JP2014047281A - Laminate film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate film having an excellent adhesiveness with a hard coat layer, etc. and resistant to the occurrence of the problem of an irregular color appearance.SOLUTION: The sought objective is achieved by a laminate film provided by forming, on at least one surface of a polyester film having a surface direction refractive index of 1.63-1.68, a coat layer having a refractive index of 1.58-1.64, a swelling ratio, within any conceivable solvent, of 130-200% according to the definition provided below, and a thickness of 50-100 nm: swelling ratio: a value ascertained, as swelling ratio E(%)=dh/d0×100, from the thickness dh, on an occasion where a coating solution (solid content concentration: 40 mass%) obtained by diluting a UV-curable composition with a solvent (methyl ethyl ketone, ethyl acetate, toluene, isopropanol, or propylene glycol monomethyl ether) is coated, dried, and cured atop the coat layer of the laminate film so as to form a hard coat layer having a thickness of 5 μm, of the coat layer following the formation thereon of the hard coat layer and the thickness d0 of the coat layer prior to the formation thereon of the hard coat layer.

Description

  The present invention relates to a laminated film. More specifically, the present invention relates to a laminated film that is excellent in adhesiveness when laminating a hard coat layer and is less likely to cause light interference spots (color spot feeling) and can be suitably used particularly as an optically easily adhesive film. Is.

  Biaxially stretched polyester films made of polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are excellent in mechanical properties, electrical properties, dimensional stability, heat resistance, transparency, chemical resistance, etc. In addition, it has high versatility compared with other transparent plastic films and has a great advantage in cost merit, so it is suitably used for optical applications. However, since the biaxially stretched polyester film has a low surface hardness, the surface tends to be damaged when it is processed into a protective film, an antireflection film, a touch panel or the like for a flat panel display. In order to prevent this, a hard coat layer such as an acrylic type is often laminated on the film surface, but the biaxially stretched polyester film has poor adhesion to the hard coat layer because the film surface is inactive. In many cases, an easy-adhesion layer using polyester or urethane is laminated on a biaxially stretched polyester film by in-line coating or offline coating.

  On the other hand, the refractive index in the plane direction of the biaxially stretched polyester film is generally about 1.65 to 1.75. For example, the refractive index of the acrylic resin layer is generally about 1.52. As described above, since there is a difference in refractive index between the two materials, color spots appear on the surface of the laminated film due to light reflection from the interface between the biaxially stretched polyester film and the acrylic resin layer (for example, hard coat layer). A feeling (interference color spot, hereinafter simply referred to as interference spot) occurs. This color spot is more pronounced as the laminated film is more transparent, and is more perceived under a special fluorescent lamp such as a three-wavelength fluorescent lamp than sunlight or an incandescent lamp.

  In order to solve such problems, it has been proposed to provide an easy-adhesion layer having an adjusted refractive index and thickness. For example, Patent Document 1 discloses that the refractive index is a refractive index in the plane direction of a biaxially stretched polyester film and a hard coat. A method has been proposed in which the refractive index is 1.55 to 1.62, which is the middle of the refractive index of the layer, and the thickness is 50 to 150 nm.

  In recent years, various solvents have come to be used as coating solutions for providing functional layers such as hard coat layers, and depending on the solvent, the easy-adhesion layer swells and dissolves, and the thickness varies. As a result, a problem that interference spots cannot be suppressed has been pointed out. With respect to such a problem, for example, in Patent Documents 2 and 3, by adding particles having a relatively large particle size with an average particle size of 0.2 to 0.7 μm, even if the thickness variation of the easy adhesion layer occurs A method for suppressing interference spots by surface roughness has been proposed.

JP 2007-253512 A JP 2009-300658 A Japanese Patent No. 4547644

  The present invention has been made in view of the above-described background art, and an object of the present invention is to provide a laminated film that is excellent in adhesiveness with a hard coat layer and the like and is less likely to cause interference spots.

  As a result of intensive studies to solve the above problems, the present inventors are expected to be able to solve the problem of swelling and dissolution of the coating layer due to the solvent by increasing the solvent resistance of the coating layer. As a result of investigating that the adhesiveness is insufficient when the solvent resistance becomes too high, and further investigations, the present invention has been completed.

  That is, the above-described problem of the present invention is that “at least one surface of a polyester film having a refractive index in the plane direction of 1.63 to 1.68 has a refractive index of 1.58 to 1.64, and a swelling ratio required by the following method. In any solvent, it is achieved by a “laminated film having a coating layer of 130 to 200% and a thickness of 50 to 100 nm”.

Swelling rate:
On the coating layer of the laminated film, a coating solution (solid content concentration of 40% by mass) obtained by diluting the following UV curable composition with a solvent (methyl ethyl ketone, ethyl acetate, toluene, isopropanol or propylene glycol monomethyl ether) is applied and dried. A hard coat layer having a thickness of 5 μm is formed by curing. From the thickness dh of the coating layer after forming the hard coat layer and the thickness d0 of the coating layer before forming the hard coat layer, the swelling ratio E (%) = The value obtained as dh / d0 × 100.
UV curable composition:
Pentaerythritol acrylate: 45% by mass
N-methylolacrylamide: 40% by mass
N-vinylpyrrolidone: 10% by mass
1-hydroxycyclohexyl phenyl ketone: 5% by mass

（Ｒ_１は炭素数２〜４のアルキレン基、Ｒ_２、Ｒ_３、Ｒ_４、およびＲ_５は、水素、炭素数１〜４のアルキル基、アリール基またはアラルキル基であり、それぞれ同じであっても異なっていてもよい）」
「塗布層が、塗布層の質量を基準として１〜３０質量％の架橋剤を含有すること」
「光学用易接着性フィルムとして用いられること」
の少なくとも１つの要件を具備するものを包含する。 Moreover, the laminated film of the present invention has, as its preferred embodiment,
“The coating layer contains 70% by mass or more of the following copolyester based on the mass of the coating layer. Copolyester:
(A2) 60-90 mol% of naphthalenedicarboxylic acid component,
(B2) Copolyester containing 1 to 10 mol% of an aromatic dicarboxylic acid component having a sulfonate group and (C2) 5 to 25 mol% of a bisphenol A ethylene oxide adduct component. "
“The copolymerized polyester further contains (D3) a glycol component having a fluorene structure represented by the following formula (I) in an amount of 5 mol% or more and less than 20 mol%.

(R ₁ is an alkylene group having 2 to 4 carbon atoms, R ₂ , R ₃ , R ₄ , and R ₅ are hydrogen, an alkyl group having 1 to 4 carbon atoms, an aryl group, or an aralkyl group. Or it may be different) "
“The coating layer contains 1 to 30% by mass of a crosslinking agent based on the mass of the coating layer.”
"Used as an easily adhesive film for optics"
Including at least one of the following requirements.

  The laminated film of the present invention has a refractive index and a thickness in a specific range on a polyester film having a plane direction refractive index in a specific range, and methyl ethyl ketone, ethyl acetate, toluene, which are usually used when a hard coat layer is applied. Since any swelling solvent of isopropanol and propylene glycol monomethyl ether has a swelling ratio within a specific range, it has characteristics that interference spots (color spots) hardly occur and adhesion is excellent. Therefore, it can be suitably used as an easily adhesive film for optics.

  The laminated film of the present invention has a coating layer to be described later on at least one side of the following polyester film.

[Polyester film]
The polyester film in the present invention needs to have a refractive index in the plane direction (an average refractive index of a refractive index in an arbitrary direction and a refractive index in a direction perpendicular to the refractive index in the film plane) of 1.63 to 1.68. Preferably, it is in the range of 1.64 to 1.67, particularly preferably 1.65 to 1.66. When the plane direction refractive index is within this range, the laminated film of the present invention provided with a coating layer described later suppresses the occurrence of interference spots when a low refractive index layer such as a hard coat layer is formed thereon. be able to. If the surface direction refractive index is too high or too low outside the above range, it is difficult to suppress the occurrence of interference spots.
Such a polyester film may be any of an unstretched film, a uniaxially stretched film, and a biaxially stretched film as long as the plane direction refractive index satisfies the above-mentioned requirements. To a biaxially stretched film.

  The polyester constituting the film is a polyester composed of an acid component and a glycol component. Examples of the acid component include terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid. Examples of the glycol component include ethylene glycol. , Diethylene glycol, butanediol, cyclohexanedimethanol and the like. Of these, polyethylene terephthalate is preferred from the viewpoint of easily obtaining a biaxially stretched film that satisfies the requirements for the refractive index in the plane direction. The term “polyethylene terephthalate” as used herein refers to a polyester having an ethylene terephthalate unit of 95 mol% or more, preferably 98 mol% or more, based on all repeating units, and particularly preferably a homopolyester not using a copolymer component. It is. In the case of copolymerized polyethylene terephthalate, for example, a dicarboxylic acid component such as isophthalic acid or naphthalenedicarboxylic acid or a glycol component such as diethylene glycol, butanediol, or cyclohexanediol can be used as the copolymerization component.

  The intrinsic viscosity of polyethylene terephthalate is preferably 0.40 dl / g or more, more preferably 0.50 to 0.90 dl / g, at 35 ° C. in o-chlorophenol. When the intrinsic viscosity is less than 0.40 dl / g, cutting may occur frequently during film formation, or the strength of the product after forming may be insufficient. On the other hand, if the intrinsic viscosity becomes too high, the melt viscosity becomes high, so that melt extrusion is difficult, and the polymerization takes a long time and the productivity may be deteriorated.

  The polyester film in the present invention preferably contains substantially no particles from the viewpoint of transparency. Here, “substantially does not contain” indicates that the content of particles in the film is 100 ppm or less, preferably 10 ppm or less, and more preferably 1 ppm or less.

[Coating layer]
The laminated film of the present invention needs to have a coating layer that satisfies the following requirements for refractive index, thickness, and swelling ratio on at least one side of the polyester film or on both sides as necessary.

(Refractive index)
The refractive index of a coating layer needs to be 1.58-1.64, Preferably it is 1.58-1.62, More preferably, it is 1.58-1.60, More preferably, 1.58-1. 59. When the refractive index of the coating layer is within this range, the refractive index between the refractive index in the plane direction of the polyester film and the refractive index of the hard coat layer usually made of an acrylic resin (approximately 1.52) Therefore, interference spots (color spot feeling) when a hard coat layer made of such an acrylic resin is coated on the coating layer can be suppressed. If this refractive index is too high or too low, it becomes difficult to suppress interference spots. Moreover, it becomes easy to make a swelling rate into a preferable range by setting it as the application layer which consists of a component which becomes such a refractive index.
In order to achieve such a refractive index, the refractive index of each component constituting the coating layer may be adjusted. For example, the refractive index of the coating layer can be increased by using copolymer polyester or particles having a high refractive index. Particularly preferably, a copolyester described later may be employed.

(Thickness)
The thickness of a coating layer needs to be 50-100 nm, Preferably it is 70-90 nm. By setting the thickness of the coating layer within this range, interference spots (color spots) when a low refractive index layer such as a hard coat layer made of an acrylic resin is provided thereon can be suppressed. If this thickness is too thin, the adhesiveness tends to decrease, and if it is too thin or too thick, it becomes difficult to suppress interference spots.

(Swell rate)
In addition to the above, the coating layer of the present invention needs to have a swelling rate of 130 to 200% in any of the following solvents, preferably 130 to 180%, more preferably 135 to It is 175%, more preferably 139 to 165%. Here, the swelling ratio is as follows. A coating solution (solid content concentration: 40% by mass) obtained by diluting the following UV curable composition with a solvent is applied onto the coating layer of the laminated film, dried and cured, and a hard coat layer having a thickness of 5 μm. From the thickness dh of the coating layer after forming the hard coat layer and the thickness d0 of the coating layer before forming the hard coat layer,
Swelling ratio E (%) = dh / d0 × 100
It is the value calculated as. Here, the following are used as the UV curable composition, and as the solvent, methyl ethyl ketone (MEK), ethyl acetate, toluene, isopropanol, and propylene, which are representative of the solvents usually used for forming a hard coat layer and the like, are used. Glycol monomethyl ether acetate (PGMEA) is used, and in any of these solvents, the swelling rate of the coating layer needs to be in the above range.
UV curable composition:
Pentaerythritol acrylate: 45% by mass
N-methylolacrylamide: 40% by mass
N-vinylpyrrolidone: 10% by mass
1-hydroxycyclohexyl phenyl ketone: 5% by mass

  When the swelling ratio is less than 130%, the adhesion to the hard coat layer is insufficient, and when the swelling ratio exceeds 200%, the thickness of the coating layer varies before and after the hard coat layer is formed. Is too large to suppress interference spots. In addition, it is important that the swelling rate is within the above range in any of the above solvents. If the swelling rate in any of the solvents is out of this range, a hard coat layer is formed using the solvent. This is because the adhesiveness becomes insufficient or it becomes difficult to suppress interference spots. In addition, since the swelling rate is easier to suppress interference spots when the hard coat layer is formed when the fluctuation due to the type of solvent is less, the difference between the maximum swelling rate and the minimum swelling rate is 50% or less. It is preferable that it is 25% or less.

  In order to achieve such a swelling rate, it is only necessary to adjust the components used in the coating layer, particularly the copolymer component constituting the binder component, to achieve a balance between lipophilicity and hydrophilicity. Specifically, a copolyester having a preferable embodiment described later can be used. The swelling rate can also be adjusted by using a crosslinking agent in the coating layer. The crosslinking agent tends to have a lower swelling ratio as the addition amount increases.

(Configuration of coating layer)
The configuration of the coating layer in the present invention is not particularly limited as long as it has the above-described requirements for the refractive index and the swelling rate. However, the refractive index and the swelling suitable for achieving the refractive index and the swelling rate of the coating layer are not limited. It is preferable to employ a copolyester having a ratio. At this time, the content of the copolyester is preferably 70% by mass or more, more preferably 80% by mass or more, and particularly preferably 85% by mass or more with respect to the mass of the coating layer.

(Copolymerized polyester)
Such a copolyester uses, for example, a component capable of increasing the refractive index such as a naphthalenedicarboxylic acid component or a glycol component having a fluorene structure and a component capable of adjusting the swelling ratio such as an aromatic dicarboxylic acid component having a sulfonate group. The refractive index and the swelling rate may be adjusted by adjusting the copolymerization amount.

  The copolymer polyester preferably used includes, for example, an aromatic dicarboxylic acid component having 60 to 90 mol% of a naphthalenedicarboxylic acid component and a sulfonate group based on the total dicarboxylic acid component (100 mol%) of the copolymer polyester. What contains 1-10 mol% and 5-25 mol% of ethylene oxide adducts of bisphenol A is mentioned.

  When the proportion of the naphthalenedicarboxylic acid component is within the above range, the refractive index of the copolyester can be increased, the refractive index of the coating layer can be easily within the above range, and interference spots can be suppressed. Can do. In addition, the swelling rate of the coating layer can be easily within the above range. If the proportion of the naphthalenedicarboxylic acid component is too small, the refractive index of the copolyester will be low, and as a result, the refractive index of the coating layer will be low and the effect of suppressing interference spots will be insufficient. On the other hand, as the proportion of the naphthalenedicarboxylic acid component increases, the refractive index of the copolyester increases, so that the proportion of other (such as a crosslinking agent and other components described later) as the coating layer can be increased. However, at the same time, the glass transition temperature (Tg) of the copolyester tends to increase and the glass transition temperature of the coating layer tends to increase, and the film forming property of the coating layer decreases and the transparency of the resulting laminated film decreases. It becomes easy. Therefore, the content of the naphthalenedicarboxylic acid component is preferably 65 mol% or more, and 85 mol% or less, more preferably 80 mol% or less, and particularly preferably 70 mol% or less.

  Here, examples of the naphthalenedicarboxylic acid component include 2,7-naphthalenedicarboxylic acid component, 2,6-naphthalenedicarboxylic acid component, 1,4-naphthalenedicarboxylic acid component, and the like, among which 2,6-naphthalenedicarboxylic acid component. Ingredients are preferred.

  Further, by having the aromatic dicarboxylic acid component having a sulfonate group in the above range based on the total acid component of the copolymer polyester, the solubility or water dispersibility when the copolymer polyester is used as an aqueous coating liquid is improved. be able to. Further, the swelling rate of the coating layer can be easily set to the above-mentioned range. However, if the amount is too large, the water resistance and blocking resistance of the coating layer tend to be low, so the content is preferably 2 to 8 mol%, particularly preferably in the range of 6 to 8 mol%.

  Examples of the aromatic dicarboxylic acid component having a sulfonate group include a 5-sodium sulfoisophthalic acid component, a 5-potassium sulfoisophthalic acid component, a 5-lithium sulfoisophthalic acid component, and a 5-phosphonium sulfoisophthalic acid component. However, the 5-sodium sulfoisophthalic acid component is most preferable from the viewpoint of improving water dispersibility.

  Furthermore, by having the ethylene oxide adduct component of bisphenol A in the above range based on the total acid component of the copolymer polyester, the Tg can be made a preferred range while maintaining the refractive index of the copolymer polyester, The film forming property of the coating layer is improved, and a laminated film having excellent transparency can be obtained. Moreover, it becomes easy to make a swelling rate into a preferable range. In addition, the range of 2-4 mol is suitable for the average addition mole number of ethylene oxide with respect to 1 mol of bisphenol A.

  The copolymer polyester described above preferably contains 5 mol% or more and less than 20 mol% of the glycol component having the fluorene structure represented by the formula (1) in addition to the above components. While maintaining Tg at a moderately low temperature, the refractive index can be within a preferred range. When the content of such a component is reduced, the refractive index of the copolyester tends to be low. On the other hand, when the content is high, the Tg of the copolyester is high, the film forming property of the coating layer is lowered, and the transparency of the laminated film is lowered. The adhesiveness tends to decrease. From such a viewpoint, the preferable lower limit is 5 mol%, and the preferable upper limit is 15 mol%, and particularly preferably 10 mol%.

  Examples of the glycol component having a fluorene structure represented by the formula (1) preferably used include a 9,9-bis [4- (2-hydroxyethoxy) phenyl] fluorene component and a 9,9-bis [4- (2 -Hydroxyethoxy) -2-methylphenyl] fluorene component.

  Further, in addition to the above components, the alkylene dicarboxylic acid component having 0 to 40 mol% of the C6-12 alkylene dicarboxylic acid component and 0 to 50 mol% of the alkylene glycol component having 4 to 10 carbon atoms, and the alkylene dicarboxylic acid It is preferable to contain so that the sum total of a component and this alkylene glycol component may be 15-50 mol%. Thereby, Tg of copolyester can be made low and Tg of an application layer can be made low. As a result, even if the polyester film is a polyethylene terephthalate film or an in-line coating method that is usually employed when forming a coating layer, a laminated film with excellent transparency can be obtained because the coating layer has excellent film-forming properties. It is done. In particular, when the simultaneous biaxial stretching method is employed and the in-line coating method is employed for forming the coating layer, the preheating / drying temperature tends to be relatively low, and thus the transparency improving effect is large and preferable. Moreover, the adhesive improvement effect can be enhanced and the blocking resistance is also excellent.

  When the total amount of the alkylene dicarboxylic acid component and the alkylene glycol component decreases, the Tg of the copolyester is difficult to decrease, and the transparency of the resulting laminated film may decrease. On the other hand, when the amount of the alkylene dicarboxylic acid component or the alkylene glycol component is increased or the sum of both is increased, the anti-blocking property is reduced, or the refractive index of the copolyester is reduced and the effect of suppressing interference spots is reduced. There is a case. In addition, the swelling rate of the coating layer may increase. From such a viewpoint, the total amount of the alkylene dicarboxylic acid component and the alkylene glycol component is preferably in the range of 20 to 50 mol%.

  Preferred examples of the alkylene dicarboxylic acid component having 6 to 12 carbon atoms (dicarboxylic acid component having an alkylene group having 4 to 10 carbon atoms) include 1,4-butanedicarboxylic acid component, 1,6-hexanedicarboxylic acid component, Examples thereof include 1,4-cyclohexanedicarboxylic acid component, 1,8-octanedicarboxylic acid component, 1,10-decanedicarboxylic acid component, and the like. Among these, from the viewpoint that an appropriate Tg can be obtained, a dicarboxylic acid component having an alkylene group having 4 to 8 carbon atoms is preferable, and a dicarboxylic acid component having an alkylene group having 4 to 6 carbon atoms is more preferable.

  Moreover, as a C4-C10 alkylene glycol component preferably used, for example, a 1,4-butanediol component, a 1,6-hexanediol component, a 1,4-cyclohexanediol component, a 1,8-octanediol component, Examples include 1,10-decanediol component. Among these, from the viewpoint that an appropriate Tg can be obtained, an alkylene glycol component having 4 to 8 carbon atoms is preferable, and an alkylene glycol component having 4 to 6 carbon atoms is more preferable.

  In addition, when other copolymerization components are added to the copolymerized polyester to impart other functions, the above-mentioned alkylene dicarboxylic acid component and the above-mentioned alkylene glycol can be easily added as an acid component and easily subjected to a polymerization reaction. Among the components, it is more preferable to contain them as an alkylene glycol component.

  Further, in addition to the above components, in order to keep the Tg of the copolyester within a more preferable range while maintaining the refractive index, terephthalic acid and / or isophthalic acid is contained in an amount of 20 to 40 mol%, particularly 24 to 34 mol%. It is preferable to contain. Among these, an isophthalic acid component is preferable because it is easy to obtain a more suitable Tg.

  Furthermore, it may contain an acid component or a diol component other than the above, and examples of the acid component include phthalic acid and phthalic anhydride, and examples of the diol component include ethylene glycol, diethylene glycol, Examples include dipropylene glycol, xylene glycol, and dimethylolpropane. If the amount is slightly more, unsaturated acid components such as maleic acid and itaconic acid, polyfunctional acid components such as trimellitic acid and pyromellitic acid, polyfunctional hydroxy components such as glycerin and trimethylolpropane, and poly (ethylene oxide) Poly (alkylene oxide) glycol components such as glycol and poly (tetramethylene oxide) glycol may be used.

  The range of preferable intrinsic viscosity (sometimes abbreviated as IV) of the copolymerized polyester of the present invention is 0.2 to 0.8 dl / g, and the lower limit is further 0.3 dl / g, particularly 0.4 dl / g. The upper limit is preferably 0.7 dl / g, particularly preferably 0.6 dl / g. Here, the intrinsic viscosity is a value measured at 35 ° C. using orthochlorophenol.

In addition, the glass transition temperature (Tg) of the copolymerized polyester of the present invention is 70 ° C. or less from the viewpoint of adhesiveness and, further, in the case of in-line coating on a polyethylene terephthalate film, from the viewpoint of coating film formation (transparency). On the other hand, from the viewpoint of blocking resistance, it is preferably 40 ° C. or higher, particularly 45 ° C. or higher. Further, the refractive index of the copolyester is easily in the range of 1.58 to 1.65, since it is easy to suppress interference spots (color spots) with the refractive index of the coating layer in the above range. It is preferably in the range of 60 to 1.63, particularly in the range of 1.61 to 1.62. In order to satisfy the Tg and refractive index of the copolyester at the same time, the above-described requirements regarding the copolyester may be adopted.
Examples of the copolymer polyester preferably used include the following copolymer polyesters.

[Preferred Embodiment 1 of Copolyester]
(A) 60-90 mol% of naphthalene dicarboxylic acid component
(B) 1 to 10 mol% of aromatic dicarboxylic acid component having a sulfonate group, and (C) 5 to 25 mol% of bisphenol A ethylene oxide adduct component
(However, the above mol% is a value with respect to 100 mol% of all dicarboxylic acid components of the copolyester.)
Copolyester containing.

[Preferred embodiment 2 of copolymerized polyester]
(A) 60-90 mol% of naphthalene dicarboxylic acid component
(B) 1-10 mol% of an aromatic dicarboxylic acid component having a sulfonate group
(C) 5-25 mol% of bisphenol A ethylene oxide adduct component, and (D) 5 mol% or more and less than 20 mol% of glycol component having a fluorene structure represented by the formula (I) (provided that the above mol% Is a value based on 100 mol% of all dicarboxylic acid components of the copolyester.)
Copolyester containing.

[Preferred embodiment 3 of copolymerized polyester]
(A) 60-90 mol% of naphthalene dicarboxylic acid component
(B) 1-10 mol% of an aromatic dicarboxylic acid component having a sulfonate group
(C) 5-25 mol% of bisphenol A ethylene oxide adduct component
(D) 5 mol% or more and less than 20 mol% of the glycol component having the fluorene structure represented by the formula (I), and (E) 15 to 50 mol% of the alkylene glycol component having 4 to 10 carbon atoms.
(However, the above mol% is a value with respect to 100 mol% of all dicarboxylic acid components of the copolyester.)
Copolyester containing.

[Preferred embodiment 4 of copolymerized polyester]
(A) 60-70 mol% of naphthalene dicarboxylic acid component
(B) 6-8 mol% of an aromatic dicarboxylic acid component having a sulfonate group
(C) 5-25 mol% of bisphenol A ethylene oxide adduct component
(D) 5 mol% or more and less than 20 mol% of the glycol component having the fluorene structure represented by the formula (I), and (F) 24 to 34 mol% of the terephthalic acid component and / or isophthalic acid component.
(However, the above mol% is a value with respect to 100 mol% of all dicarboxylic acid components of the copolyester.)
Copolyester containing.

[Preferred embodiment 5 of copolymerized polyester]
(A) 60-70 mol% of naphthalene dicarboxylic acid component
(B) 6-8 mol% of an aromatic dicarboxylic acid component having a sulfonate group
(C) 5-25 mol% of bisphenol A ethylene oxide adduct component
(D) 5 mol% or more and less than 20 mol% of the glycol component having a fluorene structure represented by the formula (I) (E) 15 to 50 mol% of an alkylene glycol component having 4 to 10 carbon atoms, and (F) terephthalate 24 to 34 mol% of acid component and / or isophthalic acid component
(However, the above mol% is a value with respect to 100 mol% of all dicarboxylic acid components of the copolyester.)
Copolyester containing.

  The copolyester of the present invention described in detail above can be produced by a conventionally known polyester production technique. For example, an acid component such as 2,6-naphthalenedicarboxylic acid or an ester-forming derivative thereof, isophthalic acid or an ester-forming derivative thereof and 5-sodium sulfoisophthalic acid or an ester-forming derivative thereof is converted to tetramethylene glycol, 9,9- It reacts with diol components such as bis [4- (2-hydroxyethoxy) phenyl] fluorene and bisphenol A ethylene oxide adduct components to form monomers or oligomers, and then polycondensates under vacuum to obtain a predetermined intrinsic viscosity. It can be produced by a method of making a copolyester. At that time, a catalyst for promoting the reaction, for example, an esterification or transesterification catalyst or a polycondensation catalyst can be used, and various additives such as a stabilizer can be added.

  The above-mentioned copolymer polyester is applied to at least one surface of the polyester film, but since the in-line coating method applied when forming the polyester film is preferable, the copolymer polyester is preferably used as an aqueous dispersion. The method for forming the aqueous dispersion is not particularly limited, and a conventionally known method may be adopted.

(Crosslinking agent)
It is preferable to mix a crosslinking agent in the coating layer of the present invention. Preferred examples of the crosslinking agent include an epoxy crosslinking agent, an oxazoline crosslinking agent, a melamine crosslinking agent, and an isocyanate crosslinking agent, and these may be used alone or in combination of two or more. May be.

  Examples of the epoxy-based crosslinking agent include polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, etc. Examples of the polyepoxy compounds include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether. , Diglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, diepoxy compound, for example, neopentyl glycol diglycidyl ether, 1,6-hexanediol Diglycidyl ether, resorcin diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene group As a co-diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, poly-1,4-butanediol diglycidyl ether, monoepoxy compound, for example, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, phenyl glycidyl ether Examples of the glycidylamine compound include N, N, N ′, N′-tetraglycidyl-m-xylylenediamine and 1,3-bis (N, N-diglycidylamino) cyclohexane.

  As the oxazoline-based crosslinking agent, a polymer containing an oxazoline group is preferable. It can be prepared by polymerization with addition polymerizable oxazoline group-containing monomers alone or with other monomers. Addition polymerizable oxazoline group-containing monomers include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, and the like can be mentioned, and one or a mixture of two or more thereof can be used. Among these, 2-isopropenyl-2-oxazoline is preferred because it is easily available industrially. The other monomer may be any monomer that can be copolymerized with an addition-polymerizable oxazoline group-containing monomer. For example, alkyl acrylate, alkyl methacrylate (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n (Meth) acrylic acid esters such as butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group); acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrene sulfone Unsaturated carboxylic acids such as acids and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); unsaturated nitriles such as acrylonitrile, methacrylonitrile; acrylamide, methacrylamide, N-alkylacrylamide, N-alkyl methacrylamide N, N-dialkylacrylamide, N, N-dialkylmethacrylate (as alkyl groups, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group) Unsaturated amides such as cyclohexyl groups, etc .; vinyl esters such as vinyl acetate, vinyl propionate, acrylic acid, methacrylic acid added with polyalkylene oxide; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether Α-olefins such as ethylene and propylene; halogen-containing α and β-unsaturated monomers such as vinyl chloride, vinylidene chloride and vinyl fluoride; α and β-unsaturated aromatics such as styrene and α-methylstyrene Group monomers and the like, one or more of these It may be used monomers.

  As the melamine-based crosslinking agent, a compound obtained by reacting methyl alcohol melamine derivative obtained by condensing melamine and formaldehyde with methyl alcohol, ethyl alcohol, isopropyl alcohol or the like as a lower alcohol and a mixture thereof are preferable. Examples of the methylol melamine derivative include monomethylol melamine, dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, hexamethylol melamine and the like.

  Examples of the isocyanate-based crosslinking agent include tolylene diisocyanate, diphenylmethane-4,4′-diisocyanate, metaxylylene diisocyanate, hexamethylene-1,6-diisocyanate, 1,6-diisocyanate hexane, tolylene diisocyanate and hexanetriol. Adduct, adduct of tolylene diisocyanate and trimethylolpropane, polyol-modified diphenylmethane-4,4'-diisocyanate, carbodiimide-modified diphenylmethane-4,4'-diisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate, 3,3 ' -Bitrylene-4,4 'diisocyanate, 3,3' dimethyldiphenylmethane-4,4'-diisocyanate, metaphenylene diisocyanate, etc. It is.

Of these cross-linking agents, oxazoline-based cross-linking agents are particularly preferred from the viewpoints of ease of handling, pot life of the coating liquid, and the like.
By including a cross-linking agent in the coating layer, the requirement for the swelling property of the coating layer with respect to the solvent can be easily set to a suitable value. However, if the amount is too large, the swelling property becomes too low and the adhesiveness is lowered. Since it exists in the tendency, it is preferable to make the content rate of a crosslinking agent into the range of 1-30 mass% per 100 mass% of mass of an application layer, and it is preferable to set it as the range of 5-10 mass% especially.

(Other ingredients)
Various additives can be blended in the coating layer of the present invention within a range not impairing the object of the present invention. For example, particles, waxes, surfactants, wetting modifiers, etc. may be added to improve film slipperiness, scratch resistance, wettability during coating, and other antistatic agents, UV absorbers, etc. Etc. may be blended.
For example, by adding particles, the slipperiness and scratch resistance of the film can be improved. Such particles may be any of organic particles, inorganic particles, and organic-inorganic composite particles. From the viewpoint of improving scratch resistance while maintaining transparency, large particles (particles), It is preferable to contain both small particles (small particles).

The average particle size of the large particles is suitably in the range of 80 to 1000 nm, more preferably in the range of 100 to 400 nm, and still more preferably in the range of 130 to 350 nm. Thereby, it is excellent in lubricity and scratch resistance. In addition, since a large particle is easy to drop | omit from an application layer, it is preferable that it is an organic inorganic composite particle which coat | covered the inorganic particle surface with organic substance (for example, acrylic).
The content of the large particles in the coating layer is preferably 0.1 to 5% by mass, more preferably 0.1 to 1% by mass with respect to the mass of the coating layer, and the effect of adding large particles is further obtained. Cheap.

The average particle size of the small particles is suitably in the range of 10 nm or more and less than 100 nm, more preferably 20 to 80 nm, still more preferably 30 to 60 nm. Thereby, it is excellent in blocking resistance. From the viewpoint of hardness, the small particles are preferably inorganic particles, and are preferably metal oxide particles. Examples of the metal oxide particles include silica particles, alumina particles, titania particles, and zirconia particles. Among these, silica particles are preferable from the viewpoint of excellent cost.
The content of the small particles in the coating layer is preferably 0.1 to 5% by mass, more preferably 1 to 3% by mass with respect to the mass of the coating layer, and the effect of adding small particles is more easily obtained.

[Characteristics of laminated film]
(Haze)
The laminated film of the present invention preferably has a haze value measured according to JIS standard K7136 of 0% or more and 1.0% or less, more preferably 0.1% or more and 0.8% or less, particularly preferably 0. .1% or more and 0.5% or less. Haze is an important evaluation index for use in optical applications. For example, when used for a display, haze is one of the indexes for evaluating the visibility of a display, and when haze exceeds 1.0%, Since the transparency of the film is lowered and the display screen of the display looks whitish, the contrast is lowered and the visibility may be lowered. In order to make the haze in such a range, in the oriented polyester film and the coating layer, particles are not used or even when used, the diameter and the amount are within the above-mentioned range, and the above-mentioned polymer binder constituting the coating layer is used. A copolyester may be used.

[Production method of laminated film]
The laminated film of the present invention described above is manufactured through a film forming process for manufacturing a biaxially oriented polyester film and a coating process for forming a coating layer. The film forming step may be a sequential biaxial stretching method or a simultaneous biaxial stretching method, but if it is a simultaneous biaxial stretching method, the film surface is hardly damaged during film formation, Since it is suitable for manufacturing the film used for an optical use, it is preferable. The coating process may be after the film forming process (so-called off-line coating method) or in the film forming process (so-called in-line coating method). For example, a thin coating layer can be easily obtained uniformly, and a strong coating layer can be obtained. Furthermore, it is excellent in productivity.

  Hereinafter, a preferable method when polyethylene terephthalate is used as the polyester and the in-line coating method is adopted by the simultaneous biaxial stretching method will be described. First, sufficiently dried polyethylene terephthalate is melted at a temperature of Tm + 10 ° C. to Tm + 30 ° C. (where Tm is the melting point of polyethylene terephthalate), extruded into a sheet, and cooled with a cooling drum to form an unstretched film. Next, a coating solution for forming a coating layer is applied to the surface of the unstretched film on which the coating layer is to be formed by a roll coater to obtain an unstretched film having a coating film. At this time, it is applied so that the thickness of the coating layer in the obtained laminated film is preferably 50 to 100 nm, more preferably 70 to 90 nm. Next, this is preheated at 90 to 110 ° C., and simultaneously in the biaxial direction with a simultaneous biaxial stretching machine at a temperature of Tg to Tg + 70 ° C. (where Tg is the glass transition temperature of polyethylene terephthalate) (the film forming machine). Axial direction (hereinafter may be referred to as longitudinal direction or MD), preferably 2.5 to 5.0 times, more preferably 3.0 to 4.0 times, lateral direction (in the film forming machine axial direction). In the vertical direction (hereinafter sometimes referred to as the width direction or TD), the film is preferably stretched 2.5 to 5.0 times, more preferably 3.0 to 4.0 times, and then (Tg + 60 ° C.). A laminated film having a coating layer on an oriented polyethylene terephthalate film can be obtained by heat setting at a temperature of ~ Tm, and preferably heat relaxation treatment to adjust the heat shrinkage rate. In addition, it is preferable that the heat setting is performed at a temperature within a range of 210 to 240 ° C. for a time of 1 to 60 seconds. In addition, the coating film is dried by the heat applied in the above step, and is cured as necessary to form a coating layer.

  In addition, the coating liquid for forming an application layer mixes each component which comprises an application layer, and adjusts it suitably diluted in consideration of a viscosity, application | coating thickness, etc. The solvent used for dilution is preferably water, that is, the coating liquid is preferably aqueous. The solid content concentration of the coating liquid is preferably 5 to 20% by mass, and a good coating appearance can be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited only to these Examples. Each characteristic value was measured by the following method.

(1) Film refractive index The refractive index of each of the longitudinal direction (MD), the width direction (TD), and the film thickness direction (Z direction) of the obtained biaxially stretched polyester film was measured with an Abbe refractometer. In addition, since the thickness of the coating layer is thin, even if the coating layer is formed on both sides, it is not affected by the refractive index of the coating layer even if measured using an Abbe refractometer from above the coating layer. The refractive index of the oriented polyester film can be determined.
Surface direction refractive index = (longitudinal direction refractive index + width direction refractive index) / 2

(2) Refractive index of coating layer The coating liquid for forming the coating layer was dried in a plate shape at 90 ° C. and measured with an Abbe refractometer (D line 589 nm) to obtain the refractive index of the coating layer.

(3) Coating layer thickness The film is fixed with an embedding resin, the cross section is cut with a microtome, stained with 2% osmic acid at 60 ° C. for 2 hours, and using a transmission electron microscope (JEM2010 manufactured by JEOL Ltd.), The thickness of the coating layer was measured.

(4) Swelling ratio The thickness of the coating layer of the film after laminating the hard coat layer was measured in the same manner as (3) above. When the coating layer thickness before laminating the hard coat layer was d0 and the coating layer thickness after laminating was dh, the swelling rate E (%) of the coating layer was determined by the following formula 1.
E = dh / d0 × 100

(5) Adhesion of hard coat layer After 100 pieces of 1 mm ² crosscuts were put in the hard coat layer of the film on which the hard coat layer was formed, cellophane tape (manufactured by Nichiban Co., Ltd.) was pasted on it and strongly pressed with a finger The film was peeled in the 90 ° direction and the number of remaining hard coat layers was evaluated as follows.
◎: 90 <remaining number ≦ 100: very good adhesion ○: 80 <remaining number ≦ 90 ... good adhesion Δ: 70 <remaining number ≦ 80 ... slightly good adhesion ×: remaining number ≦ 70 ... Adhesive failure

(6) Light interference spots Using a film with a hard coat layer, the surface opposite to the surface on which the hard coat layer is formed is painted with black magic to eliminate the effect of reflected light from the opposite surface. The spectral reflectance was measured using a spectrophotometer (UV-3101PC manufactured by Shimadzu Corporation). The reflectance at a wavelength of 500 to 600 nm was measured, and the amplitude of the reflectance was evaluated according to the following criteria. As the amplitude of the measured reflectance is larger, interference spots are generated, and the visibility as a display is lowered.
◎: Reflectance amplitude ≦ 0.5% ・ ・ ・ Interference spots extremely good ○: 0.5% <Reflectance amplitude ≦ 1.0% ・ ・ ・ Interference spots good ×: 1.0% <Reflectance amplitude・ Impaired interference spots

(7) Haze value of laminated film According to JIS K7136, the haze value of the laminated film was measured using the Nippon Denshoku Industries Co., Ltd. haze measuring device (NDH-2000).

[Examples 1 to 10, Comparative Examples 1 to 9]
Molten polyethylene terephthalate ([η] = 0.63 dl / g, Tg = 78 ° C.) is extruded from a die, cooled with a cooling drum by a conventional method to form an unstretched film, and the solid content is shown in Table 1 on both sides. An aqueous coating solution having a solid content concentration of 10% by mass consisting of the composition was uniformly coated with a roll coater so that the thickness of the coating layer obtained after stretching was as shown in Table 1.
Next, this coated film was preheated at a temperature of 100 ° C., dried, and longitudinally 3 at 120 ° C. in a simultaneous biaxial stretching machine (which is correct in the above-mentioned preferred production method, which is Tg to Tg + 10 ° C.). The film was stretched in the longitudinal and transverse directions at a magnification of 2 times and 3.7 times in the transverse direction, and heat-set at 220 ° C. for 60 seconds to obtain a laminated film having coating layers on both sides of a biaxially oriented polyethylene terephthalate film having a thickness of 125 μm.
The plane direction refractive index of the obtained laminated film was 1.66.

Furthermore, on the coating layer of the film sample cut out to B4 size from the obtained laminated film, a UV curable composition having the following composition was converted into methyl ethyl ketone, ethyl acetate, toluene, isopropanol, propylene glycol monomethyl ether acetate (PGMEA) 5 types of each of these solvents diluted to a solid content concentration of 40% by mass were prepared, applied to each using a Meyer bar, immediately dried at 70 ° C. for 1 minute, and a strength of 80 W / cm. The hard coat layer was formed by irradiating with UV light for 30 seconds with a high pressure mercury lamp. The count of the Meyer bar was adjusted so that the hard coat layer thickness after curing was 5 μm.
The evaluation results are shown in Table 2.

(UV curable composition)
Pentaerythritol acrylate: 45% by mass
N-methylolacrylamide: 40% by mass
N-vinylpyrrolidone: 10% by mass
1-hydroxycyclohexyl phenyl ketone: 5% by mass
Table 2 shows the results of interference spots and adhesion of the film having the hard coat layer laminated thereon.

  In Table 1, NDCA is 2,6-naphthalenedicarboxylic acid component, TA is terephthalic acid component, IA is isophthalic acid component, NSIA is 5-sodium sulfoisophthalic acid component, C4G is tetramethylene glycol, C8G is octamethylene glycol, BPA -4 is an ethylene oxide 4 mol adduct component of bisphenol A manufactured by Sanyo Chemical Industries (New Pole BPE-40), BPA-23P is a propylene oxide adduct component of bisphenol A manufactured by Sanyo Chemical Industries (New Pole BPE-23) , BPEF means 9,9-bis [4- (2-hydroxyethoxy) phenyl] fluorene component, and EG means ethylene glycol.

  Moreover, as an oxazoline crosslinking agent (trade name Epocross WS-700 manufactured by Nippon Shokubai Co., Ltd.) as the crosslinking agent, silica acrylic composite fine particles (average particle size: 250 nm) (trade name Soriostar, manufactured by Nippon Shokubai Co., Ltd.), and particle 2 are used. Used a silica filler (50 nm) (trade name Snowtex manufactured by Nissan Chemical Co., Ltd.), and polyoxyethylene (n = 7) lauryl ether (trade name NAROACTY N-70, manufactured by Sanyo Chemical Industries, Ltd.) was used as the surfactant. .

  The laminated film of the present invention can be suitably used as a base film on which a hard coat layer or the like is provided. Moreover, it can paste | paste on liquid crystal display surfaces, such as a touchscreen, for example, and it can use suitably also as a base film for providing various functions to a display surface.

Claims (5)

At least one side of a polyester film having a plane direction refractive index of 1.63-1.68, a refractive index of 1.58-1.64, and a swelling ratio calculated by the following method of 130% to 200% in any solvent, And the laminated film which has a coating layer whose thickness is 50-100 nm.
Swelling rate:
On the coating layer of the laminated film, a coating solution (solid content concentration of 40% by mass) obtained by diluting the following UV curable composition with a solvent (methyl ethyl ketone, ethyl acetate, toluene, isopropanol or propylene glycol monomethyl ether) is applied and dried. A hard coat layer having a thickness of 5 μm is formed by curing. From the thickness dh of the coating layer after forming the hard coat layer and the thickness d0 of the coating layer before forming the hard coat layer, the swelling ratio E (%) = The value obtained as dh / d0 × 100.
UV curable composition:
Pentaerythritol acrylate: 45% by mass
N-methylolacrylamide: 40% by mass
N-vinylpyrrolidone: 10% by mass
1-hydroxycyclohexyl phenyl ketone: 5% by mass The laminated film according to claim 1, wherein the coating layer contains 70% by mass or more of the following copolyester based on the mass of the coating layer.
Copolyester:
(A2) 60-90 mol% of naphthalenedicarboxylic acid component,
(B2) Copolyester containing 1 to 10 mol% of an aromatic dicarboxylic acid component having a sulfonate group and (C2) 5 to 25 mol% of a bisphenol A ethylene oxide adduct component.
(However, the above mol% is a value with respect to 100 mol% of all dicarboxylic acid components of the copolyester.) The copolymer polyester further comprises (D3) 5 mol% or more and less than 20 mol% of a glycol component having a fluorene structure represented by the following formula (I) (provided that the mol% is the total dicarboxylic acid component 100 of the copolymer polyester). (Value relative to mol%.)

(R ₁ is an alkylene group having 2 to 4 carbon atoms, R ₂ , R ₃ , R ₄ , and R ₅ are hydrogen, an alkyl group having 1 to 4 carbon atoms, an aryl group, or an aralkyl group. Or different)
The laminated film according to claim 2 comprising.   The laminated film according to claim 2 or 3, wherein the coating layer contains 1 to 30% by mass of a crosslinking agent based on the mass of the coating layer.   The laminated film according to any one of claims 1 to 4, which is used as an easily adhesive film for optics.