Layered polyester film

Abstract

The present invention addresses the problem of providing an antistatic film and a protection film that suppress increases in haze even after heating and drying and have a low surface resistivity, even in the case of a thin antistatic layer.　Said problem can be solved by a layered polyester film according to the present invention including, in the stated order, a first layer, a polyester film, and a second layer, said layered polyester film characterized in that the first layer is an antistatic layer, the antistatic layer is a cured layer of a composition including at least a conductive polymer and a melamine crosslinking agent, and the melamine crosslinking agent includes at least one selected from imino-type methylated melamine resins, methylol-type methylated melamine resins, full ether–type methylated melamine resins, and imino / methylol-type methylated melamine resins.

Description

Laminated Polyester Film

[0001] The present invention relates to a laminated polyester film that is suitably used as an antistatic film, and a protective film in which an adhesive layer is laminated on the laminated polyester film, and particularly to a protective film for optical components (e.g., components of organic electroluminescence (EL) and liquid crystal displays) and the like.

[0002] Films in which an adhesive layer is laminated onto a substrate film are used as protective films for various components in the manufacturing process of optical components, etc. The protective film is attached to the respective components as adherends via the adhesive layer, and serves to prevent scratches and dirt from adhering to the respective components during processing and transportation. The substrate film used for these protective films is an antistatic film having an antistatic layer laminated on at least one side. The purpose of laminating the antistatic layer is to prevent foreign matter such as dirt and dust from adhering to the protective film and to suppress static electricity that is generated when the protective film is peeled off from the adherend (see Patent Document 1).

[0003] As an antistatic film, an antistatic film containing PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)) as an antistatic agent has been proposed (see Patent Document 2).

[0004] International Publication No. 2018 / 012545 JP 2018-172473 A

[0005] Protective films having an antistatic layer are used as protective films for optical components, etc., and are particularly used in the processing of display components. In recent years, they have also been increasingly used in the processing of components for organic electroluminescent 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 heating and drying process.

[0006] For example, when laminating an adhesive layer on a protective film in this way, oligomers may precipitate during the heat drying process, increasing haze and deteriorating the film's appearance. If the visibility decreases as the haze of the protective film increases, it becomes difficult to inspect the appearance of the protective film in a state where it is attached to an adherend, which has been a problem.

[0007] In response to the above-mentioned problems with protective films, the present invention provides an antistatic film and a protective film that suppress an increase in haze even after a heat drying process and has low surface resistivity.

[0008] That is, the present invention has the following configurations. [1] A laminated polyester film having, in this order, a first layer, a polyester film, and a second layer, wherein the first layer is an antistatic layer, and the antistatic layer is a cured layer of a composition containing a conductive polymer and a melamine-based crosslinking agent, and the melamine-based crosslinking agent contains at least one selected from imino-type methylated melamine resins, methylol-type methylated melamine resins, full-ether-type methylated melamine resins, and imino-methylol-type methylated melamine resins. [2] The laminated polyester film according to [1], wherein the melamine-based crosslinking agent has a weight-average degree of polymerization of 2.5 or less. [3] The laminated polyester film according to [1] or [2], wherein the composition contains a binder resin, and wherein the content of the melamine-based crosslinking agent is 40% by mass or more relative to 100% by mass of the total of the conductive polymer, the melamine-based crosslinking agent, and the binder resin. [4] The laminated polyester film according to any one of [1] to [3], wherein the conductive polymer comprises a π-electron conjugated conductive polymer and a doping agent. [5] The laminated polyester film according to any one of [1] to [4], wherein the haze of the laminated polyester film after heating at 140°C for 10 minutes is 3% or less. [6] The laminated polyester film according to any one of [1] to [5], wherein the surface resistivity of the antistatic layer is 2 to 7 [log Ω / □]. [7] The laminated polyester film according to any one of [1] to [6], wherein the composition comprises an acetylene-based surfactant. [8] The laminated polyester film according to any one of [1] to [7], wherein the composition comprises a conductive additive. [9] The laminated polyester film according to any one of [1] to [8], wherein the second layer is an easy-adhesion layer.

[10] The laminated polyester film according to any one of [1] to [9], wherein the second layer is a cured layer of a composition containing a melamine-based crosslinking agent, and the melamine-based crosslinking agent contains at least one selected from an imino-type methylated melamine resin, a methylol-type methylated melamine resin, a full-ether-type methylated melamine resin, and an imino-methylol-type methylated melamine resin.

[11] A protective film having the laminated polyester film according to any one of [1] to

[10] , the protective film having the first layer, the polyester film, the second layer, and an adhesive layer in this order.

[0009] According to the present invention, an antistatic film is provided in which an antistatic layer having oligomer block properties is laminated on at least one side of a polyester film. This makes it possible to provide a protective film in which an adhesive layer is laminated on the antistatic film of the present invention, and even when the protective film is attached to an adherend, visual inspection is possible and peel electrification and foreign matter adhesion are suppressed during peeling. Furthermore, by providing a first layer and a second layer on the polyester film, oligomer precipitation is suppressed throughout the polyester film, even when higher temperatures are applied in a subsequent process. Oligomer precipitation is also suppressed from the second layer side, thereby suppressing the incorporation of oligomers into the adhesive. Furthermore, having a first layer and a second layer is also preferable in that it suppresses damage to the film during film transport.

[0010] The laminated polyester film of the present invention (sometimes simply referred to as an antistatic film) is a laminated polyester film having a first layer, a polyester film, and a second layer, in this order, with the antistatic layer laminated as the first layer on at least one side of the polyester film. An adhesive layer can also be laminated on one side of the antistatic film, allowing it to be used as a protective film. In one embodiment, the laminated polyester film of the present invention may have a polyester film, a second layer, and an adhesive layer, in this order. The second layer of the laminated polyester film of the present invention preferably functions as an adhesive layer, which can improve the adhesion between the polyester film and the adhesive layer. In another embodiment, the laminated polyester film of the present invention further has an adhesive layer on the second layer side, i.e., the first layer, a polyester film, a second layer, and an adhesive layer, in this order, allowing it to be used as a protective film. In the protective film, the second layer preferably functions as an adhesive layer, which can improve the adhesion between the polyester film and the adhesive layer.

[0011] For example, when the laminated polyester film of the present invention is heated and dried during the adhesive layer lamination process, an increase in haze of the protective film can be suppressed, making it possible to perform appearance inspection even when the protective film is attached to an adherend.

[0012] The present invention will be described in detail below. In this specification, unless otherwise specified, the numerical range "A to B" means "A or more and B or less."

[0013] (Polyester Film) 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" refers to 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 in an amount of 50% by mass or more. When other monomers are copolymerized, this means that the polyester repeating structural unit is contained in an amount of 50 mol% or more. Preferably, the polyester film contains 90% by mass or more of polyester resin, more preferably 95% by mass or more, and even more preferably 100% by mass, of the polyester resin in the resin composition constituting the film.

[0014] The polyester resin may be made of any material, but may be a copolymer formed by polycondensation of a dicarboxylic acid component and a diol component (i.e., a polyester having a dicarboxylic acid component and a diol component as constituent components), or a blend resin thereof.

[0015] Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as phthalic acid (specifically, terephthalic acid, isophthalic acid, orthophthalic acid), naphthalenedicarboxylic acid (specifically, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, or 1,5-naphthalenedicarboxylic acid), diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfonedicarboxylic acid, and anthracenedicarboxylic acid; 1,3-cyclopentanedicarboxylic acid; alicyclic dicarboxylic acids such as carboxylic 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, dimer acid, sebacic acid, suberic acid, and dodecadicarboxylic acid. Among these, the dicarboxylic acid component is preferably an aromatic dicarboxylic acid, more preferably phthalic acid and / or naphthalenedicarboxylic acid, and even more preferably terephthalic acid and / or 2,6-naphthalenedicarboxylic acid.

[0016] Examples of diol components constituting the polyester resin include aliphatic diols such as alkylene glycols (specifically, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, hexamethylene glycol, neopentyl glycol, decamethylene glycol, etc.); 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. Of these, the diol component is preferably an aliphatic diol, more preferably an alkylene glycol having 2 to 6 carbon atoms, and even more preferably ethylene glycol and / or 1,4-butanediol.

[0017] The polyester resin may contain one or more dicarboxylic acid components and two or more diol components. Other acid components, such as trivalent or higher carboxylic acid components (e.g., trimellitic acid), and other hydroxyl group components, such as trivalent or higher alcohol components (e.g., trimethylolpropane), may also be added as appropriate.

[0018] The polyester resin is preferably a polyester having an aromatic dicarboxylic acid and an aliphatic diol as constituent components, and more preferably a polyester having phthalic acid and / or naphthalenedicarboxylic acid and an alkylene glycol having 2 to 6 carbon atoms as constituent components.

[0019] Specific examples of polyester resins include polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Among these, polyethylene terephthalate is preferred in terms of the balance between physical properties and cost.

[0020] In order to improve the handling properties of the polyester film, such as its slipperiness and windability, inactive particles may be contained in the polyester film. However, when used for optical applications, it is preferable that the polyester film is substantially free of particles. The phrase "polyester film is substantially free of particles" refers to the particle content in the polyester film being, for example, 1% by mass or less, preferably 0.5% by mass or less, more preferably 0.1% by mass or less, and particularly preferably 0% by mass. When the polyester film is substantially free of particles, it is preferable to incorporate particles into a coating layer formed by in-line coating. It is preferable to incorporate particles into the coating layer without incorporating particles into the polyester film, as this improves transparency and makes visual inspection easier.

[0021] The haze of the polyester film used in the present invention is preferably 3% or less (particularly 3.0% or less). More preferably, it is 2.5% or less, and even more preferably, it is 2.0% or less. 1.5% or less is extremely preferable. If it is 3% or less, visual inspection is possible with the protective film attached to the adherend, and the lower the haze, the easier the visual inspection becomes, which is preferable. In particular, when the adherend is an optical component, it is preferable to adjust the haze of the polyester film to the above range.

[0022] The regional surface average roughness (Sa) of the surface of the 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 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. When Sa is 40 nm or less and P is 2 μm or less, there is no risk of the surface of the adhesive layer being roughened when the adhesive layer is laminated and wound into a roll, which is preferable.

[0023] In the present invention, the thickness of the polyester film is not particularly limited, but is preferably in the range of 12 to 188 μm, more preferably 18 to 125 μm, and even more preferably 25 to 100 μm. If the thickness is 12 μm or more, there is little risk of wrinkles occurring when the film is attached to an adherend as a protective film, and if the thickness is 188 μm or less, it is advantageous in terms of cost.

[0024] The polyester film serving as the substrate may be a single layer or a laminate of two or more layers. Furthermore, various additives may be incorporated into the polyester film as needed, as long as the effects of the present invention are achieved. Examples of additives include antioxidants, light stabilizers, antigelling agents, organic wetting agents, antistatic agents, ultraviolet absorbers, surfactants, and the like. When the polyester film has a laminated structure, it is also preferable to incorporate additives into each layer as needed, depending on the function of each layer.

[0025] The polyester film can be obtained, for example, by melt-extruding the polyester resin into a film and then cooling and solidifying it on a casting drum to form a film. The polyester film of the present invention can be either a non-stretched film or a stretched film, but a stretched film is preferred from the viewpoint 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, longitudinal and transverse sequential biaxial stretching, and longitudinal and transverse simultaneous biaxial stretching can be used.

[0026] The surface layer of the polyester film may be subjected to a surface treatment such as an anchor coat layer, corona treatment, plasma treatment, or flame treatment in order to improve adhesion to the first layer and the second layer. When an anchor coat layer is provided, it is preferably carried out by in-line coating from the viewpoint of cost, etc.

[0027] (First Layer and Antistatic Layer) In the laminated polyester film of the present invention, the first layer functions as an antistatic layer. Hereinafter, the antistatic layer corresponding to the first layer may be referred to as antistatic layer 1. In the laminated polyester film of the present invention, an antistatic layer can be laminated on at least one side of the polyester film. The antistatic layer may be laminated on only one side or both sides of the polyester film. When the antistatic layer is laminated on both sides of the polyester film, both the first and second layers function as antistatic layers. Laminating an antistatic layer on at least one side of the polyester film is preferable because it can suppress peel charging with the adherend and suppress adhesion of foreign matter even when an adhesive layer is laminated and used as a protective film. Furthermore, laminating an antistatic layer on at least one side of the polyester film is more preferable because it can prevent charging even when the film is wound or unwound.

[0028] As described above, in one embodiment of the present invention, the second layer adjacent to the adhesive layer may also have antistatic properties. When both the first and second layers are antistatic layers, the absolute value of the difference between the surface resistivity of the first layer ([logΩ / □]) and the surface resistivity of the second layer ([logΩ / □]) expressed by the following formula: |surface resistivity of first layer - surface resistivity of second layer| is, for example, 2.5 or less, preferably 1.0 or less, more preferably 0.7 or less, and even more preferably 0.5 or less. Here, in the present invention, the first layer must exhibit the function of oligomer block in addition to antistatic properties. On the other hand, the second layer is preferably a layer that improves adhesion between the polyester film and the adhesive layer while having the desired surface resistivity.

[0029] The antistatic layer 1 is a layer formed by curing a composition containing a conductive polymer and a melamine-based crosslinking agent. Such a composition may be referred to as an antistatic layer-forming composition or a first layer-forming composition.

[0030] (Conductive Polymer) The conductive polymer in the present invention is a polymer that can impart antistatic properties, and can be a polymer that utilizes ionic conductivity such as a cationic compound, a π-electron conjugated conductive polymer, or the like. In particular, it is preferable to use a π-electron conjugated conductive polymer in terms of antistatic properties under low humidity. Furthermore, π-electron conjugated conductive polymers are preferred because they can maintain a high level of antistatic performance independent of moisture in the air and therefore provide good antistatic performance in various usage environments of the protective film. Furthermore, other antistatic agents can be used in combination with the conductive polymer of the present invention as long as the effects achieved by the conductive polymer are not impaired. As the other antistatic agent, known antistatic agents such as surfactants, silicon oxide compounds, and conductive metal compounds other than the conductive polymer of the present invention can be used.

[0031] Examples of π-electron conjugated conductive polymers include aniline-based polymers containing aniline or its derivatives as a structural unit, pyrrole-based polymers containing pyrrole or its derivatives as a structural unit, acetylene-based polymers containing acetylene or its derivatives as a structural unit, and thiophene-based polymers containing thiophene or its derivatives as a structural unit. To achieve higher transparency, π-electron conjugated conductive polymers that do not contain nitrogen atoms are preferred. Among these, thiophene-based polymers containing thiophene or its derivatives as a structural unit are preferred, with polyalkylenedioxythiophenes being particularly preferred. Examples of polyalkylenedioxythiophenes include polyethylenedioxythiophene, polypropylenedioxythiophene, and poly(ethylene / propylene)dioxythiophene.

[0032] It is preferable to incorporate a doping agent into the π-electron conjugated conductive polymer (particularly a thiophene-based polymer containing thiophene or a derivative thereof as a structural unit) to further improve antistatic properties. That is, the conductive polymer preferably contains a π-electron conjugated conductive polymer and a doping agent. The amount of the doping agent incorporated is preferably 0.1 to 500 parts by mass per 100 parts by mass of the π-electron conjugated conductive polymer (particularly a polymer containing thiophene or a derivative thereof as a structural unit). By adjusting the content to 500 parts by mass or less, electron transfer is facilitated, thereby improving antistatic performance, and by adjusting the content to 0.1 parts by mass or more, dispersibility in a solvent can be improved.

[0033] The doping agent may be LiCl, R 1‐30 COOLi (R 1‐30 R: a saturated hydrocarbon group having 1 to 30 carbon atoms 1‐30 SO3Li,R 1‐30 COONa, R 1‐30 SO3Na, R 1‐30 COOK, R. 1‐30 SO3K, tetraethylammonium, I2, BF3Na, BF4Na, HClO4, CF3SO3H, FeCl3, tetracyanoquinoline (TCNQ), Na2B 10 Cl10 phthalocyanine, porphyrin, glutamic acid, alkyl sulfonates, polystyrene sulfonic acid, polystyrene sulfonates (specifically, alkali metal salts such as Na salt, K salt, Li salt, etc.), styrene-styrene sulfonate (specifically, alkali metal salts such as Na salt, K salt, Li salt, etc.) copolymer, polystyrene sulfonate anion, styrene sulfonate-styrene sulfonate anion copolymer, etc. Among these, polystyrene sulfonic acid or a derivative thereof such as polystyrene sulfonic acid, polystyrene sulfonate, styrene-styrene sulfonate copolymer, polystyrene sulfonate anion, styrene sulfonate-styrene sulfonate anion copolymer, etc. are preferred.

[0034] The content of the conductive polymer is preferably 5% by mass or more, more preferably 8% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more, relative to the total 100% by mass of the conductive polymer and the melamine-based crosslinking agent. When a π-electron conjugated conductive polymer is used as the conductive polymer and the doping agent is used, the content of the conductive polymer as defined herein refers to the total amount of the conductive polymer and the doping agent. By including the conductive polymer in such an amount, better antistatic properties can be imparted to the first layer. When the first-layer-forming composition contains a binder resin, as described below, it is also preferable to adjust the content of the conductive polymer within the above range relative to the total 100% by mass of the melamine-based crosslinking agent, the conductive polymer, and the binder resin.

[0035] The content of the conductive polymer is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, relative to 100% by mass of the total of the conductive polymer and the melamine-based crosslinking agent. When the first-layer-forming composition contains a binder resin described below, it is also preferable to adjust the content of the conductive polymer relative to 100% by mass of the total of the melamine-based crosslinking agent, the conductive polymer, and the binder resin within the above range. By including the conductive polymer in such an amount, the coating liquid does not interact with the melamine-based crosslinking agent, the coating liquid is less likely to aggregate, and high transparency can be maintained, thereby forming an antistatic layer 1 with fewer defects.

[0036] That is, the content of the conductive polymer is preferably 5 to 50% by mass, more preferably 8 to 45% by mass, even more preferably 10 to 40% by mass, still more preferably 15 to 40% by mass, and particularly preferably 20 to 40% by mass, relative to 100% by mass of the total of the conductive polymer and the melamine-based crosslinking agent. When the first layer-forming composition contains a binder resin described below, it is also preferable to adjust the content of the conductive polymer relative to 100% by mass of the total of the melamine-based crosslinking agent, the conductive polymer, and the binder resin within the above range.

[0037] The content of the conductive polymer is preferably 1 to 50% by mass, more preferably 5 to 50% by mass, and even more preferably 10 to 40% by mass, relative to 100% by mass of the total solid content in the antistatic layer 1. It is also preferable to adjust the content of the conductive polymer relative to 100% by mass of the solid content of the first layer-forming composition to fall within the above range. The solid content refers to components that become solid at, for example, 25°C.

[0038] (Melamine-based crosslinking agent) In the present invention, the antistatic layer 1 is formed from a first layer-forming composition containing a melamine-based crosslinking agent in order to form a crosslinked structure in the antistatic layer 1. The inclusion of a melamine-based crosslinking agent is preferable because it improves durability and suppresses deterioration of antistatic performance even when treated under high-temperature, high-humidity conditions. In order to increase the crosslink density of the antistatic layer 1, it is preferable to increase the reactivity of the melamine-based crosslinking agent. Highly reactive melamine-based crosslinking agents will be described later. Furthermore, in order to promote the crosslinking reaction, a catalyst or the like can be used as needed.

[0039] The melamine-based crosslinking agent used in the antistatic layer 1 of the present invention can be a commonly used one and is not particularly limited, but is preferably a crosslinking agent obtained by condensing melamine with formaldehyde and having one or more triazine rings and one or more methylol groups and / or alkoxymethyl groups in one molecule. Specifically, a methylolated melamine derivative obtained by condensing melamine with formaldehyde, or a methylolated melamine derivative containing a lower alcohol such as methyl alcohol, ethyl alcohol, isopropyl alcohol, or butyl alcohol (preferably C 1-4 Preferred are compounds obtained by etherifying melamine derivatives such as alkyl alcohols (e.g., alkyl methyl alcohols) through a dehydration condensation reaction. Examples of methylol melamine derivatives include monomethylol melamine, dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, and hexamethylol melamine. One or more types of melamine-based crosslinking agents may be used.

[0040] To enhance the reactivity of the melamine-based crosslinking agent and further increase the crosslink density of the antistatic layer, it is preferable to use a methylol-type methylated melamine or hexaalkoxymethyl melamine, which have more crosslinking points per molecule. However, hexaalkoxymethyl melamine, which has superior reactivity, is more preferable, and hexamethoxymethyl melamine is particularly preferable. Here, hexamethylol melamine is a compound represented by the formula (a) described below, in which all six Xs are methylol groups (—CH—OH). Hexaalkoxymethyl melamine is a compound obtained by subjecting a methylol melamine derivative to a dehydration condensation reaction with an alcohol, in which all six Xs are (—CH—OR, where R is an alkyl group, preferably an alkyl group having 1 to 4 carbon atoms) in the formula (a) described below. Hexamethoxymethyl melamine is a compound represented by the formula (a) described below, in which all six Xs are (—CH—OMe).

[0041] The melamine-based crosslinking agent preferably contains a melamine compound represented by the following formula (a):

[0042]

[0043] In the above (a), X represents -H, -CH-OH, or -CH-O-R, and R represents an alkyl group. Multiple Xs may be the same or different. Furthermore, the Rs may be the same or different.

[0044] The alkyl group represented by R is preferably a chain alkyl group, more preferably an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, or a tert-butyl group, and still more preferably a methyl group.

[0045] The melamine crosslinking agent used in the present invention is preferably not a single compound but a mixture of multiple compounds. Based on the structure of the compound that serves as the main component of the melamine crosslinking agent, it can be broadly classified into imino-type melamine resins (mainly imino-type melamine compounds in which, in formula (a), at least one X is -H, and preferably a majority of X are -H), methylol-type melamine resins (mainly methylol-type melamine compounds in formula (a), at least one X is -CH-OH, and preferably a majority of X are -CH-OH), full-ether-type melamine resins (mainly full-ether-type melamine compounds in formula (a), all X are -CH-OR (R is preferably an alkyl group having 1 to 4 carbon atoms)), and imino-methylol-type melamine resins (mainly imino-methylol-type melamine compounds in formula (a), at least one X is -CH-OH and at least one X is H). Here, the term "main component" refers to the component that is most abundant in the melamine-based crosslinking agent. The content of the main component in the melamine-based crosslinking agent is not particularly limited as long as it is the component that is most abundant in the melamine-based crosslinking agent, but is, for example, 30% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. In one embodiment, from the viewpoint of reactivity, a full-ether type melamine resin or a methylol type melamine resin is preferably used, more preferably a full-ether type melamine resin, and most preferably a melamine-based crosslinking agent containing hexamethoxymethylmelamine (CAS No. 3089-11-0) in which R is a methyl group as the main component. The higher the content of hexamethoxymethylmelamine in this melamine-based crosslinking agent (for example, 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more), the higher the reactivity and the higher the crosslinking density of the antistatic layer 1 can be.

[0046] In particular, the melamine-based crosslinking agent may be an imino-type methylated melamine resin mainly composed of an imino-type methylated melamine compound represented by formula (a), in which at least one X is -CH2-OMe and at least one X is -H (preferably, a majority of X are -H); a methylol-type methylated melamine resin mainly composed of a methylol-type methylated melamine compound represented by formula (a), in which at least one X is -CH2-OMe and at least one X is -CH2-OH (preferably, a majority of X are -CH2-OH); a full-ether-type methylated melamine resin mainly composed of a full-ether-type methylated melamine compound represented by formula (a), in which at least one X is -CH2-OMe and the remaining X are -CH2-OR (R is preferably an alkyl group having 1 to 4 carbon atoms); and Preferably, at least one selected from the group consisting of imino-methylol methylated melamine resins, the main component of which is an imino-methylol methylated melamine compound in which, in formula (a), at least one X is —CH—OH, at least one X is —CH—OMe, and at least one X is H. By incorporating any of these melamine-based crosslinking agents, the crosslinking density of the antistatic layer 1 according to the present invention is increased, and even if the antistatic layer is thin, there is little increase in haze even after heating. Even when a protective film comprising an adhesive layer laminated on the antistatic film is attached to an adherend, visual inspection is possible, and peel charging and foreign matter adhesion during peeling are suppressed. Furthermore, the use of these melamine-based crosslinking agents improves alcohol resistance; specifically, even when the surface of the first layer is wiped with alcohol, an increase in surface resistivity and changes in appearance can be suppressed.

[0047] Among these, from the viewpoint of further suppressing an increase in the surface resistivity of the first layer, the melamine-based crosslinking agent is preferably a methylol-type methylated melamine resin, a full-ether-type methylated melamine resin, or an imino-methylol-type methylated melamine resin, more preferably a methylol-type methylated melamine resin or a full-ether-type methylated melamine resin, and even more preferably a full-ether-type methylated melamine resin. Furthermore, from the viewpoint of further suppressing an increase in haze after a subsequent heat drying step, the melamine-based crosslinking agent is preferably a methylol-type methylated melamine resin, a full-ether-type methylated melamine resin, or an imino-type methylated melamine resin, and more preferably a full-ether-type methylated melamine resin.

[0048] The melamine-based crosslinking agent used in the antistatic layer 1 of the present invention preferably has a weight-average degree of polymerization of 2.5 or less, more preferably 2.3 or less, and even more preferably 2.0 or less. A weight-average degree of polymerization of 2.5 or less can improve compatibility with conductive polymers, suppress aggregation of the coating liquid, and form a film with fewer defects. Furthermore, in the present invention, a weight-average degree of polymerization of 2.5 or less is preferable because the increased content of mononuclear units contained in the melamine-based crosslinking agent results in an antistatic layer 1 with excellent reactivity, improved crosslink density, and less oligomer precipitation. For example, the weight-average degree of polymerization may be 1.1 or more, or even greater than 1.5. That is, the weight-average degree of polymerization of the melamine-based crosslinking agent is preferably 1.1 to 2.5, more preferably 1.1 to 2.3, and even more preferably 1.5 to 2.0, and may be greater than 1.5 but less than 2.0. The weight-average degree of polymerization can be determined from the average value calculated from the weight-average molecular weight calculated using gel permeation chromatography (GPC) in terms of standard polystyrene.

[0049] In the synthesis process of melamine-based crosslinking agents, those containing imino groups (—NH—) or polynuclear compounds may be mixed in. Even if these melamine derivatives are mixed, as long as the weight-average degree of polymerization of the melamine-based crosslinking agent is within the above range, the reactivity is excellent and each can be used suitably.

[0050] As the melamine-based crosslinking agent, a commercially available product may be used, and examples of commercially available melamine resins include the Nikalac series (manufactured by Nippon Carbide Industries Co., Ltd.).

[0051] The content of the melamine-based crosslinking agent may be 30 to 95% by mass, preferably 40 to 95% by mass, more preferably 50 to 95% by mass, even more preferably 55 to 90% by mass, and particularly preferably 60 to 90% by mass, relative to the total 100% by mass of the conductive polymer and the melamine-based crosslinking agent. When the first-layer-forming composition contains a binder resin, as described below, it is preferable to adjust the content of the melamine-based crosslinking agent relative to the total 100% by mass of the melamine-based crosslinking agent, the conductive polymer, and the binder resin within the above range. By setting the content of the melamine-based crosslinking agent to 30% by mass or more (particularly 40 or 50% by mass or more), the antistatic layer 1 can achieve a higher crosslink density due to self-crosslinking of the melamine-based compound, resulting in a dense antistatic layer, which further enhances the oligomer precipitation suppression effect and alcohol resistance, and is therefore preferred. Since a considerable portion of the solvent and acid catalyst evaporates during the drying process, it is also preferable to adjust the content of the melamine-based crosslinking agent relative to the total solid content of the melamine-based crosslinking agent and the conductive polymer (in the case where a binder resin is included, the total solid content of the melamine-based crosslinking agent, the conductive polymer, and the binder resin).

[0052] The content of the melamine-based crosslinking agent (specifically, a structure derived from a melamine-based crosslinking agent) is preferably 20 to 95% by mass, more preferably 30 to 80% by mass, and even more preferably 40 to 70% by mass, relative to 100% by mass of the total solid content in the antistatic layer 1. It may also be 50 to 95% by mass, 55 to 95% by mass, or 60 to 95% by mass. It is also preferable to adjust the content of the melamine-based crosslinking agent relative to 100% by mass of the solid content of the first layer-forming composition to fall within the above range.

[0053] The content of the melamine-based crosslinking agent is preferably 80 to 500 parts by mass, more preferably 110 to 300 parts by mass, and even more preferably 140 to 260 parts by mass, per 100 parts by mass of the conductive polymer.

[0054] (Surfactant) In order to improve the appearance of the antistatic layer 1 of the present invention, a surfactant may be used. That is, the composition for forming the first layer may contain a surfactant.

[0055] The surfactant is not particularly limited, and examples thereof include silicone surfactants, fluorine surfactants having a perfluoroalkyl group, acetylene surfactants, and hydrocarbon surfactants such as other nonionic surfactants. The surfactants may be used alone or in combination of two or more.

[0056] The silicone surfactant is preferably a polyether-modified silicone surfactant. Commercially available silicone surfactants may be used, and specific examples thereof include the Silface series (manufactured by Nissin Chemical Industry Co., Ltd.), the KF series (manufactured by Shin-Etsu Chemical Co., Ltd.), BYK-345, 347, 348, 349, 3450, 3451, 3455, and 3480 (all manufactured by BYK), DC3PA, SH7PA, DC11PA, SH21PA, SH28PA, SH29PA, SH30PA, SH8400, SH 8400 FLUID, FZ-2122, 67 Additive, 74 Additive, M Additive, and SF 8419 OIL (all manufactured by Dow-Toray Industries, Inc.). Examples of the fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl benzene sulfonic acid compounds, fluoroalkyl carboxylic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl polyoxyethylene ethanol, polyoxyalkylene ether polymer compounds having a perfluoroalkyl ether group on the side chain, and perfluoroalkyl quaternary ammonium. Commercially available products may be used as the fluorine-based surfactants, specifically, the Surflon series (manufactured by AGC Sei Chemical Co., Ltd.) and the Megafac F series (manufactured by DIC Corporation). Commercially available products may be used as the acetylene-based surfactants, specifically, the Surfynol series (manufactured by Nissin Chemical Industry Co., Ltd.), the Olfine series (manufactured by Nissin Chemical Industry Co., Ltd.), and Dynol 604, 607, and 609 (all manufactured by Nissin Chemical Industry Co., Ltd.). Other nonionic surfactants include polyoxyethylene octylphenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene sorbitan fatty acid ester.

[0057] Among the surfactants, silicone surfactants and / or acetylene surfactants are particularly preferred, and polyether-modified silicone surfactants and / or acetylene surfactants are more preferred. Furthermore, the inclusion of an acetylene surfactant is preferred because, even when the antistatic film is used as a protective film, migration of the surfactant to the protected product can be avoided, thereby reducing adverse effects on the final product. Furthermore, the protective film obtained by laminating an adhesive layer on the antistatic film of the present invention is preferably used in the manufacturing process of optical components, etc., and the acetylene surfactant is preferred because it is less likely to contaminate the manufacturing process.

[0058] The content of the surfactant is preferably 0 to 100 parts by mass, more preferably 10 to 60 parts by mass, and even more preferably 25 to 50 parts by mass, relative to 100 parts by mass of the total of the conductive polymer and the melamine-based crosslinking agent.

[0059] The content of the surfactant in the first layer forming composition, relative to 100% by mass of solids, is, for example, 0 to 40% by mass, preferably 5 to 30% by mass, and more preferably 10 to 30% by mass.

[0060] (Binder Resin) For example, the antistatic layer 1 may contain a binder resin. That is, the first layer-forming composition may contain a binder resin. The antistatic layer 1 can exhibit the effects of the present invention whether or not it contains a binder resin.

[0061] The binder resin is not particularly limited, but is preferably one that can fully exhibit the functions of the antistatic layer of the present invention. Specific examples of binder resins include polyester resins, acrylic resins, urethane resins, polyolefin resins, polyvinyl resins (such as polyvinyl alcohol), polyalkylene glycols, polyalkyleneimines, methyl cellulose, hydroxycellulose, and starches. These may be used alone or in combination of two or more.

[0062] Among these, from the viewpoint of adhesion to polyester film, polyester resin, acrylic resin, and urethane resin are preferred as the binder resin, and polyester resin (particularly, copolymer polyester resin) is more preferred. The polyester resin may be polyurethane-modified. Examples of urethane resins include polycarbonate polyurethane resin. Furthermore, acrylic resin, polyester resin, and polyurethane resin may be used in combination, and other binder resins mentioned above may be used in combination.

[0063] The glass transition temperature (Tg) of the binder resin is preferably 0 to 130° C., more preferably 15 to 120° C., and even more preferably 25 to 115° C. The Tg of the binder resin can be determined by differential scanning calorimetry (DSC).

[0064] The number average molecular weight of the binder resin is preferably 3,000 to 100,000, more preferably 4,000 to 50,000, and even more preferably 5,000 to 30,000. The number average molecular weight of the binder resin can be calculated by a standard polystyrene conversion method using gel permeation chromatography (GPC).

[0065] The content of the binder resin in 100% by mass of the solid content of the composition for forming the first layer is, for example, 40% by mass or less, preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, and may be 5% by mass or less, or 0% by mass.

[0066] Furthermore, when the composition for forming the first layer contains a binder resin, the content of the binder resin is preferably 1 to 60 mass %, more preferably 5 to 50 mass %, and even more preferably 10 to 40 mass %, relative to 100 mass % in total of the conductive polymer, the melamine-based crosslinking agent, and the binder resin.

[0067] (Conductive Aid) The first layer forming composition may further contain a conductive aid. That is, the first layer forming composition may contain a conductive aid.

[0068] The content of the conductive assistant may be 0 to 500 parts by mass, preferably 80 to 400 parts by mass, and more preferably 150 to 300 parts by mass, relative to 100 parts by mass of the total of the conductive polymer and the melamine-based crosslinking agent.

[0069] The first-layer forming composition may further contain a solvent. The inclusion of a solvent improves film-forming properties. The solvent is not particularly limited, but may be an organic solvent, water, or a mixture thereof. Examples of the organic solvent include one or more selected from the following: esters such as ethyl acetate; ketones such as methyl ethyl ketone, acetone, and cyclohexanone; cyclic ethers such as tetrahydrofuran and dioxane; aliphatic or alicyclic hydrocarbons such as n-hexane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; aliphatic or alicyclic alcohols such as methanol, ethanol, n-propanol, isopropanol, and cyclohexanol; and glycol ethers such as alkylene glycol monoalkyl ethers (e.g., ethylene glycol monomethyl ether and ethylene glycol monoethyl ether) and dialkylene glycol monoalkyl ethers. Among these, solvents with a boiling point of 150°C or less (particularly 140°C or less) are preferred. Specifically, water or a mixture of water and an alcohol (particularly an aliphatic alcohol having 1 to 4 carbon atoms) is more preferred.

[0070] The content of the solvent can be adjusted so that the solid content concentration of the first layer forming composition is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass.

[0071] In addition to the above, the antistatic layer 1 may contain other additives, such as a crosslinking agent other than a melamine-based crosslinking agent, a lubricant, a dye, an ultraviolet absorber, a silane coupling agent, etc., as needed, within the scope of not impairing the object of the present invention.

[0072] The composition for forming the first layer can be prepared by mixing a conductive polymer, a melamine-based crosslinking agent, and, if necessary, other antistatic agents, surfactants, binder resins, conductive assistants, solvents, and other additives.

[0073] The means for laminating the first layer on the polyester film is not particularly limited, and known methods such as coating, vacuum deposition, and lamination can be used. However, from the viewpoint of cost, it is preferable to provide the antistatic layer 1 by coating a coating liquid containing an antistatic agent (specifically, a composition for forming the first layer), i.e., the antistatic layer 1 is a coated layer.

[0074] The antistatic layer 1 can be formed on the surface of a substrate film by coating a coating liquid (i.e., a first layer-forming composition) prepared by dispersing or dissolving components constituting the antistatic layer 1, such as the conductive polymer and melamine-based crosslinking agent, in a solvent, and then applying and drying the coating liquid by gravure roll coating, reverse roll coating, knife coating, dip coating, bar coating, spin coating, or the like. However, there are no particular limitations on the coating method suitable for the first layer-forming composition. The antistatic layer 1 can also be formed by an in-line coating method in which the first layer is formed during the film production process, or an off-line coating method in which the first layer is formed after film production.

[0075] When forming the antistatic layer 1 by the above method, the drying temperature is usually 60°C or higher and 150°C or lower, preferably 90°C or higher and 140°C or lower. A temperature of 60°C or higher is preferred from the viewpoint of improving productivity, as it requires a short treatment time. Furthermore, if a crosslinking agent is contained, this is preferred because the crosslinking reaction proceeds sufficiently. On the other hand, a temperature of 150°C or lower is preferred because the flatness of the film is maintained.

[0076] It is preferable that the antistatic layer 1 be substantially free of silicone compounds. In the present invention, "substantially free of silicone compounds" is defined as a content of 50 ppm or less, preferably 10 ppm or less, and most preferably below the detection limit, when the silicon element is quantified by fluorescent X-ray analysis. By being substantially free of silicone compounds, even when the present antistatic film is used as a protective film, migration of silicone to the protected product can be avoided, thereby reducing adverse effects on the final product. As mentioned above, the antistatic layer 1 may contain a trace amount of silicon element. This is because, even if a silicone component is not actively added to the antistatic layer 1, contaminants from foreign matter or dirt adhering to the raw resin or the production line or equipment during the film manufacturing process may peel off and be mixed into the antistatic layer 1.

[0077] The thickness of the antistatic layer 1 of the present invention is preferably 0.005 to 1 μm. It is more preferably 0.01 to 0.5 μm, and even more preferably 0.01 to 0.2 μm. An antistatic layer having a thickness of 0.005 μm or more is preferred because the antistatic effect is further enhanced. On the other hand, in the present invention, even if the antistatic layer 1 is thin (specifically, not more than the upper limit described above), it is preferred in that an increase in haze after the subsequent heat drying step can be suppressed and an antistatic film and protective film with low surface resistivity can be provided. Furthermore, a thickness of 1 μm or less is preferred because coloration is reduced and transparency is increased.

[0078] The haze of the laminated polyester film of the present invention is preferably 3.0% or less. More preferably, it is 2.0% or less, and even more preferably, it is 1.5% or less. 1.0% or less is extremely preferable. 3.0% or less is preferable because it allows for visual inspection and the like in a state where the protective film is attached to the adherend, and is particularly preferable when the adherend is a member for optical applications. Furthermore, a smaller haze is preferable because it further improves visibility. The haze may be 0%, or, for example, 0.1% or more.

[0079] For example, in the present invention, in order to improve the handling properties of the film, the layers constituting the laminated polyester film may contain particles. When particles are contained, they may be contained on both sides (i.e., the first layer and the second layer), or only on either the first layer or the second layer. Alternatively, neither the first layer nor the second layer may contain particles.

[0080] The average primary particle diameter of the particles is preferably 10 to 500 nm, more preferably 20 to 100 nm, from the viewpoint of further reducing the haze of the resulting laminated polyester film. In this specification, the average primary particle diameter refers to the number-average particle diameter of primary particles, and can be measured, for example, by observing with a scanning electron microscope, measuring the diameters of 100 particles that can be distinguished as a single particle, and then taking the average.

[0081] From the viewpoint of further reducing the haze of the resulting laminated polyester film, the content of the particles in the first layer or the second layer is, for example, 20% by mass or less, preferably 15% by mass or less, more preferably 5% by mass or less, and may even be 0% by mass.

[0082] In particular, when at least one of the first and second layers contains particles, the particle-containing layer preferably contains 1% by mass or less of particles having a primary particle size of 500 nm or less and 15% by mass or less of particles having a primary particle size of 100 nm or less, which makes it easier to achieve a haze of 3.0% or less for the resulting laminated polyester film.

[0083] Examples of the particles include titanium oxide, barium sulfate, calcium carbonate, calcium sulfate, silica, alumina, talc, kaolin, clay, etc., and mixtures thereof, as well as other common inorganic particles such as calcium phosphate, mica, hectorite, zirconia, tungsten oxide, lithium fluoride, calcium fluoride, etc., and organic polymer particles such as styrene-based, acrylic-based, melamine-based, benzoguanamine-based, and silicone-based particles. One type of particle may be used alone, or two or more types may be used in combination.

[0084] 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. It is more preferably 2.7% or less, even more preferably 2.4% or less, even more preferably 2.0% or less, and particularly preferably 1.5% or less. A haze of 3.0% or less is preferable because visual inspections can be performed while the protective film is attached to the adherend, and is particularly preferable when the adherend is an optical component. Furthermore, a smaller haze is preferable because it further improves visibility. The haze after heating at 140°C for 10 minutes may be 0%, or may be, for example, 0.1% or more. While not limited to a specific theory, the antistatic layer 1 of the present invention can provide an antistatic layer 1 with excellent reactivity, improved crosslinking density, and resistance to oligomer precipitation. It is presumed that this results in a significant suppression of a significant increase in haze after heating at 140°C for 10 minutes.

[0085] In the present invention, the haze of the first layer surface after heating at 140°C for 10 minutes is preferably 3.0% or less, more preferably 2.7% or less, and even more preferably 2.4% or less. The haze of the first layer surface after heating at 140°C for 10 minutes may be 0%, for example, 0.1% or more. The haze of the first layer surface refers to the haze of a laminate film consisting of a polyester film and the first layer (without the second layer). As described above, the first layer is an antistatic layer that is resistant to oligomer precipitation after heating at 140°C for 10 minutes. Furthermore, the presence of the second layer enhances the oligomer block property after heating at 140°C for 10 minutes. Therefore, in the present invention, for example, after heating at 140°C for 10 minutes, the synergistic effect of the first and second layers allows the overall haze of the laminate film to be lower than the haze of the first coating layer surface.

[0086] For example, the Δhaze value, 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, may be −0.2 to 2.5, preferably −0.2 to 1.6, and more preferably −0.2 to 1.2. Having a Δhaze value within this range means that an antistatic film that is less prone to oligomer precipitation has been obtained. By providing an antistatic film that is less prone to oligomer precipitation, the visibility of the protective film is less likely to decrease even after heat drying in the adhesive layer lamination step, and visual inspection can be performed even when the protective film is attached to an adherend.

[0087] The surface resistivity of the antistatic layer 1 of the present invention is preferably 7 log Ω / □ or less (particularly 7.0 log Ω / □ or less), more preferably 6.5 log Ω / □ or less, and even more preferably 6 log Ω / □ or less (particularly 6.0 log Ω / □ or less). By setting the surface resistivity to 7 log Ω / □ or less (particularly 7.0 log Ω / □ or less), charging of the protective film can be suppressed, adhesion of foreign matter during processing can be more effectively prevented, and adverse electrical effects of charging of the protective film on the protected product can be more effectively suppressed.

[0088] The lower limit of the surface resistivity of the antistatic film (i.e., the surface resistivity of the antistatic layer 1) does not need to be particularly set, but is preferably 2 log Ω / □ or more. If the surface resistivity of the antistatic film is less than 2 log Ω / □, the processing cost of the antistatic layer increases, which is not preferred.

[0089] The total light transmittance of the antistatic film used in the present invention is preferably 80% or more, more preferably 85% or more, and even more preferably 88% or more. 90% or more is extremely preferable. 80% or more is preferable because visual inspection and the like becomes easier when the protective film is attached to the adherend, and is particularly preferable when the adherend is a member for optical applications.

[0090] The antistatic layer 1 preferably exhibits a change in surface resistivity of 1.3 times or less even after wiping with alcohol, more preferably 1.2 times or less, and even more preferably 1.1 times or less. A change of 1.3 times or less is preferable because the protective film maintains its initial surface resistivity even when alcohol is used in a process such as adhesive processing.

[0091] The area surface average roughness (Sa) of the surface of the antistatic layer 1 is preferably in the range of 1 to 40 nm, more preferably 1 to 30 nm, and even more preferably 1 to 10 nm. Furthermore, the maximum projection height (P) of the surface of the antistatic film used in the present invention (specifically, the surface of the antistatic layer 1) is preferably 2 μm or less, more preferably 1.5 μm or less, and even more preferably 0.8 μm or less. When Sa is 40 nm or less and P is 2 μm or less, there is no risk of the surface of the adhesive layer being roughened when the adhesive layer is laminated and wound into a roll, which is preferable.

[0092] (Second Coating Layer) The antistatic film of the present invention must have a first layer, a polyester film, and a second layer laminated in this order. The first layer is an antistatic layer, and the second layer is preferably an easy-adhesion layer.

[0093] The second layer is preferably an easy-adhesion layer, since when an adhesive layer is laminated on the second layer, the adhesion to the adhesive layer is good and adhesive residue can be suppressed when peeled off from the adherend. The easy-adhesion layer may also have antistatic properties and / or oligomer block properties. Having antistatic properties in the easy-adhesion layer is preferable because, even when an adhesive layer is laminated and used as a protective film, peel electrification with the adherend can be further suppressed and adhesion of foreign matter can be further suppressed. Having oligomer block properties is preferable because an increase in haze can be further suppressed even after the heat drying process, and appearance inspection can be made easier even when an adhesive layer is laminated and attached to an adherend as a protective film.

[0094] In the present invention, the second layer does not necessarily have to have antistatic properties. On the other hand, the second layer may have antistatic properties depending on the first layer and the pressure-sensitive adhesive used. Furthermore, the second layer of the present invention preferably exhibits good adhesion between the polyester film substrate and the pressure-sensitive adhesive, and may further have antistatic properties as necessary.

[0095] When the second layer has antistatic properties, it is desirable that the antistatic properties of the second layer be lower than those of the first layer, i.e., it is desirable that the surface resistivity of the second layer be higher than that of the first layer. This is because if the antistatic properties of the second layer are higher than those of the first layer, adhesion to the pressure-sensitive adhesive tends to decrease. Therefore, by satisfying the above conditions, the second layer of the present invention is preferable from the viewpoint of further enhancing both easy adhesion and antistatic properties.

[0096] The surface resistivity of the second layer of the present invention is 7 [log Ω / □] or less (particularly 7.0 [log Ω / □] or less). More preferably, it is 6.5 [log Ω / □] or less, and even more preferably, it is 6 [log Ω / □] or less (particularly, 6.0 [log Ω / □] or less). By setting the surface resistivity to 7 [log Ω / □] or less (particularly, 7.0 [log Ω / □] or less), charging of the protective film can be further suppressed, adhesion of foreign matter during processing can be further prevented, and further, adverse electrical effects of charging of the protective film on the protected product can be further suppressed.

[0097] The lower limit of the surface resistivity of the second layer does not need to be particularly set, but it is preferably 2 log Ω / □ or more (particularly 2.0 log Ω / □ or more). If the surface resistivity of the antistatic film is less than 2 log Ω / □, the processing cost of the antistatic layer increases, which is not preferable.

[0098] The components constituting the second layer (preferably the easy-adhesion layer) preferably include at least one selected from the group consisting of a binder resin, a crosslinking agent, and an antistatic agent, and more preferably include at least a crosslinking agent. That is, the second layer is preferably a cured layer of a second-layer-forming composition containing at least one selected from the group consisting of a binder resin, a crosslinking agent, and an antistatic agent, and more preferably a cured layer of a second-layer-forming composition containing at least a crosslinking agent.

[0099] (Binder Resin) The same explanation as for the binder resin used in the antistatic layer 1, including preferred embodiments thereof, can be applied to the binder resin.

[0100] (Crosslinking Agent) The crosslinking agent is not particularly limited, and specific examples include urea-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, isocyanate-based crosslinking agents, oxazoline-based crosslinking agents, carbodiimide-based crosslinking agents, and aziridine-based crosslinking agents. These may be used alone or in combination of two or more. Among these, from the viewpoint of oligomer block properties, it is preferable to use a melamine-based crosslinking agent (melamine resin). The description of the melamine-based crosslinking agent in the antistatic layer 1, including its preferred embodiments, can be applied mutatis mutandis to the melamine-based crosslinking agent.

[0101] Furthermore, when a crosslinking agent is used, a catalyst or the like can be used as needed to promote the crosslinking reaction. The catalyst may be selected appropriately depending on the type of crosslinking agent, but acid catalysts such as paratoluenesulfonic acid, methyl paratoluenesulfonate, ethyl paratoluenesulfonate, n-butyl paratoluenesulfonate, benzenesulfonic acid, sulfonic acid, and methanesulfonic acid are preferred. The amount of the catalyst is preferably 0.1 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of the crosslinking agent.

[0102] (Antistatic Agent) The antistatic agent is not particularly limited, and specific examples include conductive polymers (e.g., polymers utilizing ionic conduction such as cationic compounds, π-electron conjugated conductive polymers), surfactants, silicon oxide compounds, conductive metal compounds, conductive carbon fibers, etc. Antistatic agents may be used alone or in combination of two or more. Among these, conductive polymers are preferred, and π-electron conjugated conductive polymers are preferred in terms of antistatic properties under low humidity. Furthermore, π-electron conjugated conductive polymers are preferred because they can maintain high levels of antistatic performance independent of moisture in the air and therefore provide good antistatic performance in various usage environments of the protective film. The same description of the π-electron conjugated conductive polymer in the antistatic layer 1, including preferred embodiments thereof, can be applied mutatis mutandis to the π-electron conjugated conductive polymer. A doping agent may also be used, and the same description of the doping agent in the antistatic layer 1, including preferred embodiments thereof, can be applied mutatis mutandis to the doping agent.

[0103] A surfactant may be used in the second layer of the present invention to improve the appearance. That is, the composition for forming the second layer may contain a surfactant. Examples of surfactants that can be used include nonionic surfactants such as polyoxyethylene octylphenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene sorbitan fatty acid ester; fluorine-based surfactants such as fluoroalkyl carboxylic acid, perfluoroalkyl carboxylic acid, perfluoroalkyl benzene sulfonic acid, perfluoroalkyl quaternary ammonium, and perfluoroalkyl polyoxyethylene ethanol; and silicone-based surfactants. The surfactants described in connection with the antistatic layer 1 can also be used. The surfactants may be used alone or in combination of two or more.

[0104] Among the surfactants, silicone surfactants and / or acetylene surfactants are preferred, and polyether-modified silicone surfactants and / or acetylene surfactants are more preferred. Furthermore, from the viewpoint of suppressing migration of the surfactant to the protected product and suppressing contamination in the manufacturing process, the surfactant is preferably an acetylene surfactant.

[0105] The composition for forming the second layer may further contain a conductive aid. The same explanation as for the conductive aid in the antistatic layer 1, including preferred embodiments thereof, can be applied to the conductive aid.

[0106] In addition to the above, the composition for forming the second layer may contain other additives such as lubricants, dyes, ultraviolet absorbers, and silane coupling agents, as needed, within the scope of not impairing the object of the present invention.

[0107] In particular, from the viewpoint of further enhancing the oligomer block property, the second layer is preferably a cured layer of a second-layer-forming composition containing at least one melamine-based crosslinking agent (hereinafter sometimes referred to as a "predetermined melamine-based crosslinking agent") selected from imino-type methylated melamine resins, methylol-type methylated melamine resins, full-ether-type methylated melamine resins, and imino-methylol-type methylated melamine resins. The content of the predetermined melamine-based crosslinking agent is preferably 5 to 100% by mass, more preferably 20 to 95% by mass, even more preferably 30 to 90% by mass, still more preferably 40 to 85% by mass, and particularly preferably 50 to 85% by mass, based on 100% by mass of the solids content of the second-layer-forming composition.

[0108] The second layer is preferably a layer having antistatic properties (antistatic layer). The antistatic layer may be a cured layer of a second-layer-forming composition containing at least the antistatic agent, but is preferably the same layer as the layer described as antistatic layer 1 (i.e., a cured layer of a composition containing a conductive polymer and a specific melamine-based crosslinking agent). In this case, the types of components contained in the composition (conductive polymer, melamine-based crosslinking agent, and optionally other antistatic agents, surfactants, binder resins, conductive assistants, solvents, and other additives) and the preferred contents of the components can be determined mutatis mutandis from the description of antistatic layer 1.

[0109] As mentioned above, the second layer does not necessarily have antistatic properties. Hereinafter, a second layer that does not have antistatic properties may be referred to as a non-antistatic layer 2. The non-antistatic layer 2 is preferably a cured layer of a second-layer-forming composition containing the crosslinking agent, and more preferably a cured layer of a second-layer-forming composition containing the specified melamine-based crosslinking agent from the viewpoint of further enhancing the oligomer block property. Furthermore, it is more preferable to use the catalyst in combination to promote the crosslinking reaction. In this case, the content of the crosslinking agent (particularly the specified melamine-based crosslinking agent) is preferably 30 to 100% by mass, more preferably 40 to 95% by mass, and even more preferably 50 to 93% by mass, based on 100% by mass of the solids content of the second-layer-forming composition.

[0110] The second layer-forming composition for forming the non-antistatic layer 2 preferably further contains the surfactant. In this case, the content of the surfactant relative to 100% by mass of the solid content of the second layer-forming composition is, for example, 0 to 40% by mass, preferably 2 to 30% by mass, and more preferably 5 to 30% by mass.

[0111] The second layer-forming composition for forming the non-antistatic layer 2 may further contain the binder resin. In this case, the content of the binder resin is preferably 0 to 100 parts by mass, more preferably 0 to 70 parts by mass, and may be 20 to 70 parts by mass, relative to 100 parts by mass of the crosslinking agent.

[0112] The total content of the crosslinking agent, surfactant, and binder resin in the 100% by mass solids content of the second layer-forming composition for forming the non-antistatic layer 2 is, for example, 80% by mass, preferably 90% by mass or more, more preferably 95% by mass or more, and may be 100% by mass.

[0113] The second layer-forming composition for forming the non-antistatic layer 2 may further contain a solvent. The inclusion of a solvent improves film-forming properties. The same explanations as for the solvent in the first layer-forming composition, including preferred embodiments thereof, can be applied mutatis mutandis. The content of the solvent can be adjusted so that the solids concentration of the second layer-forming composition is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass.

[0114] In addition to the components described above, the composition for forming the second layer used to form the non-antistatic layer 2 may contain other additives, such as a lubricant, a dye, an ultraviolet absorber, or a silane coupling agent, as needed, within the scope of not impairing the object of the present invention.

[0115] The means for laminating the second layer is not particularly limited, and known methods such as coating, vacuum deposition, and lamination can be used. However, from the viewpoint of cost, it is preferable to provide a coating liquid containing a composition for forming the second layer by coating, i.e., the second layer is a coated layer.

[0116] The method for coating and laminating the second layer on the surface of the substrate film includes coating and drying the composition for forming the second layer by gravure roll coating, reverse roll coating, knife coating, dip coating, bar coating, spin coating, etc., but there are no particular restrictions on the coating method suitable for the composition for forming the second layer. The second layer can also be formed by an in-line coating method in which the second layer is formed during the film production process, or an off-line coating method in which the second layer is formed after film production. The first and second layers may be laminated simultaneously, or may be laminated one after the other.

[0117] When the second layer is formed by the above method, the drying temperature is usually 60°C or higher and 150°C or lower, preferably 90°C or higher and 140°C or lower. A temperature of 60°C or higher is preferred from the viewpoint of improving productivity, since a short treatment time is sufficient. Furthermore, when a crosslinking agent is contained, this is preferred because the crosslinking reaction proceeds sufficiently. On the other hand, a temperature of 150°C or lower is preferred because the flatness of the film is maintained.

[0118] The thickness of the second layer of the present invention is preferably 0.005 to 1 μm. More preferably, it is 0.01 to 0.5 μm, and even more preferably, it is 0.01 to 0.2 μm. When the thickness of the second layer is 0.005 μm or more, adhesion to the pressure-sensitive adhesive is obtained, which is preferable. On the other hand, when the thickness is 1 μm or less, costs can be reduced, which is preferable.

[0119] (Protective Film) An adhesive layer can be laminated on the laminated polyester film of the present invention by applying an adhesive and curing the applied adhesive. In the present invention, even if a high-temperature treatment such as heat drying is required for the curing, an increase in haze of the laminated polyester film can be suppressed.

[0120] Any adhesive can be used without particular limitations, and the resulting laminated film can be used as a protective film. The adhesive layer can be laminated on either side of the laminated polyester film (antistatic film). When using an antistatic film having an antistatic layer on only one side (i.e., antistatic layer 1), it is preferable to have an antistatic layer on the side opposite to the side on which the adhesive layer is laminated. That is, it is preferable that the protective film has the first layer, the polyester film, the second layer, and the adhesive layer in this order.

[0121] The adhesive constituting the adhesive layer may be a known adhesive such as an acrylic adhesive, a urethane adhesive, a synthetic rubber adhesive, a natural rubber adhesive, a silicone adhesive, etc. These adhesives may be used alone or in combination of two or more.

[0122] The thickness of the adhesive layer is preferably 3 to 100 μm, and more preferably 5 to 50 μm.

[0123] Furthermore, a ceramic green sheet, a resin film, or the like may be laminated on the surface of the laminated polyester film of the present invention on which the antistatic layer 1 is formed.

[0124] This application claims the benefit of priority based on Japanese Patent Application No. 2023-170467, filed on September 29, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-170467, filed on September 29, 2023, are incorporated herein by reference.

[0125] In order to explain the present invention in detail, the following examples are given, but the present invention is not limited to these examples. The evaluation methods used in the present invention are as follows.

[0126] (Surface Resistivity) The surface resistivity of the laminated polyester film of the present invention was measured using a simple low resistivity meter (Loresta AX MCP-370, manufactured by Nitto Seiko Analytech Co., Ltd.) after 24 hours of humidity conditioning under conditions of a temperature of 23°C and a humidity of 55%, and evaluated according to the following criteria. When the surface resistivity exceeded 6 [log Ω / □], it was measured using a surface resistivity measuring device (Work Surface Tester ST-3, manufactured by Simco Japan Co., Ltd.). Tables 3A and 3B show the surface resistivity of the first layer surface, and Tables 3C and 3D show the surface resistivity of the second layer surface. ⊚: Surface resistivity is 2.0 or more and 4.0 or less [log Ω / □]; ○: Surface resistivity is more than 4.0 and 7.0 or less [log Ω / □]; △: Surface resistivity is more than 7.0 [log Ω / □].

[0127] (Total Light Transmittance, Haze) The total light transmittance and haze of the laminated polyester film of the present invention were measured using a turbidity meter (NDH7000II, manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7136, with the film measured before and after heat treatment at 140°C for 10 minutes. The difference in haze before and after heat treatment (haze of film after heat treatment - haze of film before heat treatment) was also determined and defined as Δhaze.

[0128] (Alcohol resistance) The surface of the laminated polyester film of the present invention was wiped 10 times with a Kimwipe soaked in ethanol. The surface resistivity before and after the treatment was measured in the same manner as in the measurement of surface resistivity described above. The change in appearance after the treatment was evaluated according to the following criteria. Tables 3A and 3B show the results when the wiping treatment was performed on the surface of the first layer, and Tables 3C and 3D show the results when the wiping treatment was performed on the surface of the second layer. ⊚: Almost no change ◯: Slight change Δ: Changed ×: Changed to the extent that the antistatic layer was soaked away

[0129] (Adhesion) An adhesive was applied to the second layer, and the layer was attached to a SUS plate (SUS304) and left overnight. The SUS plate was then peeled off, and the appearance of the SUS plate after peeling was evaluated according to the following criteria: ◎: No adhesive residue △: A small amount of adhesive residue ×: Some adhesive residue

[0130] Example 1 A first layer forming coating liquid and a second layer forming coating liquid were obtained in the following blending amounts. (Coating liquid for forming first layer) Water 23.06 parts by mass Isopropyl alcohol 34.59 parts by mass Conductive polymer 37.5 parts by mass Crosslinker A (manufactured by Nippon Carbide Industries Co., Ltd., imino-type methylated melamine resin, solid content concentration 80% by mass) 1.13 parts by mass Conductive assistant (NMP; N-methyl-2-pyrrolidone) 3.0 parts by mass Surfactant (manufactured by Nissin Chemical Industry Co., Ltd., Olfine EXP. 4200, solid content concentration 75% by mass) 0.53 parts by mass (Coating liquid for forming second layer) Water 27.22 parts by mass Isopropyl alcohol 40.83 parts by mass Conductive polymer 28.1 parts by mass Crosslinker C (manufactured by Nippon Carbide Industries Co., Ltd., full ether-type methylated melamine resin, solid content concentration 70% by mass) 1.13 parts by mass Conductive assistant (NMP) 2.3 parts by mass Surfactant (manufactured by Nissin Chemical Industry Co., Ltd., Dynol 604) 0.40 parts by mass

[0131] (Formation of First Layer) The obtained coating liquid for forming the first layer was applied to one side of a 75 μm-thick polyester film (Cosmoshine (registered trademark) A4360, manufactured by Toyobo Co., Ltd.) using a gravure coater so as to form a wet film thickness of 7.5 μm, and then dried and cured in a hot air drying oven at 140° C. for 30 seconds to obtain a polyester film with a first layer, which is an antistatic layer.

[0132] (Formation of Second Layer) The second layer-forming coating solution was applied to the side opposite the first layer of the polyester film obtained above using a gravure coater so that the dried film thickness would be 84 nm, and the film was dried and cured in a hot air drying oven at 140°C for 30 seconds to obtain a laminated polyester film. In the obtained laminated film, the film thickness of the first layer was 113 nm, and the film thickness of the second layer was 84 nm. The film thickness of each layer was measured using an optical interference film thickness meter (F20, Filmetrics).

[0133] Example 2 A laminated polyester film was produced in the same manner as in Example 1, except that the composition of the coating liquid for forming the first layer was changed to that shown in Table 2A.

[0134] (Examples 3 and 4) A laminated polyester film was produced in the same manner as in Example 1, except that the amount of each component in the coating liquid for forming the first layer was as shown in Table 2A and the crosslinking agent was changed to Crosslinking Agent B (manufactured by Nippon Carbide Industries Co., Ltd., methylol-type methylated melamine resin, solid content concentration 70 mass%).

[0135] (Examples 5 and 6) Laminated polyester films were produced in the same manner as in Example 1, except that the amounts of each component in the coating liquid for forming the first layer were as shown in Table 2A and the crosslinking agent was changed to Crosslinking Agent C (manufactured by Nippon Carbide Industries Co., Ltd., full-ether type methylated melamine resin, solid content concentration 70 mass%).

[0136] (Example 7) A laminated polyester film was produced in the same manner as in Example 1, except that the amount of each component in the coating liquid for forming the first layer was as shown in Table 2A, the crosslinking agent was Crosslinking Agent C (manufactured by Nippon Carbide Industries Co., Ltd., full-ether type methylated melamine resin, solid content concentration 70 mass%), and the surfactant was Dynol 604 (manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 100 mass%).

[0137] Example 8 A laminated polyester film was produced in the same manner as in Example 1, except that the amount of each component in the coating liquid for forming the first layer was as shown in Table 2B, the crosslinking agent was Crosslinking Agent C (manufactured by Nippon Carbide Industries Co., Ltd., full-ether type methylated melamine resin, solid content concentration 70% by mass), and the surfactant was Surfynol SE-F (manufactured by Nissin Chemical Industry Co., Ltd., solid content concentration 81% by mass).

[0138] (Example 9) A laminated polyester film was produced in the same manner as in Example 1, except that the amount of each component in the coating liquid for forming the first layer was as shown in Table 2B, the crosslinking agent was Crosslinking Agent C (manufactured by Nippon Carbide Industries Co., Ltd., full-ether type methylated melamine resin, solid content concentration 70 mass%), and the surfactant was 67additive (manufactured by Dow-Toray Industries, Inc., solid content concentration 100 mass%).

[0139] Examples 10 and 11 A laminated polyester film was produced in the same manner as in Example 1, except that the amounts of each component in the coating liquid for forming the first layer were as shown in Table 2B, the crosslinking agent was crosslinking agent C (manufactured by Nippon Carbide Industries Co., Ltd., full-ether type methylated melamine resin, solid content concentration 70 mass%), MD1200 (manufactured by Toyobo Co., Ltd., Vylonal MD-1200, solid content concentration 35 mass%) was added as the binder resin, and Dynol 604 was used as the surfactant.

[0140] (Comparative Example 1) A laminated polyester film was produced in the same manner as in Example 10, except that the amount of each component in the coating liquid for forming the first layer was as shown in Table 2B and the crosslinking agent was Crosslinking Agent E (manufactured by Nisshinbo Chemical Inc., carbodiimide, solid content concentration 40 mass%).

[0141] Comparative Example 2 A laminated polyester film was produced in the same manner as in Example 10, except that the amount of each component in the coating liquid for forming the first layer was as shown in Table 2B and the crosslinking agent was Crosslinking Agent F (manufactured by Baxenden, blocked isocyanate, solid content concentration 40 mass%).

[0142] Examples 13 and 14 Laminated polyester films were produced in the same manner as in Example 7, except that the types and amounts of each component in the coating liquid for forming the second layer were changed to those shown in Table 2D. Note that Dryer 900 refers to Dryer 900 (solid content concentration 50 mass%) manufactured by Hitachi Chemical Polymer Co., Ltd.

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[0154] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0155] The laminated polyester film of the present invention obtained in the examples is a laminated polyester film having a first layer, a polyester film, and a second layer in this order, and the first layer is a cured layer of a composition containing a conductive polymer and a specified melamine-based crosslinking agent, so that oligomer precipitation after heating is suppressed and a film with suppressed increase in haze is obtained. Therefore, even when an adhesive layer is laminated on this laminated polyester film and used as a protective film, it is possible to provide a protective film that can be inspected for appearance and that suppresses peel electrification and foreign matter adhesion upon peeling.

[0156] In Comparative Examples 1 and 2, since no melamine-based crosslinking agent was contained, the haze increased after heating, and the obtained films showed more oligomer precipitation during the heat drying process when the adhesive layer was processed on the side opposite the antistatic layer.

[0157] The present invention relates to an antistatic film and an adhesive film obtained by laminating an adhesive layer on an antistatic film, and particularly to a protective film for optical components (for example, components of organic EL or liquid crystal displays) and the like.

Claims

1. A laminated polyester film having a first layer, a polyester film, and a second layer in this order, the first layer being an antistatic layer, the antistatic layer being a cured layer of a composition containing a conductive polymer and a melamine-based crosslinking agent, the melamine-based crosslinking agent containing at least one selected from an imino-type methylated melamine resin, a methylol-type methylated melamine resin, a full-ether-type methylated melamine resin, and an imino-methylol-type methylated melamine resin.

2. The laminated polyester film according to claim 1, wherein the weight average degree of polymerization of the melamine-based crosslinking agent is 2.5 or less.

3. The laminated polyester film according to claim 1, wherein the composition contains a binder resin, and the content of the melamine-based crosslinking agent in a total of 100% by mass of the conductive polymer, the melamine-based crosslinking agent, and the binder resin is 40% by mass or more.

4. The laminated polyester film according to claim 1, wherein the conductive polymer comprises a π-electron conjugated conductive polymer and a doping agent.

5. The laminated polyester film according to claim 1, which has a haze of 3% or less after heating at 140° C. for 10 minutes.

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

7. The laminated polyester film according to claim 1, wherein the composition comprises an acetylene-based surfactant.

8. The laminated polyester film according to claim 1, wherein the composition further comprises a conductive assistant.

9. The laminated polyester film according to claim 1, wherein the second layer is an adhesive layer.

10. The laminated polyester film according to claim 1, wherein the second layer is a cured layer of a composition containing a melamine-based crosslinking agent, and the melamine-based crosslinking agent contains at least one selected from the group consisting of imino-type methylated melamine resin, methylol-type methylated melamine resin, full ether-type methylated melamine resin, and imino-methylol-type methylated melamine resin.

11. A protective film having the laminated polyester film according to any one of claims 1 to 10, comprising the first layer, the polyester film, the second layer, and an adhesive layer in this order.

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