed and dissolved in a phenol / tetrachloroethane mixed solution of 60 / 40 (volume ratio) at 80°C for 30 minutes. After dissolving at 80°C, the mixture was cooled to room temperature, and the mixed solvent prepared in the aforementioned ratio in a volumetric flask was added to make a total volume of 20 ml. The viscosity was then measured at 30°C (unit: dI / g). An Ostwald viscometer was used to measure the intrinsic viscosity.

[0093] (7) Thickness of the plastic film Using a PEACOCK dial gauge (manufactured by Ozaki Seisakusho), the thickness Tn (n=l~200) μm was measured at 5 mm intervals along a 1 m length of film in both the longitudinal and transverse directions at 200 points, and the average value was defined as the thickness of the base film.

[0094] (8) Thermal shrinkage rate of plastic film in the longitudinal and transverse directions A sample was taken with a width of 10 mm, and markings were made at 200 mm intervals at room temperature (27°C). After measuring the interval between the markings (L0), the plastic film was placed between sheets of paper and treated in a hot air oven controlled at 150°C for 30 minutes. After removal, the interval between the markings was measured again (L), and the thermal shrinkage rate was calculated using the following formula. Samples were taken in both the vertical and horizontal directions, and the procedure was performed accordingly. Thermal shrinkage rate (%) = {(L0 - L) / L0} × 100

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

[0096] (10) Lamination strength of plastic film A laminate for evaluating laminate strength was obtained by dry lamination of a fabricated plastic film and a 40 μm thick polyethylene film (Toyobo Co., Ltd. "L4102") using a urethane-based adhesive (Toyo Morton Co., Ltd., TM569, CAT10L, and ethyl acetate in a ratio of 33.6:4.0:62.4 (by weight)) on the opposite side of the substrate film where the inorganic thin film layer would be laminated. The laminate was then aged at 40°C for 4 days. The lamination conditions were: line speed 20 m / min, dryer temperature 80°C, and coating amount after drying 3 g / m². 2 The experiment was conducted as follows: The laminate was cut into 15 mm wide and 200 mm long test pieces, and the peel strength (N / 15 mm) at the joint between the inorganic thin film layer laminate surface of the base film and the polyolefin resin layer was measured using a Toyo Baldwin "Tensilon UMT-II-500" under conditions of 23°C and 65% relative humidity. The tensile speed was 20 cm / min and the peel angle was 180 degrees.

[0097] (11) Evaluation of the appearance of plastic film after lamination is removed. The sheet after the peeling treatment in (10) was treated with Neocarmine solution at 50°C for 30 minutes, and the appearance of the plastic film after lamination was evaluated by determining the area ratio of the parts that were not stained pink. ○ level means that there is no leakage of adhesive from the surface after peeling, △ level means that the leakage of adhesive is 10% or less of the total peeled area, and × level means that it exceeds 10%.

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

[0099] (13) Thickness of the inorganic thin film layer The thickness of the aluminum oxide layer was determined using an X-ray fluorescence spectrometer (Supermini200, Rigaku Corporation). A calibration curve was created by identifying the amount of aluminum deposited on pre-prepared samples using inductively coupled plasma emission spectroscopy, determining the film thickness, and then calculating the X-ray fluorescence intensity of those samples.

[0100] Example 1 Adjustment of polyester resin recycled from PET bottles After washing away foreign matter such as remaining beverage from PET bottles used for beverages, the resulting flakes were crushed and melted in an extruder. The material was then filtered twice using filters with progressively smaller mesh sizes to remove even finer foreign matter, and finally filtered a third time using the smallest mesh size filter (50 μm) to obtain a polyester recycled material. The composition of the resulting resin was terephthalic acid / isophthalic acid / ethylene glycol = 97.0 / 3.0 / 100 (mol%), and the intrinsic viscosity of the resin was 0.70 d1 / g. This was designated as polyester A.

[0101] Manufacturing of plastic films Polyester B was prepared as a polyethylene terephthalate resin with an intrinsic viscosity of 0.62d1 / g, consisting of terephthalic acid / ethylene glycol = 100 / 100 (mol%). Polyester C was prepared as a masterbatch containing 0.3% amorphous silica with an average particle size of 1.5 μm in polyester B. Each raw material was dried at 125°C for 8 hours under reduced pressure of 33 Pa. These were mixed in a ratio of polyester A / B / C = 80 / 10 / 10 (by weight) and fed into a single-screw extruder. The temperature of the resin from the extruder to the melt line, filter, and T-die was set to 280°C. However, for the first 45 seconds from the start of the compression section of the extruder screw, the resin temperature was set to 305°C, and thereafter it was set back to 280°C.

[0102] The molten material extruded from the T-die was brought into contact with a cooling roll to form an unstretched sheet, which was then stretched 1.41 times longitudinally on a roll with a peripheral speed difference heated to 118°C (MD1), and then stretched 2.92 times longitudinally on a roll with a peripheral speed difference heated to 128°C (MD2). The longitudinally stretched sheet was then guided into a tenter, preheated to 121°C, and then stretched 4.3 times transversely at 131°C. For heat setting, it was set at 180°C with no relaxation (0%) for 2.5 seconds (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). Subsequently, it was cooled at 120°C for 6.0 seconds in the same tenter, and finally wound up on a winder to obtain a biaxially oriented polyester film (plastic film) with a thickness of 12 μm.

[0103] The aforementioned plastic film contains 80% polyester A recycled from PET bottles. The isophthalic acid content relative to the total dicarboxylic acid content in the total polyester resin constituting the plastic film is 2.4 mol%. Furthermore, the intrinsic viscosity of the constituent resin is 0.64 dl / g. The heat shrinkage rate of the plastic film at 150°C is 0.8% in the vertical direction and 0.5% in the horizontal direction. The thickness variation of the plastic film in the vertical direction was 7.6%, and the thickness variation in the horizontal direction was 6.4%. The lamination strength when polyethylene film was laminated was 6.1 N / 15 mm, and the appearance of the release surface was also at a satisfactory level. The total light transmittance of the plastic film is 84%.

[0104] This plastic film was placed in the vapor deposition apparatus. First, aluminum was deposited without adding oxygen, aiming for a total light transmittance of 18%. After the total light transmittance stabilized, oxygen was introduced and controlled to achieve a total light transmittance of 64%. The amount of oxygen introduced was 12509 sccm. The pressure in the vapor deposition chamber after oxygen introduction was 1.4 × 10⁻⁶. -3 The value was Pa. Table 1 shows the conditions for 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, the amount of trapped air was estimated to be approximately 0.4 μm thick between the plastic film layers. After storing the rolled-up transparent barrier film in a 23°C room for three weeks, the total light transmittance was measured using a turbidimeter and the absorption coefficient was calculated. The results are shown in Table 2. Table 2 also shows the OTR and WVTR measurements for a laminated film formed by laminating LLDEP onto the transparent barrier film. Furthermore, Table 2 shows the results of an acid resistance test.

[0105] Example 2 Samples were prepared using the same method as in Example 1, except that polyester A / B / C were mixed in a weight ratio of 60 / 30 / 10. The results of the evaluation of Example 2 are shown in Table 2. The content of isophthalic acid component relative to the total dicarboxylic acid component in the total polyester resin constituting the plastic film is 1.8 mol%. The intrinsic viscosity of the constituent resin is 0.63 dl / g. The heat shrinkage rate of the plastic film at 150°C is 0.9% in the vertical direction and 0.5% in the horizontal direction. The thickness variation of the plastic film in the vertical direction was 7.9%, and the thickness variation in the horizontal direction was 6.4%. The lamination strength of the polyethylene film when laminated was 6.2 N / 15 mm, and the appearance of the release surface was also at a satisfactory level. The total light transmittance of the plastic film is 83%.

[0106] Example 3 In Example 1, the sample was prepared using the same method as in Example 1, except that the vapor deposition was carried out under the conditions shown in Table 1. The results of the evaluation of Example 2 are shown in Table 2. The content of isophthalic acid component relative to the total dicarboxylic acid component in the total polyester resin constituting the plastic film is 2.4 mol%. The intrinsic viscosity of the constituent resin is 0.64 dl / g. The heat shrinkage rate of the plastic film at 150°C is 0.8% in the vertical direction and 0.5% in the horizontal direction. The thickness variation of the plastic film in the vertical direction was 7.6%, and the thickness variation in the horizontal direction was 6.4%. The lamination strength when polyethylene film was laminated was 6.1 N / 15 mm, and the appearance of the release surface was also at a satisfactory level. The total light transmittance of the plastic film is 84%.

[0107] Comparative Example 1 Samples were prepared using the same method as in Example 1, except that the vapor deposition was carried out under the conditions shown in Table 1. Table 2 shows the results of evaluating the sample of Comparative Example 1. The content of isophthalic acid component relative to the total dicarboxylic acid component in the total polyester resin constituting the plastic film is 2.4 mol%. The intrinsic viscosity of the constituent resin is 0.64 dl / g. The heat shrinkage rate of the plastic film at 150°C is 0.8% in the vertical direction and 0.5% in the horizontal direction. The thickness variation of the plastic film in the vertical direction was 7.6%, and the thickness variation in the horizontal direction was 6.4%. The lamination strength when polyethylene film was laminated was 6.1 N / 15 mm, and the appearance of the release surface was also at a satisfactory level. The total light transmittance of the plastic film is 84%.

[0108] [Table 1]

[0109] [Table 2] In Comparative Example 1, the absorption coefficient immediately after deposition was higher than 0.03 nm-1 compared to Examples 1-3, resulting in a higher OTR value after the acid resistance test and impaired barrier properties. [Industrial applicability]

[0110] This invention provides a transparent barrier film that is environmentally friendly through the reuse of PET bottles, can be manufactured at low cost, and uses an aluminum oxide layer as a barrier layer, offering excellent acid resistance and the ability to package a wide range of contents. [Explanation of Symbols]

[0111] 1: Transmittance wavelength characteristics of the plastic film (12 μm thick PET film) on the substrate 2: Transmittance wavelength characteristics of a transparent gas barrier film with laminated aluminum oxide layers 3: Spectral power wavelength characteristics of the D65 light source 4: y-color matching function 5: Plastic film 6: Coating Roll 7: Coated windows 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. In a transparent gas barrier film having an aluminum oxide layer mainly composed of aluminum oxide on at least one side of a polyethylene terephthalate base film, the absorption coefficient of the aluminum oxide layer immediately after deposition is 0.03 nm. －１ A transparent gas barrier film characterized by having a vapor deposition film thickness of 6 nm or more and 10 nm or less, wherein the base polyethylene terephthalate film contains 50% by weight or more of polyethylene terephthalate resin containing 10 mol% or less of isophthalic acid components recycled from PET bottles, and is a biaxially oriented polyethylene terephthalate film that satisfies the following requirements. (1) The content of isophthalic acid component relative to the total dicarboxylic acid component in the total polyethylene terephthalate resin constituting the base polyethylene terephthalate film is 0.5 mol% or more and 5.0 mol% or less. (2) The intrinsic viscosity of the resin constituting the base polyethylene terephthalate film is 0.58 dI / g or more and 0.70 dI / g or less. (3) The thermal shrinkage rate of the base polyethylene terephthalate film in the longitudinal and transverse directions at 150°C is 0.1% or more and 1.5% or less. (4) When a polyolefin film is laminated to the opposite side of the aluminum oxide layer laminated surface of the base polyethylene terephthalate film, the lamination strength is 4.0 N / 15 mm or more and 20.0 N / 15 mm or less. (5) Measure 200 points of thickness Tn (n=l to 200) (unit: μm) at 5 mm intervals along a 1 m length of film in both the longitudinal and transverse directions. Let Tmax be the maximum thickness, Tmin be the minimum thickness, and Tave be the average thickness. The thickness variation calculated using the following formula should be 16% or less in both the longitudinal and transverse directions. Thickness variation = {(Tmax-Tmin) / Tave} × 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 it is as described above.

3. The absorption coefficient ultimately becomes 0.002 nm -1 The transparent gas barrier film according to claim 1 or 2, characterized in that it is as follows.

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