Recycled polyester film and metallized film

Abstract

To obtain a recycled polyester film that is easy to tear by hand. [Solution] A recycled polyester film having an intrinsic viscosity IV of 0.55 dl / g or more and 0.65 dl / g or less, a rheometer viscosity ηH (Pa·s) of 120 or less at 280°C and a shear rate of 31.4 rad / s, and a Tmeta observed by differential scanning calorimetry (DSC) of 220°C or higher.

Description

Technical Field

[0001] The present invention relates to a recycled polyester film.

Background Art

[0002] Recently, as an international effort, the SDGs Promotion Headquarters has been established as a sustainable development goal, and efforts to recycle resins are becoming active as an international goal. In Japan, since around 2000, the Container and Packaging Recycling Law and the Law for the Promotion of Effective Use of Resources have been implemented, and the recycling technology of polyester resin has been almost established. However, in 2022, due to international efforts, the Plastic Resource Recycling Law incorporating the concept of "3R + Renewable" was implemented, and an attempt is being made to shift to a circular economy technology that minimizes the recycling of waste.

[0003] In the resource recycling of plastics, the recycling of PET bottles mainly composed of polyethylene terephthalate resin, which is representative of polyester, is ahead. In recent years, the scope of recycling technology has expanded from PET bottles to other industrial materials, such as packaging materials, process materials such as release and protection materials, and functional materials. Also, in recycling methods, there are material recycling (hereinafter sometimes referred to as mechanical recycling) and chemical recycling. Chemical recycling can obtain recycled polyester raw materials comparable to virgin raw materials, but because the number of processes involved in recycling increases, the cost and input energy increase, so recycled polyester resin by material recycling is widely adopted.

[0004] The reuse of material recycling of once-formed polyester raw materials is likely to affect the physical properties of recycled products, especially strength. Also, if the recycled products are reused as material recycling again, it is likely to further cause a decrease in physical properties, and the use of the recycled raw materials tends to become negative, and efforts to manage the physical properties as recycled raw materials are being studied (for example, Patent Document 1).

Prior Art Documents

[0005] [Patent Document 1] Patent No. 7666716 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a recycled polyester film that uses recycled polyester raw materials and exhibits excellent tearability. [Means for solving the problem]

[0007] In other words, a preferred embodiment of the present invention is the following configuration.

[0008] (1) A recycled polyester film having an intrinsic viscosity IV of 0.55 dl / g or more and 0.65 dl / g or less, a rheometer viscosity ηH (Pa·s) of 120 or less at 280°C and a shear rate of 31.4 rad / s, and a Tmeta observed by differential scanning calorimetry (DSC) of 220°C or higher. (2) The recycled polyester film according to (1), wherein the tear resistance of the film at the edges is 10.0 kgf / 20 mm or less in at least one of the MD direction and the TD direction. (3) The recycled polyester film according to (1) or (2), wherein the thickness of the film is 2 μm or more and 50 μm or less. (4) The film is a recycled polyester film according to any one of (1) to (3), wherein the film contains more than 0% by mass and 100% by mass or less of recycled polyester raw material with respect to the polyester resin constituting the film. (5) A metallized film having a metal layer on the recycled polyester film described in (4). [Effects of the Invention]

[0009] This invention provides a recycled polyester film that uses recycled polyester raw materials and exhibits excellent tearability. [Modes for carrying out the invention]

[0010] The recycled polyester film of the present invention is a film mainly composed of polyester resin, and is a polyester film containing recycled polyester resin. The polyester resin is a polyester obtained using an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol or derivative thereof. Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, and 4,4'-diphenylsulfondicarboxylic acid. Examples of aliphatic dicarboxylic acids include adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedionic acid, cyclohexanedicarboxylic acid and their ester derivatives. Terephthalic acid and 2,6-naphthalenedicarboxylic acid are particularly preferred. These acid components may be used individually, in combination of two or more, or partially copolymerized with oxyacids such as hydroxybenzoic acid. Examples of diol components include ethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2,2-bis(4-hydroxyethoxyphenyl)propane, isosorbate, and spiroglycol. Among these, ethylene glycol is preferably used. These diol components may be used individually or in combination of two or more. Of the above polyesters, it is preferable to use a polyester selected from polyethylene terephthalate and its copolymers, polyethylene naphthalate and its copolymers, polybutylene terephthalate and its copolymers, polybutylene naphthalate and its copolymers, polyhexamethylene terephthalate and its copolymers, and polyhexamethylene naphthalate and its copolymers.

[0011] Recycled polyester resin refers to a resin that has been melt-molded from polyester resin. The recycling method can be either chemical recycling or material recycling. It is preferable that the recycled polyester resin be primarily composed of materially recycled resin, as this can be manufactured at low cost. Here, recycling refers to recycling a polyester resin composition that has been molded into a desired shape according to the target product, or a molded product that has been further processed. Specific molded products include fibers, nonwoven fabrics, films, and bottles. In particular, molded products distributed to general consumers often suffer from significant deterioration and contamination of the resin. Therefore, as the materials to be collected for the recycled polyester resin of this invention, unused film scraps generated in the film manufacturing process within the factory, or films that have been shipped out of the factory and used in other factories, are preferred. Multiple types of recycled polyester resin can be used.

[0012] Methods of mechanical recycling include using molded materials cut into flakes to create recycled polyester resin, or directly melting and extruding flakes or films and solidifying them into pellets. It is preferable to use materials that have been peeled and separated from the film and washed with water.

[0013] One method of chemical recycling involves first removing and washing away functional layers and foreign substances, then depolymerizing the polyester using chemical equipment to return it to monomers and oligomers, and finally repolymerizing it to produce a polyester composition. The main methods of chemical recycling include the metanolysis method, glycolysis method, and hydrolysis method. The metanolysis method involves adding methanol to depolymerize the polyester, decomposing it into dimethyl terephthalate and ethylene glycol, and using these as raw materials. The glycolysis method involves adding ethylene glycol to polyethylene terephthalate, decomposing it at high temperature to produce bishydroxyethyl terephthalate (hereinafter simply referred to as BHET), and using this BHET as a raw material to produce PET. Furthermore, there is also a method in which methanol is added to this BHET, decomposing it into dimethyl terephthalate and ethylene glycol by transesterification, and purifying these to use as raw materials.

[0014] In both mechanical and chemical recycling, if functional layers or foreign matter are attached to the molded product before recycling, it is preferable to immerse it in an alkaline solvent or the like to remove the functional layers and foreign matter, wash it with water, and then extract only the film to increase the purity of the recycled polyester resin. Examples of functional layers include smoothing layers provided for the running of the film, hard coat layers such as the functional layer of an optical film, refractive index adjustment layers, adhesive layers for other components, and release layers such as release sheets. Examples of foreign matter include dust and dirt, residue from dry film resist, and residue from the material to be released. Mechanical recycling is preferred for recycled polyester resin from the viewpoint of the number of processes and cost.

[0015] The recycled polyester film of the present invention preferably contains more than 0% by mass and 100% by mass or less of recycled polyester raw material relative to the polyester resin constituting the film. More preferably, it contains 30% by mass or more, even more preferably 50% by mass or more, and even more preferably 70% by mass or more and 100% by mass or less.

[0016] The recycled polyester film of the present invention may contain 0.2% by mass or less of particles relative to the total mass of the film, from the viewpoint of handling and transportability during processing. If the film contains more than 0.2% by mass of particles relative to the total mass of the film, it may be prone to breakage during the film manufacturing process and may affect the film-forming stability. The average particle diameter is preferably 0.01 to 5 μm. Examples of particles include inorganic particles and organic particles. Examples of inorganic particles include wet and dry silica, colloidal silica, aluminum silicate, titanium dioxide, calcium carbonate, calcium phosphate, barium sulfate, aluminum oxide, mica, kaolin, and clay, while examples of organic particles include styrene, silicone, acrylic acids, methacrylic acids, polyesters, and divinyl compounds. Furthermore, two or more types of these inorganic and organic particles may be used in combination.

[0017] The recycled polyester film of the present invention has an intrinsic viscosity IV of 0.55 dl / g or more and 0.65 dl / g or less. If the intrinsic viscosity IV of the film is less than 0.55 dl / g, the strength will be low due to the small molecular weight, and if the film thickness is thin, the film tends to tear easily during film formation. Also, the rheometer viscosity ηH at 280°C and a shear rate of 31.4 rad / s, as described later, tends to be low. On the other hand, if the intrinsic viscosity IV of the film exceeds 0.65 dl / g, the strength will be high due to the large molecular weight, making it difficult to tear and resulting in poor tearability by hand. However, thinner film varieties tend to tear easily during the film formation process, especially during stretching. Considering that further recycling of the recycled polyester film of the present invention tends to decrease the intrinsic viscosity of the recycled polyester raw material, there is great significance in setting the intrinsic viscosity IV of the already completed film to 0.55 dl / g or more and 0.65 dl / g or less. Preferably, the intrinsic viscosity IV of the film is 0.58 dl / g or more and 0.63 dl / g or less.

[0018] The rheometer viscosity ηH (hereinafter sometimes simply referred to as ηH) of the film of the present invention at 280°C and a shear rate of 31.4 rad / s is 120 Pa·s or less. When ηH is 120 Pa·s or less, the film tends to tear easily and its tearability by hand improves, while when ηH exceeds 120 Pa·s, the film tends to tear less easily and its tearability by hand deteriorates. The lower limit is not particularly limited, but from the viewpoint of film formation stability, it is preferably 70 Pa·s or more, more preferably 80 Pa·s or more, and more preferably 90 Pa·s or more.

[0019] The Tmeta (hereinafter sometimes simply referred to as Tmeta) of the film observed by differential scanning calorimetry (DSC) of the present invention is 220°C or higher. Within this range, the amorphous components in the film crystallize, making the film easier to tear and improving its tearability by hand. If Tmeta is below 220°C, the amount of amorphous components in the film increases, and the film tends to be more difficult to tear. Furthermore, when Tmeta exceeds 220°C, the amorphous components crystallize, and the dimensional stability of the film during heating tends to improve.

[0020] The thermal shrinkage rate of the recycled polyester film of the present invention when heated at 150°C for 30 minutes is preferably -2.0% to 2.0% in both the MD direction and the TD direction, more preferably -1.0% to 1.5%, and even more preferably -0.5% to 1.0%.

[0021] The recycled polyester film of the present invention preferably has a film edge tear resistance of 10.0 kgf / 20 mm or less in at least one of the MD direction and the TD direction. More preferably, it is 5.0 kgf / 20 mm or less in at least one of them, and still more preferably, both the MD direction and the TD direction are 10.0 kgf / 20 mm or less. When the film edge tear resistance is 10.0 kgf / 20 mm or less in at least one of the MD direction and the TD direction, the cutting direction can be appropriately selected for processing to impart hand tearability. When the film edge tear resistance is 10.0 kgf / 20 mm or less in both the MD direction and the TD direction, the trouble of selecting the cutting direction can be saved. The lower limit is not particularly limited, but since the edge tear resistance varies depending on the film thickness, it is preferably 1.0 kgf / 20 mm or more.

[0022] For the recycled polyester film of the present invention, it is preferable that the value (γ) obtained by dividing the film edge tear resistance (kgf / 20 mm) by the film thickness (μm) is 1.00 or less in at least one of the MD direction and the TD direction. The MD direction is the film manufacturing progress direction, and the TD direction is the direction perpendicular to the MD direction in the plane.

[0023] When either of these values exceeds 1.00, the film tends to be difficult to tear. Also, preferably, when both the MD direction and the TD direction of the value (γ) are 1.0 or less, the ease of tearing of the film can be imparted. Preferably, at least one of these values is 0.90 or less, more preferably 0.70 or less, and still more preferably, both the MD direction and the TD direction have low values. Since the film edge tear resistance is a value dependent on the thickness, in the present invention, it can be represented by the value (γ) divided by the thickness.

[0024] The film edge tear resistance is measured in accordance with JIS C2318-72, and the unit is kgf / 20 mm.

[0025] The thickness of the recycled polyester film of the present invention is preferably 2 μm or more and 50 μm or less. If the film thickness exceeds 50 μm, the tearability by hand may deteriorate, so it is preferably 50 μm or less, and more preferably 25 μm or less.

[0026] The recycled polyester film of the present invention can be made to be easily torn even when its thickness is increased, by controlling the rheometer viscosity ηH and Tmeta, and furthermore, a large amount of recycled polyester raw material can be used to constitute the recycled polyester film.

[0027] A preferred embodiment or example of the film manufacturing method of the present invention will be described below.

[0028] The recycled polyester resin is not particularly limited as long as it has polyester as its main component. Furthermore, the film of the present invention can be made by blending other polyester resins in addition to recycled polyester resin. When a functional layer is laminated on the polyester film to be recycled as recycled polyester resin, methods such as immersing the film in an alkali or other chemical to dissolve and remove only the functional layer, or scraping off the functional layer by matting, can be used. In these methods, it is preferable to wash with water to remove the chemical, polymer powder scraped off, and foreign matter that was originally attached during reuse. Furthermore, it is preferable to pulverize the film from which the functional layer has been removed and dry it at a glass transition temperature of around 160°C to remove moisture. It is preferable to reduce the moisture content after drying to about 100 ppm or less. The ppm is on a mass basis. The dried pulverized film is melted in an extruder and extruded from the die in a strand shape, and rapidly cooled and solidified with cold water. It is desirable to shorten the melting time in the extruder to suppress thermal degradation. Furthermore, after the solidified strand is cut into pellet shapes using a strand cutter, it is also preferable to crystallize the surface of the pellets using a hot air dryer or the like to prevent fusion during the drying process when forming the film.

[0029] Next, a polyester resin that is substantially free of particles and the recycled polyester resin mentioned above are mixed in a predetermined ratio, dried, and then supplied to the extruder in a molten state. For the molten extrusion conditions of the polyester resin in the extruder, it is preferable to heat the inside of the extruder to a temperature of melting point (Tm) + 20°C or higher, and the area from the extruder outlet to the slit die to a temperature of melting point (Tm) + 15°C or lower.

[0030] The polymer, melted and extruded in the extruder, is filtered. Since even tiny foreign particles can become large protrusion defects if they enter the film, it is effective to use a high-precision filter that captures more than 95% of foreign particles, for example, that are 3 μm or larger. Next, the film is extruded from the die into a sheet and cooled on a casting roll to produce an unstretched film.

[0031] The stretching method may be sequential biaxial stretching or simultaneous biaxial stretching. Simultaneous biaxial stretching is preferable because it does not involve stretching by rolls, thus suppressing localized heating unevenness on the film surface and obtaining uniform quality, as well as suppressing the speed difference at the contact points between the film and rolls during stretching, and the occurrence of scratches due to the transfer of minute scratches on the rolls. Sequential biaxial stretching is preferable because it allows for individual and precise control of the characteristics in the longitudinal and width directions.

[0032] In simultaneous biaxial stretching, the unstretched film is first stretched simultaneously in the longitudinal and width directions at a stretching temperature of 80°C to 125°C, preferably 85°C to 120°C. If the stretching temperature is lower than 80°C, the film is prone to tearing, and if the stretching temperature is higher than 125°C, sufficient strength may not be obtained. Furthermore, from the viewpoint of preventing uneven stretching, the total stretching ratio in the longitudinal and width directions is 4 to 20 times, preferably 6 to 15 times. If the total stretching ratio is less than 4 times, it is difficult to obtain sufficient strength. On the other hand, if the ratio is greater than 20 times, film tearing is more likely to occur, and it may be difficult to manufacture a stable film. To obtain the required strength, it is preferable to perform another stretching at a temperature of 140°C to 200°C, preferably 160°C to 190°C, to a length of 1.02 to 1.5 times, preferably 1.05 to 1.2 times, in the longitudinal and / or widthwise directions, resulting in a total stretching ratio of 3.0 to 4.5 times, preferably 3.2 to 4.0 times, in the longitudinal direction, and 3.2 to 5.0 times, preferably 3.5 to 4.3 times, in the widthwise direction. After that, heat setting is performed at 220°C to 245°C, preferably 225°C or higher, more preferably 230°C or higher, for 0.5 seconds to 20 seconds, preferably 1.0 second to 15 seconds. If the heat setting temperature is lower than 200°C, thermal crystallization of the film may not proceed well, and the dimensional change rate may not be stable. In addition, to stabilize the physical properties of the film, the temperature difference between the top and bottom of the film during heat treatment is 20°C or less, more preferably 10°C or less, and even more preferably 5°C or less. If the temperature difference between the top and bottom of the film is greater than 20°C, it may cause deterioration of flatness during heat treatment. Subsequently, a relaxation treatment of 0.5% to 7.0% is performed in the longitudinal and / or widthwise directions during the slow cooling section.

[0033] On the other hand, the film of the present invention can also be manufactured using sequential biaxial stretching. For the initial stretching in the longitudinal direction, the stretching temperature is 80°C to 125°C, preferably 85°C to 120°C. If the stretching temperature is lower than 80°C, the film is prone to tearing, and if the stretching temperature is higher than 125°C, the film surface may be susceptible to thermal damage. The stretching ratio is 3.0 to 4.5 times in the longitudinal direction, preferably 3.2 to 4.0 times. For the subsequent stretching in the width direction, the stretching temperature is 80°C to 125°C, preferably 85°C to 120°C. The stretching ratio is 3.2 to 5.0 times in the width direction, preferably 3.5 to 4.3 times. If the temperature and stretching ratio are outside this range, problems such as uneven stretching or film tearing may occur, making it difficult to obtain a film that meets the characteristics of the present invention. In particular, when the stretching ratio during longitudinal stretching is high, the dimensional change rate in the longitudinal direction at a heating temperature of 140°C tends to exceed 0.20%. The film, which has been sequentially biaxially stretched in this manner, is then subjected to re-longitudinal stretching similar to the simultaneous biaxial stretching described above, or is stretched transversely as is, then passed through an intermediate cooling section, and finally heat-set at 220°C to 245°C, preferably 225°C or higher, more preferably 230°C or higher, for 0.5 seconds to 20 seconds, preferably 1.0 second to 15 seconds. If the heat-set temperature is lower than 200°C, the crystallization of the film will not progress, resulting in an unstable structure, and the target dimensional change rate and other characteristics may not be obtained. After that, a relaxation treatment of 0.5% to 7.0% in the longitudinal and / or width directions is performed in a slow-cooling section.

[0034] In sequential biaxial stretching, the longitudinal stretching process is a step where the film and rolls come into contact, and scratches are likely to occur due to the difference in peripheral speed between the rolls and the film. Therefore, a drive system that allows the peripheral speed of each roll to be set individually is preferred. In the longitudinal stretching process, the material of the transport rolls is selected by either heating the unstretched film to above its glass transition point before stretching, or transporting it to the stretching zone while maintaining a temperature below the glass transition point and then heating it all at once during stretching. If the unstretched film is heated to above its glass transition point before stretching, it is preferable to select from non-stick silicone rolls, ceramics, or "Teflon" (registered trademark) to prevent adhesion due to heating. Furthermore, the stretching rolls are subjected to the most stress on the film, and scratches and uneven stretching are likely to occur in this process. Therefore, the surface roughness (arithmetic mean roughness) Ra of the stretching rolls should be 0.005 μm or more and 1.0 μm or less, preferably 0.1 μm or more and 0.6 μm or less. If the surface roughness Ra is greater than 1.0 μm, the irregularities on the roll surface may be transferred to the film surface during stretching. If it is less than 0.005 μm, the roll and the film surface may stick together, making the film more susceptible to thermal damage. To control the surface roughness Ra, it is effective to appropriately adjust the particle size of the abrasive and the number of polishing cycles. When the unstretched film is transported to the stretching zone while being kept at a temperature below the glass transition point and heated all at once during stretching, it is preferable to use metal rolls with a surface roughness Ra of 0.2 μm to 0.6 μm, which have been surface-treated with hard chromium or tungsten carbide, for the transport rolls in the preheating zone. Furthermore, the film may be relaxed in the longitudinal and / or transverse directions during heat treatment.

[0035] The film obtained in this manner has low edge tear resistance and excellent tearability, making it suitable for various industrial product applications. For example, the recycled film of the present invention can be preferably used as a packaging material by applying a metal layer, a printed layer, etc. To create a metallized film, one method for laminating a metal layer is to vaporize a metal material in a vacuum and deposit the vapor onto the film to form a thin film. Examples of metal layers include aluminum and copper. Furthermore, since a large amount of recycled polyester resin can be used, it is advantageous as an environmental protection measure. [Examples]

[0036] The present invention will be described in more detail below based on comparative examples and embodiments. However, the present invention is not limited to the embodiments described below.

[0037] [Method for evaluating physical properties] (1) Intrinsic viscosity of the film IV (dl / g) A polyester resin or polyester film was dissolved in 100 mL of orthochlorophenol (solution concentration C = 1.2 g / mL), and the viscosity of the solution at 25°C was measured using an Ostwald viscometer. Similarly, the viscosity of the solvent was also measured. Using the obtained solution viscosity and solvent viscosity, [η] was calculated using the following formula (B), and the resulting value was defined as the intrinsic viscosity IV.

[0038] ηsp / C = [η] + K[η] 2 ·C ···Formula (B) (Here, ηsp = (solution viscosity / solvent viscosity) - 1, and K is the Huggins constant (assumed to be 0.343).) If there are insoluble substances in the solution in which the polyester resin or polyester film is dissolved, the solution is filtered and the mass of the filtered material is measured. The mass of the sample to be measured is obtained by subtracting the mass of the filtered material from the mass of the sample to be measured.

[0039] (2) Rheometer viscosity ηH (Pa·s) A polyester resin sample or a polyester film sample cut into 40 mm squares and stacked was prepared. It was dried in a vacuum dryer at 150°C for 8 hours until immediately before measurement. After returning to atmospheric pressure with nitrogen, 0.4 g was immediately weighed. Next, 0.4 g of the sample was packed into a parallel plate (60 mm diameter) of a RHEOSOL-G3000 rheometer (manufactured by UBM Co., Ltd.). The distance between the upper and lower plates was set to 5 mm, and the plate was melted at 280°C for 1 minute under a nitrogen atmosphere. Then, the plate distance was adjusted to 0.5 mm, and the shear viscosity ηH at a shear rate of 31.4 rad / s was measured. ηH was calculated as the arithmetic mean of two measurement results, rounded to one decimal place.

[0040] (3) The minute endothermic peak temperature Tmeta (°C) determined by differential scanning calorimetry (DSC) The minute endothermic peak temperature Tmeta(°C) was measured using a differential scanning calorimetry system "Robot DSC-RDC220" manufactured by Seiko Electronics Industries, Ltd., in accordance with JIS K7122-1987 (referencing the 1999 edition of the JIS Handbook), and the disk session "SSC / 5200" was used for data analysis. 5 mg of film was weighed into a sample pan, and the temperature was increased from 25°C to 300°C at a heating rate of 20°C / min for measurement. Tmeta(°C) was defined as the minute endothermic peak temperature before the crystal melting peak in the obtained differential scanning calorimetry chart. If the minute endothermic peak was difficult to observe, the area around the peak was magnified in the data analysis unit to read the peak.

[0041] Although the method for reading the graph of minute endothermic peaks is not described in JIS, it was performed based on the following method. First, a straight line was drawn between the values ​​of 135°C and 155°C, and the area on the endothermic side of the curve on the graph was calculated. Similarly, the area was calculated for 17 points: 140°C and 160°C, 145°C and 165°C, 150°C and 170°C, 155°C and 175°C, 160°C and 180°C, 165°C and 185°C, 170°C and 190°C, 175°C and 195°C, 180°C and 200°C, 185°C and 205°C, 190°C and 210°C, 195°C and 215°C, 200°C and 220°C, 205°C and 225°C, 210°C and 230°C, 215°C and 235°C, and 220°C and 240°C. Since the endothermic amount of minute peaks is usually between 0.2 and 5.0 J / g, only data with an area between 0.2 J / g and 5.0 J / g will be treated as valid data. From a total of 18 area data points, Tmeta(°C) will be defined as the peak temperature of the endothermic peak in the temperature range of the data point that is valid and shows the largest area. If there is no valid data, Tmeta(°C) will be considered as none.

[0042] (4) Film thickness (μm) The film was measured using the micrometer method (JIS-C-2151 (2019)). If the thickness was 50 μm or less, 10 sheets were stacked and measured, and the thickness per sheet was obtained by dividing by the number of sheets and rounding to one decimal place.

[0043] (5) End tear resistance (kgf / 20mm) The film's MD and TD directions were measured in accordance with JIS C2318-72, and the respective edge tear resistances were rounded to two decimal places.

[0044] (6) The value obtained by dividing the tear resistance by the thickness of the film (γ) The tear edge resistances (kgf / 20mm) in the MD and TD directions obtained in (5) above were divided by the film thickness (μm) in (4), and the results were rounded to two decimal places to obtain the respective values ​​(γ) in the MD and TD directions.

[0045] (7) Heat shrinkage rate (%) after heating at 150℃ for 30 minutes A polyester film was cut into strips 15 cm long and 1 cm wide. Lines parallel to the width direction were drawn 2.5 cm inward from each end of the length direction, and the distance L0 between the two parallel lines was measured. Next, the strip samples were heat-treated in a 150°C hot air oven for 30 minutes. After cooling, the distance L1 between the two parallel lines was measured to two decimal places. The dimensions before and after treatment were applied to the following formula, and the calculated value was rounded to two decimal places to obtain the thermal shrinkage rate (%).

[0046] Thermal shrinkage rate (%) = (L0 - L1) / L0 × 100.

[0047] (8) Cutting ability Each film was torn by hand from the MD and TD ends. A ◎ was given if both ends tore easily, a ○ if at least one end tore easily, a △ if at least one end tore with force, and a × if it was difficult to tear even with force applied to both ends.

[0048] [Manufacturing of polyester resin] The method for producing the polyester resin used in the polyester film in the examples is as follows.

[0049] (PET raw material a) 86 parts by mass of terephthalic acid and 37 parts by mass of ethylene glycol were subjected to an esterification reaction at 255°C while distilling off water. After the esterification reaction was complete, 0.01 parts by mass of phosphoric acid, 0.02 parts by mass of magnesium acetate, 0.01 parts by mass of lithium acetate, and 0.01 parts by mass of antimony trioxide were added. Subsequently, under reduced pressure, the mixture was heated to 290°C and the temperature was increased to carry out a polycondensation reaction to obtain a virgin polyester resin that was substantially particle-free, had an intrinsic viscosity of 0.65 dl / g, and a rheometer viscosity ηH of 272 Pa·s. This was designated as PET raw material a.

[0050] (PET raw material b) Virgin polyester raw material b-1 was obtained in the same manner as PET raw material a, except that the final torque of the stirrer used to determine the end of polymerization was changed.

[0051] Furthermore, virgin polyester raw material b-2 was obtained in the same manner as virgin polyester raw material b-1, except that before adding the metal compound when producing virgin polyester raw material b-1, calcium carbonate with a volume-average particle size of 1.1 μm was added in an amount of 1.0 mass% relative to the polyester resin. Similarly, virgin polyester raw material b-3 was obtained in the same manner as virgin polyester raw material b-1, except that the particle species was alumina with a volume-average particle size of 0.03 μm added in an amount of 1.5 mass% relative to the polyester resin. Virgin polyester raw material b-1, virgin polyester raw material b-2, and virgin polyester raw material b-3 were blended in a mass ratio of 97.9:1.9:0.2 to obtain PET raw material b.

[0052] (PET raw material c) Silicone resin (weight-average molecular weight 40,000, R2SiO 1.0 :RSiO 1.5A water slurry was mixed with divinylbenzene / styrene copolymer crosslinked particles, consisting of 80% by mass, 15% by mass, and styrene, with a volume average particle size of 0.3 μm, obtained by a seeding method to adsorb monomers (where the ratio of phenyl groups to methyl groups of hydrocarbon groups R in the silicone resin is 1:40), and this slurry was mixed with virgin polyester raw material b-1 using a vented twin-screw kneader to obtain virgin polyester resin c-1 containing 5 ppm of silicon element relative to the total polyester resin and 2.0% by mass of divinylbenzene / styrene copolymer crosslinked particles relative to the polyester resin.

[0053] Using the virgin polyester raw materials b-1 and b-2 used in the above-mentioned PET raw material b, virgin polyester raw material b-1:virgin polyester raw material b-2:virgin polyester raw material c-1 was blended in a mass ratio of 89.7:4.8:5.5 to obtain PET raw material c.

[0054] (Recovered raw material A) A film was obtained by winding a film roll, which was molded by biaxial stretching using only PET raw material a according to a standard method. While winding the film roll, an aqueous solution was applied to one side of the film using a bar coater, with the solution being adjusted so that the solid content of the polyester resin was 5% by mass, containing 100 parts by mass of polyester resin (product name Z836, manufactured by Go-O Chemical Industry Co., Ltd.), 50 parts by mass of melamine-based crosslinking agent (product name MW12LF, manufactured by Sanwa Chemical Co., Ltd.), and 3 parts by mass of fluorine-based surfactant (product name RY2, manufactured by Go-O Chemical Industry Co., Ltd.). The solution was applied so that the coating thickness after drying was 0.1 μm. After drying and curing at 120°C for 1 minute, the film was wound up to obtain an optical film roll. Subsequently, the optical film roll was cut with a crusher with a screen diameter of Φ5 mm, and the cut used film was then added to a washing tank equipped with stirring blades. A 4.0% by mass sodium hydroxide aqueous solution was added to achieve a washing concentration of 10% by mass. Furthermore, 0.02% by mass of polyoxyethylene octylphenyl ether was added to the added sodium hydroxide aqueous solution. The washing tank was heated to 85°C, and the material was washed for 20 minutes while stirring at a stirrer speed of 200 rpm, after which it was rinsed with pure water. The polyester support, which had been vacuum-dried at 120°C, was then melt-kneaded in an extruder, and coarse particles and foreign matter were filtered out using a filter with a mesh size of 5 μm. The material was then extruded from the die in a strand form, and cut while cooling to form chips, which were used as the recovered raw material A. The obtained recovered raw material A had an intrinsic viscosity IV of 0.63 dl / g and a rheometer viscosity ηH of 197 Pa·s.

[0055] (Recovered raw material B) A film was obtained by biaxial stretching using only PET raw material b as the raw material according to a standard method, and then winding the resulting film into a film roll. Next, this film was compressed and cut in a granulator to form cylindrical pellets of Φ5 mm × 20 mm, which were used as the recovered raw material B. The obtained recovered raw material B had an intrinsic viscosity IV of 0.60 dl / g and an ηH of 169 Pa·s.

[0056] (Recovered material C) Using PET raw material c, a film was formed by biaxial stretching according to a standard method and then wound into a film roll.

[0057] Next, a coating solution containing a cross-linking primer layer (product name BY24-846, manufactured by Toray Dow Corning Silicone Co., Ltd.) adjusted to a solid content of 1% by mass was applied to one side of the film unwound from the film roll using a bar coater to achieve a coating thickness of 0.5 μm after drying, and was dried and cured at 120°C for 1 minute. Within 1 hour thereafter, a coating solution containing 100 parts by mass of addition-reaction type silicone resin (product name LTC750A, manufactured by Toray Dow Corning Silicone Co., Ltd.) and 2 parts by mass of platinum catalyst (product name SRX212, manufactured by Toray Dow Corning Silicone Co., Ltd.) adjusted to a solid content of 5% by mass was applied using a bar coater to achieve a coating thickness of 0.5 μm after drying, and was dried and cured at 120°C for 1 minute before being wound up to obtain a release film roll. The silicon content of the prepared release film was measured and found to be 700 ppm.

[0058] 100 parts by mass of barium titanate (product name HPBT-1, manufactured by Fuji Titanium Industries Co., Ltd.), 10 parts by mass of polyvinyl butyral (product name BL-1, manufactured by Sekisui Chemical Co., Ltd.), 5 parts by mass of dibutyl phthalate, and 60 parts by mass of toluene-ethanol (mass ratio 30:30) were mixed with glass beads having a number average particle size of 2 mm. The mixture was then mixed and dispersed in a jet mill for 20 hours, and then filtered to prepare a paste-like ceramic slurry. The obtained ceramic slurry was applied to a release film using a die coater to a thickness of 1 μm after drying, dried, and wound up to obtain a green sheet. Subsequently, the green sheet was peeled off from the resulting laminate by adsorption to obtain a used film roll.

[0059] Used film was cut using a crusher with a screen diameter of Φ5 mm. The cut used film was then added to a washing tank equipped with stirring blades, and a 4.0% by mass sodium hydroxide aqueous solution was added to achieve a washing concentration of 10% by mass. Further, 0.02% by mass of polyoxyethylene octylphenyl ether was added to the added sodium hydroxide aqueous solution. The washing tank was heated to 85°C, and after washing for 20 minutes while stirring at a stirrer speed of 200 rpm, it was rinsed with pure water. The polyester support, which had been vacuum dried at 120°C, was then melt-kneaded in an extruder, and after filtering out coarse particles and foreign matter using a filter with a mesh size of 5 μm, it was extruded from the die in a strand form, cooled and cut into chips, which were used as the recovered raw material C. The obtained recovered raw material C had an intrinsic viscosity IV of 0.60 dl / g and an ηH of 150 Pa·s.

[0060] <Comparative Example 1> PET raw material a was mixed in a blender with 60% by mass of recovered raw material A and then dried under reduced pressure at 160°C for 8 hours before being supplied to an extruder. After melt extrusion at 280°C and filtration with a high-precision filter that captures more than 95% of foreign matter larger than 5 μm, the film was passed through a T-die maintained at 280°C and wound onto a casting drum with a surface temperature of 25°C, where it was cooled and solidified to obtain an unstretched film.

[0061] The unstretched film was preheated to 90°C using a preheating roll, then heated to 110°C from above and below using a radiation heater while being stretched 3.5 times in the longitudinal direction by utilizing the difference in peripheral speed between the rolls. Subsequently, it was cooled to 25°C using a cooling roll to obtain a uniaxially oriented film.

[0062] Next, the uniaxially oriented film was held with clips and preheated in an oven with 100°C hot air. Subsequently, in the stretching process, it was continuously heated with 120°C hot air and stretched 3.5 times in the width direction. The resulting biaxially oriented film was then introduced to the heat treatment process and heat-treated with hot air with a heat-fixing temperature of 204°C. The film that had undergone the heat treatment process was cooled from 204°C to 135°C while being subjected to a 7% relaxation treatment, and then cooled to 100°C. Next, the film was removed from the oven, the ends in the width direction were removed, and then it was wound up to obtain a polyester film with a thickness of 25 μm. The obtained physical properties are shown in Table 2.

[0063] <Example 1> A recycled polyester film with a thickness of 6 μm containing recycled materials was obtained in the same manner as in Comparative Example 1, except that, instead of the PET raw material of Comparative Example 1, the recovered raw material A and recovered raw material B were mixed in a blender in a mass ratio of 50:50, then dried under reduced pressure at 160°C for 8 hours and supplied to an extruder, the final film thickness was set to 6 μm, and the heat setting temperature was as shown in Table 1. The obtained physical properties are shown in Table 2.

[0064] <Examples 2 to 7> As shown in Tables 1 and 2, recycled polyester film was obtained in the same manner as in Example 1, except that the type of raw material, the amount of raw material used, the heat-fixing temperature, and the thickness of the final film were changed. The obtained physical properties are shown in Table 2.

[0065] [Table 1]

[0066] [Table 2]

Claims

1. A recycled polyester film having an intrinsic viscosity IV of 0.55 dl / g or more and 0.65 dl / g or less, a rheometer viscosity ηH (Pa·s) of 120 or less at 280°C and a shear rate of 31.4 rad / s, and a Tmeta observed by differential scanning calorimetry (DSC) of 220°C or higher.

2. The recycled polyester film according to claim 1, wherein the tear resistance of the film at the edges is 10.0 kgf / 20 mm or less in at least one of the MD direction and the TD direction.

3. The recycled polyester film according to claim 1, wherein the thickness of the film is 2 μm or more and 50 μm or less.

4. The film is a recycled polyester film according to any one of claims 1 to 3, wherein the film contains more than 0% by mass and 100% by mass or less of recycled polyester raw material with respect to the polyester resin constituting the film.

5. A metallized film comprising a metal layer on a recycled polyester film as described in claim 4.

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