Biaxially oriented polyethylene terephthalate film roll

Abstract

To provide a film roll produced by winding a biaxially oriented polyester film, where the film employs a recycled material derived from a PET container, can be produced with satisfactory productivity in a longer shape without being broken even when a large amount of foreign matter is contained in the recycled material, and is friendly to the global environment.SOLUTION: Provided is a biaxially oriented polyethylene terephthalate film roll produced by winding a biaxially oriented polyethylene terephthalate film into a roll, where the film employs a recycled material derived from a PET container and satisfies (1) to (3) in the following: (1) the thermal shrinkage in the film length direction as measured at 150°C for 30 minutes is from 0.5% to 2.0% inclusive; (2) the plane orientation coefficient (ΔP) of the film calculated from a refractive index measured in accordance with the JIS K 7142-1996 A method is from 0.16 to 0.17 inclusive; and (3) the number of foreign bodies whose maximum length is 1.3 mm or more is 1 or more per 1000 m2 of the film roll.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a biaxially oriented polyethylene terephthalate film roll formed by winding a biaxially oriented polyester film into a roll. More specifically, the present invention relates to a biaxially oriented polyester film roll that uses recycled raw materials derived from PET containers, is environmentally friendly, has good film-forming properties even when using recycled raw materials derived from PET containers that contain a lot of impurities, and has excellent productivity. [Background technology]

[0002] Aromatic polyesters, such as polyethylene terephthalate (PET), possess excellent mechanical properties and chemical resistance, and are widely used as molded products such as fibers and films. PET resin, in particular, is inexpensive and hygienic, making it widely used for food and beverage containers. In recent years, due to growing environmental concerns and the need for resource conservation, recycled PET containers have been practiced for some time, and their utilization methods are attracting attention.

[0003] Furthermore, it is said that using recycled materials derived from PET containers contributes to reducing CO2 emissions, and there is a desire to increase the use of recycled materials derived from PET containers as much as possible from an environmental perspective.

[0004] Recycled raw materials derived from PET containers are produced by recovering A-PET used in beverage PET bottles and containers for salads and vegetables. However, because these materials are recovered from waste that has entered the market, they contain more foreign matter compared to PET raw materials derived from fossil fuels. As a result, the resulting biaxially oriented polyester film is prone to breakage due to foreign matter, which is a problem as it reduces productivity. Foreign matter here refers to substances other than PET resin, such as the label strips on PET bottles, gravel, and chemicals such as pesticides and insecticides that consumers filled into PET bottles. One way to suppress breakage due to foreign matter is to pass the molten resin through a highly accurate filter to form the film. This method effectively removes foreign matter, thus reducing breakage due to foreign matter, but the accumulation of foreign matter on the filter causes clogging. Therefore, the filter needs to be replaced at a shorter interval, which ultimately reduces productivity. Furthermore, there is a method of removing foreign matter in stages by using filters with different mesh sizes in multiple steps, but this lengthens the melting line, reduces the molecular weight of the recycled raw material, and consequently leads to a decrease in the mechanical strength of the resulting biaxially oriented polyester film. On the other hand, the problem of foreign matter can be solved by sorting the collected PET containers into only those that are clean and free of dirt, and using them as recycled raw materials. However, if dirty PET containers cannot be recycled, it is bad for the environment.

[0005] Patent Document 1 discloses a biaxially oriented polyester film using recycled PET bottle material. In Patent Document 1, the filter back pressure rise coefficient of the recycled material is suppressed to the same level as that of PET material derived from fossil fuels, and the resulting biaxially oriented polyester film contains fewer impurities. However, if only clean PET containers are sorted and used after collection, the environmental effect is insufficient. Furthermore, even if a sufficient filtration process is carried out during the production of the recycled material, it is expected that the filter replacement cycle will be shortened, leading to a decrease in productivity. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-65282 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0007] This invention was made against the backdrop of the problems of the prior art. Specifically, the object of this invention is to provide a film roll made by winding a biaxially oriented polyester film that is made from recycled raw materials derived from PET containers, has good productivity even when the amount of foreign matter in the recycled raw materials is large, can be made into long lengths without breaking, and is environmentally friendly. [Means for solving the problem]

[0008] As a result of diligent research by the inventors, we discovered that even when using recycled raw materials derived from PET containers as raw materials, by selecting a specific range of stretching conditions and controlling the degree of surface orientation of the film, the productivity of the resulting film can be improved even with a large amount of foreign matter in the recycled raw materials, and it is possible to produce long lengths without breakage. This led to the present invention.

[0009] In other words, the present invention consists of the following configuration. [1] A biaxially oriented polyethylene terephthalate film roll made by winding a biaxially oriented polyethylene terephthalate film that satisfies the following conditions (1) to (3) using recycled raw materials derived from PET containers into a roll. (1) The thermal shrinkage rate in the longitudinal direction of the film when measured at 150°C for 30 minutes is 0.5% or more and 2.0% or less. (2) The surface orientation coefficient (ΔP) of the film, calculated from the refractive index measured according to JIS K 7142-1996 Method A, is 0.16 or more and 0.17 or less. (3) 1000m roll of film 2 There is one or more foreign objects with a maximum length of 1.3 mm or more per area. [2] The biaxially oriented polyethylene terephthalate film roll according to [1], wherein the recycled raw material derived from a PET container is a mechanically recycled polyester resin and / or a chemically recycled polyester resin. [3] The biaxially oriented polyethylene terephthalate film roll according to [1] or [2], wherein the thickness unevenness at around 800 mm in the film width direction is 18% or less. [4] The biaxially oriented polyethylene terephthalate film roll according to any one of [1] to [3], wherein the breaking strength in the film longitudinal direction is 180 MPa or more and 260 MPa or less, and the breaking elongation is 80% or more and 170% or less. [5] The film roll is 8000 m 2 The biaxially oriented polyethylene terephthalate film roll according to any one of [1] to [4], wherein the number of foreign matters having a maximum length of 1.0 mm or more per 8000 m of the film roll is 16 or more. [6] The biaxially oriented polyethylene terephthalate film roll according to any one of [1] to [5], wherein the winding length is 10000 m or more.

Advantages of the Invention

[0010] The biaxially oriented polyester film roll of the present invention uses a recycled raw material derived from a PET container as a raw material, and by setting the heat shrinkage rate, surface orientation coefficient (ΔP), and the number of foreign matters in the film longitudinal direction within a predetermined range, even if the amount of foreign matters in the recycled raw material is large, a biaxially oriented polyester film roll that is friendly to the global environment and has good film productivity and can be made longer can be obtained.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram showing the TD stretching method of the logarithmic pattern in the present invention. [Figure 2] It is a schematic diagram showing the TD stretching method of the multi-stage stretching pattern in the present invention.

Embodiments for Carrying Out the Invention

[0012] The present invention will be described in detail below. The recycled raw material derived from PET containers preferably used in the present invention is mainly composed of polyethylene terephthalate, and the form of the container to be recycled is not limited, and it may contain some coloring components. Hereinafter, a polyester resin obtained by recycling PET bottles will be described as an example, but it is not limited thereto.

[0013] [Polyester resin obtained by recycling PET bottles] As the polyester resin obtained by recycling PET bottles in the present invention, a polyester resin obtained by a physical recycling method in which used PET bottles collected from the market and society are sorted, crushed, washed to sufficiently remove surface dirt and foreign substances, and then exposed to high temperature to highly wash contaminants remaining inside the resin and then pelletized again (hereinafter sometimes referred to as a mechanically recycled polyester resin), and a polyester resin obtained by decomposing the polyester resin contained in used packaging containers to the monomer level, removing contaminants, etc., and then performing polymerization again (hereinafter sometimes referred to as a chemically recycled polyester resin) can both be preferably used.

[0014] It is preferable to use a polyester resin recycled from the market or society, including the following PET bottles, in the biaxially oriented polyester film of the present invention. By using a polyester resin recycled from the market or society, including PET bottles, the ratio of recycled raw materials in the film can be increased, and an environmentally considerate film can be obtained. The polyester resin recycled from the market or society, including PET bottles, used in the biaxially oriented polyester film of the present invention is mainly a recycled product of a container mainly composed of polyethylene terephthalate. For example, recycled products of beverage containers such as tea beverages and soft drinks can be preferably used, and they may be appropriately oriented. Colorless ones are preferred, but they may contain some coloring components.

[0015] The recycled raw material derived from PET containers, which is preferably used in the present invention, is polyester manufactured and molded by conventional polymerization and solid-phase polymerization methods, and is preferably mainly composed of polyethylene terephthalate, but may also contain other polyester components and copolymer components. It may also contain metal compounds such as antimony, germanium, and titanium as catalysts, and phosphorus compounds as stabilizers.

[0016] Germanium is often used as a catalyst in polyester for typical PET bottles, and if film is made using recycled PET bottle materials, the film will contain 1 ppm or more of germanium. However, this is merely the amount of catalyst, so it is usually at most 100 ppm or less, and typically 50 ppm or less.

[0017] The following describes mechanically recycled polyester resin and chemically recycled polyester resin.

[0018] [Mechanically recycled polyester resin] Collected used recycled PET bottles are sorted to prevent mixing with other materials and waste, labels are removed, and then they are crushed into flakes. These flakes often contain foreign matter attached to them. It is also possible that consumers have filled used PET bottles with chemical substances such as medicines and solvents. Examples include dishwashing detergents, insecticides, herbicides, pesticides, and various oils. Since ordinary washing cannot sufficiently remove chemical substances adsorbed on the surface of PET bottles, alkaline washing is preferable. The alkali metal hydroxide solution used in this washing process is either a sodium hydroxide solution or a potassium hydroxide solution. In such a washing process, pre-washing may be performed before alkaline washing. If alkaline cleaning is not performed, foreign matter will remain in the raw resin, which can lead to contamination and cause breakage during film formation, reducing productivity. Furthermore, if foreign matter remains in the film, it can affect the film's appearance and cause printing defects in subsequent printing processes.

[0019] The concentration of the alkali metal hydroxide aqueous solution used in the above cleaning process is usually in the range of 1 to 10% by weight, although this depends on the temperature, time, and stirring conditions. The cleaning time is in the range of 10 to 100 minutes, and it is preferable to carry it out while stirring to enhance the effect.

[0020] It is preferable to perform rinsing and drying after alkaline washing. Alkaline washing and rinsing may be repeated several times. If aqueous solution components of alkali metal hydroxide used in the alkaline washing process remain on the flakes, they may affect the physical properties of the final film when they pass through the subsequent melt extrusion process in the pellet granulation process and the melt extrusion process in the film formation process.

[0021] The sodium and potassium concentrations in the film obtained using recycled polyester resin from the market and society, including these PET bottles, are preferably greater than 0 ppm and 150 ppm or less, more preferably 3 to 120 ppm, and even more preferably 5 to 80 ppm. If the sodium or potassium concentration in the film is higher than 150 ppm, the heat resistance and thermal stability of the film will decrease, or discoloration will occur, which is undesirable. Also, if there are no sodium or potassium at all, the effects such as suppressing the formation of diethylene glycol will be diminished, which is also undesirable. Furthermore, recycled polyester resin from the market and society, including PET bottles, may contain small amounts of these components, making it difficult to eliminate them completely.

[0022] In this washing process, some of the PET bottle flakes are hydrolyzed by the alkali metal hydroxide aqueous solution. In addition, the degree of polymerization of the resin decreases due to the heating during the molding of the PET bottles. Furthermore, the degree of polymerization decreases again due to the heat and moisture added when the collected PET bottles are crushed for reuse and then remelted into pellets. Although they can be reused as is, depending on the intended use, a decrease in the degree of polymerization may result in inferior moldability, strength, transparency, and heat resistance, making them unsuitable for reuse in their current state.

[0023] In such cases, it is preferable to solid-phase polymerize crushed and washed PET bottle flakes, or melted flakes and pelletized material, in order to restore the reduced degree of polymerization.

[0024] In the solid-phase polymerization process, the washed flakes, or flakes that have been melt-extruded and formed into pellets, can be subjected to continuous solid-phase polymerization in an inert gas such as nitrogen gas or a noble gas at 180 to 245°C, preferably 200 to 240°C.

[0025] It is desirable to adjust the flake or pellet conditions so that the final polyester resin, including PET bottles, recycled from the market and society, has an intrinsic viscosity of 0.55 to 0.90 dl / g, preferably 0.60 to 0.85 dl / g.

[0026] The process of pelletizing flakes is described below. The flakes are melted, extruded, cooled, and granulated using an extruder equipped with a degassing device and a filtration device.

[0027] The melting process in the extruder can usually be carried out by melting and kneading at 260-300°C, preferably 265-295°C. The crushed PET bottle flakes to be fed into the extruder must be thoroughly dried, and it is preferable to dry them under conditions of 5-200 ppm, preferably 10-100 ppm, and even more preferably 15-50 ppm. If the flakes contain a large amount of moisture, hydrolysis will proceed in the melting process, and the intrinsic viscosity of the resulting polyester resin will decrease. As a means of degassing, it is preferable to have at least one vacuum vent in the molten zone of the resin.

[0028] Furthermore, it is preferable that the extruder has a filter as a filtration means that can filter and remove solid foreign matter with a particle size of 25 μm or more, preferably 15 μm or more, and more preferably 10 μm or more, from the molten resin.

[0029] The molten resin that has passed through the filter goes through a die, is cooled in water, and then cut into pellets of the desired shape and granulated. [Polyester resin composition] The biaxially oriented polyester film in the present invention consists of a polyester resin composition mainly comprising the following polyester resins. The polyester resin constituting the biaxially oriented polyester film of the present invention is a polymer synthesized from a dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative. Examples include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, with polyethylene terephthalate being preferred from the viewpoint of mechanical properties, heat resistance, and cost. Here, "main component" means a component whose content in the polyester resin composition is 80% by weight or more, preferably 90% by weight or more, more preferably 95% by weight or more, and most preferably 98% by weight or more.

[0030] Furthermore, these polyester resins may be copolymerized with other components, as long as the objectives of the present invention are not impaired. Specifically, examples of copolymerization components include isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid and its ester-forming derivatives, etc., as dicarboxylic acid components. Examples of diol components include diethylene glycol, hexamethylene glycol, neopentyl glycol, and cyclohexanedimethanol. Polyoxyalkylene glycols such as polyethylene glycol and polypropylene glycol are also examples. The copolymerization amount is preferably 10 mol% or less per constituting repeating unit, more preferably 5 mol% or less, and most preferably 3 mol% or less.

[0031] When the recycled raw material derived from PET containers of the present invention is melt-extruded at a temperature of 285°C, a filter diameter of 20 μm, and a filtration rate of 6 g / min, the lower limit of the filter back pressure rise coefficient is preferably 10 MPa / kg·cm. 2 More preferably 20 MPa / kg·cm 2 The most preferred MPa / kg·cm is 30 MPa / kg·cm. 2 That is the case. The filter back pressure rise coefficient referred to here represents the resistance to clogging of the filtration filter when the resin is melt-extruded, and can be calculated using the following formula. K = ΔP / (Q / S) Here, K: filter back pressure rise coefficient, ΔP = P1 - P0 P1: Pressure 4 hours after extrusion (MPa), P0: Pressure at the start of extrusion (MPa), Q: Extrusion discharge volume (kg / hr), S: Filter filtration area (cm²) 2 )

[0032] The filter back pressure rise coefficient when melt extruded under the above conditions was 10 MPa / kg·cm. 2 This approach effectively indicates that the recycled material is made without any sorting of PET containers, thus providing a sufficient environmental benefit. When the recycled raw material derived from the PET container of the present invention is melt-extruded at a temperature of 285°C, a filter filtration diameter of 20 μm, and a filtration rate of 6 g / min, the upper limit of the filter back pressure increase coefficient is preferably 100 MPa / kg·cm 2 and more preferably 90 MPa / kg·cm 2 and particularly preferably 80 MPa / kg·cm 2 By setting it to 100 MPa / kg·cm or less, the productivity can be improved only by adjusting the production conditions of the biaxially oriented polyester film. 2 By setting it to 100 MPa / kg·cm or less, the productivity can be improved only by adjusting the production conditions of the biaxially oriented polyester film.

[0033] [Chemical recycling polyester resin] The method for producing the chemical recycling polyester resin used in the present invention is not particularly limited. Specifically, for example, as described in JP-A-2000-169623, after the collected used PET bottles are sorted, crushed, and washed to remove foreign substances, depolymerization is performed to decompose and purify them to the raw material or intermediate raw material of the PET resin, and then they are polymerized to obtain a new PET resin. In the depolymerization, ethylene glycol (EG) is added and, in the presence of a catalyst, it is returned to bis-2-hydroxyethyl terephthalate (BHET), which is an intermediate raw material during resin production. After purification, it is repolymerized to PET. Another method is to heat-treat polyethylene terephthalate in a non-aqueous organic solvent in the presence of a catalyst containing iron oxidized from polyethylene terephthalate as an essential component to generate terephthalic acid and ethylene glycol, and then polymerize it again. The chemical recycling polyester resin is characterized in that foreign substances and different materials are removed during depolymerization / repolymerization, and it can be recycled into a polyester resin with high quality equivalent to virgin resin. Therefore, compared with the mechanical recycling polyester resin described above, it is excellent in hygiene and can be particularly preferably used for food packaging applications.

[0034] The chemically recycled polyester resin used in this invention uses bales of compressed, reduced-volume used PET bottles as its starting material. These PET bottle bales are manufactured by known methods currently employed by municipalities. Other polyethylene terephthalate waste or PET bottle flakes can be used as starting materials instead of PET bottle bales.

[0035] The PET bottle waste is compressed into bales, which are then fed into a shredder. Hot water, room temperature water, or hot water or room temperature water containing detergent is then injected to shred the bottles underwater.

[0036] Next, the mixture of PET bottle flakes and washing water discharged from the crusher is immediately subjected to specific gravity separation to separate the metal, stone, glass, and sand from the flakes. Then, the flakes are separated from the washing water, the flakes are rinsed with deionized water, and centrifugal dewatering is performed.

[0037] The crude polyethylene terephthalate flakes obtained in the above pretreatment step are depolymerized and melted, and simultaneously hydrolyzed to obtain a polyethylene terephthalate molten product with a low degree of polymerization. This is then depolymerized with excess ethylene glycol to obtain a mixed solution of crude BHET and crude ethylene glycol.

[0038] The mixed solution of crude BHET and crude ethylene glycol after the depolymerization reaction is cooled and filtered to remove unreacted linear and cyclic oligomers as high-melting-point precipitates, solid foreign matter such as solid metals and other solids, and then adsorption and ion exchange treatment is performed to remove colorants and dissolved ions, thereby removing foreign matter contained in the crude BHET.

[0039] The crude BHET and crude ethylene glycol obtained through the aforementioned purification process are subjected to a mixed solution of these two materials by distillation and evaporation to separate and distill off the ethylene glycol and obtain concentrated BHET. Alternatively, the mixed solution of the two materials is cooled to below 10°C to crystallize the BHET, and then the ethylene glycol and BHET are separated by solid-liquid separation to obtain concentrated BHET. This concentrated BHET is then vacuum-evaporated at a temperature between 190°C and 250°C, with a residence time of 10 minutes or less in the evaporator, to obtain purified bis-β-hydroxyethyl terephthalate.

[0040] After obtaining high-purity purified BHET as described above, this purified BHET is charged into a melt polycondensation reactor to obtain high-purity polyethylene terephthalate polymer.

[0041] As a method for producing fossil fuel-derived polyester resins other than mechanically recycled polyester resins and chemically recycled polyester resins among the polyester resins constituting the biaxially oriented polyester film of the present invention, one example is to first use the aforementioned dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative as the main starting materials, carry out an esterification or transesterification reaction according to a conventional method, and then carry out a polycondensation reaction at high temperature and reduced pressure.

[0042] As the intrinsic viscosity of the polyester resin constituting the biaxially oriented polyester film of the present invention From the standpoint of film-forming properties and recoverability, a range of 0.50 to 0.90 dl / g is preferred, and more Preferably, the range is 0.55 to 0.80 dl / g.

[0043] The biaxially oriented polyester film of the present invention may contain, in addition to the polyester resin composition, conventionally known additives such as lubricants, stabilizers, colorants, antioxidants, antistatic agents, and ultraviolet absorbers.

[0044] When the entire biaxially oriented polyester film of the present invention is considered to be 100% by mass, the content of the polyester resin composition is preferably 99.5% by mass or more, more preferably 99.6% by mass, and most preferably 99.7% by mass.

[0045] The aforementioned lubricant can adjust the dynamic friction coefficient of the film, and examples include inorganic lubricants such as silica, calcium carbonate, and alumina, as well as organic lubricants. Silica and calcium carbonate are preferred, and porous silica is the most preferred among them from the viewpoint of achieving both transparency and lubricity.

[0046] The lower limit of the lubricant content in the biaxially oriented polyester film of the present invention is preferably 100 ppm by mass, more preferably 300 ppm by mass, and most preferably 500 ppm by mass. By setting the lubricant content to 100 ppm by mass or more, the slipperiness of the film can be improved. The upper limit of the lubricant content in the biaxially oriented polyester film of the present invention is preferably 10,000 ppm by mass, more preferably 6,000 ppm by mass, and most preferably 2,000 ppm by mass. By keeping it below 10,000 ppm by mass, the transparency of the film can be improved.

[0047] [Method for manufacturing biaxially oriented polyester film] There are no particular limitations on the method for obtaining the biaxially oriented polyester film of the present invention, and methods such as the T-die method and the inflation method can be appropriately selected.

[0048] The film of the present invention may have a single-layer structure of at least one layer, or it may have a laminated structure of two or more layers. It may have two, three, four, or five layers.

[0049] The upper limit of the cooling roll temperature is preferably 40°C, and more preferably 20°C or lower. If the temperature is 40°C or higher, the degree of crystallization of the molten polyester resin composition does not become too high when it cools and solidifies, making stretching easier and suppressing the decrease in transparency due to crystallization. The lower limit of the cooling roll temperature is preferably 0°C. A temperature of 0°C or higher allows for sufficient suppression of crystallization during the cooling and solidification of the molten polyester resin composition. Furthermore, when the cooling roll temperature is within the above range, it is preferable to lower the humidity of the environment around the cooling roll to prevent condensation.

[0050] The thickness of the unstretched sheet is preferably in the range of 15 to 2500 μm. More preferably it is 600 μm or less, and most preferably 400 μm or less.

[0051] Next, we will explain the stretching method. Stretching can be done using either simultaneous biaxial stretching or sequential biaxial stretching.

[0052] The lower limit of the stretching temperature in the longitudinal direction (hereinafter also referred to as the MD direction) is preferably 90°C, more preferably 100°C, and particularly preferably 110°C. A temperature of 110°C or higher can reduce the stretching stress, thereby suppressing fracture caused by foreign matter. The upper limit of the stretching temperature in the MD direction is preferably 140°C, more preferably 130°C, and particularly preferably 120°C. Below 140°C, the stretching stress increases due to crystallization, which not only suppresses fracture caused by foreign matter but also results in good mechanical strength for the film.

[0053] The lower limit of the stretching ratio in the MD direction is preferably 2.5 times, more preferably 2.8 times, and particularly preferably 3.1 times. When it is 2.5 times or higher, not only is the mechanical strength of the film good, but the thickness uniformity is also good, leading to improved winding quality when it is made into a roll. The upper limit of the MD-direction stretch ratio is preferably 4.0 times, more preferably 3.8 times, and particularly preferably 3.6 times. If it is 4.0 times or less, the stretch stress can be reduced, thereby suppressing fracture caused by foreign matter.

[0054] It is preferable to have a relaxation step in the MD direction between the stretching step in the MD direction and the subsequent stretching step in the width direction (hereinafter also referred to as the TD direction). The lower limit of the MD relaxation rate is preferably 1%, more preferably 3%, and particularly preferably 5%. If it is 1% or higher, the amorphous components in the film are relaxed, which can reduce the stretching stress in the subsequent TD stretching process, and consequently suppress fracture caused by foreign matter. The upper limit of the MD relaxation rate is preferably 10%, more preferably 8%, and particularly preferably 6%. If it is 10% or less, wrinkles due to shrinkage can be suppressed, improving the quality of the film, and the decrease in mechanical strength due to orientation relaxation can be suppressed. The method of MD relaxation is not particularly limited, but one example is to heat with a hot air heater and then use the speed difference between the rolls to perform the relaxation process.

[0055] The lower limit of the stretching temperature in the TD direction is preferably 90°C, more preferably 100°C, and particularly preferably 110°C. A temperature of 110°C or higher can reduce the stretching stress, thereby suppressing fracture caused by foreign matter. The upper limit of the stretching temperature in the TD direction is preferably 140°C, more preferably 130°C, and particularly preferably 120°C. Below 140°C, the stretching stress increases due to crystallization, which not only suppresses fracture caused by foreign matter but also results in good mechanical strength for the film.

[0056] The lower limit of the stretching ratio in the TD direction is preferably 2.5 times, more preferably 3.0 times, and particularly preferably 3.5 times. When it is 2.5 times or higher, not only is the mechanical strength of the film good, but the thickness uniformity is also good, leading to improved winding quality when it is made into a roll. The upper limit of the TD direction stretch ratio is preferably 5.0 times, more preferably 4.5 times, and particularly preferably 4.0 times. If it is 5.0 times or less, the stretch stress can be reduced, thereby suppressing fracture caused by foreign matter.

[0057] The stretching pattern in the TD direction is preferably logarithmic or multi-stage stretching. Specifically, as shown in Figures 1 and 2, the logarithmic TD stretching pattern is a TD stretching pattern in which the stretching is large in the first half and gradual in the second half, compared to the usual linear stretching pattern. By using such a TD stretching pattern, most of the stretching can be completed in the first half when the film stretching stress is low, and the stretching stress applied during stretching can be reduced. As a result, fracture due to foreign matter can be suppressed.

[0058] Next, we will describe the details of adopting a logarithmic TD extension pattern. As mentioned above, a logarithmic TD extension pattern refers to a TD extension pattern in which the extension is large in the first half and gradually slows down in the second half. If the number of TD extension zones is N and the extension angle θN in the Nth extension area, then the extension in each extension zone extends in the width direction under the condition that θn > θn+1. (When θn = θn+1, it is a normal straight extension.) The amount of change in the stretching angle when it changes from stretching angle θn to stretching angle θn+1 can be appropriately selected to obtain the desired performance. However, if the angle change rate, expressed as {(θn-θn+1) / θn}×100 (unit: %), exceeds 50%, it becomes necessary to make the stretching magnification extremely large in the initial stage of TD stretching in order to stretch to the predetermined maximum magnification. This can lead to excessively large stretching stress in the initial stage of stretching, potentially worsening film formation. When the angle change rate is 0%, θ1=θ2, which is the same as the stretching conditions in a conventional tenter. Therefore, when adopting a logarithmic TD stretching pattern, the angle change rate is preferably in the range of 0.5% to 50%, more preferably in the range of 1% to 30%, and particularly preferably in the range of 1.5% to 20%. By setting the stretching angle in the logarithmic TD stretching pattern within the above range, most of the stretching can be completed in the first half when the film stretching stress is low, thus reducing the stretching stress applied during stretching. As a result, fracture due to foreign matter can be suppressed.

[0059] Next, we will discuss multi-stage stretching in TD. Multi-stage stretching involves applying two or more stretching processes compared to the usual single-stage stretching, which can reduce the stretching stress applied during TD stretching. As a result, fracture due to foreign matter can be suppressed.

[0060] TD multi-stage stretching is preferably two to five stages. Multi-stage stretching allows for changing the stretching temperature at each stage and thus changing the stretching stress, which is preferable as it allows for lowering the stretching stress during TD stretching. As shown in Figure 2, in multi-stage stretching, it is preferable to have a temperature pattern in which the temperature decreases from the first stretching stage to the final stretching stage, with a temperature difference of 2°C or more at each stage of stretching. The lower limit of the number of stretching stages is preferably two or more. Two or more stretching stages can reduce the stretching stress and suppress fracture caused by foreign matter. The upper limit for the number of extension stages is preferably five or fewer. Limiting the extension to five stages or fewer prevents the equipment from becoming excessively large. Furthermore, when performing multi-stage stretching, a fixed-length zone can be appropriately provided after each stretching stage. By providing a fixed-length zone after each stretching stage, the internal stress generated during stretching can be relieved in the fixed-length zone, thereby further reducing the stretching stress during the next stretch and suppressing film breakage.

[0061] The lower limit of the heat-fixing temperature is preferably 170°C, more preferably 180°C, and particularly preferably 190°C. A temperature of 170°C or higher can reduce the thermal shrinkage rate. The upper limit of the heat-fixing temperature is preferably 230°C, more preferably 220°C, and particularly preferably 210°C. A temperature of 230°C or lower can suppress the decrease in mechanical strength due to the brittleness of the biaxially oriented polyester film.

[0062] The lower limit of the TD relaxation rate is preferably 0.5%, more preferably 1.0%, and particularly preferably 2.0%. A rate of 0.5% or higher allows for keeping the thermal shrinkage rate in the TD direction low. The upper limit of the TD relaxation rate is preferably 10%, more preferably 8%, and particularly preferably 6%. A rate of 10% or less can prevent sagging and improve flatness.

[0063] By employing the aforementioned preferred film-forming conditions, it is possible to continuously obtain long films of biaxially oriented polyester film containing foreign matter without breakage, and to satisfy the following preferred film characteristics.

[0064] [Structure and properties of biaxially oriented polyester film] The lower limit of the thickness of the biaxially oriented polyester film of the present invention is preferably 5 μm, more preferably 10 μm, and particularly preferably 15 μm. By setting the thickness to 5 μm or more, breakage caused by foreign matter can be suppressed. The upper limit of the thickness of the biaxially oriented polyester film of the present invention is preferably 100 μm, more preferably 70 μm, and particularly preferably 40 μm.

[0065] The lower limit of the surface orientation coefficient (ΔP) of the biaxially oriented polyester film of the present invention is preferably 0.160, more preferably 0.161, and particularly preferably 0.162. By setting it to 0.160 or higher, the mechanical strength can be kept sufficiently high. The upper limit of ΔP for the biaxially oriented polyester film of the present invention is preferably 0.170, more preferably 0.169, and particularly preferably 0.168. By setting it to 0.170 or less, stretching stress during the stretching process can be suppressed, and as a result, fracture caused by foreign matter during the stretching process can be suppressed.

[0066] The lower limit of the tensile strength in the MD direction of the biaxially oriented polyester film of the present invention is preferably 180 MPa, more preferably 185 MPa, and particularly preferably 190 MPa. A strength of 180 MPa or higher provides sufficient mechanical strength when used in a bag. The upper limit of the tensile strength in the MD direction of the biaxially oriented polyester film of the present invention is 260 MPa, more preferably 255 MPa, and particularly preferably 250 MPa. If the tensile strength is 260 MPa or less, it is possible to substantially suppress fracture caused by foreign matter during the stretching process, resulting in good film-forming properties.

[0067] The lower limit of the MD-direction elongation at break of the biaxially oriented polyester film of the present invention is preferably 80%, more preferably 90%, and particularly preferably 100%. When it is 80% or higher, it is possible to substantially suppress breakage caused by foreign matter during the stretching process, resulting in good film-forming properties. The upper limit of the break elongation in the MD direction of the biaxially oriented polyester film of the present invention is 170%, more preferably 160%, and particularly preferably 150%. If it is 170% or less, the mechanical strength of the bag made from it will be sufficient.

[0068] The lower limit of the thermal shrinkage rate in the MD direction of the biaxially oriented polyester film of the present invention is preferably 0.5%, more preferably 0.8%, and particularly preferably 1.1%. If it is 0.5% or higher, it is possible to suppress the film becoming brittle and the decrease in mechanical strength. The upper limit of the thermal shrinkage rate in the MD direction of the biaxially oriented polyester film of the present invention is preferably 2.0%, more preferably 1.7%, and particularly preferably 1.4%. When it is 2.0% or less, breakage caused by foreign matter during the stretching process can be substantially suppressed, and good film-forming properties are obtained.

[0069] The upper limit of the thickness variation per 800 mm in the width direction of the biaxially oriented polyester film roll of the present invention is preferably 18%, more preferably 16%, and particularly preferably 14%. If it is 18% or less, the winding quality when it is made into a roll will be good.

[0070] 1000m of the biaxially oriented polyester film roll of the present invention 2 There is one or more foreign matter with a maximum length of 1.3 mm or more per unit area. If there is one or more foreign matter with a maximum length of 1.3 mm or more per 1000 m2, under conventional film-forming conditions, these foreign matter can easily cause breakage during stretching, making stable film formation difficult. However, by using the film-forming conditions described in the present invention and stretching the film so that the thermal shrinkage rate and plane orientation degree are within a predetermined range, stable stretching becomes possible even if foreign matter is present as described above. On the other hand, the 1000m of the biaxially oriented polyester film roll of the present invention 2 Preferably, the minimum number of foreign objects with a maximum length of 1.3 mm or more per unit is 10 or less. If the number of foreign objects exceeding 10 exceeds 1.3 mm, the number of defects after printing will increase, potentially reducing the yield in the secondary processing stage.

[0071] 8000m of the biaxially oriented polyester film roll of the present invention 2The number of foreign objects with a maximum length of 1.0 mm or more per unit area is 16 or more. When there are 16 or more foreign objects with a maximum length of 1.0 mm or more per 8000 m2, conventional films have many points of breakage, making it difficult to produce long, continuous films. However, by using the film production conditions described in the present invention and stretching the film so that the thermal shrinkage rate and plane orientation degree are within a predetermined range, stable stretchability can be ensured even if foreign objects are present as described above, making it possible to obtain long film rolls. On the other hand, the 8000m of the biaxially oriented polyester film roll of the present invention 2 It is preferable that the maximum number of foreign objects with a maximum length of 1.0 mm or more per unit be 80 or less. If the number of foreign objects of 1.0 mm or more exceeds 80, the number of defects after printing will increase, which may reduce the yield in the secondary processing stage.

[0072] A printed layer may be laminated onto the biaxially oriented polyester film of the present invention. Water-based and solvent-based resin-containing printing inks are preferably used as the printing ink for forming the printed layer. Examples of resins used in the printing ink include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. The printing ink may contain known additives such as antistatic agents, light-blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, defoaming agents, crosslinking agents, anti-blocking agents, and antioxidants.

[0073] The printing method for creating the printed layer is not particularly limited, and known printing methods such as offset printing, gravure printing, and screen printing can be used. For drying the solvent after printing, known drying methods such as hot air drying, hot roll drying, and infrared drying can be used.

[0074] The biaxially oriented polyester film of the present invention may be provided with a gas barrier layer, such as an inorganic thin film layer or a metal foil, as long as the objectives of the present invention are not impaired.

[0075] When an inorganic thin film layer is used as a gas barrier layer, the inorganic thin film layer is a thin film made of a metal or an inorganic oxide. There are no particular restrictions on the material that forms the inorganic thin film layer as long as it can be made into a thin film, but from the viewpoint of gas barrier properties, inorganic oxides such as aluminum, silicon dioxide (silica), aluminum oxide (alumina), and mixtures of silicon dioxide and aluminum oxide are preferred. In particular, a composite oxide of silicon dioxide and aluminum oxide is preferred because it can achieve both flexibility and density in the thin film layer.

[0076] In this composite oxide, the mixing ratio of silicon oxide and aluminum oxide is preferably in the range of 20-70% Al by mass ratio of the metal content. On the other hand, if it is 70% or less, the inorganic thin film layer can be made softer, which can suppress the destruction of the thin film and the reduction of gas barrier properties during secondary processing such as printing and lamination. Here, silicon oxide refers to various silicon oxides such as SiO and SiO2 or mixtures thereof, and aluminum oxide refers to various aluminum oxides such as AlO and Al2O3 or mixtures thereof.

[0077] The thickness of the inorganic thin film layer is typically 1 to 100 nm, preferably 5 to 50 nm. A thickness of 1 nm or less makes it easier to obtain more satisfactory gas barrier properties. On the other hand, a thickness of 100 nm or less offers advantages in terms of flexibility and manufacturing cost.

[0078] There are no particular restrictions on the method for forming an inorganic thin film layer; for example, any known deposition method such as vacuum deposition, sputtering, ion plating (physical vapor deposition methods (PVD)), or chemical vapor deposition (CVD) can be used as appropriate. Below, a typical method for forming an inorganic thin film layer will be described using a silicon oxide / aluminum oxide thin film as an example. For example, when using vacuum deposition, a mixture of SiO2 and Al2O3, or a mixture of SiO2 and Al, is preferably used as the deposition raw material. These deposition raw materials are usually particles, and it is desirable that the size of each particle is such that the pressure during deposition does not change, with a preferred particle size of 1 to 5 mm. For heating, methods such as resistance heating, high-frequency induction heating, electron beam heating, and laser heating can be used. It is also possible to use reactive deposition by introducing oxygen, nitrogen, hydrogen, argon, carbon dioxide, water vapor, etc. as a reaction gas, or by using means such as ozone addition or ion assistance. Furthermore, the film formation conditions can be arbitrarily changed, such as by applying a bias to the substrate (laminated film to be deposited) or by heating or cooling the substrate. Such deposition materials, reaction gases, bias of the deposition target, heating and cooling, etc., can be similarly modified when using sputtering or CVD methods. Furthermore, a printed layer may be laminated on the above inorganic thin film layer.

[0079] When an inorganic thin film layer is provided on the biaxially oriented polyester film of the present invention, it is preferable to provide a protective layer on top of the inorganic thin film layer. The gas barrier layer made of metal oxide is not a completely dense film, but has minute defects scattered throughout. By coating the metal oxide layer with a specific protective resin composition described later to form a protective layer, the resin in the protective compatible resin composition penetrates into the defects in the metal oxide layer, resulting in the effect of stabilizing the gas barrier properties. In addition, by using a material that also has gas barrier properties for the protective layer itself, the gas barrier performance of the laminated film is greatly improved.

[0080] Examples of the protective layer include resins such as urethane, polyester, acrylic, titanium, isocyanate, imine, and polybutadiene, to which curing agents such as epoxy, isocyanate, and melamine are added. Examples of solvents used to form the protective layer include aromatic solvents such as benzene and toluene; alcoholic solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; esteric solvents such as ethyl acetate and butyl acetate; and polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.

[0081] The biaxially oriented polyester film of the present invention may have layers of other materials laminated onto it. Methods for this include laminating the biaxially oriented polyester film after its manufacture or laminating it during the film formation process.

[0082] The biaxially oriented polyester film of the present invention can be used as a packaging material by forming a heat-sealable resin layer called a sealant (also referred to as a sealant layer) on the biaxially oriented polyester film. The sealant layer is usually formed by an extrusion lamination method or a dry lamination method. Any thermoplastic copolymer 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.

[0083] The sealant layer may be a single-layer film or a multi-layer film, and the choice should depend on the required function. For example, to provide moisture resistance, a multi-layer film with a resin such as ethylene-cyclic olefin copolymer or polymethylpentene can be used. The sealant layer may also contain various additives such as flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers, and tackifiers. The thickness of the sealant layer is preferably 10 to 100 μm, and more preferably 20 to 60 μm.

[0084] The lower limit of the roll width of the polyester film roll of the present invention is preferably 400 mm or more, more preferably 1000 mm or more, and even more preferably 1500 mm or more, from the viewpoint of improving productivity in the secondary processing step. On the other hand, the upper limit of the polyester film roll width in the present invention is preferably 3000 mm or less, and more preferably 2500 mm or less. If the width of the polyester film roll exceeds 3000 mm, handling becomes difficult, and the film is more prone to wrinkling due to the sagging of the roll. Furthermore, the lower limit of the winding length of the polyester film roll of the present invention is preferably 1000m or more, more preferably 2000m or more, and even more preferably 4000m or more, from the viewpoint of productivity in the secondary processing step. On the other hand, the lower limit of the winding length of the polyester film roll of the present invention is 100,000 m, preferably 80,000 m, and more preferably 70,000 m. When the length of a polyester film roll exceeds 100,000 meters, the weight of the roll increases significantly, making it difficult to handle.

[0085] Furthermore, the polyester film roll of the present invention preferably uses a paper tube, a plastic core, a metal core, or the like as the core for winding the film, and can be appropriately selected depending on the application. It is preferable that the gap difference in the width direction of the core after removing the film from the polyester film roll of the present invention is 0.5 mm or less. When a paper tube is used as the core, the paper tube deforms (distorts) due to distortion of the film and natural shrinkage when stored after the film has been wound. In this case, if the difference in distortion of the paper tube in the width direction (gap difference in the width direction) is large, wrinkles will form on the core side of the film roll, which is undesirable. Therefore, the gap difference of the paper tube after removing the film from the film roll is preferably 0.4 mm or less, and more preferably 0.3 mm or less.

[0086] Furthermore, when a paper tube is used as the core of the polyester film roll of the present invention, the flattening pressure resistance of the paper tube core after the film has been removed from the film roll is preferably 1700 N / 100 mm or higher. If the pressure resistance is lower than 1700 N / 100 mm, the paper tube will be distorted by the internal stress applied after the film has been wound up, causing wrinkles in the core of the roll, which is undesirable. Preferably, it is 1800 N / 100 mm or higher, and more preferably 1900 N / 100 mm or higher. The higher the pressure resistance, the better. Means for obtaining high flattening pressure resistance of the paper tube include increasing the thickness of the paper tube, or using a hard paper tube or ultra-hard paper tube designed for high strength.

[0087] Furthermore, in the heat-shrinkable polyester film roll of the present invention, in order to make the gap difference of the paper core after removing the film from the film roll 0.5 mm or less as described above, it is preferable that the gap difference in the width direction of the paper core before winding the film used for winding be 0.3 mm or less. If the distortion difference in the width direction of the paper core is 0.4 mm or more, the position of distortion when winding the film will be diagonal, which makes it easy for wrinkles (winding core wrinkles) to occur and is undesirable. The gap difference in the width direction of the paper core is more preferably 0.2 mm or less, and even more preferably 0.1 mm or less. Means for reducing the gap difference of the paper core include using a paper core with high hardness that is less likely to deform due to vibrations during transportation, storing the paper core in a moisture-proof bag until use to prevent deformation due to moisture absorption, and storing the paper core in a room with constant temperature and humidity to prevent deformation due to moisture absorption.

[0088] Furthermore, the average value of the winding hardness in the width direction of the polyester film roll surface of the present invention is preferably 500 or more and 850 or less. If it is less than 500, the winding state will be soft, and core wrinkles will be in a good direction, but misalignment will occur on the film roll end face, which is undesirable. If the winding hardness is higher than 850, the winding state will be hard, and wrinkles will easily occur due to thickness unevenness, which is undesirable. The average value of the winding hardness in the width direction of the film roll surface is preferably 550 or more and 800 or less, and more preferably 600 or more and 750 or less. Particularly preferably it is above 650 and 750 or less. [Examples]

[0089] Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[0090] [Back pressure rise coefficient of recycled materials] After drying the recycled raw material pellets at 135°C for 12 hours, they were extruded under the conditions of 285°C, a filter diameter of 20 μm, a discharge rate of 6 g / min, and a discharge time of 4 hours. The filter back pressure rise coefficient was then determined using the following formula. K = ΔP / (Q / S) Here, K: filter back pressure rise coefficient, ΔP = P1 - P0 P1: Pressure 4 hours after extrusion (MPa), P0: Pressure at the start of extrusion (MPa), Q: Extrusion discharge volume (kg / hr), S: Filter filtration area (cm²) 2 )

[0091] [Thickness of biaxially oriented film] Measurements were taken using a dial gauge in accordance with JIS K7130-1999 Method A.

[0092] [Thermal shrinkage rate of biaxially oriented film] The thermal shrinkage rate was measured using a dimensional change test method in accordance with JIS-C-2318, except that the test temperature was 150°C and the heating time was 15 minutes.

[0093] [Refractive index of biaxially oriented film] A 5mm x 5mm sample was cut from the center of the film width. For the sample, the refractive index in the longitudinal direction (Nx), the refractive index in the width direction (Ny), and the refractive index in the thickness direction (Nz) were measured using an Abbe refractometer (NAR-1T, manufactured by Atago Co., Ltd.) with sodium D line as the light source and diiodomethane as the contact liquid, according to JIS K 7142-1996 Method A. The surface orientation coefficient (ΔP) was calculated using the following formula. Surface orientation coefficient (ΔP) = [(Nx + Ny) / 2] - Nz

[0094] [Strength and elongation of biaxially oriented film] In accordance with JIS K 7127, a test sample measuring 15 mm wide and 100 mm long was cut along the longitudinal direction of the film. The test sample was subjected to tensile testing using a tensile testing machine (Shimadzu Corporation Autograph AG-I) under conditions of a gauge length of 50 mm and a tensile speed of 200 mm / min. The breaking strength and elongation at break of the test sample were calculated from the obtained stress-strain curve.

[0095] [Evaluation of film-forming properties of biaxially oriented films] For each example and comparative example, a score of ○ was given if continuous film formation of 10,000 m was possible without breakage, and a score of × was given if breakage occurred and continuous film formation of 10,000 m was not possible.

[0096] [Foreign matter evaluation of biaxially oriented film (1000 square meters)] A film roll with a width of 800 mm and a length of 1250 m (1000 square meters) was rewound using a rewinding machine. During rewinding, the number of defects was investigated using a defect detection machine (FUTEC F MAX MR). The number of defects with a longest portion measuring 1.3 mm or more was determined. Less than 1 defect of 1.3mm or larger: C 1.3mm or larger: 1 to 10 defects: A

[0097] [Foreign matter evaluation of biaxially oriented film (8000 square meters)] A film roll, 800mm wide and 10,000m (8,000 square meters) long, was rewound using a rewinding machine. During rewinding, the number of defects was investigated using a defect detection device (FUTEC F MAX MR). The number of defects with a longest portion measuring 1.0mm or larger was determined. 15 or fewer defects larger than 1.0 mm: C Number of defects larger than 1.0 mm: 16 or more, but 80 or less: A

[0098] [Evaluation of thickness variations in the width direction] Samples were taken from the film roll, measuring 800 mm in the width direction and 40 mm in the length direction. The thickness in the width direction was continuously measured at 5 m / s using a film tester continuous thickness measuring instrument (manufactured by Fujiwork Corporation). The maximum thickness during measurement was defined as Tmax., the minimum thickness as Tmin., and the average thickness as Tave. The thickness unevenness in the width direction of the film was calculated using the following formula. Thickness unevenness = {(Tmax.-Tmin.) / Tave.} × 100(%)

[0099] [Evaluation of filter clogging] For each example and comparative example, a "○" was given if film formation could be completed continuously for one week without changing the filter, and a "×" was given if the filter became clogged in less than one week, making continuous film formation difficult.

[0100] (Polyester A: Mechanically recycled polyester resin derived from PET containers) After washing away foreign matter such as residual contents from the PET container, the material was crushed to obtain flakes. The obtained flakes were washed with a 3.5% sodium hydroxide solution under stirring conditions of 10% by weight, 85°C, and 30 minutes. After alkaline washing, the flakes were removed and washed with distilled water under stirring conditions of 10% by weight, 25°C, and 20 minutes. This washing was repeated two more times, changing the water with distilled water each time. After washing, the flakes were dried, and 0.10 parts by mass of silica particles with an average particle size of 2.5 μm were added to the flakes. Then, the mixture was melted in an extruder, and finer foreign matter was filtered off twice using filters with progressively smaller mesh sizes, and finally filtered again using the smallest mesh size filter (50 μm) to obtain polyester A. The back pressure rise coefficient of polyester A is 96 MPa / kg·cm. 2 That was the case.

[0101] (Polyester B: Mechanically recycled polyester resin derived from PET containers) Polyester B was obtained using the same method as polyester A. The back pressure rise coefficient for polyester B is 64 MPa / kg·cm. 2 That was the case.

[0102] (Polyester C: Mechanically recycled polyester resin derived from PET containers) Polyester C was obtained using the same method as for polyester A. The back pressure rise coefficient for polyester C is 32 MPa / kg·cm. 2 That was the case.

[0103] (Polyester D: Mechanically recycled polyester resin derived from PET containers) Polyester D was obtained using the same method as for polyester A. The back pressure rise coefficient for polyester D is 10 MPa / kg·cm. 2 That was the case.

[0104] (Polyester E: Mechanically recycled polyester resin derived from PET containers) Polyester E was obtained using the same method as for polyester A, except that only clean PET containers were selected for use. The back pressure rise coefficient for polyester E is 8 MPa / kg·cm. 2 That was the case.

[0105] (Polyester F: Mechanically recycled polyester resin derived from PET containers) Polyester F was obtained using the same method as for polyester A. The back pressure rise coefficient for polyester F is 105 MPa / kg·cm. 2 That was the case.

[0106] (Polyester G: Chemically recycled polyester resin derived from PET containers) As a chemically recycled polyester resin made from recycled PET bottles used in the production of the biaxially oriented polyester film described later, we used one synthesized using the following method. The separated and collected PET bottle bales were fed into a wet shredder. A mixture of 1,000 liters of water and 500 g of liquid dish soap was circulated within the wet shredder while the bales were shredded. A gravity separator connected to the shredder separated heavier materials such as metal, sand, and glass, causing them to settle. Flakes were then extracted from the upper layer. These flakes were rinsed with pure water and centrifuged to remove the remaining flakes.

[0107] 30 kg of the above-mentioned recovered flakes, melted while still undried, was charged into a mixture of 150 kg of ethylene glycol and 150 g of zinc acetate dihydrate, which had been preheated, in an autoclave with a stirrer. After removing the deposits with lower boiling points than ethylene glycol, such as water and acetic acid, the mixture was reacted at a temperature of 195-200°C for 4 hours using a reflux condenser.

[0108] After the reaction was complete, the reactor contents were cooled to 97-98°C, and suspended solids and precipitates were removed by hot filtration using a filter.

[0109] After hot filtration, the filtrate was further cooled to confirm that the crude BHET was completely dissolved, and then pre-purified by passing it through an activated carbon bed and then an anion / cation exchange mixed bed at 50-51°C for 30 minutes.

[0110] The above pre-purification liquid was again charged into a stirred autoclave and heated to distill off excess ethylene glycol at atmospheric pressure at 198°C to obtain a molten concentrated BHET.

[0111] The resulting molten concentrated BHET was allowed to cool naturally while being stirred under a nitrogen gas atmosphere, and then removed from the autoclave to obtain a fine-grained block of concentrated BHET.

[0112] After heating and melting this fragment block again to 130°C, it was supplied to a thin-film vacuum evaporator using a metering pump, where it was evaporated, cooled, and condensed to obtain purified BHET.

[0113] This purified BHET was used as a raw material for melt polymerization to obtain chemically recycled polyester resin G with an intrinsic viscosity of 0.696 dl / g. The back pressure rise coefficient of polyester G is 7 MPa / kg·cm. 2 That was the case.

[0114] [Example 1] Polyester A was fed into the extruder. After the resin was melted at 280°C in the extruder, the molten resin was passed through a 50 μm filter mesh, and then through a 100 μm filter mesh. Subsequently, it was cast from a 280°C T-die and adhered to a 10°C cooling roll by electrostatic adhesion to obtain an unstretched sheet. Next, the obtained unstretched sheet was stretched 3.6 times in the MD direction at a temperature of 115°C. Immediately after longitudinal stretching, the film was passed through a heating furnace set to 95°C using a hot air heater, and a 3% relaxation treatment was performed in the longitudinal direction using the speed difference between the rolls at the inlet and outlet of the heating furnace. Next, it was passed through a tenter and stretched 4.6 times in the TD direction at 120°C, followed by a heat setting treatment of 3 seconds and a relaxation treatment of 5% for 1 second at 210°C to obtain a biaxially oriented polyester film with a thickness of 12 μm. The resin composition and film-forming conditions of the biaxially oriented polyester film are shown in Table 1. The physical properties and evaluation results of the obtained film are also shown in Table 1.

[0115] [Example 2] Except for changing the relaxation rate immediately after longitudinal stretching to 0%, and further changing the stretching method on the tenter to a three-stage stretching method, and providing a fixed length region of 1 m between the first and second stages and between the second and third stages, a biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1. The physical properties and evaluation results are shown in Table 1.

[0116] [Example 3] A biaxially oriented polyester film with a thickness of 12 μm was obtained by fabricating the film in the same manner as in Example 1, except that the relaxation rate immediately after longitudinal stretching was changed to 0%, and the stretching pattern on the tenter was changed to a logarithmic shape. The stretching angles on the tenter were adjusted so that the refraction angle θ1 of the first stage was 12.6°, the refraction angle θ2 of the second stage was 8.2°, and the angle change rate was 34.9%, and the stretching ratio was set so that the total stretching ratio was the same as in Example 1. The physical properties and evaluation results are shown in Table 1.

[0117] [Example 4] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the relaxation rate immediately after longitudinal stretching was changed to 1%. The physical properties and evaluation results are shown in Table 1.

[0118] In the following, all instances of Example 5 shall be interpreted as Reference Example 1. [Example 5] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the relaxation rate immediately after longitudinal stretching was changed to 10%. The physical properties and evaluation results are shown in Table 1.

[0119] [Example 6] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the longitudinal stretching ratio was changed to 3.9 times. The physical properties and evaluation results are shown in Table 1.

[0120] [Example 7] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the longitudinal stretching ratio was changed to 2.6 times. The physical properties and evaluation results are shown in Table 1.

[0121] [Example 8] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the transverse stretching ratio was changed to 4.9 times. The physical properties and evaluation results are shown in Table 1.

[0122] In the following, all instances of Example 9 should be interpreted as Reference Example 2. [Example 9] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the transverse stretching ratio was changed to 2.6 times. The physical properties and evaluation results are shown in Table 1.

[0123] [Example 10] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the resin was changed to polyester B. The physical properties and evaluation results are shown in Table 1.

[0124] [Example 11] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the resin was changed to polyester C. The physical properties and evaluation results are shown in Table 1.

[0125] [Example 12] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the resin was changed to polyester D. The physical properties and evaluation results are shown in Table 1. [Example 13] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the resin was changed to polyester G. The physical properties and evaluation results are shown in Table 1.

[0126] [Comparative Example 1] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the filter mesh through which the molten resin passes was changed to 20 μm and 50 μm, and the relaxation rate immediately after longitudinal stretching was changed to 0%. The filter mesh became clogged, resulting in a defective product.

[0127] [Comparative Example 2] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the filter mesh through which the molten resin passes was changed to 20 μm and 50 μm, the resin was changed to polyester D, and the relaxation rate immediately after longitudinal stretching was changed to 0%. The filter mesh became clogged and the result was unsatisfactory.

[0128] [Comparative Example 3] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the resin was changed to polyester E and the relaxation rate immediately after longitudinal stretching was set to 0%. The obtained biaxially oriented polyester film had few foreign matter particles and did not clog the filter mesh, but because clean PET containers were selected and recycled as raw materials, the environmental friendliness was insufficient.

[0129] [Comparative Example 4] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the resin was changed to polyester F and the relaxation rate immediately after longitudinal stretching was set to 10%. The obtained biaxially oriented polyester film had many fractures caused by foreign matter and poor film formation properties.

[0130] [Comparative Example 5] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the relaxation rate immediately after longitudinal stretching was set to 12%. The obtained biaxially oriented polyester film had a low plane orientation coefficient and poor mechanical strength.

[0131] [Comparative Example 6] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming a film in the same manner as in Example 1, except that the relaxation rate immediately after longitudinal stretching was set to 0%. The obtained biaxially oriented polyester film had many fractures caused by foreign matter and poor film formation properties.

[0132] [Comparative Example 7] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the longitudinal stretching ratio was 4.1 times. The obtained biaxially oriented polyester film had many fractures caused by foreign matter and poor film formation properties.

[0133] [Comparative Example 8] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the longitudinal stretching ratio was increased to 2.3 times. The obtained biaxially oriented polyester film had a low surface orientation coefficient and poor mechanical strength.

[0134] [Comparative Example 9] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the transverse stretching ratio was 5.1 times. The obtained biaxially oriented polyester film had poor film-forming properties, with many fractures caused by foreign matter.

[0135] [Comparative Example 10] A biaxially oriented polyester film with a thickness of 12 μm was obtained by forming the film in the same manner as in Example 1, except that the transverse stretching ratio was increased to 2.3 times. The obtained biaxially oriented polyester film had a low surface orientation coefficient and poor mechanical strength.

[0136] [Table 1A]

[0137] [Table 1B]

[0138] [Table 1C]

[0139] [Table 1D] [Industrial applicability]

[0140] The biaxially oriented polyester film roll of the present invention offers good film productivity even with a high amount of foreign matter in the recycled raw materials, and allows for the production of long rolls. It can be widely applied in the field of packaging films, such as those for food packaging, and is expected to make a significant contribution to industry, given the strong demand for reducing environmental impact these days.

Claims

1. A polyester resin composition comprising polyethylene terephthalate and an inorganic lubricant, wherein the polyester resin composition contains recycled raw materials derived from PET containers, and the polyester resin composition may contain 10 mol% or less of a component selected from the group consisting of isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebatic acid, diethylene glycol, hexamethylene glycol, neopentyl glycol, cyclohexanedimethanol, polyethylene glycol, and polypropylene glycol as copolymerization components, and a biaxially oriented polyethylene terephthalate film roll having a roll length of 1000 m or more, wherein the biaxially oriented polyethylene terephthalate film having a thickness of 5 μm to 100 μm that satisfies the following (1) to (3). (1) The thermal shrinkage rate in the longitudinal direction of the film when measured at 150°C for 30 minutes is 0.5% or more and 2.0% or less. (2) The surface orientation coefficient (ΔP) of the film, calculated from the refractive index measured according to JIS K 7142-1996 Method A, is 0.161 or more and 0.170 or less. (3) Film roll 8000m ２ There are 16 or more foreign objects with a maximum length of 1.0 mm or more per sample.

2. The biaxially oriented polyethylene terephthalate film roll according to claim 1, characterized in that the recycled raw material derived from the PET container according to claim 1 is a mechanically recycled polyester resin and / or a chemically recycled polyester resin.

3. The biaxially oriented polyethylene terephthalate film roll according to claim 1 or 2, characterized in that the thickness variation per 800 mm in the film width direction is 18% or less.

4. A biaxially oriented polyethylene terephthalate film roll according to any one of claims 1 to 3, characterized in that the film longitudinal breaking strength is 180 MPa or more and 260 MPa or less, and the elongation at break is 80% or more and 170% or less.

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