JP7447658B2 - laminated polyester film - Google Patents

Description

The present invention relates to a laminated polyester film, and more particularly to a laminated polyester film useful as an antistatic film.

Polyester films, represented by polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, etc., and are also excellent in cost performance, so they are used as a basis for various applications. However, polyester film is easily charged with electricity during friction, peeling of the adhesive layer, etc., and problems such as adhesion of foreign matter and dust and electrostatic discharge problems occur.

Therefore, measures have been taken to prevent charging, such as applying a conductive substance to the surface. The conductive substances applied to the polyester film include cationic substances containing cationic groups such as quaternary ammonium groups, and anionic substances containing anionic groups such as sulfonate and phosphonate groups. is mainly used. These are ionically conductive, and their antistatic ability is susceptible to ambient humidity and moisture. Particularly under low humidity conditions, the conductivity decreases and the desired antistatic ability cannot be obtained.

On the other hand, examples of conductive substances include electronically conductive compounds, which can exhibit more excellent antistatic properties than the above-mentioned ionically conductive compounds. It is also suitable for being less susceptible to the effects of humidity. As the electronically conductive compound, conductive carbon materials such as carbon nanotubes and graphene, and conductive organic polymers such as polyacetylene, polyphenylene, polyaniline, polypyrrole, polyisothianaphthene, and polythiophene have been proposed.

These conductive organic polymers are often expensive and strongly colored, so it is better to reduce the amount of coating as much as possible, but as the amount of coating is reduced, the stability of the conductivity will be impaired. Specifically, there is a drawback that the conductivity deteriorates over time when the conductive layer is exposed to the atmosphere under illuminance at the indoor light level (hereinafter referred to as "atmospheric exposure").

On the other hand, when carbon nanotubes are used as conductive materials, they are expected to be stable against exposure to light and air, but conventional techniques require a large amount of conductive material to be applied, resulting in lower costs and lower transparency (haze). ), the total light transmittance is not necessarily sufficient (for example, see Patent Document 1).
Further, a resin film formed from a thermoplastic resin material has a coating layer on at least one side, and the coating layer includes a conductive film containing a polyether compound or its precursor and a conductive fibrous filler. It has been proposed (see Patent Document 2). The conductive film has transparency, low specific surface resistivity, and excellent antistatic performance, but there is room for further improvement.

By the way, in the case of stretched polyester films, it is advantageous in terms of productivity and economy to provide a coating film by a so-called in-line coating method in which coating is performed during the film forming process. However, when a conductive layer is provided by an in-line coating method, sufficient antistatic performance is often not achieved. This is thought to be because when the conductive layer is stretched as the film is stretched, it is not possible to follow the stretching of the film while holding the conductive mechanism. Furthermore, the coating layer in such a case has poor appearance, making it difficult to apply it to optical members. Therefore, there is a need for an in-line coating method that exhibits excellent antistatic properties and causes fewer defects in appearance.

Japanese Patent Application Publication No. 2015-051621 Japanese Patent Application Publication No. 2007-223182

The present invention has been made in view of the above circumstances, and the problem to be solved is to have excellent antistatic properties with an extremely small amount of applied conductive material, and to have transparency, economic efficiency, and the above-mentioned resistance to atmospheric exposure. The purpose of the present invention is to provide a multilayer polyester film.

As a result of intensive studies regarding the above-mentioned problems, the present inventor discovered that the above-mentioned problems could be solved by providing an antistatic layer made of a combination of specific types of compounds, and thus completed the present invention. Ta.

That is, the gist of the present invention has the following aspects.
[1] A laminated polyester film having an antistatic layer on at least one side of the polyester film, the antistatic layer containing the following compounds (A) and (B).
(A) Carbon nanotubes (B) Sugar alcohol having 4 or more carbon atoms [2] The laminated polyester film according to the above [1], wherein the antistatic layer further contains the following compound (C).
(C) One or more resins selected from the group consisting of urethane resins, polyesters, and acrylic resins.
[3] The laminated polyester film according to [1] or [2] above, wherein the antistatic layer is stretched in at least one direction.
[4] The laminated polyester film according to any one of [1] to [3] above, which has a haze increase rate of 1.0% or less when compared to a polyester film not provided with an antistatic layer.
[5] The laminated polyester film according to any one of [1] to [4] above, which has a total light transmittance of 85% or more.
[6] The laminated polyester film according to any one of [1] to [5] above, wherein the sugar alcohol has 4 to 6 carbon atoms.
[7] The laminated polyester film according to any one of [1] to [6] above, wherein the sugar alcohol has the same number of carbon atoms and the same number of hydroxyl groups.

According to the present invention, it is possible to provide a laminated polyester film that has excellent antistatic properties even with a very small amount of conductive agent, and has transparency, resistance to atmospheric exposure, and economic efficiency.

The laminated polyester film of the present invention has an antistatic layer on at least one side of a polyester film as a base film, and the antistatic layer contains a compound (A) carbon nanotubes and a compound (B) a sugar alcohol having 4 or more carbon atoms. It is a laminated polyester film containing.
The laminated polyester film of the present invention is preferably stretched in at least one direction, and may be stretched in two directions: the one direction and a direction perpendicular thereto.

<Base film (polyester film)>
The base film (hereinafter sometimes simply referred to as "film") in the laminated polyester film of the present invention is made of polyester. Such polyesters include dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, adipic acid, sebacic acid, 4,4'-diphenyldicarboxylic acid, 1,4-cyclohexyldicarboxylic acid, or esters thereof. , ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, and 1,4-cyclohexanedimethanol. Polyesters made of these acid components and glycol components can be produced using any commonly used method.
For example, by conducting a transesterification reaction between a lower alkyl ester of an aromatic dicarboxylic acid and a glycol, or by directly esterifying an aromatic dicarboxylic acid and a glycol, substantially the bisglycol of the aromatic dicarboxylic acid is produced. A method is employed in which an ester or a low polymer thereof is formed, and then this is heated under reduced pressure to undergo polycondensation. Depending on the purpose, aliphatic dicarboxylic acids may be copolymerized.

Typical examples of the polyester of the present invention include polyethylene terephthalate, polyethylene-2,6-naphthalate, and poly-1,4-cyclohexane dimethylene terephthalate. It may be a polymerized polyester, and may contain other components and additives as necessary.

The polyester film of the present invention can contain particles for the purpose of ensuring running properties of the film, preventing scratches, and the like.

The particle size and content of the particles are selected depending on the use and purpose of the film, but the amount of particles when included is usually 0.0003 to 1.0% by mass, preferably 0.0005% by mass based on the polyester. It is in the range of ~0.5% by mass. When the amount of particles contained is 0.0003% by mass or more, the effect of the particles can be sufficiently obtained, and when the amount is 1.0% by mass or less, the transparency of the film is good.

When the polyester film of the base material contains particles, the average particle size of the particles is preferably in the range of 0.01 to 5 μm. When the average particle diameter is 0.01 μm or more, the effect of the particles can be sufficiently obtained, and when it is 5 μm or less, the surface roughness of the film does not become too rough, and the particles are difficult to fall off from the film surface. From the above viewpoint, the average particle diameter of the particles is more preferably 0.5 to 3 μm, and even more preferably 0.8 to 2 μm.

Examples of particles to be contained in the polyester film include inorganic particles such as silica, calcium carbonate, magnesium carbonate, calcium phosphate, kaolin, talc, titanium oxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, and molybdenum sulfide. Crosslinked polymer particles, organic particles such as calcium oxalate, particles precipitated during the polyester manufacturing process, etc. can be used.

In addition, various stabilizers, lubricants, antistatic agents, etc. can be added to the film as appropriate.

Note that when there are no particles in the film, or when there are only a few particles, the film becomes highly transparent and has a good appearance, but may be difficult to handle due to insufficient slip properties. Therefore, it may be necessary to take measures such as knurling the polyester film or incorporating particles into the antistatic layer.

As a method for forming the film of the present invention, a commonly known film forming method can be employed, and there are no particular limitations. For example, a sheet obtained by melt extrusion is first stretched 2 to 6 times at 70 to 145°C using a roll stretching method to obtain a uniaxially stretched polyester film, and then placed in a tenter at right angles to the previous stretching direction. A film is obtained by stretching the film 2 to 6 times in the direction of 80 to 160°C and further heat treating (heat setting) at 150 to 250°C for 1 to 600 seconds. Furthermore, in this case, it is preferable to use a method in which the material is relaxed by 0.1 to 20% in the longitudinal direction and/or the lateral direction in the heat treatment zone and/or the cooling zone at the heat treatment outlet.

The polyester film in the present invention may have either a single layer or a multilayer structure. In the case of a multilayer structure, the surface layer and the inner layer, or both surface layers, can be made of different polyesters depending on the purpose.
The thickness of the polyester film in the present invention is not particularly limited, but is preferably in the range of 5 to 150 μm. If it is 5 μm or more, it is easy to handle, and if it is 150 μm or less, it is advantageous in terms of cost. From the above viewpoint, the thickness of the polyester film is more preferably 10 to 100 μm, and even more preferably 25 to 75 μm.

The transparency of the polyester film in the present invention is not particularly limited, but if transparency is required, in order to take advantage of the transparent feature of the antistatic layer of the present invention, the haze of the base film must be 1.5% or less. , more preferably 1.0% or less. Note that haze is a value measured by the method described in Examples.
Further, the transparency of the antistatic layer in the present invention can be evaluated by the difference (increase in haze) between the haze of the laminated film and the base film according to the present invention. It is preferably at most 0.5%, more preferably at most 0.5%, even more preferably from 0 to 0.3%, particularly preferably from 0 to 0.2%.

The total light transmittance of the polyester film in the present invention is not particularly limited, but is preferably 85% or more, more preferably 87% or more. Note that the total light transmittance is a value measured by the method described in Examples.

<Antistatic layer>
Specifically, the antistatic layer in the present invention is a functional layer that has a low surface resistivity and has a mechanism for leaking electric charges. It can be said that the lower the surface resistivity of the antistatic layer, the better the antistatic property. If the surface resistivity is 1×10 ¹² Ω or less, it can be said to have antistatic properties, and if the surface resistivity is 1×10 ⁸ Ω or less, it can be said to have good antistatic properties.
In the laminated film of the present invention, the antistatic layer may be provided on only one side of the film or on both sides. Alternatively, an antistatic layer may be provided on one side and another functional layer may be provided on the back side.

There is no particular restriction on the lower limit of the surface resistivity, but in consideration of the cost of the conductive agent, it is preferably 1×10 ⁴ Ω, more preferably 1×10 ⁶ Ω.

Next, compounds (A) and (B) used in the present invention will be explained.

<Compound (A)>
Compound (A) is a carbon nanotube. By using carbon nanotubes, the laminated film of the present invention has excellent antistatic properties and resistance to atmospheric exposure. The diameter of the tube is usually 50 nm or less, preferably 10 nm or less, more preferably 5 nm or less. In order to achieve both transparency and conductivity, a thin material, that is, a material with a small diameter is preferable. The length of the carbon nanotube is preferably 0.5 to 100 μm, more preferably 2 to 20 μm. The longer the length, the easier it is to exhibit conductivity, but if it is too long, there is a risk of filter clogging and other negative effects on the coating process.
The number of layers of carbon nanotubes is not particularly limited, but if the number of layers is too large, the number of conductive paths per unit mass will decrease, so it is preferably three or less layers.
The method for manufacturing carbon nanotubes is not particularly limited, but examples include known manufacturing methods such as chemical vapor deposition, catalytic vapor deposition, arc discharge, and laser evaporation.

The content of compound (A) in the antistatic layer according to the present invention is preferably in the range of 0.01 to 50% by mass based on the total solid content. If it is 0.01% by mass or more, the content and dispersion state of carbon nanotubes on the film will be good, and sufficient conductivity will be obtained. On the other hand, if it is 50% by mass or less, the coating appearance will be good. From the above viewpoint, the content of compound (A) is more preferably 0.1 to 10% by mass, still more preferably 0.2 to 4.5% by mass, particularly preferably 0.3 to 3.5% by mass. It is.
In addition, since carbon nanotubes do not change during the process of forming a film on a film, the content (preparation amount) of carbon nanotubes in the coating solution for forming the antistatic layer, which will be described later, is the same as the amount of carbon nanotubes in the antistatic layer. The content can be set to .
Moreover, the content of compound (A) in the antistatic layer can also be directly measured by a transmission electron microscope, Raman spectrum, X-ray diffraction, thermogravimetric analysis, or the like.

In the present invention, when preparing the coating liquid for forming the antistatic layer, it is preferable to mix the carbon nanotubes in a dispersion liquid in which the carbon nanotubes are dispersed in a dispersion medium. The dispersion medium is not particularly limited and may be aqueous or organic solvent-based, but aqueous is preferred from the viewpoint of ease of handling and working environment. As the aqueous dispersion medium, water alone may be used or a mixture of water and alcohol may be used, but water is preferably used as the main component. In that case, it is preferable to use a dispersant for dispersion. The dispersant is not particularly limited, and nonionic surfactants or anionic surfactants are preferably used, and anionic surfactants such as alkylbenzene sulfonates are particularly preferred. Specific examples include octylbenzenesulfonate, nonylbenzenesulfonate, and dodecylbenzenesulfonate.

The content per area of the compound (A) in the antistatic layer according to the present invention is appropriately set in consideration of the required surface resistance value, cost, etc., but is generally 0.01 mg/m ² to 10 mg/m 2 . m ² , preferably 0.02 mg/m ² to 2 mg/m ² , more preferably 0.05 mg/m ² to 0.95 mg/m ² . When it is at least the lower limit of this range, sufficient conductivity is obtained, and when it is at most the upper limit of this range, transparency is good and it is advantageous in terms of cost.

<Compound (B)>
Compound (B) is a sugar alcohol having 4 or more carbon atoms. By using sugar alcohol, it is possible to ensure high transparency and high conductivity even with a small amount of carbon nanotubes. Although the principle is not clear, the sugar alcohol suppresses the occurrence of cracks and prevents deterioration of haze when the laminated film having the antistatic layer of the present invention is stretched. Furthermore, since the carbon nanotubes are arranged in a specific manner in the antistatic layer, it is presumed that high conductivity can be ensured even with a small amount of carbon nanotubes.
The sugar alcohol in the present invention refers to a chain polyhydric alcohol with a reduced carbonyl group such as aldose or ketose, or a cyclic polyhydric alcohol such as cyclitol. Specific examples include sugar alcohols with 4 carbon atoms such as erythritol and threitol obtained by reducing monosaccharides; sugar alcohols with 5 carbon atoms such as ribitol, arabinitol, and xylitol; sorbitol, mannitol, iditol, talitol, and thalitol. Examples include chain sugar alcohols such as sugar alcohols with 6 carbon atoms such as lactitol. Also included are cyclic sugar alcohols obtained by reducing cyclic monosaccharides, typified by cyclitols such as inositol. Further examples include disaccharide alcohols such as maltitol, lactitol, and reduced isomaltulose obtained by reducing disaccharides.
The sugar alcohol in the present invention is preferably a sugar alcohol having the same number of hydroxyl groups as the number of carbon atoms in order to ensure high transparency and high conductivity. Examples of such sugar alcohols include sorbitol and erythritol.
In addition, when the above-mentioned sugar alcohol has stereoisomers, all of these stereoisomers are included.

The compound (B) is preferably a sugar alcohol having 4 to 12 carbon atoms, more preferably a sugar alcohol having 4 to 6 carbon atoms, and particularly preferably a sugar alcohol having 6 carbon atoms.
Furthermore, the sugar alcohol is preferably a chain one, particularly a chain sugar alcohol having 4 to 6 carbon atoms.
In addition, the above-mentioned sugar alcohols may be used alone or in combination of two or more.

The content of compound (B) in the antistatic layer according to the present invention is preferably in the range of 10 to 99.99% by mass based on the total solid content. If it is 10% by mass or more, sufficient antistatic performance can be obtained, and if it is 99.99% by mass or less, sufficient transparency can be obtained. From the above viewpoint, the content of compound (B) is more preferably 50 to 98% by mass, even more preferably 60 to 95% by mass, and particularly preferably 70 to 95% by mass.
Note that when the coating liquid for forming the antistatic layer is dried and solidified on the film, at least a portion of the compound (B) may be condensed due to dehydration, but the condensed sugar alcohol may also be ).

<Compound (C)>
In the present invention, it is further preferable that the compound (C) contains one or more selected from the group consisting of polyester, acrylic resin, and urethane resin. Compound (C) has a role as a binder and contributes to improving the dispersibility of compound (A).
The content of compound (C) in the antistatic layer according to the present invention is preferably in the range of 0 to 90% by mass, more preferably 1 to 50% by mass, and more preferably 2 to 40% by mass, based on the total solid content. % by weight is more preferable, and 5 to 20% by weight is particularly preferable. Within this range, it is easy to obtain good antistatic performance, coating film strength, and good appearance.
In the present invention, since it is preferable that the coating liquid for forming the antistatic layer is aqueous, it is preferable that the compound (C) is also water-soluble or easily dispersed in water. Therefore, it is preferable that the compound (C) has a hydrophilic group such as a hydroxyl group or a carboxyl group.

(polyester)
The polyester in the present invention includes, for example, those consisting of polyhydric carboxylic acids and polyhydric hydroxy compounds as shown below as main components. That is, examples of polyvalent carboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, and 2,6- Naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, Succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic acid monopotassium salt, and their ester-forming derivatives can be used. Examples of valent hydroxy compounds include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, Neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetra Methylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, potassium dimethylolpropionate, and the like can be used. One or more of these compounds may be selected as appropriate, and a polyester may be synthesized by a conventional polycondensation reaction.

Preferably, the polyhydric carboxylic acid is copolymerized with sulfoisophthalic acid as part of the polycarboxylic acid to introduce a sulfonic acid group into the polyester skeleton, and then neutralized to make it hydrophilic. The amount to be copolymerized is usually 1 to 10 mol%, preferably 2 to 8 mol%, based on the total polyhydric carboxylic acid. Water dispersion stability can be further improved by introducing an appropriate amount of sulfonic acid groups.

(acrylic resin)
The acrylic resin in the present invention is a polymer made of polymerizable monomers having carbon-carbon double bonds, such as acrylic and methacrylic monomers. These may be either homopolymers or copolymers. Also included are copolymers of these polymers and other polymers (eg, polyester, polyurethane, etc.). For example, block copolymers and graft copolymers. More specifically, acrylic resin grafted polyester, acrylic resin grafted polyurethane, etc. may be mentioned. By containing these resins, the strength of the resulting antistatic layer and the adhesion to the base film can be improved.
Alternatively, it also includes a polymer (in some cases, a mixture of polymers) obtained by polymerizing a polymerizable monomer having a carbon-carbon double bond in a polyester solution or polyester dispersion. Similarly, polymers obtained by polymerizing polymerizable monomers having carbon-carbon double bonds in polyurethane solutions and polyurethane dispersions (in some cases, mixtures of polymers) are also included. Similarly, polymers (or polymer mixtures in some cases) obtained by polymerizing polymerizable monomers having carbon-carbon double bonds in other polymer solutions or dispersions are also included. Furthermore, in order to further improve adhesion, it is also possible to contain a hydroxyl group or an amino group.

The polymerizable monomer having a carbon-carbon double bond is not particularly limited, but typical examples include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid. Various carboxyl group-containing monomers such as acids, and their salts; 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, monobutyl hydroxyfumarate, mono Various hydroxyl group-containing monomers such as butyl hydroxy itaconate; various alkyl ( meth)acrylic acid esters; various nitrogen-containing compounds such as (meth)acrylamide, diacetone acrylamide, or (meth)acrylonitrile; hydroxyl group-containing nitrogen-containing compounds such as N-methylol(meth)acrylamide; styrene, α - Various styrene derivatives such as methylstyrene, divinylbenzene, vinyltoluene; various vinyl esters such as vinyl propionate; various silicon-containing polymers such as γ-methacryloxypropyltrimethoxysilane, vinyltrimethoxysilane, etc. phosphorus-containing vinyl monomers; various vinyl halides such as vinyl chloride and polypylidene chloride; various conjugated dienes such as butadiene.

Among the above, preferred are polymers obtained by polymerizing polymerizable monomers including acrylic and methacrylic monomers, and more preferably, the polymerizable monomers include alkyl (meth)acrylic esters. Furthermore, when the coating liquid is aqueous, the polymerizable monomer preferably has a hydrophilic group such as a hydroxyl group or a carboxyl group from the viewpoint of dissolving or dispersing the compound (C) easily. Therefore, the acrylic resin is also preferably a polymer formed by polymerizing an alkyl (meth)acrylic acid ester and a polymerizable monomer containing a hydrophilic group-containing monomer such as a hydroxyl group-containing monomer or a carboxyl group-containing monomer.
Further, the acrylic resin may be an emulsion polymer obtained by polymerizing a polymerizable monomer in the presence of a surfactant, for example.

(Urethane resin)
The urethane resin in the present invention is a polymeric compound having a urethane bond in its molecule, and is preferably water-dispersible or water-soluble. In the present invention, they may be used alone or in combination of two or more.

In order to impart water dispersibility or water solubility, it is common and preferred to introduce hydrophilic groups such as hydroxyl groups, carboxyl groups, sulfonic acid groups, sulfonyl groups, phosphoric acid groups, and ether groups into urethane resins. Among the hydrophilic groups, carboxyl groups or sulfonic acid groups are particularly preferred from the viewpoint of coating film properties and adhesion.

One of the methods for producing the urethane resin that is a component of the antistatic layer according to the present invention is by reacting a hydroxyl group-containing compound with an isocyanate. As the hydroxyl group-containing compound used as a raw material, polyols are preferably used, and examples thereof include polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in plural kinds.

Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, polyhexamethylene ether glycol, and the like.

Examples of polyester polyols include polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides. and polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-Methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol , 2-methyl-2-propyl-1,3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2 , 5-dimethyl-2,5-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2 -hexyl-1,3-propanediol, cyclohexanediol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyl dialkanolamine, lactone diol, etc.).

Examples of polycarbonate polyols include polycarbonate diols obtained by dealcoholization reaction from polyhydric alcohols and dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, etc., such as poly(1,6-hexylene) carbonate, poly( Examples include 3-methyl-1,5-pentylene) carbonate.

Among these, polyester polyols are preferred.

The polyisocyanate compounds used to obtain the urethane resin include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and toridine diisocyanate; α, α, α', α' -Aliphatic diisocyanates with aromatic rings such as tetramethylxylylene diisocyanate; Aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate; cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl Examples include alicyclic diisocyanates such as methane diisocyanate and isopropylidene dicyclohexyl diisocyanate. These may be used alone or in combination.

A chain extender may be used when synthesizing a urethane resin, and there are no particular restrictions on the chain extender as long as it has two or more active groups that react with isocyanate groups. Alternatively, a chain extender having two amino groups can be mainly used.

Examples of chain extenders having two hydroxyl groups include aliphatic glycols such as ethylene glycol, propylene glycol, and butanediol; aromatic glycols such as xylylene glycol and bishydroxyethoxybenzene; and esters such as neopentyl glycol hydroxypivalate. Glycols such as glycol can be mentioned.

Examples of the chain extender having two amino groups include aromatic diamines such as tolylene diamine, xylylene diamine, and diphenylmethane diamine; ethylene diamine, propylene diamine, hexane diamine, and 2,2-dimethyl-1,3-propane diamine. , 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine Aliphatic diamines such as 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, 1,4-diaminocyclohexane, 1,3-bisaminomethylcyclohexane, etc. can be mentioned.

Also preferably used is a method in which a carboxyl group is introduced into the urethane skeleton using dimethylolpropionic acid, dimethylolbutanoic acid, etc., and then neutralized with a basic compound to make the urethane hydrophilic.

As compound (C), polyester is preferable, and polyester having a naphthalene skeleton is particularly preferable.

In the present invention, there are no particular obstacles in selecting compounds (A), (B) and (C) that do not contain halogen atoms. Therefore, in the present invention, it is easy to make the antistatic layer halogen-free, and from the viewpoint of environmental protection, it is preferable that the antistatic layer does not contain halogen, especially chlorine.

(Other resin components)
Furthermore, if necessary, one or more binder resins other than compound (C) can be used in combination with compound (C). Examples of such binder resins include polyether resins, epoxy resins, and amide resins. Each of these may have a substantially composite structure due to copolymerization or the like.

(surfactant)
The antistatic layer of the present invention can contain a surfactant in order to improve the applicability to a film. The surfactant is not particularly limited, and anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants can be used, but from the viewpoint of not affecting conductivity, Anionic surfactants and nonionic surfactants are preferred.
In particular, it is preferable to use a nonionic material containing (poly)alkylene oxide, (poly)glycerin, or a derivative thereof in its structure because it does not impede the conductivity of the resulting coating layer. More preferably, the hydrophobic portion has a fluorine-substituted alkyl group or a carbon-carbon triple bond structure.
When a surfactant is used, it is preferably used in an amount of 1 to 10% by weight in the antistatic layer.
However, if there is no need to improve coating properties, such as when the polyester film is surface-treated or when a non-aqueous coating liquid is used, the surfactant may not be contained.

The antistatic layer according to the present invention may be crosslinked with a crosslinking reactive compound, if necessary. It is preferable that the crosslinking-reactive compound is included in the coating solution described below, and the antistatic layer is crosslinked by subsequent heating or the like. Crosslinking-reactive compounds mainly improve the cohesiveness, surface hardness, scratch resistance, solvent resistance, and water resistance of the antistatic layer through crosslinking reactions with functional groups contained in other resins and compounds, and through self-crosslinking. can do. As crosslinking reactive compounds that can be used, amino resins such as melamine, benzoguanamine, and urea, as well as isocyanate, oxazoline, epoxy, and glyoxal compounds are preferably used. It also includes polymer-type crosslinking reactive compounds in which other polymer skeletons have reactive groups.

The antistatic layer according to the present invention includes an antifoaming agent, a coating improver, a thickener, an organic lubricant, a mold release agent, organic particles, an inorganic particle, an antioxidant, an ultraviolet absorber, a blowing agent, and a dye. , may contain additives such as pigments. These additives may be used alone, or two or more types may be used in combination as necessary.

<Preparation of laminated film>
The method for forming the antistatic layer according to the present invention includes the above compounds (A) and (B), and if necessary, the compound (C), a surfactant, other resin components, a crosslinking reactive compound, and A method of preparing a coating liquid containing other additives and applying the coating liquid to a film is preferably used.
The coating liquid in the present invention is preferably an aqueous solution or an aqueous dispersion from the viewpoint of handling, working environment, and stability of the coating liquid composition. An organic solvent may be contained as long as it does not exceed this range.
The coating method may be in-line coating, in which the film surface is treated during the polyester film production process, or off-line coating, in which the film is coated outside the system once it has been produced. . More preferably, in-line coating is employed.

In-line coating is a method in which coating is performed within the process of producing a polyester film, and specifically, it is a method in which coating is performed at any stage from melt extrusion of polyester to stretching, heat setting, and winding. Usually, the coating is applied to an unstretched sheet obtained by melting and quenching, a stretched uniaxially stretched film, a biaxially stretched film before heat setting, or a film after heat set before winding up. Although not limited to the following, for example, in sequential biaxial stretching, a method in which a uniaxially stretched film stretched in the longitudinal direction (longitudinal direction) is coated and then stretched in the transverse direction is particularly excellent. According to this method, film formation and antistatic layer formation can be performed at the same time, which is advantageous in terms of manufacturing costs.Also, since stretching is performed after coating, the thickness of the antistatic layer can be changed by the stretching ratio. It is also possible to perform thin film coating more easily than offline coating. Further, by providing an antistatic layer on the film before stretching, the antistatic layer can be stretched together with the base film, thereby making it possible to firmly adhere the antistatic layer to the base film. Furthermore, in the production of biaxially oriented polyester film, by holding the edges of the film with clips and stretching it, the film can be restrained in both the vertical and horizontal directions. Can be heated to high temperatures while maintaining its properties. Therefore, since the heat treatment performed after coating can be performed at a high temperature that cannot be achieved by other methods, the film-forming properties of the antistatic layer are improved, and the antistatic layer and the base film are bonded more firmly. Furthermore, the antistatic layer itself can be made stronger, and performance such as moisture and heat resistance can be improved.

In the present invention, when drying the coating film after application, it is desirable to maintain the temperature at 150° C. or higher even when the in-line coating is not used. If the temperature is 150°C or higher, drying time can be shortened, productivity can be increased, and the strength of the coating film itself or adhesion can be increased.

Examples of methods for forming the antistatic layer of the present invention include gravure coating, reverse roll coating, die coating, air doctor coating, blade coating, rod coating, bar coating, curtain coating, knife coating, transfer roll coating, squeeze coating, Conventionally known coating methods such as impregnation coating, kiss coating, spray coating, calendar coating, and extrusion coating can be used.

In order to improve the applicability and adhesion of the coating liquid to the film, the film may be subjected to chemical treatment, corona discharge treatment, plasma treatment, etc. before coating.

The coating amount of the coating solution for forming the antistatic layer is usually 0.005 to 1.5 g/m ² , preferably 0.01 to 0.5 g/m ² , more preferably 0. .02 to 0.2 g/m ² . When the coating amount is 0.005 g/m ² or more, sufficient performance as an antistatic layer is obtained, and when it is 1.5 g/m ² or less, the appearance and transparency are good, preventing blocking of the film and increasing cost. does not occur.

<Optical properties of laminated film>
The laminated film of the present invention has excellent transparency. More specifically, the total light transmittance is preferably 85% or more, more preferably 87% or more. Further, the haze is preferably 1.5% or less, more preferably 1.0% or less.

The laminated film of the present invention is a laminated film that has excellent antistatic properties, excellent atmospheric exposure resistance and transparency, and has high productivity. Therefore, it is useful as an antistatic film, and is suitable for flat panel displays and their manufacturing process components, touch panel peripheral components, release films, heat-sensitive ribbons, receiver papers, printing plates, carrier tapes, trays, magazines, semiconductor device packaging, etc. It can be used for.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. The evaluation methods and sample processing methods in Examples and Comparative Examples are as follows.

(Evaluation method)
(1) Transparency of laminated film (haze increase due to antistatic layer)
According to JIS-K7136, the haze and total light transmittance of the film were measured using an integrating sphere turbidimeter NDH-2000 manufactured by Nippon Denshoku Kogyo Co., Ltd. The difference in haze between a film without an antistatic layer and a film with an antistatic layer was calculated, and the increase in haze due to the provision of an antistatic layer was determined and evaluated as the transparency of the antistatic layer. It can be said that the smaller the increase in haze, the better the transparency of the antistatic layer. In this method, it can be said that transparency is excellent if the haze difference is 1.0% or less, and particularly excellent if it is 0.5% or less. On the other hand, if it exceeds 1.0%, it can be said to be inferior (×). Further, the total light transmittance will also be described.

(2) Surface resistivity (Ω)
The surface resistivity of the antistatic layer was measured based on the method below. Since the method (2-1) cannot measure a surface resistivity higher than 1×10 ⁸ Ω, the method (2-2) was used for samples that could not be measured using the method (2-1).
(2-1) Using Mitsubishi Chemical's low resistivity meter: Loresta GP MCP-T600, the sample was conditioned for 30 minutes in a measurement atmosphere of 23°C and 50% RH, and then the surface resistivity was measured using the four-probe method. It was measured.
(2-2) Using a high-resistance measuring device manufactured by Hewlett-Packard Japan: HP4339B and a measuring electrode: HP16008B (double ring), the sample was conditioned for 30 minutes in a measurement atmosphere of 23°C and 50% RH, and then the surface Resistivity was measured.

(3) Atmospheric exposure test The test film was pasted on the wall of a constant temperature and humidity chamber adjusted to 23°C and 50% RH with the measurement surface facing away from the wall (indoor side), and after 28 days had passed. The surface resistivity was measured and compared with that before pasting. This wall surface was not exposed to outdoor light and was constantly illuminated by white fluorescent lamps at approximately 500 lux.
○: Increase in surface resistivity after treatment is less than 2 times △: Increase in surface resistivity after treatment is 2 times or more and less than 10 times ×: Increase in surface resistivity after treatment is 10 times or more

The polyester raw materials used for the base material in Examples and Comparative Examples are as follows.
(Polyester 1) Polyethylene terephthalate with an intrinsic viscosity of 0.64, substantially free of particles

(Polyester 2) Polyethylene terephthalate with an intrinsic viscosity of 0.65, containing 0.2% by mass of amorphous silica with an average particle size of 2.4 μm

Moreover, the following was used as the coating composition.
(A1): Paint in which carbon nanotubes with an average outer diameter of 1.8 nm and 1 to 2 layers are dispersed in water using an anionic dispersant (TUBALL INK H ₂ O manufactured by OCSiAl)

(B1) Sorbitol (B2) Erythritol

(C1) Aqueous dispersion of polyester copolymerized with the following composition Monomer composition:
(Acid component) 2,6-naphthalene dicarboxylic acid/5-sodium sulfoisophthalic acid = 92/8 (mol%)
(Diol component) Ethylene glycol/diethylene glycol = 80/20 (mol%)
(C2) Aqueous dispersion of acrylic resin polymerized with the following composition Emulsion polymer of ethyl acrylate/n-butyl acrylate/methyl methacrylate/N-methylolacrylamide/acrylic acid = 65/21/10/2/2 (mass%) (Emulsifier: anionic surfactant)

(D1) A nonionic surfactant having a structure having polyethylene oxide in the side chain as shown in the following formula

In the above formula, m and n are integers indicating the number of moles of ethylene oxide added, and in this case, the average of m+n was 10.

(D2) Fluorinated nonionic surfactant with a structure having a branched perfluoroalkenyl group as a hydrophobic group and a polyethylene oxide chain (average chain length 12 units) as a hydrophilic group.

(H1) Polyvinyl alcohol with saponification degree of 88 mol% and polymerization degree of 600

(P1) Paint containing a compound (PEDOT/PSS) in which polyethylene dioxythiophene is doped with polystyrene sulfonic acid as a conductive agent and a binder etc. (AS-Inline manufactured by Agfagewald)

Example 1
A mixture of sufficiently dried polyester 1 and polyester 2 at a ratio of 92% and 8%, respectively, was used as the raw material for the outer layer, and only polyester 1 was used as the raw material for the middle layer, and each was supplied to two extruders, After each is melted at 285°C, it is coextruded on a cooling roll set at 40°C in a layer configuration of 2 types and 3 layers (outer layer/middle layer/outer layer = 1:10:1 discharge rate), cooled, and solidified. A stretched film was obtained. This film was stretched 3.7 times in the longitudinal direction while passing through a group of heating rolls at 85° C. to form a uniaxially oriented film. After applying the coating composition of Example 1 shown in Table 1 below on one side of this uniaxially oriented film, the coating composition was introduced into a tenter stretching machine, and the coating composition was dried using the heat. It was stretched 4.3 times. Next, heat treatment was performed at 230° C. to obtain a biaxially oriented polyethylene terephthalate film having a film thickness of 50 μm.
The coating composition was prepared by calculating the concentration from the undried coating amount and the stretching ratio so that the coating amount after drying and stretching would be the desired value, and adding water to achieve the calculated concentration.
The obtained film had a haze value of 0.7% and a total light transmittance of 87%. At this time, a film that was not coated was also sampled and measured in the same manner. As a result, the haze value was 0.7% and the total light transmittance was 88%. Therefore, in Example 1, the haze increase was 0.0%. Table 2 shows the evaluation results along with surface resistivity and resistance to atmospheric exposure.

Examples 2 to 5
A laminated film was obtained in the same manner as in Example 1 except that the coating liquid was changed as shown in Table 1. The evaluation results for the laminated film are shown in Table 2.

Comparative examples 1 to 3
A laminated film was obtained in the same manner as in Example 1 except that the coating liquid was changed as shown in Table 1. The evaluation results for the laminated film are shown in Table 2.

In Comparative Example 1 using polyvinyl alcohol, which is widely used as a transparent binder, a transparent film was obtained. Regardless, the surface resistivity showed an extremely large value. On the other hand, in comparison with Comparative Example 1, the surface resistivity of the laminated film of Example 1 was 1/10,000 or less.
Further, in a comparison between Example 3 and Comparative Example 1, it was found that the conductivity equivalent to or higher than that of Comparative Example 1 was achieved with one-tenth the amount of conductive agent, and the laminated film of the present invention has antistatic properties and economic efficiency. It turns out that it is very useful from this point of view.
Furthermore, in Comparative Example 2 lacking Compound (B), transparency was impaired and surface resistivity increased.
Furthermore, in Comparative Example 3 using an organic conductive polymer, it was found that the surface resistivity significantly increased due to exposure to the atmosphere and lacked stability.

As described above, the laminated film of the present invention had excellent transparency and exhibited stable antistatic performance even with an extremely small amount of conductive agent (compound (A)).

According to the present invention, an antistatic film having excellent conductivity, transparency, resistance to atmospheric exposure, and high productivity can be provided at a low cost, and therefore has high industrial value.

Claims (10)

A laminated polyester film having an antistatic layer on at least one side of the polyester film, the antistatic layer containing the following compounds (A) and (B), and having a surface resistivity of 2×10 ⁶ Ω or more.
(A) Carbon nanotubes (B) Sugar alcohol with 4 or more carbon atoms The laminated polyester film according to claim 1, wherein the antistatic layer further contains the following compound (C).
(C) One or more resins selected from the group consisting of urethane resins, polyesters, and acrylic resins. The laminated polyester film according to claim 1 or 2, wherein the antistatic layer is stretched in at least one direction. The laminated polyester film according to any one of claims 1 to 3, which has a haze increase rate of 1.0% or less when compared to a polyester film not provided with an antistatic layer. The laminated polyester film according to any one of claims 1 to 4, which has a total light transmittance of 85% or more. The laminated polyester film according to any one of claims 1 to 5, wherein the sugar alcohol has 4 to 6 carbon atoms. The laminated polyester film according to any one of claims 1 to 6, wherein the sugar alcohol has the same number of carbon atoms and the same number of hydroxyl groups. The laminated polyester film according to any one of claims 1 to 7, wherein the content of the carbon nanotubes (A) is 3% by mass or less based on the total solid content. The laminated polyester film according to any one of claims 2 to 8, wherein the content of the compound (C) is 2% by mass or more based on the total solid content. The laminated polyester film according to any one of claims 1 to 9, wherein the antistatic layer further contains a surfactant.