JP7625837B2 - Laminated polyester film and its manufacturing method - Google Patents

Description

The present invention relates to a laminated polyester film and a method for producing the same.

Thermoplastic resin films, especially biaxially oriented polyester films, have excellent mechanical and electrical properties, dimensional stability, transparency, and chemical resistance, and are therefore widely used in many applications, including magnetic recording materials and packaging materials.

However, since polyester is generally an insulating resin, biaxially oriented polyester film has the disadvantage that it does not have antistatic properties as it is. Antistatic properties are imparted with the aim of suppressing foreign matter defects caused by dust adhesion due to static electricity, and the bias of electric charge can be neutralized by imparting electrical conductivity to the surface or inner layer of an insulating material. Among the methods for imparting antistatic properties to polyester film, the method of providing a conductive coating layer on the surface of the polyester film makes it easy to impart electrical conductivity while taking advantage of the various stable properties of the film, and various methods have been investigated to impart antistatic properties.

For example, there is a method of applying a styrene sulfonic acid copolymer, which is an ion-conductive antistatic agent (Patent Document 1), a method of combining a polythiophene-based conductive agent, which is an electron-conductive antistatic agent, with an epoxy crosslinking agent to achieve both transparency and antistatic properties in the coating film (Patent Document 2), and a method of using carbon nanotubes as an antistatic agent (Patent Document 3).

Japanese Unexamined Patent Publication No. 61-204240 JP 2004-58648 A Patent No. 4454426 JP 2010-013135 A

However, the antistatic method of Patent Document 1, which uses an ion-conductive antistatic agent, has problems in that it has insufficient conductivity and is prone to losing performance due to wear. Furthermore, the techniques of Patent Documents 2 and 3 have problems such as a decrease in antistatic properties during corona discharge treatment, which will be described later, the antistatic components being colored and prone to losing transparency, and furthermore affecting characteristics in terms of quality control.

The biaxially oriented polyester film with antistatic properties is used for applications such as protective films and cover tapes for electronic components and OLED components. Here, the problems are explained using cover tapes for electronic components as an example. When peeling the cover tape from the electronic components, the electronic components may accidentally pop out due to the peeling charge of the cover tape, resulting in the electronic components being scattered, or a discharge may occur between the charged tape and the electronic components, resulting in the electronic components being electrically destroyed. In general, when electronic components are packaged using the cover tape and carrier tape, the electronic components are inspected from the cover tape side, for example, to check whether different types are mixed in, whether the lead terminals of the IC chip are bent, or whether the filling direction is incorrect. In order to make these inspections easier, there is a strong demand for transparency in the cover tape, and highly transparent transparent polyester films and transparent polyolefin films that have been antistatically treated have been used.

However, in the process of producing the cover tape, multiple layers such as primer and sealant are formed on the conductive polyester film substrate, and friction during the processing process reduces the antistatic properties, which is an issue. Furthermore, as mentioned in Patent Document 4, for example, surface treatments such as discharge treatments may be performed to increase the adhesion between the polyester film substrate and the sealant material, but it has become clear that this treatment reduces the antistatic properties in the technology mentioned in the above patented technology.

The object of the present invention is to provide a laminated polyester film that has excellent antistatic properties and can maintain its excellent antistatic properties even after discharge treatment, and a method for producing the same.

The laminated polyester film and the method for producing the same according to the present invention have the following configurations.
(1) A laminated polyester film having a resin layer (X) on at least one surface of a polyester film, the resin layer (X) containing carbon nanotubes (a) and inorganic particles (b).
(2) The laminated polyester film according to (1), wherein when the surface resistivity of the surface of the resin layer (X) is P1 (Ω/□), the following formula 1 is satisfied:
P1<1.0 ⁹ (Formula 1)
(3) The laminated polyester film according to (2), wherein when the surface resistivity of the resin layer (X) surface after subjecting the resin layer (X) surface to a corona discharge treatment under the following conditions is defined as P2 (Ω/□), the following formula 2 is satisfied.
P2/P1≦100 (Formula 2)
[Corona discharge treatment conditions]
Corona discharge treatment was carried out under the conditions of output 100 W, discharge gap with the ceramic electrode 1 mm, electrode movement speed 6 m/min, and treatment number 5 times.
(4) The laminated polyester film according to any one of (1) to (3), wherein the inorganic particles (b) are oxide particles containing at least one element selected from the group consisting of Si, Al, Ti, Zr, Se, and Fe.
(5) The laminated polyester film according to any one of (1) to (4), wherein the content of the carbon nanotubes (a) in the resin layer (X) is 0.05% by weight or more and 5.0% by weight or less based on the entire resin layer (X).
(6) The laminated polyester film according to any one of (1) to (5), wherein the content of the inorganic particles (b) in the resin layer (X) is 5.0% by weight or more based on the entire resin layer (X).
(7) The laminated polyester film according to any one of (1) to (6), which is used for an application in which a discharge treatment is performed.
(8) A method for producing a laminated polyester film according to any one of (1) to (7), comprising the steps of applying a coating composition (x) containing carbon nanotubes (a) and inorganic particles (b) to at least one surface of a polyester film before completion of crystal orientation, and then stretching the polyester film by a uniaxial or biaxial stretching method to complete the crystal orientation of the polyester film.

According to the present invention, the laminated polyester film of the present invention has excellent antistatic properties, and furthermore, the laminated polyester film of the present invention has excellent antistatic properties even after discharge treatment.

The laminated polyester film of the present invention is a laminated polyester film having a resin layer (X) on at least one side of the polyester film, and the resin layer (X) is a laminated polyester film containing carbon nanotubes (a) (hereinafter referred to as CNT (a)) and inorganic particles (b).

<Polyester film as base material>
In the laminated polyester film of the present invention, a resin layer (X) is provided on at least one surface of a polyester film (substrate film) serving as a substrate.

In the present invention, the polyester constituting the polyester film serving as the substrate is a general term for polymers in which the main bonding chain in the main chain is an ester bond formed by polycondensation of a dicarboxylic acid and a diol. Preferred polyesters include those in which at least one dicarboxylic acid selected from ethylene terephthalate, ethylene-2,6-naphthalate, butylene terephthalate, propylene terephthalate, and 1,4-cyclohexanedimethylene terephthalate is the main constituent resin. These constituent resins may be used alone or in combination of two or more.

The substrate film used in the laminated polyester film of the present invention may be a single layer film or a laminated film of two or more layers. For example, a laminated film may be used which is a composite film having an inner layer and a surface layer, in which the inner layer does not substantially contain particles, and only the surface layer contains particles.

In addition, various additives such as antioxidants, heat stabilizers, weather stabilizers, UV absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, antistatic agents, nucleating agents, and crosslinking agents may be added to the polyester resin composition constituting the polyester film substrate to the extent that they do not impair the properties of the polyester resin composition.

It is also preferable to use a biaxially oriented polyester film as the polyester film that serves as the substrate of the present invention. Here, "biaxial orientation" refers to a film that shows a biaxially oriented pattern in wide-angle X-ray diffraction. A biaxially oriented polyester film can generally be obtained by stretching an unstretched polyester sheet by about 2.5 to 5 times in each of the longitudinal and transverse directions of the sheet, and then subjecting it to heat treatment to complete the crystal orientation.

The layer thickness of the polyester film that serves as the substrate of the present invention is appropriately selected depending on the application, but is usually preferably 10 to 500 μm, and more preferably 20 to 300 μm.

<Resin layer (X)>
The resin layer (X) of the present invention must contain CNTs (a) and inorganic particles (b).

By forming such a resin layer (X), a laminated polyester film having the resin layer (X) on at least one side of the polyester film has excellent antistatic properties and also has excellent antistatic properties after performing a discharge treatment.

The resin layer (X) used in the laminated polyester film of the present invention is described below.

(1) Resin layer (X)
The resin layer (X) of the present invention is required to contain CNT (a) and inorganic particles (b). It is more preferable that the resin layer (X) satisfies the following formula 1 when the surface resistivity of the resin layer (X) surface is P1 (Ω/□).
P1<1.0×10 ⁹ (Formula 1)
The method for measuring the surface resistivity of the resin layer (X) surface before and after the corona discharge treatment test will be described later.

When P1 is 1.0×10 ⁹ or more, the antistatic property is deteriorated, and there is a practical problem when used for a protective film or cover tape for electronic parts that require a high level of antistatic property. P1 is preferably 10×1.0 ⁸ or less, and more preferably 1.0×10 ⁷ or less.

As a method for making P1 satisfy formula 1, there is a method of incorporating CNT(a) into resin layer (X), preferably a method of forming a resin layer from coating composition (x) containing CNT(a) to obtain resin layer (X).

Furthermore, it is further preferable that the resin layer (X) of the present invention satisfies the following formula 2 when the surface resistivity of the resin layer (X) surface after subjecting the resin layer (X) surface to a corona discharge treatment under the following conditions is defined as P2 (Ω/□).
P2/P1≦100 (Formula 2)
[Corona discharge treatment conditions] Corona discharge treatment was carried out under the following conditions: output 100 W, discharge gap with ceramic electrode 1 mm, electrode movement speed 6 m/min, and treatment number 5 times.

The corona discharge treatment method and the method for measuring the surface resistivity of the resin layer (X) surface before and after the corona discharge treatment test will be described later.

If P2/P1 exceeds 100, this indicates that the antistatic properties after discharge treatment such as corona discharge treatment or plasma discharge treatment are deteriorated, and this may cause practical problems when used in applications where surface treatment such as discharge treatment is performed to improve the adhesiveness of the sealant material. In addition, P2/P1 is preferably 0.1 or more and 100 or less. More preferably, it is 0.1 or more and 50 or less.

A method for making P2/P1 satisfy formula 2 includes a method of incorporating CNT (a) and inorganic particles (b) into resin layer (X), preferably a method of forming a resin layer from a coating composition (x) containing CNT (a) and inorganic particles (b) to obtain resin layer (X).

(2) CNT (a)
In the laminated polyester film of the present invention, the resin layer (X) must contain CNT (a). In the present invention, CNT refers to a seamless tube in which a honeycomb-structured graphene sheet composed only of carbon atoms is rolled into a cylindrical shape. A graphene sheet wound in one layer is called a single-walled CNT, a graphene sheet wound in two layers is called a double-walled CNT, and a graphene sheet wound in three or more layers is called a multi-walled CNT. The CNT (a) used in the present invention is preferably a straight or bent single-walled CNT, a straight or bent double-walled CNT, a straight or bent multi-walled CNT, or a combination thereof.

The honeycomb structure refers to a network structure that is mainly composed of six-membered rings, but due to the structure of CNTs, the bent parts of the tube or the closed parts of the cross section may have ring structures other than six-membered rings, such as five-membered rings or seven-membered rings.

Of the above CNTs, the CNT (a) used in the present invention is preferably a straight or bent single-walled CNT or a straight and/or bent double-walled CNT from the viewpoint of electrical conductivity. Single-walled CNT and double-walled CNT are excellent in terms of dispersibility in solvents, durability, and manufacturing costs. On the other hand, multi-walled CNTs with three or more layers are excellent in terms of dispersibility and manufacturing costs, but may not provide sufficient electrical conductivity.

In addition, the CNT (a) used in the present invention preferably has a diameter of 1 nm or more. In addition, the diameter of CNT (a) is preferably 50 nm or less, more preferably 10 nm or less. If the diameter exceeds 50 nm, the CNT will have a multilayer structure of three or more layers, and the conductive path may diverge between the layers, resulting in a decrease in conductivity. In addition, if a CNT with a diameter of more than 50 nm is used to achieve the same conductivity as a CNT with a diameter of 50 nm or less, a large amount of CNT is required, which not only significantly impairs the transparency of the conductive film, but also makes it difficult to achieve sufficient conductivity even if the amount is increased without limit. Furthermore, if the diameter of the CNT exceeds 50 nm, the adhesiveness and abrasion resistance of the conductive layer may be reduced. On the other hand, it is difficult to manufacture CNT with a diameter of less than 1 nm.

The aspect ratio of the CNT (a) used in the present invention is preferably 100 or more. The aspect ratio of the CNT is preferably 5000 or less. By setting the aspect ratio of the CNT within the above range, the electrical conductivity of the resin layer (X) can be increased. When the aspect ratio of the CNT is set within the above range, when the in-line coating method described below is used in forming the resin layer (X), the CNTs are appropriately loosened in the stretching process, and a network can be formed in which the conductive paths between the CNTs are not broken and sufficient gaps are secured between the CNTs. When such a network structure is formed, it is possible to increase the transparency of the film while exhibiting good electrical conductivity properties.

The aspect ratio is the length of the carbon tube (nm) divided by the diameter of the carbon tube (nm) (carbon tube length (nm)/carbon tube diameter (nm)).

CNTs with such properties can be obtained by known manufacturing methods such as chemical vapor deposition, catalytic vapor phase growth, arc discharge, and laser evaporation. When producing CNTs, fullerenes, graphite, and amorphous carbon are simultaneously produced as by-products, and catalytic metals such as nickel, iron, cobalt, and yttrium also remain, so it is preferable to remove these impurities and purify the CNTs. To remove impurities, ultrasonic dispersion treatment is effective in combination with acid treatment using nitric acid, sulfuric acid, etc., and separation using a filter is even more preferable in terms of improving purity.

Single-walled CNTs and double-walled CNTs are generally thinner than multi-walled CNTs, and if uniformly dispersed, they can secure a larger number of conductive paths per unit volume, resulting in high conductivity. However, depending on the manufacturing method, a large amount of semiconducting CNTs may be produced as a by-product, and in such cases, it becomes necessary to selectively manufacture or select conductive CNTs. Multi-walled CNTs generally exhibit conductivity, but if the number of layers is too large, the number of conductive paths per unit weight decreases. Therefore, even when using multi-walled CNTs, it is preferable that the CNT diameter is 50 nm or less, more preferably 20 nm or less, and even more preferably 10 nm or less. In addition, when using single-walled CNTs or double-walled CNTs, due to their structure, it is preferable that the diameter is 20 nm or less, and even more preferably 10 nm or less, from the viewpoint of conductivity.

The content of CNT (a) in the resin layer (X) used in the present invention is preferably 0.05% by weight or more and 10.0% by weight or less, based on the entire resin layer (X). More preferably, it is 0.5% by weight or more and 10% by weight or less, and even more preferably, it is 1.0% by weight or more and 5.0% by weight or less. If it is less than 0.05% by weight, the resin layer (X) does not have sufficient antistatic performance. If it exceeds 10.0% by weight, the cohesive force due to the intermolecular force between the CNTs increases, and the dispersibility of the CNTs decreases, which may deteriorate the transparency of the resin layer (X) and the coating appearance.

(3) Inorganic particles (b)
In the present invention, it is necessary that the resin layer (X) contains inorganic particles (b) in addition to the CNTs (a). The inorganic particles (b) used in the present invention include Si, Al, Ti, Examples of the oxide particles include oxide particles containing at least one element selected from the group consisting of Zr, Se and Fe.

Representative examples of the inorganic particles (b) used in the present invention include _SiO2 , _Al2O3 , _TiO2 , _{and ZrO2} .

When CNT (a) and inorganic particles (b) are contained in the resin layer (X) of the laminated polyester film of the present invention, the electrical conductivity of the resin layer (X) can be greatly improved (the surface resistivity value can be greatly reduced). This is presumably because the inclusion of inorganic particles (b) in the resin layer (X) reduces the volume of space in which CNTs can exist in the resin (X) layer, thereby improving the density of the CNTs and making it easier for the CNTs to form a network with each other, which makes it easier to form a conductive path and improves the antistatic properties. In addition, as a result of intensive research by the present inventors, it was surprisingly found that when CNT (a) and inorganic particles (b) are contained in the resin layer (X) of the laminated polyester film, the decrease in antistatic properties can be suppressed even when a discharge treatment is performed. Although it is not clear how this effect is achieved, it is presumed that when a discharge treatment is performed on a resin layer (X) containing CNTs, the CNTs (a) are damaged and the conductive paths of the CNTs (a) are destroyed, whereas when inorganic particles (b) are present, the inorganic particles (b) are densely arranged around the CNTs (a), making the CNTs (a) less susceptible to damage and resulting in excellent antistatic properties even after the discharge treatment.

In addition, the content of inorganic particles (b) in the resin layer (X) is preferably 5.0% by weight or more based on the entire resin layer (X). More preferably, it is 10.0% by weight or more, and even more preferably, it is 20.0% by weight or more. Such a content is preferable because it is easy to make the surface resistance value P1 (Ω/□) of the resin layer (X) surface 1.0×10 ⁹ or less. It is also preferable because it is easy to make P2/P1 100 or less. On the other hand, from the viewpoint of transparency and processability, it is preferable that it is 25.0% by weight or less.

The inorganic particles (b) used in the laminated polyester film of the present invention are preferably a composition (bc) having an acrylic resin (c) on a part or all of the surface of the inorganic particles (b). By using a composition (bc) having an acrylic resin (c), the inorganic particles (b) in the resin layer (X) of the laminated polyester film can be nano-dispersed, which is preferable because it is highly effective in suppressing damage to the CNTs during discharge treatment.

The method of forming composition (bc) having acrylic resin (c) on all or part of the surface of inorganic particles (b) is not particularly limited, but examples include a method of surface treating inorganic particles (b) with acrylic resin (c) described below. Specific examples include the following methods (i) to (iv). In the present invention, surface treatment refers to a treatment in which acrylic resin (c) is adsorbed and attached to all or part of the surface of inorganic particles (b) containing a specific element.

(i) A method in which a mixture of inorganic particles (b) and acrylic resin (c) is mixed in advance, added to a solvent, and then dispersed.

(ii) A method of adding inorganic particles (b) and acrylic resin (c) in that order to a solvent and dispersing them.

(iii) A method in which inorganic particles (b) and acrylic resin (c) are pre-dispersed in a solvent and the resulting dispersion is mixed.

(iv) A method in which inorganic particles (b) are dispersed in a solvent, and then acrylic resin (c) is added to the resulting dispersion.

Any of these methods can achieve the desired effect.

As dispersion equipment, a dissolver, a high-speed mixer, a homomixer, a meader, a ball mill, a roll mill, a sand mill, a paint shaker, an SC mill, an annular mill, a pin mill, etc. can be used.

The dispersion method involves using the above device to rotate the rotating shaft at a peripheral speed of 5 to 15 m/s. The rotation time is 5 to 10 hours.

In addition, it is more preferable to use dispersion beads such as glass beads during dispersion in order to improve dispersibility. The bead diameter is preferably 0.05 to 0.5 mm, more preferably 0.08 to 0.5 mm, and particularly preferably 0.08 to 0.2 mm.

Methods for mixing and stirring include shaking the container by hand, using a magnetic stirrer or stirring blade, irradiating with ultrasound, or dispersing with vibration.

The presence or absence of acrylic resin (c) adsorbed/attached to all or part of the surface of inorganic particles (b) can be confirmed by the following analytical method. The measurement object is centrifuged (rotation speed 3,0000 rpm, separation time 30 minutes) using a Hitachi tabletop ultracentrifuge (manufactured by Hitachi Koki Co., Ltd.: CS150NX) to settle inorganic particles (b) (and acrylic resin (c) adsorbed to the surface of inorganic particles (b)), and the supernatant liquid is removed and the sediment is concentrated and dried. The concentrated and dried sediment is analyzed by X-ray photoelectron spectroscopy (XPS) to confirm the presence or absence of acrylic resin (c) on the surface of inorganic particles (b). When it is confirmed that acrylic resin (c) is present on the surface of inorganic particles (b) in an amount of 1% by weight or more relative to the total weight of inorganic particles (b) of 100% by weight, it is deemed that acrylic resin (c) is adsorbed/attached to the surface of gold inorganic particles (b).

(4) Resin (c)
In the present invention, it is preferable that the resin layer (X) contains a resin (c) containing at least one resin selected from the group consisting of a polyester resin, an acrylic resin, a urethane resin, and an acrylic urethane copolymer resin, from the viewpoints of improving the film-forming properties of the resin layer and maintaining the antistatic properties.

The polyester resin used in the resin layer (X) in the present invention may be, for example, a polyester having a skeleton similar to that of the polyester exemplified as the polyester constituting the polyester film serving as the substrate described above.

As a method for obtaining a laminated polyester film having a resin layer (X) containing the CNT (a), inorganic particles (b), and resin (c), for example, a method of applying a coating composition (x) containing the CNT (a), inorganic particles (b), and resin (c) to at least one side of a polyester film and then forming a resin layer (X) can be mentioned. When the resin (c) contains a polyester resin and water is used as a solvent for the coating composition (x), it is preferable that the polyester resin is copolymerized with a compound containing a carboxylate group or a compound containing a sulfonate group in order to improve the adhesiveness of the polyester resin or to facilitate the water solubility of the polyester resin. Examples of compounds containing a carboxylate group include trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, 4-methylcyclohexene-1,2,3-tricarboxylic acid, trimesic acid, 1,2,3,4-butanetetracarboxylic acid, 1,2,3,4-pentanetetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexene-1,2-di ... and 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid. furyl)-3-cyclohexene-1,2-dicarboxylic acid, cyclopentane tetracarboxylic acid, 2,3,6,7-naphthalene tetracarboxylic acid, 1,2,5,6-naphthalene tetracarboxylic acid, ethylene glycol bistrimellitate, 2,2',3,3'-diphenyl tetracarboxylic acid, thiophene-2,3,4,5-tetracarboxylic acid, ethylene tetracarboxylic acid, or alkali metal salts, alkaline earth metal salts, and ammonium salts thereof can be used, but are not limited to these.

Examples of the compound containing a sulfonate group include, but are not limited to, sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, sulfo-p-xylylene glycol, 2-sulfo-1,4-bis(hydroxyethoxy)benzene, and alkali metal salts, alkaline earth metal salts, and ammonium salts thereof.
Preferred polyester resins include copolymers using terephthalic acid, isophthalic acid, sebacic acid, 5-sodium sulfoisophthalic acid, trimellitic acid, pyromellitic acid, 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid as the acid component and ethylene glycol, diethylene glycol, 1,4-butanediol, or neopentyl glycol as the glycol component.

The acrylic resin used in the present invention refers to a resin obtained by copolymerizing an acrylic monomer, which will be described later, and other monomers as necessary, by a known acrylic resin polymerization method such as emulsion polymerization or suspension polymerization.

Examples of acrylic monomers used in acrylic resins include alkyl acrylates (alkyl groups include methyl, ethyl, n-propyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, cyclohexyl, etc.), alkyl methacrylates (alkyl groups include methyl, ethyl, n-propyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, cyclohexyl, etc.), hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, and 2-hydroxypropyl methacrylate, acrylamide, methacrylamide, N-methyl methacrylamide, N-methyl acrylamide, Examples of such monomers include amide group-containing monomers such as N-methylolacrylamide, N-methylolmethacrylamide, N,N-dimethylolacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, and N-phenylacrylamide; amino group-containing monomers such as N,N-diethylaminoethylacrylate and N,N-diethylaminoethylmethacrylate; glycidyl group-containing monomers such as glycidylacrylate and glycidylmethacrylate; and monomers containing a carboxyl group or a salt thereof, such as acrylic acid, methacrylic acid, and salts thereof (sodium salt, potassium salt, ammonium salt, etc.).

These acrylic monomers can also be used in combination with other monomers. Examples of other monomers that can be used include glycidyl group-containing monomers such as allyl glycidyl ether, monomers containing acid anhydride groups such as maleic anhydride and itaconic anhydride, vinyl isocyanate, allyl isocyanate, styrene, vinyl methyl ether, vinyl ethyl ether, vinyl trisalkoxysilane, alkyl maleic acid monoesters, alkyl fumaric acid monoesters, acrylonitrile, methacrylonitrile, alkyl itaconic acid monoesters, vinylidene chloride, vinyl acetate, vinyl chloride, and vinylpyrrolidone.

One or more acrylic monomers are polymerized, but when other monomers are used in combination, it is preferable that the proportion of acrylic monomers in the total monomers is 50% by weight or more, and preferably 70% by weight or more.

The urethane resin used in the present invention refers to a resin obtained by reacting a polyhydroxy compound with a polyisocyanate compound by a known urethane resin polymerization method such as emulsion polymerization or suspension polymerization.

Examples of polyhydroxy compounds include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene glycol, hexamethylene glycol, tetramethylene glycol, 1,5-pentanediol, diethylene glycol, triethylene glycol, polycaprolactone, polyhexamethylene adipate, polyhexamethylene sebacate, polytetramethylene adipate, polytetramethylene sebacate, trimethylolpropane, trimethylolethane, pentaerythritol, polycarbonate diol, and glycerin.

Furthermore, as described above, in the laminated polyester film of the present invention, it is preferable that the inorganic particles (b) are a composition (bc) having an acrylic resin (c) on a part or all of their surface. By using a composition (bc) having an acrylic resin (c), the inorganic particles (b) in the laminated polyester film can be nano-dispersed, and the transparency of the laminated polyester film can be maintained.

The acrylic resin (c) in the present invention is preferably a resin having a monomer unit (c 1 ) represented by formula ( ₁ ), a monomer unit (c 2 ) represented by formula ( ₂ ), and a monomer unit (c ₃ ) represented by formula (3).

(In formula (1), R ₁ group represents a hydrogen atom or a methyl group, and n represents an integer of 9 or more and 34 or less).

(In formula (2), the _R2 group represents a hydrogen atom or a methyl group, and the _R4 group represents a group containing two or more saturated carbon rings).

(In formula (3), the _R3 group represents a hydrogen atom or a methyl group, and the _R5 group represents a hydroxyl group, a carboxyl group, a tertiary amino group, a quaternary ammonium salt group, a sulfonic acid group, or a phosphate group.)
Here, the acrylic resin (c) in the present invention is preferably a resin having a monomer unit (d ₁ ) represented by formula (1).

In formula (1), when an acrylic resin having a monomer unit with n less than 9 is used, the dispersibility of the inorganic particles (b) in the aqueous solvent (details of the aqueous solvent will be described later) becomes unstable. When an acrylic resin having a monomer unit with n less than 9 in formula (1) is used, the inorganic particles (b) may aggregate violently in the coating composition, and in some cases, the inorganic particles (b) may settle in the aqueous solvent. As a result, the effect of suppressing damage to the CNT during discharge treatment may be impaired. On the other hand, an acrylic resin having a monomer unit with n greater than 34 in formula (1) has extremely low solubility in aqueous solvents, so that aggregation of the acrylic resin is likely to occur in the aqueous solvent. Such aggregates are larger than the wavelength of visible light, so that it may not be possible to obtain a laminated polyester film with good transparency. By using a resin having a monomer unit (c ₁ ) represented by the above formula (1), the inorganic particles (b) are dispersed in an aqueous solvent with appropriate interactions, while after drying, the inorganic particles (b) have anisotropy and finely aggregate at the nano-order level in the resin layer (X) of the laminated polyester film, thereby suppressing exposure of the CNTs (a) and improving corona resistance.

In order for the acrylic resin (c) in the present invention to have the monomer unit (c ₁ ) represented by formula (1), it is necessary to use a (meth)acrylate monomer (c ₁ ') represented by the following formula (4) as a raw material and polymerize it.

The (meth)acrylate monomer (c ₁ ') is preferably a (meth)acrylate monomer represented by formula (4) in which n is an integer of 9 or more and 34 or less, more preferably a (meth)acrylate monomer in which n is an integer of 11 or more and 32 or less, and even more preferably a (meth)acrylate monomer in which n is an integer of 13 or more and 30 or less.

The (meth)acrylate monomer (c ₁ ') is not particularly limited as long as it is a (meth)acrylate monomer in which n in formula (4) is 9 or more and 34 or less, but specific examples thereof include decyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, 1-methyltridecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate, eicosyl (meth)acrylate, docosyl (meth)acrylate, tetracosyl (meth)acrylate, triacontyl (meth)acrylate, etc., with dodecyl (meth)acrylate and tridecyl (meth)acrylate being particularly preferred. These may be used alone or in a mixture of two or more.

It is also important that the acrylic resin (c) in the present invention is a resin having the monomer unit (c ₂ ) represented by the above formula (2).

In formula (2), if an acrylic resin having a monomer unit containing only one saturated carbon ring is used, the function as a steric hindrance becomes insufficient, and the inorganic particles (b) may aggregate or settle in the coating composition, or in some cases, the inorganic particles (b) may settle in the aqueous solvent. As a result, the transparency of the laminated polyester film may be impaired.

Since such aggregates have a wavelength larger than that of visible light, it may be impossible to obtain a laminated polyester film having good transparency. In order for the acrylic resin (c) in the present invention to have the monomer unit (c ₂ ) represented by formula (2), it is necessary to use a (meth)acrylate monomer (c') represented by the following formula (5) as a raw material and polymerize it.

Examples of the (meth)acrylate monomer ( _c2 ') represented by formula (5) include compounds having various cyclic structures such as a bridged condensed cyclic structure (having a structure in which two or more rings are bonded to each other, each sharing two elements) and a spirocyclic structure (having a structure in which two cyclic structures are bonded to each other, each sharing one carbon element), specifically, a bicyclo, tricyclo, or tetracyclo group, and among these, a (meth)acrylate containing a bicyclo group is particularly preferred from the viewpoint of compatibility with the binder.

Examples of the (meth)acrylate containing a bicyclo group include isobornyl (meth)acrylate, bornyl (meth)acrylate, disilocyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, adamantyl (meth)acrylate, and dimethyladamantyl (meth)acrylate, with isobornyl (meth)acrylate being particularly preferred.

Furthermore, the acrylic resin (c) in the present invention is preferably a resin having a monomer unit (c ₃ ) represented by the above formula (3).

When an acrylic resin having a monomer unit in which the _R5 group in formula (3) does not have any of a hydroxyl group, a carboxyl group, a tertiary amino group, a quaternary ammonium group, a sulfonic acid group, and a phosphate group is used, the compatibility of the acrylic resin in an aqueous solvent becomes insufficient, and the acrylic resin may precipitate in the coating composition, and the inorganic particles (b) may aggregate or settle accordingly, or the inorganic particles (b) may aggregate during the drying process.

Such aggregates are larger than the wavelength of visible light, and therefore it may be impossible to obtain a laminated polyester film having good transparency. In order for the acrylic resin (c) in the present invention to have the monomer unit (c ₃ ) represented by formula (3), it is necessary to use a (meth)acrylate monomer (c ₃ ') represented by formula (6) as a raw material and polymerize it.

Examples of the (meth)acrylate monomer (c ₃ ') represented by formula (6) include the following compounds.

Examples of (meth)acrylate monomers having a hydroxyl group include monoesters of polyhydric alcohols such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2,3-dihydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and polyethylene glycol mono(meth)acrylate with (meth)acrylic acid, or compounds obtained by ring-opening polymerization of the monoesters with ε-caprolactone, with 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate being particularly preferred.

Examples of (meth)acrylate monomers having a carboxyl group include α,β-unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid, or half esters of hydroxyalkyl (meth)acrylates and acid anhydrides, with acrylic acid and methacrylic acid being particularly preferred.

Tertiary amino group-containing monomers include N,N-dialkylaminoalkyl (meth)acrylates such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, and N,N-dimethylaminopropyl (meth)acrylate, and N,N-dialkylaminoalkyl (meth)acrylamides such as N,N-dimethylaminoethyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylamide, and N,N-dimethylaminopropyl (meth)acrylamide, with N,N-dimethylaminoethyl (meth)acrylate being particularly preferred.

As the quaternary ammonium base-containing monomer, a quaternary ammonium base-containing monomer obtained by reacting the above-mentioned tertiary amino group-containing monomer with a quaternizing agent such as epihalohydrin, benzyl halide, or alkyl halide is preferable. Specific examples include (meth)acryloyloxyalkyltrialkylammonium salts such as 2-(methacryloyloxy)ethyltrimethylammonium chloride, 2-(methacryloyloxy)ethyltrimethylammonium bromide, and 2-(methacryloyloxy)ethyltrimethylammonium dimethylphosphate; (meth)acryloylaminopropyltrimethylammonium chloride and (meth)acryloylaminoalkyltrialkylammonium salts such as methacryloylaminopropyltrimethylammonium bromide; tetraalkyl(meth)acrylates such as tetrabutylammonium(meth)acrylate; and trialkylbenzylammonium(meth)acrylates such as trimethylbenzylammonium(meth)acrylate. In particular, 2-(methacryloyloxy)ethyltrimethylammonium chloride is preferable.

Examples of sulfonic acid group-containing monomers include (meth)acrylamide-alkanesulfonic acids such as butylacrylamidosulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid, and sulfoalkyl (meth)acrylates such as 2-sulfoethyl (meth)acrylate, with 2-sulfoethyl (meth)acrylate being particularly preferred.

Examples of phosphate group-containing acrylic monomers include acid phosphooxyethyl (meth)acrylate, with acid phosphooxyethyl (meth)acrylate being particularly preferred.

Among these, it is particularly preferred that the acrylic resin (c) is a resin having a monomer unit ( _c3 ) represented by the above formula (3), and the _R5 group in formula (3) is a hydroxyl group or a carboxyl group, since this has a high adsorptivity with the inorganic particles (b) described later and can form a stronger film.

The acrylic urethane copolymer resin used in the present invention is not particularly limited as long as it is a resin in which an acrylic resin and a urethane resin are copolymerized, but an acrylic urethane copolymer resin in which an acrylic resin is used as a skin layer and a urethane resin is used as a core layer is particularly preferred because it has excellent adhesion to the laminate that is laminated on the present laminated polyester film.

The laminated polyester film must have a resin layer (X) on at least one side of the polyester film (substrate film) that serves as the substrate, but may also have a resin layer (X) on the other side, or may have a resin layer (Y) different from the resin layer (X). The resin constituting the resin layer (Y) is not particularly limited, but examples thereof include polyester resin, acrylic resin, urethane resin, epoxy resin, amide resin, and copolymer resins of these resins. These resins may also be used alone or in combination. By providing a resin layer on the opposite side to the resin layer (X), for example, the resin layer on the opposite side to the resin layer (X) of the laminated polyester film of the present invention may contain slippery particles, which further improves the handling properties of the film, and is therefore preferred.

(5) Crosslinking agent (d)
The laminated polyester film of the present invention may contain a crosslinking agent (d) in addition to the CNT (a), inorganic particles (b), and resin (c) in the resin layer (X). When formed from a coating composition containing the crosslinking agent (d), the resin layer (X) of the laminated polyester film has a dense crosslinked structure, which is preferable because it has excellent stability of antistatic performance. Examples of the crosslinking agent (d) include melamine compounds, oxazoline compounds, carbodiimide compounds, isocyanate compounds, and epoxy compounds.

As the melamine-based compound, for example, melamine, a methylolated melamine derivative obtained by condensing melamine with formaldehyde, a compound partially or completely etherified by reacting a lower alcohol with methylolated melamine, and a mixture thereof can be used. Specifically, a compound having a triazine and a methylol group is particularly preferable. In the present invention, the melamine compound means a component derived from a melamine compound when the melamine compound described below forms a crosslinked structure with a urethane resin, an acrylic resin, an oxazoline compound, a carbodiimide compound, an isocyanate compound, an epoxy compound, or the like. In addition, the melamine-based compound may be either a monomer or a condensate consisting of a dimer or more polymer, or a mixture thereof. As the lower alcohol used for etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol, etc. can be used. The groups include imino groups, methylol groups, or alkoxymethyl groups such as methoxymethyl groups and butoxymethyl groups in one molecule, such as imino group-type methylated melamine resins, methylol group-type methylated melamine resins, methylol group-type methylated melamine resins, and fully alkylated methylated melamine resins. Among these, methylol melamine resins are the most preferred. Furthermore, to promote the thermal curing of melamine compounds, an acid catalyst such as p-toluenesulfonic acid may be used.

When such a melamine compound is used, not only does the melamine compound self-condense, but the reaction between the hydroxyl and carboxyl groups in the acrylic resin and the melamine compound also proceeds, resulting in a stronger layer and a film with excellent antistatic stability.

The term "oxazoline compound" refers to the oxazoline compound described below, or a component derived from the oxazoline compound when the oxazoline compound forms a crosslinked structure with a urethane resin, an acrylic resin, a melamine compound, an isocyanate compound, or a carbodiimide compound. The oxazoline compound is not particularly limited as long as it has an oxazoline group as a functional group in the compound, but is preferably an oxazoline group-containing copolymer obtained by copolymerizing at least one monomer containing an oxazoline group and at least one other monomer.

As monomers containing an oxazoline group, 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, 2-isopropenyl-5-ethyl-2-oxazoline, etc. can be used, and one or a mixture of two or more of these can also be used. Among them, 2-isopropenyl-2-oxazoline is suitable because it is easily available industrially.

In the oxazoline compound, the at least one other monomer used for the monomer containing an oxazoline group is not particularly limited as long as it is a monomer that can be copolymerized with the monomer containing an oxazoline group. For example, acrylic acid esters or methacrylic acid esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, etc., unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, etc., acrylonitrile, methacrylic acid, etc., and the like can be used. Unsaturated nitriles such as lylonitrile, unsaturated amides such as acrylamide, methacrylamide, N-methylol acrylamide, and N-methylol methacrylamide, vinyl esters such as vinyl acetate and vinyl propionate, vinyl ethers such as methyl vinyl ether and ethyl vinyl ether, olefins such as ethylene and propylene, halogen-containing α,β-unsaturated monomers such as vinyl chloride, vinylidene chloride, and vinyl fluoride, and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene can be used, and mixtures of one or more of these can also be used.

In the present invention, the carbodiimide compound refers to the carbodiimide compound described below, or a component derived from the carbodiimide compound when the carbodiimide compound forms a crosslinked structure with a urethane resin, an acrylic resin, a melamine compound, an isocyanate compound, or an oxazoline compound. The carbodiimide compound is not particularly limited as long as it has one or more carbodiimide groups or cyanamide groups in a tautomeric relationship therewith as functional groups in the compound.

A known technique can be applied to the production of a carbodiimide compound, and generally, a carbodiimide compound is obtained by polycondensing a diisocyanate compound in the presence of a catalyst. As the diisocyanate compound that is the starting material for the carbodiimide compound, an aromatic, aliphatic, or alicyclic diisocyanate can be used, and specifically, tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, etc. can be used.

(6) CNT dispersant (e)
In the present invention, the coating composition (x) for forming the resin layer (X) preferably contains a CNT dispersant (e) in addition to the CNTs (a) and inorganic particles (b).

Examples of CNT dispersants (e) include water-soluble cellulose and/or water-soluble cellulose derivatives, polystyrene sulfonates, polyvinylpyrrolidone polymers, etc. Among these, water-soluble cellulose and/or water-soluble cellulose derivatives are preferred.

Representative examples of polystyrene sulfonates used in the present invention include sodium polystyrene sulfonate and calcium polystyrene sulfonate.

A representative example of the polyvinylpyrrolidone-based polymer used in the present invention is polyvinylpyrrolidone.

A representative example of the water-soluble cellulose derivative used in the present invention is a metal salt of carboxycellulose. Here, carboxycellulose is cellulose in which the hydroxyl group of the glucopyranose monomer constituting the cellulose skeleton is replaced with a carboxyl group (when the glucopyranose monomer has multiple hydroxyl groups, at least one of the hydroxyl groups is replaced with a carboxyl group). Here, the term "carboxyl group" refers not only to a carboxyl group in the narrow sense, but also to a carboxyalkyl group. By using a metal salt of carboxycellulose, the water solubility can be dramatically increased and the CNT dispersion ability can be improved. Among the metal salts of carboxycellulose, metal salts of carboxyalkylcellulose are preferred because of their good water solubility, and metal salts of carboxymethylcellulose, which are inexpensive and widely used industrially, are more preferred, and among these, sodium carboxymethylcellulose and calcium carboxymethylcellulose are preferred. Sodium carboxymethylcellulose is particularly preferred.

By including the above-mentioned CNT dispersant (e) in the coating composition (x), the CNTs are easily dissolved in water, and the CNT dispersant (e) is uniformly dispersed in the solvent in the vicinity of the CNTs, suppressing aggregation due to the affinity between CNTs. In other words, a coating composition containing stable and finely dispersed CNTs can be produced.

In the present invention, the CNT dispersant (e) is preferably 0.1% by weight or more and 15% by weight or less based on the weight of the solid content in the coating composition (x). More preferably, it is 0.1% by weight or more and 7.5% by weight. By making the content of the CNT dispersant (e) 0.1% by weight or more, the CNT (a) in the coating composition (x) and the resin layer (X) can be uniformly dispersed, which is preferable in terms of transparency and antistatic properties.

In addition, in the present invention, the ratio of the content of CNT (a) and CNT dispersant (e) in the coating composition (x), (e)/(a), is preferably 0.5 or more and 15 or less. More preferably, it is 0.5 or more and 5 or less. By making (e)/(a) 0.5 or more, the CNTs do not aggregate when mixed with the resin (c) or the crosslinking agent (d), and the coating composition (x) can be stably prepared. Furthermore, if (e)/(a) exceeds 15.0, the amount of CNT dispersant (e) becomes excessive relative to the CNT (a), and the antistatic properties of the resin layer (X) may be deteriorated.

(7) Paint composition (x)
The laminated polyester film of the present invention can be prepared, for example, by coating a coating composition ( The laminate can be prepared by laminating a resin layer (X) on a polyester film using a resin (x).

The coating composition (x) containing CNT (a) and inorganic particles (b) may contain a small amount of water-soluble organic solvent in order to improve the storage stability and handling of the coating agent. Examples of the water-soluble organic solvent include water-soluble alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, water-soluble ketones such as acetone, and water-soluble ethers such as methyl cellosolve, cellosolve, butyl cellosolve, carbitol, and butyl carbitol. These can be used alone or in combination. The content of the water-soluble organic solvent is preferably 10% by weight or less, more preferably 7% by weight or less, and even more preferably 5% by weight or less, based on the total amount of the coating composition (x) in terms of explosion resistance and environmental pollution.

Methods for obtaining a laminated polyester film having a resin layer (X) formed from a coating composition (x) containing CNT (a) and inorganic particles (b) include a method of laminating a resin layer (X) on a polyester film. Among these, a method of coating (applying) a coating composition (x) constituting the resin layer (X) on a polyester film and laminating it is preferable. Coating methods for the coating agent include a method of coating in a separate process from the polyester film manufacturing process, that is, a so-called offline coating method, and a so-called in-line coating method, in which coating is performed during the polyester film manufacturing process to obtain a laminated polyester film in which the resin layer (X) is laminated on the polyester film at once. However, in terms of cost and uniformity of the coating thickness, it is preferable to adopt the in-line coating method, and the solvent of the coating liquid used in this case is preferably water-based from the viewpoints of environmental pollution and explosion resistance, and the most preferable embodiment is to use water.

For example, a polyester film that has not yet been oriented by melt extrusion is stretched in the longitudinal direction by about 2.5 to 5 times, and the coating composition (x) that constitutes the resin layer (X) is continuously applied to the uniaxially stretched film. The coated film is dried while passing through a stepwise heated zone, and is stretched by about 2.5 to 5 times in the width direction. It can also be obtained by a method (in-line coating method) in which the film is continuously guided to a heating zone at 150 to 250°C to complete the crystalline orientation.

In the present invention, the crosslinking reaction between the resin (c) and the crosslinking agent (d) is promoted by performing high-temperature heat treatment in the heating zone, improving the stability of the antistatic performance of the resin layer (X). Therefore, in terms of performance, it is preferable to adopt the in-line coating method.

Methods for applying a coating composition (water-based coating agent) using water as a solvent include, for example, reverse coating, spray coating, bar coating, gravure coating, rod coating, and die coating.

Before applying the coating composition (x), it is preferable to subject the surface of the polyester film substrate to a corona discharge treatment or the like. This improves the adhesion between the polyester film and the resin layer (X) and improves the coatability.

The resin layer (X) may contain crosslinking agents, antioxidants, heat stabilizers, weather stabilizers, UV absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, surfactants, and the like, as long as the effects of the invention are not impaired.

(8) Laminated Polyester Film The laminated polyester film of the present invention preferably has a haze of 3.0% or less, since this improves visibility when various inspections are carried out through the laminated polyester film, and more preferably has a haze of 2.5% or less.

<Method of manufacturing laminated polyester film>
Next, a method for producing a laminated polyester film will be described. First, a polyethylene terephthalate (hereinafter, abbreviated as PET) film will be used as the polyester film, but the method is not limited thereto. First, PET pellets are thoroughly vacuum-dried, then fed into an extruder, melt-extruded into a sheet at about 280°C, and cooled and solidified to produce an unstretched (unoriented) PET film (film A). This film is stretched 2.5 to 5.0 times in the longitudinal direction with a roll heated to 80 to 120°C to obtain a uniaxially oriented PET film (film B). The coating composition of the present invention, which has been prepared to a predetermined concentration, is applied to one side of this film B. At this time, a surface treatment such as a corona discharge treatment may be performed on the coating surface of the PET film before coating. By performing a surface treatment such as a corona discharge treatment, the wettability of the coating composition to the PET film can be improved, the coating composition can be prevented from being repelled, and a uniform coating thickness can be achieved.

After coating, the PET film is held at the ends with clips and guided to a heat treatment zone (preheating zone) at 80-130°C to dry out the solvent in the coating composition. After drying, the film is stretched 1.1-5.0 times in the width direction. It is then guided to a heat treatment zone (thermal setting zone) at 160-240°C and heat-treated for 1-30 seconds to complete the crystal orientation.

In this heat treatment step (heat fixing step), a relaxation treatment of 3 to 15% may be performed in the width direction or length direction as necessary. In addition, particles may be added to the polyester film raw material to impart functions such as runnability (slipperiness), weather resistance, and heat resistance to the laminated polyester film, as long as the effects of the invention are not impaired. Additives such as heat stabilizers, oxidation stabilizers, weather stabilizers, ultraviolet absorbers, and slip agents can be used as the material of the particles added to the polyester film raw material. In addition, the coating agent used in this case is preferably a water-based coating agent in terms of environmental pollution and explosion resistance.

[Methods for measuring characteristics and evaluating effects]
(1) Measurement method of transparency The transparency was evaluated by haze (%). The haze was measured by leaving the laminated polyester film for 1 hour under normal conditions (temperature 23°C, relative humidity 65%) and then using a turbidity meter "NDH5000" manufactured by Nippon Denshoku Industries Co., Ltd. The average value of three measurements was regarded as the haze of the laminated polyester film.

(2) Appearance of Coating The appearance of the coating was evaluated by placing the laminated polyester film 30 cm directly under a three-wavelength fluorescent lamp (manufactured by Panasonic Corporation, three-wavelength neutral white (F.L 15EX-N 15W)) and visually observing the film while changing the viewing angle. A or better was evaluated as good, and B was evaluated as a level that does not pose any practical problems.

S: No agglomerates or uneven coating are observed. A: Slight agglomerates or uneven coating are observed.

B: Aggregates and uneven coating are visible.

C: Agglomerates and uneven coating are noticeable.

(3) Method for measuring and evaluating antistatic properties (surface resistivity) Antistatic properties were evaluated based on surface resistivity. The measurement surface was the resin layer (X) lamination surface of the laminated polyester film. The unit was Ω/□.

(3-1) Method for evaluating surface resistivity P1 of resin layer (X) surface before corona discharge treatment test After leaving the laminated polyester film under normal conditions (temperature 23°C, relative humidity 65%) for 24 hours, the surface resistivity was measured in that atmosphere after applying a voltage of 100V for 10 seconds using a digital ultra-high resistance/micro ammeter (Advantest Corporation, R8340A). The measured value was taken as the surface resistivity P1 (Ω/□) of the resin layer (X) surface before the moist heat treatment test. A surface resistivity of 9×10 ¹¹ Ω/□ or less indicates that the film has antistatic properties at a level that is not problematic in practical use, and a surface resistivity of 5×10 ¹⁰ Ω/□ or less indicates that the film has excellent antistatic properties.

(3-2) Evaluation method of surface resistivity value P2 of resin layer (X) surface after corona discharge treatment test The laminated polyester film was cut into 10 cm x 20 cm. Next, using a corona surface modification evaluation device TEC-4AX manufactured by Kasuga Electric Co., Ltd., the laminated polyester film was placed on an earth plate so that the resin layer (X) was facing upward, and corona discharge treatment was performed under the conditions of a corona discharge treatment output of 100 W, a discharge gap with the ceramic electrode of 1 mm, an electrode moving speed of 6 m/min, and a treatment number of 5 times. The surface resistivity of the laminated polyester film sample subjected to the corona discharge treatment was determined by the same method as in (3-1). The measured value was taken as the surface resistivity value P2 (Ω/□) of the resin layer (X) surface after the moist heat treatment test. A surface resistivity of 9×10 ¹¹ Ω/□ or less indicates that the antistatic property is at a level that does not cause practical problems, and a surface resistivity of 5×10 ¹⁰ Ω/□ or less indicates that the antistatic property is excellent.

(4) Method for Analyzing Inorganic Particle Types Contained in Resin Layer (X) (4-1) Presence or Absence of Inorganic Particles in Resin Layer (X) The surface of the resin layer (X) was observed at 100,000 times magnification using a SEM (scanning electron microscope), and elemental analysis was performed by EDX (energy dispersive X-ray spectroscopy) to determine the presence or absence of inorganic particles.

Specifically, the surface shape was observed using a Hitachi High-Technologies field emission scanning electron microscope (model number S-4800), and element detection was measured using a Bruker AXS QUANTAX Flat QUAD System (model number Xflash 5060FQ) to confirm the presence or absence of oxide particles containing at least one element selected from the group consisting of Si, Al, Ti, Zr, Se, and Fe.

(4-2) Content of inorganic particles in resin layer (X) The content of inorganic particles contained in the cross section of the resin molded body was measured by observing the cross section using a transmission electron microscope (TEM) according to the following method. First, an ultra-thin section of the cross section of the resin layer (X) was photographed at a magnification of 100,000 times using a TEM. Next, the image was converted to grayscale using image processing software EasyAccess Ver6.7.1.23, the white balance was adjusted so that the brightest and darkest parts were within an 8-bit tone curve, and the contrast was adjusted so that the boundaries of the individual filler components were clearly distinguishable. Next, using software (image processing software ImageJ/developer: National Institutes of Health (NIH)), the pixels were binarized at the aforementioned boundary, and the area of each inorganic particle was extracted using the Analyze Particles function, and the total occupied area rate of the corresponding area was calculated from the result, which was taken as the volume filling rate.

Next, the present invention will be described based on examples, but the present invention is not limited thereto. Examples 1 to 3, 7, 8, 14, 15, 18 to 20, 24, 25, 30 and 34 are to be read as Reference Examples 1 to 3, 7, 8, 14, 15, 18 to 20, 24, 25, 30 and 34. In addition, a method for synthesizing a CNT aqueous dispersion (ae) containing CNT (a) and a CNT dispersant (e), a method for synthesizing an aqueous dispersion of an acrylic resin (c) and an aqueous solution of a polyester resin (c-2) are shown as Reference Examples.

(Reference Example 1) Preparation of CNT aqueous dispersion (ae-1) containing CNT (a) and CNT dispersant (e) A CNT aqueous dispersion was prepared by placing 1.0 mg of straight double-walled CNT (manufactured by Science Laboratory, diameter 5 nm, aspect ratio 3000):a-1 as the CNT, 3.0 mg of CNT dispersant (e) sodium carboxymethylcellulose (Sigma-Aldrich Japan K.K.) (hereinafter abbreviated as CMC-Na) and 666 mg of water in a sample tube, and irradiating the dispersion with ultrasonic waves for 30 minutes using an ultrasonic crusher (Tokyo Rikakiki Co., Ltd. VCX-502, output 250 W, direct irradiation) to obtain a CNT aqueous dispersion (ae-1) (CNT (a-1) concentration 0.15 wt %, CNT dispersant (e) 0.45 wt %, CNT dispersant (e)/CNT (a-1)=3.0) consisting of uniform CNT (a-1) and CNT dispersant (e).

(Reference Example 2) Preparation of CNT aqueous dispersion (ae-2) consisting of CNT (a) and CNT dispersant As the CNT, 1.0 mg of single-walled CNT a-2 (manufactured by Science Laboratory, diameter 1.1 nm, aspect ratio 5000), 3.0 mg of sodium carboxymethylcellulose (Sigma-Aldrich Japan K.K.) (hereinafter abbreviated as CMC-Na) as the CNT dispersion (e), and 666 mg of water were placed in a sample tube to prepare a CNT aqueous dispersion, which was irradiated with ultrasonic waves for 30 minutes using an ultrasonic crusher (VCX-502 manufactured by Tokyo Rikakiki Co., Ltd., output 250 W, direct irradiation) to obtain a CNT aqueous dispersion (ae-2) (CNT (a-2) concentration 0.15 wt %, CNT dispersant (e) 0.45 wt %, CNT dispersant (e)/CNT (a) = 3.0) consisting of uniform CNT (a-2) and CNT dispersant (e).

(Reference Example 3)
Emulsion (EM-1) containing composition (bc) having acrylic resin (c) on the surface of inorganic particles (b)
A typical acrylic resin reaction vessel equipped with a stirrer, a thermometer, and a reflux condenser was charged with 100 parts by weight of isopropyl alcohol as a solvent, and the mixture was heated and stirred while being maintained at 100°C.
A mixture consisting of 40 parts by weight of eicosyl methacrylate with n=19 as (meth)acrylate (c'-1), 40 parts by weight of isobornyl methacrylate having two rings as (meth)acrylate (c'-2), and 20 parts by weight of 2-hydroxyethyl acrylate as (meth)acrylate having a hydroxyl group (c'-3) was added dropwise to the mixture over a period of 3 hours. After the dropwise addition was completed, the mixture was heated at 100°C for 1 hour, and then an additional catalyst mixture consisting of 1 part by weight of t-butylperoxy 2-ethylhexaate was added. The mixture was then heated at 100°C for 3 hours and cooled to obtain acrylic resin (c-1).

Inorganic particles (b) containing aluminum element ("NanoTek" Al ₂ O ₃ slurry (manufactured by C.I. Chemical Co., Ltd., number average particle size 60 nm: b-1) were used, and the "NanoTek" Al ₂ O ₃ slurry and the above acrylic resin (c-1) were added in that order to an aqueous solvent, and dispersed by the following method to obtain an emulsion (EM-1) containing a mixed composition (bc) of inorganic particles (b-1) and acrylic resin (c-1) (the method (ii) above).
The ratio (weight ratio) of the amounts of inorganic particles (b-1) and acrylic resin (c-1) added was (b-1)/(c-1)=50/50 (the weight ratio was rounded off to the nearest whole number). The dispersion treatment was carried out using a homomixer and rotating the mixture at a peripheral speed of 10 m/s for 5 hours. The weight ratio of particles (b-1) and acrylic resin (c-1) in the finally obtained composition (bc) was (b-1)/(c-1)=40/60 (the weight ratio was rounded off to the nearest whole number).

The obtained composition (bc) was centrifuged (rotation speed 3000 rpm, separation time 30 minutes) using a Hitachi tabletop ultracentrifuge (manufactured by Hitachi Koki Co., Ltd.: CS150NX) to settle the inorganic particles (b) (and the acrylic resin (c) adsorbed on the surface of the inorganic particles (b)). The supernatant was then removed and the sediment was concentrated and dried. The concentrated and dried sediment was analyzed by X-ray photoelectron spectroscopy (XPS), and it was confirmed that the acrylic resin (c) was present on the surface of the inorganic particles (b). In other words, it was found that the acrylic resin (c) was adsorbed and attached to the surface of the inorganic particles (b), and the obtained composition (bc) corresponds to particles having the acrylic resin (c) on the surface of the inorganic particles (b).

(Reference Example 4)
Emulsion (EM-2) containing composition (bc) having acrylic resin (c) on the surface of inorganic particles (b)
EM-2 was obtained in the same manner as in Reference Example 3, except that a Si-containing colloidal silica slurry (manufactured by Nissan Chemical Industries, Ltd., number average particle diameter 80 nm): b-2 was used as the inorganic particles (a).

(Reference Example 5)
Emulsion (EM-3) containing composition (bc) having acrylic resin (c) on the surface of inorganic particles (b)
EM-3 was obtained in the same manner as in Reference Example 3, except that "Nanouse (registered trademark)" ZR (manufactured by Nissan Chemical Industries, Ltd., number average particle diameter 90 nm): b-3 containing Zr element was used as the inorganic particles (b).

(Reference Example 6)
Emulsion (EM-4) containing composition (bc) having acrylic resin (c) on the surface of inorganic particles (b)
EM-4 was obtained in the same manner as in Reference Example 3, except that "NanoTek" _TiO2 slurry containing Ti element (manufactured by CI Chemical Co., Ltd., number average particle diameter 36 nm): b-4 was used as the inorganic particles (b).

(Reference Example 7)
Polyester resin (c-2)
50 parts by mass of terephthalic acid, 50 parts by mass of isophthalic acid, 50 parts by mass of ethylene glycol, and 30 parts by mass of neopentyl glycol were charged into a nitrogen-purged reactor together with 0.3 parts by mass of antimony trioxide and 0.3 parts by mass of zinc acetate as polymerization catalysts, and a polymerization reaction was carried out at 190 to 220°C under normal pressure for 12 hours while removing water, to obtain a polyester glycol. Next, 5 parts by mass of 5-sodium sulfoisophthalic acid and xylene as a solvent were charged into the reactor to the obtained polyester glycol, and polymerization was carried out for 3 hours while distilling off xylene at 260°C under a reduced pressure of 0.2 mmHg, to obtain a polyester resin (c-2) having a hydrophilic functional group. This polyester resin (c-2) was dissolved in an aqueous solvent containing ammonia water and butyl cellulose to obtain an aqueous solution.

Example 1
Coating composition:
The CNT aqueous dispersion (ae-1), emulsion (EM-1), acrylic resin (c-1), and melamine compound (d) were mixed so that the solid mass ratio was (ae-1)/(EM-1)/(c)/(d) = 2/2.5/95/2 (CNT (a-1)/inorganic particles (b-1)/acrylic resin (c-1)/melamine compound (d) = 0.5/1/96.5/2).
Furthermore, in order to improve the coatability onto polyester film, a fluorosurfactant ("Pluscoat" RY-2, manufactured by GOO Chemical Industry Co., Ltd.) was added in an amount of 0.1 part by mass per 100 parts by mass of the total mixed coating composition.

Melamine compound (d): "Nicalac" (registered trademark) MW-035 (solid content concentration 70% by mass, solvent: water), manufactured by Sanwa Chemical Co., Ltd.
・Polyester film:
PET pellets (intrinsic viscosity 0.64 dl/g) containing 4% by mass of silica particles with a primary particle size of 0.3 μm were thoroughly vacuum-dried, fed to an extruder, melted at about 280° C., extruded into a sheet, and cooled and solidified by wrapping the sheet around a mirror-finished casting drum with a surface temperature of 25° C. using an electrostatic casting method. This unstretched film was heated to 90° C. and stretched 3.1 times in the longitudinal direction to produce a uniaxially stretched film (film B).

・Laminated film After subjecting the uniaxially stretched film to a corona discharge treatment in air, the coating composition shown in Table 1 was applied to a coating thickness of about 6 μm using a wire bar coater. Then, both ends in the width direction of the uniaxially stretched film to which the coating composition was applied were held with clips and introduced into a preheating zone. The atmospheric temperature in the preheating zone was set to 90 to 100 ° C, and the solvent of the coating composition was dried. Then, the film was continuously stretched 3.6 times in the width direction in a 100 ° C stretching zone, and then heat-treated for 20 seconds in a 240 ° C heat treatment zone to form a resin layer, and further subjected to a 5% relaxation treatment in the width direction at the same temperature to obtain a laminated film in which the crystal orientation of the polyester film was completed. In the obtained laminated film, the thickness of the PET film was 50 μm and the thickness of the resin layer was 70 nm.

The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity and the change in surface resistivity P2/P1 were excellent, and the transparency was also good.

(Examples 2 to 17)
A laminate film was obtained in the same manner as in Example 1, except that the solid mass ratios of CNT (a-1), inorganic particles (b-1), resin (c), and crosslinking agent (d) were changed as shown in Table 1. The properties of the obtained laminate film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Example 18)
A laminated film was obtained in the same manner as in Example 7, except that (EM-2) (inorganic particles (b-2) as inorganic particles (b)) was used as the emulsion. The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Examples 19 to 23)
A laminate film was obtained in the same manner as in Examples 8 to 12, except that the solid mass ratios of CNT (a-1), inorganic particles (b-2), resin (c), and crosslinking agent (d) were changed as shown in Table 1. The properties of the obtained laminate film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Example 24)
A laminated film was obtained in the same manner as in Example 7, except that (EM-3) (inorganic particles (b-3) were used as the inorganic particles (b)) was used as the emulsion. The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Examples 25 to 29)
A laminate film was obtained in the same manner as in Examples 8 to 12, except that the solid mass ratios of CNT (a-1), inorganic particles (b-3), resin (c), and crosslinking agent (d) were changed as shown in Table 1. The properties of the obtained laminate film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Example 30)
A laminated film was obtained in the same manner as in Example 9, except that (EM-4) (inorganic particles (b-4) as inorganic particles (b)) was used as the emulsion. The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Examples 31 and 32)
A laminate film was obtained in the same manner as in Examples 10 and 11, except that the solid mass ratios of CNT (a-1), inorganic particles (b-4), resin (c), and crosslinking agent (d) were changed as shown in Table 1. The properties of the obtained laminate film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Example 33)
A laminated film was obtained in the same manner as in Example 10, except that the CNT aqueous dispersion (ae-2) was used instead of the CNT aqueous dispersion (ae). The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Example 34)
A laminated film was obtained in the same manner as in Example 7, except that the CNT aqueous dispersion (ae-1), inorganic particles (b-1), acrylic resin (c), and melamine compound (d) were mixed in a solid content ratio of (ae-1)/(b-1)/(c)/(d)=4/1/96/2). The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Example 35)
CNT water dispersion (ae-1), emulsion (EM-1), polyester resin (c-2), and melamine compound (d) were mixed so that the solid content mass ratio was (ae-1)/(EM-1)/(c-2)/(d)=4/25/50/24 (CNT (a-1)/inorganic particles (b-1)/acrylic resin (c-1)/polyester resin (c-2)/melamine compound (d)=1/10/15/50/24). Furthermore, in order to improve the coatability to the polyester film, a fluorine-based surfactant ("Pluscoat" RY-2 manufactured by GOO Chemical Industry Co., Ltd.) was added so that it was 0.1 parts by mass per 100 parts by mass of the total mixed coating composition. Thereafter, a laminated film was obtained in the same manner as in Example 1. The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Example 36)
A laminated film was obtained in the same manner as in Example 35, except that the crosslinking agent (d) was changed from the melamine compound (d) to the oxazoline compound (d-2). The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

Oxazoline compound (d-2): "Epocross" (registered trademark) WS-700 (solid content concentration 25% by mass, solvent: water) manufactured by Nippon Shokubai Co., Ltd.
(Example 37)
A laminated film was obtained in the same manner as in Example 35, except that the crosslinking agent (d) was changed from the melamine compound (d) to the carbodiimide compound (d-3). The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

Carbodiimide compound (d-3): "Carbodilite" (registered trademark) V02-L2 (solid content concentration 40 mass%, solvent: water) manufactured by Nisshinbo Chemical Co., Ltd.
(Example 38)
A laminated film was obtained in the same manner as in Example 35, except that the crosslinking agent (d) was changed so that the solid content mass ratio was melamine compound (d)/oxazoline compound (d-2)=12/12. The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Example 39)
A laminated film was obtained in the same manner as in Example 35, except that the crosslinking agent (d) was changed so that the solid content mass ratio was oxazoline compound (d-2)/carbodiimide compound (d-3)=12/12. The properties of the obtained laminated film are shown in Table 1. The initial surface resistivity, the change in surface resistivity P2/P1, and the transparency were all good.

(Comparative Example 1)
A laminated film was obtained in the same manner as in Example 7, except that the inorganic particles (b) were not used. The properties of the obtained laminated polyester film are shown in Table 1. Since the inorganic particles (b) were not used, the change in surface resistivity P2/P1 was poor.

(Comparative Example 2)
A laminated film was obtained in the same manner as in Example 10, except that the inorganic particles (b) and the resin (c) were changed so that the solid content mass ratio was (b)/(c)=10/90. The properties of the obtained laminated film are shown in Table 1. Since CNT (a) was not used, the initial surface resistivity was poor.

The laminated polyester film of the present invention has excellent antistatic properties and can maintain excellent antistatic properties even after discharge treatment, making it suitable for use in applications that involve discharge treatment.

Claims (6)

A laminated polyester film having a resin layer (X) on at least one side of a polyester film, the resin layer (X) containing single-layered or double-layered carbon nanotubes (a) having a diameter of 50 nm or less and inorganic particles (b) , the laminated polyester film satisfying the following formulas 1 and 2, when the surface resistivity of the resin layer (X) surface is P1 (Ω/□) and the surface resistivity of the resin layer (X) surface after subjecting the resin layer (X) surface to a corona discharge treatment under the following conditions is P2 (Ω/□) .
P1<1.0×10 ⁸ (Formula 1)
P2/P1≦50 (Formula 2)
[Corona discharge treatment conditions]
Corona discharge treatment was carried out under the conditions of output 100 W, discharge gap with the ceramic electrode 1 mm, electrode movement speed 6 m/min, and treatment number 5 times. 2. The laminated polyester film according to claim 1 , wherein the inorganic particles (b) are oxide particles containing at least one element selected from the group consisting of Si, Al, Ti, Zr, Se, and Fe. 3. The laminated polyester film according to claim 1, wherein the content of the carbon nanotubes (a) in the resin layer (X) is 0.05% by weight or more and 5.0% by weight or less based on the entire resin layer (X). 4. The laminated polyester film according to claim 1 , wherein the content of the inorganic particles (b) in the resin layer (X) is 5.0% by weight or more based on the total weight of the resin layer (X). The laminated polyester film according to any one of claims 1 to 4 , which is used for an application in which a discharge treatment is performed. A method for producing a laminated polyester film according to any one of claims 1 to 5 , comprising the steps of applying a coating composition (x) containing carbon nanotubes (a) and inorganic particles (b) to at least one surface of a polyester film before completion of crystal orientation, and then stretching the polyester film by a uniaxial or biaxial stretching method to complete the crystal orientation of the polyester film.