JP2018069573A - Laminated polyester film, and blue light-cut film for protecting screen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated polyester film high in durability to ultraviolet light (weatherability), high in visibility of a screen when using as protection of the screen having an LED light source, high in performance to cut blue light emitted from the screen, and not having a yellow tint, and a blue light-cut film for protecting a screen.SOLUTION: A laminated polyester film comprises a substrate polyester film having a layer containing an ultraviolet light absorber and a fluorescent whitening agent where the color tone bvalue is in the range of -5 to +3, the average light transmittance in a wave length region of not less than 380 nm and less than 500 nm is not greater than 70%, and the average light transmittance in a wave length region of not less than 500 nm and not greater than 780 nm is not less than 85%.SELECTED DRAWING: None

Description

  The present invention relates to a laminated polyester film and a blue light cut film for screen protection.

  Polyester film, especially biaxially stretched polyester film represented by polyethylene terephthalate resin film is excellent in electrical property, mechanical property, thermal property, workability and chemical resistance. It is used in many applications including metal insulating materials, metal vapor deposition materials, plate making materials, magnetic recording materials, display materials, transfer materials, window paste materials and the like. In particular, for pasting the front panel glass surface of so-called flat panel displays such as transparent touch panels, base films for prism sheets used in liquid crystal display devices, cathode ray tubes, LCD (Liquid Crystal Display), PDP (Plasma Display Panel), etc. In addition, it is widely used in various optical applications such as a base film of a protective film provided with a functional layer such as antistatic, antireflection, and electromagnetic wave shielding.

As such a functional film, for example, for the purpose of easily providing a polyester film having no scratches and excellent transparency, a primary particle size of 0 is provided on both surfaces of a polyester layer substantially free of particles. A layer having a thickness of 0.01 to 0.15 μm and a Mohs hardness of 5 or more, and a multilayer structure in which surface layers each having a thickness of 3 times or more of the primary particle diameter of the particles are laminated. A transparent multilayer polyester film having an internal haze per mm of 5.0% or less is disclosed (for example, see Patent Document 1).
Also, when used as various optical members such as liquid crystal displays, plasma displays, organic EL (electroluminescence), projection displays, etc., it is possible to achieve high brightness and to provide high quality images without unevenness and defects. For the purpose of providing a polyester film having good optical performance, the film haze is 3.0% or less, and the fluorescent whitening agent is contained in an amount of 0.01 to 1.0% by weight. An optically biaxially oriented polyester film is disclosed (for example, see Patent Document 2).

JP-A-11-157036 JP 2006-176551 A

As the problem to be solved of the invention described in Patent Document 1, since the polyester film is easily scratched, there is a drawback that the appearance and optical characteristics are easily impaired.
In addition, PDAs (Personal Digital Assistants), mobile phones, portable game machines, and the like are increasingly used outdoors, and the time for direct exposure to sunlight is increasing. Sun rays contain ultraviolet rays that deteriorate the thermoplastic resin film, and when exposed to sunlight for a long time, the film deteriorates, causing problems in visibility and adhesion of the laminate, and the film substrate itself. The problem of yellowing occurred.

In addition, blue light having a light wavelength of 380 nm to 500 nm having strong energy among visible rays may pass through the cornea and the lens, damage the macula of the retina, and cause eye disease (age-related macular degeneration). .
Furthermore, blue light has been found to be a major factor in VDT (Visual Display Terminal) syndrome such as eye strain and dry eye.

A display using an LED (Light Emitting Diode) light source used for a liquid crystal display of a personal computer or a smartphone has a feature that the wavelength of blue light is strong.
Recently, there is an increasing demand for blue light cut films for PCs and smartphones. By reducing the light transmittance in the blue light wavelength region, the light transmittance outside the blue light wavelength region is reduced to less than 85%. The brightness of the screen may be lowered.
In addition, by reducing the wavelength range of blue light, due to a decrease in the transmittance of the blue light wavelength range, there is a problem of coloring that the film becomes yellowish.

  The present invention has been made in view of the above circumstances, and the problem to be solved is that it has high durability (weather resistance) against ultraviolet rays, and when it is used for protection of a screen using an LED as a light source, the screen is visually recognized. To provide a laminated polyester film and a blue light cut film for screen protection that are highly resistant and have a high performance (blue light cut performance) for cutting blue light irradiated from the screen without being yellowish. is there.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by adopting a specific configuration, and the present invention has been completed.

That is, the present invention
<1> A laminated polyester film comprising a base polyester film having a layer containing an ultraviolet absorber and a fluorescent brightening agent,
The color tone b ^* value measured by a single method by the transmission method is in the range of −5 to +3, the average light transmittance in the wavelength region from 380 nm to less than 500 nm is 70% or less, and the wavelength region in the range from 500 nm to 780 nm. Is a laminated polyester film having an average light transmittance of 85% or more.

<2> The laminated polyester film according to <1>, wherein the light transmittance at 380 nm is 5.0% or less.

<3> The base polyester film has a surface layer and an intermediate layer, the intermediate layer is a layer containing the ultraviolet absorber and a fluorescent brightening agent, and the ultraviolet absorber in the surface layer and The laminated polyester film according to <1> or <2>, wherein the content of the optical brightener is less than 0.01% by mass and less than 0.005% by mass, respectively.

<4> The laminated polyester film according to <3>, wherein the surface layer is a polyester layer having an ester cyclic trimer content of 0.7% by mass or less.

<5> The laminated polyester film according to <4>, wherein the polyester layer further contains particles.

<6> In any one of <3> to <5>, the content of the ultraviolet absorber in the layer containing the ultraviolet absorber and the fluorescent brightener is 0.20 to 10.0 mass%. It is a laminated polyester film of description.

<7> Any one of <3> to <6>, wherein the content of the optical brightener in the layer containing the ultraviolet absorber and the optical brightener is 0.01 to 1.0% by mass. Is a laminated polyester film described in 1.

<8> Any of <1> to <7>, wherein the ultraviolet absorber is at least one selected from the group consisting of a benzophenone compound, a 1,3,5-triazine compound, and a benzoxazinone compound Or a laminated polyester film according to any one of the above.

<9> The laminated polyester film according to any one of <1> to <8>, wherein an adhesive layer containing a crosslinking agent is adjacent to a surface layer of the base polyester film.

<10> A blue light cut film for screen protection using the laminated polyester film according to any one of <1> to <9>.

  According to the present invention, it has high durability (weather resistance) against ultraviolet rays, and when it is used to protect a screen using an LED as a light source, the visibility of the screen is high, and further, the blue light emitted from the screen It is possible to obtain a laminated polyester film and a blue light cut film for screen protection that have a high performance of cutting and that is not yellowish.

<Laminated polyester film>
The laminated polyester film of the present invention is a laminated polyester film comprising a base polyester film having a layer containing an ultraviolet absorber and a fluorescent brightening agent, and a color tone b ^* value measured by a single sheet by a transmission method is -5 to 5. The average light transmittance in the wavelength region at 380 nm or more and less than 500 nm is 70% or less, and the average light transmittance in the wavelength region at 500 nm or more and 780 nm or less is 85% or more.

[Laminated structure of laminated polyester film]
The laminated polyester film of the present invention has at least a base polyester film (hereinafter sometimes simply referred to as “base film”), and in addition to an adhesive layer adjacent to the base film, a hard coat layer, etc. Various functional layers. The base film may be a laminated film in which a layer containing an ultraviolet absorber and a fluorescent brightener and a layer other than the layer containing the ultraviolet absorber and the fluorescent brightener are laminated, or the ultraviolet absorber. In addition, a laminated film in which a plurality of layers containing an optical brightener is laminated may be used, but a layer containing an ultraviolet absorber and an optical brightener is referred to as an intermediate layer (hereinafter, the intermediate layer is referred to as “I layer”). S / I / S three-layer structure in which the intermediate layer is sandwiched by a surface layer that does not contain an ultraviolet absorber and a fluorescent brightening agent (hereinafter, the surface layer may be referred to as “S layer”) It is preferable that it is a laminated body which has.
The base film of the laminated polyester film may have a structure of 4 or more layers, and when the intermediate layer of 2 or more layers is defined as I-1, I-2, and so on, S / I-1 / I -2 /.../ S.
In the following, the term “surface layer” refers to the surface layer of the substrate film, and the term “intermediate layer” refers to the intermediate layer of the substrate film. Therefore, the surface layer of the base film may be the outermost layer of the laminated polyester film of the present invention, or the hard coat layer bonded through the adhesive layer adjacent to the surface layer of the base film is the laminate of the present invention. It may be the outermost layer of the polyester film.

The surface layer that does not contain the ultraviolet absorber and the optical brightener is preferably a polyester layer having an ester cyclic trimer content of 0.7% by mass or less, and the polyester layer may further contain particles. preferable. In addition, "it does not contain an ultraviolet absorber and an optical brightener" means that the surface layer does not substantially contain an ultraviolet absorber and an optical brightener, and the ultraviolet absorber and the optical brightener in the surface layer. It means that the content is less than 0.01% by mass and less than 0.005% by mass, respectively.
By setting it as such a laminated structure, the low molecular weight ultraviolet absorber and fluorescent whitening agent contained in the intermediate layer are less likely to precipitate from the polyester film. As a result, it is possible to suppress the problem of contamination of lines due to bleeding out of ultraviolet absorbers and the like in the polyester film production line, and the problem of contamination of subsequent process lines that impart functionality.

As described above, an adhesive layer containing a crosslinking agent or the like may be adjacent to the surface layer of the base film of the laminated polyester film of the present invention in order to obtain adhesion to other members.
The adhesive layer is preferably adjacent to at least one side of the surface layer of the base film of the laminated polyester film, and the laminated structure of the base film and the adhesive layer (R layer) of the laminated polyester film of the present invention is R / S. More preferably, it is / I / S.

Further, the laminated polyester film of the present invention is obtained by extruding a polyester layer and a layer containing an ultraviolet absorber and a fluorescent brightening agent by co-extrusion from a die of an extruder, so-called coextrusion method. It is preferably obtained as a stretched and heat-treated product.
An adhesive layer containing a crosslinking agent or the like may also be co-melt extruded with a polyester layer and a layer containing an ultraviolet absorber and a fluorescent whitening agent by blending a polyester and a crosslinking agent to form a composition. From the viewpoint of properties, it is preferable to form the composition by dissolving a cross-linking agent or the like in a solvent or the like and applying it to the surface of the polyester layer as a coating solution.
Hereinafter, a polyester layer and a layer containing an ultraviolet absorber and a fluorescent brightening agent will be described mainly with respect to a co-extruded three-layer film (S / I / S), but unless the gist of the present invention is exceeded, The laminated polyester film of the present invention is not limited to a three-layer film.

〔polyester〕
The polyester constituting the laminated polyester film of the present invention is a polyester produced by melt polycondensation of dicarboxylic acid or its ester (acid component) and a glycol component.
Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, 4,4′-diphenyldicarboxylic acid, 1,4-cyclohexyldicarboxylic acid, and the like.
Examples of the glycol component include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol and the like.

Polyesters composed of these acid components and glycol components can be produced by arbitrarily using a commonly used method.
For example, a transesterification reaction between a lower alkyl ester of an aromatic dicarboxylic acid and a glycol, or a direct esterification of an aromatic dicarboxylic acid and a glycol, to form a substantially bisglycol of an aromatic dicarboxylic acid A method is employed in which an ester or a low polymer thereof is formed and then polycondensed by heating under reduced pressure. Depending on the purpose, an aliphatic dicarboxylic acid may be copolymerized.

  Typical examples of the polyester include polyethylene terephthalate, polyethylene-2,6-naphthalate, poly-1,4-cyclohexanedimethylene terephthalate, and the like. In addition, polyester obtained by copolymerizing the above acid component and glycol component. It may be, and may contain other components and additives as necessary.

  There is no restriction | limiting in particular as a polymerization catalyst of polyester, A conventionally well-known compound can be used, For example, an antimony compound, a titanium compound, a germanium compound, a manganese compound, an aluminum compound, a magnesium compound, a calcium compound etc. are mentioned. Among these, antimony compounds have the advantage of being inexpensive and having high catalytic activity. Titanium compounds and germanium compounds are preferable because they have high catalytic activity and can be polymerized in a small amount, and since the amount of metal remaining in the laminated polyester film is small, the brightness of the laminated polyester film is increased. Furthermore, since a germanium compound is expensive, it is more preferable to use a titanium compound.

When the laminated polyester film is exposed to an environment at a high temperature for a long time (for example, at 150 ° C. for 1 hour), an oligomer contained in the laminated polyester film (low molecular weight component of polyester, particularly ester cyclic trimer). However, it may precipitate on the surface of the laminated polyester film and crystallize. This precipitation or the like may cause deterioration in visibility due to whitening of the appearance of the laminated polyester film, post-processing defects, contamination of the polyester film production line and production members, and the like.
In the present invention, in order to suppress the precipitation amount of the ester cyclic trimer after heating the laminated polyester film, a base polyester film having a polyester layer having an ester cyclic trimer content of 0.7% by mass or less is used. It is preferable that it is a laminated polyester film provided. Various known methods can be used as a method for producing a polyester having a low ester cyclic trimer content. Examples thereof include a method of solid-phase polymerization after polyester production.

  The content of the ester cyclic trimer contained in the laminated polyester film is about 1% by mass in a general production method. The laminated polyester film of the present invention preferably has a polyester layer with an ester cyclic trimer content of 0.7% by mass or less, more preferably 0.6% by mass or less. is there. When there are few ester cyclic trimers in a lamination | stacking polyester film, the ester cyclic trimer precipitation prevention effect to the polyester film surface is exhibited especially highly. Even if the polyester film is used in processing steps under high temperature for a long time or other harsh conditions because the content of the ester cyclic trimer in the polyester layer is 0.7% by mass or less, the laminated polyester Deterioration of the haze of the film can be suppressed, and problems such as ester cyclic trimer adhering to and depositing on the transport roll contacting the laminated polyester film in the processing step can be suppressed.

  The polyester used for forming a polyester layer having an ester cyclic trimer content of 0.7% by mass or less in the present invention has an ester cyclic trimer content of 0.7% by mass or less, more preferably. Is mainly used for polyesters of 0.6% by mass or less, particularly preferably 0.5% by mass or less. Precipitation of the ester cyclic trimer is easily prevented by mainly using a polyester having a content of the ester cyclic trimer in the polyester raw material of 0.7% by mass or less.

  The polyester layer having an ester cyclic trimer content of 0.7% by mass or less in the present invention preferably comprises 70% by mass or more of a polyester having an ester cyclic trimer content of 0.7% by mass or less. More preferably, it is composed of 80% by mass or more. By being 70 mass% or more, the film haze after heating a polyester film is hard to deteriorate, and when processing as a product, it is hard to impair an optical characteristic and visibility.

  A method of suppressing the ester cyclic trimer after heating is also possible by designing the polyester film to have a laminated structure and using a polyester raw material with a low ester cyclic trimer content in each polyester layer of the polyester film. .

  Moreover, precipitation of the ester cyclic trimer from the laminated polyester film is effectively suppressed when the polyester layer having an ester cyclic trimer content of 0.7% by mass or less is thicker. The film thickness of the 0.7 mass% or less polyester layer is preferably 1.5 μm or more, more preferably 2.0 μm or more, and particularly preferably 2.5 μm or more. When the film thickness of the polyester layer of 0.7% by mass or less is 1.5 μm or more, a sputtering process under a long-time heating environment at 150 ° C. and a high tension condition, high temperature and high humidity Even when used in processing steps under harsh conditions such as durability tests under atmosphere, the film haze is unlikely to increase greatly, and optical properties and visibility are less likely to be impaired after processing as a product.

(particle)
The laminated polyester film in the present invention can contain particles for the purpose of ensuring the running property of the film or preventing scratches.
The particles are preferably contained in the surface layer of the base film of the laminated polyester film, and more preferably contained in the polyester layer located on the surface layer.
Examples of such particles include inorganic particles such as silica, calcium carbonate, magnesium carbonate, calcium phosphate, kaolin, talc, aluminum oxide, titanium oxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, and molybdenum sulfide. Further, organic particles such as crosslinked polymer particles and calcium oxalate, and precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  The particle size and content of the particles used are selected according to the use and purpose of the laminated polyester film, but the average particle size (d50) is usually 3 μm or less, preferably 0.02 μm to 2.8 μm, Preferably it is the range of 0.03 micrometer-2.5 micrometers. When the average particle diameter of the particles is 3 μm or less, the surface roughness of the laminated polyester film is hardly increased, and the particles are less likely to fall off the surface of the laminated polyester film.

  About particle content, it is 3 mass% or less normally with respect to the polyester layer containing particle | grains, Preferably it is 0.0003-1 mass%, More preferably, it is the range of 0.0005-0.5 mass%. When there are no particles or when there are few particles, the transparency of the film increases and a good film is obtained. Moreover, the slipperiness | lubricity can be improved because the particle content in the polyester layer containing particle | grains is 0.0003 mass% or more.

  The method for adding particles to the polyester layer is not particularly limited, and a conventionally known method can be adopted. For example, the particles can be added at any stage for producing the polyester constituting each layer, but preferably added to the reaction system after completion of the esterification or transesterification reaction during the production of the polyester.

[Layer containing UV absorber and fluorescent brightener]
The base polyester film provided in the laminated polyester film of the present invention has a layer containing an ultraviolet absorber and a fluorescent brightening agent.
When the base film contains an ultraviolet absorber, deterioration of the laminated polyester film can be suppressed, and high weather resistance can be obtained. In addition, since the base film contains a fluorescent brightening agent, the average light transmittance in the blue light wavelength region is reduced, and the average light transmittance in the blue light wavelength region (380 nm to less than 500 nm) is 70% or less. In addition, the average light transmittance outside the blue light wavelength region (500 nm or more and 780 nm or less) is 85% or more, and the color tone b ^* value measured by a single sheet by the transmission method is in the range of −5 to +3.

(UV absorber)
Examples of ultraviolet absorbers include benzophenone compounds, 1,3,5-triazine compounds, benzoxazinone compounds, and the like, which can be used alone or in combination of two or more. In consideration of this, a benzoxazinone-based compound that is difficult to be yellowed is preferably used.
An example of a benzoxazine-based compound used as an ultraviolet absorber is 2,2- (1,4-phenylene) bis [4H-3,1-benzoxazin-4-one].

  The content of the ultraviolet absorber in the layer containing the ultraviolet absorber and the optical brightener is usually 0.20 to 10.0 mass%, preferably 0.30 to 1.8 mass%. When the ultraviolet absorber is 0.10% by mass or more, deterioration of the laminated polyester film due to ultraviolet rays is easily suppressed, and when it is 10.0% by mass or less, the ultraviolet absorber bleeds out on the surface of the laminated polyester film. This can be suppressed, and deterioration of the surface functionality such as lowering of adhesiveness can be prevented.

(Fluorescent brightener)
Examples of the fluorescent brightening agent include dibenzoxazole compounds and the like, and these can be used alone or in combination.
Examples of the dibenzoxazole-based compound include 2,2- (4,4-diphenolvinyl) dibenzoxazole.
A commercially available product may be used as the fluorescent brightening agent, and examples thereof include a product “OB-1” manufactured by Eastman, a product “S-FGRH” manufactured by Eastwell, and the like.

The content of the fluorescent brightening agent in the layer containing the ultraviolet absorber and the fluorescent brightening agent is preferably 0.01 to 1.0% by mass, more preferably 0.01 to 0.5% by mass.
When the content of the fluorescent brightening agent is 0.01% by mass or more, it is easy to reduce the average light transmittance in the wavelength range of blue light to 70% or less. On the other hand, in order to suppress the coloring problem that the color tone of the film changes by being 1.0% by mass or less, and to suppress precipitation (bleed out) of the fluorescent whitening agent on the surface of the laminated polyester film, Problems that adversely affect the use, such as making the film cloudy, can be prevented.

  As a method of adding the ultraviolet absorber and the fluorescent brightening agent to the layer containing the ultraviolet absorbent and the fluorescent brightening agent, it may be added during the polyester production process, or the polyester raw material may be applied after being made into a chip shape. It may also be added during the polyester melt extrusion process. As a polyester raw material master batch added at a high concentration by such a method, a method of adding in a melt extrusion process at the time of forming a polyester film can also be adopted. In any case, the effect of the present invention can be exhibited if the obtained polyester film contains an ultraviolet absorber and a fluorescent brightening agent.

(Optical properties of laminated polyester film)
The laminated polyester film of the present invention has a color tone b ^* value measured by a single sheet by a transmission method in the range of -5 to +3, an average light transmittance in a wavelength region of 380 nm to less than 500 nm, and 70% or less, and The average light transmittance in the wavelength region of 500 nm or more and 780 nm or less is 85% or more.
The method for measuring the color tone b ^* value and the average light transmittance in each wavelength region will be described in Examples.

  About the laminated polyester film of this invention, the average light transmittance in the wavelength range in 380 nm or more and less than 500 nm becomes like this. Preferably it is 65% or less. If the average light transmittance in the wavelength region of 380 nm or more and less than 500 nm is 70% or more, it cannot be said that the light of blue light wavelength is sufficiently cut, and the object of the present invention cannot be achieved.

  Moreover, about the laminated polyester film of this invention, the average light transmittance in the wavelength range in 500 nm or more and 780 nm or less is 85% or more. When the average light transmittance in the wavelength region of 500 nm or more and 780 nm or less is less than 85%, when the laminated polyester film is pasted on the screen, the screen becomes dark and characters and the like become difficult to see. Increasing the transmittance is preferable because the characters on the screen can be clearly seen.

  In the laminated polyester film of the present invention, the light transmittance at 380 nm is preferably 5.0% or less, more preferably 2.0% or less, and further preferably 1.0% or less. When the light transmittance at 380 nm is 5.0% or less, it is sufficient to prevent each layer from being deteriorated by ultraviolet rays transmitted through the laminated polyester film.

The laminated polyester film of the present invention has a color tone b ^* value measured by a single sheet by a transmission method in the range of −5 to +3. That is, the color tone b ^* value measured with one laminated polyester film by the transmission method is in the range of −5 to +3.
The L ^* a ^* b ^* color system is defined by JIS Z8781-4: 2013, and lightness is represented by L ^* , and chromaticity indicating hue and saturation is represented by a ^* and b ^* . Color tone b ^* value is indeed a large value of positive, it means that the laminated polyester film has a large degree of yellowing, I see a large value of the color tone b ^* value is negative, the laminated polyester film is a tint of bluish . In the laminated polyester film of the present invention, that the color tone b ^* value is in the range of −5 to +3 means that the laminated polyester film is not yellowed, bluish, and excellent in appearance of the laminated polyester film. To do.
The laminated polyester film of the present invention preferably has a color tone b ^* value in the range of −2 to +1 measured by a single sheet by a transmission method.

As described above, the base film of the laminated polyester film of the present invention is a laminate of three or more layers having a layer containing an ultraviolet absorber and a fluorescent brightener as any layer other than the surface layer, that is, as an intermediate layer. A configuration is preferred.
In this case, the fluorescent whitening agent can be contained in both surface layers, but the content of the fluorescent whitening agent in both surface layers is preferably lower than the content of the fluorescent whitening agent in the intermediate layer. When the fluorescent whitening agent is contained in both the surface layer and the intermediate layer, the content of the fluorescent whitening agent in the laminated polyester film should be in the above-mentioned range as the content of all the polyesters constituting the laminated polyester film. Is preferred.
More specifically, the layer containing the ultraviolet absorber and the optical brightener is the intermediate layer of the laminated polyester film of the present invention, and the content of the ultraviolet absorber and the optical brightener in the surface layer sandwiching the intermediate layer is It is preferably less than 0.01% by mass and less than 0.005% by mass, respectively (preferably, the contents of the ultraviolet absorber and the fluorescent brightening agent in the surface layer are each 0% by mass). By setting it as this structure, it can prevent that one or both of an ultraviolet absorber and a fluorescent whitening agent precipitate from the surface of a laminated polyester film (bleed out).

  Furthermore, in the laminated polyester film of the present invention, conventionally known antioxidants, heat stabilizers, lubricants, dyes, pigments in addition to the above-mentioned particles, ultraviolet absorbers and fluorescent brighteners, if necessary. Etc. can be added.

  The thickness of the base film of the laminated polyester film in the present invention is not particularly limited as long as it can be formed as a film, but is usually 10 to 300 μm, preferably 15 to 250 μm, more preferably 20 to 200 μm. Range.

  In addition, it is preferable that the haze of the laminated polyester film obtained by this invention is 3% or less. More preferably, it is 1.5% or less, More preferably, it is 1.2% or less. When the haze of the laminated polyester film is 3% or less, it is difficult to damage the appearance as an optical film application.

  In the production of the laminated polyester film of the present invention, the means for forming a laminated structure is not limited. However, from the viewpoint of not reducing the transparency of the laminated polyester film, a coextrusion method that completely eliminates the possibility of interfacial peeling at the laminated interface is recommended. The Hereinafter, although an example of the manufacturing method of the laminated | multilayer film of this invention is shown, this invention is not limited to the following examples.

  In the present invention, a polyester chip dried by a known method is supplied to a melt extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer to be melted. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition point to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In the present invention, the sheet thus obtained is preferably stretched in the biaxial direction to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 1.3 to 6 times at 80 to 130 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then 90 to 160 ° C. in the lateral direction. And stretched 1.3 to 6 times. Heat treatment is preferably performed at 150 to 240 ° C. for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable.

  The laminated polyester film of the present invention may be composed of only the above-mentioned base film, but it is preferable to provide a hard coat layer for improving the surface hardness. In this case, since the polyester film is generally inactive, the adhesion is poor, and in order to improve the adhesion with the hard coat layer, an adhesive layer for improving the adhesion is formed on the base film. Is preferably provided in advance. Therefore, it is preferable to provide an adhesive layer on at least one side in order to improve the adhesion with the hard coat.

  A method for forming such an adhesive layer is not particularly limited, but a method of forming a coating layer by applying a solution or dispersion of an adhesive material on a base film is simple and preferable, and more specifically. The so-called in-line coating method in which coating is performed before the entrance of the tenter (before completion of orientation crystallization) and drying in the tenter is preferable.

  The hard coat layer is not particularly limited as long as it can improve the surface hardness of the laminated polyester film of the present invention, and examples thereof include a layer containing an acrylic resin, a urethane resin, a melamine resin, and the like.

  The coating layer for improving the adhesion with the hard coat layer is not particularly limited as long as it improves the adhesion, but in the present invention, the absolute reflectance is an arbitrary wavelength having a wavelength of 400 to 800 nm. It is preferable to have a coating layer that is 4.0% or more at a wavelength of.

  As the coating layer, a binder polymer is used to improve antireflection performance, transparency, adhesion to various surface functional layers when various surface functional layers are laminated on the coating layer, etc. It is preferable to do this.

  The “binder polymer” used in the present invention is a number average molecular weight (Mn) measured by gel permeation chromatography (GPC) according to a polymer compound safety evaluation flow scheme (sponsored by the Chemical Substance Council in November 1985). Is defined as a polymer compound having a film forming property of 1000 or more. The standard material was polystyrene.

  Specific examples of the binder polymer include polyester resin, acrylic resin, urethane resin, polyvinyl alcohol, polyalkylene glycol, polyalkyleneimine, methylcellulose, hydroxycellulose, and starches. In terms of improving adhesion with the surface functional layer, polyester resins, acrylic resins, and urethane resins are more preferably used, and further, an aromatic group is contained in these compounds in that the absolute reflectance can be designed high. It is more preferable.

  Further, the coating layer may contain a crosslinking agent within a range not impairing the gist of the present invention. Various known resins can be used as the cross-linking agent, but at least one selected from melamine compounds, epoxy compounds, oxazoline compounds, and isocyanate compounds is preferable. Among these, a melamine compound is more preferable because it can be designed to have a high absolute reflectance.

  Examples of the melamine compound in the present invention include methoxymethylated melamine and butoxymethylated melamine which are alkylol or alkoxyalkylolated melamine compounds, and those obtained by co-condensing urea or the like with a part of melamine can also be used. .

  In addition, a coupling agent such as a metal chelate compound can be used in the coating layer. Specifically, titanium acetylacetonate, titanium ethylacetoacetate, titanium octanediolate, titanium lactate, titanium triethanolaminate. And titanium compounds such as titanium oxalate, or zirconium compounds such as zirconium acetylacetonate, zirconium ethyl acetoacetate, zirconium acetate, and zirconium stearate.

  In addition, for the purpose of improving the adhesion and slipperiness of the coating layer, the coating layer may contain inert particles. Specific examples include silica, alumina, kaolin, calcium carbonate, titanium oxide, and organic particles. Can be mentioned.

  Furthermore, as long as it does not impair the gist of the present invention, the coating layer has an antifoaming agent, a coating property improving agent, a thickening agent, an organic lubricant, an antistatic agent, an antioxidant, a foaming agent, a dye and the like as necessary. May be contained.

  A laminated polyester film is produced by applying the above-described series of compounds as a solution or a dispersion to a base film with a coating solution adjusted to a solid content concentration of about 0.1 to 50% by mass. preferable.

  Furthermore, in the case of in-line coating, the above-described series of compounds is used as an aqueous solution or water dispersion, and the coating liquid adjusted with a solid content concentration of about 0.1 to 50% by mass as a guide is applied on the base film. It is preferred to produce a laminated polyester film. Moreover, in the range which does not impair the main point of this invention, a small amount of organic solvents may be contained in the coating liquid for the purpose of improving dispersibility in water, improving film-forming properties, and the like. Only one type of organic solvent may be used, or two or more types may be used as appropriate.

Although there is no restriction | limiting in the application quantity (after drying) of the coating layer provided on a base film regarding the laminated polyester film in this invention, Usually 0.005-1g / m < ² >, Preferably 0.005-0.5g / it is in the range of m ^2. When the coating amount is 0.005 g / m ² or more, the uniformity of the coating thickness is unlikely to be insufficient. On the other hand, when it is 1 g / m ² or less, problems such as a decrease in slipperiness hardly occur.

  In the present invention, as a method for providing the coating layer, a conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating or the like can be used. Regarding the coating method, there is a description example in “Coating method” published by Yasuharu Harasaki in 1979.

  Moreover, you may use together heating and active energy ray irradiation, such as ultraviolet irradiation, as needed. The base film of the laminated polyester film in the present invention may be subjected to surface treatment such as corona treatment or plasma treatment in advance.

  In addition, when the laminated polyester film of the present invention is used for optics, an antistatic agent, a colorant, a conductive material, etc. are added for the purpose of imparting other functionality to the hard coat layer provided for improving the surface hardness. Furthermore, a functional laminated thin film may be formed thereon for the purpose of reflecting external light, electric shock caused by static electricity, prevention of dust adhesion, and electromagnetic wave shielding.

  The coating liquid used in the present invention is preferably an aqueous solution or an aqueous dispersion in terms of handling and working environment, but contains water as the main medium and contains an organic solvent as long as it does not exceed the gist of the present invention. You may do it.

  In addition, the laminated polyester film of the present invention may be mixed with other thermoplastic resins such as polyethylene naphthalate and polytrimethylene terephthalate during co-extrusion of the polyester as long as the effects of the present invention are not impaired. Can do. Further, antioxidants, surfactants, lubricants, light-shielding agents, matting agents, and coloring agents such as dyes and pigments may be mixed. In addition, for the purpose of improving the slipperiness and abrasion resistance of the film, inert inorganic or organic fine particles can be blended with the polyester as necessary.

  For the laminated polyester film in the present invention, for example, for a touch panel, a high degree of transparency may be required even after being exposed to a high temperature atmosphere for a long time. From this viewpoint, in order to cope with a high degree of transparency, the film haze change amount (ΔH) by heating (180 ° C., 90 minutes) is preferably 0.7% or less, more preferably 0.5% or less, More preferably, it is 0.3% or less. Since ΔH is 0.7% or less, precipitation of ester cyclic trimer can be suppressed and film haze can be prevented from rising, so that visibility is not easily lowered. It is suitable for applications that require high performance.

In addition, from the viewpoint of the precipitation amount of the ester cyclic trimer, the amount of the ester cyclic trimer extracted from the film surface with dimethylformamide by heating the laminated polyester film in the present invention (180 ° C., 90 minutes) Preferably it is 1.0 mg / m ² or less, more preferably 0.8 mg / m ² or less, and even more preferably 0.6 mg / m ² or less. By being 1.0 mg / m ² or less, the amount of precipitation of the ester cyclic trimer is suppressed even in the subsequent step, for example, at a high temperature atmosphere such as 180 ° C. and 90 minutes, The transparency of the film is not easily lowered, and there is little concern about process contamination.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. In addition, the measurement methods and definitions of various physical properties and characteristics in the present invention are as follows. Further, “part” means “part by mass” unless otherwise specified.

The polyester used in the examples and comparative examples was prepared as follows.
<Method for producing polyester (A)>
100 parts of dimethyl terephthalate and 60 parts of ethylene glycol are used as starting materials, 0.09 part of magnesium acetate tetrahydrate as a catalyst is taken in the reactor, the reaction start temperature is 150 ° C., and the reaction temperature is gradually increased as methanol is distilled off. The temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After 0.04 part of ethyl acid phosphate was added to this reaction mixture, 0.03 part of antimony trioxide was added and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.68 dl / g due to a change in stirring power of the reaction tank, and the polymer was discharged from the reaction tank under nitrogen pressure. The intrinsic viscosity of the obtained polyester (A) was 0.68 dl / g.

<Method for producing polyester (B)>
Polyester (A) is pre-crystallized at 160 ° C. in advance, and then solid-phase polymerized in a nitrogen atmosphere at a temperature of 220 ° C., and has an intrinsic viscosity of 0.75 and an ester cyclic trimer content of 0.46% by mass. Polyester (B) was obtained.

<Method for producing polyester (C)>
In the production method of polyester (A), after adding 0.04 part of ethyl acid phosphate, 0.8 part of silica particles having an average particle diameter of 2.2 μm dispersed in ethylene glycol and 0.04 part of antimony trioxide are added. In addition, polyester (C) was obtained using the same method as the production method of polyester (A) except that the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.64 dl / g. The intrinsic viscosity of the obtained polyester (C) was 0.64 dl / g.

<Method for producing polyester (D)>
98.5 parts of polyester (A) and 1.5 parts of fluorescent brightener “S-FGRH” manufactured by Eastwell are blended and melt-kneaded using a twin screw extruder to produce a fluorescent brightener master batch. did. The intrinsic viscosity of the obtained polyester (D) was 0.61 dl / g.

<Method for producing polyester (E)>
90.0 parts of polyester (A) and 2,2- (1,4-phenylene) bis [4H-3,1-benzooxazin-4-one] (CYTECOR UV-3638, molecular weight, manufactured by CYTEC) as an ultraviolet absorber 369, benzoxazine) was blended with 10.0 parts and melt-kneaded using a twin screw extruder to prepare an ultraviolet absorbent master batch polyester (E). The intrinsic viscosity of the obtained polyester (E) was 0.59 dl / g.

<Preparation of coating solution>

Examples of compounds constituting the coating layer are as follows.
(Coating liquid composition example: mass ratio)
a / b / c / d = 47/20/30/3
Here, a is a polyester dispersion of terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / ethylene glycol / diethylene glycol / triethylene glycol = 31/16/3/22/21 (molar ratio), b is Methyl methacrylate / ethyl acrylate / acrylonitrile / N-methylol methacrylamide = 45/45/5/5 (molar ratio) emulsion polymer (emulsifier: anionic surfactant), c is hexamethoxymethylmelamine (melamine type) (Crosslinking agent), d is an aqueous dispersion (inorganic particles) of silicon oxide having a particle diameter of 0.06 μm.

[Example 1]
A material obtained by blending polyester (B) and polyester (C) at a mass ratio of [polyester (B) / polyester (C)] of 95.0 / 5.0 was used as a surface layer material. Polyester (A), polyester (D), and polyester (E) were blended at 93.5 / 1.5 / 5.0 in a mass ratio [polyester (A) / polyester (D) / polyester (E)]. The material was used as an intermediate layer raw material. The surface layer raw material and the intermediate layer raw material are respectively supplied to two extruders and heated and melted at 285 ° C., and then the S layer is the outermost layer (surface layer), the I layer is the intermediate layer, and two types and three layers (S / I / S) and co-extrusion so that the thickness composition ratio becomes S / I / S = 4/96/4, and cooling and solidifying while closely contacting a mirror surface cooling drum having a surface temperature of 40 to 50 ° C. using an electrostatic contact method To produce an unstretched polyethylene terephthalate film. The film was stretched 3.4 times in the longitudinal direction using the difference in peripheral speed of the roll while passing through a heated roll group at 85 ° C., and then the coating agent was applied to one side of the longitudinally stretched film, and tenter stretching was performed. The film is stretched 4.0 times in the transverse direction at 100 ° C, heated to 230 ° C, and then relaxed by 2% in the transverse direction to form a coating layer having a coating layer thickness (after drying) of 0.03 µm. A biaxially oriented polyethylene terephthalate film having a substrate film thickness of 100 μm was obtained. The obtained polyester film had the characteristics shown in Table 1.

[Examples 2 to 4]
In Example 1, it manufactured like Example 1 except having changed the compounding ratio of polyester (A), polyester (D), and polyester (E) into the quantity shown in Table 1, and obtained a lamination polyester film. It was. The obtained laminated polyester film had the characteristics shown in Table 1.

Example 5
In Example 1, it manufactured similarly to Example 1 except not apply | coating a coating liquid (it does not provide a coating layer), and obtained the laminated polyester film. The obtained laminated polyester film had the characteristics shown in Table 1.

[Comparative Examples 1 to 5]
In Example 1, it manufactured like Example 1 except having changed the compounding ratio of polyester (A), polyester (D), and polyester (E) into the quantity shown in Table 1, and obtained a lamination polyester film. It was. The obtained laminated polyester film had the characteristics shown in Table 1.

[Comparative Example 6]
Polyester (A), polyester (D), and polyester (E) were mixed in a mass ratio [polyester (A) / polyester (D) / polyester (E)] as 92.0 / 2.0 / 6.0. A single layer polyester film using one extruder was produced using the raw material. The film forming conditions were the same as in Example 1 except that the film was a single layer, and the thickness of the base film was 100 μm.

  In addition, the evaluation method in an Example and a comparative example is as follows.

(1) Measurement of intrinsic viscosity (dl / g) of polyesters (A) to (E) 1 g of each polyester is precisely weighed, and 1 g of polyester is added to 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (mass ratio). And dissolved. Using the obtained solution, the intrinsic viscosities of polyesters (A) to (E) at 30 ° C. were measured with an Ubbelohde capillary viscometer.

(2) Measuring method of light transmittance The light transmittance at each wavelength of the polyester film was measured using a spectrophotometer “V-670” manufactured by JASCO Corporation. The average value of the light transmittance of 380 nm to 500 nm was calculated from the light transmittance measured at each wavelength (every 10 nm).

(3) Color tone b ^* Method for measuring the value For each polyester film, the color tone b ^{* of a} single sheet by a transmission method using a spectral colorimeter “CM-3700d” manufactured by Konica Minolta Co., Ltd. according to JIS Z 8722: 2009 ^. The value was measured.

(4) Measurement of total light transmittance and haze For each polyester film, the total light transmittance is in accordance with JIS K 7361-1: 1997, and haze is in accordance with JIS K 7136: 2000. Haze was measured by a total “NDH2000”.

(5) Adhesive A composition comprising 77 parts of KAYARAD DPIIA manufactured by Nippon Kayaku Co., Ltd., 18 parts of KAYARAD R-128II manufactured by Nippon Kayaku Co., Ltd., and 5 parts of IRGACURE651 manufactured by Ciba Geigy Co., Ltd. was diluted to 30% by mass with toluene. Each component was dissolved to prepare a hard coat mixed coating solution. The obtained mixed coating solution was applied to one surface (the coating layer side when the coating layer was laminated) of the base film of the polyester film so that the dry film thickness was about 6 μm. Next, using a high-pressure mercury lamp with an energy of 120 W / cm, the coated surface was irradiated with an energy ray for about 10 seconds at an irradiation distance of 100 mm to cure the coated surface to form a hard coat layer. Ten cross cuts with a 10 mm interval were put on the hard coat surface of the polyester film, and a 18 mm wide tape (Cello Tape (registered trademark) CT-18, manufactured by Nichiban Co., Ltd.) was stuck thereon. The tape was pulled abruptly at a peeling angle of 180 degrees and evaluated according to the following criteria.
A: The hard coat layer does not peel off from the surface of the base film at all. B: The hard coat layer peels off from the surface of the base film.

(6) Weather resistance Ultraviolet long life fade meter (FAL-3 type) manufactured by Suga Test Instruments Co., Ltd. was used and irradiated with ultraviolet rays at 63 ± 3 ° C. for 1000 hours. The appearance of the film after the test was observed and evaluated according to the following criteria.
A: No deterioration B: Slight yellowing deterioration is observed C: Yellowing deterioration is conspicuous

(7) Blue light cut performance It evaluated on the following reference | standard from the average value of the light transmittance of 380 nm-500 nm.
A: Average value of light transmittance is 65% or less B: Average value of light transmittance is more than 65% and less than 70% C: Average value of light transmittance is 71% or more and more than 70%

(8) Evaluation of visibility The polyester film was mounted in the liquid crystal panel for mobiles, and visibility was confirmed.
A: The polyester film has no yellowing and cloudiness, and the visibility of the screen is good.
B: Although the polyester film is slightly cloudy, there is no problem in the visibility of the screen.
C: The visibility of the screen is hindered by yellowing or white turbidity of the polyester film or both.

(9) Comprehensive evaluation Based on the evaluation results of the polyester film form (laminated or single layer), optical properties of the polyester film, and adhesion evaluation, weather resistance evaluation, blue light cut performance evaluation, and visibility evaluation. The evaluation was made according to the following criteria.
AA: The polyester film is a laminated polyester film, the optical properties of the laminated polyester film are in the range of color tone b ^* value of −5 to +3, and the average light transmittance in the wavelength region of 380 nm to less than 500 nm is 70% or less. In addition, the average light transmittance in the wavelength region of 500 nm or more and less than 780 nm is 85% or more, and adhesion evaluation, weather resistance evaluation, blue light cut performance evaluation, and visibility evaluation are all A evaluations.
A: The polyester film is a laminated polyester film, the optical properties of the laminated polyester film are in the range of color tone b ^* value of −5 to +3, and the average light transmittance in the wavelength region of 380 nm to less than 500 nm is 70% or less. In addition, the average light transmittance in a wavelength region of 500 nm or more and less than 780 nm is 85% or more, and any one of adhesion evaluation, weather resistance evaluation, blue light cut performance evaluation, and visibility evaluation is B In the evaluation, the other evaluation is A evaluation.
B: The polyester film is a laminated polyester film, the optical properties of the laminated polyester film are in the range of color tone b ^* value of -5 to +3, and the average light transmittance in the wavelength region of 380 nm to less than 500 nm is 70% or less. In addition, the average light transmittance in the wavelength region of 500 nm or more and less than 780 nm is 85% or more, and any two or more of adhesion evaluation, weather resistance evaluation, blue light cut performance evaluation, and visibility evaluation are B Includes evaluation and does not include C evaluation.
C: Even if the polyester film is a single-layer polyester film or a laminated polyester film, the optical properties of the laminated polyester film are not in the range of color tone b ^* value of -5 to +3, or from 380 nm to less than 500 nm The average light transmittance in the wavelength region exceeds 70%, or the average light transmittance in the wavelength region at 500 nm or more and less than 780 nm is less than 85%.

The laminated polyester film and the laminated blue light cut film for screen protection of the present invention are suitable as an optical polyester film, and in particular, it is preferably used for protecting a screen using an LED as a light source, such as a liquid crystal display or a smartphone. it can.
For example, when the laminated polyester film of the present invention and the laminated blue light cut film for screen protection are used for protecting a screen using an LED as a light source, the outdoor use that is exposed to sunlight is performed. In addition, it is effective in preventing VDT syndrome such as eye strain and dry eye by cutting light in the blue light wavelength range peculiar to LED.

Claims (10)

A laminated polyester film comprising a base polyester film having a layer containing a UV absorber and a fluorescent brightener;
The color tone b ^* value measured by a single method by the transmission method is in the range of −5 to +3, the average light transmittance in the wavelength region from 380 nm to less than 500 nm is 70% or less, and the wavelength region in the range from 500 nm to 780 nm. A laminated polyester film having an average light transmittance of 85% or more.   The laminated polyester film according to claim 1, wherein the light transmittance at 380 nm is 5.0% or less.   The base polyester film has a surface layer and an intermediate layer, the intermediate layer is a layer containing the ultraviolet absorber and the fluorescent whitening agent, and the ultraviolet absorber and the fluorescent whitening in the surface layer. The laminated polyester film according to claim 1 or 2, wherein the content of the agent is less than 0.01% by mass and less than 0.005% by mass, respectively.   The laminated polyester film according to claim 3, wherein the surface layer is a polyester layer having an ester cyclic trimer content of 0.7% by mass or less.   The laminated polyester film according to claim 4, wherein the polyester layer further contains particles.   The laminated polyester film according to any one of claims 3 to 5, wherein a content of the ultraviolet absorber in the intermediate layer is 0.20 to 10.0 mass%.   The laminated polyester film according to any one of claims 3 to 6, wherein a content of the optical brightener in the intermediate layer is 0.01 to 1.0 mass%.   The ultraviolet absorber is at least one selected from the group consisting of a benzophenone compound, a 1,3,5-triazine compound, and a benzoxazinone compound. The laminated polyester film described in 1.   The laminated polyester film according to any one of claims 1 to 8, wherein an adhesive layer containing a crosslinking agent is adjacent to a surface layer of the base polyester film.   The blue light cut film for screen protection using the laminated polyester film of any one of Claims 1-9.