Laminated polyester film

Abstract

To provide a laminated polyester film which is excellent in handleability, and at a wavelength where the relative luminosity factor is high, shows little glare on the surface due to reflection light, and which furthermore at a wavelength where the relative luminosity factor is low, is suitably visible.SOLUTION: A laminated polyester film is provided, comprising, on at least one surface of a polyester film, a resin layer formed using a resin composition. The resin composition includes a fluorine-containing compound and particles, has an absolute reflectivity of 2.0% or less at a wavelength of 550 nm and has an absolute reflectivity of 2.1% or more at at least one wavelength of 450 nm or 650 nm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a laminated polyester film.

Background Art

[0002] Polyester films typified by polyethylene terephthalate films and polyethylene naphthalate films have excellent properties such as mechanical properties, dimensional stability, flatness, heat resistance, chemical resistance, and optical properties, and are used in various applications because of their excellent cost performance.

[0003] As an example of the use of polyester films, films with adjusted reflection performance such as antireflection properties and low reflectivity have been proposed. When used in these applications, a method of laminating a functional layer with a low refractive index design or a low reflection design on the surface of the polyester film has been studied.

[0004] For example, Patent Document 1 discloses a laminated polyester film that can solve various problems of a TAC film, has a high total light transmittance, and is particularly suitable for use as a protective film on the rear side of a rear polarizing plate. A laminated polyester film having a resin layer having one minimum value in the range of wavelengths of 300 to 800 nm and the minimum value being 3.5% or less is disclosed.

[0005] Further, Patent Documents 2 and 3 disclose an antireflection film that can reduce the color tone of reflected light and suppress the occurrence of color unevenness, and the difference between the maximum value and the minimum value of the spectral reflectance in the range of wavelengths from 400 nm to 700 nm on the film surface on the low refractive index layer side is 0.2% or more and 0.9% or more.

[0006] Furthermore, Patent Document 4 discloses an optical laminated film having low reflectance, little glare and reflection, and excellent visibility. More specifically, it discloses an optical laminated film having a reflectance of 0.8% or less at a wavelength of 550 nm and a reflectance of 1.2% or less at wavelengths of 430 to 700 nm.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] In recent years, polyester films are sometimes used for face shields and partitions (e.g., acrylic plates for infection prevention measures), etc., and low reflectivity is also required for such applications. However, the films described in Patent Documents 1 to 4 are all assumed to be used only for optical applications, and may not be suitable for the above applications. Specifically, the laminated polyester film of Patent Document 1 has a high minimum value of absolute reflectance and insufficient suppression of surface glare caused by reflected light. On the other hand, the films described in Patent Documents 2 to 4 have a small difference in reflectance between wavelengths with high specific visibility and wavelengths with low specific visibility, and although surface glare can be suppressed, it is difficult to appropriately visually recognize the film itself.

[0009] In addition, for example, as a processing step of a face shield, there are a step of cutting into a sheet shape, a step of punching into a predetermined shape, a step of bending, etc. In a series of processes, intermediate products or final products during manufacturing may be stacked and stored. In such cases, appropriate handleability between sheets is required. That is, as objects that come into contact with the sheet surface (resin layer surface) exposed, the sheets come into contact with each other frequently in addition to the guide rolls for conveyance. Therefore, it is required to balance the adjustment of reflection performance and handleability.

[0010] Therefore, the present invention has been made in view of the above circumstances, and the problem to be solved is that at wavelengths with high specific sensitivity, there is little glare on the surface due to reflected light, and yet at wavelengths with low specific sensitivity, the film itself can be moderately visible, and to provide a laminated polyester film with excellent handleability.

Means for Solving the Problem

[0011] As a result of intensive studies, the present inventors have found that the above problems can be solved by having the following configuration. The present invention has the following aspects.

[0012] [1] A laminated polyester film having a resin layer formed using a resin composition on at least one side of a polyester film, wherein the resin composition contains a fluorine-containing compound and particles, the absolute reflectance at a wavelength of 550 nm is 2.0% or less, and the absolute reflectance at at least one of a wavelength of 450 nm or 650 nm is 2.1% or more.

[0013] [2] The laminated polyester film according to [1] above, wherein the absolute reflectance has one minimum value in the wavelength range of 450 to 650 nm, and the minimum value is 2.0% or less.

[0014] [3] The laminated polyester film according to [1] or [2] above, wherein the resin composition further contains a crosslinking agent.

[0015] [4] The arithmetic mean roughness (Ra) of the surface of the resin layer when measured with a scanning probe microscope is 1.3 nm or more, and the laminated polyester film according to any one of [1] to [3] above.

[0016] [5] The particle size of the particles is 0.3 times or more the thickness of the resin layer, and the laminated polyester film according to any one of [1] to [4] above.

[0017] [6] The particle size of the particles is 20 to 900 nm, and the laminated polyester film according to any one of [1] to [5] above.

[0018] [7] The resin layer is provided on both sides of the polyester film, and the laminated polyester film according to any one of [1] to [6] above.

[0019] [8] The resin layer is in direct contact with the polyester film, and the laminated polyester film according to any one of [1] to [7] above.

[0020] [9] It is for a face shield or a partition, and the laminated polyester film according to any one of [1] to [8] above. [Advantages of the Invention]

[0021] According to the present invention, at wavelengths with high specific visibility, there is little glare on the surface due to reflected light, and yet, at wavelengths with low specific visibility, a laminated polyester film with excellent handleability that allows the film itself to be moderately visible is provided. [Embodiments for Carrying Out the Invention]

[0022] Next, an example of an embodiment of the present invention will be described. However, the present invention is not limited to the embodiments described below.

[0023] [[Laminated Polyester Film]] An example of a laminated polyester film according to an embodiment of the present invention (hereinafter, also referred to as "this laminated polyester film") includes a resin layer formed using a resin composition on at least one side of a polyester film (hereinafter, also referred to as "this polyester film"). Further, the resin composition contains a fluorine-containing compound and particles. Furthermore, this laminated polyester film has an absolute reflectance at a wavelength of 550 nm of 2.0% or less, and an absolute reflectance at at least one of a wavelength of 450 nm or 650 nm of 2.1% or more. In the present invention, "absolute reflectance" is also simply referred to as "reflectance".

[0024] As the laminated structure of this laminated polyester film, a structure in which a resin layer is formed on one side of the polyester film and the surface of the other side is left as the surface of the polyester film may be used, or a structure in which another layer is formed on one side of the other side may be used. Moreover, a structure in which resin layers are formed on both sides of the polyester film may be used. Furthermore, another layer may be provided between the polyester film and the resin layer, but it is preferable that the resin layer is in direct contact with the polyester film.

[0025] <Polyester film> This polyester film serves as a base material for this laminated polyester film. This polyester film may have a single-layer structure or a multilayer structure. When this polyester film has a multilayer structure, this polyester film may have a two-layer structure, a three-layer structure, etc., and may have four or more layers as long as the gist of the present invention is not deviated from, and the number of layers is not particularly limited. Moreover, this polyester film may be an unstretched film (sheet) or a stretched film. Among them, it is preferably a stretched film stretched in a uniaxial direction or a biaxial direction. Among them, it is more preferably a biaxially stretched film in terms of excellent balance of mechanical properties and flatness.

[0026] The polyester that is the raw material of this polyester film may be a homopolyester or a copolyester. When it is composed of a homopolyester, it is preferably obtained by polycondensing an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative homopolyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), etc., and polyethylene terephthalate is preferred.

[0027] On the other hand, the copolyester is preferably, for example, a polycondensation polymer of a dicarboxylic acid component and a glycol component. Examples of the dicarboxylic acid component include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, and oxycarboxylic acid (for example, p-hydroxybenzoic acid, etc.). Also, examples of the glycol component include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol. The copolyester preferably contains terephthalic acid as the dicarboxylic acid component and ethylene glycol as the glycol component. In addition, the copolyester may contain a structural unit derived from a bifunctional compound other than the dicarboxylic acid component and the glycol component. The structural unit derived from a bifunctional compound other than the dicarboxylic acid component and the glycol component is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total moles of all the structural units constituting the polyester. Examples of the bifunctional compound include various hydroxycarboxylic acids and aromatic diols.

[0028] The content of terephthalic acid in all dicarboxylic acid components constituting the present polyester film is preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more. In addition, the content of ethylene glycol in all glycol components constituting the present polyester film is preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more. Note that the upper limit of the content of terephthalic acid and ethylene glycol is 100 mol%.

[0029] There is no particular limitation on the polymerization catalyst for the polyester, and conventionally known compounds can be used. Examples include titanium compounds, germanium compounds, antimony compounds, manganese compounds, aluminum compounds, magnesium compounds, and calcium compounds.

[0030] In order to suppress the precipitation amount of the oligomer component, a film may be produced using a polyester having a low content of the oligomer component as a raw material. As a method for producing a polyester having a low content of the oligomer component, various known methods can be used. Examples include a method of subjecting the polyester to solid-phase polymerization after production. In addition, the present polyester film may have a three-layer or more structure, and the outermost layer of the present polyester film may be a layer using a polyester raw material having a low content of the oligomer component, thereby suppressing the precipitation amount of the oligomer component. Further, the polyester may be obtained by subjecting it to an esterification or transesterification reaction and then further increasing the reaction temperature and performing melt polycondensation under reduced pressure.

[0031] Particles can also be blended in the present polyester film mainly for the purpose of imparting slipperiness and preventing the generation of scratches in each process. The types of particles to be combined are not particularly limited as long as they can impart lubricity. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide; and organic particles such as acrylic resin, styrene resin, urea resin, phenol resin, epoxy resin, and benzoguanamine resin. Furthermore, during the polyester manufacturing process, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst can also be used.

[0032] The shape of the particles to be used is not particularly limited either, and any of spherical, massive, rod-shaped, flat-shaped, etc. may be used. Also, there are no particular restrictions on their hardness, specific gravity, color, etc. These series of particles may be used in combination of two or more types as necessary.

[0033] In addition, the average particle diameter of the particles to be used is usually 5 μm or less, preferably in the range of 0.01 to 3 μm. When it is 5 μm or less, the surface roughness of the film does not become too rough, and there are no problems when forming various surface functional layers in subsequent processes, which is preferable. Also, if the average particle diameter is within such a range, haze can be suppressed low, and it is easy to ensure transparency for the entire laminated polyester film. Note that when the particles are in powder form, the average particle diameter can be taken as the particle diameter (d50) at the cumulative volume fraction of 50% in the equivalent spherical distribution obtained by measuring the powder using a centrifugal sedimentation type particle size distribution measuring device (for example, "SA-CP3 type" manufactured by Shimadzu Corporation). For the average particle diameter of the particles in the film, layer, or resin, the diameters of 10 or more particles can be measured by observing them with a scanning electron microscope (SEM), and the average value can be obtained. In that case, for non-spherical particles, the average value of the longest diameter and the shortest diameter can be measured as the diameter of each particle.

[0034] When incorporating particles into this polyester film, for example, it is preferable to provide a surface layer and an intermediate layer and incorporate the particles into the surface layer. In this case, more preferably, a multilayer structure having a surface layer containing particles, an intermediate layer, and a surface layer containing particles in this order may be used. The thickness of the layer containing particles depends on the average particle size and content of the particles, but is usually in the range of 0.5 to 125 μm, preferably 1 to 10 μm. If it is 0.5 μm or more, there will be no particle dropout, and if it is 125 μm or less, sufficient transparency will be achieved. The content of the particles depends on the average particle size as well. In the layer containing particles, it is usually 5000 ppm or less, preferably 50 to 1000 ppm, more preferably 100 to 500 ppm. When there are no particles or the particle content is low, sufficient slipperiness cannot be imparted. Although the transparency of the polyester film increases, the slipperiness may become insufficient. Therefore, when it is necessary to improve the slipperiness, etc., it may be necessary to incorporate particles into the resin layer described later. Also, if it is 5000 ppm or less, sufficient transparency of the polyester film can be ensured. Also, the value of the thickness (μm) of the layer containing particles × the content of the particles (ppm) is usually 80,000 or less, preferably 100 to 20,000, more preferably 500 to 8000, and even more preferably 1000 to 4000. When there are multiple layers containing particles, the total value of them is used. In an example of a suitable application of this laminated polyester film, when looking through the film like a face shield or partition, the amount of particles in the film thickness direction affects the clarity described later. Therefore, if the value of the layer thickness × the particle content is 80,000 or less, there will be less cloudiness and it will be possible to maintain a good view.

[0035] To enhance the transparency of the film and obtain the clarity described later, it is preferable that "substantially no particles are contained". When substantially no particles are contained, the slipperiness of the film becomes insufficient, but with the resin layer according to the present invention, a laminated polyester film having slipperiness while maintaining transparency can be obtained. In addition, the above-mentioned "substantially free of particles" means, for example, in the case of inorganic particles, a content of 50 ppm or less, preferably 40 ppm or less when quantitatively analyzing inorganic elements by fluorescent X-ray analysis. This is because even if particles are not actively added to the polyester film as the base material, contaminants derived from foreign substances or dirt adhering to the lines and equipment in the raw material resin or film manufacturing process may peel off and mix into the film.

[0036] The method of adding particles to this polyester film is not particularly limited, and a conventionally known method can be adopted. For example, in the case of a multilayer polyester film, it can be added at any stage of manufacturing the polyester constituting each layer, but it is preferably added after the completion of the esterification or transesterification reaction.

[0037] In addition, in this polyester film, conventionally known ultraviolet absorbers, antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. can be added as necessary in addition to the above-mentioned particles.

[0038] The thickness of the polyester film is not particularly limited as long as it is within the range where the film can be formed, but from the viewpoints of mechanical strength, handleability, productivity, etc., it is preferably 1 μm or more, more preferably 10 μm or more, still more preferably 25 μm or more, particularly preferably 50 μm or more, and preferably 500 μm or less, more preferably 300 μm or less, still more preferably 250 μm or less, particularly preferably 200 μm or less.

[0039] Next, the manufacturing examples of the present polyester film will be specifically described, but it is not limited to the following manufacturing examples. For example, when manufacturing a biaxially stretched film, it is preferable to use the method of extruding the dried pellets of the polyester raw material described above from a die as a molten sheet using an extruder and cooling and solidifying it with a cooling roll to obtain an unstretched sheet. In this case, in order to improve the flatness of the sheet, it is preferable to enhance the adhesion between the sheet and the rotating cooling drum, and the electrostatic printing adhesion method and / or the liquid coating adhesion method are preferably adopted.

[0040] Next, the obtained unstretched sheet is stretched in the biaxial direction. In that case, first, the above-mentioned unstretched sheet is stretched in one direction by a roll or tenter-type stretching machine. The stretching temperature is usually 70 to 120 °C, preferably 80 to 110 °C, and the stretching ratio is usually 2.5 to 7.0 times, preferably 3.0 to 6.0 times. Then, it is stretched in a direction perpendicular to the stretching direction of the first stage. In that case, the stretching temperature is usually 70 to 170 °C, and the stretching ratio is usually 3.0 to 7.0 times, preferably 3.5 to 6.0 times. Then, subsequently, heat treatment is carried out at a temperature of usually 180 to 270 °C under tension or under relaxation within 30% to obtain a biaxially stretched film. In the above stretching, a method of performing the stretching in one direction in two or more stages can also be adopted. In that case, it is preferable to perform it so that the final biaxial stretching ratios are respectively within the above ranges.

[0041] In addition, the simultaneous biaxial stretching method can also be adopted in the manufacture of the present polyester film. The simultaneous biaxial stretching method is a method of simultaneously stretching and orienting the above-mentioned unstretched sheet in the machine direction and the width direction in a state where the temperature is controlled at usually 70 to 120 °C, preferably 80 to 110 °C. As the stretching ratio, the area ratio is preferably 4 to 50 times, more preferably 7 to 35 times, and even more preferably 10 to 25 times. Then, subsequently, heat treatment is carried out at a temperature of usually 170 to 250 °C under tension or under relaxation within 30% to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching device adopting the above-mentioned stretching method, conventionally known stretching methods such as a screw method, a pantograph method, and a linear drive method can be adopted.

[0042] <Resin layer> This laminated film includes a resin layer (hereinafter also referred to as "the present resin layer") formed from a resin composition on at least one side of a polyester film. As described above, the present resin layer is formed from a resin composition (hereinafter also referred to as "the present composition"), and the present composition contains a fluorine-containing compound and particles.

[0043] (Fluorine-containing compound) The present composition contains a fluorine-containing compound for the purpose of adjusting the reflection performance. From the viewpoint of enhancing the strength of the resin layer, the fluorine-containing compound used in the present composition preferably contains a fluorine-containing resin. Specific examples of the fluorine-containing resin include fluorinated olefin copolymer resins having monomers such as vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, etc.; fluorine-based copolymer resins obtained by polymerizing a polyalkylene ether in which some or all of the hydrogen atoms are substituted with fluorine atoms, such as fluoromethylene ether, difluoromethylene ether, fluoroethylene ether, difluoroethylene ether, tetrafluoroethylene ether, hexafluoropropylene ether, etc., and other monomers; fluorine-based copolymer resins obtained by graft-polymerizing a hydroxy group-containing fluorine resin copolymer and a (meth)acrylic acid ester compound or other monomers; vinyl polymers having a perfluoroalkyl group, etc. Among them, from the viewpoint of being able to form a resin layer with excellent film-forming properties and excellent transparency, it is preferable to contain a fluorine resin copolymer containing a polyalkylene ether group in which some or all of the hydrogen atoms are fluorinated. Among the polyalkylene ethers in which some or all of the hydrogen atoms are substituted with fluorine atoms, it is preferable to contain at least one of difluoromethylene ether, difluoroethylene ether, and tetrafluoroethylene ether. In addition, when the fluorine-containing resin is composed of a fluorine-containing monomer, from the viewpoints of dispersibility in a solvent and compatibility with other resins, it is preferably made into a mixed dispersion with a polymer component contained as other components described below.

[0044] Examples of the fluorine-based copolymer resin obtained by polymerizing a polyalkylene ether in which some or all of the hydrogen atoms are substituted with fluorine atoms and other monomers include urethane resins having a polyfluoroalkylene ether group, polyester resins having a polyfluoroalkylene ether group, and acrylic resins having a polyfluoroalkylene ether group. From the viewpoint of excellent adhesion to a polyester film, it preferably contains a urethane resin having a polyfluoroalkylene ether group. Examples of the other monomers constituting the urethane resin having a polyfluoroalkylene ether group include isocyanate compounds. Examples of the isocyanate compounds include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate; aliphatic diisocyanates having an aromatic ring such as α,α,α’,α’-tetramethylxylylene diisocyanate; aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic diisocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and isopropylidene dicyclohexyl diisocyanate.

[0045] Other monomers constituting the urethane resin include polyols not containing fluorine atoms, polyols having a carboxy group such as dimethylolpropanoic acid, dimethylolbutanoic acid, bis-(2-hydroxyethyl)propanoic acid, and bis-(2-hydroxyethyl)butanoic acid. Among these, from the viewpoint of being able to self-emulsify when water is used as a dispersion solvent, it preferably contains a polyol having a carboxy group, and dimethylolpropanoic acid is more preferable.

[0046] The content of the fluorine-containing compound in the composition is preferably in the range of 50 to 99% by mass, more preferably 70 to 98% by mass, and still more preferably 80 to 95% by mass, as a proportion of the total non-volatile components in the resin composition. By setting the content to 50% by mass or more, the refractive index of the resin layer can be sufficiently reduced, and it becomes possible to suppress the reflectance and the glare. Also, by setting the content to 99% by mass or less, the handleability of the film and the adhesion to the polyester film can be improved by using other components in combination.

[0047] (Particles) The composition contains particles for the purpose of improving handleability such as blocking and slipperiness. By the composition containing particles, it has excellent handleability even in applications where at least a part of the surface of the resin layer is used in an exposed state. Specific examples of the particles are the same as the particles that can be contained in the aforementioned polyester film. Among them, the handleability can be improved without impairing the desired reflection characteristics, and from the viewpoint of transparency, it is preferable to contain silica. From the viewpoint of imparting slipperiness, as described later, it is preferable that the particle size of the particles is equal to or larger than a certain size with respect to the thickness of the resin layer. On the other hand, from the viewpoint of enhancing the transparency of the film and maintaining a clear feeling, as described later, it is preferable that the particle size of the particles is equal to or smaller than a certain size. Therefore, in the laminated polyester film of the present invention, by adjusting the particle content contained in the polyester film and then adjusting the particle size of the particles contained in the resin layer, it becomes possible to maintain excellent transparency and slipperiness. When this laminated polyester film has excellent transparency, it can be more preferably used in applications where a clear feeling is required, such as face shields and partitions.

[0048] The particle size of the particles is preferably 0.3 times or more, more preferably 0.5 times or more, still more preferably 0.8 times or more, particularly preferably 1.5 times or more, and preferably 8.0 times or less, more preferably 6.0 times or less, still more preferably 4.0 times or less, relative to the thickness of the resin layer. By setting the particle size of the particles to 0.3 times or more relative to the thickness of the resin layer, unevenness can be formed on the surface of the resin layer to improve the slipperiness. On the other hand, by setting the particle size to 8.0 times or less, the transparency of the film becomes good.

[0049] The particle size of the particles is preferably 20 to 900 nm, more preferably 50 to 600 nm, still more preferably 80 to 500 nm, particularly preferably 150 to 400 nm. If the particle size is 900 nm or less, the transparency of the film becomes good. On the other hand, if the particle size is 20 nm or more, the slipperiness can be improved more effectively.

[0050] The content of the particles in the composition is preferably in the range of 0.05 to 20% by mass, more preferably 0.1 to 10% by mass, still more preferably 0.2 to 8% by mass, more preferably 0.3 to 5% by mass, as a proportion of the total non-volatile components in the resin composition. If the content of the particles is within such a range, the haze value can be made good, the desired reflection characteristics can be maintained without impairment, and the handleability can be appropriately improved.

[0051] (Crosslinking agent) The composition preferably further contains a crosslinking agent for the purpose of improving the durability of the resin layer and the adhesion to the base material (polyester film). That is, the resin layer may be crosslinked with a crosslinking agent or may contain a compound derived from the crosslinking agent. As the crosslinking agent, from the viewpoint of improving the durability of the resin layer, it is preferable to contain a melamine compound. As crosslinking agents other than melamine compounds, conventionally known crosslinking agents can be used, and examples include epoxy compounds, carbodiimide compounds, oxazoline compounds, isocyanate compounds, and silane coupling compounds. These may be used alone or in combination of two or more.

[0052] A melamine compound refers to a compound having a melamine skeleton in the compound. For example, an alkylolated melamine derivative, a compound obtained by reacting an alcohol with an alkylolated melamine derivative to partially or completely etherify it, and mixtures thereof can be used. Examples of alkylolation include methylolation, ethylolation, isopropylation, n-butylation, isobutylation, etc. Among these, from the viewpoint of reactivity, methylolation is preferred. As the alcohol used for etherification, methanol, ethanol, isopropanol, n-butanol, isobutanol, etc. are preferably used, and among these, methanol is more preferred. Further, the melamine compound may be either a monomer or a multimer of dimer or higher, or a mixture thereof may be used. Furthermore, those obtained by co-condensing urea or the like with a part of melamine can also be used, and in order to increase the reactivity of the melamine compound, it is also possible to further use a catalyst in this composition.

[0053] It should be noted that the above crosslinking agent is preferably designed to react in the drying process or the film-forming process to improve the performance of the resin layer. It is presumed that unreacted substances of the crosslinking agent, compounds after reaction, or mixtures thereof are present in the formed resin layer.

[0054] When this composition further contains a crosslinking agent, its content is preferably in the range of 1 to 50% by mass, more preferably 3 to 30% by mass, and still more preferably 5 to 20% by mass as the ratio in the total non-volatile components in the resin composition. By setting the content to 1% by mass or more, the durability of the resin layer and the adhesion to the polyester film can be enhanced. Also, by setting the content to 50% by mass or less, excellent reflectance can be achieved.

[0055] (Other Components) In this composition, various conventionally known polymer components, such as polyester resins, acrylic resins, urethane resins, etc., can be used in combination as binders in order to improve the appearance of the resin layer and the adhesion to the polyester film (base material). As described above, in order to enhance the dispersibility of the fluorine-containing compound in the solvent, a dispersion obtained by mixing the polymer component with the fluorine-containing compound may be used.

[0056] Also, within a range that does not impair the gist of the present invention, in addition to the above components, additives such as defoamers, coating property improvers, surfactants, thickeners, organic lubricants, ultraviolet absorbers, antioxidants, foaming agents, dyes, pigments, etc. may be further appropriately blended.

[0057] (Solvent) This composition may be diluted with a solvent to form a coating solution. That is, as a liquid coating solution, for example, it may be applied to this polyester film and dried and cured as necessary to form a resin layer. Note that each component (fluorine-containing compound, particles, and optionally added components, etc.) constituting this composition may be dissolved in a solvent or dispersed in a solvent. When it is made into a coating solution, the concentration of the total non-volatile components of the resin composition in the coating solution is preferably 0.1 to 50% by mass. If it is 0.1% by mass or more, a resin layer with a desired thickness can be efficiently formed. On the other hand, if it is 50% by mass or less, the appearance of the resin layer can be improved by suppressing the viscosity during coating, and the stability in the coating solution can be enhanced.

[0058] The solvent is not particularly limited, and either water or an organic solvent can be used. From the perspective of environmental protection, it is preferable to use water as the main solvent (50% by mass or more), and it is more preferable to make the fluorine-containing compound into an aqueous dispersion. Regarding the water content, it is preferably 60% by mass or more, more preferably 70% by mass or more. The aqueous coating solution may contain a small amount of an organic solvent. The specific amount of the organic solvent should be less than that of water on a mass basis. For example, it may be less than 50% by mass, preferably less than 30% by mass, more preferably less than 20% by mass in the solvent. Examples of the organic solvent used in combination with water include alcohols such as ethanol, isopropanol, ethylene glycol, and glycerin; ethers such as ethyl cellosolve, t-butyl cellosolve, propylene glycol monomethyl ether, and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate; amines such as dimethylethanolamine, etc. These can be used alone or in combination of a plurality. By appropriately selecting and containing these organic solvents in the aqueous coating solution as necessary, the stability and coatability of the coating solution may be improved.

[0059] When only an organic solvent is used as the above solvent, examples of such an organic solvent include aromatic hydrocarbons such as toluene; aliphatic hydrocarbons such as hexane, heptane, and isooctane; esters such as ethyl acetate and butyl acetate; ketones such as ethyl methyl ketone and isobutyl methyl ketone; alcohols such as ethanol and 2-propanol; ethers such as diisopropyl ether and dibutyl ether, etc. These may be used alone in consideration of solubility, coatability, boiling point, etc., or a plurality of types may be mixed and used.

[0060] It can be presumed that unreacted substances, post-reaction compounds, or mixtures thereof of each component (fluorine-containing compound, particles, and optionally added components, etc.) constituting the present composition are present in the resin layer.

[0061] (Method for forming the resin layer) Next, the method for forming the resin layer constituting the present laminated polyester film will be described. The method for forming the present resin layer is not particularly limited, and for example, conventionally known coating methods such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, etc. can be used. In addition, as the method for forming the resin layer, there are in-line coating and off-line coating. Regarding the drying and curing conditions, it is not particularly limited. For example, when providing the resin layer by off-line coating, usually, heat treatment is preferably performed with a reference of 80 to 200 °C for 3 to 40 seconds, preferably 100 to 180 °C for 3 to 40 seconds. On the other hand, when providing the resin layer by in-line coating, usually, heat treatment is preferably performed with a reference of 70 to 280 °C for 3 to 200 seconds.

[0062] In the present invention, the resin layer is preferably formed by in-line coating that treats the film surface during the film formation process of the polyester film. In-line coating is a method of performing coating within the process of manufacturing a polyester film. Specifically, it is a method of performing coating at an arbitrary stage from when polyester is melt-extruded to after stretching and before heat setting and winding up. Usually, coating is performed on any of the unstretched sheet obtained by melting and quenching, the uniaxially stretched film, the biaxially stretched film before heat setting, and the film after heat setting and before winding up.

[0063] Although not limited to the following, for example, in sequential biaxial stretching, a method of coating the uniaxially stretched film stretched particularly in the longitudinal direction (vertical direction) and then stretching it in the transverse direction is excellent. According to such a method, film formation and resin layer formation can be performed simultaneously, so there is an advantage in terms of manufacturing cost. Also, since stretching is performed after coating, the thickness of the resin layer can be changed according to the stretching ratio, and thin film coating can be performed more easily compared to off-line coated films.

[0064] Further, by providing a resin layer on the film before stretching, the resin layer can be stretched together with the polyester film, whereby the resin layer can be firmly adhered to the polyester film.

[0065] Furthermore, in the production of a biaxially stretched polyester film, by stretching while gripping the film edge with a clip or the like, the film can be restrained in the longitudinal and transverse directions, and in the heat setting step, a high temperature can be applied while maintaining flatness without wrinkles. Therefore, since the heat treatment applied after coating can be set to a high temperature that cannot be achieved by other methods, the film-forming property of the resin layer is improved, and the resin layer and the polyester film can be more firmly adhered. Furthermore, a strong resin layer can be obtained, and the performance such as migration resistance and moisture and heat resistance to various functional layers that can be formed on the resin layer can be improved.

[0066] Also, regardless of whether it is offline coating or inline coating, heat treatment and irradiation with active energy rays such as ultraviolet rays may be used in combination as necessary. The polyester film constituting this laminated polyester film may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

[0067] The thickness of the resin layer, as the thickness of the resin layer in the finally obtained laminated polyester film, is preferably 0.05 to 0.15 μm, more preferably 0.07 to 0.12 μm, and even more preferably 0.08 to 0.11 μm. By setting the thickness of the resin layer in the range of 0.05 to 0.15 μm, the absolute reflectance at wavelengths of 450 nm, 550 nm, and 650 nm can be controlled.

[0068] <Physical properties of the laminated polyester film> This laminated polyester film has an absolute reflectance at a wavelength of 550 nm of 2.0% or less, and an absolute reflectance at at least one of wavelengths of 450 nm or 650 nm of 2.1% or more. The "specific luminous sensitivity" is defined as the spectral sensitivity of the visual sensation to light being the luminous sensitivity, and further normalizing the peak value of the luminous sensitivity to 1. In the present invention, the wavelength with high specific luminous sensitivity is 550 nm, and the wavelengths with low specific luminous sensitivity are 450 nm or 650 nm. Therefore, in this laminated polyester film, if the absolute reflectance at the wavelength of 550 nm with high specific luminous sensitivity exceeds 2.0%, sufficient visibility cannot be obtained due to the glare on the surface caused by the reflected light. From the viewpoint of suppressing the glare on the surface and improving the visibility, the absolute reflectance is preferably 1.8% or less, more preferably 1.6% or less, and still more preferably 1.5% or less. Also, in this laminated polyester film, if the absolute reflectance at at least one of the wavelengths of 450 nm or 650 nm with low specific luminous sensitivity is less than 2.1%, it becomes difficult to appropriately visually recognize the film itself. From the viewpoint of enabling appropriate visual recognition of the film itself, the absolute reflectance is preferably 2.3% or more, more preferably 2.5% or more, and still more preferably 3.0% or more. The absolute reflectance of this laminated polyester film can be measured by the method described in the examples.

[0069] Furthermore, the difference in absolute reflectance (reflectance difference) between the maximum value of the absolute reflectance at the wavelengths of 450 nm and 650 nm and the absolute reflectance at the wavelength of 550 nm is preferably 0.5% or more, more preferably 1.0% or more, still more preferably 1.5% or more, and particularly preferably 2.0% or more. If the reflectance difference is 0.5% or more, the film can be more appropriately visually recognized. The upper limit value of the reflectance difference is not particularly limited, but is about 20%.

[0070] From the perspective of reducing the reflectance of wavelengths with high specific sensitivity to suppress glare and improving the visibility of the film, this laminated polyester film preferably has one minimum value in the absolute reflectance range of 450 to 650 nm, and the minimum value is preferably 2.0% or less. From the above perspective, the minimum value is more preferably in the range of 480 to 620 nm, and even more preferably in the range of 500 to 600 nm. Also, from the same perspective, the minimum value is more preferably 1.8% or less, even more preferably 1.6% or less, and particularly preferably 1.5% or less.

[0071] The arithmetic mean roughness (Ra) of the surface of the resin layer of this laminated polyester film is preferably 1.3 nm or more, more preferably 1.5 nm or more, even more preferably 2.0 nm or more, and particularly preferably 2.8 nm or more. If the arithmetic mean roughness is 1.3 nm or more, appropriate slipperiness can be obtained. On the other hand, the upper limit value of the arithmetic mean roughness is not particularly limited, but is about 500 nm. Also, the ten-point mean roughness (Rzjis) of the surface of the resin layer is preferably 4 nm or more, more preferably 7 nm or more, even more preferably 10 nm or more, and particularly preferably 20 nm or more. If the ten-point mean roughness is 4 nm or more, appropriate slipperiness can be obtained. On the other hand, the upper limit value of the ten-point mean roughness is not particularly limited, but is about 1000 nm. In addition, the arithmetic mean roughness (Ra) and the ten-point mean roughness (Rzjis) of the surface of the resin layer are measured by the method described in the examples using an atomic force microscope (scanning probe microscope). If it is measured by an atomic force microscope (scanning probe microscope), it is possible to capture a finer structure of the surface and obtain a numerical value that strongly reflects the effect of the resin layer. With the numerical value ranges of the arithmetic mean roughness (Ra) and the ten-point mean roughness (Rzjis) by this method, a resin layer with excellent slipperiness can be obtained without impairing the transparency of the film. The above arithmetic mean roughness (Ra) and ten-point mean roughness (Rzjis) can be adjusted by the particle size and content of the particles contained in the resin layer.

[0072] In addition, the arithmetic mean roughness (Sa) of the resin layer surface can also be measured by a non-contact surface roughness meter using light interference, specifically, it can be measured by the method described in the examples. With the numerical values obtained by this method, numerical values reflecting a wider area of the laminated polyester film can be obtained. Therefore, by considering both the arithmetic mean roughness (Ra) and the arithmetic mean roughness (Sa), it becomes possible to consider the characteristics of the surface state in more detail. Specifically, when the arithmetic mean roughness (Sa) is low, the transparency of the film is better. On the other hand, when the arithmetic mean roughness (Ra) is high, it can represent better slipperiness. Therefore, by multiplying the respective numerical values, a film with excellent slipperiness can be obtained without sacrificing transparency. The arithmetic mean roughness (Sa) can be adjusted by the particle size and content of the particles contained in the polyester film and the particle size and content of the particles contained in the resin layer. The numerical value (Ra×Sa) obtained by multiplying the arithmetic mean roughness (Ra) and the arithmetic mean roughness (Sa) is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more. If Ra×Sa is 5 or more, a film with excellent slipperiness can be obtained.

[0073] The coefficient of kinetic friction between the surface of the resin layer of the present laminated polyester film and the opposite surface is preferably 1.4 or less, more preferably 1.3 or less, even more preferably 1.0 or less, and particularly preferably 0.5 or less. When the present laminated polyester film is wound up or stacked in a sheet state, the surface opposite to the resin layer surface comes into contact, so the coefficient of kinetic friction between the surface of the resin layer and the opposite surface is important. Therefore, if the coefficient of kinetic friction is 1.4 or less, the slipperiness is good, and the handleability of the present laminated polyester film is improved. In addition, when the present laminated polyester film has the present resin layer on both sides, the coefficient of kinetic friction can be efficiently reduced compared to the case where the present resin layer is provided on only one side. Therefore, when it is desired to significantly improve the handling property, it is preferable to provide the resin layers on both sides, and it can be particularly preferably used for applications where the sheets (resin layers) come into contact with each other frequently, such as for face shields and the like. The above-mentioned coefficient of kinetic friction can be measured by the method described in the examples.

[0074] The haze of this laminated polyester film is preferably 2.0% or less, more preferably 1.8% or less, still more preferably 1.6% or less, and particularly preferably 1.5% or less. If it is within the range with haze, it can be said that the transparency is good. The lower limit value is not particularly limited and is about 0.01%.

[0075] The total light transmittance of this laminated polyester film is preferably 92% or more, more preferably 95% or more, and still more preferably 97% or more. If the total light transmittance is 92% or more, sufficient visibility can be ensured. The upper limit value of the total light transmittance is 100%.

[0076] <Applications of the laminated polyester film> This laminated polyester film can be used for various applications without particular limitation. Among them, at wavelengths with high specific visibility, while suppressing the glare on the surface due to reflected light to provide good visibility, at wavelengths with low specific visibility, it can be suitably used in applications that require the property of being able to moderately visualize the film itself. Such applications include face shields and partitions. Specifically, when this laminated polyester film has a resin layer on only one side, since the side opposite to the resin layer can be bonded to something and used, it can be particularly preferably used for partitions (for example, acrylic plates for infection prevention measures). On the other hand, when it has resin layers on both sides, since a single laminated polyester film can be used as it is, it can be particularly preferably used for face shields.

[0077] <<Explanation of terms>> In the present invention, when referring to "film", it includes "sheet", and when referring to "sheet", it includes "film". In the present invention, when described as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", and also includes the meaning of "preferably greater than X" or "preferably less than Y". Also, when described as "X or more" (X is an arbitrary number), unless otherwise specified, it includes the meaning of "preferably greater than X", and when described as "Y or less" (Y is an arbitrary number), unless otherwise specified, it includes the meaning of "preferably less than Y".

Example

[0078] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

[0079] <Evaluation method> (1) Intrinsic viscosity of polyester (dl / g) 1 g of polyester from which incompatible components have been removed was precisely weighed, 100 mL of a mixed solvent of phenol / tetrachloroethane = 50 / 50 (mass ratio) was added and dissolved, and the viscosity (IV) was measured at 30°C using a viscosity measuring device "VMS-022UPC·F10" (manufactured by Rikai Co., Ltd.).

[0080] (2) Average particle diameter The average particle diameter was determined as the average value of the diameters of 10 or more particles observed with a scanning electron microscope (SEM). In this case, for non-spherical particles, the average value of the longest diameter and the shortest diameter was measured as the diameter of each particle.

[0081] (3) Thickness of the resin layer The surface of the resin layer was stained with RuO4 and embedded in an epoxy resin. Thereafter, the sections prepared by the ultramicrotomy method were stained with RuO4, and the cross-section of the resin layer was measured using a transmission electron microscope (TEM) (manufactured by Hitachi High-Technologies Corporation, H-7650, acceleration voltage 100 kV).

[0082] (4) Measurement of absolute reflectance In the present invention, when the laminated polyester film has a resin layer on only one side, the absolute reflectance was measured by the following measurement method a, and when the laminated polyester film has resin layers on both sides, the absolute reflectance was measured by the following measurement method b. In the measurement of the absolute reflectance, the wavelength (lowest reflectance wavelength) at the minimum value of the reflectance and the minimum value (lowest reflectance), and the absolute reflectances at wavelengths 450 nm, 550 nm, and 650 nm were evaluated. Further, the difference between the maximum value of the absolute reflectances at wavelengths 450 nm and 650 nm and the absolute reflectance at wavelength 550 nm was evaluated as the reflectance difference. (Measurement method a) When the laminated polyester film has a resin layer on only one side, a black tape (Vinyl Tape VT-50 manufactured by Nichiban Co., Ltd.) was attached to the measurement back surface (polyester film surface) of the laminated polyester film, and using a spectrophotometer (Ultraviolet-Visible Spectrophotometer V-670 and Automatic Absolute Reflectance Measuring Device ARMN-735 manufactured by JASCO Corporation), in synchronous mode, incident angle 5°, N polarization, response Fast, data acquisition interval 1.0 nm, bandwidth 10 nm, scanning speed 1000 m / min, the absolute reflectance of the resin layer surface in the wavelength range of 300 to 800 nm was measured. (Measurement method b) When the laminated polyester film has resin layers on both sides, unlike the above measurement method a, no black tape was attached, and using a spectrophotometer (Ultraviolet-Visible Spectrophotometer V-670 and Automatic Absolute Reflectance Measuring Device ARMN-735 manufactured by JASCO Corporation), in synchronous mode, incident angle 5°, N polarization, response Fast, data acquisition interval 1.0 nm, bandwidth 10 nm, scanning speed 1000 m / min, the absolute reflectance of the resin layer surface in the wavelength range of 300 to 800 nm was measured.

[0083] (5) Arithmetic mean roughness (Ra) and ten-point mean roughness (Rzjis) of the resin layer surface Using a scanning probe microscope (SPM-9700 manufactured by Shimadzu Corporation), measurements were carried out under the following conditions. Probe: Silicon cantilever Scanning mode: Dynamic mode Scanning range: 25 μm × 25 μm Scan speed: 0.8 Hz Number of pixels: 512 × 512 data points From the obtained data, the arithmetic mean roughness (Ra) and ten-point mean roughness (Rzjis) in an area of 5 μm × 5 μm were determined. Five data points were obtained from non-overlapping ranges of one measurement data, and this was done from two measurement data, and a total of 10 points were averaged to obtain the result.

[0084] (6) Arithmetic mean roughness (Sa) of the resin layer surface The film surface was measured using a non-contact surface and layer cross-section shape measurement system VertScan (registered trademark) R550GML manufactured by Rhodia Systems Co., Ltd. with a CCD camera: SONY HR-50 1 / 3’, objective lens: 20 times, lens barrel: 1X Body, zoom lens: No Relay, wavelength filter: 530 white, measurement mode: Wave. A region of 640 μm × 480 μm was measured, and using the output by fourth-order polynomial correction, the arithmetic mean roughness Sa value was obtained by averaging 10 points.

[0085] (7) Coefficient of kinetic friction The coefficient of kinetic friction between the resin layer surface of the laminated polyester film and the opposite side was determined by the following method. The film was attached to a smooth glass plate with a width of 10 mm and a length of 100 mm. Then, a film cut to a width of 18 mm and a length of 120 mm was pressed against a metal pin with a diameter of 8 mm. The metal pin was slid along the longitudinal direction of the glass plate with a load of 30 g at a speed of 40 mm / min to measure the frictional force. The average value of the coefficient of friction between 4 mm and 6 mm of sliding was evaluated as the coefficient of kinetic friction. The measurement was carried out in an atmosphere of room temperature 23 ± 1°C and humidity 50 ± 0.5%RH. Also, the number of measurements (N) was 10 times, and the average value was adopted. Coefficient of dynamic friction (μd) = Fd / weight of the weight (In the above formula, the unit of Fd is g-weight, and the unit of the weight of the weight is g-weight)

[0086] (8) Glitter evaluation The reflection and reflection state of the laminated polyester films obtained in the examples, comparative examples, and reference examples were visually observed from the resin layer side and evaluated according to the following evaluation criteria. When the laminated polyester film has a resin layer on only one side, the observation was performed with the black tape used in measurement method a of absolute reflectance attached. A: Reflection is not visible and not noticeable B: Slight reflection is visible but not noticeable C: Reflection is strongly visible and noticeable

[0087] (9) Visibility evaluation of the film itself The visibility of the laminated polyester films obtained in the examples, comparative examples, and reference examples was visually observed from the resin layer side and evaluated according to the following evaluation criteria. When the laminated polyester film has a resin layer on only one side, the observation was performed with the black tape used in measurement method a of absolute reflectance attached. A: A slight bluish or reddish tint can be confirmed, and the film itself can be visually recognized B: The film itself is difficult to visually recognize

[0088] (10) Clarity evaluation The cloudiness of the laminated polyester films obtained in the examples, comparative examples, and reference examples was visually observed from the resin layer side and evaluated according to the following evaluation criteria. A: Appears very clear B: Has a very slight cloudiness C: Has a slight cloudiness D: Has a strong cloudiness and is difficult to see

[0089] (11) Haze and total light transmittance Measured in accordance with JIS K 7136 using a haze meter HM-150 manufactured by Murakami Color Technology Laboratory Co., Ltd.

[0090] <Materials Used> The polyesters used in the examples, comparative examples, and reference examples are as follows.

[0091] [Polyester (A)] Using 100 parts by mass of dimethyl terephthalate and 55 parts by mass of ethylene glycol as starting materials, 0.04 part by mass of magnesium acetate tetrahydrate as a catalyst was placed in the reactor. The reaction start temperature was set at 150°C, and as methanol was distilled off, the reaction temperature was gradually increased, reaching 230°C after 3 hours. After 4 hours, the transesterification reaction was substantially completed. After adding 0.02 part by mass of ethyl acid phosphate to this reaction mixture, 0.04 part by mass of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. The temperature was gradually increased from 230°C to 280°C. On the other hand, the pressure was gradually reduced from normal pressure and finally set at 0.3 mmHg. After the start of the reaction, when the intrinsic viscosity reached 0.65 dl / g as determined by the change in the stirring power of the reaction vessel, the reaction was stopped, and the polymer was discharged under nitrogen pressure to obtain polyester (A) with an intrinsic viscosity of 0.65 dl / g.

[0092] [Polyester (B)] Using 100 parts by mass of dimethyl terephthalate and 45 parts by mass of ethylene glycol as starting materials, 0.06 part by mass of magnesium acetate tetrahydrate as a catalyst was placed in the reactor. The reaction start temperature was set at 150°C, and as methanol was distilled off, the reaction temperature was gradually increased, reaching 230°C after 3 hours. After 4 hours, the transesterification reaction was substantially completed. After adding 0.03 part by mass of ethyl acid phosphate to this reaction mixture, 0.2 part by mass of silica particles with an average particle size of 2.7 μm dispersed in ethylene glycol and 0.03 part by mass of antimony trioxide were added, and a polycondensation reaction was carried out for 4 hours. The temperature was gradually increased from 230°C to 280°C. On the other hand, the pressure was gradually reduced from normal pressure and finally set at 0.3 mmHg. After the start of the reaction, when the intrinsic viscosity reached 0.65 dl / g as determined by the change in the stirring power of the reaction vessel, the reaction was stopped, and the polymer was discharged under nitrogen pressure to obtain polyester (B) with an intrinsic viscosity of 0.65 dl / g.

[0093] The resin composition obtained by stirring and mixing with the composition shown in Table 1 below was diluted with water to prepare coating liquids 1 to 10. The compounds used are as follows.

[0094] [Fluorine-containing compound (I)] An aqueous dispersion of a fluorine-based polyether urethane resin with isophorone diisocyanate / dimethylolpropanoic acid / perfluoroether glycol (difluoroethylene oxide:difluoromethylene oxide:tetrafluoroethylene oxide = 5:43:52 (mol%)) = 40 / 23 / 37 (mol%)

[0095] [Particles (IIA)] Spherical silica particles with an average particle diameter of 45 nm

[0096] [Particles (IIB)] Spherical silica particles with an average particle diameter of 65 nm

[0097] [Particles (IIC)] Spherical silica particles with an average particle diameter of 140 nm

[0098] [Particles (IID)] Spherical silica particles with an average particle diameter of 200 nm

[0099] [Particles (IIE)] Spherical silica particles with an average particle diameter of 450 nm

[0100] [Crosslinking agent (III)] Melamine compound: hexamethoxymethylol melamine

[0101] [Polyester resin (IVA)] An aqueous dispersion of a polyester resin having a condensed polycyclic structure copolymerized with the following composition Monomer composition: (acid component) 2,6-naphthalenedicarboxylic acid / sebacic acid / 5-sodium sulfoisophthalic acid / / (diol component) ethylene glycol / hexanediol / diethylene glycol = 72 / 22 / 6 / / 54 / 34 / 12 (mol%)

[0102] [Metal Oxide (IVB)] Zirconium Oxide Particles with an Average Particle Size of 0.02 μm

[0103] (Example 1) A mixed raw material obtained by mixing Polyester (A) and (B) at a ratio of 92% by mass and 8% by mass, respectively, was used as the raw material for the outermost layer (surface layer), and only Polyester (A) was used as the raw material for the intermediate layer. Each of the raw materials for the outermost layer and the intermediate layer was supplied to two extruders, melted at 285 °C each, and then co-extruded and cooled and solidified on a cooling roll set at 40 °C in a layer configuration of two types and three layers (discharge amount of surface layer / intermediate layer / surface layer = 8 / 84 / 8) to obtain an unstretched sheet. Next, this film was stretched 3.3 times in the longitudinal direction while passing through a heating roll group at 85 °C to obtain a uniaxially stretched film. Coating liquid 1 having the composition shown in Table 1 below was applied to one side of this uniaxially stretched film, and then this film was led to a tenter stretching machine, stretched 4.0 times in the width direction at 100 °C, further heat-treated at 230 °C, and then subjected to a relaxation treatment of 2% in the width direction to obtain a laminated polyester film with a resin layer thickness of 0.10 μm and a polyester film thickness of 100 μm excluding the resin layer. The evaluation results are shown in Table 2.

[0104] (Example 2) A laminated polyester film was obtained in the same manner as in Example 1, except that the coating liquid shown in Table 2 was used. The evaluation results are shown in Table 2.

[0105] (Examples 3 to 11) A laminated polyester film was obtained in the same manner as in Example 1, except that resin layers were formed on both sides of the polyester film using the coating liquid shown in Table 2 and the thickness of the resin layer was set to the value shown in Table 2. The evaluation results are shown in Table 2.

[0106] (Examples 12 to 15) Using only polyester (A) as the raw material for the outermost layer (surface layer) and only polyester (A) as the raw material for the intermediate layer, a resin layer was formed on both sides of the polyester film using the coating solution shown in Table 2, and the thickness of the resin layer was set to the value shown in Table 2. A laminated polyester film was obtained in the same manner as in Example 3 except for these. The evaluation results are shown in Table 2.

[0107] (Example 16) A mixed raw material in which polyesters (A) and (B) were mixed at a ratio of 82% by mass and 18% by mass, respectively, was used as the raw material for the outermost layer (surface layer), and only polyester (A) was used as the raw material for the intermediate layer. Each of the raw materials for the outermost layer and the intermediate layer was supplied to two extruders, melted at 285 °C, and then co-extruded and cooled and solidified on a cooling roll set at 40 °C in a layer configuration of two types and three layers (discharge amount of surface layer / intermediate layer / surface layer = 5 / 90 / 5) to obtain an unstretched sheet. Next, this film was stretched 3.3 times in the longitudinal direction while passing through a heating roll group at 85 °C to obtain a uniaxially stretched film. Coating solution 2 having the composition shown in Table 1 below was applied to both sides of this uniaxially stretched film, and then this film was guided to a tenter stretching machine and stretched 4.0 times in the width direction at 100 °C. Further, after heat treatment at 230 °C, a relaxation treatment of 2% in the width direction was performed to obtain a laminated polyester film having a resin layer thickness of 0.10 μm and a polyester film thickness of 100 μm excluding the resin layer. The evaluation results are shown in Table 2.

[0108] (Example 17) A laminated polyester film was obtained in the same manner as in Example 16 except that a mixed raw material in which polyesters (A) and (B) were mixed at a ratio of 70% by mass and 30% by mass, respectively, was used as the raw material for the outermost layer (surface layer) and co-extruded in a layer configuration of two types and three layers (discharge amount of surface layer / intermediate layer / surface layer = 4 / 92 / 4). The evaluation results are shown in Table 2.

[0109] (Comparative Example 1) A laminated polyester film was obtained in the same manner as in Example 1 except that the coating solution shown in Table 2 was used. The evaluation results are shown in Table 2.

[0110] (Comparative Examples 2 to 4) A laminated polyester film was obtained in the same manner as in Example 1, except that a resin layer was formed on both sides of the polyester film using the coating liquid shown in Table 2 and the thickness of the resin layer was set to the value shown in Table 2. The evaluation results are shown in Table 2.

[0111] (Comparative Example 5) A laminated polyester film was obtained in the same manner as in Example 1, except that no resin layer was provided. Next, coating liquid 10 having the composition shown in Table 1 was applied to one side of the obtained laminated polyester film so that the thickness of the resin layer was 0.15 μm, and heat treatment was performed in an oven at 150 °C for 30 seconds to obtain a laminated polyester film having a resin layer with a refractive index of 1.43. Next, coating liquid 2 having the composition shown in Table 1 was applied on top of the resin layer of the obtained laminated polyester film having a refractive index of 1.43 so that the thickness of the resin layer was 0.09 μm, and heat treatment was performed in an oven at 150 °C for 30 seconds to obtain a laminated polyester film having two resin layers provided on one side. The evaluation results are shown in Table 2.

[0112] (Comparative Example 6) A laminated polyester film (resin layer formed from coating liquid 2 / resin layer formed from coating liquid 10 / polyester film / resin layer formed from coating liquid 10 / resin layer formed from coating liquid 2) having two resin layers provided on both sides was obtained in the same manner as in Comparative Example 5, except that a resin layer was formed on both sides of the polyester film using the coating liquid shown in Table 2. The evaluation results are shown in Table 2.

[0113]

Table 1

[0114]

Table 2

[0115] Note that the "polyester film conditions" in Table 2 indicate the conditions of the layer thickness, the particle content, and the layer thickness × particle content in the surface layer, which is the layer containing particles, among the polyester films used in the examples and comparative examples of the present invention. The details of the polyester film conditions are as shown in Table 3.

[0116]

Table 3

[0117] As shown by the results in Table 2, the laminated polyester film of the present invention has a low absolute reflectance at a wavelength of 550 nm and suppressed glare, so that the visibility through the film is good. Also, since the absolute reflectance at a wavelength of 450 nm or 650 nm is high, it is easy to visually recognize the film itself. Furthermore, it can be seen that the arithmetic mean roughness (Ra) is 1.3 or more, the coefficient of kinetic friction between the films is low, and the handleability is also excellent. On the other hand, in Comparative Example 1 in which the resin layer does not contain particles, the coefficient of kinetic friction is large and the handleability is insufficient. Also, in Comparative Examples 2 to 4 in which the absolute reflectance at a wavelength of 550 nm exceeds 2.0%, glare could not be suppressed. Further, in Comparative Examples 5 and 6 in which the absolute reflectance at a wavelength of 450 nm or 650 nm is less than 2.1%, although glare was suppressed, it was difficult to visually recognize the film itself.

[0118] (Reference Example 1) In the laminated polyester film of Example 2, the absolute reflectance was measured by changing the measurement method from a to b as described above. The evaluation results are shown in Table 4.

[0119]

Table 4

[0120] As shown by the results in Table 4, when the resin layer is provided on only one side, reflected light is generated from the opposite side (the side without the resin layer). Therefore, it can be seen that when nothing is processed on the surface of the opposite side, the reflectance is high and the glare is not suppressed. Therefore, when the resin layer is provided on only one side, in applications where the opposite side of the resin layer is attached to another member and used, at wavelengths with high specific visibility, there is little surface glare due to reflected light, and at the same time, at wavelengths with low specific visibility, the film itself can be moderately visually recognized and can be preferably used. As shown in Table 2, if resin layers are provided on both sides, it becomes possible to preferably use it in various applications.

Industrial Applicability

[0121] The laminated polyester film of the present invention is a film with excellent handleability that can suppress surface glare due to reflected light at wavelengths with high specific visibility and can moderately visually recognize the film itself at wavelengths with low specific visibility. Therefore, the laminated polyester film of the present invention can be preferably used as a face shield or for partitions.

Claims

1. A laminated polyester film comprising a resin layer formed using a resin composition on at least one side of a polyester film, wherein the resin layer is in direct contact with the polyester film, the resin composition contains a fluorine-containing compound and particles, and the absolute reflectance at a wavelength of 550 nm is 2.0% or less, and the absolute reflectance at at least one of a wavelength of 450 nm or 650 nm is 2.1% or more.

2. A laminated polyester film comprising a resin layer formed using a resin composition on at least one side of a polyester film, wherein the resin composition contains a fluorine-containing compound and particles, the absolute reflectance at a wavelength of 550 nm is 2.0% or less, and the absolute reflectance at at least one of a wavelength of 450 nm or 650 nm is 2.1% or more, and the laminated polyester film is for a face shield or a partition.

3. The laminated polyester film according to claim 1 or 2, wherein the absolute reflectance has one minimum value in the range of wavelengths from 450 to 650 nm, and the minimum value is 2.0% or less.

4. The laminated polyester film according to any one of claims 1 to 3, wherein the resin composition further contains a crosslinking agent.

5. The laminated polyester film according to any one of claims 1 to 4, wherein the arithmetic mean roughness (Ra) of the surface of the resin layer when measured with a scanning probe microscope is 1.3 nm or more.

6. The laminated polyester film according to any one of claims 1 to 5, wherein the particle size of the particles is 0.3 times or more the thickness of the resin layer.

7. The laminated polyester film according to any one of claims 1 to 6, wherein the particle size of the particles is from 20 to 900 nm.

8. The laminated polyester film according to any one of claims 1 to 7, comprising the resin layer on both sides of the polyester film.

Images