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 in a roll shape. More specifically, the present invention relates to a biaxially oriented polyester film roll that uses a recycled raw material derived from PET containers, is friendly to the global environment, has good film-forming properties even when using a recycled raw material derived from PET containers with many foreign substances, and is excellent in productivity.

Background Art

[0002] Aromatic polyesters typified by polyethylene terephthalate (PET) have excellent mechanical properties, chemical resistance, etc., and are widely used as molded products such as fibers and films. In particular, PET resin is inexpensive and also excellent in terms of hygiene, so it is widely used as food containers and beverage containers. Due to the recent increase in environmental problems and the aspect of resource conservation, used PET containers have been recycled for a long time, and their utilization methods have attracted attention.

[0003] Also, it is said that using a recycled raw material derived from PET containers leads to CO2 reduction, and there is a desire to increase the usage rate of the recycled raw material derived from PET containers as much as possible from the perspective of the global environment.

[0004] The recycled raw material derived from PET containers is produced by collecting A-PET used in beverage PET bottles and containers for salads, vegetables, etc. However, since it is made from collecting materials that have gone into the market and become garbage, the amount of foreign substances contained in the raw material is larger compared to PET raw materials derived from fossil fuels. Therefore, the resulting biaxially oriented polyester film has many breaks caused by foreign substances, and the problem is that productivity deteriorates. The foreign substances mentioned here refer to substances other than PET resin, such as the label strips of PET bottles, gravel, and chemicals such as pesticides and insecticides that consumers filled in PET bottles. In order to suppress breaks caused by foreign substances, there is a method of forming a film by passing the molten resin through a filter with a high filtration accuracy. By this means, since foreign substances are sufficiently removed, breaks caused by foreign substances are reduced, but clogging occurs due to the deposition of foreign substances on the filter. Therefore, it is necessary to replace the filter at a fast cycle, and as a result, productivity deteriorates. Furthermore, there is also a method of removing foreign substances step by step by using filters with different pore sizes in multiple times, but the melting line becomes long, the molecular weight of the recycled raw material decreases, and as a result, the mechanical strength of the resulting biaxially oriented polyester film also decreases. On the other hand, if only the clean PET containers without dirt, etc. are selected from the collected PET containers and used as recycled raw materials, the problem of foreign substances can be solved. However, it is bad for the environment if dirty PET containers cannot be recycled.

[0005] Patent Document 1 discloses a biaxially oriented polyester film using a recycled raw material of PET bottles. In Patent Document 1, the filter back pressure increase coefficient of the recycled raw material is suppressed to be equivalent to that of PET raw materials derived from fossil fuels, and the resulting biaxially oriented polyester film also has few foreign substances. However, when only the clean collected PET containers are selected and used, the environmental countermeasure effect is insufficient. Also, even when a sufficient filtration process is carried out during the production of the recycled raw material, it is expected that the filter replacement cycle will be shortened and productivity will decrease.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-65282 [Disclosure of the Invention] [Problems to be Solved by the Invention]

[0007] 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 film roll formed by winding a biaxially oriented polyester film that uses a recycled raw material derived from a PET container, has good productivity of the obtained film even when the amount of foreign matter in the recycled raw material is large, can be elongated without breakage, and is environmentally friendly to the global environment. [Means for Solving the Problems]

[0008] As a result of intensive studies by the present inventors, even when a recycled raw material derived from a PET container is used as a raw material, by selecting a specific stretching condition range and controlling the surface orientation degree of the film, good productivity of the obtained film can be obtained even when the amount of foreign matter in the recycled raw material is large, and it has been found that it can be elongated without breakage, leading to the present invention.

[0009] That is, the present invention has the following configuration. [1] A biaxially oriented polyethylene terephthalate film roll formed by winding a biaxially oriented polyethylene terephthalate film that uses a recycled raw material derived from a PET container and satisfies the following (1) to (3). (1) The thermal shrinkage rate in the longitudinal direction of the film 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 based on JIS K 7142-1996 Method A is 0.16 or more and 0.17 or less. (3) The number of foreign matters having a maximum length of 1.3 mm or more per 1000 m of the film roll is 1 or more. 2 ​[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 elongation at break is 80% or more and 170% or less. [5] The film roll 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 environmentally friendly, has good film productivity, and can be made longer can be obtained.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

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, the container form of the recycling source 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 a 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 repolymerization (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 and 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 and 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 and 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 materials derived from PET containers preferably used in the present invention are polyesters produced and molded by ordinary polymerization methods and solid-phase polymerization methods, preferably mainly composed of polyethylene terephthalate, and may contain other polyester components and copolymer components. They may 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 polyesters for ordinary PET bottles. If a film is formed using recycled PET bottle raw materials, the film will contain 1 ppm or more of germanium. However, since it is only the catalyst content, it is usually at most 100 ppm or less, and normally 50 ppm or less.

[0017] Hereinafter, the mechanical recycling polyester resin and the chemical recycling polyester resin will be described.

[0018] [Mechanical Recycling Polyester Resin] The collected used recycled PET bottles are sorted so that other materials and garbage are not mixed, and after removing labels and the like, they are crushed into flakes. These flakes often have foreign substances attached or mixed in. It is also conceivable that consumers fill used PET bottles with chemical substances such as chemicals and solvents. For example, detergents for tableware, insecticides, herbicides, agricultural chemicals, and various oils can be considered. Since normal cleaning cannot sufficiently remove the chemical substances adsorbed on the surface of the PET bottle, it is preferable to perform alkali cleaning. As the solution of the alkali metal hydroxide used in this cleaning process, a sodium hydroxide solution or a potassium hydroxide solution is used. In such a cleaning process, preliminary cleaning may be performed before alkali cleaning. If alkali cleaning is not performed, they will remain as foreign substances in the raw material resin. These will not only be mixed in and cause breakage during film formation, resulting in a decrease in productivity, but also remain as foreign substances in the film, which may cause defects in the appearance of the film and printing failures in the subsequent printing process.

[0019] Although the concentration of the aqueous solution of the alkali metal hydroxide used in the above washing step depends on temperature, time, and stirring conditions, it is usually in the range of 1 to 10% by weight. Also, the time required for washing is in the range of 10 to 100 minutes, and it is preferably carried out with stirring to enhance the effect.

[0020] Following the alkali washing, it is preferable to perform rinsing and drying. The alkali washing and rinsing may be repeated several times. If the aqueous solution component of the alkali metal hydroxide used for washing remains in the flakes in the alkali washing step, it may affect the physical properties of the finally obtained film by passing through the melt extrusion step in the subsequent pellet granulation step or the melt extrusion step during film formation.

[0021] Preferably, the concentrations of sodium and potassium in the film obtained using recycled polyester resin from the market and society, including these PET bottles, are 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 concentration of sodium or potassium contained in the film is higher than 150 ppm, it is not preferable because the heat resistance and thermal stability of the film may decrease or it may become colored. Also, if it is completely absent, the effect of suppressing the formation of diethylene glycol, etc., becomes weak, so it is not preferable. Also, recycled polyester resin from the market and society, including PET bottles, may contain a small amount of these components, and it is difficult to make it completely absent.

[0022] In such a washing process, a part of the PET bottle flakes is hydrolyzed by an aqueous solution of an alkali metal hydroxide. Also, the degree of polymerization of the resin decreases due to the heating during the molding of the PET bottle. Furthermore, when the recycled PET bottles are pulverized for reuse and then melted and pelletized again, the degree of polymerization decreases due to the influence of heat and moisture added during the process. Although it can be reused as it is, depending on the intended use, if the degree of polymerization decreases, the moldability, strength, transparency, heat resistance, etc. may be inferior, and it may not be possible to reuse it as it is.

[0023] In such a case, in order to recover the decreased degree of polymerization, it is preferable to perform solid-phase polymerization on the flakes of the pulverized and washed PET bottles or the melted and pelletized flakes.

[0024] The solid-phase polymerization step can be carried out by continuously performing solid-phase polymerization on the washed flakes or the flakes melted and pelletized by melt extrusion in an inert gas such as nitrogen gas or noble gas at 180 - 245 °C, preferably 200 - 240 °C.

[0025] Finally, as a recycled polyester resin including PET bottles, it is desirable to adjust the conditions of the flakes or pellets under the condition that the intrinsic viscosity is 0.55 - 0.90 dl / g, preferably 0.60 - 0.85 dl / g.

[0026] The process of pelletizing the flakes will be described. The flakes are melted, extruded, cooled, and pelletized using an extruder having a degassing means and a filtering means.

[0027] In the melting process in the extruder, it can usually be carried out by melt-kneading at 260 to 300 °C, preferably 265 to 295 °C. The crushed flakes of the PET bottles to be fed need to be sufficiently dried, and it is preferable to carry out drying under conditions of 5 to 200, preferably 10 to 100 ppm, and more preferably 15 to 50 ppm. When there is a lot of moisture in the flakes, the hydrolysis reaction proceeds in the melting process, and the intrinsic viscosity of the obtained polyester resin decreases. As the degassing means, it is preferable to have at least one vacuum vent in the melting zone of the resin.

[0028] Further, the extruder preferably has a filter as a filtering means that can filter and remove solid foreign matters having a particle size of 25 μm or more, preferably 15 μm or more, and more preferably 10 μm or more in the molten resin.

[0029] The molten resin that has passed through the filter passes through a die, is cooled in water, and then cut into pellets of a desired shape and granulated. [Polyester Resin Composition] The biaxially oriented polyester film in the present invention is composed of a polyester resin composition containing the following polyester resin as a main component. 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. For example, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate can be mentioned, and polyethylene terephthalate is preferable from the viewpoints of mechanical properties, heat resistance, cost, etc. The main component here means that the 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] In addition, other components may be copolymerized with these polyester resins as long as the object of the present invention is not impaired. Specifically, examples of the copolymerization component include, as the dicarboxylic acid component, isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid, and ester-forming derivatives thereof. Examples of the diol component include diethylene glycol, hexamethylene glycol, neopentyl glycol, and cyclohexanedimethanol. Also included are polyoxyalkylene glycols such as polyethylene glycol and polypropylene glycol. The copolymerization amount is preferably within 10 mol% per repeating unit constituting the copolymer, more preferably within 5 mol%, and most preferably 3 mol% or less.

[0031] 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 lower limit of the filter back pressure increase coefficient is preferably 10 MPa / kg·cm 2 and more preferably 20 MPa / kg·cm 2 and particularly preferably 30 MPa / kg·cm 2 is. Here, the filter back pressure increase coefficient refers to the clogging resistance of the filtration filter when the resin is melt-extruded and is obtained by the following formula. K = ΔP / (Q / S) Here, K: filter back pressure increase coefficient, ΔP = P1 - P0 P1: pressure after 4 hours of extrusion (MPa), P0: pressure at the start of extrusion (MPa), Q: extrusion discharge amount (kg / hr), S: filter filtration area (cm 2 )

[0032] When the filter back pressure increase coefficient during melt extrusion under the above-described conditions is 10 MPa / kg·cm 2 or more, it indicates that the recycled raw material is substantially a state where PET containers are not sorted, and sufficient environmental response effects can be obtained. 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] [Chemically recycled polyester resin] The method for producing the chemically recycled polyester resin used in the present invention is not particularly limited. Specifically, for example, as described in JP-A-2000-169623, after sorting, pulverizing, and washing the collected used PET bottles to remove foreign matters, depolymerization is performed to decompose and purify them into raw materials or intermediate raw materials of PET resin, and then polymerized to obtain a new PET resin. For 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 chemically recycled polyester resin is characterized in that foreign matters 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 above-mentioned mechanically recycled polyester resin, it is excellent in hygiene and can be particularly preferably used for food packaging applications.

[0034] The chemical recycling polyester resin used in the present invention uses a bale obtained by reducing the volume and compressing used PET bottles as a starting material. This PET bottle bale is manufactured by a known method currently adopted by municipalities. Instead of the PET bottle bale, other polyethylene terephthalate waste or PET bottle flakes can be used as the starting material.

[0035] The PET bottle bale obtained by reducing the volume and compressing PET bottle waste is put into a crusher, and warm water or normal temperature water or warm water or normal temperature water containing a detergent is injected for pulverization in water.

[0036] Next, the mixture of PET bottle flakes and washing water discharged from the crusher is immediately subjected to specific gravity separation to separate metal, stone, glass, sand and flakes. Then, the flakes and the washing water are separated, and the flakes are rinsed with ion-exchanged water and centrifugally dehydrated.

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

[0038] After the depolymerization reaction is completed, the mixed solution of crude BHET and crude ethylene glycol is cooled and filtered to remove unreacted linear and cyclic oligomers as high melting point precipitates, coagulates of residual foreign plastics other than polyethylene terephthalate, and solid foreign matters such as metals. Then, adsorption and ion exchange treatment are carried out to remove colored substances and dissolved ions, thereby removing foreign matters contained in the crude BHET.

[0039] A distillation and evaporation operation is performed on the two-component mixed solution of crude BHET and crude ethylene glycol obtained through the previous pre-purification process to separate and distill ethylene glycol to obtain concentrated BHET, or the two-component mixed solution is cooled to 10°C or lower to crystallize BHET, and then ethylene glycol and BHET are separated by solid-liquid separation to obtain concentrated BHET. This concentrated BHET is vacuum-evaporated at a temperature exceeding 190°C and not exceeding 250°C, and with the residence time of the concentrated BHET in the evaporator being 10 minutes or less, 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 a high-purity polyethylene terephthalate polymer.

[0041] Among the polyester resins constituting the biaxially oriented polyester film of the present invention, as a method for producing a polyester resin derived from fossil fuels other than the mechanically recycled polyester resin and the chemically recycled polyester resin, first, using the aforementioned dicarboxylic acid or its ester-forming derivative and diol or its ester-forming derivative as the main starting materials, an esterification or transesterification reaction is carried out according to a conventional method, and then a polycondensation reaction is carried out under high temperature and reduced pressure. Examples of such methods include those produced in this way.

[0042] Regarding the intrinsic viscosity of the polyester resin constituting the biaxially oriented polyester film of the present invention from the viewpoints of film-forming properties and recyclability, etc., a range of 0.50 to 0.90 dl / g is preferable, and more preferably it is in the range of 0.55 to 0.80 dl / g.

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

[0044] When the entire biaxially oriented polyester film of the present invention is 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 lubricant can adjust the coefficient of kinetic friction of the film, and examples thereof include inorganic lubricants such as silica, calcium carbonate, and alumina, as well as organic lubricants. Silica and calcium carbonate are preferred, and among them, porous silica is most preferred from the viewpoint of achieving both transparency and slipperiness.

[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 it 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 setting it to 10,000 ppm by mass or less, the transparency of the film can be improved.

[0047] [Method for producing biaxially oriented polyester film] As a method for obtaining the biaxially oriented polyester film of the present invention, there is no particular limitation, and it can be appropriately selected, such as the T-die method or the inflation method.

[0048] The film of the present invention may have a single-layer structure of at least one layer, or 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, more preferably 20°C or lower. When it is 40°C or higher, the crystallinity when the molten polyester resin composition cools and solidifies does not become too high, stretching becomes easier, and a decrease in transparency due to crystallization can also be suppressed. The lower limit of the temperature of the cooling roll is preferably 0 °C. When it is 0 °C or higher, the crystallization inhibition effect when the molten polyester resin composition cools and solidifies can be sufficiently exerted. Further, when the temperature of the cooling roll is in the above range, it is preferable to lower the humidity of the environment near the cooling roll to prevent dew 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, it is 400 μm or less.

[0051] Next, the stretching method will be described. The stretching method can be 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. When it is 110 °C or higher, the stretching stress can be lowered, so that breakage due to foreign matter can be suppressed. The upper limit of the stretching temperature in the MD direction is preferably 140 °C, more preferably 130 °C, and particularly preferably 120 °C. When it is 140 °C or lower, not only can the stretching stress be increased due to crystallization and as a result, breakage due to foreign matter can be suppressed, but also the mechanical strength of the film becomes good.

[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 more, not only does the mechanical strength of the film become good, but also the thickness unevenness becomes good, leading to an improvement in the winding quality when made into a roll. The upper limit of the stretching ratio in the MD direction is preferably 4.0 times, more preferably 3.8 times, and particularly preferably 3.6 times. When it is 4.0 times or less, the stretching stress can be lowered, so that breakage due to foreign matter can be suppressed.

[0054] It is preferable that there is 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%. When it is 1% or more, the amorphous component in the film is relaxed, the stretching stress in the subsequent TD stretching step can be reduced, and as a result, breakage due to foreign matter can be suppressed. The upper limit of the MD relaxation rate is preferably 10%, more preferably 8%, and particularly preferably 6%. When it is 10% or less, wrinkles due to shrinkage can be suppressed, the quality of the film can be improved, and moreover, a decrease in mechanical strength due to orientation relaxation can be suppressed. The method of MD relaxation is not particularly limited, and examples thereof include a method in which relaxation treatment is performed using a speed difference between rolls after heating with a hot air heater.

[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. When it is 110°C or higher, the stretching stress can be reduced, so breakage due to foreign matter can be suppressed. The upper limit of the stretching temperature in the TD direction is preferably 140°C, more preferably 130°C, and particularly preferably 120°C. When it is 140°C or lower, the stretching stress increases due to crystallization, and as a result, not only can breakage due to foreign matter be suppressed, but the mechanical strength of the film also becomes good.

[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 more, not only does the mechanical strength of the film become good, but also the thickness unevenness becomes good, leading to an improvement in the winding quality when made into a roll. The upper limit of the draw ratio in the TD direction is preferably 5.0 times, more preferably 4.5 times, and particularly preferably 4.0 times. When it is 5.0 times or less, the drawing stress can be reduced, so that breakage due to foreign matter can be suppressed.

[0057] The draw pattern in the TD direction is preferably logarithmic or multi-stage drawing. Specifically, as described in FIGS. 1 and 2, the logarithmic TD draw pattern is a TD draw pattern that draws largely in the first half of the drawing and gently in the second half of the drawing compared to the normal linear pattern. By using such a TD draw pattern, most of the drawing can be completed in the first half with a low film drawing stress, and the drawing stress applied during drawing can be reduced. As a result, breakage due to foreign matter can be suppressed.

[0058] Next, the details when adopting the logarithmic TD draw pattern will be described. The logarithmic TD draw pattern refers to the TD draw pattern that draws largely in the first half of the drawing and gently in the second half of the drawing as described above. When the number of TD draw zones is N and the draw angle θN in the Nth draw area is defined, the draw angle in each draw zone is drawn in the width direction under the condition that θn > θn+1. (When θn = θn+1, it is the drawing in a normal straight line.) The amount of change when the stretching angle changes from the stretching angle θn to the stretching angle θn+1 can also be appropriately selected in order to obtain the target performance. However, when the angle change rate expressed by {(θn - θn+1) / θn}×100 (unit: %) is too large exceeding 50%, in order to stretch to a predetermined maximum magnification, it is inevitably necessary to extremely increase the stretching magnification at the initial stage of TD stretching. As a result, the stretching stress at the initial stage of stretching becomes too large, and conversely, the film forming property may deteriorate. When the angle change rate is 0%, since θ1 = θ2, it 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% or more and 50% or less, more preferably in the range of 1% or more and 30% or less, and particularly preferably in the range of 1.5% or more and 20% or less. 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 with a low film stretching stress, and the stretching stress applied during stretching can be reduced. As a result, breakage due to foreign matter can be suppressed.

[0059] Next, multi-stage stretching in the TD direction will be described. Multi-stage stretching is to perform two or more stretching steps on the normal single-stage stretching, and the stretching stress applied during TD stretching can be reduced. As a result, breakage due to foreign matter can be suppressed.

[0060] The TD multi-stage stretching is preferably two-stage stretching or more and five-stage stretching or less. By multi-stage stretching, it is possible to change each stretching temperature and vary the stretching stress, and it is preferable that the stretching stress during TD stretching can be reduced. As shown in FIG. 2, in multi-stage stretching, it is preferable to adopt a temperature pattern in which a temperature difference of 2°C or more is provided in each stage of stretching and the temperature is decreased from the first stage of stretching to the final stage of stretching. The lower limit of the number of stretching stages is preferably two-stage stretching or more. When it is two-stage stretching or more, the stretching stress can be reduced, and breakage caused by foreign matter can be suppressed. The upper limit of the number of stretching stages is preferably five stages or less. When it is five-stage stretching or less, it is possible to prevent the equipment from becoming too large. Also, when performing multi-stage stretching, zones with a fixed length can be appropriately provided after each stretching stage. By providing a zone with a fixed length after each stretching stage, the internal stress generated during stretching can be relaxed in the fixed-length zone, so that the stretching stress during the next stretching can be further reduced, and breakage of the film can be suppressed.

[0061] The lower limit of the heat setting temperature is preferably 170 °C, more preferably 180 °C, and particularly preferably 190 °C. When it is 170 °C or higher, the heat shrinkage rate can be reduced. The upper limit of the heat setting temperature is preferably 230 °C, more preferably 220 °C, and particularly preferably 210 °C. When it is 230 °C or lower, a decrease in mechanical strength due to embrittlement of the biaxially oriented polyester film can be suppressed.

[0062] The lower limit of the TD relaxation rate is preferably 0.5%, more preferably 1.0%, and particularly preferably 2.0%. When it is 0.5% or higher, the heat shrinkage rate in the TD direction can be kept low. The upper limit of the TD relaxation rate is preferably 10%, more preferably 8%, and particularly preferably 6%. When it is 10% or lower, occurrence of slack etc. can be prevented, and planarity can be improved.

[0063] By adopting the above-described preferred film-forming conditions, a long film can be continuously obtained without breakage in the film-forming of a biaxially oriented polyester film containing foreign matter, and the following preferred film characteristics can be satisfied.

[0064] [Configuration and Characteristics 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 it to 5 μm or more, breakage due to 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 more, the mechanical strength can be kept sufficiently high. The upper limit of ΔP of 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, the stretching stress in the stretching process can be suppressed, and as a result, breakage caused by foreign matters in the stretching process can be suppressed.

[0066] The lower limit of the breaking 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. When it is 180 MPa or more, the mechanical strength of the bagged product becomes sufficient. The upper limit of the breaking 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. When it is 260 MPa or less, breakage caused by foreign matters in the stretching process can be substantially suppressed, and the film-forming property becomes good.

[0067] The lower limit of the elongation at break in the MD direction 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 more, breakage caused by foreign matters in the stretching process can be substantially suppressed, and the film-forming property becomes good. The upper limit of the elongation at break in the MD direction of the biaxially oriented polyester film of the present invention is 170%, more preferably 160%, and particularly preferably 150%. When it is 170% or less, the mechanical strength of the bagged product becomes sufficient.

[0068] The lower limit of the heat 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%. When it is 0.5% or more, it is possible to suppress the film from becoming brittle and the mechanical strength from decreasing. The upper limit of the heat 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, it is possible to substantially suppress breakage caused by foreign matters in the stretching process, and the film-forming property becomes good.

[0069] The upper limit of the thickness unevenness 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%. When it is 18% or less, the winding quality when made into a roll becomes good.

[0070] The number of foreign matters having a maximum length of 1.3 mm or more per 1000 m of the biaxially oriented polyester film roll of the present invention is 1 or more. When there is 1 or more foreign matter having a maximum length of 1.3 mm or more per 1000 m2, these foreign matters tend to cause breakage during stretching under conventional film-forming conditions, making stable film formation difficult. On the other hand, by stretching the film using the film-forming conditions described in the present invention so that the heat shrinkage rate and the surface orientation degree are within a predetermined range, even if foreign matters exist as described above, stable stretching becomes possible. 2 On the other hand, the lower limit of the number of foreign matters having a maximum length of 1.3 mm or more per 1000 m of the biaxially oriented polyester film roll of the present invention is preferably 10 or less. When the number of foreign matters of 1.3 mm or more exceeds 10, the defects after printing increase, and there is a risk of reducing the yield in the secondary processing step. On the other hand, per 1000 m of the biaxially oriented polyester film roll of the present invention 2 The lower limit of the number of foreign matters having a maximum length of 1.3 mm or more is preferably 10 or less. When the number of foreign matters of 1.3 mm or more increases beyond 10, the defects after printing increase, and there is a risk of reducing the yield in the secondary processing step.

[0071] Per 8000 m of the biaxially oriented polyester film roll of the present invention 2The number of foreign substances with a maximum length of 1.0 mm or more per unit area is 16 or more. When there are 16 or more foreign substances with a maximum length of 1.0 mm or more per 8000 m2, there are many causes of breakage in conventional films, making it difficult to produce long continuous films. On the other hand, by stretching the film using the film-forming conditions described in the present invention so that the heat shrinkage rate and the surface orientation degree are within a predetermined range, even if there are foreign substances as described above, stable stretchability can be ensured, and it becomes possible to obtain a long film roll. On the other hand, in an 8000 m 2 The upper limit of the number of foreign substances with a maximum length of 1.0 mm or more per unit area is preferably 80 or less. If the number of foreign substances of 1.0 mm or more exceeds 80, the defects after printing will increase, and there is a risk of reducing the yield of the secondary processing step.

[0072] A printing layer may be laminated on the biaxially oriented polyester film of the present invention. As the printing ink for forming the printing layer, water-based and solvent-based resin-containing printing inks can be preferably used. Examples of the resin 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, antiblocking agents, and antioxidants.

[0073] The printing method for providing the printing 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] A gas barrier layer such as an inorganic thin film layer or a metal foil can be provided on the biaxially oriented polyester film of the present invention as long as the object of the present invention is not impaired.

[0075] When an inorganic thin film layer is used as the gas barrier layer, the inorganic thin film layer is a thin film made of a metal or an inorganic oxide. The material for forming the inorganic thin film layer is not particularly limited as long as it can form a thin film. From the viewpoint of gas barrier properties, inorganic oxides such as aluminum, silicon oxide (silica), aluminum oxide (alumina), and a mixture of silicon oxide and aluminum oxide are preferably mentioned. In particular, from the viewpoint of achieving both flexibility and denseness of the thin film layer, a composite oxide of silicon oxide and aluminum oxide is preferable.

[0076] In this composite oxide, the mixing ratio of silicon oxide and aluminum oxide is preferably in the range of 20 to 70% in terms of the mass ratio of the metal component. On the other hand, when it is 70% or less, the inorganic thin film layer can be made soft, and it is possible to suppress the destruction of the thin film during secondary processing such as printing and lamination and the resulting decrease in gas barrier properties. Here, the silicon oxide referred to here is various silicon oxides such as SiO and SiO2 or a mixture thereof, and the aluminum oxide is various aluminum oxides such as AlO and AL2O3 or a mixture thereof.

[0077] The film thickness of the inorganic thin film layer is usually 1 to 100 nm, preferably 5 to 50 nm. When the film thickness of the inorganic thin film layer is 1 nm or less, more satisfactory gas barrier properties are easily obtained. On the other hand, when it is 100 nm or less, it is advantageous in terms of bending resistance and manufacturing cost.

[0078] As a method for forming an inorganic thin film layer, there are no particular limitations. For example, known vapor deposition methods such as physical vapor deposition (PVD) methods like vacuum evaporation, sputtering, and ion plating, or chemical vapor deposition (CVD) methods can be appropriately employed. Hereinafter, a typical method for forming an inorganic thin film layer will be described using a silicon oxide-aluminum oxide-based thin film as an example. For example, when adopting the vacuum evaporation method, a mixture of SiO2 and Al2O3, or a mixture of SiO2 and Al, etc. is preferably used as the evaporation raw material. Usually, particles are used as these evaporation raw materials, and at that time, it is desirable that the size of each particle is such that the pressure during evaporation does not change, and a preferable particle diameter is 1 to 5 mm. For heating, methods such as resistance heating, high-frequency induction heating, electron beam heating, and laser heating can be adopted. Also, it is possible to introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide gas, water vapor, etc. as reaction gases, or to adopt reactive evaporation using means such as ozone addition and ion assist. Furthermore, the film formation conditions can be arbitrarily changed, such as applying a bias to the object to be vapor-deposited (the laminated film to be subjected to vapor deposition), or heating or cooling the object to be vapor-deposited. Such evaporation materials, reaction gases, the bias of the object to be vapor-deposited, heating and cooling, etc. can be similarly changed when adopting the sputtering method or the CVD method. Furthermore, a printing layer may be laminated on the above inorganic thin film layer.

[0079] When providing an inorganic thin film layer on the biaxially oriented polyester film of the present invention, it is preferable to provide a protective layer on the inorganic thin film layer. The gas barrier layer made of a metal oxide is not a completely dense film, and minute defective portions are scattered. By forming a protective layer by coating a specific resin composition for a protective layer, which will be described later, on the metal oxide layer, the resin in the protective compatible resin composition penetrates into the defective portions of the metal oxide layer, and as a result, the effect that the gas barrier property becomes stable can be obtained. In addition, by using a material having a gas barrier property for the protective layer itself, the gas barrier performance of the laminated film will also be 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 the solvent used for forming the protective layer include aromatic solvents such as benzene and toluene; alcohol solvents such as methanol and ethanol; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate and butyl acetate; and polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.

[0081] Layers of other materials may be laminated on the biaxially oriented polyester film of the present invention. As methods thereof, a method of laminating after producing the biaxially oriented polyester film and a method of laminating during film formation can be adopted.

[0082] The biaxially oriented polyester film of the present invention can be used as a packaging material, for example, by forming a heat-sealable resin layer (also referred to as a sealant layer) called a sealant on the biaxially oriented polyester film. The formation of the sealant layer is usually carried out by an extrusion lamination method or a dry lamination method. As the thermoplastic copolymer for forming the heat-sealable resin layer, any copolymer that can sufficiently exhibit sealant adhesiveness may be used, and polyethylene resins such as HDPE, LDPE, and LLDPE, polypropylene resin, ethylene-vinyl acetate copolymer, ethylene-α-olefin random copolymer, ionomer resin, etc. can be used.

[0083] The sealant layer may be a single-layer film or a multi-layer film, and may be selected according to the required functions. For example, in terms of imparting moisture resistance, a multi-layer film with a resin such as ethylene-cyclic olefin copolymer or polymethylpentene interposed can be used. Further, various additives such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier may be blended in the sealant layer. The thickness of the sealant layer is preferably 10 to 100 μm, 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 roll width of the polyester film roll of the present invention is preferably 3000 mm or less, and more preferably 2500 mm or less. When the width of the polyester film roll exceeds 3000 mm, handling becomes difficult, and wrinkles are likely to occur in the film due to the deflection of the roll. Also, the lower limit of the winding length of the polyester film roll of the present invention is preferably 1000 m or more, more preferably 2000 m or more, and even more preferably 4000 m or more from the viewpoint of productivity in the secondary processing step. On the other hand, the upper limit of the winding length of the polyester film roll of the present invention is 100000 m, preferably 80000 m, and more preferably 70000 m. When the winding length of the polyester film roll exceeds 100000 m, the weight of the roll increases and handling becomes difficult.

[0085] In addition, for the core around which the film is wound in the polyester film roll of the present invention, a paper tube, a plastic core, a metal core, etc. are preferably used and can be appropriately selected according to the application. The gap difference in the width direction of the core after removing the film from the polyester film roll of the present invention is preferably 0.5 mm or less. When a paper tube is used particularly as the core, if it is stored after winding the film, the paper tube is deformed (distorted) due to film distortion, natural shrinkage, etc. At that time, if the distortion difference (gap difference in the width direction) of the paper tube in the width direction is large, wrinkles will occur on the core side of the film roll, which is not preferable. Therefore, the gap difference in 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] When a paper tube is used as the core of the polyester film roll of the present invention, the flat compressive strength of the paper tube of the core after removing the film from the film roll is preferably 1700 N / 100 mm or more. If the compressive strength is lower than 1700 N / 100 mm, the paper tube will be distorted by the internal stress applied after winding the film, and wrinkles will occur in the roll core part, which is not preferable. Preferably it is 1800 N / 100 mm or more, and more preferably 1900 N / 100 mm or more. The higher the compressive strength, the more preferable. As means for obtaining a high flat compressive strength of the paper tube, methods such as increasing the thickness of the paper tube and using a hard paper tube or an ultra-hard paper tube designed to be of high strength can be mentioned.

[0087] In addition, in the heat-shrinkable polyester film roll of the present invention, in order to make the gap difference of the paper tube after removing the film from the film roll as described above 0.5 mm or less, the gap difference in the width direction of the paper tube before winding the film used for winding is preferably 0.3 mm or less. If the distortion difference in the width direction of the paper tube is 0.4 mm or more, the position where the film is distorted when winding the film will be in an oblique direction, so wrinkles (winding core wrinkles) are likely to occur, which is not preferable. The gap difference in the width direction of the paper tube is more preferably 0.2 mm or less, and even more preferably 0.1 mm or less. As means for reducing the gap difference of the paper tube, using a paper tube with high hardness and difficult to deform by vibration during transportation such as transportation, storing the paper tube in a moisture-proof bag until use so that the paper tube does not deform by absorbing moisture, and storing the paper tube in a room with constant temperature and humidity so that it does not deform by absorbing moisture can be mentioned.

[0088] In addition, the average value of the winding hardness in the width direction of the surface layer of the polyester film roll of the present invention is preferably 500 or more and 850 or less. If it is less than 500, the winding state will be a soft winding and the winding core wrinkles will be in a good direction, but misalignment will occur on the end face of the film roll, which is not preferable. If the winding hardness is higher than 850, the winding state will be a hard winding, and wrinkles are likely to occur due to thickness unevenness, which is not preferable. The average value of the winding hardness in the width direction of the surface layer of the film roll is preferably 550 or more and 800 or less, and more preferably 600 or more and 750 or less. Particularly preferably, it exceeds 650 and is 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 increase coefficient of recycled raw material] After drying the recycled raw material pellets at 135°C for 12 hours, they were extruded under the conditions of a temperature of 285°C, a filter filtration diameter of 20 μm, a discharge rate of 6 g / min, and a discharge time of 4 hours, and the filter back pressure increase coefficient was determined by the following formula. K = ΔP / (Q / S) Here, K: filter back pressure increase coefficient, ΔP = P1 - P0 P1: pressure after 4 hours of extrusion (MPa), P0: pressure at the start of extrusion (MPa), Q: extrusion discharge rate (kg / hr), S: filter filtration area (cm 2 )

[0091] [Thickness of biaxially oriented film] Measurement was carried out 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 by 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 sample of 5 mm in length × 5 mm in width was cut out from the central position in the film width direction. For the sample, in accordance with JIS K 7142-1996 Method A, using a sodium D line as the light source and diiodomethane as the contact liquid, the refractive index (Nx) in the film longitudinal direction, the refractive index (Ny) in the width direction, and the refractive index (Nz) in the thickness direction were measured with an Abbe refractometer (manufactured by Atago Co., Ltd., NAR-1T). The surface orientation coefficient (ΔP) was calculated by the following formula. Surface orientation coefficient (ΔP) = [(Nx + Ny) / 2] - Nz

[0094] [Tensile Strength of Biaxially Oriented Film] In accordance with JIS K 7127, a test sample with a width of 15 mm and a length of 100 mm was cut out in the longitudinal direction of the film. The test sample was subjected to a tensile test using a tensile testing machine (Autograph AG-I manufactured by Shimadzu Corporation) under the 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 Property of Biaxially Oriented Film] When it was possible to continuously form a film of 10,000 m without breakage during film formation of each example and comparative example, it was evaluated as ○, and when breakage occurred and it was impossible to continuously form a film of 10,000 m, it was evaluated as ×.

[0096] [Foreign Matter Evaluation of Biaxially Oriented Film (1000 Square Meters)] A film roll wound with a width of 800 mm and a roll length of 1250 m (1000 square meters) was rewound using a rewinder. During rewinding, the number of defects was investigated using a defect detector (F MAX MR manufactured by FUTEC). The number of defects with the longest part of the defect being 1.3 mm or more in size was determined. Less than 1 defect with a size of 1.3 mm or more: C 1 to 10 defects with a size of 1.3 mm or more: A

[0097] [Foreign Matter Evaluation of Biaxially Oriented Film (8000 Square Meters)] A film roll wound with a width of 800 mm and a roll length of 10,000 m (8000 square meters) was rewound using a rewinder. During rewinding, the number of defects was investigated using a defect detector (F MAX MR manufactured by FUTEC). The number of defects with the longest part of the defect being 1.0 mm or more in size was determined. 15 or fewer defects with a size of 1.0 mm or more: C 16 to 80 defects with a size of 1.0 mm or more: A

[0098] [Evaluation of Thickness Non-uniformity in Width Direction] Sampled 800 mm in the width direction and 40 mm in the longitudinal direction from the film roll, and continuously measured the thickness in the width direction at 5 m / s using a film tester continuous thickness measuring device (manufactured by Fuji Works). The maximum thickness during measurement was designated as Tmax., the minimum thickness as Tmin., and the average thickness as Tave., and the thickness unevenness in the film width direction was calculated from the following formula. Thickness unevenness = {(Tmax. - Tmin.) / Tave.} × 100 (%)

[0099] [Evaluation of filter clogging] When the film of each example and comparative example could be continuously formed for one week without changing the filter during film formation, it was evaluated as ○, and when the filter became clogged within less than one week and continuous film formation became difficult, it was evaluated as ×.

[0100] (Polyester A: Mechanically recycled polyester resin derived from PET containers) After washing away foreign substances such as the content residue from the PET container, it was pulverized to obtain flakes. The obtained flakes were washed with a 3.5 wt% sodium hydroxide solution under stirring under the conditions of a flake concentration of 10 wt%, 85 °C, and 30 minutes. After alkali washing, the flakes were taken out, and washing was performed under stirring using distilled water under the conditions of a flake concentration of 10 wt%, 25 °C, and 20 minutes. This water washing was repeated two more times by replacing it with distilled water. After water washing, the flakes were dried, and then 0.10 part by mass of silica particles with an average particle diameter of 2.5 μm was added to the flakes. Then, it was melted with an extruder, and the filter was sequentially changed to finer ones with different mesh sizes to filter out finer foreign substances two more times, and finally filtered with a filter having the smallest mesh size of 50 μm to obtain Polyester A. The back pressure increase coefficient of Polyester A was 96 MPa / kg·cm 2 It was.

[0101] (Polyester B: Mechanically recycled polyester resin derived from PET containers) Polyester B was obtained in the same manner as Polyester A. The back pressure increase coefficient of Polyester B was 64 MPa / kg·cm 2 It was.

[0102] (Polyester C: Mechanically recycled polyester resin derived from PET containers) Polyester C was obtained in the same manner as Polyester A. The back pressure increase coefficient of Polyester C was 32 MPa / kg·cm 2 .

[0103] (Polyester D: Mechanically recycled polyester resin derived from PET containers) Polyester D was obtained in the same manner as Polyester A. The back pressure increase coefficient of Polyester D was 10 MPa / kg·cm 2 .

[0104] (Polyester E: Mechanically recycled polyester resin derived from PET containers) Polyester E was obtained in the same manner as Polyester A, except that only clean PET containers were selected. The back pressure increase coefficient of Polyester E was 8 MPa / kg·cm 2 .

[0105] (Polyester F: Mechanically recycled polyester resin derived from PET containers) Polyester F was obtained in the same manner as Polyester A. The back pressure increase coefficient of Polyester F was 105 MPa / kg·cm 2 .

[0106] (Polyester G: Chemically recycled polyester resin derived from PET containers) As the chemically recycled polyester resin regenerated from PET bottles used in the production of the biaxially oriented polyester film described below, the one synthesized using the following method was used. The separately collected and recycled PET bottle flakes were put into a wet grinder, and a mixture of 500 g of liquid kitchen detergent added to 1,000 liters of water was circulated in the wet grinder while pulverizing. Metals, sand, glass, etc. with a large specific gravity were precipitated by a specific gravity separator connected to the grinder, and flakes were taken out from the upper layer. These flakes were rinsed with pure water and centrifugally dehydrated to obtain recovered flakes.

[0107] 30 kg of the melted recovered flakes in an undried state were charged into a mixed solution of 150 kg of ethylene glycol and 150 g of zinc acetate dihydrate that had been preheated in an autoclave equipped with a stirrer. After removing fractions with a boiling point lower than that of ethylene glycol, such as water and acetic acid, the reaction was carried out at a temperature of 195 - 200 °C for 4 hours using a reflux condenser.

[0108] After the reaction was completed, the temperature of the reactor contents was lowered to 97 - 98 °C, and hot filtration was performed with a filter to remove suspended matter and precipitates.

[0109] The filtrate after hot filtration was further cooled. After confirming that the crude BHET was completely dissolved, it was passed through an activated carbon bed and then an anion / cation exchange mixed bed at 50 - 51 °C over 30 minutes for pre-purification treatment.

[0110] The above pre-purified treatment solution was charged again into a stirred autoclave and heated to distill off the excess ethylene glycol at 198 °C under normal pressure, obtaining a molten solution of concentrated BHET.

[0111] The obtained molten solution of concentrated BHET was allowed to cool naturally while stirring in a nitrogen gas atmosphere, and then taken out of the autoclave to obtain fine piece blocks of concentrated BHET.

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

[0113] Using this purified BHET as a raw material, melt polymerization was carried out to obtain a chemical recycling polyester resin G with an intrinsic viscosity of 0.696 dl / g. The back pressure increase coefficient of polyester G was 7 MPa / kg·cm 2 It was.

[0114] [Example 1] Polyester A was fed into an extruder. After melting the resin in the extruder at 280 °C, the molten resin was passed through a filter mesh of 50 μm and then through a filter mesh of 100 μm. Subsequently, it was cast from a T-die at 280 °C and adhered to a cooling roll at 10 °C by an electrostatic adhesion method 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. The film immediately after longitudinal stretching was passed through a heating furnace set at 95 °C with 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. Subsequently, it was passed through a tenter and stretched 4.6 times in the TD direction at 120 °C, and a heat setting treatment at 210 °C for 3 seconds and a relaxation treatment of 5% for 1 second were carried out 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. Also, the physical properties and evaluation results of the obtained film are shown in Table 1.

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

[0116] [Example 3] The relaxation rate immediately after longitudinal stretching was changed to 0%, and the stretching pattern in the tenter was changed to a logarithmic shape. A biaxially oriented polyester film with a thickness of 12 μm was obtained in the same manner as in Example 1. The refraction angle θ1 of the first stage of the tenter was adjusted to 12.6°, the refraction angle θ2 of the second stage was adjusted to 8.2°, and the angle change rate was adjusted to 34.9%. The stretching ratio was set so that the total stretching ratio was equivalent to that of 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 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] Hereinafter, all of Example 5 shall be read as Reference Example 1. [Example 5] A biaxially oriented polyester film with a thickness of 12 μm was obtained by film formation 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 film formation 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 film formation 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 film formation 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] Hereinafter, all of Example 9 shall be read as Reference Example 2. [Example 9] A biaxially oriented polyester film with a thickness of 12 μm was obtained by film formation 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 film formation 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 film formation 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 meshes through which the molten resin passes were changed to 20 μm and 50 μm, and the relaxation rate immediately after longitudinal stretching was changed to 0%. Clogging of the filter mesh occurred, and it was defective.

[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 meshes through which the molten resin passes were 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%. Clogging of the filter mesh occurred, and it was defective.

[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 matters and no clogging of the filter mesh, but since clean PET containers were selected as the recycled raw material, the environmental response effect 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 breaks due to foreign matters and poor film-forming properties.

[0130] [Comparative Example 5] A biaxially oriented polyester film with a thickness of 12 μm was obtained by film formation 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 surface orientation coefficient and poor mechanical strength.

[0131] [Comparative Example 6] A biaxially oriented polyester film with a thickness of 12 μm was obtained by film formation 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 breaks caused by foreign matters and poor film-forming properties.

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

[0133] [Comparative Example 8] A biaxially oriented polyester film with a thickness of 12 μm was obtained by film formation in the same manner as in Example 1, except that the longitudinal stretching ratio was set 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 film formation in the same manner as in Example 1, except that the transverse stretching ratio was set to 5.1 times. The obtained biaxially oriented polyester film had many breaks caused by foreign matters and poor film-forming properties.

[0135] [Comparative Example 10] A biaxially oriented polyester film with a thickness of 12 μm was obtained by film formation in the same manner as in Example 1, except that the transverse stretching ratio was set 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 has good film productivity and can be made into a long length even when there is a large amount of foreign matter in the recycled raw material, and can be widely applied in the field of packaging films such as for food packaging. Since reduction of environmental impact has been strongly desired recently, it is expected to greatly contribute to the industrial world.

Claims

1. The polyester resin composition comprises a polyester resin composition containing recycled raw materials derived from PET containers, the polyester composition being a polyester resin composition comprising polyethylene terephthalate which 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, sebacic acid, diethylene glycol, hexamethylene glycol, neopentyl glycol, cyclohexanedimethanol, polyethylene glycol, and polypropylene glycol as a copolymerization component, and an inorganic lubricant; and the biaxially oriented polyethylene terephthalate film roll is obtained by winding up a biaxially oriented polyethylene terephthalate film having a thickness of 5 μm or more and 100 μm or less, which satisfies the following (1) to (3), and has a winding length of 1000 m or more. (1) The heat 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 plane orientation coefficient (ΔP) of the film calculated from the refractive index measured based on JIS K 7142-1996 Method A is 0.161 or more and 0.170 or less. (3) 8,000m film roll ２ There are 16 or more foreign objects with a maximum length of 1.0 mm or more per unit.

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

4. 4. The biaxially oriented polyethylene terephthalate film roll according to claim 1, wherein the breaking strength in the longitudinal direction of the film is 180 MPa or more and 260 MPa or less, and the breaking elongation is 80% or more and 170% or less.

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