Polyethylene terephthalate film, release film, and method for producing polyethylene terephthalate film

Abstract

The objective of the present invention is to provide: a polyethylene terephthalate film which, even when a recycled resin is used, can reduce internal foreign matter, specifically, coarse internal foreign matter containing calcium carbonate particles, that is, coarse aggregates of calcium carbonate particles in a film; a method for producing the same; and a release film. The polyethylene terephthalate film includes siloxane and calcium carbonate particles. The content of a Si element derived from the siloxane is 30 ppm to 500 ppm with respect to the total mass of the polyethylene terephthalate film. In a fluorescence spectrum of the polyethylene terephthalate film as measured with excitation light having a wavelength of 330 nm, the ratio of a fluorescence emission intensity at 460 nm to a fluorescence emission intensity at 395 nm is 0.43 to 0.60.

Description

Polyethylene terephthalate film, release film, and method for manufacturing polyethylene terephthalate film

[0001] This invention relates to polyethylene terephthalate film, release film, and a method for producing polyethylene terephthalate film. In particular, this invention relates to polyethylene terephthalate film useful as a base film used with a functional layer, and a method for producing the same.

[0002] Films containing functional layers with various properties on the surface of a substrate such as synthetic resin (hereinafter sometimes referred to as "substrate film") are used in fields such as electronic components, optical components, labels, and release agents. Used films, films that do not meet specifications, and films damaged during distribution are usually discarded (hereinafter sometimes referred to as "films scheduled for disposal").

[0003] Patent Document 1 discloses a method for measuring the amount of impurities in used film, a method for recycling used film, and a method for making film from recycled raw materials, i.e., recycled raw materials. Patent Document 1 discloses the removal of the silicone-containing release layer, barium titanate, and adhesive residue formed on the surface of the base film.

[0004] Japanese Patent Publication No. 2021-115862

[0005] To make effective use of resources, it is preferable to recycle films that are scheduled for disposal. In particular, the volume of films having a functional layer and a base film (i.e., films with functional layers), such as release films, has been increasing in circulation in recent years, and the amount of waste has also increased accordingly. Therefore, there is a need to recycle and utilize release films. In other words, there is a need for release films that are scheduled for disposal to be reused in the manufacture of release films.

[0006] Furthermore, recycling yield is a crucial factor in establishing a circular recycling system. The technology described in Patent Document 1 exhibits a recycling yield that fluctuates depending on the amount of impurities contained in the film, and the recycling yield tends to worsen as the amount of impurities increases. For example, in the technology described in Patent Document 1, thermal recycling is applied when the amount of film impurities exceeds 0.2% by weight when the total weight of the film is considered to be 100% by weight, and in this case, the recycling yield is 0%.

[0007] Furthermore, release films are always required to have low surface roughness from the perspective of surface transfer to molded products, and the same applies to recycled films. Also, the presence of foreign matter inside the film is highly likely to adversely affect the surface roughness (hereinafter, foreign matter inside the film may be referred to as internal foreign matter). However, when recycling, there is a problem that internal foreign matter tends to increase compared to the production of ordinary films due to the many heating and melting processes involved. Internal foreign matter refers to, for example, aggregates of lubricant particles, PET degradation products, and metals mixed in when recycling films with functional layers. In particular, there is a problem that internal foreign matter containing calcium carbonate particles tends to increase.

[0008] Therefore, the object of the present invention is to provide a polyethylene terephthalate film, a method for producing the same, and a release film that can reduce internal foreign matter, specifically coarse internal foreign matter containing calcium carbonate particles, i.e., coarse aggregates of calcium carbonate particles in the film, even when recycled resin is used. Some preferred embodiments of the present invention relate to polyethylene terephthalate films obtained from raw materials recovered from films destined for disposal, particularly films with functional layers, such as release films. These preferred embodiments can provide polyethylene terephthalate films with superior recycling yield and less coarse internal foreign matter containing calcium carbonate particles compared to the amount of internal foreign matter contained in conventional films.

[0009] As a result of diligent research to solve the above problems, the inventors of the present invention have succeeded in controlling the number of coarse internal foreign matter containing calcium carbonate particles in recycled film to a predetermined range, and have found that the above problems can be solved, thus completing the present invention.

[0010] More specifically, in recent years, there has been an increasing need for activities to reduce environmental impact, including SDGs and carbon neutrality. Therefore, the inventors of this invention diligently studied how to improve the recycling yield in process films, such as release films. As a result, they found that, among various factors, controlling the recycling process in process films is necessary to improve the recycling yield. However, simply increasing the recycling yield may result in insufficient performance of the properties originally required for process films such as release films. Therefore, when using polyethylene terephthalate film as a base material for process films such as release films, it is necessary to achieve a good balance between improving the recycling yield and suppressing the generation of internal foreign matter. Considering this situation, the inventors of this invention have found that even polyethylene terephthalate film reproduced from resin obtained by recycling functional layered films can achieve a good balance between high recyclability and suppression of the increase in internal foreign matter, and have developed the polyethylene terephthalate film and its manufacturing method according to the present invention.

[0011] The present invention provides the following embodiments: [Claim 1] A polyethylene terephthalate film having a surface on which a functional layer is provided, wherein the polyethylene terephthalate film contains siloxane and calcium carbonate particles, the Si element content derived from the siloxane is 30 ppm or more and 500 ppm or less with respect to the total mass of the polyethylene terephthalate film, and in a fluorescence spectrum measured with excitation light at a wavelength of 330 nm, the ratio of the fluorescence emission intensity at 460 nm to the fluorescence emission intensity at 395 nm is 0.43 or more and 0.60 or less. [Claim 2] The polyethylene terephthalate film according to Claim 1, wherein the siloxane contains at least one of an organopolysiloxane having an alkenyl group and an organopolysiloxane having an epoxy group. [Claim 3] The number of internal foreign matter containing calcium element and measuring 50 μm or more is 350 / 100 cm. ２The polyethylene terephthalate film according to item 1 or 2, wherein the following: [Item 4] The polyethylene terephthalate film according to any one of items 1 to 3, wherein the total haze is 15% or less and the external delta haze is 7.0% or less. [Item 5] The polyethylene terephthalate film according to any one of items 1 to 4, comprising 30% to 100% by mass, preferably 50% to 100% by mass, of a resin obtained by material recycling and / or chemical recycling of a functional layer film. [Item 6] The polyethylene terephthalate film according to any one of items 1 to 5, wherein the content of the calcium carbonate particles is 500 ppm to 5000 ppm, preferably 600 ppm to 4500 ppm, relative to the total mass of the polyethylene terephthalate film. [Item 7] The polyethylene terephthalate film according to any one of items 1 to 6, wherein the average particle size of the calcium carbonate particles is 0.1 μm to 5.0 μm, preferably 0.4 μm to 5.0 μm. [Item 8] The polyethylene terephthalate film according to any one of items 1 to 7, wherein the intrinsic viscosity (IV) is 0.400 dL / g or more and 0.700 dL / g or less, preferably 0.510 dL / g or more and 0.580 dL / g or less. [Item 9] The polyethylene terephthalate film according to any one of items 1 to 8, wherein the polyethylene terephthalate resin content in the polyethylene terephthalate film is 80% by mass or more, preferably 90% by mass or more. [Item 10] The polyethylene terephthalate film according to any one of items 1 to 9, wherein the polyethylene terephthalate resin content in the polyethylene terephthalate film is 95% by mass or more, preferably 98% by mass or more. [Item 11] The polyethylene terephthalate film according to any one of items 1 to 10, wherein the repeating units of ethylene terephthalate in the polyethylene terephthalate resin are 90 mol% or more, preferably 95 mol% or more. [Item 12] The polyethylene terephthalate film according to any one of items 1 to 11, wherein the polyethylene terephthalate resin content in the polyethylene terephthalate film is 95% by mass or more, preferably 98% by mass or more.[Item 13] The polyethylene terephthalate film according to any one of items 1 to 12, wherein the content of Si elements derived from the siloxane is 30 ppm or more and 300 ppm or less, preferably 30 ppm or more and 200 ppm or less. [Item 14] The polyethylene terephthalate film according to any one of items 1 to 13, wherein the content of Si elements derived from the siloxane is 40 ppm or more and 500 ppm or less, preferably 40 ppm or more and 300 ppm or less. [Item 15] The polyethylene terephthalate film according to any one of items 1 to 14, wherein the ratio of the fluorescence emission intensity at 460 nm to the fluorescence emission intensity at 395 nm is 0.45 or more, preferably 0.47 or more. [Item 16] The polyethylene terephthalate film according to any one of items 1 to 15, wherein the ratio of the fluorescence emission intensity at 460 nm to the fluorescence emission intensity at 395 nm is 0.49 or more, preferably 0.50 or more. [Clause 17] The polyethylene terephthalate film according to any one of Clauses 1 to 16, wherein the ratio of the fluorescence emission intensity at 460 nm to the fluorescence emission intensity at 395 nm is 0.57 or less, preferably 0.55 or less. [Clause 18] The polyethylene terephthalate film according to any one of Clauses 1 to 17, wherein the siloxane is derived from the resin obtained by material recycling and / or chemical recycling of the functional layered film. [Clause 19] The polyethylene terephthalate film according to any one of Clauses 1 to 18, wherein at least a portion of the polyethylene terephthalate resin is derived from the resin obtained by material recycling and / or chemical recycling of the functional layered film. [Clause 20] The number of internal foreign matter is 210 / 100 cm. ２ More than or equal to 230 pieces / 100cm ２The polyethylene terephthalate film according to any one of items 1 to 19. [Item 21] The polyethylene terephthalate film according to any one of items 1 to 20, wherein the polyethylene terephthalate film is a biaxially oriented polyethylene terephthalate film. [Item 22] A release film comprising the polyethylene terephthalate film according to any one of items 1 to 21 and the functional layer provided on the surface of the polyethylene terephthalate film, wherein the functional layer is a release layer. [Item 23] A method for manufacturing the polyethylene terephthalate film according to any one of items 1 to 21, comprising the following steps: (Step 1) A grinding step comprising grinding the film with the functional layer to form a pulverized product. (Step 2) A chipping step comprising chipping the pulverized product obtained in Step 1 to form recycled chips. (Step 3) A step of preparing recycled chips obtained in Step 2 and polyethylene terephthalate chips different from these recycled chips, such that when formed into a film, the Si element content derived from siloxane is 30 ppm or more and 500 ppm or less relative to the total mass of the polyethylene terephthalate film; (Step 4) A recycled film forming step of melt-extruding the recycled chips and polyethylene terephthalate chips prepared in Step 3 to form a film.

[0012] The present invention provides a polyethylene terephthalate film, a method for producing the same, and a release film that can reduce coarse internal foreign matter containing calcium carbonate particles, even when using recycled resin.

[0013] The present invention will be described in detail below. The polyethylene terephthalate film according to the embodiment of the present invention has a surface on which a functional layer is provided. Below, a single-layer film in which the polyethylene terephthalate film forms a single layer will be mainly described. However, the embodiments of the present invention are not limited thereto. Both sides of the polyethylene terephthalate film are composed of a first surface and a second surface. The second surface is the surface opposite to the first surface. Below, the case in which the surface on which the functional layer is provided is the first surface will be described. At least one of the first surface and the second surface of the polyethylene terephthalate film may be surface-treated. Examples of surface treatments include corona treatment and plasma treatment. The first surface is preferably surface-treated, and is preferably corona-treated or plasma-treated.

[0014] The polyethylene terephthalate film contains a siloxane. This siloxane is, for example, at least one of the following: an organopolysiloxane having an alkenyl group, an organopolysiloxane having an epoxy group, etc. The alkenyl group is, for example, a vinyl group. The Si element content derived from the siloxane is 30 ppm to 500 ppm relative to the total mass of the polyethylene terephthalate film. The siloxane may be derived from the functional layer (especially the release layer) of a recycled functional layered film. The siloxane may be silicone (silicone resin as an example). The Si element content derived from the siloxane can be measured by the method described in the examples below.

[0015] Since polyethylene terephthalate film contains siloxane-derived Si elements, it can be manufactured using recycled chips (for example, chips recycled from silicone-based release films, or chips recycled from release films used in the manufacture of ceramic green sheets). Therefore, it can contribute to reducing the environmental burden. This will be explained below. When polyethylene terephthalate film is made using chips recycled from silicone-based release films, i.e., films with a silicone-based release layer (for example, material recycling, chemical recycling), the polyethylene terephthalate film may contain siloxane-derived Si elements from the silicone-containing release layer. Thus, when polyethylene terephthalate film is made using recycled chips, the polyethylene terephthalate film may contain siloxane-derived Si elements. Since the polyethylene terephthalate film of the present invention contains siloxane-derived Si elements, it can be manufactured using such recycled chips (for example, chips recycled from silicone-based release films, or chips recycled from release films used in the manufacture of ceramic green sheets). Therefore, the polyethylene terephthalate film of the present invention can contribute to reducing the environmental burden. Furthermore, while the polyethylene terephthalate film of the present invention is preferably manufactured using recycled chips, it may also be manufactured without using recycled chips. Moreover, since the upper limit of the total amount of Si elements derived from siloxane is 500 ppm, recycled chips that can be used in the manufacture of polyethylene terephthalate film may contain these components to some extent. In other words, it is permissible for recycled chips that can be used in the manufacture of polyethylene terephthalate film to contain these components to some extent. Therefore, the recycling yield (see Patent Document 1), specifically the recycling yield of recycled chips that can be used in the manufacture of polyethylene terephthalate film, can be improved.In one embodiment, the polyethylene terephthalate film may contain 30% to 100% by mass of resin obtained by material recycling and / or chemical recycling of a film with a functional layer. Here, "film with a functional layer" includes a base material (i.e., base film) and a functional layer. In this specification, material recycling and / or chemical recycling may also be simply referred to as recycling. In addition, as a representative example, it may be referred to as material recycling. The following description mainly concerns a configuration in which the polyethylene terephthalate film is used for release purposes (typically as a base film for release films), but the polyethylene terephthalate film is not limited to this configuration. The polyethylene terephthalate film may be used for other purposes.

[0016] In one embodiment, the polyethylene terephthalate film of the present invention contains a resin obtained by material and / or chemical recycling of a functional layered film. The functional layered film may be a release film, for example, a used release film. In the polyethylene terephthalate film of the present invention, the content of the resin obtained by material and / or chemical recycling of a functional layered film may be, for example, 5% by mass or more and 100% by mass or less, 8% by mass or more and 98% by mass or less, or 10% by mass or more and 95% by mass or less. If it is 5% by mass or more, the amount of petroleum-derived raw materials used can be reduced, thus being environmentally friendly. This content is preferably 30% by mass or more and 100% by mass or less, more preferably 40% by mass or more and 100% by mass or less, and even more preferably 50% by mass or more and 100% by mass or less. The used release film may mean, for example, a release film after forming and laminating an object to be released on a release layer and then peeling the object to be released from the release layer.

[0017] In one embodiment, the recycled functional layered film is a release film used in molding resin sheets containing inorganic compounds. Examples of inorganic compounds include metal particles, metal oxides, and minerals, such as calcium carbonate, silica particles, aluminum particles, and barium titanate particles. Examples of resins included in the resin sheet include polyvinyl acetal resin and poly(meth)acrylic acid ester resin. For example, the functional layered film is used in the manufacture of resin sheets that require high smoothness, such as semiconductor components, ceramic green sheets, and optical films. By recycling films used in such applications, haze and surface roughness can be reduced. Furthermore, it is preferable that the functional layered film (a release film as an example) contains particles in order to maintain smoothness while exhibiting windability.

[0018] The recyclable functional layered film may be a film in which a functional layer is provided on at least one surface of a base film containing a thermoplastic resin. The base film is preferably a polyester film, and may be, for example, the polyethylene terephthalate film according to the present invention. This allows the polyethylene terephthalate film according to the present invention to be recycled multiple times, making it suitable for the efficient use of resources required in a circular economy. The present invention allows for the reuse of components other than polyester resin, as long as it does not deviate from the scope of the present invention. Particularly preferably, a functional layered film in which the functional layer is directly laminated on a base film can be used as a material and / or chemically recycled chip. By using a functional layered film in which the functional layer is directly laminated on a base film, impurities originating from the functional layered film can be reduced, thereby further reducing haze and surface roughness. When the base film of the recyclable functional layered film is a polyester film, examples of polyester resins for the polyester film include polyethylene terephthalate resin, polyethylene naphthalate resin, polybutylene terephthalate resin, and polycyclohexanedimethanol-terephthalate resin. Among these, polyethylene terephthalate resin is preferred.

[0019] When the base film of the recycled functional layered film is a polyester film, the polyester resin contained in the polyester film is preferably an aromatic polyester obtained by polycondensation of a diol component and an aromatic dicarboxylic acid component. Examples of aromatic dicarboxylic acid components include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of diol components include ethylene glycol. The polyethylene terephthalate resin preferably has 90 mol% or more, more preferably 95 mol% or more, of repeating units of ethylene terephthalate, and may also have small amounts of other dicarboxylic acid components and diol components copolymerized. From a cost standpoint, polyethylene terephthalate manufactured solely from terephthalic acid and ethylene glycol is preferred. Furthermore, the base film of the recycled functional layered film may contain known additives, such as antioxidants, light stabilizers, ultraviolet absorbers, and crystallizers.

[0020] The base film of the functional layered film that is recycled may contain particles. The particle content in the base film may be 0.01% by mass or more and 1.0% by mass or less, relative to the total mass of the base film.

[0021] Regarding recyclable films with functional layers, examples of functional layers include antistatic layers, release layers, and adhesive layers. Among these, release layers are preferred.

[0022] In a recyclable functional layered film, the functional layer may contain a siloxane (e.g., silicone, silicone resin). Examples of siloxanes include organopolysiloxanes having alkenyl groups and organopolysiloxanes having epoxy groups. The siloxane may have a crosslinked structure, i.e., a three-dimensional network structure. The organopolysiloxane having alkenyl groups may be an organopolysiloxane having residual vinyl groups, obtained by the addition reaction of at least organohydrogenpolysiloxane and methylvinylpolysiloxane under a platinum catalyst. Examples of siloxanes include siloxanes derived from silane coupling agents. One example is a siloxane formed by the hydrolysis of alkoxysilyl groups in a silane coupling agent and the condensation reaction of silanol groups produced by the hydrolysis.

[0023] The polyethylene terephthalate film of the present invention contains a polyethylene terephthalate resin. Examples of the polyethylene terephthalate resin include recycled polyethylene terephthalate resin and virgin polyethylene terephthalate resin. As the recycled polyethylene terephthalate resin, polyethylene terephthalate resin derived from chips obtained by material recycling and / or chemical recycling of functional layered films is preferred.

[0024] In the polyethylene terephthalate film of the present invention, the polyethylene terephthalate resin preferably contains 90 mol% or more, more preferably 95 mol% or more, of repeating units of ethylene terephthalate. The polyethylene terephthalate resin may also be copolymerized with small amounts of other dicarboxylic acid components and diol components.

[0025] The polyethylene terephthalate resin content in the polyethylene terephthalate film according to the present invention is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. This may be, for example, 98% by mass or more, or 100% by mass.

[0026] The polyethylene terephthalate film of the present invention is calcium carbonate (CaCO3). ３ It is preferable that the film contains ) particles. Calcium carbonate particles are preferable as lubricant particles from the viewpoint of transparency and cost, and can therefore be added to polyethylene terephthalate film as lubricant particles. As for the calcium carbonate particles, light calcium carbonate surface-treated with a polyacrylic acid-based polymer compound is preferable from the viewpoint of preventing the lubricant particles from falling off. The calcium carbonate particles may also be calcium carbonate particles surface-treated with a surface treatment agent containing a polymer compound having a carbonyl group, for example, a polymer compound having a carbonyl group at its terminal. The length of the longest side of the calcium carbonate particles is preferably, for example, 0.5 μm or more and 5.0 μm or less. The average particle diameter of the calcium carbonate particles is preferably 0.1 μm or more and 5.0 μm or less, more preferably 0.2 μm or more and 5.0 μm or less, even more preferably 0.4 μm or more and 5.0 μm or less, even more preferably 0.6 μm or more and 4.5 μm or less, and even more preferably 0.7 μm or more and 4.0 μm or less. When the particle size is 0.1 μm or larger, air can be uniformly released when the film is rolled up, both during production and use, resulting in a good rolled appearance and good flatness, making it suitable for the manufacture of ultrathin ceramic green sheets (hereinafter referred to as having good handling properties). When the particle size is 5.0 μm or smaller, surface irregularities are reduced, and there is no transfer to molded products (e.g., semiconductor components, ceramic green sheets, optical films), which is preferable. The average particle size of calcium carbonate particles can be measured by the method described in the examples. From the viewpoint of film slipperiness and ease of air release, the calcium carbonate particle content is preferably 500 ppm to 5000 ppm relative to the total mass of polyethylene terephthalate film, and more preferably 600 ppm to 4500 ppm. When it is 500 ppm or larger, it is preferable because it has good handling properties. When it is 5000 ppm or smaller, there is no transfer to molded products, which is preferable. Here, the calcium carbonate particle content can be calculated, for example, by measuring the calcium (Ca) element content and then determining the Ca element content.

[0027] The polyethylene terephthalate film of the present invention may contain lubricant particles other than calcium carbonate particles. The explanation of the average particle size of the lubricant particles is omitted as it overlaps with the explanation of the average particle size of calcium carbonate particles. The explanation of the lubricant particle content is omitted as it overlaps with the explanation of the calcium carbonate particle content. The polyethylene terephthalate film of the present invention may contain particles other than lubricant particles. The polyethylene terephthalate film of the present invention may contain inorganic particles such as titanium oxide particles, alumina-silica composite oxide particles, hydroxyapatite particles, and silica particles, and may also contain organic polymer particles such as styrene particles, acrylic particles, melamine particles, and silicone particles. Examples of organic polymer particles include heat-resistant organic particles, such as cross-linked polyacrylic particles, cross-linked polystyrene particles, and benzoguanamine particles. Porous colloidal silica is preferred as silica particles. The polyethylene terephthalate film may contain two or more types of particles with different materials. It may also contain two or more types of particles with the same material but different average particle sizes.

[0028] The particle content is preferably 500 ppm to 5000 ppm relative to the polyethylene terephthalate film, and more preferably 500 ppm to 4800 ppm. When it is 500 ppm or more, the handling properties are good and therefore preferable. When it is 5000 ppm or less, surface irregularities can be suppressed and the transfer of irregularities to molded products can be prevented. The average particle diameter of the particles can be measured by observing the particles in the cross-section of the polyethylene terephthalate film with a scanning electron microscope, observing 100 particles, and taking the average value. The shape of the particles is not particularly limited as long as it satisfies the purpose of the present invention, and spherical particles or irregularly shaped non-spherical particles can be used. The particle diameter of irregularly shaped particles can be calculated as the equivalent diameter of a circle. The equivalent diameter of a circle is the value obtained by dividing the area of ​​the observed particle by pi (π), calculating the square root, and multiplying by 2.

[0029] The polyethylene terephthalate film of the present invention may be a biaxially oriented polyethylene terephthalate film. The intrinsic viscosity (IV) of the polyethylene terephthalate film in the present invention is preferably 0.400 dL / g or more and 0.700 dL / g or less, for example, preferably 0.410 dL / g or more and 0.650 dL / g or less, and more preferably 0.430 dL / g or more and 0.620 dL / g or less. Particularly preferably it is 0.510 dL / g or more and 0.580 dL / g or less. When the intrinsic viscosity is 0.400 dL / g or more, breakage is less likely to occur during the stretching process, which is preferable. Also, biaxial stretching can be performed without impairing film-forming properties. Furthermore, when it is 0.700 dL / g or less, the cutability is good when cutting to a predetermined product width, and dimensional defects do not occur, which is preferable. Also, the filter filtration pressure can be suppressed, and there is no impediment to operability.

[0030] In the polyethylene terephthalate film of the present invention, the total haze is preferably 15% or less. More preferably 14% or less, and more preferably 13% or less. When the polyethylene terephthalate film is used, for example, as a release film for processes, false detections during defect detection can be suppressed. Furthermore, from the viewpoint of manufacturing cost, the total haze is preferably 5% or more. More preferably 7% or more, and more preferably 10% or more. These upper and lower limits can be combined as appropriate, and the total haze may be, for example, 5% to 15%, or 10% to 15%, etc.

[0031] In the polyethylene terephthalate film of the present invention, the external delta haze is preferably 7.0% or less. The external delta haze corresponds to the amount of oligomer precipitated from within the film. The external delta haze can be used as an indicator of the amount of oligomer precipitated. When the external delta haze is 7.0% or less, the rolls are not contaminated during the process and operability does not deteriorate. In addition, the defect rate of products due to appearance defects during processing can be reduced. It is even more preferably 6.0% or less, more preferably 5.0% or less, particularly preferably 4.5% or less, and most preferably 4.0% or less. Furthermore, from the viewpoint of manufacturing cost, the external delta haze is preferably 1.0% or more. It is even more preferably 2.0% or more, and more preferably 3.0% or more. These upper and lower limits can be combined as appropriate, and the external delta haze is, for example, 1.0% to 7.0%, or 3.0% to 7.0%, etc. It is known that the external delta haze increases due to oligomer precipitation before and after heating. It is thought that limiting the external haze can reduce the influence of the inside of the film. While increasing the siloxane content (for example, silicone resin) to reduce internal impurities tends to worsen external delta haze, selecting the right type of siloxane can suppress thermal reactivity, thereby achieving both a reduction in internal impurities and a reduction in external delta haze.

[0032] The polyethylene terephthalate film according to the present invention preferably has a thickness of 12 μm to 100 μm, more preferably 12 μm to 85 μm, and more preferably 15 μm to 80 μm. If the film thickness is 12 μm or more, there is no risk of deformation due to heat during film production or when used as a process film. On the other hand, if the film thickness is 100 μm or less, the amount of film to be discarded after use is not excessively large, which reduces the environmental burden, and furthermore, it is economically superior because the amount of material per unit area of ​​release film used is reduced.

[0033] In one aspect, a resin layer substantially free of inorganic particles, for example, a polyester resin layer, may be provided on the functional layer side of the surface of the polyethylene terephthalate film, or a resin layer substantially free of particles having a particle size of 1.0 μm or more, for example, a polyester resin layer, may be provided on the functional layer side of the surface of the polyethylene terephthalate film.

[0034] The polyethylene terephthalate film of the present invention contains Si element derived from siloxane. Specifically, the polyethylene terephthalate film contains 30 ppm or more and 500 ppm or less of Si element derived from siloxane with respect to the total mass of the polyethylene terephthalate film. Here, in the conventional recycled film, there has been a tendency to actively remove the Si element in order to prevent an increase in coarse foreign matter. On the other hand, in the present invention, since the content of the Si element derived from siloxane is 30 ppm or more, aggregation of calcium carbonate particles can be inhibited, and coarse internal foreign matter containing calcium carbonate particles in the polyethylene terephthalate film can be reduced. This is considered to be because siloxane improves the affinity between calcium carbonate particles and polyethylene terephthalate resin, and as a result, improves the dispersibility of calcium carbonate particles.

[0035] The content of the Si element derived from siloxane is preferably 30 ppm or more and 500 ppm or less, more preferably 30 ppm or more and 300 ppm or less, still more preferably 30 ppm or more and 200 ppm or less with respect to the total mass of the polyethylene terephthalate film of the present invention. Also, it is more preferably 40 ppm or more and 500 ppm or less, still more preferably 40 ppm or more and 300 ppm or less, and particularly preferably 40 ppm or more and 200 ppm or less.

[0036] When the content of the Si element derived from the siloxane is within the above range, for example, the handling property of the polyethylene terephthalate film becomes good, and further, the unevenness on the film surface can be suppressed, and the transfer of the unevenness to the molded product can be prevented. Also, when the content of the Si element derived from the siloxane is 30 ppm or more, coarse internal foreign matters containing calcium carbonate particles can be reduced. In addition, the heat resistance of the polyethylene terephthalate film is improved.

[0037] The description of the siloxane in the polyethylene terephthalate film of the present invention is omitted because it overlaps with the description of the siloxane in the film with a functional layer to be recycled.

[0038] Regarding the method for producing the polyethylene terephthalate film of the present invention, when using chips obtained by recycling a release film, residues of the release object (i.e., the molded product) may exist on the surface of the release layer of the release film to be recycled. Therefore, in the present invention, a removal step including removing the adhered matter from the release film may be performed (details will be described later). By the removal step, it is possible to increase the purity of the base film and improve the optical physical properties, mechanical strength, etc. For example, the release object can include an adhesive, an optical film, a ceramic green sheet, etc., and some of these may exist as adhered matter on the release film to be recycled. Also, a high adhesion to the release object is required for the release layer of the release film to be recycled. For example, the release layer for an adhesive, the release layer for an optical film, and the release layer for a ceramic green sheet can be used in the manufacturing process of the release object and the manufacturing process of the apparatus using the same, etc., so it is necessary to show high adhesion between these processes. Also, the release layer of the release film to be recycled may be a release layer exposed to conditions of high temperature (for example, 60 ° C or higher) and / or high humidity (for example, 70% or higher), or a release layer subjected to high stretching conditions.

[0039] (Step to remove deposits from functional layered film) A functional layered film to be recycled (i.e., a functional layered film as a raw material for recycled resin) has a functional layer provided on at least one side of the base film. In other words, a functional layered film includes a base film and a functional layer provided on at least one side of the base film. After use, a functional layered film may have deposits remaining on its surface, for example, on the surface of the functional layer. Also, with respect to functional layered films, used films, films that have not met specifications, and films damaged during distribution are usually discarded. It is desirable to remove deposits from such films scheduled for disposal (i.e., functional layered films scheduled for disposal) as long as it does not impair the final film properties. Depending on the condition of the deposits, the step of removing deposits may be omitted. The method for manufacturing polyethylene terephthalate film in the present invention may include removing deposits not only from the surface of the functional layer but also from the side of the base film opposite to the functional layer. It may also include a step of removing deposits attached to the base film.

[0040] The present invention provides a method for producing polyethylene terephthalate film, comprising the following steps: (Step 1), (Step 2), (Step 3), and (Step 4). (Step 1) A grinding step, comprising grinding a functional layered film to form a pulverized product. (Step 2) A chipping step, comprising chipping the pulverized product obtained in Step 1 to form recycled chips. (Step 3) A preparation step, comprising preparing recycled chips obtained in Step 2 and polyethylene terephthalate chips different from these recycled chips, such that when the film is formed, the Si element content derived from siloxane is 30 ppm or more and 500 ppm or less relative to the total mass of the polyethylene terephthalate film. (Step 4) A recycled film forming step, comprising melt-extruding the recycled chips and polyethylene terephthalate chips prepared in Step 3 to form a film. By including steps 1 to 4, the present invention provides a method for producing polyethylene terephthalate film without impairing the physical properties of the recycled film, even without including a step for removing adhering substances.

[0041] (Step 1: Grinding Process) In the grinding process, the grinding process can be carried out without removing any deposits from the surface of the functional layer-attached film. For example, deposits such as adhesives, ceramic green sheets, and impurities may be present on the surface of the functional layer. Alternatively, some of these deposits may be removed before the grinding process. By removing some of the deposits, it becomes easier to control the content of Si elements derived from siloxane. The manufacturing method of the present invention does not require the removal of the functional layer itself, and a portion of the functional layer may be removed in order to control the content of Si elements derived from siloxane. The manufacturing method of the present invention allows the functional layer and substrate with deposits present to be subjected to the grinding process as is. Therefore, compared to conventional recycling technologies, the processes and time required for manufacturing recycled chips and forming films can be greatly reduced. Furthermore, the amount of waste can be reduced.

[0042] The manufacturing method of the present invention includes a grinding step, which as step 1 includes grinding a film with a functional layer to form a pulverized product. For example, it includes grinding a substrate containing at least adhering material to form a pulverized product. In one embodiment, the functional layer from which the adhering material has been removed may be further ground and then mixed with the pulverized product of the substrate. In the present invention, a pulverized functional layer product obtained by grinding the functional layer from which the adhering material has been removed may be mixed with the pulverized product obtained by grinding at least the substrate. Alternatively, the pulverized product may be obtained with the functional layer from which the adhering material has been removed laminated on the substrate, or the functional layer from which the adhering material has been removed and the substrate may be separated and then ground using the same grinder, or they may be ground in a separate step using different grinders. The film with a functional layer can be ground using a grinder such as a single-screw grinder, twin-screw grinder, tri-screw grinder, or cutter mill. Specifically, these grinders house a rotor with multiple rotating blades attached at regular intervals around its periphery in a housing with multiple fixed blades, and grind the solid material by cutting it between the tips of the rotating blades and the tips of the fixed blades as the rotor rotates. Of the pulverized material, those that pass through a screen of a predetermined mesh size can be obtained as pulverized products. Any known method that can pulverize a functional layered film to a predetermined size can be used.

[0043] The pulverized product obtained in the pulverization process can be, for example, in the form of flakes, powder, lumps, or strips. Flake form is preferred. Flake-shaped pulverized product refers to a product that is thin or flattened. The size of the screen holes used in the pulverization process is preferably 1 mm to 10 mm, and more preferably 3 mm to 8 mm. If the screen hole size is less than 1 mm, the pulverized product becomes powdery and difficult to handle. If it exceeds 10 mm, the bulk density becomes too low, making it difficult to control the discharge amount in the extrusion process described later. When the width of the functional layered film is narrow, for example 20 mm or less, cutting in the direction of flow is also acceptable.

[0044] (Step 2: Chip Formation Process) In order to form recycled chips in the chip formation process, it is desirable to granulate the crushed material by melt extrusion. Examples of granulation equipment for chip formation include single-screw extruders, twin-screw extruders, and multi-screw extruders. Twin-screw extruders or multi-screw extruders, which combine control of mixing strength and suppression of resin degradation, are preferred. The granulation form can be cylindrical, pillow-shaped, spherical, or ellipsoidal. The manufacturing method of the present invention may include a step of filtering the granulated material with a filter. Filtering the granulated material with a filter can remove coarse foreign matter that may cause roughness on the surface of the resulting film. The step of filtering the granulated material with a filter may be repeated multiple times. However, since the polyethylene terephthalate film in the present invention contains 30 ppm to 500 ppm of Si elements derived from siloxane with respect to the total mass of the film, it is not necessary to completely remove the siloxane contained in the functional layered film.

[0045] (Steps 3 and 4: Film manufacturing and formation process) In the present invention, by forming a recycled film using recycled chips so that the Si element derived from siloxane is between 30 ppm and 500 ppm, it is possible to reduce coarse internal foreign matter containing calcium carbonate particles.

[0046] If internal foreign matter larger than 50 μm is present in the film, the internal foreign matter may be exposed on the film surface or the film surface may become raised. Therefore, the polyethylene terephthalate film of the present invention has a number of calcium element-containing internal foreign matter larger than 50 μm of 350 pieces / 100 cm. ２ The following is preferable: 350 pieces / 100 cm ２ If the particle size exceeds this limit, the surface roughness increases, which can transfer to the molded product and have adverse effects. Note that internal foreign matter containing calcium elements and larger than 50 μm may be internal foreign matter containing calcium carbonate particles and larger than 50 μm.

[0047] Furthermore, in the fluorescence spectrum measured with excitation light at a wavelength of 330 nm, the polyethylene terephthalate film of the present invention preferably has a ratio (i.e., E1 / E2) of 0.43 to 0.60 of the fluorescence emission intensity at 460 nm (hereinafter sometimes referred to as E1) to the fluorescence emission intensity at 395 nm (hereinafter sometimes referred to as E2) in the fluorescence spectrum measured with excitation light at a wavelength of 330 nm. E1 / E2 can be positioned as an indicator of the degree of oxidative degradation of the polyethylene terephthalate resin. This will be explained below. The fluorescence emission intensity at 460 nm, i.e., E1, in the fluorescence spectrum measured with excitation light at a wavelength of 330 nm is proportional to the amount of monohydroxyterephthalate. Monohydroxyterephthalate is produced when polyester resin containing terephthalate units undergoes oxidative degradation. For example, when polyethylene terephthalate resin undergoes oxidative degradation, monohydroxyterephthalate is produced in the main chain of polyethylene terephthalate. Therefore, the more the oxidative degradation of the polyester resin containing terephthalate units progresses, the greater the amount of monohydroxyterephthalate. On the other hand, the fluorescence emission intensity at 395 nm in the fluorescence spectrum measured with excitation light at a wavelength of 330 nm, i.e., E2, is proportional to the amount of polyester aggregates or aggregates. The amount of aggregates or aggregates is less affected by the progression of oxidative degradation of polyester resins containing terephthalate units compared to the amount of monohydroxyterephthalate. In light of the above, E1 / E2 can be positioned as an indicator of the degree of oxidative degradation of polyethylene terephthalate resin.

[0048] When E1 / E2 of the polyethylene terephthalate film is 0.60 or less, the degree of oxidative degradation of the polyethylene terephthalate resin is not excessively high, and thus the yellowness that the polyethylene terephthalate film can exhibit can be reduced. That is, the color b value per unit thickness can be reduced. In addition, internal foreign matters caused by PET degradation products can also be reduced. Therefore, when a coating solution is applied to provide a functional layer on the polyethylene terephthalate film, holes that may occur in the coating solution on the polyethylene terephthalate film can be further reduced. The recession of the edge of the coating solution on the polyethylene terephthalate film can also be further reduced. E1 / E2 is preferably 0.55 or less, and more preferably 0.50 or less. ＊ In addition, internal foreign matters caused by PET degradation products can also be reduced. Therefore, when a coating solution is applied to provide a functional layer on the polyethylene terephthalate film, holes that may occur in the coating solution on the polyethylene terephthalate film can be further reduced. The recession of the edge of the coating solution on the polyethylene terephthalate film can also be further reduced. E1 / E2 is preferably 0.55 or less, and more preferably 0.50 or less.

[0049] When E1 / E2 of the polyethylene terephthalate film is 0.43 or more, the thermal dimensional stability can be improved. This is presumably because the degree of oxidative degradation of the polyethylene terephthalate resin is not excessively low, and thus the molecular chains are cut to some extent by oxidative degradation, and as a result, the crystallinity is improved. E1 / E2 may be, for example, 0.45 or more, or may be 0.47 or more. E1 / E2 can be controlled, for example, by the method for producing recycled resin, the content of recycled resin, and the like.

[0050] The color b value per 1 μm thickness of the polyethylene terephthalate film ＊ is preferably 0.010 or less, and more preferably 0.050 or less. When this color b value is 0.010 or less, when the polyethylene terephthalate film is used as a base film for, for example, a process release film, false detection during defect detection can be suppressed. This color b value may be, for example, 0.002 or more, or may be 0.003 or more. ＊ When this color b value is 0.010 or less, when the polyethylene terephthalate film is used as a base film for, for example, a process release film, false detection during defect detection can be suppressed. This color b value ＊ may be, for example, 0.002 or more, or may be 0.003 or more.

[0051] In one aspect, what remains after removing the functional layer from the film with a functional layer may contain 0.01 part by mass or more and 1.0 part by mass or less, for example, 0.21 part by mass or more and 1.0 part by mass or less of functional layer residues, residues adhering to the functional layer, for example, the material to be released.

[0052] The method for removing the remaining deposits is not particularly limited. For example, methods include removing them by attaching an adhesive roll and peeling it off, removing them by vacuuming, scraping them off with a blade, removing them with high-pressure water or air, removing them by blowing sand or dry ice onto them, removing them by immersing the film in a cleaning layer and adsorbing them with microbubbles, removing them by floating them with micro-vibrations such as ultrasound, and removing them by dissolving them with supercritical CO2. These methods may be combined. These methods are not particularly limited, but in terms of efficiency, methods that can be processed by roll-to-roll are preferred. In this process, the functional layer may be removed along with the deposits, or the functional layer may remain on the base film without being removed.

[0053] Here, the step of removing deposits from the functional layer-attached film may include removing adhesives, ceramic green sheets, impurities, etc., remaining on the surface of the functional layer. Alternatively, it may be a step of removing the functional layer from the base film. Preferably, the step of removing deposits is a step of removing the functional layer, for example, a release layer or a smooth-slip layer, from the base film. By removing the functional layer, the recovery rate of resin derived from the base film can be increased, and the recycled film can exhibit physical properties that are not inferior to those of the base film before recycling.

[0054] In one embodiment, the polyethylene terephthalate film of the present invention includes a resin obtained by separating the base material portion, i.e., the base film, from a used or unused functional layered film and material recycling the base material portion. For example, in the case of a release film used in the manufacture of ceramic green sheets, it is desirable to remove the residue of the material to be released (green sheet) and the release layer, and material recycle the base material portion. In the manufacturing method of the present invention, the functional layered film may be crushed while the residue of the material to be released (green sheet) and / or the release layer remain on the release film.

[0055] The method for biaxial stretching of polyethylene terephthalate film in the present invention is not particularly limited, and conventionally used methods can be used. For example, the polyester can be melted in an extruder, extruded into a film, cooled in a rotating cooling drum to obtain an unstretched film, and then the unstretched film can be obtained by biaxial stretching. The biaxially stretched film can be obtained, for example, by sequentially biaxially stretching a uniaxially stretched film in the longitudinal or transverse direction in the transverse or longitudinal direction, or by simultaneously biaxially stretching an unstretched film in the longitudinal and transverse directions.

[0056] A filter may be used between the time the recycled chips are melted and extruded. The filter used for such filtration can be a known filter, which can be appropriately selected depending on the level of surface defects to be addressed. Generally, the smaller the 95% filtration accuracy (the particle size of glass beads that remain on the filter after 95% or more of the glass beads have passed through), the more small the foreign matter can be removed. Therefore, from the viewpoint of reducing foreign matter that creates minute surface defects, which is the problem in this invention, it is preferable that the 95% filtration accuracy of the filter used be 30 μm or less, and more preferably 20 μm or less. On the other hand, the smaller the 95% filtration accuracy, the more foreign matter can be removed, which means that foreign matter that cannot pass through the filter and is trapped will accumulate more quickly. When such foreign matter that cannot pass through the filter accumulates, the amount of thermoplastic resin that can pass through the filter decreases, making it difficult to extrude the thermoplastic resin into a sheet, or the filter may succumb to the pressure trying to extrude the thermoplastic resin, causing the trapped foreign matter to leak out of the filter. Therefore, while there is no lower limit to the 95% filtration accuracy of the filter, it is preferable that it be 5 μm or larger, and more preferably 10 μm or larger. If such accumulated foreign matter leaks out, the subsequent products will be defective. Such filters for molten resin may also be inserted during the process from molten state to extrusion when manufacturing recycled chips. The filtration accuracy of the filter in this case should be appropriately selected according to the desired level of defects in the chip. It is preferable to select a filter size that can remove aggregates of functional layers that are unnecessary for the film's properties, without removing particles necessary for maintaining slipperiness, etc.

[0057] The film-forming method in this invention is not limited, but specifically, recycled chips and polyethylene terephthalate chips different from these recycled chips (for example, virgin polyethylene terephthalate chips) are thoroughly vacuum-dried, then supplied to an extruder, melt-extruded into a sheet at approximately 255°C to 280°C, and cooled and solidified to form an unstretched PET sheet. The obtained unstretched PET sheet is stretched 3.0 to 6.0 times in the longitudinal direction on a roll heated to 75°C to 140°C to obtain a uniaxially oriented PET film. Furthermore, the ends of the film are gripped with clips and guided into a hot air zone heated to 75°C to 140°C, and after drying, stretched 3.0 to 6.0 times in the width direction. Subsequently, it can be guided into a heat treatment zone at 180°C to 260°C and heat-treated for 1 to 60 seconds. During this heat treatment process, a 0 to 10% relaxation treatment may be applied in the width direction or longitudinal direction as needed.

[0058] (Resin Sheet) In one embodiment, the polyethylene terephthalate film of the present invention can be used as a base material in a release film for resin sheet molding. The resin sheet is not particularly limited and may be applied to the manufacture of adhesives and optical films. In one embodiment, the release film for resin sheet molding contains the above inorganic compound. In one embodiment, the resin sheet containing the inorganic compound is a ceramic green sheet. For example, the ceramic green sheet may contain barium titanate as the inorganic compound. In one embodiment, the resin sheet has a thickness of 0.2 μm or more and 1.0 μm or less.

[0059] (Release Film) In one embodiment, the release film of the present invention comprises a polyethylene terephthalate film and a release layer. The release layer is provided on the surface of the polyethylene terephthalate film. That is, the release film comprises a polyethylene terephthalate film and a release layer laminated on the surface of the polyethylene terephthalate film.

[0060] The description of the release layer of the release film is omitted because it overlaps with the description of the release layer of the functional layered film (i.e., the recyclable functional layered film) described above. Therefore, the description of the release layer of the functional layered film described above can also be treated as a description of the release layer of the release film according to the present invention.

[0061] The present invention will be described in more detail below using examples, but the present invention is not limited in any way by these examples. The characteristic values ​​used in the present invention were evaluated using the following method.

[0062] (1) Intrinsic viscosity (IV) Single-layer polyethylene terephthalate film or polyester resin (specifically recycled PET1, 2, 3, 4, PET10, MB10) was crushed and dried, and then dissolved in a mixed solvent of phenol / tetrachloroethane = 60 / 40 (mass ratio). After removing inorganic particles from this solution by centrifugation, the flow time of the solution at a concentration of 0.4 (g / dL) and the flow time of the solvent alone were measured using an Ubbelohde viscometer at 30°C. The intrinsic viscosity was calculated from the ratio of these times using Huggins' equation, assuming that Huggins' constant is 0.38.

[0063] (2) Approximately 1.2 g of a siloxane-derived Si element analysis sample (specifically, single-layer polyethylene terephthalate film or polyester resin) was taken and heated to 120°C in a mixed solvent of CHCl3 (chloroform):HFIP (hexafluoro-2-propanol):TCE (1,1,2,2-tetrachloroethane) = 9:1:5 to remove the unmelted portion. The obtained molten portion was left at room temperature to obtain the sample to be measured. As a pretreatment, approximately 1 g of the sample to be measured was taken and treated with nitric acid, ultrapure water and hydrofluoric acid using a microwave sample decomposition device (UltraWAVE, manufactured by Milestone General Co., Ltd.). This obtained the measurement solution (purified product). Subsequently, the amount of Si element derived from siloxane was measured using an ICP emission spectrometer (SPECTRO BLUE TI, manufactured by SPECTRO).

[0064] (3) As a pretreatment for Ca analysis, approximately 0.5 g of the sample (specifically, single-layer polyethylene terephthalate film or polyester resin) was taken, carbonized and ashed, and the residue was dissolved in dilute hydrochloric acid to prepare the sample for measurement. Subsequently, the amount of elemental Ca was measured using an ICP emission spectrometer (SPECTRO BLUE TI, manufactured by SPECTRO). By measuring the amount of elemental Ca, calcium carbonate particles CaCO ３ The content was calculated.

[0065] (4) Average particle size: Calcium carbonate particles (CaCO) ３ The particles were observed using a scanning electron microscope (Hitachi, Ltd., S-510 model), and the magnification was adjusted appropriately according to the particle size. Photographs were then taken and enlarged copies were made. Next, the outer circumference of at least 200 randomly selected particles was traced, and the equivalent circular diameter of the particles was measured from these traced images using an image analysis device. The average of these measurements was defined as the average particle diameter.

[0066] (5) Coating properties (Preparation of release film) A coating film thickness (wet amount) of 5 g / m² is applied to the surface of a single-layer polyethylene terephthalate film. ２Using reverse gravure printing, the coating solution described below was applied, and then dried at 100°C for 2 seconds 0.5 seconds after application (hereinafter sometimes referred to as "initial drying"). Without any break after the initial drying (i.e., continuously from the initial drying), it was heated at 130°C for 7 seconds, and then wound into a roll 8 seconds after the heating was completed. In this way, 100 release films were produced in each example. (Coating solution used to produce the release film) The composition of the coating solution used to produce the release film was as follows: The solid content of the coating solution was 1.0% by mass, the surface tension was 27 mN / m, and the viscosity was 5 mPa·s. This coating solution was used after being passed through a filter that could remove 99% or more of foreign matter larger than 0.5 μm. 57.93 parts by mass of methyl ethyl ketone 40.00 parts by mass of toluene Resin solution A (a long-chain alkyl group-containing acrylic polyol solution with a solid content of 40% by mass. The method of preparation will be described later.) 1.75 parts by mass of crosslinking agent (hexamethoxymethylol melamine, solid content 100% by mass) 0.25 parts by mass of silicone-based release agent (polyether-modified polydimethylsiloxane, TSF4446, solid content 100% by mass, manufactured by Momentive) 0.05 parts by mass of acid catalyst (p-toluenesulfonic acid) 0.02 parts by mass (Preparation of resin solution A) Stearyl (meth)acrylate was mixed in the ratio of 20 mol%, hydroxyethyl (meth)acrylate, and methyl (meth)acrylate, and then diluted with toluene to a solid content concentration of 40% by mass. Azobisisobutyronitrile was added at a rate of 0.5 mol% and copolymerized under a nitrogen atmosphere. This yielded resin solution A with a solid content of 40% by mass (i.e., a long-chain alkyl group-containing acrylic polyol solution). The weight-average molecular weight of the polymer obtained at this time was 30,000. (Quality judgment) Using a wire bar, the wet coating amount was 5 g / m ２After applying the coating solution to the surface of a single-layer polyethylene terephthalate film by hand, the condition of the coating solution was judged to be satisfactory according to the following criteria: ○ After 5 seconds, the coating solution was evenly spread (i.e., no holes were formed in the coating solution, and the coating solution had not receded by more than 1 cm in the width direction from the edge of the single-layer polyethylene terephthalate film). △ After 5 seconds, the coating solution was spread (i.e., no holes were formed in the coating solution), but it had receded by more than 1 cm in the width direction from the edge of the single-layer polyethylene terephthalate film. × The coating solution was not spread uniformly in the width direction, specifically, holes were formed in the coating solution.

[0067] (6) Haze Measurement [External Haze, Internal Haze, Total Haze] A 5 cm x 5 cm sample was cut from a single-layer polyethylene terephthalate film, and the total haze was measured at 25°C for all wavelengths of visible light in accordance with JIS-K7136 using a turbidimeter (NDH5000) manufactured by Nippon Denshoku Industries Ltd. The haze of a laminate consisting of only Zedel oil sandwiched between two quartz glass plates (hereinafter, "Haze (H1)") and the haze of a laminate consisting of a single-layer polyethylene terephthalate film uniformly wetted with Zedel oil sandwiched between two quartz glass plates (hereinafter, "Haze (H2)") were measured in the same manner. Next, the internal haze was determined according to the following formula: Internal haze = Haze (H2) - Haze (H1) The external haze was determined by subtracting the internal haze from the total haze. Note that total haze, internal haze, and external haze all refer to haze across all wavelengths of visible light. The external haze obtained in this way will hereafter be called the pre-heating external haze (H3). A single-layer polyethylene terephthalate film was heated in an oven at 150°C for 30 minutes, and the same measurement was performed. The external haze obtained in this way will hereafter be called the post-heating external haze (H4). The external delta haze was calculated from the post-heating external haze (H4) and the pre-heating external haze (H3) using the following formula: External delta haze = Post-heating external haze (H4) - Pre-heating external haze (H3)

[0068] (7) Method for evaluating internal foreign matter (100 cm of single-layer polyethylene terephthalate film) 2 (The evaluation area was defined as follows:) (7-1) A single-layer polyethylene terephthalate film was observed with a microscope (Hirox: RH-2000), and the focus was set on the surface layer, then shifted to the deeper layers, and the locations of foreign matter (i.e., internal foreign matter) present up to the surface layer on the opposite side were marked. (7-2) Of the internal foreign matter marked in (7-1), those in which Ca was detected using SEM-EDS were further marked. (7-3) Of the internal foreign matter marked in both (7-1) and (7-2), the number of internal foreign matter larger than 50 μm was counted using a microscope (Hirox: RH-2000).

[0069] (8) The environmental impact of single-layer polyethylene terephthalate film was determined according to the following criteria: ○: Recycled resin content of 20% by mass or more ×: Recycled resin content of less than 20% by mass

[0070] (9) Fluorescence emission intensity A single-layer polyethylene terephthalate film was weighed and a 1.0% by mass trifluoroacetic acid solution was prepared (hereinafter referred to as the "prepared solution"). The prepared solution was placed in a sample measurement cell (10 mm inner diameter x 10 mm, 45 mm height), covered with a quartz glass plate, and mounted in the sample holder of a spectrofluorometer (Hitachi High-Tech, F-7000 model). Excitation light was incident on the cell, and the emitted fluorescence was extracted in a perpendicular direction and introduced into the spectrometer to measure the fluorescence spectrum under the following conditions. Measurement conditions: SCAN SPEED: 1200 nm / min; EXCITATION SLIT: 5 nm; EMISSION SLIT: 5 nm; EXCITATION WAVELENGTH: 330 nm; EMISSION START WAVELENGTH: 350 nm; EMISSION END WAVELENGTH: 800 nm

[0071] In the fluorescence emission intensity obtained by the above method, the fluorescence emission intensity at 395 nm (E2) can be treated as a peak intensity originating from polyester aggregates or aggregates. On the other hand, the fluorescence emission intensity at 460 nm (E1) can be treated as a peak originating from the oxidized structure in the polyester molecular chain (Reference: Norman S. Allen et al. Polymer Degradation and Stability, G000, vol. 67, no. 2, p325-334).

[0072] (10) Color b ＊ Ten single-layer polyethylene terephthalate films were stacked and placed in a colorimeter (JE2000, manufactured by Nippon Denshoku Industries Co., Ltd.), and color b was measured using the reflection method. ＊ The value was calculated. Color b per 1 μm thickness ＊ The value was calculated using the following formula: Color b per 1 μm thickness. ＊ Value = (Color b with 10 layers of film) ＊ Value) / (10 x film thickness)

[0073] (Preparation of Recycled PET 1) Used release film 100 was used, which had a PET film 101 containing 2000 ppm of calcium carbonate particles with a particle size of 0.6 μm and a silicone-based release layer 102 provided on one side of the PET film 101. The release film 100 was a film used in the manufacture of multilayer ceramic capacitors. The silicone-based release layer 102 is a layer obtained by coating one side of the PET film 101 with a composition such as a cationic polymerizable ultraviolet-curable silicone resin (manufactured by Arakawa Chemical Industries, Ltd., Silicolys UV POLY 215, 100% solids), and contains siloxane A. In the manufacture of multilayer ceramic capacitors, a ceramic green sheet was formed on the silicone-based release layer 102 of the release film 100 and wound into a roll. Then, the release film 100 was unwound and the ceramic green sheet was peeled off from the release film 100. A cleaning process was performed by immersing the release film 100 used in the manufacture of multilayer ceramic capacitors in a cleaning tank to remove green sheet residue (fine particles). The release film 100 was put through a single-screw mill and pulverized at a speed of 1000 kg / hour using a 4 mm perforated screen to obtain pulverized film. The obtained pulverized film was fed into a twin-screw extruder to obtain recycled PET 1. The intrinsic viscosity of recycled PET 1 was 0.57 dL / g, and the Si concentration derived from siloxane A was 184 ppm. This siloxane A is an organopolysiloxane having epoxy groups (i.e., an epoxy-modified organopolysiloxane). The evaluation results and various conditions are shown in Table 1.

[0074] (Preparation of Recycled PET2) A PET film 101 and a used release film 200 having a silicone-based release layer 202 on one side of the PET film 101 were used. The silicone-based release layer 202 is a layer obtained by coating one side of the PET film 101 with a composition such as a curable silicone resin (LTC856 manufactured by Toray Dow Corning), and contains siloxane B. That is, recycled PET2 was obtained in the same manner as recycled PET1, except that a release film 200 used in the manufacture of a multilayer ceramic capacitor was used instead of the release film 100 used in the manufacture of a multilayer ceramic capacitor. The intrinsic viscosity of recycled PET2 was 0.57 dL / g, and the Si concentration derived from siloxane B was 276 ppm. This siloxane B is an organopolysiloxane having an alkenyl group (i.e., an alkenyl group-modified organopolysiloxane). The evaluation results and various conditions are shown in Table 1.

[0075] (Preparation of Recycled PET3) PET film 101 was subjected to a single-screw mill and pulverized at a speed of 1000 kg / hour using a 4 mm perforated screen to obtain pulverized film. The obtained pulverized film was fed into a twin-screw extruder to obtain recycled PET3. The intrinsic viscosity of recycled PET3 was 0.57 dL / g, and the Si concentration derived from siloxane was 0 ppm. The evaluation results and various conditions are shown in Table 1.

[0076] (Preparation of Recycled PET4) Recycled PET4 was obtained in the same manner as recycled PET1, except that the above washing step was not performed. Recycled PET4 contains the residue of the ceramic green sheet. The intrinsic viscosity of recycled PET4 was 0.55 dL / g, and the Si concentration derived from siloxane A was 184 ppm. This siloxane A is an organopolysiloxane having epoxy groups (i.e., an epoxy group-modified organopolysiloxane). The evaluation results and various conditions are shown in Table 1.

[0077] The numerical values ​​"102" and "202" for the silicone-based release layers are used solely to distinguish between the two silicone-based release layers. Similarly, the numerical values ​​"100" and "200" for the release films are also used solely for distinction.

[0078] (Preparation of polyethylene terephthalate resin (PET10)) An esterification reactor consisting of a three-stage complete mixing tank with a stirrer, a partial condenser, a raw material inlet, and a product outlet was used as the esterification reactor. Terephthalic acid (TPA) was added at a rate of 2 tons / hr, ethylene glycol (EG) at a rate of 2 moles per mole of TPA, and antimony trioxide was added in an amount such that the Sb atoms in the generated PET amounted to 160 ppm. These slurries were continuously supplied to the first esterification reactor of the esterification reactor and reacted at atmospheric pressure at 255°C with an average residence time of 4 hours. Next, the reaction product in the first esterification reactor was continuously removed from the system and supplied to the second esterification reactor, and 8% by mass of the EG distilled off from the first esterification reactor was supplied to the second esterification reactor relative to the generated polymer (generated PET). Furthermore, an EG solution containing magnesium acetate in an amount that results in 65 ppm of Mg atoms relative to the generated PET, and an EG solution containing trimethyl phosphate (TMPA) in an amount that results in 20 ppm of P atoms relative to the generated PET, were added to the second esterification reaction vessel, and the reaction was carried out at atmospheric pressure at 260°C for an average residence time of 1.5 hours. Next, the reaction product from the second esterification reaction vessel was continuously removed from the system and supplied to the third esterification reaction vessel, and an EG solution containing TMPA in an amount that results in 20 ppm of P atoms relative to the generated PET was added, and the reaction was carried out at atmospheric pressure at 260°C for an average residence time of 0.5 hours. The esterification reaction product generated in the third esterification reaction vessel was continuously supplied to a three-stage continuous polycondensation reactor for polycondensation, and then filtered through a stainless steel sintered filter material (nominal filtration accuracy, 90% cut of 5 μm particles) to obtain PET 10, a polyethylene terephthalate resin (pellet form) with an intrinsic viscosity of 0.62 dL / g.

[0079] (Preparation of polyethylene terephthalate calcium carbonate masterbatch (MB10)) The above PET10 and calcium carbonate particles with an average particle size of 0.6 μm were melted and kneaded in a twin-screw extruder to prepare a masterbatch with a calcium carbonate particle concentration of 16,000 ppm.

[0080] (Example 1) After drying each of the above polyester resins, they were mixed and melted at 290°C in a melt extruder. Two-stage filtration was performed using a filter made of sintered stainless steel fibers with a 95% cut diameter of 15 μm and a filter made of sintered stainless steel particles with a 95% cut diameter of 15 μm. Subsequently, the raw material, which was a mixture of PET10 (32.5% by mass), MB10 (7.5% by mass), recycled PET1 (26% by mass), and recycled PET3 (34% by mass), was extruded (casted) into a sheet at a speed of 45 m / min through a feed block. The sheet was then electrostatically adhered and cooled on a casting drum at 30°C using an electrostatic adhesion method to obtain an unstretched polyethylene terephthalate sheet.

[0081] The electrostatic adhesion conditions at this time were as follows: the electrode material was tungsten, cylindrical (wire) with a diameter of 0.2 mm and a length of 0.5 m, with a constant current control of 5 mA, an electrode tension of 5 kg, and an electrode renewal rate of 5 m / hour.

[0082] Next, the unstretched polyethylene terephthalate sheet was heated with an infrared heater and then stretched 3.5 times in the longitudinal direction by the speed difference between the rolls at a roll temperature of 80°C. After that, it was guided to a tenter and stretched 4.2 times in the transverse direction at 140°C. Next, it was heat-treated at 210°C in a heat-setting zone. After that, a 2.3% relaxation treatment was performed in the transverse direction at 170°C to obtain a mill roll (width 5.0 m) of biaxially oriented polyethylene terephthalate film with a thickness of 20 μm.

[0083] The mill roll was moved to a slitter and treated with an anti-static device (Kasuga Electric Co., Ltd., high-density anti-static treatment system) and a web cleaner (Shinko Co., Ltd., ultrasonic cleaner system). The mill roll was then cut to a width of 1400 mm and wound onto a core material with resin-impregnated paper (6-inch inner diameter, 12 mm wall thickness, 8% moisture content, surface roughness (SRa = 4.3 nm, SRp = 41.4 nm), and flattening compressive strength of 200 kg / 100 mm) at a maximum speed of 400 m / min using a contact roll with a rubber hardness of 60 degrees, with a contact pressure of 200 kg / m and tension of 15 MPa. This yielded a biaxially oriented polyethylene terephthalate film roll. From the biaxially oriented polyethylene terephthalate film roll, a biaxially oriented polyethylene terephthalate film was cut to obtain a single-layer polyethylene terephthalate film with a thickness of 20 μm. Various evaluations were performed on this single-layer polyethylene terephthalate film. The evaluation results are shown in Table 2.

[0084] Furthermore, the dust level in the atmosphere of the film manufacturing process was Class 1000.

[0085] (Examples 2-4, Comparative Examples 1-4, 6, and Reference Example 5) Single-layer polyethylene terephthalate films were obtained in the same manner as in Example 1, except that the raw materials were changed to those shown in Table 2. Various evaluations were performed on these single-layer polyethylene terephthalate films. The evaluation results are shown in Table 2.

[0086] "GS residue present" means that the raw material contains residue from ceramic green sheets. On the other hand, "GS residue absent" means that the raw material does not contain residue from ceramic green sheets.

[0087]

[0088] RP content refers to the percentage of recycled resin contained in a product.

[0089] When recycled resin was used as a raw material for polyethylene terephthalate film, the number of coarse internal impurities (specifically, 50 μm or larger) containing calcium carbonate particles increased (see Comparative Example 3 and others). In Examples 1-4, Comparative Examples 1, 2, 4, 6, and Reference Example 5, where recycled resin was used as a raw material for polyethylene terephthalate film, the higher the Si element content derived from siloxane, the lower the number of coarse internal impurities containing calcium carbonate particles (see Comparative Example 2 and Reference Example 5, for example). In other words, the higher the Si element content derived from siloxane, the better the dispersion of calcium carbonate particles.

[0090] In Comparative Example 2, the coating liquid did not spread uniformly, and holes formed in the coating liquid. This is thought to be due to an excessively large number of coarse internal foreign matter containing calcium carbonate particles. In Comparative Examples 1 and 4, the edges of the coating liquid receded. This is also thought to be due to an excessively large number of coarse internal foreign matter containing calcium carbonate particles.

[0091] Furthermore, even with the same Si content derived from siloxane, the smaller the E1 / E2 ratio, the more uniformly the coating solution spread (see Example 1 and Comparative Example 6). A smaller E1 / E2 ratio suggests less internal foreign matter caused by PET degradation, and as a result, Example 1, with its smaller E1 / E2 ratio, is thought to have spread more uniformly than Comparative Example 6.

[0092] The present invention relates to polyethylene terephthalate film, a method for producing the same, or a release film, and therefore has industrial applicability.

Claims

1. A polyethylene terephthalate film having a surface on which a functional layer is provided, wherein the polyethylene terephthalate film contains siloxane and calcium carbonate particles, the content of Si elements derived from the siloxane is 30 ppm or more and 500 ppm or less relative to the total mass of the polyethylene terephthalate film, and in a fluorescence spectrum measured with excitation light at a wavelength of 330 nm, the ratio of the fluorescence emission intensity at 460 nm to the fluorescence emission intensity at 395 nm is 0.43 or more and 0.60 or less.

2. The polyethylene terephthalate film according to claim 1, wherein the siloxane comprises at least one of an organopolysiloxane having an alkenyl group and an organopolysiloxane having an epoxy group.

3. The number of internal foreign matter containing calcium element and measuring 50 μm or larger is 350 per 100 cm. ２ The polyethylene terephthalate film according to claim 1, which is as follows:

4. The polyethylene terephthalate film according to claim 1, wherein the total haze is 15% or less and the external delta haze is 7.0% or less.

5. The polyethylene terephthalate film according to claim 1, comprising 30% by mass or more and / or 100% by mass or less of resin obtained by material recycling and / or chemical recycling of a functional layer film.

6. The polyethylene terephthalate film according to claim 1, wherein the content of calcium carbonate particles is 500 ppm or more and 5000 ppm or less relative to the total mass of the polyethylene terephthalate film.

7. The polyethylene terephthalate film according to claim 1, wherein the average particle size of the calcium carbonate particles is 0.1 μm or more and 5.0 μm or less.

8. The polyethylene terephthalate film according to claim 1, wherein the intrinsic viscosity (IV) is 0.400 dL / g or more and 0.700 dL / g or less.

9. A release film comprising a polyethylene terephthalate film according to any one of claims 1 to 8, and the functional layer provided on the surface of the polyethylene terephthalate film, wherein the functional layer is a release layer.

10. A method for producing a polyethylene terephthalate film according to any one of claims 1 to 8, comprising the following steps: (Step 1) A grinding step comprising grinding a film with a functional layer to form a pulverized product. (Step 2) A chipping step comprising chipping the pulverized product obtained in Step 1 to form recycled chips. (Step 3) A step of preparing recycled chips obtained in Step 2 and polyethylene terephthalate chips different from these recycled chips, such that when the film is formed, the content of Si elements derived from siloxane is 30 ppm or more and 500 ppm or less relative to the total mass of the polyethylene terephthalate film. (Step 4) A recycled film forming step comprising melt-extruding the recycled chips and polyethylene terephthalate chips prepared in Step 3 to form a film.

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