Laminated polyester film

Abstract

Provided are a laminated polyester film and a protective film that exhibit excellent substrate adhesion properties, antistatic properties, and oligomer-blocking properties for suppressing an increase in haze even after a heat drying step.　The present invention pertains to a laminated polyester film having a polyester substrate film and a resin layer. The resin layer is obtained by curing a resin layer-forming composition. The resin layer-forming composition contains a polyester resin, a crosslinking agent, a polythiophene conductive polymer, and a stretching aid. The glass transition temperature of the polyester resin contained in the resin layer-forming composition is at least 30°C. The difference in haze of the laminated polyester film between before being heated and after being heated for 10 minutes at 140°C is at most 2%.

Description

Laminated polyester film

[0001] The present invention relates to a laminated polyester film and an adhesive laminated polyester film (sometimes referred to as a protective film) having an adhesive layer laminated on a laminated polyester film, and more particularly to a protective film for optical components (for example, components of organic EL and liquid crystal displays).

[0002] Films with an adhesive layer laminated onto a base film are used as protective films for various components in the manufacturing process of optical components and other materials. These protective films are bonded to each component via the adhesive layer, preventing scratches and dirt from adhering during processing and transportation of the components. The base film used for these protective films is typically a laminated polyester film with an antistatic layer laminated on at least one side. The purpose of laminating the antistatic layer is to prevent the adhesion of foreign matter such as dust and dirt to the protective film and to suppress static electricity generated when the protective film is peeled from the substrate. (See Patent Document 1)

[0003] Silicone adhesives, primarily composed of silicone, are attracting attention as adhesives suitable for applications requiring high levels of weather resistance and heat resistance. Silicone adhesives are typically used in tape (film) form with the adhesive layer as the adhesive layer. Before use, they are usually stored with one or both sides covered with a release film, and the release film is peeled off before use. In release films used in this type of application, release static electricity may occur when peeling the film from the adherend such as the adhesive, making antistatic treatment of the release film itself desirable. Patent Document 2 proposes a release film that combines release properties and antistatic properties in a single layer, containing PEDOT:PSS as an antistatic agent, and allowing for the elimination of fluorinated silicone or a reduction in the amount of fluorinated silicone used (see Patent Document 2).

[0004] As a laminated polyester film having an antistatic layer, a film has been proposed that uses a PEDOT:PSS and an acrylic copolymer having a styrene structure to provide good antistatic properties regardless of the usage environment, and oligomer-blocking properties that reduce the precipitation of oligomers from the polyester film when treated at high temperatures, with just one layer (see Patent Document 3).

[0005] As an antistatic film, an amount of antistatic agent has been proposed characterized by a mass ratio of the total of polythiophene compounds and acidic polymers to sugar alcohols in the range of 60:40 to 20:80 (see Patent Document 4).

[0006] International Publication 2018 / 012545 Japanese Patent Publication No. 2022-129913 Japanese Patent Publication No. 2022-155385 Japanese Patent Publication No. 2008-179809

[0007] This invention was made against the backdrop of the problems of the prior art described above. Protective films having an antistatic layer are used as protective films for optical components and the like, and are particularly used in the processing of components for displays. In recent years, they have also been increasingly used in the processing of components for organic EL displays (especially OLED displays). In order to bond the protective film to the optical component, an adhesive layer is provided on at least one side of the protective film, and the process of laminating this adhesive layer includes a heat drying process.

[0008] For example, when an adhesive layer is laminated onto a protective film in this manner, oligomers may precipitate during the heat drying process, causing haze to increase and degrading the film's appearance. The increased haze on the protective film reduces visibility, making visual inspection of the protective film in its bonded state difficult, which posed a problem. Patent Document 4 discloses a technology involving a polythiophene compound, an acidic polymer, and a sugar alcohol. However, the technology in Patent Document 4 may result in high surface resistance after the stretching process.

[0009] As a result of diligent research by the inventors, it was found that, for example, when using a stretched film, the antistatic properties may deteriorate after the stretching process. Furthermore, a problem arose in that the static electricity generated when peeling the protective film from the adherend could not be suppressed due to the deterioration of antistatic properties.

[0010] This invention was made against the backdrop of the problems of the prior art. Specifically, the object of this invention is to provide a laminated polyester film and a protective film that have oligomer blocking properties that suppress the rise of haze even after the heating and drying process, and excellent antistatic properties even after the stretching process.

[0011] That is, the present invention comprises the following configurations: [1] A laminated polyester film having a polyester base film and a resin layer, wherein the resin layer is a layer obtained by curing a resin layer forming composition, the resin layer forming composition comprises a polyester resin, a crosslinking agent, a polythiophene-based conductive polymer and a stretching aid, the glass transition temperature of the polyester resin contained in the resin layer forming composition is 30°C or higher, and the difference in haze between the haze before heating the laminated polyester film and the haze after heating at 140°C for 10 minutes is 2% or less. [2] The laminated polyester film according to [1], wherein the polyester resin contained in the resin layer forming composition 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 oxazoline-based crosslinking agents or isocyanate-based 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 10 [logΩ / □]. [5] The polyester film according to any one of [1] to [4], wherein the content of the polythiophene-based conductive polymer is 0.02 to 1.00 in mass ratio with the stretching aid. [6] The polyester film according to any one of [1] to [5], wherein the stretching aid contains a sugar alcohol. [7] The laminated polyester film according to any one of [1] to [6], wherein the water contact angle of the resin layer is 30° or more. [8] The laminated polyester film according to any one of [1] to [7], wherein the resin layer is provided in contact with the polyester base film. [9] The adhesive laminated polyester film according to any one of items [1] to [8], wherein the adhesive layer, the polyester base film, and the resin layer are in this order.

[0012] The present invention provides a laminated polyester film having oligomer blocking properties on at least one side of the polyester film and excellent antistatic properties even after the stretching process. The present invention can further provide a laminated polyester film that can have an adhesive layer, and even when the laminated polyester film having an adhesive layer is bonded to an adherend, visual inspection is possible, and peeling charge and foreign matter adhesion are suppressed during peeling.

[0013] The present invention will be described in detail below.

[0014] (Polyester Film Substrate) The polyester film used as a substrate in the present invention is a film mainly composed of polyester resin. Here, "a film mainly composed of polyester resin" means a film formed from a resin composition containing 50% by mass or more of polyester resin. When blended with other polymers, this means that the polyester resin is contained at 50% by mass or more, and when other monomers are copolymerized, this means that the repeating structural units of polyester are contained at 50 mol% or more. Preferably, the polyester film contains 90% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass of polyester resin in the resin composition constituting the film.

[0015] While the polyester resin material is not particularly limited, copolymers formed by polycondensation of a dicarboxylic acid component and a diol component, or blends thereof, can be used. Examples of dicarboxylic acid components include 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, diphenylsulfoncarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, 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, dimer acid, sebacic acid, suberic acid, and dodecadicarboxylic acid.

[0016] Examples of diol components that make up polyester resins include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone.

[0017] The dicarboxylic acid and diol components that make up the polyester resin may be one or more of each. In addition, other acid components such as trimellitic acid and other hydroxyl group components such as trimethylolpropane may be added as appropriate.

[0018] Examples of polyester resins include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Among these, polyethylene terephthalate is preferred due to its balance of physical properties and cost.

[0019] While there are no particular limitations on the catalyst used for polycondensation in the production of polyester resins, antimony trioxide is preferred because it is inexpensive and has excellent catalytic activity. Germanium compounds or titanium compounds are also preferred. Even more preferred polycondensation catalysts include catalysts containing aluminum and / or its compounds and phenolic compounds, catalysts containing aluminum and / or its compounds and phosphorus compounds, and catalysts containing aluminum salts of phosphorus compounds.

[0020] In the present invention, the thickness of the polyester film is not particularly limited, but it is preferably in the range of 12 to 188 μm. More preferably 18 to 125 μm, and even more preferably 25 to 100 μm. A thickness of 12 μm or more reduces the risk of wrinkles forming when laminating the protective film to the substrate, and a thickness of 188 μm or less is cost-effective.

[0021] Furthermore, the polyester film substrate in the present invention is not particularly limited in terms of its layer structure. It may be a single-layer polyester film, a two-layer structure with different components, or a polyester film substrate consisting of at least three layers, including an outer layer and an inner layer. In addition, various additives may be included in the film as needed, within the range that the effects of the present invention are achieved. Examples of additives include antioxidants, lightfastening agents, gelation inhibitors, organic wetting agents, antistatic agents, ultraviolet absorbers, and surfactants. If the film has a laminated structure, it is also preferable to include additives according to the function of each layer as needed.

[0022] Polyester film can be obtained, for example, by melt-extruding the above-mentioned polyester resin into a film, and then cooling and solidifying it in a casting drum to form the film. The polyester film of the present invention can be either an unstretched film or a stretched film, but a stretched film is preferable in terms of durability, such as mechanical strength and chemical resistance. When the polyester film is a stretched film, the stretching method is not particularly limited, and methods such as longitudinal uniaxial stretching, transverse uniaxial stretching, sequential longitudinal and transverse biaxial stretching, and simultaneous longitudinal and transverse biaxial stretching can be employed.

[0023] (Resin layer: Antistatic layer) A laminated polyester film having a resin layer can be used as an antistatic film. In this case, the resin layer functions as an antistatic layer. 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. In this case, the resin layer (antistatic layer) is provided in contact with the polyester film substrate. The resin layer (antistatic layer) may be laminated on only one side of the substrate or on both sides. By laminating the resin layer (antistatic layer), even when an adhesive layer is laminated and used as a protective film, peeling charge with the adherend is suppressed and the adhesion of foreign matter is suppressed, which is preferable. In another embodiment, the present invention provides an adhesive laminated polyester film having a polyester substrate film, a resin layer, and an adhesive layer in this order. The adhesive laminated polyester film of the present invention can be used as a protective film for optical components (for example, components of organic EL or liquid crystal displays).

[0024] The resin layer of the present invention is a layer obtained by curing a resin layer forming composition, the resin layer forming composition comprising a polyester resin, a crosslinking agent, a polythiophene-based conductive polymer, and a stretching aid. Such a composition may be referred to as an antistatic layer forming composition.

[0025] The means for laminating the resin layer (antistatic layer) are not particularly limited, and known methods such as coating, vacuum deposition, and bonding can be used, but from a cost standpoint, it is preferable to apply a coating liquid containing an antistatic agent by coating.

[0026] The following details each composition that forms the resin layer (antistatic layer). (Conductive Polymer) This invention includes a polythiophene-based conductive polymer. The conductive polymer in this invention is a polymer that can impart antistatic properties. In this invention, the polythiophene-based conductive polymer is classified as a π-electron conjugated conductive polymer, and further details will be described later.

[0027] For example, in addition to the polythiophene-based conductive polymer, the following conductive polymers may be used in combination. The conductive polymer in the present invention is a polymer that can impart antistatic properties, and polymers that utilize ion conduction, such as cationic compounds, and π-electron conjugated conductive polymers can be used. From the viewpoint of antistatic properties under low humidity, it is preferable to use a π-electron conjugated conductive polymer. Furthermore, π-electron conjugated conductive polymers are preferred because they can maintain a high level of antistatic performance without depending on the moisture in the air, and therefore have good antistatic performance in various usage environments of protective films. In addition, an antistatic agent can be used in combination to the extent that it does not impair the effects performed by the conductive polymer according to the present invention. As the antistatic agent, polymers other than the conductive polymer in the present invention, such as cationic compounds that utilize ion conduction, and π-electron conjugated conductive polymers may be used, and surfactants, silicon dioxide compounds, conductive metal compounds, etc., can be used. In one embodiment, a π-electron conjugated conductive polymer is preferred for the conductive polymer in order to achieve both excellent antistatic properties and oligomer blocking properties. In polymers that utilize ion conduction, such as cationic compounds, adding the necessary amount to achieve excellent surface resistivity may reduce oligomer blocking properties; therefore, π-electron conjugated conductive polymers are preferable.

[0028] In one embodiment, oxazoline-based or isocyanate-based crosslinking agents are preferred to avoid contamination of the process, and oxazoline-based crosslinking agents are preferred to enhance the oligomer blocking effect. Furthermore, catalysts and the like can be used as needed to promote the crosslinking reaction.

[0029] Examples of π-electron conjugated conductive polymers include aniline polymers containing aniline or its derivatives as constituent units, pyrrole polymers containing pyrrole or its derivatives as constituent units, acetylene polymers containing acetylene or its derivatives as constituent units, and thiophene polymers containing thiophene or its derivatives as constituent units. To obtain high transparency, π-electron conjugated conductive polymers that do not contain nitrogen atoms are preferable, and among these, thiophene polymers containing thiophene or its derivatives as constituent units are preferable in terms of transparency, and polyalkylenedioxythiophene is particularly preferable. Examples of polyalkylenedioxythiophene include polyethylenedioxythiophene, polypropylenedioxythiophene, and poly(ethylene / propylene)dioxythiophene. In this invention, thiophene polymers are also referred to as polythiophene conductive polymers. By including polythiophene conductive polymers, this invention can achieve both excellent antistatic properties and oligomer blocking properties. In particular, the resin layer, comprising the polyester resin described in the present invention, a crosslinking agent, and a stretching aid, can achieve both superior antistatic properties and oligomer blocking properties by including a polythiophene-based conductive polymer. Furthermore, although a detailed mechanism has not been analyzed, uniform antistatic properties can be observed throughout the entire film even after stretching.

[0030] Thiophene-based polymers containing thiophene or its derivatives as constituent units may be doped with a doping agent to further improve their antistatic properties. For example, a doping agent of 0.1 to 500 parts by mass per 100 parts by mass of the polymer containing thiophene or its derivatives as constituent units may be added. If the amount is too high, electron transfer becomes difficult, leading to a decrease in antistatic performance. Conversely, if the amount is too low, there is a problem of reduced dispersibility in the solvent. Examples of these doping agents include LiCl, R1-30COOLi (R1-30: saturated hydrocarbon group with 1 to 30 carbon atoms), R1-30SO3Li, R1-30COONa, R1-30SO3Na, R1-30COOK, R1-30SO3K, tetraethylammonium, I2, BF3Na, BF4Na, HClO4, CF3SO3H, FeCl3, tetracyanoquinoline (TCNQ), Na2B10Cl10, phthalocyanine, porphyrin, glutamic acid, alkyl sulfonates, sodium polystyrene sulfonate (K,Li) salt, styrene-sodium styrene sulfonate (K,Li) salt copolymer, polystyrene sulfonate anion, styrene sulfonate-styrene sulfonate anion copolymer, and the like.

[0031] In the present invention, the amount of conductive polymer in the resin layer forming composition (coating liquid) that forms the antistatic layer is preferably 0.5% by mass or more, more preferably 0.7% by mass or more, even more preferably 1% by mass or more, and particularly preferably 1.5% by mass or more, when the total solid content of the resin layer forming composition is 100% by mass. For example, it may be 3% by mass or more. Furthermore, the amount of conductive polymer is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, particularly preferably 4% by mass or more, and most preferably 5% by mass or more, relative to the total of the conductive polymer, polyester resin, and crosslinking agent. When a π-electron conjugated conductive polymer is used as the antistatic agent, and the doping agent is used, the content of the π-electron conjugated conductive polymer in the antistatic layer as defined in this application refers to the total amount of the conductive polymer and the doping agent. By including the antistatic agent in such amounts, good antistatic properties can be provided.

[0032] In the present invention, when the total solid content of the resin layer forming composition is 100% by mass, the upper limit of the conductive polymer content is preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, particularly preferably 12% by mass or less, and most preferably 10% by mass or less. For example, it may be 0.5% by mass or more and 10% by mass or less, 0.7% by mass or more and 9.5% by mass or less, or 1.0% by mass or more and 8.5% by mass or less. Furthermore, the amount of conductive polymer is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 12% by mass or less, and particularly preferably 10% by mass or less, relative to the total of the conductive polymer, polyester resin, and crosslinking agent. When a π-electron conjugated conductive polymer is used as an antistatic agent, and the doping agent is used, the content of the π-electron conjugated conductive polymer in the antistatic layer as defined in this application refers to the total amount of the conductive polymer and the doping agent. By including the antistatic agent in this quantity, it does not cause interactions with the resin or crosslinking agent, the coating liquid is less likely to aggregate, and the drawbacks of the antistatic layer are minimized, allowing for high transparency to be maintained.

[0033] (Polyester Resin) The polyester resin used in combination with the resin layer in the present invention may be linear, but more preferably it is a polyester resin composed of a dicarboxylic acid and a branched diol (glycol). The dicarboxylic acid referred to here may be terephthalic acid, isophthalic acid, or 2,6-naphthalenedicarboxylic acid as its main component, as well as aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid. Furthermore, branched glycols are diols having branched alkyl groups, and examples include 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, 2-methyl-2-isopropyl-1,3-propanediol, 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.

[0034] The most preferred dicarboxylic acid as a component of the above-mentioned polyester resin is terephthalic acid, isophthalic acid, or naphthalenedicarboxylic acid. In addition to the above-mentioned dicarboxylic acid, it is preferable to copolymerize 5-sulfoisophthalic acid or the like in the range of 1 to 10 mol% in order to impart water dispersibility to the copolymerized polyester resin. Examples include sulfoterephthalic acid, 5-sulfoisophthalic acid, and 5-sodium sulfoisophthalic acid.

[0035] It can be stated that aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid are contained in all dicarboxylic acid components in a proportion of preferably 80 mol% or more, more preferably 90 mol% or more, and still more preferably 95 mol% or more. The inclusion of the aromatic dicarboxylic acid in the above content makes it easy to increase Tg and improves oligomer blocking properties. The upper limit of the aromatic dicarboxylic acid component in all dicarboxylic acid components is preferably 100 mol% or less.

[0036] It can be stated that naphthalenedicarboxylic acid is contained in all dicarboxylic acid components in a proportion of preferably 10 mol% or more, more preferably 30 mol% or more, still more preferably 50 mol% or more, particularly preferably 60 mol% or more, and most preferably 70 mol% or more. Setting the content to 10 mol% or more makes it easy to increase Tg and improves oligomer blocking properties. The upper limit of naphthalenedicarboxylic acid in all dicarboxylic acid components is preferably 100 mol% or less, more preferably 95 mol% or less, still more preferably 90 mol% or less, and particularly preferably 85 mol% or less. Here, in the present invention, the inclusion of a polyester resin containing naphthalenedicarboxylic acid can exhibit excellent oligomer blocking properties as described above. According to a more preferred embodiment, the resin layer contains a polyester resin containing naphthalenedicarboxylic acid and at least one crosslinking agent selected from oxazoline-based crosslinking agents and isocyanate-based crosslinking agents, which can more effectively prevent oligomer precipitation in the resin layer. Although the detailed mechanism has not been analyzed, it is presumed that, for example, the combination of a polyester resin containing naphthalenedicarboxylic acid and a specific crosslinking agent provides a three-dimensional structure inside the resin layer that can effectively suppress oligomer precipitation.

[0037] Regarding the polyester resin described above, the branched glycol component, which is the more preferred embodiment described above, is preferably contained in the total glycol component in a proportion of 10 mol% or more, and more preferably 15 mol% or more. A proportion of 10 mol% or more is preferable because it results in good oligomer blocking properties. The upper limit of the glycol component in the total glycol component is preferably 100 mol% or less, more preferably 90 mol% or less, and even more preferably 80 mol% or less. Among the glycol components other than the above compounds, ethylene glycol is the most preferred. In small amounts, diethylene glycol, propylene glycol, butanediol, hexanediol, or 1,4-cyclohexanedimethanol may also be used.

[0038] The glass transition temperature (Tg) of the polyester resin is preferably 30°C or higher, more preferably 40°C or higher, more preferably 45°C or higher, even more preferably 50°C or higher, particularly preferably 55°C or higher, and most preferably 60°C or higher. Including a polyester resin exhibiting the above glass transition temperature improves blocking resistance and improves oligomer blocking properties. The glass transition temperature (Tg) of the polyester resin is preferably 130°C or lower, more preferably 120°C or lower, and even more preferably 115°C or lower. Exhibiting the above glass transition temperature prevents cracking of the coating (cracking of the resin layer). In the present invention, the resin layer forming composition includes a polyester resin, a crosslinking agent, and a polythiophene-based conductive polymer, and since the glass transition temperature of the polyester resin is 30°C or higher, it can exhibit excellent chemical resistance. Furthermore, the difference between the haze of the laminated polyester film before heating and the haze after heating at 140°C for 10 minutes can be reduced to 2% or less. While this invention should not be interpreted in a way that limits it to a specific theory, in this invention, the glass transition temperature of the polyester resin is 30°C or higher, and by using a crosslinking agent, the resin layer becomes hard and less mobile, and the precipitation of oligomers can be suppressed.

[0039] The lower limit of the reduced viscosity of the polyester resin is preferably 0.1 dl / g, more preferably 0.2 dl / g. The upper limit of the reduced viscosity of the polyester resin is preferably 1.5 dl / g, more preferably 1.0 dl / g.

[0040] The lower limit of the number average molecular weight of the polyester resin is preferably 0.3×10 ４ , more preferably 0.4×10 ４ , still more preferably 0.5×10 ４ . Setting the number average molecular weight to 0.3×10 ４ or higher enables the coating film to be toughened. The upper limit of the number average molecular weight of the polyester resin is preferably 2×10 ４ , more preferably 1.7×10 ４ , still more preferably 1.5×10 ４ .

[0041] The lower limit of the acid value of the polyester resin is preferably 1 eq / ton, more preferably 5 eq / ton, and still more preferably 7 eq / ton. Setting the acid value to 1 eq / ton or higher improves the reaction with the crosslinking agent. The upper limit of the acid value of the polyester resin is preferably 500 eq / ton, more preferably 300 eq / ton, and still more preferably 100 eq / ton.

[0042] When the total solid content of the resin layer-forming composition is 100% by mass, the polyester resin content is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more. A content of 5% by mass or more is preferable because it provides good adhesion to the substrate and oligomer blocking properties. The polyester resin content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 50% by mass or less. A polyester resin content of 80% by mass or less is preferable because it provides good oligomer blocking properties. For example, the polyester resin content is 8% by mass or more and 50% by mass or less, for example, 8% by mass or more and 45% by mass or less. Furthermore, the polyester resin content is preferably 20% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, particularly preferably 35% by mass or more, and most preferably 40% by mass or more, relative to the total of the conductive polymer, polyester resin, and crosslinking agent. The polyester resin content is preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, particularly preferably 70% by mass or less, and most preferably 65% ​​by mass or less, relative to the total of the conductive polymer, polyester resin, and crosslinking agent. As described herein, the resin layer forming composition for the resin layer of the present invention contains a polythiophene-based conductive polymer, a polyester resin, and a crosslinking agent in these ratios, so that it can have a good balance of surface resistivity, Δ-haze value, and alcohol resistance. It can also exhibit good oligoblocking properties. Furthermore, in the present invention, including a sugar alcohol as a stretching aid under the conditions described herein, and further including a polyester resin under the conditions described herein, can contribute to suppressing cracking of the antistatic layer after the film stretching process.

[0043] (Crosslinking Agent) In the present invention, the antistatic layer is formed from a composition containing a crosslinking agent in order to form a crosslinked structure in the antistatic layer. Including a crosslinking agent is preferable because it improves durability and suppresses the deterioration of antistatic performance even when processed under high temperature and high humidity conditions. Specific crosslinking agents include urea-based, epoxy-based, melamine-based, isocyanate-based, oxazoline-based, carbodiimide-based, and aziridine-based agents. In one embodiment, epoxy-based, isocyanate-based, oxazoline-based, and carbodiimide-based crosslinking agents are preferred, oxazoline-based and isocyanate-based crosslinking agents are preferred because they do not contaminate the process, and oxazoline-based crosslinking agents are preferred to enhance the oligomer blocking effect. Oxazoline-based crosslinking agents make it easier to obtain oligomer blocking properties even when the Tg of the polyester contained in the resin layer (antistatic layer) is low. In addition, catalysts and the like can be used as needed to promote the crosslinking reaction. Here, in the present invention, in the case of the in-line coating method, melamine-based crosslinking agents may cause process contamination, so it is desirable not to include melamine-based crosslinking agents. During the heat treatment process, formaldehyde and other by-products used to generate melamine may produce unpleasant odors or have adverse effects on human health.

[0044] Examples of oxazoline crosslinking agents include 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.).

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The oxazoline group content of the oxazoline-based crosslinking agent is preferably 1.0 mmol / g or more, more preferably 2.0 mmol / g or more, and still more preferably 3.0 mmol / g or more. Setting the content to 1.0 mmol / g or more is preferable because it improves crosslinkability. The upper limit of the oxazoline group content is 15 mmol / g, more preferably 12 mmol / g, and still more preferably 10 mmol / g.

[0049] The number-average molecular weight of the oxazoline-based crosslinking agent is preferably 0.5×10 ４ or more, more preferably 1×10 ４ or more, and still more preferably 2×10 ４ or more. Setting the molecular weight within the above range is preferable because it improves oligomer blocking properties. The number-average molecular weight of the oxazoline-based crosslinking agent is preferably 10×10 ４ or less, more preferably 8×10 ４ or less, and still more preferably 6×10 ４ or less. Satisfying the above condition is preferable because it improves oligomer blocking properties.

[0050] The glass transition temperature (Tg) of the oxazoline-based resin is preferably 10°C or higher, more preferably 20°C or higher, and still more preferably 30°C or higher. Setting the temperature to the above value or higher is preferable because it improves blocking resistance and provides favorable oligomer blocking properties. The glass transition temperature (Tg) of the oxazoline-based crosslinking agent is preferably 100°C or lower, more preferably 80°C or lower, and still more preferably 70°C or lower. Satisfying the above condition can prevent cracking of the resin layer.

[0051] Examples of isocyanate-based crosslinking agents include blocked isocyanate-based crosslinking agents. Examples of 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, oximes such as acetaldehyde oxime, acetone oxime, and methyl ethyl ketoxime, and amines such as diphenylaniline, aniline, and ethyleneimine.

[0052] 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, thereby suppressing the occurrence of minute surface irregularities and improving 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, in order to raise the boiling point of the blocking agent, it is preferable to use a blocking agent with a large molecular weight, and the molecular weight of the blocking agent is preferably 50 or more, more preferably 60 or more, and even more preferably 80 or more.

[0053] 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, crosslinking reactions with urethane resins and the like proceed, 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.

[0054] Examples of blocking agents used in the blocked isocyanates of the present invention that have a dissociation temperature of 120°C or lower and a boiling point of 150°C or higher include the aforementioned sodium bisulfite, 3,5-dimethylpyrazole, 3-methylpyrazole, dimethyl malonate, diethyl malonate, acetone oxime, and methyl ethyl ketoxime. Among these, pyrazole compounds, represented by 3,5-dimethylpyrazole and 3-methylpyrazole, are preferred in terms of resistance to humid heat and yellowing.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] When the total solid content of the resin layer-forming composition that forms the resin layer (antistatic layer) is 100% by mass, the crosslinking agent content is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more. A content of 5% by mass or more is preferable because it provides good adhesion to the substrate, oligomer blocking properties, and toughness of the coating film. The crosslinking agent content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 50% by mass or less. A crosslinking agent content of 80% by mass or less is preferable because it provides good oligomer blocking properties and adhesion to the substrate. For example, the crosslinking agent content is 8% by mass or more and 50% by mass or less, for example, 8% by mass or more and 45% by mass or less. Furthermore, the lower limit of the crosslinking agent content is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, particularly preferably 25% by mass or more, and most preferably 30% by mass or more, relative to the total of the conductive polymer, polyester resin, and crosslinking agent. A content above this level improves oligomer blocking properties. The crosslinking agent content is preferably 75% by mass or less, more preferably 70% by mass or less, even more preferably 65% ​​by mass or less, and most preferably 60% by mass or less, relative to the total of the conductive polymer, polyester resin, and crosslinking agent, resulting in good antistatic properties after the stretching process. The optimal crosslinking agent content may be changed depending on the Tg of the polyester used. For example, for polyesters with a Tg of 35°C or higher, a crosslinking agent content of 20% by mass or more is preferred. For polyesters with a Tg of 30°C or higher, a crosslinking agent content of 25% by mass or more is preferred. In particular, being within the above range improves oligomer blocking properties and, when using a stretched film, suppresses cracking of the antistatic layer after the stretching process. In this invention, the excellent oligomer blocking properties prevent, for example, the precipitation of oligomers and the resulting increase in haze and deterioration of the film's appearance during the heat drying process when an adhesive layer is laminated onto a protective film. Furthermore, since the increase in haze of the protective film can be suppressed, and the resulting decrease in visibility can be prevented, it is also excellent for visual inspection when the protective film is bonded to an object.

[0059] In the present invention, other 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 resin, acrylic resin, cellulose resin, polyolefin resin, and polyacetal resin. The amount of other resins is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, relative to the total amount of the resin component (polyester resin and other resins). Adding other resins can improve the wettability of the surface and the appearance of the coating.

[0060] The present invention includes a stretching aid, which can be a glycol-based, glycerin-based, or sugar alcohol-based agent. Sugar alcohols are particularly preferred. The inclusion of a stretching aid not only improves stretchability but also enables excellent antistatic properties across the entire surface of the film. One type of stretching aid may be used, or multiple types may be used in combination.

[0061] 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, obtained by reducing monosaccharides; 5-carbon sugar alcohols such as ribitol, arabinitol, and xylitol; and 6-carbon sugar alcohols such as sorbitol, mannitol, isitol, talitol, and galactitol. Cyclic sugar alcohols, such as cyclitols including inositol, are also mentioned. Disaccharide alcohols obtained by reducing disaccharides, such as maltitol, lactitol, and isomaltulose reductions, can also be cited. If the above sugar alcohols have stereoisomers, all of those stereoisomers are included. Furthermore, the above sugar alcohols may be used individually or in combination of two or more types.

[0062] 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.

[0063] When the total amount of solids added to the resin layer forming the antistatic layer is 100% by mass, the content of the stretching aid is 10% to 74.5% by mass. By keeping the stretching aid within a predetermined range, oligomer blocking properties and excellent antistatic properties after the stretching process can be achieved. Furthermore, a film is provided that exhibits high antistatic properties and can withstand high-speed peeling.

[0064] In this invention, the excellent antistatic properties reduce cracking of the resin layer even after stretching. As a result, the resin layer (antistatic layer) can make uniform contact with the adherend over the entire surface of the film. Furthermore, by reducing cracking, this invention allows for uniform surface resistivity over the entire surface of the film. For this reason, this invention is optimally suited as a protective film for optical materials (optical films, displays, etc.) that are more susceptible to static electricity than conventional materials. In addition, because cracking of the resin layer can be reduced or suppressed, the peeling process from the adherend can be performed at a faster speed than conventional methods. This is because, at the time the laminated polyester film of this invention is attached to the adherend, cracking of the resin layer is suppressed, and when peeling the invention from the adherend, the remaining resin layer on the adherend, especially at the points of film breakage or cracking, is also suppressed.

[0065] When the total solid content of the resin layer-forming composition is 100% by mass, the stretching aid is preferably 10% by mass or more, more preferably more than 10% by mass, and even more preferably 10.1% by mass or more. For example, it may be 13% by mass or more, or 15% by mass or more. This range is preferable because it can prevent cracking of the coating film and tends to have excellent antistatic properties after the stretching process. When the total solid content of the resin layer-forming composition is 100% by mass, the stretching aid is preferably 74.5% by mass or less, more preferably 73.5% by mass or less, and even more preferably 72% by mass or less. This range is preferable because it tends to improve oligomer blocking properties. For example, the amount of the stretching aid may be 10% by mass or more and 74.5% by mass or less, 13% by mass or more and 73.5% by mass or less, or 15% by mass or more and 72% by mass or less. When the stretching aid contains components other than sugar alcohols, the amount of other stretching aids is selected so that at least the sugar alcohol content is within the above range. Furthermore, it is desirable that the content of other stretching aids be less than the content of sugar alcohols. In the present invention, by including a polyester resin, a crosslinking agent, and a polythiophene-based conductive polymer, and having a sugar alcohol content of 10% by mass or more and 74.5% by mass or less, it is considered that the functions of the conductive polymer can be fully exhibited, and furthermore, the film properties, which are greatly influenced by the polyester resin and crosslinking agent, can be fully exhibited.

[0066] In this proposal, the mass ratio of the polythiophene-based conductive polymer to the stretching aid is 0.02 or more and 1.00 or less. Note that the mass ratio of the polythiophene-based conductive polymer to the stretching aid may simply be indicated as (conductive polymer / sugar alcohol). By setting the mass ratio of the polythiophene-based conductive polymer to the stretching aid within a predetermined range, excellent oligomer blocking properties and superior antistatic properties after the stretching process can be achieved. In this invention, in addition to the polythiophene-based conductive polymer and the stretching aid, at least a polyester resin and a crosslinking agent are included as components. Here, in the combination of polyester resin and crosslinking agent according to the present invention, by keeping the mass ratio of the conductive polymer to the stretching aid within the above range, the functions of the conductive polymer and the stretching aid can be effectively exhibited without mutual interference. Furthermore, the functions exhibited by the polyester resin and the crosslinking agent can also be effectively exhibited. In other words, the present invention can exhibit a good balance of oligomer blocking properties that suppress the rise of haze even after the heat drying process, excellent antistatic properties even after the stretching process, suppression of cracking of the antistatic layer after the stretching process, and alcohol resistance.

[0067] The mass ratio of the polythiophene-based conductive polymer to the stretching aid may be 0.03, 0.05 or higher, or 0.10 or higher. This range is preferable because it tends to improve oligomer blocking properties. Alternatively, the mass ratio of the polythiophene-based conductive polymer to the stretching aid may be 0.80 or less, for example, 0.50 or less, or 0.40 or less. More preferably, it may be 0.30 or less, or 0.25 or less. This range is preferable because it can prevent cracking of the coating film and tends to have excellent antistatic properties after the stretching process. For example, the mass ratio of the polythiophene-based conductive polymer to the stretching aid may be 0.02 or more and 0.80 or less, 0.02 or more and 0.50 or less, 0.02 or more and 0.30 or less, or 0.10 or more and 0.25 or less. With this relationship, the present invention can prevent film cracking during stretching and prevent a decrease in antistatic properties caused by film cracking. It can also have excellent oligomer blocking properties.

[0068] The resin layer in the present invention may contain a surfactant to improve its appearance. Examples of surfactants include silicone-based surfactants, fluorine-based surfactants having a perfluoroalkyl group, and hydrocarbon-based surfactants such as acetylene-based surfactants. Preferably, silicone-based surfactants or acetylene-based surfactants are used, as they are considered to have a lower environmental impact compared to fluorine-based surfactants. More preferably, acetylene-based surfactants are used to maintain the surface free energy and water contact angle of the resin layer within a predetermined range.

[0069] When the total solid content of the resin layer-forming composition is 100% by mass, the amount of surfactant added is preferably 0.001% by mass or more, and more preferably 0.005% by mass or more. This range is preferable because it can be expected to improve the appearance. The amount of surfactant added is preferably 0.5% by mass or less, and more preferably 0.2% by mass or less. This range is preferable because it can achieve good haze.

[0070] In the present invention, it is also preferable to add particles to the resin layer in order to further improve the blocking resistance of the resin layer. Examples of particles to be contained in the resin layer in the present invention include titanium dioxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, or mixtures thereof, as well as other general inorganic particles, such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride in combination, and other inorganic particles, and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles.

[0071] The average particle size of the particles in the resin layer (average particle size based on the number of particles measured by a scanning electron microscope (SEM); the same applies hereinafter) is preferably 0.04 to 2.0 μm, and more preferably 0.04 to 1.0 μm. An average particle size of 0.04 μm or more for inert particles is preferable because it facilitates the formation of irregularities on the film surface, improving handling properties such as film slipperiness and windability, and resulting in good processability during lamination. On the other hand, an average particle size of 2.0 μm or less for inert particles is preferable because it reduces the likelihood of particle detachment. The particle concentration in the resin layer is preferably 1 to 20% by mass of the solid components. For example, particles with two different average particle sizes may be included. In this case, it is desirable that the average particle sizes of the two types of particles are each within the range of 0.04 to 2.0 μm.

[0072] The average particle size was measured by observing the particles in a cross-section of a laminate of a polyester film substrate and an easy-adhesion layer (hereinafter also referred to as a laminated polyester film) using a scanning electron microscope. Thirty particles were observed, and the average value was used as the average particle size.

[0073] The shape of the particles is not particularly limited as long as it satisfies the objectives of the present invention, 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 of a circle. The equivalent diameter of a circle is obtained by dividing the area of ​​the observed particle by π, calculating the square root, and multiplying by 2.

[0074] While it is preferable that the resin layer does not contain a release agent, it may contain a release agent if it satisfies the objectives of the present invention. The amount of the release agent is preferably less than 5% by mass, more preferably less than 3% by mass, even more preferably less than 2% by mass, and particularly preferably less than 1% by mass, relative to the total of the conductive polymer, polyester resin, and crosslinking agent. Examples of release agents that can be used include silicone, fluororesin, wax, and long-chain alkyl-containing compounds. Silicone, fluorine-containing compounds, long-chain alkyl-containing compounds, etc., may be added as surfactants, and this is not ruled out. Furthermore, the amount of surfactant may be 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0.1% by mass or less, relative to the total of the conductive polymer, polyester resin, and crosslinking agent.

[0075] Water and alcohol are preferred solvents. A mixture of these may also be used.

[0076] The water content in the solvent is preferably 60% by mass or more, more preferably 70% by mass, even more preferably 80% by mass, and particularly preferably 85% by mass. This level of water content prevents interaction with the conductive polymer, reduces the likelihood of the coating liquid agglomerating, minimizes the drawbacks of the antistatic layer, and maintains high transparency. The water content in the solvent is preferably 100% by mass or less.

[0077] The lower limit of the solid content in the resin layer-forming composition is preferably 0.1% by mass, more preferably 0.3% by mass, and even more preferably 0.5% by mass. By setting it within the above range, the oligomer blocking properties, substrate adhesion, and antistatic layer of the present invention can be achieved. The upper limit of the solid content in the resin layer-forming composition is preferably 10% by mass, more preferably 7% by mass, and even more preferably 5% by mass. By setting it below the above range, a laminated polyester film can be obtained in which the composition is less prone to aggregation and has fewer defects.

[0078] The lower limit of the film thickness of the antistatic layer of the present invention is 0.001 μm or more, more preferably 0.005 μm or more, and even more preferably 0.01 μm or more. A film thickness greater than or equal to the above is preferable because it provides an antistatic effect and an oligomer-blocking effect. The upper limit of the film thickness of the antistatic layer is 1 μm, more preferably 0.5 μm, even more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less. A film thickness of 1 μm or less is preferable because it results in less discoloration and higher transparency.

[0079] The surface resistivity of the laminated polyester film of the present invention is preferably 10 [logΩ / □] or less. More preferably, it is 8 [logΩ / □] or less, even more preferably, 7.5 [logΩ / □] or less, and preferably 7 [logΩ / □] or less. By setting the surface resistivity to 10 [logΩ / □] or less, the adhesion of foreign matter to the laminated polyester can be suppressed, and furthermore, peeling charge when the adhesive layer is laminated and peeled off can be suppressed. In addition, there is no particular lower limit for the surface resistivity of the laminated polyester film, but for example, it is preferably 2.0 [logΩ / □] or more, and preferably 3.0 [logΩ / □] or more. Setting the surface resistivity of the laminated polyester film to less than 2.0 [logΩ / □] may increase the processing cost of the antistatic layer containing the polythiophene-based conductive polymer. However, this condition does not impair the function as a protective film.

[0080] The haze of the laminated polyester film used in the present invention before heating at 140°C for 10 minutes is preferably 3.0% or less. More preferably 2.5% or less, even more preferably 2.0% or less, and particularly preferably 1.7% or less. A haze of 3.0% or less is preferable because it allows for visual inspection of the protective film when it is bonded to the substrate, and is particularly preferable when the substrate is a component for optical applications. The haze is preferably even lower, and may be substantially 0% (0% or more), or for example, 0.1% or more.

[0081] The haze of the laminated polyester film of the present invention after heating at 140°C for 10 minutes is preferably 3.0% or less. More preferably 2.6% or less, and even more preferably 2.4% or less. 2.3% or less is extremely preferable. 3.0% or less is preferable because it allows for visual inspection of the protective film while it is bonded to the substrate, and is particularly preferable when the substrate is an optical component. The haze after heating at 140°C for 10 minutes may be 0, or for example, 0.1% or more. While it should not be interpreted as being limited to a specific theory, having the resin layer (antistatic layer) according to the present invention makes it possible to obtain an antistatic layer with excellent reactivity, improved crosslinking density, and reduced 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.

[0082] For example, the Δ-haze value (haze difference), obtained by subtracting the haze of the laminated polyester film before heating from the haze of the laminated polyester film after heating at 140°C for 10 minutes, is -0.2% or more, more preferably 0% or more, even more preferably 0.01% or more, and particularly preferably 0.05% or more. The Δ-haze value is 2.00% or less, more preferably 1.50% or less, even more preferably 1.20% or less, and preferably 1.10% or less. Particularly preferably 1.00% or less. The Δ-haze value may also be 0.8% or less, and particularly preferably 0.7% or less. By having the Δ-haze value 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 easily decrease 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.

[0083] The total light transmittance of the laminated polyester film is, for example, 80% to 95%, preferably 85% to 95%.

[0084] The alcohol resistance (resistance change rate) of the laminated polyester film of the present invention is preferably 200% or less, more preferably 150% or less, even more preferably 100% or less, and particularly preferably 50% or less. The alcohol resistance (resistance change rate) is preferably even lower, and may be substantially 0% (0% or more), or for example, 0.1% or more. Because the alcohol resistance (resistance change rate) is within this range, the antistatic properties and oligomer blocking properties are less likely to deteriorate even if alcohol is used for cleaning during the manufacturing process.

[0085] The average surface roughness (Sa) of the laminated polyester film used in the present invention is preferably in the range of 1 to 40 nm, more preferably 1 to 30 nm, and even more preferably 1 to 10 nm. The maximum protrusion height (P) of the surface of the laminated polyester film used in the present invention is preferably 2 μm or less, more preferably 1.5 μm or less, and even more preferably 0.8 μm or less. If Sa is 40 nm or less and P is 2 μm or less, there is no risk of roughening the adhesive surface when the adhesive layer is laminated and wound into a roll, which is preferable.

[0086] The surface free energy of the laminated polyester film of the present invention is preferably 65 mJ / m ２ The following is more more preferable: 60 mJ / m ２ The following applies: The surface free energy is, for example, 40 mJ / m ２ The above is preferable to 50 mJ / m ２ That concludes the explanation. If the surface free energy is within the above range, the adhesion between the antistatic layer and the adhesive layer laminated on top of it will be excellent.

[0087] The water contact angle of the laminated polyester film of the present invention is preferably 90° or less, more preferably 60° or less. The water contact angle is 30° or more, preferably 40° or more, and more preferably 65°. It exhibits excellent adhesion to adhesive layers and the like laminated on top of the antistatic layer.

[0088] The contact angle of diiodomethane in the laminated polyester film of the present invention is preferably 40° or less, more preferably 35° or less. The contact angle of diiodomethane is preferably 20° or more, more preferably 25° or more. Excellent adhesion to adhesive layers laminated on the antistatic layer.

[0089] (Manufacturing of Laminated Polyester Film) The method for manufacturing the laminated polyester film of the present invention will be explained using an example with a polyethylene terephthalate (hereinafter sometimes abbreviated as PET) film substrate, but it is not limited to this.

[0090] After thoroughly vacuum-drying the PET resin, it is supplied to an extruder, and the molten PET resin at approximately 280°C is melt-extruded from the T-die onto a rotating cooling roll in a sheet shape. The sheet is then cooled and solidified by electrostatic application to obtain an unstretched PET sheet. The unstretched PET sheet may be a single-layer structure or a multi-layer structure obtained by co-extrusion.

[0091] The obtained unstretched PET sheet is subjected to uniaxial or biaxial stretching to achieve crystal orientation. For example, in the case of biaxial stretching, the sheet is stretched 2.5 to 5.0 times in the longitudinal direction on a roll heated to 80 to 120°C to obtain a uniaxially stretched PET film. Then, the ends of the film are held with clips and guided into a hot air zone heated to 80 to 180°C, where it is stretched 2.5 to 5.0 times in the width direction. In the case of uniaxial stretching, it is stretched 2.5 to 5.0 times in a tenter. After stretching, it is then guided into a heat treatment zone and heat treatment is performed to complete the crystal orientation.

[0092] The lower limit of the heat treatment zone temperature is preferably 170°C, and more preferably 180°C. A temperature of 170°C or higher in the heat treatment zone is preferable because it ensures sufficient curing and good blocking properties in the presence of liquid water, eliminating the need for a longer drying time. On the other hand, the upper limit of the heat treatment zone temperature is preferably 250°C, and more preferably 240°C. A temperature of 240°C or lower in the heat treatment zone is preferable because it does not risk degrading the physical properties of the film.

[0093] The antistatic layer can be applied after the film is manufactured or during the manufacturing process. In particular, from the viewpoint of productivity, it is preferable to apply the coating solution to at least one side of the PET film after it has been unstretched or uniaxially stretched, and then stretch and heat-treat it in at least one axial direction to form an easily adhesive layer.

[0094] Any known method can be used to apply this coating solution to the PET film. 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, curtain coating method, and the like. These methods can be used individually or in combination.

[0095] In one embodiment, the present invention provides an adhesive laminated polyester film having an adhesive layer, a substrate, and an antistatic layer (resin layer) in that order. The adhesive layer is not particularly limited and may include known adhesives. Alternatively, the present invention can provide a laminate having a substrate, an antistatic layer (resin layer), and an adhesive layer in that order.

[0096] The adhesive layer can be made from various materials, including rubber, acrylic, urethane, polyester, polyolefin, and silicone, without any particular limitations. Furthermore, as long as it does not impair the optical properties, two or more materials can be mixed and used, or multiple layers can be constructed. Fillers, particles, and additives can also be added.

[0097] The thickness of the adhesive layer is preferably 1 to 500 μm, and more preferably 3 to 300 μm. A thickness of more than 1 μm is preferable because it provides sufficient adhesive strength and does not lift or peel off even when bent. A thickness of less than 500 μm is preferable because it minimizes the reduction in visibility during visual inspection.

[0098] The adhesive layer can be applied using various methods, including knife coaters, die coaters, gravure coaters, and Meyer bar coaters, without any particular limitations, and can be selected appropriately depending on viscosity and film thickness.

[0099] When curing the adhesive layer, there are no particular limitations on the curing method; methods such as curing with ultraviolet light, electron beams, or heat can be used and selected as appropriate.

[0100] 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.

[0101] (Surface Resistivity) The surface resistivity of the laminated polyester film surface of the present invention was measured using a surface resistance meter (Simco Japan Co., Ltd., Work Surface Tester ST-3) after 24 hours of humidity control under conditions of 23°C and 55% humidity, and evaluated according to the following criteria: ◎: Surface resistivity of 4.8 or more and 7 or less [logΩ / □] ○: Surface resistivity of more than 7 and 10 or less [logΩ / □] △: Surface resistivity of less than 4.8 [logΩ / □] ×: Surface resistivity of more than 10 [logΩ / □]

[0102] (Total light transmittance, haze) The total light transmittance and haze of the film of the present invention were measured in accordance with JIS K 7136 using a turbidimeter (Nippon Denshoku, NDH7000II) before heating and before and after heating at 140°C for 10 minutes. The difference between the haze before heating and the haze after heating at 140°C for 10 minutes was calculated as Δhaze. The haze before heating and Δhaze were evaluated according to the following measurement criteria. Haze before heating ◎: Haze is 0 or more and 1.0% or less 〇: Haze is greater than 1.0% and 2.0% or less △: Haze is greater than 2.0% and 3.0% or less ×: Haze is greater than 3.0% Δ Haze ◎: Δ Haze is 0 or more and 0.70% or less 〇: Δ Haze is greater than 0.70% and 1.10% or less △: Δ Haze is greater than 1.10% and 2.0% or less ×: Δ Haze is greater than 2.0% Δ Haze is the difference between the haze before heating the laminated polyester film and the haze after heating at 140°C for 10 minutes.

[0103] (Alcohol Resistance) The surface resistivity of the film of the present invention was measured before and after wiping it 10 times back and forth using a Kimwipe impregnated with ethanol, and evaluated according to the following criteria: ◎: Change rate of 0 or more and 47% or less 〇: Change rate of more than 47% and 60% or less △: Change rate of more than 60% and 100% or less ×: Change rate of more than 100% or less

[0104] (Surface Free Energy, Water Contact Angle, Diiodomethane Contact Angle) Under conditions of 25°C and 50% RH, droplets of water (droplet volume 1.8 μL) and diiodomethane (appropriate liquid volume 0.9 μL) were prepared on the release surface of the release film using a contact angle meter (Kyowa Interface Science Co., Ltd.: Fully Automatic Contact Angle Meter DM-701), and their contact angles were measured. The contact angles were taken 30 seconds after dropping each liquid onto the release film. The contact angle data for water and diiodomethane obtained by the above method were calculated using the "Kitazaki-Hata" theory to determine the dispersion component γsd, polar component γsp, and hydrogen bonding component γsh of the surface free energy of the release film, and the sum of these components was defined as the surface free energy γs. This calculation was performed using the calculation software within the contact angle meter software (FAMAS).

[0105] (Glass transition temperature Tg) In accordance with JIS K7121-1987, a differential scanning calorimeter (Seiko Instruments, DSC6200) was used to heat 10 mg of a resin sample at a rate of 20°C / min over a temperature range of 25 to 300°C, and the extrapolation glass transition onset temperature obtained from the DSC curve was defined as the glass transition temperature.

[0106] (Resin Composition) The resin was dissolved in deuterated chloroform, and 1H-NMR analysis was performed using a Varian Gemini-200 nuclear magnetic resonance analyzer (NMR). The molar percentage ratio of each component was determined from the integral ratio.

[0107] The following raw materials were used to form the conductive polymers in the examples and comparative examples. (Conductive polymer A) (A-1) Polythiophene-based conductive polymer (AS-G1C, manufactured by Shin-Etsu Polymer Co., Ltd., solid content concentration 1.2% by mass) (A-2) Polythiophene-based conductive polymer (ICP1010, manufactured by AGFA, solid content concentration 1.2% by mass)

[0108] (Polyester resin B) The polyester resins shown in Table 1 were used.

[0109]

[0110] (Crosslinking agent C) (C-1) Oxazoline-based crosslinking agent (WS-700, manufactured by Nippon Shokubai Co., Ltd., solid content concentration 25% by mass) (C-2) Isocyanate-based crosslinking agent (BI200, manufactured by Baxenden, solid content concentration 40% by mass) (C-3) Carbodiimide-based crosslinking agent (SV-02, manufactured by Nisshinbo Chemical Co., Ltd., solid content concentration 40% by mass)

[0111] (Stretching agent D) (D) Sorbitol (solid content concentration 100% by mass)

[0112] (Surfactant E) (E-1) Acetylene-based (manufactured by Nisshin Chemical Industry Co., Ltd., solid content concentration 100% by mass)

[0113] (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)

[0114] (Manufacturing of polyester resin F for base material) (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.

[0115] (Polymerization of polyester resin F for base material) 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 with an intrinsic viscosity (IV) (solvent: phenol / tetrachloroethane = 60 / 40) of 0.61 dl / , which was substantially free of particles.

[0116] (Example 1) (1) A coating solution for the antistatic layer was obtained using the formulation amounts described in the preparation table 2A of the coating solution. (Antistatic layer coating solution) Water 67.70 parts by mass Isopropyl alcohol 9.65 parts by mass Conductive polymer A-1 11.67 parts by mass Polyester resin B-1 3.72 parts by mass Crosslinking agent C-1 3.72 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

[0117] (2) Manufacturing of laminated polyester film As a film raw material polymer, resin pellets of polyester resin F were dried at 135°C for 6 hours under a reduced pressure of 133 Pa. Thereafter, 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.

[0118] 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.

[0119] Next, the coating solution was applied to one side of the PET film so that the final coating amount after drying (after biaxial stretching) was 0.13 g / m². After the coating solution dried, the film was stretched 4.0 times in the width direction at 110°C, and with the width direction of the film fixed, it was heated at 230°C for 5 seconds. A further 3% widthwise relaxation treatment was performed to obtain a laminated polyester film having a 100 μm easy-adhesion layer.

[0120] (Examples 2-19, Comparative Examples 1 and 2) Laminated polyester films were obtained in the same manner as in Example 1, except that the mass ratio of components (A) to (E) was changed, with the composition shown in Table 2A. Furthermore, the surface resistivity, total light transmittance, Δ-haze, alcohol resistance, surface free energy, and contact angle of the laminated polyester films of the examples and comparative examples were evaluated using the method described above.

[0121] Tables 2A, 2B, and 2C show various evaluation results for the examples and comparative examples.

[0122]

[0123]

[0124]

[0125] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments described above, and all modifications within the scope of the claims are intended to be included in the meaning of equivalents and within the scope.

[0126] 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. Therefore, 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. When the antistatic layer of the film according to the examples of the present invention was visually inspected after the stretching process, no film cracking was observed. Therefore, the present invention can provide a laminated polyester film and protective film that have oligomer blocking properties and excellent antistatic properties even after the stretching process. Examples 15 to 19 tend to have slightly inferior surface resistivity or optical properties compared to Examples 1 to 14. However, Examples 15 to 19 can be appropriately used in, for example, small organic EL or liquid crystal displays, depending on the required characteristics of the organic EL or liquid crystal display.

[0127] Comparative Example 1, lacking a crosslinking agent, tended to exhibit higher haze after heating compared to the sample used in the Examples. Comparative Example 2, due to the use of an isocyanate compound as the crosslinking agent and the low Tg of the polyester, exhibited insufficient oligomer blocking properties.

[0128] (Example 21) (1) Preparation of coating solution A coating solution for the antistatic layer was obtained using the proportions listed in Table 3A. (Coating solution for the antistatic layer) Water 68.36 parts by mass Isopropyl alcohol 9.73 parts by mass Conductive polymer A-1 11.67 parts by mass Polyester resin B-1 3.72 parts by mass Crosslinking agent C-1 3.72 parts by mass Stretching aid D 0.28 parts by mass Particle I 0.5 parts by mass Particle II 2.00 parts by mass Surfactant E-1 0.04 parts by mass

[0129] (2) Manufacturing of laminated polyester film As a film raw material polymer, resin pellets of polyester resin F were dried at 135°C for 6 hours under a reduced pressure of 133 Pa. Thereafter, 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.

[0130] 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.

[0131] Next, the coating solution is applied to one side of the PET film, with a final (after biaxial stretching) drying amount of 0.13 g / m². ２ The film was coated in the following manner. After drying the coating solution, it was stretched to 4.0 times its original width at 110°C, and with the film's width direction fixed, it was heated at 230°C for 5 seconds. Further relaxation treatment of 3% in the width direction was performed to obtain a laminated polyester film having a 100 μm easy-adhesion layer. The physical properties of the obtained film are described in Tables 3A, 3B, and 3C. (Examples 22-31 and Comparative Examples 21-24) Laminated polyester films were manufactured and evaluated in the same manner as in Example 21, except for changes to the conditions described in Table 3A. The physical properties of the obtained films are described in Tables 3A, 3B, and 3C.

[0132]

[0133]

[0134]

[0135] 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 onto 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. When the antistatic layer of the film according to the examples of the present invention was visually inspected after the stretching process, no film cracking was observed. Therefore, the present invention can provide a laminated polyester film and a protective film that have oligomer blocking properties and excellent antistatic properties even after the stretching process.

[0136] Comparative Example 21, lacking a crosslinking agent, tended to exhibit higher haze after heating compared to the sample used in the Examples. Comparative Example 22, lacking a stretching aid, failed to meet the required antistatic properties within the scope of the present invention. Furthermore, its oligomer blocking and alcohol resistance were insufficient. Comparative Example 23, with a stretching aid content outside the scope of the present invention, exhibited insufficient oligomer blocking properties. It is believed that the insufficient oligomer blocking properties were due to the stretching aid content exceeding the scope of the present invention. Comparative Example 24, with a stretching aid content outside the scope of the present invention, exhibited insufficient antistatic properties. This tendency is presumed to be caused by extremely small film cracks occurring on the resin layer surface after the stretching process, resulting in insufficient antistatic properties. These resin layer cracks can be observed, for example, using a scanning electron microscope (SEM).

[0137] 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

A laminated polyester film having a polyester base film and a resin layer, The aforementioned resin layer is a layer obtained by curing a resin layer forming composition. The resin layer forming composition comprises a polyester resin, a crosslinking agent, a polythiophene-based conductive polymer, and a stretching aid. The glass transition temperature of the polyester resin contained in the resin layer forming composition is 30°C or higher. A laminated polyester film in which the difference between the haze before heating and the haze after heating at 140°C for 10 minutes is 2% or less. 　 The laminated polyester film according to claim 1, wherein the polyester resin contained in the resin layer forming composition is a copolymer polyester containing naphthalenedicarboxylic acid as an acid component. 　 The laminated polyester film according to claim 1, wherein the crosslinking agent comprises at least one selected from oxazoline-based crosslinking agents or isocyanate-based crosslinking agents. 　 The laminated polyester film according to claim 1, wherein the surface resistivity of the resin layer is 2 to 10 [logΩ / □]. 　 The laminated polyester film according to claim 1, wherein the content of the polythiophene-based conductive polymer is 0.02 to 1.00 in mass ratio with respect to the stretching aid. 　 The laminated polyester film according to claim 1, wherein the stretching aid comprises a sugar alcohol. 　 The laminated polyester film according to claim 1, wherein the water contact angle of the resin layer is 30° or more. 　 The laminated polyester film according to claim 1, wherein the resin layer is provided in contact with the polyester substrate film. 　 In the laminated polyester film according to any one of claims 1 to 8, The material comprises an adhesive layer, the polyester substrate film, and the resin layer in this order. Adhesive laminated polyester film.

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