JP2023056047A - Biaxially oriented polyethylene terephthalate film roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: 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

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to a biaxially oriented polyethylene terephthalate film roll obtained by winding a biaxially oriented polyester film into a roll. More specifically, a biaxially oriented polyester film 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 containing many foreign substances, and has excellent productivity. Regarding rolls.

Aromatic polyesters represented by polyethylene terephthalate (PET) have excellent mechanical properties, chemical resistance, etc., and are widely used as molded articles such as fibers and films. In particular, PET resin is inexpensive and excellent in terms of sanitation, so it is widely used as food containers and beverage containers. In recent years, from the standpoint of increasing environmental problems and saving resources, used PET containers have been recycled for some time, and attention is being focused on how to utilize them.

It is also said that the use of recycled raw materials derived from PET containers will lead to a reduction in CO ₂ , and there is a demand to increase the usage rate of recycled raw materials derived from PET containers even if only a little, from the standpoint of the global environment.

Recycled raw materials derived from PET containers are produced by recovering A-PET used in PET bottles for beverages and containers for salads, vegetables, and the like. However, since waste materials on the market are collected and used as recycled raw materials, the amount of foreign matter contained in the raw materials is greater than that of PET raw materials derived from fossil fuels. Therefore, the resulting biaxially oriented polyester film is often broken due to foreign matter, and the problem is that the productivity deteriorates. The term "foreign matter" as used herein refers to substances other than PET resin, such as band labels of PET bottles, gravel, and chemicals such as pesticides and insecticides that consumers have filled in PET bottles. In order to suppress breakage caused by foreign matter, there is a method of forming a film by passing a molten resin through a filter with high filtration accuracy. By this means, the foreign matter is sufficiently removed, so breakage caused by the foreign matter is reduced, but clogging occurs due to accumulation of the foreign matter on the filter. Therefore, it is necessary to replace the filter at a short period, resulting in deterioration of productivity. Furthermore, there is also a method of stepwise removal of foreign matter by using filters with different mesh sizes for multiple times. It also leads to a decrease in the mechanical strength of the axially oriented polyester film.
On the other hand, the problem of foreign matter can be solved by sorting out only the collected PET containers that are free from stains and the like and using them as recycled raw materials. However, it is bad for the environment if dirty PET containers cannot be recycled.

Patent Document 1 discloses a biaxially oriented polyester film using recycled PET bottle raw materials. In Patent Document 1, the coefficient of increase in filter back pressure of the recycled raw material is suppressed to the same level as that of the fossil fuel-derived PET raw material, and the resulting biaxially oriented polyester film also contains less foreign matter. However, when only clean PET containers are sorted out and used, the effect of environmental measures is insufficient. In addition, even if 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 the productivity will be reduced.

JP 2014-65282 A

The present invention has been made against the background of such problems of the prior art. That is, the object of the present invention is to provide a film using recycled raw materials derived from PET containers. To provide a film roll obtained by winding an eco-friendly biaxially oriented polyester film.

As a result of intensive studies by the present inventors, even if 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 plane orientation degree of the film, the amount of foreign matter in the recycled raw material The inventors have found that the productivity of the film obtained is good even if there is a large amount of the film, and that the film can be elongated without breakage, leading to the present invention.

That is, the present invention consists of the following configurations.
[1] A biaxially oriented polyethylene terephthalate film roll obtained by winding a biaxially oriented polyethylene terephthalate film satisfying the following (1) to (3) using a recycled raw material derived from a PET container.
(1) Thermal shrinkage 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 plane orientation coefficient (ΔP) of the film calculated from the refractive index measured according to JIS K 7142-1996 A method is 0.16 or more and 0.17 or less.
(3) The number of foreign matter with a maximum length of 1.3 mm or more per 1000 m ² of film roll is 1 or more.
[2] The biaxially oriented polyethylene terephthalate film roll of [1], wherein the recycled raw material derived from the PET container of [1] is a mechanically recycled polyester resin and/or a chemically recycled polyester resin.
[3] The biaxially oriented polyethylene terephthalate film roll of [1] or [2], wherein the thickness unevenness around 800 mm in the film width direction is 18% or less.
[4] The biaxially oriented polyethylene according to any one of [1] to [3], which has a breaking strength in the longitudinal direction of the film of 180 MPa or more and 260 MPa or less and a breaking elongation of 80% or more and 170% or less. Terephthalate film roll.
[5] The biaxially oriented polyethylene terephthalate according to any one of [1] to [4], wherein the number of foreign substances having a maximum length of 1.0 mm or more is 16 or more per 8000 m ² of the film roll. film roll.
[6] The biaxially oriented polyethylene terephthalate film roll according to any one of [1] to [5], which has a winding length of 10,000 m or more.

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 the thermal shrinkage in the longitudinal direction of the film, the plane orientation coefficient (ΔP), and the number of foreign substances are within a predetermined range. A biaxially oriented polyester film roll, which is friendly to the global environment, can be obtained with good film productivity even when the amount of foreign matter in the recycled raw material is large, and which can be made long.

1 is a schematic diagram showing a logarithmic pattern TD stretching method in the present invention; FIG. It is a schematic diagram showing a TD stretching method of a multi-stage stretching pattern in the present invention.

The present invention will be described in detail below.
The recycled raw material derived from the PET container 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 may contain some coloring components. A polyester resin made from recycled PET bottles will be described below as an example, but the present invention is not limited to this.

[Polyester resin made from recycled PET bottles]
As the polyester resin made from recycled PET bottles in the present invention, used PET bottles collected from the market and society are sorted, pulverized, and washed to sufficiently remove surface stains and foreign matter, and then exposed to high temperature. Polyester resin obtained by a physical recycling method (hereinafter sometimes referred to as mechanically recycled polyester resin) that is pelletized again after thoroughly washing contaminants remaining inside the resin, and used packaging containers Any polyester resin obtained by decomposing the contained polyester resin to the monomer level, removing contaminants, etc. and polymerizing again (hereinafter sometimes referred to as chemically recycled polyester resin) can be suitably used. can.

For the biaxially oriented polyester film in the present invention, it is preferable to use a polyester resin recycled from the market or society, including the following PET bottles. By using polyester resin recycled from the market and society, including PET bottles, the ratio of recycled raw materials in the film can be increased, making it possible to obtain an environmentally friendly film.
Polyester resin recycled from the market and society, including PET bottles used in the biaxially oriented polyester film of the present invention, is mainly composed of recycled containers mainly made of polyethylene terephthalate. , Recycled containers for beverages such as soft drinks can be preferably used, and may be appropriately oriented, and preferably colorless, but may contain a small amount of coloring component.

The PET container-derived recycled raw material preferably used in the present invention is a polyester produced and molded by a conventional polymerization method and a solid phase polymerization method, preferably mainly composed of polyethylene terephthalate, and other polyester components, It may contain a copolymer component. A metal compound such as antimony, germanium or titanium as a catalyst and a phosphorus compound as a stabilizer may be included.

Germanium is often used as a catalyst in polyesters for PET bottles, and if a film is formed using recycled PET bottle raw materials, the film will contain 1 ppm or more of germanium. However, since this is just the content of the catalyst, it is usually at most 100 ppm or less, and usually 50 ppm or less.

The mechanically recycled polyester resin and the chemically recycled polyester resin are described below.

[Mechanical recycled polyester resin]
Collected used recycled PET bottles are sorted so that other materials and garbage do not mix, and after removing labels and other materials, they are pulverized into flakes. These flakes are often contaminated with foreign matter. In addition, it is conceivable that a consumer fills a used PET bottle with a chemical substance such as a drug or a solvent. For example, detergents for tableware, insecticides, herbicides, agricultural chemicals, and various oils can be considered. Since chemical substances adsorbed on the surface of the PET bottle cannot be sufficiently removed by ordinary washing, alkali washing is preferred. A sodium hydroxide solution or a potassium hydroxide solution is used as the alkali metal hydroxide solution used in this washing step. In such a cleaning process, preliminary cleaning may be performed before alkaline cleaning.
If alkali cleaning is not carried out, foreign matter remains in the raw material resin, and when these foreign matter is mixed in, it triggers breakage during film formation and lowers productivity. It can cause the appearance of the film and print defects in the printing process performed later.

The concentration of the alkali metal hydroxide aqueous solution used in the washing step is usually in the range of 1 to 10% by weight, depending on the temperature, time and stirring conditions. In addition, the time required for washing is in the range of 10 to 100 minutes, and it is preferable to wash while stirring in order to enhance the effect.

It is preferable to perform rinsing and drying following alkaline cleaning. Alkali cleaning and rinsing may be repeated several times. In the alkali washing process, the aqueous solution component of the alkali metal hydroxide used for washing remains in the flakes, so that the flakes go through the melt extrusion process in the subsequent pellet granulation process and the melt extrusion process during film formation. may affect the physical properties of the resulting film.

It is preferable that the concentration of sodium and potassium in the film obtained using the polyester resin recycled from the market or society, including these PET bottles, is greater than 0 ppm and 150 ppm or less, more preferably 3 to 3. 120 ppm, more preferably 5 to 80 ppm. If the concentration of sodium or potassium contained in the film is higher than 150 ppm, the heat resistance and thermal stability of the film will be lowered, and the film will be colored, which is not preferable. In addition, if it is completely absent, the effect of suppressing the production of diethylene glycol is diminished, which is not preferable. Polyester resins recycled from the market and society, including PET bottles, may contain a small amount of these components, and it is difficult to completely eliminate them.

In such a washing process, some of the PET bottle flakes are hydrolyzed by the aqueous alkali metal hydroxide solution. In addition, the degree of polymerization of the resin decreases due to heating during molding of the PET bottle. Furthermore, the degree of polymerization decreases due to the effects of heat and moisture applied when the collected PET bottles are pulverized for reuse and then melted and pelletized again. Although it can be reused as it is, depending on the intended use, if the degree of polymerization is lowered, the moldability, strength, transparency, heat resistance, etc. may deteriorate, and it may not be possible to reuse it as it is.

In such a case, in order to recover the lowered degree of polymerization, it is preferable to melt the flakes of PET bottles that have been pulverized and washed, pelletize the flakes, and carry out solid state polymerization.

In the solid-phase polymerization step, the washed flakes or the flakes melt-extruded and pelletized are continuously solid-phase polymerized in an inert gas such as nitrogen gas or rare gas at 180 to 245 ° C., preferably 200 to 240 ° C. It can be done by

As a polyester resin recycled from the market and society, including PET bottles, the intrinsic viscosity is 0.55 to 0.90 dl / g, preferably 0.60 to 0.85 dl / g. Alternatively, it is desirable to adjust the pellet conditions.

The process of pelletizing flakes will now be described. The flakes are melted, extruded, cooled and granulated using an extruder with degassing and filtering means.

The melting step in the extruder can be carried out by melt-kneading usually at 260 to 300°C, preferably 265 to 295°C. The flakes obtained by pulverizing the PET bottle to be charged must be sufficiently dried, and the drying is preferably performed under conditions of 5 to 200 ppm, preferably 10 to 100 ppm, more preferably 15 to 50 ppm. When the flakes contain a large amount of water, the hydrolysis reaction proceeds in the melting process, and the intrinsic viscosity of the obtained polyester resin decreases. As a degassing means, it is preferable to have at least one vacuum vent in the melting zone of the resin.

In addition, the extruder preferably has a filter capable of filtering and removing solid foreign matters having a particle size of 25 μm or more, preferably 15 μm or more, more preferably 10 μm or more, of the molten resin as filtering means.

The molten resin that has passed through the filter passes through a die, is cooled in water, is cut into pellets of a desired shape, and is granulated.
[Polyester resin composition]
The biaxially oriented polyester film in the present invention comprises 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. Examples thereof include polyethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate, and polyethylene terephthalate is preferred from the viewpoint of mechanical properties, heat resistance, cost, and the like.
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 98% by weight or more Most preferred.

Further, these polyester resins may be copolymerized with other components as long as the object of the present invention is not impaired. Specifically, examples of copolymerization components include dicarboxylic acid components such as isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid and ester-forming derivatives thereof. Diol components include diethylene glycol, hexamethylene glycol, neopentyl glycol, and cyclohexanedimethanol. Also included are polyoxyalkylene glycols such as polyethylene glycol and polypropylene glycol. The amount of copolymerization is preferably 10 mol % or less, more preferably 5 mol % or less, most preferably 3 mol % or less per constituent repeating unit.

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 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 , It is more preferably 20 MPa/kg·cm ² , and particularly preferably 30 MPa/kg·cm ² .
The coefficient of increase in filter back pressure referred to here represents the resistance to clogging of the filtration filter when the resin is melt-extruded, and is obtained by the following formula.
K=ΔP/(Q/S)

where, K: filter back pressure increase coefficient, ΔP = P1-P0
P1: pressure 4 hours after extrusion (MPa), P0: pressure at the start of extrusion (MPa), Q: extrusion discharge rate (kg/hr), S: filter filtration area (cm ² )

By setting the coefficient of increase in filter back pressure to 10 MPa/kg·cm ² or more when melt-extruded under the conditions described above, it indicates that the recycled raw material is in a state where the PET container is not substantially sorted. , a sufficient environmental response effect 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 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 , It is more preferably 90 MPa/kg·cm ² , and particularly preferably 80 MPa/kg·cm ² . By setting the viscosity to 100 MPa/kg·cm ² or less, good productivity can be achieved simply by adjusting the production conditions of the biaxially oriented polyester film.

[Chemical recycled polyester resin]
The method for producing the chemically recycled polyester resin used in the present invention is not particularly limited, but specifically, for example, as described in JP-A-2000-169623, collected used PET bottles are sorted, crushed, and washed. After removing the foreign substances, depolymerization is carried out to decompose and refine the raw materials or intermediate raw materials of the PET resin, and the material is polymerized to produce a new PET resin. For depolymerization, ethylene glycol (EG) is added in the presence of a catalyst to return to bis-2-hydroxyethyl terephthalate (BHET), which is an intermediate raw material used in resin production. After purification, this is repolymerized into PET. or after heat treatment in a non-aqueous organic solvent in the presence of a catalyst containing iron obtained by oxidizing polyethylene terephthalate as an essential component as described in JP-A-2000-302707 to produce terephthalic acid and ethylene glycol. , and a method of polymerizing again.
The feature of chemically recycled polyester resin is that foreign matter and different materials are removed during depolymerization/repolymerization, and it can be recycled into polyester resin with the same high quality as virgin resin, so it is more hygienic than the mechanically recycled polyester resin mentioned above. Since it is excellent, it can be used particularly preferably for food packaging.

The chemically recycled polyester resin used in the present invention uses bales obtained by reducing 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 PET bottle bales, other polyethylene terephthalate waste or PET bottle flakes can be used as starting material.

PET bottle bales obtained by volume-reducing and compressing PET bottle waste are put into a pulverizer, and hot water, room temperature water, or hot water or room temperature water containing a detergent is poured into the pulverizer, and pulverized in water.

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

The crude polyethylene terephthalate flakes obtained in the above pretreatment step are depolymerized and melted and at the same time hydrolyzed to obtain a polyethylene terephthalate melt with a low degree of polymerization, which is then depolymerized with excess ethylene glycol to produce two types of crude BHET and crude ethylene glycol. A mixed solution is obtained.

After the completion of the depolymerization reaction, the mixed solution of crude BHET and crude ethylene glycol is cooled and filtered to remove unreacted linear and cyclic oligomers as high-melting precipitates, coagulates of residual different plastics other than polyethylene terephthalate, Solid contaminants such as metals are removed, followed by adsorption/ion exchange treatment to remove colored matter and dissolved ions, thereby removing contaminants contained in the crude BHET.

The mixed solution of crude BHET and crude ethylene glycol obtained through the pre-purification step is subjected to distillation/evaporation operation to separate and distill ethylene glycol to obtain concentrated BHET, or the mixed solution of the two types is heated at 10°C. After cooling to the following to crystallize BHET, ethylene glycol and BHET are solid-liquid separated to obtain concentrated BHET, and this concentrated BHET is concentrated at a temperature exceeding 190 ° C. and not exceeding 250 ° C. in an evaporator. Purified bis-β-hydroxyethyl terephthalate is obtained by vacuum evaporation so that the BHET has a retention time of 10 minutes or less.

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.

Among the polyester resins constituting the biaxially oriented polyester film of the present invention, as a method for producing a fossil fuel-derived polyester resin other than the mechanically recycled polyester resin and the chemically recycled polyester resin, first, the above-mentioned dicarboxylic acid or its ester-forming property Using a derivative and a diol or an ester-forming derivative thereof as main starting materials, a method of producing by carrying out an esterification or transesterification reaction according to a conventional method, and then further carrying out a polycondensation reaction at high temperature and under reduced pressure. be done.

The intrinsic viscosity of the polyester resin constituting the biaxially oriented polyester film of the present invention is preferably in the range of 0.50 to 0.90 dl/g, more preferably 0.55, from the viewpoint of film-forming properties and re-recoverability. ~0.80 dl/g.

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., in addition to the polyester resin composition. .

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 It is 99.7% by mass.

The lubricant can adjust the coefficient of dynamic friction of the film, and includes inorganic lubricants such as silica, calcium carbonate and alumina, as well as organic lubricants. Silica and calcium carbonate are preferred, and porous silica is most preferred from the viewpoint of achieving both transparency and slipperiness.

The lower limit of the lubricant content in the biaxially oriented polyester film of the present invention is preferably 100 mass ppm, more preferably 300 mass ppm, and most preferably 500 mass ppm. By making it 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 10000 mass ppm, more preferably 6000 mass ppm, and most preferably 2000 mass ppm. By making it 10000 ppm by mass or less, the transparency of the film can be improved.

[Method for producing biaxially oriented polyester film]
The method for obtaining the biaxially oriented polyester film of the present invention is not particularly limited, and can be appropriately selected from a T-die method, an inflation method, and the like.

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 be two layers, three layers, four layers, or five layers.

The upper limit of the cooling roll temperature is preferably 40°C, more preferably 20°C or less. When the temperature is 40° C. or higher, the degree of crystallinity does not become too high when the melted polyester resin composition cools and solidifies, and stretching becomes easier, and a decrease in transparency due to crystallization can be suppressed.
The lower limit of the chill roll temperature is preferably 0°C. When the temperature is 0°C or higher, the effect of suppressing crystallization when the molten polyester resin composition is cooled and solidified can be sufficiently exhibited. Further, 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 dew condensation.

The thickness of the unstretched sheet is preferably in the range of 15-2500 μm. It is more preferably 600 μm or less, and most preferably 400 μm or less.

Next, the stretching method will be explained. The stretching method may be simultaneous biaxial stretching or sequential biaxial stretching.

The lower limit of the stretching temperature in the longitudinal direction (hereinafter also referred to as MD direction) is preferably 90°C, more preferably 100°C, and particularly preferably 110°C. When the temperature 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 MD direction is preferably 140°C, more preferably 130°C, and particularly preferably 120°C. If the temperature is 140° C. or less, the stretching stress increases due to crystallization, and as a result, not only is it possible to suppress breakage due to foreign matter, but also the mechanical strength of the film is improved.

The lower limit of the draw ratio in the MD direction is preferably 2.5 times, more preferably 2.8 times, and particularly preferably 3.1 times. If it is 2.5 times or more, not only will the mechanical strength of the film be good, but also the thickness unevenness will be good, leading to an improvement in the winding quality of the roll.
The upper limit of the draw 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 breakage due to foreign matter can be suppressed.

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%, 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 process 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%, particularly preferably 6%. When it is 10% or less, wrinkles due to shrinkage can be suppressed, and not only can the quality of the film be improved, but also a decrease in mechanical strength due to relaxation of orientation can be suppressed.
Although the method of MD relaxation is not particularly limited, for example, there is a method of applying relaxation treatment using a speed difference between rolls after heating with a hot air heater.

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 the temperature 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. If the temperature is 140° C. or less, the stretching stress increases due to crystallization, and as a result, not only is it possible to suppress breakage due to foreign matter, but also the mechanical strength of the film is improved.

The lower limit of the draw ratio in the TD direction is preferably 2.5 times, more preferably 3.0 times, and particularly preferably 3.5 times. If it is 2.5 times or more, not only will the mechanical strength of the film be good, but also the thickness unevenness will be good, leading to an improvement in the winding quality of the 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 stretching stress can be reduced, so breakage due to foreign matter can be suppressed.

The drawing pattern in the TD direction is preferably logarithmic or multistage drawing. Specifically, as shown in FIGS. 1 and 2, the logarithmic TD stretching pattern is a TD stretching pattern that stretches greatly in the first half of the stretching and gently stretches in the second half of the stretching, as opposed to the normal linear TD stretching pattern. ing. 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, breakage due to foreign matter can be suppressed.

Next, the details of the case of adopting the logarithmic TD stretching pattern will be described. As described above, the logarithmic TD stretching pattern refers to a TD stretching pattern that stretches greatly in the first half of stretching and gently stretches in the second half of stretching. When the drawing angle is θN, the film is drawn in the width direction under the condition that the drawing angle in each drawing zone satisfies θn>θn+1. (The case of θn=θn+1 is normal straight drawing)
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 desired performance. However, when the angle change rate expressed by {(θn−θn+1)/θn}×100 (unit: %) exceeds 50% and is large, TD stretching is inevitably necessary for stretching up to a predetermined maximum ratio. Since it is necessary to increase the draw ratio extremely at the initial stage, the drawing stress at the initial stage of the drawing becomes too large, which may adversely deteriorate the film formability. When the angle change rate is 0%, θ1 = θ2, which is the same as the stretching conditions in a conventional tenter. % or less, more preferably 1% or more and 30% or less, and particularly preferably 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 when the film stretching stress is low, and the stretching stress applied during stretching can be reduced. As a result, breakage due to foreign matter can be suppressed.

Next, multistage drawing in TD will be described. Multi-stage stretching is to perform two or more stages of stretching in contrast to ordinary one-stage stretching, and the stretching stress applied during TD stretching can be reduced. As a result, breakage due to foreign matter can be suppressed.

The TD multi-stage drawing is preferably two-stage stretching or more and five-stage stretching or less. Multi-stage stretching is preferable because it is possible to change the stretching stress by changing the stretching temperature, and the stretching stress during the TD stretching can be reduced. As shown in FIG. 2, 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 in the multi-stage stretching, and the temperature is lowered from the first stage of stretching to the final stage of stretching.
The lower limit of the number of drawing steps is preferably two or more steps. Stretching stress can be lowered|hung as it is two-step drawing or more, and the breakage|rupture resulting from a foreign material can be suppressed.
The upper limit of the number of stretching steps is preferably 5 or less. If the drawing is 5 stages or less, it is possible to prevent the equipment from becoming too large.
In the case of multi-stage stretching, a zone having a fixed length can be appropriately provided after each stretching step. By providing a constant-length zone after each stretching step, the internal stress generated during stretching can be relieved in the constant-length zone, which can further reduce the stretching stress during the next stretching and suppress film breakage. can do.

The lower limit of the heat setting temperature is preferably 170°C, more preferably 180°C, and particularly preferably 190°C. A heat shrinkage rate can be made small as it is 170 degreeC or more.
The upper limit of the heat setting temperature is preferably 230°C, more preferably 220°C, and particularly preferably 210°C. When the temperature is 230° C. or less, it is possible to suppress a decrease in mechanical strength due to brittleness of the biaxially oriented polyester film.

The lower limit of the TD relaxation rate is preferably 0.5%, more preferably 1.0%, particularly preferably 2.0%. When it is 0.5% or more, 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%, particularly preferably 6%. If it is 10% or less, it is possible to prevent the occurrence of slackness and the like, and it is possible to improve the flatness.

By adopting the preferable film-forming conditions, it is possible to continuously obtain a long film without breaking in the film-forming of a biaxially oriented polyester film containing foreign matter, and to satisfy the following preferable film properties. can do.

[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, particularly preferably 15 μm. By setting the thickness to 5 μm or more, it is possible to suppress breakage caused by foreign matter.
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.

The lower limit of the plane orientation coefficient (ΔP) of the biaxially oriented polyester film of the invention is preferably 0.160, more preferably 0.161, and particularly preferably 0.162. By making it 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, particularly preferably 0.168. By making it 0.170 or less, it is possible to suppress the stretching stress in the stretching process, and as a result, it is possible to suppress breakage caused by foreign matter in the stretching process.

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 bag product is 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, particularly preferably 250 MPa. When it is 260 MPa or less, it is possible to substantially suppress breakage caused by foreign matter in the stretching step, resulting in good film formability.

The lower limit of the breaking elongation 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, it is possible to substantially suppress breakage caused by foreign matter in the stretching step, resulting in good film formability.
The upper limit of the breaking elongation in the MD direction of the biaxially oriented polyester film of the present invention is 170%, preferably 160%, and particularly preferably 150%. When it is 170% or less, the mechanical strength is sufficient when made into a bag product.

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, the film is brittle, and a decrease in mechanical strength can be suppressed.
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 matter in the stretching step, resulting in good film formability.

The upper limit of 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 of the roll becomes good.

The number of foreign matter having a maximum length of 1.3 mm or more per 1000 m ² of the biaxially oriented polyester film roll of the present invention is 1 or more. If there is at least one foreign matter with a maximum length of 1.3 mm or more per 1000 m2, the foreign matter tends to cause breakage during stretching under conventional film forming conditions, making stable film formation difficult. On the other hand, by stretching the film so that the heat shrinkage rate and the degree of plane orientation of the film are within a predetermined range using the film forming conditions described in the present invention, even if foreign matter is present as described above, stable Stretching becomes possible.
On the other hand, the lower limit of the number of foreign substances having a maximum length of 1.3 mm or more per 1000 m ² of the biaxially oriented polyester film roll of the present invention is preferably 10 or less. If there are more than 10 foreign substances of 1.3 mm or more, the number of defects after printing increases, and there is a risk of lowering the yield of the secondary processing step.

The number of foreign matters having a maximum length of 1.0 mm or more per 8000 m ² of the biaxially oriented polyester film roll of the present invention 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 triggers for breakage in conventional films, and it is difficult to continuously form a long film. On the other hand, by stretching the film so that the heat shrinkage rate and the degree of plane orientation of the film are within a predetermined range using the film-forming conditions described in the present invention, even if foreign substances are present as described above, stable stretchability can be ensured, and a long film roll can be obtained.
On the other hand, the upper limit of the number of foreign substances having a maximum length of 1.0 mm or more per 8000 m ² of the biaxially oriented polyester film roll of the present invention is preferably 80 or less. If there are more than 80 foreign substances with a size of 1.0 mm or more, the number of defects after printing increases, which may reduce the yield of the secondary processing step.

A printed 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. Resins used in printing inks include acrylic resins, urethane resins, polyester resins, vinyl chloride resins, vinyl acetate copolymer resins, and mixtures thereof. Known additives such as antistatic agents, light blocking agents, ultraviolet absorbers, plasticizers, lubricants, fillers, colorants, stabilizers, lubricants, antifoaming agents, cross-linking agents, anti-blocking agents, and antioxidants are added to printing inks. agents may be included.

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

The biaxially oriented polyester film of the present invention can be provided with a gas barrier layer such as an inorganic thin film layer or a metal foil as long as the object of the present invention is not impaired.

When an inorganic thin film layer is used as the gas barrier layer, the inorganic thin film layer is a thin film made of metal or inorganic oxide. The material for forming the inorganic thin film layer is not particularly limited as long as it can be made into a thin film. Oxides are preferred. In particular, a composite oxide of silicon oxide and aluminum oxide is preferable from the viewpoint of achieving both flexibility and denseness of the thin film layer.

In this composite oxide, the mixing ratio of silicon oxide and aluminum oxide is preferably in the range of 20 to 70% by mass of Al in terms of the metal content. On the other hand, if it is 70% or less, the inorganic thin film layer can be softened, and it is possible to suppress deterioration of the gas barrier properties due to destruction of the thin film during secondary processing such as printing and lamination. Here, silicon oxide means various silicon oxides such as SiO and SiO ₂ or mixtures thereof, and aluminum oxide means various aluminum oxides such as AlO and AL ₂ O ₃ or mixtures thereof.

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, it becomes easier to obtain more satisfactory gas barrier properties. On the other hand, when it is 100 nm or less, it is advantageous in terms of bending resistance and manufacturing cost.

The method for forming the inorganic thin film layer is not particularly limited. Laws should be adopted accordingly. A typical method for forming an inorganic thin film layer will be described below using a silicon oxide/aluminum oxide thin film as an example. For example, when a vacuum deposition method is employed, a mixture of SiO ₂ and Al ₂ O ₃ or a mixture of SiO ₂ and Al is preferably used as the deposition raw material. Particles are usually used as these vapor deposition raw materials, and the size of each particle is preferably such that the pressure during vapor deposition does not change, and the preferred particle diameter is 1 to 5 mm. Methods such as resistance heating, high-frequency induction heating, electron beam heating, and laser heating can be employed for heating. It is also possible to introduce oxygen, nitrogen, hydrogen, argon, carbon dioxide gas, water vapor, etc. as reaction gases, or adopt reactive vapor deposition using means such as addition of ozone and ion assist. Furthermore, film formation conditions can be arbitrarily changed, such as applying a bias to the object to be vapor-deposited (laminated film to be vapor-deposited), heating or cooling the object to be vapor-deposited. Such vapor deposition material, reaction gas, bias of the object to be vapor-deposited, heating/cooling, etc. can be similarly changed when adopting the sputtering method or the CVD method. Furthermore, a printed layer may be laminated on the inorganic thin film layer.

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. A gas barrier layer made of a metal oxide is not a completely dense film, and is dotted with minute defects. By forming a protective layer by applying a specific resin composition for a protective layer to 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, As a result, the effect of stabilizing the gas barrier property is obtained. In addition, by using a material with gas barrier properties for the protective layer itself, the gas barrier properties of the laminated film are greatly improved.

Examples of the protective layer include resins such as urethane, polyester, acrylic, titanium, isocyanate, imine, and polybutadiene with addition of curing agents such as epoxy, isocyanate, and melamine. . Examples of the solvent (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; ethyl acetate and butyl acetate. ester-based solvents such as ethylene glycol monomethyl ether; and polyhydric alcohol derivatives such as ethylene glycol monomethyl ether.

The biaxially oriented polyester film of the present invention may be laminated with layers of other materials. As the method, a method of laminating the biaxially oriented polyester film after production and a method of laminating the film during film formation can be employed.

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 called a sealant (also called a sealant layer) on the biaxially oriented polyester film. 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 one can be used as long as it can sufficiently exhibit sealant adhesiveness, and HDPE, LDPE. Polyethylene resins such as LLDPE, polypropylene resins, ethylene-vinyl acetate copolymers, ethylene-α-olefin random copolymers, ionomer resins and the like can be used.

The sealant layer may be a single layer film or a multilayer film, and may be selected according to the required functions. For example, a multi-layer film in which a resin such as an ethylene-cyclic olefin copolymer or polymethylpentene is interposed can be used in order to impart moisture resistance. Further, the sealant layer may contain various additives such as flame retardants, slip agents, antiblocking agents, antioxidants, light stabilizers and tackifiers.
The thickness of the sealant layer is preferably 10-100 μm, more preferably 20-60 μm.

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 from the viewpoint of improving productivity in the secondary processing step, and further preferably 1500 mm or more. preferable.
On the other hand, the upper limit of the width of the polyester film roll of the present invention is preferably 3000 mm or less, more preferably 2500 mm or less. When the width of the polyester film roll exceeds 3000 mm, handling becomes difficult, and the film tends to wrinkle due to roll deflection.
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 lower limit of the winding length of the polyester film roll of the present invention is 100,000 m, preferably 80,000 m, more preferably 70,000 m.
When the winding length of the polyester film roll exceeds 100,000 m, the weight of the roll increases and handling becomes difficult.

In the polyester film roll of the present invention, a paper tube, a plastic core, a metal core, or the like is preferably used 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 is deformed (distorted) due to distortion or natural shrinkage of the film when the film is stored after being wound. At that time, if the difference in distortion of the paper tube in the width direction (the gap difference in the width direction) is large, wrinkles will occur on the core side of the film roll, which is not preferable. Therefore, the gap between the paper tubes after removing the film from the film roll is preferably 0.4 mm or less, more preferably 0.3 mm or less.

Further, when a paper tube is used as the core of the polyester film roll of the present invention, the flat pressure resistance of the core paper tube 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, which is not preferable. It is preferably 1800 N/100 mm or more, more preferably 1900 N/100 mm or more. The higher the pressure resistance, the better. Examples of means for obtaining a high flat pressure resistance strength of a paper tube include methods such as increasing the thickness of the paper tube, and using a hard paper tube or an ultra-hard paper tube designed to have high strength.

In the heat-shrinkable polyester film roll of the present invention, in order to make the gap difference between the paper tubes after removing the film from the film roll as described above 0.5 mm or less, the film used for winding is The gap difference in the width direction of the paper tube before winding is preferably 0.3 mm or less. If the difference in distortion in the width direction of the paper tube is 0.4 mm or more, the position where the film is distorted is in an oblique direction when winding the film, which is not preferable because wrinkles (winding core wrinkles) tend to occur. The gap difference in the width direction of the paper tube is more preferably 0.2 mm or less, and still more preferably 0.1 mm or less. As a means to reduce the gap difference between paper tubes, use a paper tube that has high hardness and does not easily deform due to vibration during transportation. There is a method of storing the paper tube in a room with constant temperature and humidity so that it does not deform due to moisture absorption.

Moreover, the average value of the roll 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 wound state will be soft and the core wrinkles will be in a good direction, but the end face of the film roll will be displaced, which is not preferable. If the winding hardness is higher than 850, the wound state becomes hard and wrinkles are likely to occur due to uneven thickness, which is not preferable. The average value of the roll hardness in the width direction of the surface layer of the film roll is preferably 550 or more and 800 or less, more preferably 600 or more and 750 or less. Particularly preferably, it is more than 650 and 750 or less.

EXAMPLES 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.

[Back pressure increase factor of recycled raw material]
After drying the recycled raw material pellets at 135° C. for 12 hours, they were extruded under conditions of a temperature of 285° C., a filter diameter of 20 μm, a discharge rate of 6 g/min, and a discharge time of 4 hours, and the coefficient of increase in filter back pressure was determined by the following formula.
K=ΔP/(Q/S)

where, K: filter back pressure increase coefficient, ΔP = P1-P0
P1: pressure 4 hours after extrusion (MPa), P0: pressure at the start of extrusion (MPa), Q: extrusion discharge rate (kg/hr), S: filter filtration area (cm ² )

[Thickness of biaxially oriented film]
It was measured using a dial gauge in accordance with JIS K7130-1999 A method.

[Thermal Shrinkage of Biaxially Oriented Film]
The heat shrinkage rate was measured by the dimensional change test method according to JIS-C-2318 except that the test temperature was 150° C. and the heating time was 15 minutes.

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

[Strength and elongation of biaxially oriented film]
Based on JIS K 7127, a test sample having 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 tester (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 obtained stress-strain curve was used to calculate the breaking strength and breaking elongation of the test sample.

[Evaluation of Formability of Biaxially Oriented Film]
When the films of Examples and Comparative Examples could be continuously deposited for 10,000 m without breakage during film deposition, they were evaluated as ◯.

[Foreign matter evaluation of biaxially oriented film (1000 square meters)]
A film roll wound with a width of 800 mm and a winding length of 1250 m (1000 square meters) was rewound using a rewinder. At the time of rewinding, the number of defects was investigated using a defect detector (F MAX MR manufactured by FUTEC). The number of defects having a size of 1.3 mm or more in the longest part of the defect was determined.
Less than 1 defect of 1.3 mm or more: C
Number of defects of 1.3 mm or more: 1 or more, 10 or less: A

[Foreign matter evaluation of biaxially oriented film (8000 square meters)]
A film roll wound with a width of 800 mm and a winding length of 10000 m (8000 square meters) was rewound using a rewinder. At the time of rewinding, the number of defects was investigated using a defect detector (F MAX MR manufactured by FUTEC). The number of defects having a size of 1.0 mm or more in the longest part of the defect was obtained.
15 or less defects of 1.0 mm or more: C
16 or more and 80 or less defects of 1.0 mm or more: A

[Evaluation of thickness unevenness in the width direction]
A sample of 800 mm in the width direction and 40 mm in the longitudinal direction was sampled from the film roll, and the thickness in the width direction was continuously measured at 5 m/sec using a film tester continuous thickness measuring device (manufactured by Fujiwork). The maximum thickness at the time of measurement is Tmax. , the minimum thickness is Tmin. , the average thickness of Tave. Then, the thickness unevenness in the film width direction was calculated from the following formula.
Thickness unevenness={(Tmax.-Tmin.)/Tave. }×100(%)

[Evaluation of filter clogging]
○ indicates that the film could be formed continuously for one week without replacing the filter during the film formation of each example or comparative example. It was evaluated as ×.

(Polyester A: PET container-derived mechanically recycled polyester resin)
After washing away foreign matter such as content residue from the PET container, the PET container was pulverized to obtain flakes. The flakes thus obtained were washed with a 3.5% by weight sodium hydroxide solution under the conditions of a flake concentration of 10% by weight, 85° C., and 30 minutes while stirring. After washing with alkali, the flakes were taken out and the flake concentration was 10% by weight. Washing was performed with distilled water at 25° C. for 20 minutes while stirring. This washing was repeated two more times by exchanging with distilled water. After washing with water and drying the flakes, 0.10 parts by mass of silica particles having an average particle size of 2.5 μm were added to the flakes. After that, it is melted in an extruder, and the filter is changed to a filter with a fine opening size in order to filter out finer foreign matters twice. Obtained. The back pressure increase coefficient of polyester A was 96 MPa/kg·cm ² .

(Polyester B: PET container-derived mechanically recycled polyester resin)
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 .

(Polyester C: PET container-derived mechanically recycled polyester resin)
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 .

(Polyester D: PET container-derived mechanically recycled polyester resin)
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 .

(Polyester E: PET container-derived mechanically recycled polyester resin)
Polyester E was obtained in the same manner as polyester A, except that the PET container used was selected only for clean ones. The back pressure increase coefficient of Polyester E was 8 MPa/kg·cm ² .

(Polyester F: PET container-derived mechanically recycled polyester resin)
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 .

(Polyester G: chemically recycled polyester resin derived from PET containers)
As a chemically recycled polyester resin recycled from a PET bottle used in the production of a biaxially oriented polyester film to be described later, one synthesized using the following method was used.
PET bottle bales that have been sorted and collected are put into a wet pulverizer, and 1,000 liters of water and 500 g of liquid kitchen detergent are added to the wet pulverizer and pulverized while being circulated through the wet pulverizer. Metal, sand, glass, and other materials with high specific gravity were precipitated by a specific gravity separator, and flakes were taken out from the upper layer. The flakes were rinsed with pure water and dehydrated by centrifugation to obtain recovered flakes.

In an autoclave equipped with a stirrer, 30 kg of the recovered flakes melted in an undried state are charged into a preheated mixture of 150 kg of ethylene glycol and 150 g of zinc acetate dihydrate, and ethylene such as water and acetic acid is added. After removing fractions having a boiling point lower than that of glycol, the mixture was reacted at a temperature of 195-200° C. for 4 hours using a reflux condenser.

After completion of the reaction, the temperature of the content in the reactor was lowered to 97 to 98° C., and hot filtration was performed with a filter to remove floating matters and precipitates.

The filtrate after hot filtration is further cooled, and after confirming that the crude BHET is completely dissolved, it is passed through an activated carbon bed and then an anion/cation exchange mixed bed at 50 to 51° C. for 30 minutes for prepurification. processed.

The above-mentioned pre-purified liquid was charged again into the stirring autoclave and heated to distill excess ethylene glycol at 198° C. under normal pressure to obtain a concentrated BHET melt.

The resulting concentrated BHET melt was allowed to cool naturally while being stirred in a nitrogen gas atmosphere, and then removed from the autoclave to obtain a concentrated BHET fragment block.

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

Using this purified BHET as a raw material, melt polymerization was performed to obtain a chemically recycled polyester resin G having an intrinsic viscosity of 0.696 dl/g. The back pressure increase coefficient of polyester G was 7 MPa/kg·cm ² .

[Example 1]
Polyester A was charged into the extruder. After melting the resin at 280° C. in an extruder, the molten resin was passed through a filter mesh of 50 μm and then through a filter mesh of 100 μm. Thereafter, it was cast from a T-die at 280° C. and brought into close contact with a cooling roll at 10° C. by an electrostatic adhesion method to obtain an unstretched sheet.
Then, 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 subjected to a 3% relaxation treatment in the longitudinal direction using the speed difference between rolls at the entrance and exit of the heating furnace. Then, it is passed through a tenter and stretched 4.6 times in the TD direction at 120 ° C., and subjected to heat setting treatment at 210 ° C. for 3 seconds and 5% relaxation treatment for 1 second to form a biaxially oriented polyester film having a thickness of 12 μm. Obtained. Table 1 shows the resin composition of the biaxially oriented polyester film and film forming conditions. Table 1 shows the physical properties and evaluation results of the obtained film.

[Example 2]
The relaxation rate immediately after longitudinal stretching was changed to 0%, and the stretching method in the tenter was changed to 3-stage stretching, with a fixed length of 1 m between the 1st and 2nd stages and between the 2nd and 3rd stages. A biaxially oriented polyester film having a thickness of 12 μm was obtained by film formation in the same manner as in Example 1, except that regions were provided. Table 1 shows physical properties and evaluation results.

[Example 3]
A biaxially oriented polyester film having 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 0% and the stretching pattern in the tenter was changed to logarithmic. The stretching angle of the tenter was adjusted so that the first stage refraction angle θ1: 12.6°, the second stage refraction angle θ2: 8.2°, and the angle change rate was 34.9%. The draw ratio was set so as to be the same as in Example 1. Table 1 shows physical properties and evaluation results.

[Example 4]
A biaxially oriented polyester film having 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%. Table 1 shows physical properties and evaluation results.

Hereinafter, Example 5 is entirely replaced with Reference Example 1.
[Example 5]
A biaxially oriented polyester film having 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 10%. Table 1 shows physical properties and evaluation results.

[Example 6]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was changed to 3.9 times. Table 1 shows physical properties and evaluation results.

[Example 7]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was changed to 2.6 times. Table 1 shows physical properties and evaluation results.

[Example 8]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that the transverse draw ratio was changed to 4.9 times. Table 1 shows physical properties and evaluation results.

Hereinafter, Example 9 is entirely replaced with Reference Example 2.
[Example 9]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1 except that the transverse draw ratio was changed to 2.6 times. Table 1 shows physical properties and evaluation results.

[Example 10]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that polyester B was used as the resin. Table 1 shows physical properties and evaluation results.

[Example 11]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that polyester C was used as the resin. Table 1 shows physical properties and evaluation results.

[Example 12]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that polyester D was used as the resin. Table 1 shows physical properties and evaluation results.
[Example 13]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that polyester G was used as the resin. Table 1 shows physical properties and evaluation results.

[Comparative Example 1]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that the filter mesh through which the molten resin was passed was 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.

[Comparative Example 2]
A film having a thickness of 12 μm was formed in the same manner as in Example 1 except that the filter mesh through which the molten resin was passed 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%. A biaxially oriented polyester film was obtained. Clogging of the filter mesh occurred and it was defective.

[Comparative Example 3]
A biaxially oriented polyester film having a thickness of 12 μm was obtained 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 changed to 0%. The obtained biaxially oriented polyester film contained few foreign matter and did not clog the filter mesh, but the environmental friendliness effect was insufficient because clean PET containers were sorted out and used as recycled raw materials.

[Comparative Example 4]
A biaxially oriented polyester film having a thickness of 12 μm was obtained 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 changed to 10%. The resulting biaxially oriented polyester film was often broken due to foreign matter, and was poor in film formability.

[Comparative Example 5]
A biaxially oriented polyester film having 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 12%. The obtained biaxially oriented polyester film had a low plane orientation coefficient and poor mechanical strength.

[Comparative Example 6]
A biaxially oriented polyester film having 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 0%. The resulting biaxially oriented polyester film was often broken due to foreign matter, and was poor in film formability.

[Comparative Example 7]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was changed to 4.1 times. The resulting biaxially oriented polyester film was often broken due to foreign matter, and was poor in film formability.

[Comparative Example 8]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was changed to 2.3 times. The obtained biaxially oriented polyester film had a low plane orientation coefficient and poor mechanical strength.

[Comparative Example 9]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that the transverse draw ratio was changed to 5.1 times. The resulting biaxially oriented polyester film was often broken due to foreign matter, and was poor in film formability.

[Comparative Example 10]
A biaxially oriented polyester film having a thickness of 12 μm was obtained in the same manner as in Example 1, except that the transverse draw ratio was changed to 2.3 times. The obtained biaxially oriented polyester film had a low plane orientation coefficient and poor mechanical strength.

The biaxially oriented polyester film roll of the present invention has good productivity of the film obtained even if the amount of foreign matter in the recycled raw material is large and can be made long, and is widely used in the field of packaging films such as food packaging. It can be applied, and it is expected that it will greatly contribute to the industrial world because there is a strong desire to reduce the environmental burden these days.

Claims (5)

It consists of a polyester resin composition containing recycled raw materials derived from PET bottles, and the polyester composition contains isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid, diethylene glycol, hexa A polyester resin composition made of polyethylene terephthalate which may contain 10 mol% or less of a component selected from the group consisting of methylene glycol, neopentyl glycol, cyclohexanedimethanol, polyethylene glycol, and polypropylene glycol, and the following (1) to ( A biaxially oriented polyethylene terephthalate film roll obtained by winding a biaxially oriented polyethylene terephthalate film that satisfies 3) and having a winding length of 1000 m or more.
(1) Thermal shrinkage 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 plane orientation coefficient (ΔP) of the film calculated from the refractive index measured according to JIS K 7142-1996 A method is 0.161 or more and 0.170 or less.
(3) The number of foreign matter with a maximum length of 1.3 mm or more per 1000 m ² of film roll is 1 or more. 2. The biaxially oriented polyethylene terephthalate film roll according to claim 1, wherein the recycled raw material derived from the PET bottle 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, wherein the thickness unevenness per 800 mm in the film width direction is 18% or less. 4. The biaxially oriented polyethylene terephthalate film roll according to any one of claims 1 to 3, 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. 5. The biaxially oriented polyethylene terephthalate film roll according to any one of claims 1 to 4, wherein the number of foreign substances having a maximum length of 1.0 mm or more per 8000 m 2 of the film roll is 16 or more.

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