polyester film

Abstract

To provide a polyester film to which a recycled resin is applied, and that has small variation in film surface roughness and has good handling property.SOLUTION: A polyester film contains a recycled polyester resin composition, and satisfies the following expression (I): (Ra-σ) / Ra<15%. Here, (Ra-σ) / Ra is a value obtained by the following method. Arithmetic average roughness (Ra) and its standard deviation (Ra-σ) are determined by cutting the polyester film into 10 cm square, using a non-contact optical type roughness measurement device (NewView7300 made by Zygo), using a 50-power objective lens, randomly changing a place with a measurement area of 139 μm×104 μm and measuring 40 visual fields, and using a surface analysis software MetroPro incorporated in the measurement device and a band-pass filter of a wavelength of 1.65-50 μm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polyester film containing a polyester resin composition derived from recycling.

Background Art

[0002] Polyester is excellent in mechanical properties, thermal properties, chemical resistance, electrical properties, and moldability, and is used in various applications. Among polyesters, polyethylene terephthalate (hereinafter referred to as PET) is particularly widely used in applications that require high quality, such as optical films and release films, because of its excellent transparency and processability. However, since process films such as release films are discarded after use, there has been a demand for reducing the environmental impact in recent years.

[0003] As a measure to reduce the environmental impact, there is thermal recycling in which polyester resin to be discarded is burned to obtain thermal energy. However, when thermal recycling is performed, carbon dioxide is generated and the polyester raw material is lost. Therefore, it is necessary to newly use petroleum raw materials to reproduce polyester. In response to these problems, Patent Document 1 discloses a technique related to a film recovered from a PET bottle.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 discloses a laminated film made using polyester resin recycled from PET bottles. However, repeated material recycling of polyester resin by remelting it leads to thermal decomposition, hydrolysis, and oxidative decomposition of the polyester resin, resulting in discoloration, generation of foreign matter, and a decrease in molecular weight. This leads to a decline in quality, particularly in surface roughness, and poor handling properties of the film surface.

[0006] The object of the present invention is to provide a polyester film that uses recycled resin, has low variation in film surface quality, particularly in surface roughness, and exhibits excellent handling properties. [Means for solving the problem]

[0007] As a result of diligent research to solve the above problems, we have arrived at a polyester film with minimal variation in film surface roughness by applying recycled resin. The object of the present invention is achieved by the following means.

[0008] (1) A polyester resin composition derived from recycled materials 70% by weight or more Including and satisfying the following equation (I) Biaxial stretching for mold release process Polyester film.

[0009] 4.5%≦ (Ra-σ) / Ra ≦6.5 % (I) Here, (Ra-σ) / Ra is the value obtained as follows: A polyester film is cut into 10cm squares, and 40 field measurements are taken using a non-contact optical roughness meter (Zygo NewView7300) with a 50x objective lens, measuring an area of ​​139μm × 104μm at randomly changed locations. The arithmetic mean roughness (Ra) and its standard deviation (Ra-σ) are then calculated using the MetroPro surface analysis software built into the meter, with a band-pass filter for wavelengths of 1.65 to 50μm. (2) The polyester resin composition is as described in (1), comprising a polyester resin composition derived from chemical recycling that depolymerizes polyester resin and a polyester resin composition derived from material recycling that remelts polyester. Biaxial stretching for mold release process Polyester film. (3) The same as in (1), characterized in that two or more layers are stacked. Biaxial stretching for mold release process Polyester film. (4) The method described in (3) which includes a polyester resin composition derived from chemical recycling on one of the surface layers. Biaxial stretching for mold release process Polyester film. ( 5 The biaxially oriented polyester film for process release is selected from one of the following: release film for multilayer ceramic capacitor manufacturing, film for dry film resist, film for polarizing plate release, or film for optical release. (1) The description Biaxial stretching for mold release process Polyester film. [Effects of the Invention]

[0010] This invention provides a polyester film that uses recycled resin, exhibits minimal variation in film surface roughness, and has excellent handling properties. [Modes for carrying out the invention]

[0011] The present invention will be described in detail below. The polyester film of the present invention is a film made using a polyester resin composition obtained by polycondensation of a dicarboxylic acid component and a diol component. Various dicarboxylic acid components can be used as the dicarboxylic acid component, such as aromatic dicarboxylic acids, linear aliphatic dicarboxylic acids, and alicyclic dicarboxylic acids. Among these, aromatic dicarboxylic acids and their ester-forming derivative components are preferred from the viewpoint of mechanical properties, heat resistance, and hydrolysis resistance of the polyester resin composition. In particular, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and their ester-forming derivative components are preferred from the viewpoint of polymerizability and mechanical properties, with terephthalic acid being the most preferred.

[0012] Various diols can be used as the diol component. For example, aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, butanediol, and neopentyl glycol; alicyclic diols such as cyclohexanedimethanol and cyclohexanediethanol; and aromatic diols such as bisphenol A, bisphenol S, styrene glycol, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene, and 9,9'-bis(4-hydroxyphenyl)fluorene. Among these, ethylene glycol is particularly preferred from the viewpoint of mechanical properties.

[0013] Furthermore, the present invention may also involve copolymerization using multiple types of dicarboxylic acid components, diol components, and hydroxycarboxylic acids, as long as the effects of the present invention are not impaired.

[0014] The polyester film of the present invention must contain a polyester resin composition derived from recycled materials. Recycling can include material recycling and chemical recycling, as described below. From the viewpoint of reducing environmental impact, it is preferable to materially recycle used polyester, but the polyester resin composition obtained by material recycling may contain impurities derived from used polyester or impurities generated by thermal degradation during recycling. Chemical recycling makes it easier to remove impurities contained in used polyester during the recycling process. By combining these various recycled polyester resin compositions as needed, it is possible to obtain a high-quality polyester film with minimal environmental impact.

[0015] The polyester film of the present invention must satisfy the following formula (I).

[0016] (Ra-σ) / Ra<15% (I) (Ra-σ) and Ra are values calculated using a non-contact optical roughness measuring instrument (Zygo NewView 7300) with a 50x objective lens on a 10 cm square cutout of the polyester film, at a measurement area of 139 μm × 104 μm, by randomly changing the location and performing 40-field measurements, and are calculated using a band-pass filter with a wavelength of 1.65 - 50 μm by the surface analysis software MetroPro built into the measuring instrument. Ra in formula (I) is the arithmetic mean surface roughness, and Ra-σ is the standard deviation of that Ra. Formula (I) is the standard deviation divided by the average value and represents the coefficient of variation, and the smaller the value, the more uniform the surface roughness. In the polyester film of the present invention, it is necessary that this coefficient of variation (Ra-σ) / Ra is less than 15%, more preferably less than 7%, and even more preferably less than 6%. This Ra-σ is easily affected by the quality of the polyester resin composition derived from material recycling, but by satisfying the above range, it becomes a polyester film having handling properties suitable for a film for mold release in a process where surface uniformity is required.

[0017] The polyester film of the present invention preferably contains a polyester resin composition derived from chemical recycling and a polyester resin composition derived from material recycling.

[0018] A polyester resin composition derived from chemical recycling is a polyester resin composition obtained by using used polyester products such as PET bottles, polyester films, clothes, containers, etc., and scraps generated in the molding process, depolymerizing them, and performing repolymerization after purification treatment, etc. When using a polyester film as a raw material for recycling, it is preferable to use a biaxially stretched polyester for mold release.

[0019] The methods of chemical recycling of polyester resin compositions include a method of depolymerizing with ethylene glycol to obtain bis-hydroxyethyl terephthalate and its oligomers, and then repolymerizing; a method of depolymerizing with ethylene glycol and then performing methanol decomposition to obtain dimethyl terephthalate and then repolymerizing; and a method of performing hydrolysis to obtain terephthalic acid and then repolymerizing, but are not limited thereto. In chemical recycling, it depolymerizes into monomers and oligomers such as bis-hydroxyethyl terephthalate and its oligomers, dimethyl terephthalate, and terephthalic acid, purifies them, and repolymerizes them using these as raw materials, so it becomes possible to obtain physical properties equivalent to those of virgin polyester resin compositions that have not undergone recycling. A virgin polyester resin composition is an unused polyester resin composition manufactured using petroleum-derived raw materials or bio-derived raw materials. Incidentally, if necessary, new dicarboxylic acid components or glycol components may be mixed into the low polymers depolymerized by chemical recycling.

[0020] A polyester resin composition derived from material recycling is a polyester resin obtained by collecting used polyesters such as PET bottles, polyester films, clothes, and containers, as well as scraps generated in the molding process, and, if necessary, performing operations such as pulverization, washing, and foreign matter removal, and then melting and molding them into flakes or pellets and then melting them into films or the like. When using a polyester film as a raw material for recycling, it is preferable to use a biaxially stretched polyester for mold release.

[0021] A polyester resin composition derived from material recycling has a history of multiple hot moldings and use as molded products, so the degradation of the polyester resin itself has progressed, and its quality is lower than that of virgin polyester resin compositions.

[0022] The polyester film of the present invention needs to contain a polyester resin composition derived from recycling, and may contain, as other components, a virgin polyester resin composition that has not undergone recycling.

[0023] In the polyester film of the present invention, the polyester resin composition derived from chemical recycling is preferably 3% by weight or more, more preferably 5% by weight or more, and even more preferably 10% by weight or more of the total. As an upper limit, from the viewpoint of environmental impact and cost, it is preferably 80% by weight or less, and more preferably 60% by weight or less. Furthermore, the polyester resin composition derived from material recycling is preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 80% by weight or more of the total. As an upper limit, from the viewpoint of film quality, it is preferably 90% by weight or less. Material recycling is a preferred recycling method in terms of environmental impact and cost, but repeated processes such as melt molding and pelletizing subject the polyester resin composition to thermal history. This thermal history can lead to thermal decomposition, hydrolysis, and oxidative decomposition, which can result in a decrease in film quality. In addition, material recycling involves a mixture of recycled raw materials with various histories, and their quality is not necessarily consistent. When a polyester film is manufactured using such recycled raw materials, variations in film quality, particularly in surface roughness, may occur due to variations in the quality of the original raw materials. Therefore, for release films where surface uniformity is required, a polyester film with uniform surface roughness can be obtained by using a method that combines a polyester resin composition derived from material recycling and a polyester resin composition derived from chemical recycling, or by applying a coating to the film surface while using a resin composition derived from material recycling. In the present invention, it is preferable to use both a polyester resin composition derived from chemical recycling and a polyester resin composition derived from material recycling, making it possible to achieve high film quality while reducing the environmental impact as a recycled film.

[0024] Furthermore, in order to reduce environmental impact and improve film quality, the total amount of recycled polyester resin composition is preferably 70% by weight or more of the total polyester film, more preferably 80% by weight or more, and even more preferably 90% by weight or more.

[0025] The polyester film of the present invention is preferably a laminated film of two or more layers. In particular, it is preferable that one of the surface layers contains a polyester resin composition derived from chemical recycling. Chemical recycling allows for the restoration of quality to the same level as virgin polyester resin compositions, even when using polyester resin that has undergone repeated molding and material recycling and has been subjected to thermal history as the raw material. Furthermore, particles and other additives can be added as needed during repolymerization, making it possible to produce a high-quality polyester film, especially when used in the surface layer.

[0026] The polyester film of the present invention may be in any stretched form, such as an unstretched film, a uniaxially oriented film, or a biaxially oriented film, but from the viewpoint of mechanical strength, a biaxially oriented film is preferred. Furthermore, the polyester film of the present invention can be suitably used as a biaxially oriented polyester film for process release. This is because the film for this application becomes unnecessary after release and can be suitably utilized as a raw material for recycling, and further recycling it for this application is preferable from the viewpoint of a circular economy. Specifically, such process release films can be suitably used as release films for the manufacture of multilayer ceramic capacitors (MLCCs), films for dry film resists, films for polarizing plate release, and films for optical release.

[0027] The following is an example of a method for obtaining a biaxially oriented polyester film. Methods such as the molten casting method, in which polyester resin is heated and melted in an extruder and extruded from a die onto a cooled cast drum to form a sheet, and the solution casting method, in which polyester resin is dissolved in a solvent, the solution is extruded from a die onto a support such as a cast drum or endless belt to form a film, and then the solvent is dried and removed from this film layer to form a sheet, can also be used.

[0028] Furthermore, in the case of laminated films, a method is preferably used in which the polyester resin of each layer to be laminated is introduced into a separate extruder, melted, and then combined, and co-extruded from a die onto a cooled cast drum to process it into a sheet (a method of melt film formation by co-extrusion). This method will be described in detail below.

[0029] First, polyester resin is fed into the extruder corresponding to each layer and heated, melted, and extruded. The layers are laminated using a confluence block and co-extruded from the die onto a cast drum cooled to a surface temperature of 10-60°C. The film is then cooled and solidified using electrostatic force to create an unstretched film. At this time, it is preferable to filter the polyester resin melted in the extruder. Since even very small foreign matter can become large protrusions and defects in the film, it is effective to use a high-precision filter that captures 95% or more of foreign matter larger than 5 μm.

[0030] Next, the unstretched film is guided to a group of rolls heated to a temperature of 70-140°C and stretched 3-4 times in the longitudinal direction (vertical direction, i.e., the direction in which the sheet moves), and then cooled in a group of rolls heated to a temperature of 20-50°C. Subsequently, the sheet is guided to a tenter while both ends are held with clips and stretched 3-4 times in the direction perpendicular to the longitudinal direction (width direction) in an atmosphere heated to a temperature of 80-240°C. After stretching, a relaxation treatment of 0.1-5% in the longitudinal and width directions may also be applied. As for the biaxial stretching method, in addition to the sequential biaxial stretching method in which the longitudinal and width directions are stretched separately as described above, either the simultaneous biaxial stretching method in which the longitudinal and width directions are stretched at the same time is acceptable. [Examples]

[0031] The present invention will be described in more detail below with reference to the following examples. The physical properties in the examples were measured by the following method. Furthermore, Examples 5, 6, and 7 are equivalent to Comparative Examples 2, 3, and 4.

[0032] (1) Surface roughness (Ra) and standard deviation (Ra-σ) of polyester film A 10cm square was cut from a polyester film, and 40 field measurements were taken using a non-contact optical roughness meter (Zygo NewView7300) with a 50x objective lens, measuring an area of ​​139μm × 104μm at randomly changed locations. The surface analysis software MetroPro, built into the meter, was used to determine the arithmetic mean roughness (Ra) and its standard deviation (Ra-σ) using a band-pass filter with a wavelength of 1.65 to 50μm.

[0033] (2) Total thickness of the polyester film (unit: μm) The total thickness of the film layers was determined using a dial gauge in accordance with JIS K7130 (1992) A-2 method. Ten layers of film were stacked, and the thickness in the direction normal to the film surface was measured at five arbitrary points. The average value of these measurements was then divided by 10 to obtain the total thickness.

[0034] (3) Lamination thickness of polyester film (unit: μm) The thickness of each layer of the laminated film was determined by cutting a cross-section of the film parallel to the film width direction using a microtome, observing the cross-section at 5000x magnification with a Hitachi field emission scanning electron microscope (model S-4000), determining the ratio of the particle-containing layer to the total layer thickness, and calculating the particle-containing layer thickness from the total layer thickness measured in (2).

[0035] (4) Handling performance evaluation Using a slip tester manufactured by Toyo Seiki Co., Ltd., the value was measured three times when the top and bottom layers of two films were rubbed together in accordance with JIS K7125 (1999), and the static friction coefficient μs was calculated from the average value. The static friction coefficient was used as an indicator of handling performance and evaluated according to the following criteria. ◎ and ○ were considered passing grades. ◎: Greater than 0.1 and less than or equal to 0.3 ○: Greater than 0.3 and less than or equal to 0.5 ×: Exceeds 0.5.

[0036] (5) Particle detachment evaluation The first layer of a biaxially oriented polyester film was subjected to 100 reciprocating cycles using Toray Industries' Toraysee® (registered trademark) at a load of 500 g / cm, a speed of 60 mm / sec, and a reciprocating distance of 120 mm. A Japan Abrasion Society-type friction fastness tester (AB-301, manufactured by Tester Sangyo Co., Ltd.) was used as the abrasion resistance test apparatus. After the test, the powder on the Toraysee® surface was visually observed and evaluated according to the following criteria. ◎ and ○ were considered pass. ◎: No powder at all on Toraysee (registered trademark) ○: Some powder can be seen on the Toraysee (registered trademark) product. ×: Powder is visible throughout the Toraysee (registered trademark) product.

[0037] (Reference example) Resin A: Polyester resin derived from chemical recycling Resin B: Polyester resin derived from material recycling Resin C: Virgin polyester resin Resin D: A polyester resin derived from chemical recycling, containing 1 wt% silica particles with a volume-average particle size of 1.1 μm. Furthermore, the polyester resin derived from chemical recycling is obtained by recovering biaxially oriented polyester film used for process release, depolymerizing it with ethylene glycol, filtering and purifying it, and then repolymerizing it. The polyester resin derived from material recycling is obtained by recovering biaxially oriented polyester film used for process release containing particles, cutting and washing it, remelting it, and then pelletizing it.

[0038] (Example 1) For the first and third layers of the polyester film, resin A was blended in a ratio of 50 parts by weight and resin D in a ratio of 50 parts by weight. After vacuum drying at 160°C for 2 hours, the mixture was fed into the extruder for the first layer and the extruder for the third layer. Similarly, for the second layer of the polyester film, resin A was blended in a ratio of 20 parts by weight and resin B in a ratio of 80 parts by weight. After vacuum drying at 160°C for 2 hours, the mixture was fed into the extruder for the second layer. The respective raw materials were melted at 280°C in the extruder and then combined and laminated in a lamination confluence block to create a three-layer laminate with the first, second, and third layers in the thickness direction of the film. Subsequently, the laminate was extruded onto a casting drum with a surface temperature of 25°C to create a laminated sheet with a three-layer structure. Next, the sheet was preheated with a group of heated rolls, then stretched 3.5 times in the longitudinal direction (vertical direction, i.e., the direction of sheet travel) at a temperature of 90°C, and then cooled with a group of temperature rolls at 25°C to obtain a uniaxially oriented film. The obtained uniaxially oriented film was stretched 3.8 times in the direction perpendicular to the longitudinal direction (width direction) in a 110°C heating zone inside a tenter while both ends were held with clips. Subsequently, it was heat-set at a temperature of 230°C for 10 seconds in the heat treatment zone inside the tenter. After uniform slow cooling in the cooling zone, it was wound up to obtain a polyester film with a thickness of 25 μm. The physical properties of the obtained polyester film are shown in Table 1.

[0039] The polyester film obtained in Example 1 had surface properties suitable for use as a release film in processes, etc.

[0040] (Examples 2-7) A polyester film was obtained in the same manner as in Example 1, except that the resin composition was changed as shown in Table 1. The physical properties of the obtained polyester film are shown in Table 1. The polyester films obtained in Examples 2 and 3 had surface properties suitable for use as release films in processes, etc. The polyester film obtained in Example 4 showed some variation in surface roughness, but it had surface properties suitable for use as a release film in processes and the like. The polyester film obtained in Example 5 had slightly worse handling properties, but was of a quality suitable for use as a release film in processes, etc. The polyester films obtained in Examples 6 and 7 showed some variation in surface roughness and slightly worsened handling properties, but were of a quality suitable for use as release films in processes, etc.

[0041] (Example 8) As the resin for the first layer of the polyester film, resin A was blended in a ratio of 50 parts by weight and resin D in a ratio of 50 parts by weight. After being dried under reduced pressure at 160°C for 2 hours, the mixture was fed into an extruder for the first layer. Similarly, as the resin for the second layer of the polyester film, resin A was blended in a ratio of 10 parts by weight, resin B in a ratio of 80 parts by weight and resin C in a ratio of 10 parts by weight. After being dried under reduced pressure at 160°C for 2 hours, the mixture was fed into an extruder for the second layer. The respective raw materials were melted at 280°C in the extruder and then combined and laminated in a lamination confluence block to form a two-layer laminate consisting of the first and second layers. Subsequently, the laminate was extruded onto a casting drum with a surface temperature of 25°C to create a laminated sheet with a two-layer structure. Next, the sheet was preheated with a group of heated rolls, then stretched 3.5 times in the longitudinal direction (vertical direction, i.e., the direction of sheet travel) at a temperature of 90°C, and then cooled with a group of temperature rolls at 25°C to obtain a uniaxially oriented film. The obtained uniaxially oriented film was stretched 3.8 times in the direction perpendicular to the longitudinal direction (width direction) in a 110°C heating zone inside a tenter while both ends were held with clips. Subsequently, it was heat-set at a temperature of 230°C for 10 seconds in the heat treatment zone inside the tenter. After uniform slow cooling in the cooling zone, it was wound up to obtain a polyester film with a thickness of 25 μm. The physical properties of the obtained polyester film are shown in Table 1.

[0042] The polyester film obtained in Example 8 had surface properties suitable for use as a release film in processes, etc.

[0043] (Example 9) In the film manufacturing process of Example 4, a coating step was added between the longitudinal stretching and transverse stretching steps, and a 50 nm thick coating layer containing silica particles with an average diameter of 0.3 μm was applied to both surfaces of the film. The physical properties are shown in Table 1.

[0044] The polyester film obtained in Example 9 had surface properties suitable for use as a release film in processes, etc.

[0045] (Comparative Example 1) As the resin constituting the first layer of the polyester film, resin B was dried under reduced pressure at 160°C for 2 hours and then fed into the extruder for the first layer. Each raw material was melted at 280°C in the extruder and extruded onto a casting drum with a surface temperature of 25°C to create a sheet. Subsequently, the sheet was preheated with a group of heated rolls, then stretched 3.5 times in the longitudinal direction (vertical direction, i.e., the direction in which the sheet moves) at a temperature of 90°C, and then cooled with a group of temperature rolls at 25°C to obtain a uniaxially oriented film. Holding both ends of the obtained uniaxially oriented film with clips, it was stretched 3.8 times in the direction perpendicular to the longitudinal direction (width direction) in a heating zone of 110°C in a tenter. Subsequently, it was heat-set at a temperature of 230°C for 10 seconds in the heat treatment zone of the tenter. Then, after uniform slow cooling in the cooling zone, it was wound up to obtain a polyester film with a thickness of 25 μm. The physical properties of the obtained polyester film are shown in Table 1.

[0046] The polyester film obtained in Comparative Example 1 had a large variation in surface roughness and poor handling properties, making it unsuitable for use as a release film in process manufacturing.

[0047] [Table 1] [Industrial applicability]

[0048] The polyester film obtained in this manner is useful for optical applications, agricultural materials, horticultural materials, fishing materials, civil engineering and construction materials, stationery, medical supplies, automotive parts, electrical and electronic components, and other applications, and is particularly suitable as a release film for processes where high quality is required.

Claims

1. A biaxially oriented polyester film for process release containing 70% by weight or more of a recycled polyester resin composition and satisfying the following formula (I). 4.5%≦(Ra-σ) / Ra≦6.5% (I) Here, (Ra-σ) / Ra is a value obtained as follows: A polyester film is cut into 10 cm squares, and 40 field measurements are taken using a non-contact optical roughness meter (Zygo NewView 7300) with a 50x objective lens, measuring an area of ​​139 μm × 104 μm at random locations. The arithmetic mean roughness (Ra) and its standard deviation (Ra-σ) are then calculated using the MetroPro surface analysis software built into the meter, with a band-pass filter for wavelengths of 1.65 to 50 μm.

2. The biaxially oriented polyester film for process release according to claim 1, wherein the polyester resin composition comprises a polyester resin composition derived from chemical recycling that depolymerizes polyester resin and a polyester resin composition derived from material recycling that remelts polyester.

3. The biaxially oriented polyester film for process release according to claim 1, characterized in that it is laminated in two or more layers.

4. The biaxially oriented polyester film for process release according to claim 3, comprising a polyester resin composition derived from chemical recycling on one of its surface layers.

5. The biaxially oriented polyester film for process release according to claim 1, wherein the biaxially oriented polyester film for process release is selected from any of the following: a release film for manufacturing multilayer ceramic capacitors, a film for dry film resists, a film for polarizing plate release, and a film for optical release.

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