Laminated polyester film

Abstract

Provided is a laminated polyester film and a protective film which inhibit an increase in haze even after a heat drying step and are excellent in an oligomer blocking property, an antistatic property, and adhesion to a substrate. The laminated polyester film has a polyester film substrate and a resin layer. The resin layer is a layer obtained by curing a composition for forming a resin layer containing: a polyester-based resin having a glass transition point temperature of 40°C or higher; a crosslinking agent; and a polythiophene-based conductive polymer.

Description

Laminated polyester film

[0001] The present invention relates to a laminated polyester film and an adhesive laminated polyester film having an adhesive layer provided on the laminated polyester film.

[0002] Polyester film is widely used as a base material for protective films that protect various components from scratches and dirt. For example, optical components used in smartphones and tablet devices have protective films laminated to them during the manufacturing process to prevent scratches and dirt from adhering to them. This protective film usually has a structure in which an adhesive layer is provided on one side of a base film made of polyester film. In addition, it is common for an antistatic layer to be laminated on the surface of the base film to prevent the adhesion of dirt and dust and to suppress static electricity generated when peeling from the adherend (for example, Patent Documents 1 and 2).

[0003] In recent years, with the increasing resolution of displays, protective films require greater transparency. However, when protective films are heat-treated, a problem arises where low-molecular-weight oligomers precipitate (bleed out) from the base film onto the film surface. This oligomer precipitation not only increases the film's haze (cloudiness) and impairs its appearance, but also contaminates the optical components to which it is adhered.

[0004] To address these challenges, technologies are known that achieve both antistatic performance and oligomer-blocking properties to suppress oligomer precipitation. For example, a technology has been proposed that provides an antistatic layer containing the conductive polymer PEDOT:PSS and a specific acrylic copolymer (for example, Patent Document 3).

[0005] International Publication 2018 / 012545 Pamphlet Japanese Patent Publication No. 2022-129913 Japanese Patent Publication No. 2022-155385

[0006] However, the oligomer blocking properties of conventional protective films were not always sufficient. In particular, protective films would experience increased haze due to heating, making precise visual inspection difficult while the protective film was applied.

[0007] The present invention has been made in view of the above, and aims to provide a laminated polyester film that has excellent oligomer blocking properties that can effectively suppress the rise of haze even after heat treatment, as well as stable antistatic performance during storage and adhesion between the substrate and the resin layer.

[0008] That is, the present invention has the following configuration: [1] A laminated polyester film having a polyester film substrate and a resin layer, wherein the resin layer is a layer formed by curing a resin layer-forming composition containing a polyester resin having a glass transition temperature of 40°C or higher, a crosslinking agent, and a polythiophene-based conductive polymer.

[0009] [2] The laminated polyester film according to [1], wherein the polyester resin is a copolymer polyester containing naphthalenedicarboxylic acid as an acid component. [3] The laminated polyester film according to [1] or [2], wherein the crosslinking agent comprises at least one selected from the group consisting of oxazoline crosslinking agents and isocyanate crosslinking agents. [4] The laminated polyester film according to any one of [1] to [3], wherein the surface resistivity of the resin layer is 2 to 7 [log Ω / □]. [5] The laminated polyester film according to any one of [1] to [4], wherein the difference (Δ haze) between the haze value before heating the laminated polyester film and the haze value after heat treatment at 140°C for 10 minutes is 2.00% or less. [6] The laminated polyester film according to any one of [1] to [5], wherein the total amount of the polythiophene-based conductive polymer, the polyester resin, and the crosslinking agent is 80% by mass or more of the solid content of the resin layer. [7] The laminated polyester film according to any one of [1] to [6], wherein the resin layer is provided in contact with the polyester film substrate.

[0010] [8] The laminated polyester film according to any one of [1] to [7], wherein the glass transition temperature of the polyester resin is 60°C or higher and 115°C or lower. [9] The laminated polyester film according to any one of [1] to [8], wherein the crosslinking agent is an oxazoline crosslinking agent.

[10] The laminated polyester film according to [6], wherein the content of the polyester resin is 15% by mass or higher and 55% by mass or less in 100% by mass of the solid content of the resin layer, and the content of the crosslinking agent is 40% by mass or higher and 75% by mass or less.

[11] The laminated polyester film according to any one of [1] to

[10] , wherein the acid component constituting the polyester resin contains 70 mol% or higher and 85 mol% or less of naphthalenedicarboxylic acid and 5 mol% or higher and 15 mol% or less of sebacic acid in 100 mol% of the total dicarboxylic acid component.

[0011]

[12] An adhesive laminated polyester film having an adhesive layer on the polyester film substrate opposite to the resin layer of the laminated polyester film according to any one of [1] to

[11] .

[0012] According to the present invention, it is possible to provide a laminated polyester film that has excellent oligomer-blocking properties that can effectively suppress the rise of haze even after heat treatment, as well as stable antistatic performance during storage and adhesion between the substrate and the resin layer.

[0013] The laminated polyester film according to this disclosure comprises a polyester film substrate (sometimes referred to as the "substrate") and a resin layer (sometimes referred to as the "antistatic layer"). The resin layer is a layer formed by curing a resin layer-forming composition (sometimes referred to as the "coating liquid") containing a polythiophene-based conductive polymer, a polyester resin having a glass transition temperature of 40°C or higher, and a crosslinking agent. In this disclosure, the coating liquid (hereinafter also referred to as the coating liquid) refers to a coating liquid (including a solvent) formulated for resin layer formation. The present invention will now be described in detail.

[0014] (Polyester Film Substrate) The polyester film used as a substrate in this disclosure is composed mainly of polyester resin. Here, "main component" means that polyester resin accounts for 50% by mass or more of the total resin components constituting the film, preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably substantially 100% by mass.

[0015] The composition of the polyester resin is not particularly limited, but it is obtained by polycondensing dicarboxylic acid and diol components as the main constituent monomers. The polyester resin can be a homopolymer, copolymer, or a blend of multiple resins. Examples of dicarboxylic acid components include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonic acid, and anthracenedicarboxylic acid; alicyclic dicarboxylic acids such as 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, and hexahydroisophthalic acid; and aliphatic dicarboxylic acids such as malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, dimeric acid, sebacic acid, suberic acid, and dodecadicarboxylic acid.

[0016] Examples of diol components include aliphatic diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, propylene glycol, 1,5-pentanediol, 1,6-hexadiol (hexamethylene glycol), neopentyl glycol, and decamethylene glycol; alicyclic diols such as 1,2-cyclohexanedimethanol and 1,4-cyclohexanedimethanol; and aromatic diols such as 2,2-bis(4-hydroxyphenyl)propane and bis(4-hydroxyphenyl)sulfone.

[0017] The dicarboxylic acid and diol components constituting the polyester resin may each consist of one or more types. Furthermore, polycarboxylic acids with three or more functions, such as trimellitic acid, or polyalcohols with three or more functions, such as trimethylolpropane, may be used as copolymerization components.

[0018] Examples of polyester resins include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, among which polyethylene terephthalate is preferred due to its balance of physical properties and cost. The polyester resin can be a homopolyester consisting of a single repeating unit, a copolymerized polyester consisting of two or more monomer components, or a blended resin made by mixing several of these. When using a copolymerized polyester, in addition to the monomer components that constitute the main repeating unit (for example, terephthalic acid and ethylene glycol in PET), one or more of the dicarboxylic acid components and diol components exemplified above can be used as copolymerized components, to the extent that they do not impair the effects of the present invention.

[0019] The thickness of the polyester film substrate is not particularly limited, but from the viewpoint of processability as a protective film (i.e., resistance to wrinkling after application to a substrate) and cost, it is preferably 12 μm or more and 188 μm or less, more preferably 18 μm or more and 125 μm or less, and even more preferably 25 μm or more and 100 μm or less.

[0020] The layer structure of the base material and additives are not particularly limited. The polyester film base material may be a single layer or a multilayer structure in which multiple resin films with different properties or compositions are laminated. The multilayer structure can be, for example, a two-layer structure with mutually different components, or a three-layer or more structure having an outer layer and an inner layer. It is also preferable that all layers of the laminated film are polyester films. Furthermore, within the range that the effects of the present invention are achieved, various additives such as antioxidants, lightfastness agents, gelation inhibitors, organic wetting agents, antistatic agents, ultraviolet absorbers, and surfactants may be included in one or more layers as needed.

[0021] Method for manufacturing polyester film substrates: Polyester film substrates are manufactured, for example, through a process of polymerizing polyester resin and a process of forming the resulting polyester resin into a film.

[0022] Polymerization of polyester resins. The catalyst used for the polycondensation of polyesters is not particularly limited, but antimony trioxide is preferred because it is inexpensive and has excellent catalytic activity. Other catalysts such as germanium compounds, titanium compounds, and aluminum compounds can also be used. In one embodiment, the catalyst may be a catalyst containing aluminum and / or a compound thereof and a phenolic compound, a catalyst containing aluminum and / or a compound thereof and a phosphorus compound, or a catalyst containing an aluminum salt of a phosphorus compound.

[0023] The film formation process can be carried out using known methods. For example, in the melt extrusion method, polyester resin is first melted and extruded into a sheet from a T-stand or the like. Next, it is cooled and solidified on a cooled casting drum to produce an unstretched sheet. After that, it is preferable to perform a stretching treatment to improve mechanical strength and dimensional stability. As for the stretching treatment, uniaxial stretching in the longitudinal direction and / or width direction, or biaxial stretching in both directions can be employed. Specific stretching methods include longitudinal uniaxial stretching, transverse uniaxial stretching, longitudinal and transverse sequential biaxial stretching, and longitudinal and transverse simultaneous biaxial stretching. Depending on the application, it may also be used as an unstretched film without stretching treatment.

[0024] The components forming the resin layer are described below. (Resin layer: Antistatic layer) In one embodiment, the laminated polyester film of the present disclosure has at least one resin layer on a polyester film substrate. This resin layer functions as an antistatic layer to impart antistatic performance to the film. The resin layer is a layer formed by applying and curing a resin layer forming composition (coating liquid) containing (A) a conductive polymer, (B) a polyester resin, and (C) a crosslinking agent as essential components. The crosslinked structure formed by this curing contributes to improving oligomer blocking properties. The resin layer can be provided on one or both sides of the substrate. In one embodiment, the laminated polyester film of the present invention has a polyester film substrate and a resin layer, and for example, there may be other layers between the polyester film substrate and the resin layer. Preferably, the resin layer (antistatic layer) is provided in contact with the polyester film substrate. In one embodiment, by providing an adhesive layer on the polyester film substrate opposite to the resin layer provided on one side of the substrate, an adhesive laminated polyester film can be made that can be attached as a protective film to an object such as an optical component (for example, a component of an organic EL or liquid crystal display). The provision of a resin layer is preferable because it suppresses the adhesion of dust due to static electricity to the surface of the adhesive laminated polyester film (resin layer side), and also attenuates the peeling charge that occurs when peeling the adhesive laminated polyester film from the object, thereby suppressing the adhesion of foreign matter.

[0025] (A) Conductive polymer The conductive polymer is a component that imparts antistatic properties to the resin layer. Any polymer capable of imparting antistatic properties is acceptable, and polymers that utilize ion conduction, such as cationic compounds, and π-electron conjugated conductive polymers are preferred. In particular, π-electron conjugated conductive polymers are more preferred because they exhibit stable performance even under low humidity conditions and contribute to achieving both excellent antistatic properties and oligomer blocking properties. In one embodiment, one or more antistatic agents such as silicon dioxide compounds, conductive metal compounds, and surfactants can be used in combination, as long as they do not impair the effect of the conductive polymer.

[0026] As the π-electron conjugated conductive polymer, there may be mentioned aniline-based polymers containing aniline or its derivatives as a constituent unit, pyrrole-based polymers containing pyrrole or its derivatives as a constituent unit, acetylene-based polymers containing acetylene or its derivatives as a constituent unit, thiophene-based polymers containing thiophene or its derivatives as a constituent unit, and the like. In the application of an optical film where high transparency is required, a thiophene-based polymer having excellent transparency is preferable. Among the thiophene-based polymers, polyalkylenedioxythiophene is preferable, and specifically, there may be mentioned polyethylene dioxythiophene, polypropylene dioxythiophene, poly(ethylene / propylene) dioxythiophene, and the like. In the present invention, the thiophene-based polymer is also referred to as a polythiophene-based conductive polymer.

[0027] In one embodiment of the doping agent, in order to further improve the antistatic property of the thiophene-based polymer, a doping agent may be used in combination. The addition amount of the doping agent is preferably 0.1 part by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the thiophene-based polymer. If the doping agent is too much, electron transfer becomes difficult and the antistatic performance may decrease, and if it is too little, the dispersibility in the solvent may decrease. As the doping agent, there are inorganic compounds such as LiCl, I ３ , BF ３ Na, BF ４ Na, HClO ４ , FeCl ３ , Na ２ B １０ Cl １０ , etc.; CF ３ SO ３ H, glutamic acid, alkyl sulfonate, R １‐３０ COOLi (where R １‐３０ is a saturated hydrocarbon group having 1 to 30 carbon atoms, the same applies hereinafter), R １‐３０ SO ３ Li, R １‐３０ COONa, R １‐３０ SO3Na, R １‐３０ COOK, R １‐３０ SO ３Organic acids such as K and their salts; π - electron acceptor compounds such as tetracyanoquinoline (TCNQ); polymeric anions (polyelectrolytes) such as polystyrene sulfonic acid and its salts (Na, K, Li salts), styrene - styrene sulfonic acid copolymers and their salts, polyacrylic acid and its salts, polyvinyl sulfonic acid and its salts; and other doping agents such as tetraethylammonium, phthalocyanine, and porphyrin can also be mentioned.

[0028] When the total solid content (total of conductive polymer, polyester - based resin, and cross - linking agent) in the resin layer - forming composition (coating solution) for forming the antistatic layer is set to 100% by mass, from the viewpoint of improving the antistatic performance, the content of the conductive polymer is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, even more preferably 4% by mass or more, and particularly preferably 5% by mass or more. On the other hand, considering the stability of the resin layer - forming composition (coating solution) and the transparency of the resin layer, the content of the conductive polymer is preferably 25% by mass or less, more preferably 20% by mass or less, still more preferably 15% by mass or less, even more preferably 12% by mass or less, and particularly preferably 10% by mass or less. When a doping agent is used in combination, the "content of the conductive polymer" refers to the total amount of the conductive polymer and the doping agent. By containing the antistatic agent in such an amount, for example, aggregation of the resin layer - forming composition (coating solution) due to interaction with the polyester - based resin or cross - linking agent can be suppressed. Therefore, the resin layer (antistatic layer) has few defects and can maintain high transparency. In the present disclosure, since only the solvent component is removed in the drying and curing process after coating in the resin layer - forming composition (coating solution), the ratio of each solid content (conductive polymer, polyester - based resin, cross - linking agent) in the resin layer - forming composition can be directly used as the solid content ratio in the finally formed resin layer.

[0029] (B) Polyester resin The polyester resin contributes to improving the adhesion between the base material and the resin layer and improving the oligomer block property. The polyester resin used in the present disclosure has a dicarboxylic acid component and a diol (preferably glycol) component as constituent units and has a glass transition temperature (Tg) of 40°C or higher. The polyester resin used for the resin layer may be linear, but more preferably, it is a polyester resin having a dicarboxylic acid and a diol (glycol) having a branched structure as constituent components.

[0030] Dicarboxylic acid component (acid component) The dicarboxylic acid component is not particularly limited, and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as adipic acid and sebacic acid can be used, and a preferred configuration is as follows.

[0031] From the viewpoint of increasing the glass transition temperature (Tg) and obtaining excellent oligomer block properties, the dicarboxylic acid component preferably contains an aromatic dicarboxylic acid as a main component. The content of at least one selected from the group consisting of aromatic dicarboxylic acids, preferably terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid, in 100 mol% of the total dicarboxylic acid component is preferably 80 mol% or more, more preferably 90 mol% or more, still more preferably 95 mol% or more, and may be 100 mol%.

[0032] In one embodiment, naphthalenedicarboxylic acid is more preferable because it can significantly improve the glass transition temperature and oligomer blocking properties. The content of naphthalenedicarboxylic acid (particularly 2,6-naphthalenedicarboxylic acid) in 100 mol% of the total dicarboxylic acid components is preferably 10 mol% or more, more preferably 30 mol% or more, even more preferably 50 mol% or more, even more preferably 60 mol% or more, particularly preferably 70 mol% or more, and most particularly preferably 100 mol%. In one embodiment, the upper limit of naphthalenedicarboxylic acid when other dicarboxylic acid components are included is preferably less than 100 mol%, more preferably 95 mol% or less, even more preferably 90 mol% or less, and particularly preferably 85 mol% or less, taking into consideration the balance with these other components. Examples of other dicarboxylic acid components include terephthalic acid, isophthalic acid, and sebacic acid, which may be used individually or in combination of two or more. In particular, it is preferable to include sebacic acid in an amount of 5 mol% or more and 15 mol% or less.

[0033] In one embodiment, when the resin layer forming composition is an aqueous coating liquid, monomers having a sulfonic acid base may be copolymerized to impart water dispersibility to the polyester resin. Specific examples include sulfoterephthalic acid, 5-sulfoisophthalic acid, and 5-sodium sulfoisophthalic acid, and the copolymerization ratio is preferably 1 to 10 mol% of 100 mol% of the total dicarboxylic acid component.

[0034] In one embodiment, a polyester resin containing naphthalenedicarboxylic acid can more effectively suppress oligomer precipitation when combined with a specific crosslinking agent. It is particularly preferable to combine it with at least one crosslinking agent selected from oxazoline-based crosslinking agents or isocyanate-based crosslinking agents. Although the detailed mechanism is not clear, it is presumed that, for example, the combination of a polyester resin containing naphthalenedicarboxylic acid and a specific crosslinking agent results in a three-dimensional structure within the resin layer that effectively suppresses oligomer precipitation.

[0035] Diol component (glycol component): Both linear diols and branched diols can be used as the diol component, and they can be used alone or in combination of two or more.

[0036] Specific examples of diols with a branched structure include neopentyl glycol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol, 2-methyl-2-butyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, and 2-methyl-2-isopropyl-1,3-propanediol. Examples include 2-methyl-2-n-hexyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-ethyl-2-n-butyl-1,3-propanediol, 2-ethyl-2-n-hexyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol, 2-n-butyl-2-propyl-1,3-propanediol, and 2,2-di-n-hexyl-1,3-propanediol. Examples of linear diols include ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethanol, with ethylene glycol being preferred among these.

[0037] In one embodiment, when the diol component is composed of two or more diols, the two components may consist only of linear diols, only of diols having a branched structure, or a combination of linear diols and diols having a branched structure. In one embodiment, from the viewpoint of achieving a high level of both oligomer blocking properties and durability (alcohol resistance), it is particularly preferable that the diol component be a combination of specific linear diols to form the main component (50 mol% or more and 100 mol% or less of the total diol component). For example, by copolymerizing ethylene glycol with 1,6-hexanediol having an appropriate carbon chain length in a specific ratio, the flexibility of the resin is improved, and both the toughness of the coating film and excellent oligomer blocking properties can be achieved. In addition, a small amount of diethylene glycol or the like may be used in combination as needed. For example, a configuration in which ethylene glycol is the main component of the total diol components (for example, 50 mol% or more), and the remainder is made up of at least one selected from the group consisting of diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethanol is also preferred. In one embodiment, a configuration in which ethylene glycol is the main component of the total diol components (for example, 50 mol% or more), and the remainder (50 mol% or less) is made up of one or more diols having the above-mentioned branched structure (preferably neopentyl glycol) is also preferred. In one embodiment, a configuration in which two or more diols having the above-mentioned branched structure are used as the total diol components is also preferred.

[0038] In one embodiment, the content of the branched diol is preferably 10 mol% or more, more preferably 15 mol% or more, preferably 100 mol% or less, more preferably 90 mol% or less, and even more preferably 80 mol% or less, in the total diol components.

[0039] Physical Properties Glass Transition Temperature (Tg) The glass transition temperature (Tg) of the polyester resin is 40°C or higher, preferably 45°C or higher, more preferably 50°C or higher, even more preferably 55°C or higher, and even more preferably 60°C or higher. A polyester resin with a glass transition temperature of 40°C or higher maintains a hard state in the resin layer when heated, resulting in improved blocking resistance and good oligomer blocking properties. On the other hand, if the glass transition temperature of the polyester resin becomes too high, the resin layer may become brittle and prone to cracking, so it is preferably 130°C or lower, more preferably 120°C or lower, and even more preferably 115°C or lower. In one embodiment, the resin layer forming composition includes a polyester resin, a crosslinking agent, and a polythiophene-based conductive polymer, and if the glass transition temperature of the polyester resin is 40°C or higher, it can exhibit excellent chemical resistance and contribute to making the difference (Δhaze) between the haze value before heating the laminated polyester film and the haze value after heating at 140°C for 10 minutes 2.00% or less.

[0040] The reduced viscosity of the polyester resin is preferably 0.1 dl / g or more and 1.5 dl / g or less, and more preferably 0.2 dl / g or more and 1.0 dl / g or less.

[0041] From the viewpoint of ensuring toughness of the number-average molecular weight resin layer, the number-average molecular weight of the polyester resin is preferably 0.3 × 10⁶. ４ More preferably 0.4 × 10 ４ More preferably 0.5 × 10 ４ That concludes the explanation. The upper limit of the number-average molecular weight of the polyester resin is preferably 2 × 10⁻⁶. ４ , more preferably 1.7 × 10 ４ More preferably 1.5 × 10 ４ That is the case.

[0042] To enhance the reactivity with the acid value crosslinking agent, the acid value of the polyester resin is preferably 1 eq / ton or higher, more preferably 5 eq / ton or higher, and even more preferably 7 eq / ton. The upper limit of the acid value of the polyester resin is preferably 500 eq / ton, more preferably 300 eq / ton, and even more preferably 100 eq / ton.

[0043] When the total solid content (total solid content) of the conductive polymer, polyester resin, and crosslinking agent in the resin layer forming composition (coating liquid) for forming the antistatic layer is 100% by mass, the polyester resin content is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and even more preferably 25% by mass or more. Increasing the polyester resin content is preferable as it improves adhesion to the substrate. The upper limit of the polyester resin content is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, even more preferably 55% by mass or less, and particularly preferably 50% by mass or less. By adjusting the polyester resin content, it is possible to maintain an appropriate ratio of conductive polymer and crosslinking agent, and to balance antistatic properties and durability, which is preferable.

[0044] (C) Crosslinking Agent A crosslinking agent is a component that reacts with polyester resins to form a strong three-dimensional network structure within the resin layer, improving durability (chemical resistance, scratch resistance). This crosslinked structure also contributes to improving oligomer blocking properties. Specific crosslinking agents include urea-based, epoxy-based, melamine-based, isocyanate-based, oxazoline-based, carbodiimide-based, and aziridine-based agents. Among these, from the viewpoint of achieving both oligomer blocking properties and durability, and especially excellent alcohol resistance, it is preferable to use at least one selected from the group consisting of oxazoline-based crosslinking agents and isocyanate-based crosslinking agents, and in particular to enhance the oligomer blocking effect, oxazoline-based crosslinking agents are preferred. Furthermore, catalysts and the like can be used as needed to promote the crosslinking reaction. Note that melamine-based crosslinking agents should be avoided in the inline coating method because of concerns about contamination of the film manufacturing process by by-products such as formaldehyde and impact on the work environment.

[0045] Oxazoline-based crosslinking agents include, for example, polymers having oxazoline groups obtained by copolymerizing a polymerizable unsaturated monomer having an oxazoline group with other polymerizable unsaturated monomers as needed using conventionally known methods (e.g., solution polymerization, emulsion polymerization, etc.).

[0046] Examples of polymerizable unsaturated monomers having an oxazoline group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline. These may be used individually or in combination of two or more.

[0047] Other polymerizable unsaturated monomers include, for example, alkyl or cycloalkyl esters of (meth)acrylic acid having 1 to 24 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, lauryl (meth)acrylate, and isobornyl (meth)acrylate; hydroxyalkyl esters of (meth)acrylic acid having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate; vinyl aromatic compounds such as styrene and vinyltoluene; adducts of (meth)acrylamide, dimethylaminopropyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate, glycidyl (meth)acrylate with amines; polyethylene glycol (meth)acrylate; N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, and (meth)acrylonitrile. These can be used individually or in combination of two or more.

[0048] Other polymerizable unsaturated monomers are preferably hydrophilic monomers, from the viewpoint of improving compatibility with other resins, wettability, and crosslinking reaction efficiency when using the resulting oxazoline group-containing crosslinking agent as a water-soluble crosslinking agent. Examples of hydrophilic monomers include 2-hydroxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, monomers having polyethylene glycol chains such as monoester compounds of (meth)acrylic acid and polyethylene glycol, 2-aminoethyl (meth)acrylate and its salts, (meth)acrylamide, N-methylol (meth)acrylamide, N-(2-hydroxyethyl) (meth)acrylamide, (meth)acrylonitrile, sodium styrene sulfonate, etc. Among these, monomers having polyethylene glycol chains such as methoxypolyethylene glycol (meth)acrylate and monoester compounds of (meth)acrylic acid and polyethylene glycol, which have high solubility in water, are preferred.

[0049] The oxazoline group content of the oxazoline crosslinking agent is preferably 1.0 mmol / g or more and 15 mmol / g or less, more preferably 2.0 mmol / g or more and 12 mmol / g or less, and even more preferably 3.0 mmol / g or more and 10 mmol / g or less, from the viewpoint of crosslinkability.

[0050] From the viewpoint of oligomer blocking properties, the number-average molecular weight of the oxazoline crosslinking agent is preferably 0.5 × 10⁶. ４ The above is 10 x 10 ４ More specifically, 1 x 10 ４ The above 8 x 10 ４ More preferably, 2 × 10 ４ The above 6 x 10 ４ The following applies:

[0051] The glass transition temperature (Tg) of the oxazoline resin is preferably 10°C or higher and 100°C or lower, more preferably 20°C or higher and 80°C or lower, and even more preferably 30°C or higher and 70°C or lower, from the viewpoint of improving blocking resistance, improving oligomer blocking properties, and suppressing cracking of the resin layer.

[0052] In one embodiment of isocyanate-based crosslinking agents, blocked isocyanate-based crosslinking agents are used. Blocked isocyanate-based crosslinking agents include, for example, those in which reactive isocyanate groups are protected with a blocking agent. Blocking agents include bisulfite compounds such as sodium bisulfite, pyrazole compounds such as 3,5-dimethylpyrazole, 3-methylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 4-nitro-3,5-dimethylpyrazole, phenols such as phenol and cresol, aliphatic alcohols such as methanol and ethanol, active methylene compounds such as dimethyl malonate and acetylacetone, mercaptans such as butyl mercaptan and dodecyl mercaptan, acid amides such as acetanilide and acetic acid amide, lactams such as ε-caprolactam and δ-valerolactam, acid imides such as succinimide and maleimide, oxime compounds such as acetaldehyde oxime, acetone oxime, and methyl ethyl ketoxime, and amines such as diphenylaniline, aniline, and ethyleneimine.

[0053] The lower limit of the boiling point of the blocking agent, the blocked isocyanate, is preferably 150°C, more preferably 160°C, even more preferably 180°C, particularly preferably 200°C, and most preferably 210°C. The higher the boiling point of the blocking agent, the more suppressed the volatilization of the blocking agent is by heat application during the drying process after coating the coating solution or, in the case of the in-line coating method, during the film formation process. This suppresses the occurrence of minute surface irregularities on the coated surface and improves the transparency of the film. There is no particular upper limit to the boiling point of the blocking agent, but from the viewpoint of productivity, it is thought that the upper limit is around 300°C. Since the boiling point is related to the molecular weight, it is preferable to use a blocking agent with a large molecular weight in order to raise the boiling point of the blocking agent. The molecular weight of the blocking agent is preferably 50 or more, more preferably 60 or more, and even more preferably 80 or more.

[0054] The upper limit of the dissociation temperature of the blocking agent is preferably 200°C, more preferably 180°C, even more preferably 160°C, particularly preferably 150°C, and most preferably 120°C. The blocking agent dissociates due to the heat applied during the drying process after application of the coating solution or, in the case of the in-line coating method, during the film formation process, generating regenerated isocyanate groups. As a result, the crosslinking reaction with urethane resin and the like proceeds, improving adhesion. If the dissociation temperature of the blocked isocyanate is below the above temperature, the dissociation of the blocking agent proceeds sufficiently, resulting in good adhesion, especially resistance to heat and humidity.

[0055] In one embodiment, the blocking agent used in the blocked isocyanate of the present invention may have a dissociation temperature of 120°C or lower and a boiling point of 150°C or higher. Specific examples include the aforementioned sodium bisulfite, 3,5-dimethylpyrazole, 3-methylpyrazole, dimethyl malonate, diethyl malonate, acetone oxime, and methyl ethyl ketoxime. Among these, pyrazole compounds, such as 3,5-dimethylpyrazole and 3-methylpyrazole, are preferred in terms of resistance to humid heat and yellowing.

[0056] The aforementioned blocked isocyanate is preferably bifunctional or more, and a trifunctional or more blocked isocyanate is even more preferable from the viewpoint of crosslinking properties of the coating film.

[0057] The trifunctional or more polyisocyanates, which are precursors to the blocked isocyanates of the present invention, can be suitably obtained by introducing isocyanate monomers. Examples include burettes, isocyanurates, and adducts obtained by modifying isocyanate monomers such as aromatic diisocyanates, aliphatic diisocyanates, aromatic aliphatic diisocyanates, or alicyclic diisocyanates, which have two isocyanate groups. A burette is a self-condensate having a burette bond formed by the self-condensation of isocyanate monomers, such as the burette of hexamethylene diisocyanate. An isocyanurate is a trimer of an isocyanate monomer, such as the trimer of hexamethylene diisocyanate, the trimer of isophorone diisocyanate, and the trimer of tolylene diisocyanate. Adduct compounds are isocyanate compounds with three or more functions, obtained by reacting an isocyanate monomer with a low-molecular-weight active hydrogen-containing compound with three or more functions. Examples include compounds obtained by reacting trimethylolpropane with hexamethylene diisocyanate, trimethylolpropane with tolylene diisocyanate, trimethylolpropane with xylylene diisocyanate, and trimethylolpropane with isophorone diisocyanate. From the viewpoint of oligomer blocking properties, isocyanurate compounds are preferred.

[0058] The aforementioned isocyanate monomers include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5-naphthylene diisocyanate, 1,4-naphthylene diisocyanate, phenylene diisocyanate, tetramethylxylylene diisocyanate, 4,4'-diphenyl ether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, and 2,2'-diphenylpropane-4,4'-diisocyanate. Examples include aromatic diisocyanates such as nate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, and xylylene diisocyanate; alicyclic diisocyanates such as isophorone diisocyanate and 4,4-dicyclohexylmethane diisocyanate, and 1,3-bis(isocyanate-methyl)cyclohexane; hexamethylene diisocyanate; and aliphatic diisocyanates such as 2,2,4-trimethylhexamethylene diisocyanate. From the viewpoint of transparency, resistance to yellowing, adhesion, and resistance to humid and heat, aliphatic and alicyclic isocyanates and their modified forms are preferred.

[0059] The crosslinking agent content in the resin layer-forming composition, relative to the total solid content of the conductive polymer, polyester resin, and crosslinking agent (total solid content) of 100% by mass, is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more. Increasing the crosslinking agent content is preferable as it improves adhesion to the substrate, oligomer blocking properties, and toughness of the resin layer. The upper limit of the crosslinking agent content is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. A crosslinking agent content of 90% by mass or less is preferable as it improves oligomer blocking properties and adhesion to the substrate.

[0060] The resin layer of this disclosure is formed by applying and curing a resin layer-forming composition (coating liquid) obtained by dissolving or dispersing the above essential components (A) conductive polymer, (B) polyester resin, (C) crosslinking agent and optional components described later in a solvent. The total amount of (A) conductive polymer, (B) polyester resin, and (C) crosslinking agent in 100% by mass of the solid content of the resin layer of this disclosure is preferably 80% by mass or more, more preferably 90% by mass or more, and may be substantially 100% by mass. It is also preferable that the above conductive polymer (A) is a polythiophene-based conductive polymer. The remainder may be the optional components listed below. It is preferable that the total amount of components (A) to (C) is higher so that the effects of the present invention can be expressed at a higher level.

[0061] In one embodiment of the optional components, one or more known optional components may be included for the purpose of improving properties such as antistatic properties, stretchability, coating appearance, and blocking resistance, to the extent that they do not impair the effects of the present disclosure.

[0062] Other Resins: In this invention, resins other than (B) polyester resins may be used in combination, as long as they do not affect the performance. Examples of resins that can be used in combination include polyurethane resins, acrylic resins, cellulose resins, polyolefin resins, and polyacetal resins.

[0063] Stretching aid (sugar alcohol) In one embodiment, it is preferable to include a sugar alcohol to improve the antistatic performance and stretchability of the film. Sugar alcohols refer to chain-like polyhydric alcohols obtained by reducing the carbonyl group of aldoses and ketoses, or cyclic polyhydric alcohols such as cyclitols. Specific examples include chain-like sugar alcohols such as erythritol and threitol, which are obtained by reducing monosaccharides; 5-carbon sugar alcohols such as ribitol, arabinitol, and xylitol; and 6-carbon sugar alcohols such as sorbitol, mannitol, iditol, talitol, and galactitol. Cyclic sugar alcohols, such as cyclitols like inositol, are also included. Disaccharide alcohols such as maltitol, lactitol, and isomaltulose reductions, which are obtained by reducing disaccharides, can also be exemplified. If the above sugar alcohol has stereoisomers, all of those stereoisomers are included. Furthermore, the sugar alcohol may be used alone or in combination of two or more types.

[0064] From the viewpoint of achieving both high antistatic properties and transparency, sugar alcohols having 4 to 12 carbon atoms are preferred, sugar alcohols having 4 to 6 carbon atoms are more preferred, and sugar alcohols having 6 carbon atoms are particularly preferred. Chain-like sugar alcohols are preferred. From the above viewpoint, among the sugar alcohols, sorbitol, xylitol, and arabitol are preferred, and sorbitol is more preferred.

[0065] The lower limit of the amount of sugar alcohol added to the total coating solution is preferably 0.1% by mass, more preferably 0.2% by mass, and even more preferably 0.5% by mass. Amounts above this are preferable because they prevent cracking of the coating film and provide good antistatic properties. The upper limit of the amount of sugar alcohol added to the total coating solution is preferably 4% by mass, more preferably 3.5% by mass, and even more preferably 3% by mass. Amounts below this are preferable because they improve blocking resistance.

[0066] It is also preferable to include a surfactant in order to improve the wettability of the surfactant coating solution and enhance the appearance of the coating. Examples of surfactants include silicone-based surfactants, fluorine-based surfactants having perfluoroalkyl groups, and hydrocarbon-based surfactants such as acetylene-based surfactants.

[0067] From the viewpoint of improving appearance and suppressing the deterioration of haze, the amount of surfactant added to the total coating solution is preferably 0.001% by mass or more and 0.5% by mass or less, more preferably 0.005% by mass or more and 0.2% by mass or less.

[0068] In one embodiment, it is preferable to include particles to improve the blocking resistance of the resin layer. The particles can be either inorganic or organic particles, such as titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, or mixtures thereof. Other common inorganic particles, such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, etc., used in combination with other inorganic particles, or organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles, are also acceptable.

[0069] The average particle size (average particle size based on the number of particles measured by a scanning electron microscope (SEM); the same applies hereinafter) is preferably 0.04 μm or more and 2.0 μm or less, and more preferably 0.1 μm or more and 1.0 μm or less. An average particle size of 0.04 μm or more is preferable because it facilitates the formation of irregularities on the film surface, improving handling properties such as the slipperiness and winding properties of the film, and resulting in good processability during lamination. On the other hand, an average particle size of 2.0 μm or less is preferable because it makes it less likely for particles to fall off the coating film. The particle concentration in the solid component of the resin layer is preferably 1 to 20% by mass.

[0070] The method for measuring the average particle size involves observing the particles in a cross-section of a laminated polyester film having a polyester film substrate and a resin layer using a scanning electron microscope. Thirty particles are observed, and the average value is taken as the average particle size.

[0071] The shape of the particles is not particularly limited as long as it satisfies the purposes of this disclosure, and spherical particles or irregularly shaped non-spherical particles can be used. The particle size of irregularly shaped particles can be calculated as the equivalent diameter. The equivalent diameter is obtained by dividing the area of ​​the observed particle by π, calculating the square root, and multiplying by 2.

[0072] Water or a mixed solvent of water and alcohols is preferred as the solvent used in the resin layer forming composition.

[0073] The water content in the solvent is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more. A higher water content prevents interaction with the conductive polymer, makes the coating solution less likely to aggregate, reduces the drawbacks of the antistatic layer, and allows for high transparency to be maintained. The upper limit of the water content in the solvent may be 100% by mass, but is preferably less than 100% by mass.

[0074] The solid content concentration of the coating solution is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 7% by mass or less, and even more preferably 0.5% by mass or more and 5% by mass or less. Increasing the solid content concentration contributes to achieving the oligomer blocking properties, substrate adhesion, and antistatic layer of the present invention. On the other hand, lowering the solid content concentration makes the coating solution less prone to aggregation, resulting in a coating film with fewer appearance defects.

[0075] Characteristics of Laminated Polyester Films The thickness of the resin layer that functions as an antistatic layer in a laminated polyester film is preferably 0.001 μm or more and 1 μm or less, more preferably 0.005 μm or more and 0.5 μm or less, and even more preferably 0.01 μm or more and 0.3 μm or less, with an upper limit of 0.1 μm or less being even more preferable. A thicker film thickness is preferable because it provides an antistatic effect and an oligomer blocking effect. On the other hand, a thinner film thickness is preferable because it reduces discoloration and increases transparency.

[0076] Surface Resistivity The surface resistivity of the laminated polyester film is preferably 10 [log Ω / □] or less. More preferably 8 [log Ω / □] or less, even more preferably 7.5 [log Ω / □] or less, and even more preferably 7 [log Ω / □] or less. Lowering the surface resistivity is preferable because it suppresses the adhesion of foreign matter to the laminated polyester and suppresses peeling charge when an adhesive layer is laminated and peeled off. Furthermore, there is no particular lower limit for the surface resistivity of the laminated polyester film, but from the viewpoint of production cost, for example, it is preferably 2 [log Ω / □] or more, more preferably 3 [log Ω / □] or more. In this disclosure, "Ω / □" means "ohms per square" and can be written as "Ω / sq.".

[0077] For haze-laminated polyester films, it is preferable to have excellent transparency (low haze) when considering the visual inspection properties for optical applications, particularly the visual inspection properties after lamination of the film and the substrate. The initial haze is preferably 3.0% or less, more preferably 2.5% or less, even more preferably 2.0% or less, and even more preferably 1.5% or less, with no particular lower limit, and may be substantially 0% (0% or more) or 0.1% or more.

[0078] Difference in haze value before and after heating (Δ-haze) In one embodiment, oligomer blocking properties can also be evaluated by the haze value after heat treatment and / or the difference in haze value before and after heat treatment (Δ-haze). Specifically, the haze value after heat treatment of the laminated polyester film at 140°C for 10 minutes is preferably 3.00% or less, more preferably 2.50% or less, even more preferably 2.00% or less, and even more preferably 1.50% or less. A lower haze value after heating is preferable because it allows for visual inspection of the laminated polyester film when it is bonded to the adherend. Although it should not be interpreted as being limited to a specific theory, by having the resin layer (antistatic layer) according to the present invention, it is possible to obtain an antistatic layer that is highly reactive, has improved crosslinking density, and is less prone to oligomer precipitation. As a result, it is presumed that a significant increase in haze after heating at 140°C for 10 minutes can be suppressed.

[0079] Furthermore, the Δ-haze value, obtained by subtracting the haze of the laminated polyester film before heating from the haze value after heating the laminated polyester film at 140°C for 10 minutes, is preferably -0.20% or more and 2.00% or less, more preferably 0% or more and 1.50% or less, even more preferably 0.01% or more and 1.20% or less, and even more preferably 0.05% or more and 1.00% or less, with the upper limit of the Δ-haze value being particularly preferably 0.80% or less, and even more particularly preferably 0.50% or less. If the Δ-haze value is within this range, an antistatic layer in which oligomers are less likely to precipitate can be obtained. By forming an antistatic layer in which oligomers are less likely to precipitate, the visibility of the protective film does not decrease easily even after heat drying in the adhesive layer lamination process, and it is possible to perform visual inspection even when the protective film is laminated to an adherend.

[0080] Durability (Alcohol Resistance) Laminated polyester films preferably have high durability against solvent contact during manufacturing processes. For example, the alcohol resistance (rate of change in surface resistance due to alcohol wiping: resistance value change rate) is preferably 200% or less, more preferably 150%, even more preferably 100%, and even more preferably 50%, and the resistance value change rate may be substantially 0% (0% or more), or for example, 0.1% or more. If the alcohol resistance (surface resistivity change rate) is within this range, it is possible to achieve the effect that the antistatic properties and oligomer blocking properties do not easily deteriorate even when alcohol is used for cleaning during the manufacturing process.

[0081] The surface shape of the surface resin layer can affect the quality when the adhesive layer is laminated and wound into a roll. The average surface roughness (Sa) of the resin layer surface of the laminated polyester film is preferably 1 nm or more and 40 nm or less, more preferably 1 nm or more and 30 nm or less, and even more preferably 1 nm or more and 10 nm or less. The maximum protrusion height (Sp) on the surface of the laminated polyester film is preferably 2 μm or less, more preferably 1.5 μm or less, and even more preferably 0.8 μm or less. In one embodiment, if Sa is 40 nm or less and Sp is 2 μm or less, it is preferable because there is no risk of roughening the adhesive surface when the adhesive layer is laminated and wound into a roll.

[0082] Adhesive Layer The adhesive laminated polyester film of this disclosure may also preferably have an adhesive layer on the surface of the polyester film substrate opposite to the resin layer (antistatic layer) of the laminated polyester film. If the resin layer is provided on both sides of the substrate, the adhesive layer may be provided on either one side.

[0083] Types of Adhesives The adhesive used to form the adhesive layer is not particularly limited as long as it is commonly used for protective film applications. Examples include acrylic adhesives, silicone adhesives, rubber adhesives, and urethane adhesives. Among these, acrylic or silicone adhesives are preferred due to their low contamination of the optical component to which they are adhered, as well as their excellent transparency and weather resistance. Furthermore, these adhesives may contain various additives such as tackifiers, softeners, antioxidants, and fillers, as long as their properties are not impaired.

[0084] (Manufacturing of Laminated Polyester Film) The laminated polyester film of this disclosure is manufactured by a drafting method that includes the steps of manufacturing a polyester film substrate and forming a resin layer (antistatic layer) on the substrate. In one embodiment, when an adhesive laminated polyester film is to be manufactured, the step of forming an adhesive layer is further included. The following description will use polyethylene terephthalate (hereinafter sometimes abbreviated as PET) film as the substrate as an example, but this disclosure is not limited thereto.

[0085] The polyester film used as the base material for the polyester film substrate is manufactured by a known melt extrusion film-forming method. Generally, it is manufactured through the steps of producing an unstretched sheet, stretching, and heat fixing. Process for producing an unstretched sheet (melt extrusion, cooling and solidification process) First, the polyester resin (PET resin) to be used as the raw material is vacuum dried and then supplied to an extruder and melted at approximately 280°C. Next, the molten PET resin is extruded from a T-die into a sheet shape and cast onto a rotating cooling roll with a cooled surface to cool and solidify, thereby obtaining an unstretched PET sheet. At this time, electrostatic application or the like can be used as a means to make the resin adhere to the rotating cooling roll. Furthermore, the unstretched PET sheet may be a single-layer structure produced by a single extruder, or it may be a multi-layer structure produced by a co-extrusion method using multiple extruders.

[0086] In the stretching process, the obtained unstretched sheet is subjected to a stretching treatment to improve the mechanical strength and dimensional stability of the film. The stretching method may be either uniaxial stretching or biaxial stretching. In the case of biaxial stretching, sequential biaxial stretching or simultaneous biaxial stretching is employed. For example, in biaxial stretching, the unstretched sheet is stretched 2.5 to 5.0 times in the longitudinal direction using a group of rolls heated to 80 to 120°C to obtain a uniaxially stretched PET film. Then, the film is guided to a tenter while the ends are held with clips, and stretched 2.5 to 5.0 times in the width direction in a hot air atmosphere heated to 80 to 180°C. In the case of uniaxial stretching, the film is stretched 2.5 to 5.0 times within the tenter.

[0087] After stretching in the heat-setting process, the film is heat-set in a tenter with or without tension released to ensure dimensional stability and suppress thermal shrinkage. The heat-setting temperature is preferably 170°C or higher and 250°C or lower, more preferably 180°C or higher and 250°C or lower. A higher heat-setting temperature allows for sufficient crystallization, improving dimensional stability and ensuring sufficient hardening, resulting in good blocking properties in the presence of liquid water, which is preferable and eliminates the need for a longer drying time. On the other hand, a lower heat-setting temperature avoids the deterioration of the film's physical properties due to thermal decomposition.

[0088] Formation of the resin layer (antistatic layer) The formation of the resin layer (antistatic layer) can be carried out by either an offline coating method performed outside the film manufacturing line for the base film, or an in-line coating method performed within the film manufacturing line. However, from the viewpoint of productivity, the in-line coating method is particularly preferred. In the in-line coating method, a resin layer forming composition (coating liquid) is applied to at least one side of an unstretched sheet or a film after uniaxial stretching. After application, the coating liquid is dried and cured using the heat from the subsequent stretching and heat setting processes to form a strong resin layer.

[0089] The method of applying this coating solution to the film is not particularly limited, and any known coating technique can be appropriately selected. Specific examples include the reverse roll coating method, gravure coating method, kiss coating method, die coater method, roll brush method, spray coating method, air knife coating method, wire bar coating method, pipe doctor method, impregnation coating method, and curtain coating method. These methods can be used individually or in combination.

[0090] While other known methods such as vacuum deposition and bonding can be used to laminate the resin layer (antistatic layer) besides the coating method described above, applying a coating solution containing an antistatic agent by coating is preferable from a cost standpoint.

[0091] Formation of the adhesive layer The adhesive laminated polyester film of this disclosure is manufactured by providing an adhesive layer on the surface of the polyester film substrate opposite to the resin layer (antistatic layer) of the laminated polyester film manufactured in the above process.

[0092] As for the method of forming the adhesive layer, either a direct application method, in which an adhesive solution is directly applied to the substrate surface of the laminated polyester film and dried and cured, or a transfer method, in which an adhesive layer is first formed on a release-treated film (release film) and then transferred (laminated) to the substrate surface of the laminated polyester film, can be employed. The method of applying the adhesive is not particularly limited, and known application devices such as comma coaters, gravure coaters, die coaters, reverse roll coaters, and lip coaters can be used. After application, a heat treatment is performed to dry and cure the adhesive layer. The heating conditions are set appropriately according to the type and thickness of the adhesive used, but are generally in the temperature range of 70 to 150°C for about 30 seconds to several minutes. The laminated polyester film of the present invention exhibits particularly excellent oligomer blocking properties in this heating process, so the increase in haze due to heating can be effectively suppressed.

[0093] In order to protect the surface of the release film adhesive layer, it is also a preferred embodiment to laminate a release film onto the surface of the adhesive layer. As the release film, a polyethylene terephthalate film or a polypropylene film is used, on one side of which a release agent such as a silicone-based or fluorine-based agent is applied. Finally, the adhesive laminated polyester film, in which the adhesive layer and the release film are laminated, is usually wound into a roll to become the final product.

[0094] This application claims the benefit of priority under Japanese Application No. 2024-176051, filed on 7 October 2024. The entire specification of Japanese Application No. 2024-176051 is incorporated herein by reference.

[0095] To explain the present invention in detail, examples will be given below, but of course, the present invention is not limited to these examples. The evaluation method used in the present invention is as follows.

[0096] (Surface Resistivity) The surface resistivity of the antistatic layer surface of the laminated polyester film was measured under the following conditions to evaluate its antistatic performance. Measurement conditions: After 24 hours of humidity control at a temperature of 23°C and a humidity of 55%, the surface resistivity of the antistatic layer surface was measured using a surface resistance meter (Simco Japan, Work Surface Tester ST-3). Judgment criteria: ◎ (Excellent): Surface resistivity [logΩ / □] is 5.00 or less ○ (Good): Surface resistivity [logΩ / □] is greater than 5.00 and 7.00 or less △ (Acceptable): Surface resistivity [logΩ / □] is greater than 7.00

[0097] (Total Light Transmittance, Haze) The total light transmittance of laminated polyester films before and after heating was measured under the following conditions to evaluate the oligomer blocking properties. Measurement conditions: In accordance with JIS K 7136, the haze (%) of the film was measured using a turbidimeter (NDH7000II, manufactured by Nippon Denshoku Industries Co., Ltd.). Next, the film was heat-treated at 140°C for 10 minutes and the haze (%) was measured. From the haze values ​​before and after heat treatment, Δ-haze was calculated using the following formula: Δ-haze (%) = haze value after heat treatment - haze value before heat treatment Judgment criteria: ◎ (Excellent): Δ-haze is 0.50% or less 〇 (Good): Δ-haze is greater than 0.50% and 1.00% or less △ (Acceptable): Δ-haze is greater than 1.00% and 2.50% or less × (Unacceptable): Δ-haze is greater than 2.50%

[0098] (Alcohol Resistance) The alcohol resistance of the laminated polyester film was measured under the following conditions to evaluate its durability. Measurement conditions: The surface of the antistatic layer of the laminated polyester film was wiped 10 times back and forth with Kimwipes (registered trademark) manufactured by Nippon Paper Crecia Co., Ltd., which had been thoroughly impregnated with ethanol. The surface resistivity before and after the wiping treatment was measured with the above surface resistance meter, and the rate of change was calculated and evaluated using the following formula. Rate of change in surface resistivity (%) = {(Surface resistivity after treatment - Surface resistivity before treatment) / Surface resistivity before treatment} × 100 Judgment criteria: ◎ (Excellent): Rate of change of 30% or less 〇 (Good): Rate of change of more than 30% and 50% or less △ (Acceptable): Rate of change of more than 50% and 100% or less × (Unacceptable): Rate of change of more than 100%

[0099] (Glass transition temperature: Tg) The glass transition temperature (Tg) of the resin sample was measured in accordance with JIS K7121-1987. Using a differential scanning calorimeter (Seiko Instruments, DSC6200), the extrapolation glass transition onset temperature was determined from the DSC curve when 10 mg of the resin sample was heated from 25°C to 300°C in a nitrogen atmosphere at a heating rate of 20°C / min.

[0100] (Analysis of resin composition) Polyester resin is mixed with deuterated chloroform (CDCl ３ ) is dissolved and a nuclear magnetic resonance analyzer (NMR: Varian Gemini-200) is used to analyze the proton nuclear magnetic resonance ( １ The 1H-NMR spectrum was measured. From the obtained spectrum, the copolymer composition (mol%) of the resin was calculated from the signal integration ratio of characteristic protons originating from each monomer unit.

[0101] The following raw materials were used to form the conductive polymer in the examples and comparative examples of raw materials used: (Conductive polymer A) (A-1) Polythiophene-based conductive polymer (manufactured by Agfa Material Japan, ICP1010, solid content concentration 1.2% by mass)

[0102] (Polyester resin B) The polyester resins (B-1 to B-4) shown in Table 1 were used.

[0103]

[0104] (Crosslinking agent C) (C-1) Oxazoline-based crosslinking agent (manufactured by Nippon Shokubai Co., Ltd., WS-700, solid content concentration 25% by mass) (C-2) Carbodiimide-based crosslinking agent (manufactured by Nisshinbo Chemical Co., Ltd., SV-02, solid content concentration 40% by mass) (C-3) Isocyanate-based crosslinking agent (manufactured by Baxenden, BI200, solid content concentration 40% by mass)

[0105] (Stretching agent D) (D) Sorbitol (solid content concentration 100% by mass)

[0106] (Surfactant E) (E-1) Acetylene-based surfactant (manufactured by Nisshin Chemical Industry Co., Ltd., solid content concentration 100% by mass)

[0107] (Particles) (Particle I) Silica sol with an average particle size of 450 nm (solid content concentration 40% by mass) (Particle II) Silica sol with an average particle size of 45 nm (solid content concentration 20% by mass)

[0108] Preparation of base film (polyester resin F) (Preparation of antimony trioxide solution) Antimony trioxide (manufactured by Sigma-Aldrich Japan LLC) was placed in a flask together with ethylene glycol, stirred at 150°C for 4 hours to dissolve, and then cooled to room temperature to prepare a 20 g / l antimony trioxide ethylene glycol solution.

[0109] (Polymerization of polyester resin F) High-purity terephthalic acid and twice its molar amount of ethylene glycol were charged into a 2-liter stainless steel autoclave equipped with a stirrer. 0.3 mol% of triethylamine was added relative to the acid component, and an esterification reaction was carried out at 250°C under a pressure of 0.25 MPa while distilling off water from the system to obtain a mixture of bis(2-hydroxyethyl) terephthalate and oligomer (hereinafter referred to as the BHET mixture) with an esterification rate of approximately 95%. The above antimony trioxide solution was used as a polycondensation catalyst and added to this BHET mixture so that the amount of antimony atoms relative to the acid component in the polyester was 0.04 mol%, and then stirred at 250°C for 10 minutes under atmospheric pressure in a nitrogen atmosphere. Subsequently, the temperature was gradually increased to 280°C over 60 minutes while the pressure of the reaction system was gradually reduced to 13.3 Pa (0.1 Torr). A polycondensation reaction was then carried out at 280°C and 13.3 Pa for 68 minutes to obtain a polyester resin F with an intrinsic viscosity (IV) (solvent: phenol / tetrachloroethane = 60 / 40) of 0.61 dl / g and substantially free of particles.

[0110] (Example 1) (1) Preparation of coating liquid for antistatic layer The raw materials were mixed and stirred according to the following formulation to prepare an antistatic layer coating liquid (resin layer forming composition: coating liquid). (Composition of coating liquid for antistatic layer) Water 68.15 parts by mass Isopropyl alcohol 9.65 parts by mass Conductive polymer A-1 11.67 parts by mass Polyester resin B-1 1.86 parts by mass Crosslinking agent C-1 5.58 parts by mass Stretching aid D 1.00 parts by mass Particle I 0.05 parts by mass Particle II 2.00 parts by mass Surfactant E-1 0.04 parts by mass

[0111] (2) Preparation of Laminated Polyester Film As the film raw material polymer, resin pellets of polyester resin F were dried at 135°C for 6 hours under reduced pressure of 133 Pa. Then, they were supplied to an extruder and melt-extruded into a sheet at approximately 280°C, and rapidly cooled and solidified on a rotating cooling metal roll maintained at a surface temperature of 20°C to obtain an unstretched PET sheet. This unstretched PET sheet was heated to 100°C using a heated roll group and an infrared heater, and then stretched 3.5 times in the longitudinal direction using a roll group with different peripheral speeds to obtain a uniaxially oriented PET film.

[0112] Next, the coating solution prepared in (1) above is applied to one side of the PET film, with a final coating amount of 0.13 g / m² after drying (after biaxial stretching). ２ The coating was applied in this manner. After the coating solution dried, the film was stretched to 4.0 times its original width at 110°C, and then, with the film's width direction fixed, it was heated in a 230°C oven for 5 seconds. Finally, a 3% widthwise relaxation treatment was performed to obtain a laminated polyester film with a thickness of 100 μm.

[0113] (Examples 2-15, Comparative Example 1) Laminated polyester films were prepared in the same manner as in Example 1, except that the composition of the antistatic coating liquid was changed as shown in Tables 2 and 3. In Comparative Example 1, the crosslinking agent C was not used.

[0114] Table 4 shows the evaluation results of the films prepared in each example and comparative example.

[0115]

[0116]

[0117]

[0118] Results and Discussion Examples 1 to 15 showed significantly suppressed Δ-haze after heating compared to Comparative Example 1, which did not contain a crosslinking agent, confirming that the configuration of the present disclosure exhibits excellent oligomer blocking properties. In particular, Examples 10 to 12, which used polyester resin B-3 with a glass transition temperature (Tg) of 110°C, showed extremely excellent oligomer blocking properties with a Δ-haze of 0.25 or less. Furthermore, regarding alcohol resistance, the performance varied greatly depending on the type of crosslinking agent. Durability decreased in Examples 4 and 13, which used a carbodiimide-based crosslinking agent (C-2), but good results were obtained in the example using an oxazoline-based crosslinking agent (C-1). The laminated polyester film of the present invention obtained in the examples provides a laminated polyester film in which an antistatic layer with low haze after heating is laminated on at least one side of the polyester film. Even when an adhesive layer is laminated on this laminated polyester film and used as a protective film, visual inspection is possible, and a protective film that suppresses peeling charge and foreign matter adhesion during peeling can be provided.

[0119] Furthermore, since Comparative Example 1 did not contain a crosslinking agent, it tended to have higher haze after heating compared to the sample used in the Examples.

[0120] The present invention relates to laminated polyester films and adhesive films obtained by laminating an adhesive layer onto a laminated polyester film, and more particularly to protective films for optical components (for example, components of organic EL and liquid crystal displays).

Claims

1. A laminated polyester film comprising a polyester film substrate and a resin layer, wherein the resin layer is a layer formed by curing a resin layer-forming composition containing a polyester resin having a glass transition temperature of 40°C or higher, a crosslinking agent, and a polythiophene-based conductive polymer.

2. The laminated polyester film according to claim 1, wherein the polyester resin is a copolymer polyester containing naphthalenedicarboxylic acid as an acid component.

3. The laminated polyester film according to claim 1, wherein the crosslinking agent comprises at least one selected from the group consisting of oxazoline-based crosslinking agents and isocyanate-based crosslinking agents.

4. The laminated polyester film according to claim 1, wherein the surface resistivity of the resin layer is 2 to 7 [log Ω / □].

5. The laminated polyester film according to claim 1, wherein the difference (Δhaze) between the haze value of the laminated polyester film before heating and the haze value after heat treatment at 140°C for 10 minutes is 2.00% or less.

6. The laminated polyester film according to claim 1, wherein the total amount of the polythiophene-based conductive polymer, the polyester resin, and the crosslinking agent is 80% by mass or more of the solid content of the resin layer.

7. The laminated polyester film according to claim 1, wherein the resin layer is provided in contact with the polyester film substrate.

8. The laminated polyester film according to claim 1, wherein the glass transition temperature of the polyester resin is 60°C or higher and 115°C or lower.

9. The laminated polyester film according to claim 1, wherein the crosslinking agent is an oxazoline-based crosslinking agent.

10. The laminated polyester film according to claim 6, wherein the content of the polyester resin is 15% by mass or more and 55% by mass or less in 100% by mass of the solid content of the resin layer, and the content of the crosslinking agent is 40% by mass or more and 75% by mass or less.

11. The laminated polyester film according to claim 1, wherein the acid component constituting the polyester resin contains 70 mol% or more and 85 mol% or less of naphthalenedicarboxylic acid and 5 mol% or more and 15 mol% or less of sebacic acid, based on 100 mol% of the total dicarboxylic acid component.

12. An adhesive laminated polyester film having an adhesive layer on the polyester film substrate opposite to the resin layer of the laminated polyester film according to any one of claims 1 to 11.

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