阅读说明：本技术 层叠膜及其制造方法、以及偏振片 (Laminated film, method for producing same, and polarizing plate ) 是由 三浦拓也 于 2019-01-21 设计创作，主要内容包括：本发明提供一种层叠膜,其依次具有由第1树脂形成的第1层、由第2树脂形成的第2层和由第3树脂形成的第3层；第2树脂包含嵌段共聚物氢化物的烷氧基甲硅烷基改性物；第2树脂具有规定的水分含有率；第2树脂具有比第1树脂的弯曲弹性模量低且比第3树脂的弯曲弹性模量也低的弯曲弹性模量；第1树脂和第3树脂中的一者或两者包含含有脂环式结构的聚合物；第1树脂具有规定的水蒸气透过率；第1层的厚度和第3层的厚度的和与第2层的厚度的比在规定范围内。(The present invention provides a laminated film, which sequentially comprises a 1 st layer formed by a 1 st resin, a 2 nd layer formed by a 2 nd resin and a 3 rd layer formed by a 3 rd resin; the 2 nd resin contains an alkoxysilyl-modified product of block copolymer hydride; the 2 nd resin has a predetermined moisture content; the 2 nd resin has a flexural modulus of elasticity lower than that of the 1 st resin and also lower than that of the 3 rd resin; one or both of the 1 st resin and the 3 rd resin comprise a polymer containing an alicyclic structure; the 1 st resin has a prescribed water vapor transmission rate; the ratio of the sum of the thickness of the 1 st layer and the thickness of the 3 rd layer to the thickness of the 2 nd layer is within a prescribed range.)

1. A laminated film comprising, in order, a 1 st layer formed of a 1 st resin, a 2 nd layer formed of a 2 nd resin, and a 3 rd layer formed of a 3 rd resin,

the 2 nd resin contains an alkoxysilyl-modified product of a block copolymer hydride,

the 2 nd resin has a moisture content of 0.020% by mass or less as measured by the Karl Fischer method after being immersed in water at 37 ℃ for 24 hours and left to stand in an environment at 23 ℃ and a humidity of 70% for 24 hours,

the 2 nd resin has a flexural modulus of elasticity lower than that of the 1 st resin and also lower than that of the 3 rd resin,

one or both of the 1 st resin and the 3 rd resin comprise a polymer containing an alicyclic structure,

in the case of forming the 1 st resin into a film having a thickness of 100 μm, the water vapor transmission rate measured in accordance with JIS K7129B (1992) was 5 g/(m)²Day) of the day or less,

the ratio of the sum of the thickness of the 1 st layer and the thickness of the 3 rd layer to the thickness of the 2 nd layer is 1 or more and 4 or less.

2. The laminate film according to claim 1, wherein one or both of the 1 st resin and the 3 rd resin have a flexural modulus of elasticity of 1900MPa or more and 2800MPa or less in a film having a thickness of 4 mm.

3. The laminate film according to claim 1 or 2, wherein one or both of the 1 st resin and the 3 rd resin comprise a polymer which has crystallinity and contains an alicyclic structure.

4. The laminated film according to any one of claims 1 to 3, wherein the thickness of the laminated film is 50 μm or less.

5. A polarizing plate comprising a polarizer and the laminated film according to any one of claims 1 to 4.

6. A method for producing the laminated film according to any one of claims 1 to 4, comprising:

a step of drying the 2 nd resin, and

and forming a 1 st layer, a 2 nd layer and a 3 rd layer from the 1 st resin, the dried 2 nd resin and the dried 3 rd resin.

Technical Field

The present invention relates to a laminated film, a method for producing the same, and a polarizing plate.

Background

The polarizing plate generally has a polarizer and a polarizer protective film as an optical film for protecting the polarizer. As polarizer protective films, laminated films having a 3-layer structure have been proposed in patent documents 1 and 2.

Disclosure of Invention

Problems to be solved by the invention

A polarizing plate is sometimes provided in an image display device. In recent years, flexible image display devices such as, for example, organic electroluminescent display devices (hereinafter, appropriately referred to as "organic EL display devices") have been receiving attention. For a polarizing plate provided on such a flexible image display device, excellent bending resistance is desired. Therefore, excellent bending resistance is also desired for a laminated film as a polarizer protective film.

Further, the polarizing plate may be exposed to a high temperature environment, such as a polarizing plate provided in an in-vehicle image display device. Therefore, excellent heat resistance is desired for a laminated film as a polarizer protective film.

Further, it is also desirable that the laminated film as described above does not contain bubbles inside. In particular, in an optical film such as a polarizer protective film, since air bubbles are a cause of impairing the optical characteristics thereof, it is highly desirable that air bubbles are not contained.

However, in the prior art, a laminated film which is excellent in both heat resistance and bending resistance and can suppress bubble formation has not been obtained.

The present invention has been made in view of the above problems, and an object thereof is to provide a laminated film which is excellent in both heat resistance and bending resistance and can suppress bubble formation, a method for producing the same, and a polarizing plate having the laminated film.

Means for solving the problems

The present inventors have conducted intensive studies in order to solve the above problems. As a result, the present inventors have found that when a laminated film combination having a 1 st layer made of a 1 st resin, a 2 nd layer made of a 2 nd resin, and a 3 rd layer made of a 3 rd resin in this order satisfies predetermined requirements, both heat resistance and bending resistance can be improved, and formation of bubbles can be suppressed, and have completed the present invention.

That is, the present invention includes the following aspects.

[1] A laminated film comprising, in order, a 1 st layer formed of a 1 st resin, a 2 nd layer formed of a 2 nd resin, and a 3 rd layer formed of a 3 rd resin,

the above-mentioned second resin 2 comprises an alkoxysilyl-modified product of a block copolymer hydride,

the 2 nd resin has a moisture content of 0.020% by mass or less as measured by the Karl Fischer method after being immersed in water at 37 ℃ for 24 hours and left to stand in an environment at 23 ℃ and a humidity of 70% for 24 hours,

the 2 nd resin has a flexural modulus of elasticity lower than that of the 1 st resin and lower than that of the 3 rd resin,

one or both of the 1 st resin and the 3 rd resin contain a polymer containing an alicyclic structure,

when the above-mentioned No. 1 resin was formed into a film having a thickness of 100. mu.m, the water vapor transmission rate measured in accordance with JIS K7129B (1992) was 5 g/(m)²Day) of the day or less,

the ratio of the sum of the thickness of the 1 st layer and the thickness of the 3 rd layer to the thickness of the 2 nd layer is 1 or more and 4 or less.

[2] The laminated film according to [1], wherein one or both of the 1 st resin and the 3 rd resin have a flexural modulus of elasticity of 1900MPa or more and 2800MPa or less, the film having a thickness of 4 mm.

[3] The laminated film according to item [1] or item [2], wherein one or both of the 1 st resin and the 3 rd resin comprise a polymer, and the polymer has crystallinity and contains an alicyclic structure.

[4] The laminated film according to any one of [1] to [3], wherein a thickness of the laminated film is 50 μm or less.

[5] A polarizing plate comprising a polarizer and the laminated film according to any one of [1] to [4 ].

[6] A method for producing a laminated film according to any one of [1] to [4], comprising:

drying the 2 nd resin; and

and forming a 1 st layer, a 2 nd layer and a 3 rd layer from the 1 st resin, the dried 2 nd resin and the dried 3 rd resin.

Effects of the invention

According to the present invention, a laminated film which is excellent in both heat resistance and bending resistance and can suppress bubble formation, and a method for producing the same can be provided; and a polarizing plate having the laminated film.

Drawings

Fig. 1 is a cross-sectional view schematically showing a laminated film according to an embodiment of the present invention.

Detailed Description

The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and may be modified and implemented arbitrarily without departing from the scope and range of equivalents of the claims of the present invention.

In the following description, unless otherwise specified, "polarizing plate" includes not only a rigid member but also a member having flexibility such as a resin film.

In the following description, unless otherwise specified, "ultraviolet light" refers to light having a wavelength of 10nm or more and less than 400 nm.

[1. summary of laminated film ]

Fig. 1 is a cross-sectional view schematically showing a laminated film 10 according to an embodiment of the present invention.

As shown in fig. 1, the laminated film 10 according to one embodiment of the present invention includes a 1 st layer 110, a 2 nd layer 120, and a 3 rd layer 130 in this order. Further, the laminated film 10 satisfies the following requirements (i) to (vi).

(i) The 2 nd resin contains an alkoxysilyl-modified product of block copolymer hydride.

(ii) The 2 nd resin has a moisture content of not more than a predetermined value as measured by the Karl Fischer method after being immersed in water at 37 ℃ for 24 hours and left to stand in an environment at 23 ℃ and a humidity of 70% for 24 hours.

(iii) The 2 nd resin has a flexural modulus of elasticity lower than that of the 1 st resin and also lower than that of the 3 rd resin.

(iv) One or both of the 1 st resin and the 3 rd resin contain a polymer containing an alicyclic structure.

(v) When the 1 st resin is a film having a thickness of 100 μm, the water vapor transmission rate measured according to JIS K7129B (1992) is a predetermined value or less.

(vi) Thickness T of layer 1 110₁₁₀And thickness T of layer 3 130₁₃₀And T₁₁₀+T₁₃₀Thickness T of layer 2₁₂₀Ratio of (T) (₁₁₀+T₁₃₀)/T₁₂₀"is within the specified range.

The laminated film 10 satisfying the above requirements (i) to (vi) is excellent in both heat resistance and bending resistance, and can suppress the formation of bubbles. Therefore, the laminated film 10 can be preferably used for optical applications such as a polarizer protective film.

The laminated film 10 may have any layer in addition to the 1 st layer 110, the 2 nd layer 120, and the 3 rd layer 130. However, it is preferred that layer 1 110 be in direct contact with layer 2 120. Also, it is preferable that the 2 nd layer 120 is in direct contact with the 3 rd layer 130. Here, the state in which two layers are in contact with each other is "direct", which means that no other layer is present between the two layers. Therefore, the laminated film 10 is preferably a film having a 3-layer structure of only the 1 st layer 110, the 2 nd layer 120, and the 3 rd layer 130.

[2. layer 1]

The 1 st layer is formed of the 1 st resin. As the 1 st resin, a resin containing a polymer and optionally further containing an optional component may be used. The polymer can be used alone in 1, also can be used in any ratio of more than 2.

In the laminated film, a resin containing a polymer containing an alicyclic structure is used as one or both of the 1 st resin and the 3 rd resin (requirement (iv)). Hereinafter, the alicyclic structure-containing polymer is appropriately referred to as "alicyclic structure-containing polymer". Therefore, when the 3 rd resin contained in the 3 rd layer contains the alicyclic structure-containing polymer, the 1 st resin may or may not contain the alicyclic structure-containing polymer. On the other hand, in the case where the 3 rd resin contained in the 3 rd layer does not contain a polymer having an alicyclic structure, the 1 st resin contains a polymer having an alicyclic structure. Of these, it is preferable that both the 1 st resin and the 3 rd resin contain the alicyclic structure-containing polymer.

The alicyclic structure-containing polymer is excellent in mechanical strength, and therefore, the bending resistance of the laminate film can be improved. Further, the alicyclic structure-containing polymer is generally low in hygroscopicity. Therefore, by using the resin containing the alicyclic structure-containing polymer, the water vapor transmission rate of the laminated film can be effectively reduced. This can suppress deformation of the laminated film in a high humidity environment in general, and therefore, can improve the moisture resistance of the laminated film. Further, the alicyclic structure-containing polymer is generally excellent in transparency, dimensional stability and lightweight property.

The alicyclic structure-containing polymer is a polymer having an alicyclic structure in a repeating unit, and examples thereof include a polymer obtained by polymerization using a cyclic olefin as a monomer, and a hydrogenated product thereof. Further, as the alicyclic structure-containing polymer, any of a polymer having an alicyclic structure in the main chain and a polymer having an alicyclic structure in the side chain can be used. Among them, the alicyclic structure-containing polymer preferably contains an alicyclic structure in its main chain. Examples of the alicyclic structure include a cycloalkane structure, a cycloalkene structure, and the like, and a cycloalkane structure is preferable from the viewpoint of thermal stability and the like.

The number of carbon atoms included in 1 alicyclic structure is preferably 4 or more, more preferably 5 or more, further preferably 6 or more, preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. When the number of carbon atoms included in 1 alicyclic structure is within the above range, mechanical strength, heat resistance, and moldability can be highly balanced.

The proportion of the repeating unit having an alicyclic structure in the alicyclic structure-containing polymer is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 70% by mass or more, and particularly preferably 90% by mass or more. By setting the ratio of the repeating unit having an alicyclic structure to be as high as described above, heat resistance can be improved.

In addition, in the alicyclic structure-containing polymer, the remaining portion other than the repeating unit having an alicyclic structure is not particularly limited and can be appropriately selected depending on the purpose of use.

The alicyclic structure-containing polymer contained in one or both of the 1 st resin and the 3 rd resin may be a polymer having crystallinity, a polymer having no crystallinity, or a combination of both. Here, the polymer having crystallinity means a polymer having a melting point Mp. The polymer having a melting point Mp is a polymer that can be observed by a Differential Scanning Calorimeter (DSC). By using the alicyclic structure-containing polymer having crystallinity, the mechanical strength of the laminated film can be particularly effectively improved, and therefore the bending resistance can be remarkably improved. Further, by using the alicyclic structure-containing polymer having no crystallinity, the production cost of the laminated film can be reduced.

Examples of the alicyclic structure-containing polymer having crystallinity include the following polymers (. alpha.) to polymers (). Among them, the polymer (. beta.) is preferable as the alicyclic structure-containing polymer having crystallinity, from the viewpoint of easily obtaining a laminated film excellent in heat resistance.

Polymer (α): a ring-opened polymer of a crystalline, cyclic olefin monomer.

Polymer (β): a crystalline, hydrogenated product of the polymer (alpha).

Polymer (γ): addition polymers of crystalline, cyclic olefin monomers.

Polymer (): crystalline, hydrogenated products of the polymer (γ), and the like.

Specifically, the alicyclic structure-containing polymer having crystallinity is more preferably a dicyclopentadiene ring-opening polymer having crystallinity and a hydrogenated product of the dicyclopentadiene ring-opening polymer having crystallinity, and particularly preferably a hydrogenated product of the dicyclopentadiene ring-opening polymer having crystallinity. Here, the dicyclopentadiene ring-opening polymer refers to the following polymers: the proportion of the structural unit derived from dicyclopentadiene is usually 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and still more preferably 100% by mass of the total structural units.

The hydride of the dicyclopentadiene ring-opening polymer is preferably in a high proportion of syndiotactic diads (Racemo Diad). Specifically, the proportion of the syndiotactic diads in the repeating units in the hydrogenated product of the dicyclopentadiene ring-opening polymer is preferably 51% or more, more preferably 60% or more, and particularly preferably 65% or more. A high ratio of syndiotactic diads indicates a high syndiotacticity. Therefore, there is a tendency that: the higher the ratio of syndiotactic diads, the higher the melting point of the hydride of the dicyclopentadiene ring-opening polymer.

The ratio of the syndiotactic diad group can be based on that described in the examples described later¹³C-NMR spectrum analysis.

The alicyclic structure-containing polymer having crystallinity may be uncrystallized before the production of the laminate film. However, after the production of the laminated film, the alicyclic structure-containing polymer having crystallinity contained in the laminated film is generally crystallized, and thus can have high crystallinity. The specific range of crystallinity can be appropriately selected depending on the desired performance, and is preferably 10% or more, and more preferably 15% or more. When the crystallinity of the alicyclic structure-containing polymer contained in the laminate film is not less than the lower limit of the above range, the laminate film can be provided with high heat resistance and chemical resistance. The crystallinity can be measured by X-ray diffraction.

The melting point Mp of the alicyclic structure-containing polymer having crystallinity is preferably 200 ℃ or higher, more preferably 230 ℃ or higher, and preferably 290 ℃ or lower. By using the alicyclic structure-containing polymer having crystallinity and having such a melting point Mp, a multilayer film having a further excellent balance between moldability and heat resistance can be obtained.

The alicyclic structure-containing polymer having crystallinity as described above can be produced by, for example, the method described in international publication No. 2016/067893.

On the other hand, examples of the alicyclic structure-containing polymer having no crystallinity include: (1) norbornene-based polymers, (2) monocyclic cyclic olefin polymers, (3) cyclic conjugated diene polymers, (4) vinyl alicyclic hydrocarbon polymers, and hydrogenated products thereof. Among them, norbornene-based polymers and hydrogenated products thereof are more preferable from the viewpoint of transparency and moldability.

Examples of the norbornene-based polymer include: a ring-opening polymer of a norbornene monomer, a ring-opening copolymer of a norbornene monomer and another monomer capable of ring-opening copolymerization, and a hydride thereof; addition polymers of norbornene monomers, addition copolymers of norbornene monomers and other copolymerizable monomers, and the like. Among them, the hydrogenated ring-opening polymer of a norbornene-based monomer is particularly preferable from the viewpoint of transparency.

The above-mentioned alicyclic structure-containing polymer may be selected from, for example, the polymers disclosed in Japanese patent laid-open publication No. 2002-321302.

Since there are various commercially available resins containing an alicyclic structure-containing polymer having no crystallinity, a product having desired characteristics can be appropriately selected from among them and used. Examples of such commercially available products include product groups having trade names of "ZEONOR" (manufactured by kushoku corporation), "ARTON" (manufactured by JSR corporation), "APEL" (manufactured by mitsui chemical corporation), and "TOPAS" (manufactured by polyplascs co.

The weight average molecular weight (Mw) of the polymer contained in the 1 st resin is preferably 10000 or more, more preferably 15000 or more, particularly preferably 20000 or more, preferably 100000 or less, more preferably 80000 or less, and particularly preferably 50000 or less. The polymer having such a weight average molecular weight is excellent in the balance of mechanical strength, moldability and heat resistance.

The molecular weight distribution (Mw/Mn) of the polymer contained in the 1 st resin is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably 1.8 or more, preferably 3.5 or less, more preferably 3.4 or less, and particularly preferably 3.3 or less. When the molecular weight distribution is not less than the lower limit of the above range, the productivity of the polymer can be improved and the production cost can be suppressed. Further, when the molecular weight distribution is not more than the upper limit of the above range, the amount of low molecular weight components is reduced, and therefore, relaxation due to exposure to high temperature can be suppressed, and the stability of the laminated film can be improved.

The weight average molecular weight Mw and the number average molecular weight Mn of the polymer can be measured as values in terms of polyisoprene using gel permeation chromatography (hereinafter, abbreviated as "GPC") using cyclohexane as a solvent. In the case where the resin is insoluble in cyclohexane, toluene may be used as a solvent. When the solvent is toluene, the weight average molecular weight Mw and the number average molecular weight Mn can be measured as values in terms of polystyrene.

From the viewpoint of obtaining a laminated film particularly excellent in heat resistance and bending resistance, the proportion of the polymer in the 1 st resin is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, even more preferably 95 to 100% by mass, and particularly preferably 98 to 100% by mass.

The 1 st resin may contain any of the ingredients in combination with the above-described polymers. Examples of the optional components include: inorganic fine particles; stabilizers such as antioxidants, heat stabilizers, ultraviolet absorbers, and near infrared absorbers; resin modifiers such as lubricants and plasticizers; colorants such as dyes and pigments; and an antistatic agent. These optional components may be used alone in 1 kind, or 2 or more kinds may be used in combination in an arbitrary ratio. However, from the viewpoint of remarkably exerting the effect of the present invention, it is preferable that the content ratio of any component is small. For example, the total ratio of the optional components is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, further preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, relative to 100 parts by mass of the polymer contained in the 1 st resin. Further, by reducing the content of the optional component contained in the 1 st resin, bleeding of the optional component can be suppressed.

The 1 st resin has low moisture permeability. Therefore, when the resin 1 is formed into a film having a thickness of 100 μm, the water vapor transmission rate measured under the conditions of 40 ℃ and 90% RH according to JIS K7129B (1992) is not more than a predetermined value (requirement (v)). Specifically, the water vapor transmission rate is usually 5 g/(m)²Day) or less, preferably 2 g/(m)²Day) or less, more preferably 1.5 g/(m)²Day) or less, particularly preferably 1 g/(m)²Day) below. By using the 1 st resin having such a low moisture permeability, the water vapor barrier ability of the 1 st layer can be improved, and therefore, the penetration of water vapor into the 2 nd layer can be suppressed. Therefore, deterioration of the 2 nd layer by water vapor can be suppressed, and thus, the 2 nd layer can exhibit excellent performance to improve the heat resistance and the bending resistance of the laminated film. Further, by using the 1 st resin having a high water vapor barrier ability, the water vapor barrier ability of the laminated film can be improved, and therefore, in the case of using the laminated film as a polarizer protective film, the polarizer can be effectively protected from moisture. The lower limit of the water vapor transmission rate is preferably zero, and may be 0.1 g/(m)²Day).

The water vapor transmission rate can be measured by forming the 1 st resin into a film having a thickness of 100 μm and using the film. The water vapor permeability can be measured using a commercially available water vapor permeability measuring apparatus under conditions of a temperature of 40 ℃ and a humidity of 90% RH.

The 1 st resin preferably has a high flexural modulus of elasticity. Specifically, the flexural modulus of the film of the 1 st resin having a thickness of 4mm is preferably 1900MPa or more, more preferably 2000MPa or more, particularly preferably 2100MPa or more, preferably 2800MPa or less, more preferably 2700MPa or less, and particularly preferably 2600MPa or less. By setting the flexural modulus of the film of the 1 st resin to be not less than the lower limit of the above range, the rigidity of the 1 st layer can be improved, and therefore, the handleability of the laminated film can be improved. In addition, by setting the bending elastic modulus of the film of the 1 st resin to be equal to or less than the upper limit value of the above range, the flexibility of the laminated film can be improved, and therefore, the bending resistance of the laminated film can be effectively improved.

The flexural modulus can be measured by forming the 1 st resin into a film having a thickness of 4mm and using the film. The flexural modulus can be measured at a temperature of 23 ℃ in accordance with JIS K7171.

The glass transition temperature Tg of the 1 st resin is preferably 80 ℃ or higher, more preferably 85 ℃ or higher, still more preferably 90 ℃ or higher, preferably 250 ℃ or lower, and more preferably 170 ℃ or lower. When the polymer having a glass transition temperature in such a range is used at high temperature, deformation and stress are less likely to occur, and the heat resistance is excellent.

The thickness of the 1 st layer may be set to a thickness such that the ratio of the sum of the thickness of the 1 st layer and the thickness of the 3 rd layer to the thickness of the 2 nd layer falls within a predetermined range (requirement (vi)). Specifically, the thickness ratio is usually 1 or more, preferably 1.2 or more, particularly preferably 1.4 or more, and usually 4 or less, preferably 3 or less, particularly preferably 2 or less. When the thickness ratio is within the above range, the excellent physical properties of each of the 1 st layer, the 2 nd layer and the 3 rd layer can be combined to obtain a laminated film having excellent heat resistance and bending resistance. In particular, the heat resistance can be effectively improved by setting the thickness ratio to be equal to or higher than the lower limit of the above range, and the bending resistance can be effectively improved by setting the thickness ratio to be equal to or lower than the upper limit of the above range.

The specific thickness of the 1 st layer is preferably 5 μm or more, more preferably 8 μm or more, particularly preferably 10 μm or more, preferably 20 μm or less, more preferably 18 μm or less, and particularly preferably 15 μm or less. When the thickness of the 1 st layer is not less than the lower limit of the above range, the properties of the laminate, such as heat resistance and bending resistance, can be effectively improved by the action of the 1 st layer. In addition, the penetration of moisture into the 2 nd layer can be effectively suppressed. Further, by providing the layer 1 with such a thickness, bleeding of any component contained in the layer 2 can be effectively suppressed. On the other hand, by setting the thickness of the 1 st layer to be equal to or less than the upper limit of the above range, the laminated film can be made thinner.

[3. layer 2]

The 2 nd layer is formed of the 2 nd resin. As the 2 nd resin, a resin containing an alkoxysilyl-modified product of a block copolymer hydride and optionally further containing an optional component (requirement (i)) can be used. In the following description, the above-mentioned block copolymer may be appropriately referred to as "block copolymer [1 ]. In the following description, the hydrogenated product of the block copolymer [1] may be appropriately referred to as "hydrogenated product [2 ]. Further, in the following description, the alkoxysilyl-modified product of the hydride [2] of the block copolymer [1] may be appropriately referred to as "alkoxysilyl-modified product [3 ].

The block copolymer [1] preferably comprises a polymer block [ A ] containing an aromatic vinyl compound unit and a polymer block [ B ] containing a chain-like conjugated diene compound unit. Among them, the block copolymer [1] particularly preferably has 2 or more polymer blocks [ A ] per 1 molecule of the block copolymer [1] and 1 or more polymer blocks [ B ] per 1 molecule of the block copolymer [1 ].

The polymer block [ A ] is a polymer block containing an aromatic vinyl compound unit. The aromatic vinyl compound unit herein means a structural unit having a structure obtained by polymerizing an aromatic vinyl compound.

Examples of the aromatic vinyl compound corresponding to the aromatic vinyl compound unit of the polymer block [ a ] include: styrene; styrenes having an alkyl group having 1 to 6 carbon atoms as a substituent, such as α -methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2, 4-dimethylstyrene, 2, 4-diisopropylstyrene, 4-tert-butylstyrene, and 5-tert-butyl-2-methylstyrene; styrenes having a halogen atom as a substituent, such as 4-chlorostyrene, dichlorostyrene, and 4-monofluorostyrene; styrenes having an alkoxy group having 1 to 6 carbon atoms as a substituent, such as 4-methoxystyrene; styrenes having an aryl group as a substituent, such as 4-phenylstyrene; and vinylnaphthalenes such as 1-vinylnaphthalene and 2-vinylnaphthalene. These can be used alone in 1 kind, also can be more than 2 kinds in any ratio combination use. Among them, styrene or a polar group-free aromatic vinyl compound such as styrene having an alkyl group having 1 to 6 carbon atoms as a substituent is preferable from the viewpoint of reducing the hygroscopicity, and styrene is particularly preferable from the viewpoint of being industrially easily available.

The content of the aromatic vinyl compound unit in the polymer block [ a ] is preferably 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 99% by mass or more. By making the amount of the aromatic vinyl compound unit in the polymer block [ a ] as large as described above, the rigidity and heat resistance of the 2 nd layer can be improved.

The polymer block [ A ] may contain an arbitrary structural unit in addition to the aromatic vinyl compound unit. The polymer block [ A ] may contain 1 arbitrary structural unit alone, or may contain 2 or more arbitrary structural units in combination at an arbitrary ratio.

Examples of the optional structural unit that the polymer block [ a ] may contain include a chain conjugated diene compound unit. Here, the chain conjugated diene compound unit means a structural unit having a structure obtained by polymerizing a chain conjugated diene compound. Examples of the chain conjugated diene compound corresponding to the chain conjugated diene compound unit include the same ones as those exemplified as the chain conjugated diene compound corresponding to the chain conjugated diene compound unit contained in the polymer block [ B ].

Examples of the optional structural unit that the polymer block [ a ] may contain include a structural unit having a structure obtained by polymerizing an optional unsaturated compound other than the aromatic vinyl compound and the chain-like conjugated diene compound. Examples of the optional unsaturated compound include: vinyl compounds such as chain vinyl compounds and cyclic vinyl compounds; unsaturated cyclic acid anhydrides; unsaturated imide compounds, and the like. These compounds may have a substituent such as a nitrile group, an alkoxycarbonyl group, a hydroxycarbonyl group, or a halogen group. Among them, from the viewpoint of hygroscopicity, olefin compounds containing no polar group are preferable, for example: a chain olefin having 2 to 20 carbon atoms per 1 molecule, such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-eicosene, 4-methyl-1-pentene, 4, 6-dimethyl-1-heptene, and the like; cyclic olefins having 5 to 20 carbon atoms per 1 molecule such as vinylcyclohexene, and chain olefins having 2 to 20 carbon atoms per 1 molecule are more preferable, and ethylene and propylene are particularly preferable.

The content of an arbitrary structural unit in the polymer block [ a ] is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 1% by mass or less.

The number of the polymer blocks [ A ] in the 1-molecule block copolymer [1] is preferably 2 or more, preferably 5 or less, more preferably 4 or less, and particularly preferably 3 or less. The plural polymer blocks [ A ] in the molecule 1 may be the same as or different from each other.

The polymer block [ B ] is a polymer block containing a chain-like conjugated diene compound unit. As described above, the chain conjugated diene compound unit means a structural unit having a structure formed by polymerizing a chain conjugated diene compound.

Examples of the chain conjugated diene compound corresponding to the chain conjugated diene compound unit of the polymer block [ B ] include 1, 3-butadiene, isoprene, 2, 3-dimethyl-1, 3-butadiene, 1, 3-pentadiene, and the like. These can be used alone in 1 kind, also can be more than 2 kinds in any ratio combination use. Among these, from the viewpoint of reducing the hygroscopicity, a chain-like conjugated diene compound containing no polar group is preferable, and 1, 3-butadiene and isoprene are particularly preferable.

The content of the chain-like conjugated diene compound unit in the polymer block [ B ] is preferably 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 99% by mass or more. By increasing the amount of the chain conjugated diene compound unit in the polymer block [ B ] as described above, the flexibility of the 2 nd layer can be improved.

The polymer block [ B ] may contain an arbitrary structural unit in addition to the chain-like conjugated diene compound unit. The polymer block [ B ] may contain 1 arbitrary structural unit alone, or may contain 2 or more arbitrary structural units in combination at an arbitrary ratio.

Examples of the optional structural unit that can be contained in the polymer block [ B ] include an aromatic vinyl compound unit and a structural unit having a structure obtained by polymerizing an optional unsaturated compound other than an aromatic vinyl compound and a chain-like conjugated diene compound. Examples of the aromatic vinyl compound unit and the structural unit having a structure obtained by polymerizing an arbitrary unsaturated compound include the same ones as those exemplified as the structural unit that can be contained in the polymer block [ A ].

The content of any structural unit in the polymer block [ B ] is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 1% by mass or less. By reducing the content of an arbitrary structural unit in the polymer block [ B ], the flexibility of the 2 nd layer can be improved.

The number of the polymer blocks [ B ] in the 1-molecule block copolymer [1] is usually not less than 1, and may be not less than 2. When the number of the polymer blocks [ B ] in the block copolymer [1] is 2 or more, these polymer blocks [ B ] may be the same as or different from each other.

The block system of the block copolymer [1] may be a linear block or a radial block. Among them, the linear block is preferable because it is excellent in mechanical strength. In the case of the embodiment in which the block copolymer [1] has a linear block, the viscosity of the 2 nd layer can be suppressed to a desired low value by forming the polymer blocks [ a ] at both ends of the molecular chain of the block copolymer [1 ].

Particularly preferred block modes of the block copolymer [1] are: a triblock copolymer in which the polymer block [ A ] is bonded to both ends of the polymer block [ B ] as represented by [ A ] to [ B ] to [ A ]; as shown in [ A ] - [ B ] - [ A ] - [ B ] - [ A ], the polymer block [ B ] is bonded to both ends of the polymer block [ A ], and further, a pentablock copolymer in which the polymer block [ A ] is bonded to the other ends of the two polymer blocks [ B ] is bonded. In particular, triblock copolymers such as [ a ] - [ B ] - [ a ] are particularly preferable because they can be easily produced and physical properties can be easily controlled within a desired range.

In the block copolymer [1], the ratio (wA/wB) of the weight percentage wA of the polymer block [ A ] to the weight percentage wB of the polymer block [ B ] to the total of the block copolymer [1] is preferably within a specific range. Specifically, the ratio (wA/wB) is preferably 40/60 or more, more preferably 50/50 or more, particularly preferably 70/30 or more, preferably 95/5 or less, more preferably 90/10 or less, and particularly preferably 85/15 or less. By setting the ratio wA/wB to be equal to or higher than the lower limit of the above range, the rigidity and heat resistance of the 2 nd layer can be improved, and birefringence can be reduced. Further, by setting the ratio wA/wB to be equal to or less than the upper limit of the above range, the flexibility of the 2 nd layer can be improved. Here, the weight percentage wA of the polymer block [ A ] represents the weight percentage of the whole of the polymer block [ A ], and the weight percentage wB of the polymer block [ B ] represents the weight percentage of the whole of the polymer block [ B ].

The weight average molecular weight (Mw) of the block copolymer [1] is preferably 30000 or more, more preferably 40000 or more, particularly preferably 50000 or more, preferably 200000 or less, more preferably 150000 or less, particularly preferably 100000 or less.

The molecular weight distribution (Mw/Mn) of the block copolymer [1] is preferably 3 or less, more preferably 2 or less, particularly preferably 1.5 or less, and preferably 1.0 or more.

The weight average molecular weight (Mw) and the molecular weight distribution (Mw/Mn) of the block copolymer [1] can be measured as values in terms of polystyrene by Gel Permeation Chromatography (GPC) using Tetrahydrofuran (THF) as a solvent.

As the method for producing the block copolymer [1], for example, the method described in International publication No. 2015/099079 and Japanese patent application laid-open No. 2016-204217 can be used.

The hydride [2] is a polymer obtained by hydrogenating the unsaturated bond of the block copolymer [1 ]. Here, the unsaturated bond of the block copolymer [1] to be hydrogenated includes aromatic and non-aromatic carbon-carbon unsaturated bonds of the main chain and side chain of the block copolymer [1 ].

Hydride [2]]The hydrogenation ratio (c) is preferably 90% or more, more preferably 97% or more, and particularly preferably 99% or more. Hydrides [2] unless otherwise stated]The hydrogenation ratio of (A) is: block copolymer [1]The main chain and the side chain, and the ratio of the bond to be hydrogenated in the aromatic and non-aromatic carbon-carbon unsaturated bonds. The higher the hydrogenation ratio, the better the transparency, heat resistance and weather resistance of the 2 nd layer can be, and further, the more easily the birefringence of the 2 nd layer can be reduced. Here, the hydride [2]]Can be obtained by a hydrogenation based on¹H-NMR was measured. Hydride [2]]The upper limit of the hydrogenation rate of (3) may be 100% or less.

In particular, the hydrogenation rate of the nonaromatic carbon-carbon unsaturated bond is preferably 95% or more, and more preferably 99% or more. By increasing the hydrogenation rate of the nonaromatic carbon-carbon unsaturated bond, the light resistance and oxidation resistance of the 2 nd layer can be further improved.

The hydrogenation ratio of the aromatic carbon-carbon unsaturated bond is preferably 90% or more, more preferably 93% or more, and particularly preferably 95% or more. The glass transition temperature of the polymer block obtained by hydrogenating the polymer block [ a ] can be increased by increasing the hydrogenation rate of the aromatic carbon-carbon unsaturated bond, and therefore, the heat resistance of the 2 nd layer can be effectively improved. Further, the photoelastic coefficient of the 2 nd resin can be reduced.

The weight average molecular weight (Mw) of the hydride [2] is preferably 30000 or more, more preferably 40000 or more, further preferably 45000 or more, preferably 200000 or less, more preferably 150000 or less, further preferably 100000 or less. By setting the weight average molecular weight (Mw) of the hydride [2] within the above range, the mechanical strength and heat resistance of the 2 nd layer can be improved, and further, the birefringence of the 2 nd layer can be easily reduced.

The molecular weight distribution (Mw/Mn) of the hydride [2] is preferably 3 or less, more preferably 2 or less, particularly preferably 1.8 or less, and preferably 1.0 or more. By setting the molecular weight distribution (Mw/Mn) of the hydride [2] in the above range, the mechanical strength and heat resistance of the 2 nd layer can be improved, and further, the birefringence of the 2 nd layer can be easily reduced.

The weight average molecular weight (Mw) and the molecular weight distribution (Mw/Mn) of the hydride [2] can be measured as values in terms of polystyrene by Gel Permeation Chromatography (GPC) using tetrahydrofuran as a solvent.

The above-mentioned hydride [2] can be produced by hydrogenating the block copolymer [1 ]. As the hydrogenation method, a hydrogenation method which can increase the hydrogenation rate and which causes less chain cleavage reaction of the block copolymer [1] is preferable. Examples of such hydrogenation methods include those described in International publication No. 2015/099079 and Japanese patent application laid-open No. 2016 and 204217.

The alkoxysilyl-modified product [3] is a polymer obtained by introducing an alkoxysilyl group into the hydride [2] of the block copolymer [1 ]. In this case, the alkoxysilyl group may be directly bonded to the hydride [2] or indirectly bonded via a 2-valent organic group such as an alkylene group. The alkoxysilyl-modified product [3] has excellent adhesion to various materials. Therefore, the 2 nd layer formed of the 2 nd resin containing the alkoxysilyl-modified product [3] is excellent in adhesion to the 1 st and 3 rd layers. Therefore, peeling of the 2 nd layer due to heat and stress can be suppressed, and thus the heat resistance and the bending resistance of the laminated film can be improved.

The amount of the alkoxysilyl group introduced into the alkoxysilyl-modified product [3] is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, particularly preferably 0.3 part by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably 3 parts by mass or less, per 100 parts by mass of the hydride [2] before introduction of the alkoxysilyl group. When the introduction amount of the alkoxysilyl group is within the above range, the degree of crosslinking between alkoxysilyl groups decomposed by moisture or the like can be suppressed from excessively increasing, and thus the adhesion of the 2 nd layer can be maintained high.

The amount of the alkoxysilyl group introduced may be used¹H-NMR spectrum. In addition, when the introduced amount of the alkoxysilyl group is measured, the number of times of integration can be increased when the introduced amount is small.

The weight average molecular weight (Mw) of the alkoxysilyl-modified product [3] is generally not much changed from the weight average molecular weight (Mw) of the hydride [2] before introduction of the alkoxysilyl group because the amount of the alkoxysilyl group introduced is small. However, when the alkoxysilyl group is introduced, the hydride [2] is generally subjected to a modification reaction in the presence of a peroxide, and therefore the crosslinking reaction and cleavage reaction of the hydride [2] proceed, and the molecular weight distribution tends to change greatly. The weight average molecular weight (Mw) of the alkoxysilyl-modified product [3] is preferably 30000 or more, more preferably 40000 or more, still more preferably 45000 or more, preferably 200000 or less, more preferably 150000 or less, still more preferably 100000 or less. The molecular weight distribution (Mw/Mn) of the alkoxysilyl-modified product [3] is preferably 3.5 or less, more preferably 2.5 or less, particularly preferably 2.0 or less, and preferably 1.0 or more. When the weight average molecular weight (Mw) and the molecular weight distribution (Mw/Mn) of the alkoxysilyl-modified product [3] are within these ranges, good mechanical strength and tensile elongation of the 2 nd layer can be maintained.

The weight average molecular weight (Mw) and the molecular weight distribution (Mw/Mn) of the alkoxysilyl-modified product [3] can be measured as values in terms of polystyrene by Gel Permeation Chromatography (GPC) using tetrahydrofuran as a solvent.

The alkoxysilyl-modified product [3] can be produced by introducing an alkoxysilyl group into the hydride [2] of the block copolymer [1 ]. Examples of the method for introducing an alkoxysilyl group into the hydride [2] include the methods described in International publication No. 2015/099079 and Japanese patent application laid-open No. 2016-204217.

From the viewpoint of obtaining a laminated film particularly excellent in heat resistance and bending resistance, the ratio of the alkoxysilyl-modified product [3] in the 2 nd resin is preferably 90 to 100% by mass, more preferably 93 to 100% by mass, even more preferably 95 to 100% by mass, and particularly preferably 97 to 100% by mass.

The resin 2 may further contain an optional component in combination with the alkoxysilyl modifier [3 ]. Any of the components may be used alone in 1 kind, or 2 or more kinds may be used in combination in any ratio. Since the 2 nd layer is disposed between the 1 st layer and the 3 rd layer, the movement of any component contained in the 2 nd layer is prevented by the 1 st layer and the 3 rd layer. Therefore, bleeding of any component contained in the 2 nd resin can be suppressed in the laminated film.

Examples of the optional component include the same ones as those contained in the 1 st resin. Among them, ultraviolet absorbers are preferable. The ultraviolet absorber is a compound having an ability to absorb ultraviolet rays. By using the 2 nd resin containing an ultraviolet absorber, the laminated film can have ultraviolet blocking ability. Therefore, in the case where the laminated film is used as a polarizer protective film, the polarizer can be protected from ultraviolet rays.

As the ultraviolet absorber, an organic compound is preferably used. By using an ultraviolet absorber as an organic compound, the transmittance of light in the visible wavelength of the laminated film can be generally increased and the haze of the laminated film can be reduced, as compared with the case of using an ultraviolet absorber as an inorganic compound. Examples of the ultraviolet absorber as the organic compound include triazine-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, acrylonitrile-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, azomethine-based ultraviolet absorbers, indole-based ultraviolet absorbers, naphthalimide-based ultraviolet absorbers, phthalocyanine-based ultraviolet absorbers, and the like. Specific examples of these ultraviolet absorbers include those described in jp 2017-68227 a.

The proportion of the optional component in the 2 nd resin is preferably 3% by mass or more, more preferably 5% by mass or more, particularly preferably 7% by mass or more, preferably 20% by mass or less, more preferably 15% by mass or less, and particularly preferably 10% by mass or less. When the ratio of the optional component is not less than the lower limit of the above range, the function of the optional component can be effectively exerted in the laminated film. Further, by setting the ratio of any component to be not more than the upper limit of the above range, gelation of the 2 nd resin can be easily suppressed.

The 2 nd resin was immersed in water at 37 ℃ for 24 hours, left to stand in an environment at 23 ℃ and 70% humidity for 24 hours, and then measured for moisture content by the karl fischer method, and the moisture content was usually 0.020% by mass or less, preferably 0.015% by mass or less, more preferably 0.010% by mass or less, and particularly preferably 0.008% by mass or less (requirement (ii)). As the 2 nd resin used for the laminated film, a resin having a reduced moisture content by being subjected to an appropriate drying treatment is used. This can suppress the formation of bubbles and pores in the laminated film. Further, by making the moisture content of the 2 nd resin low, it can be expected that the bending resistance of the laminated film can be effectively improved.

The moisture content of the 2 nd resin was measured by immersing the 2 nd resin in water at 37 ℃ for 24 hours, and further leaving the resin at 37 ℃ and a relative humidity of 70% for 24 hours. The measurement can be performed by using a karl fischer moisture meter, with the heating temperature of the sample set at 150 ℃ and the heating time set at 10 minutes.

The 2 nd resin has a flexural modulus of elasticity lower than that of the 1 st resin and also lower than that of the 3 rd resin (element (iii)). This can improve the bending resistance of the laminated film.

Preferred specific ranges are shown below. The difference between the lower one of the flexural modulus of the film having a thickness of 4mm formed of the 1 st resin and the flexural modulus of the film having a thickness of 4mm formed of the 3 rd resin and the flexural modulus of the film having a thickness of 4mm formed of the 2 nd resin is referred to as "difference in flexural modulus". The difference in flexural modulus of elasticity is preferably 1000MPa or more, more preferably 1100MPa or more, particularly preferably 1200MPa or more, preferably 2100MPa or less, more preferably 2000MPa or less, and particularly preferably 1900MPa or less. By setting the difference in bending modulus to be equal to or greater than the lower limit of the above range, the bending resistance of the laminated film can be effectively improved. Further, by setting the difference in bending elastic modulus to be equal to or less than the upper limit of the above range, it is possible to suppress the problem that the bending elastic modulus of the 1 st resin and the 3 rd resin is too large and the action of the 2 nd layer becomes relatively too small, and therefore, the bending resistance of the laminated film can also be effectively improved.

The bending modulus of the film of the 2 nd resin having a thickness of 4mm is preferably 550MPa or more, more preferably 600MPa or more, particularly preferably 650MPa or more, preferably 1000MPa or less, more preferably 900MPa or less, and particularly preferably 800MPa or less. By setting the flexural modulus of elasticity of the film made of the 2 nd resin to be not less than the lower limit of the above range, the rigidity of the 2 nd layer can be improved, and therefore, the handleability of the laminated film can be improved. In addition, by setting the bending elastic modulus of the film made of the 2 nd resin to the upper limit value or less of the above range, the flexibility of the laminated film can be improved, and therefore, the bending resistance of the laminated film can be effectively improved.

The flexural modulus of the 2 nd resin can be measured by the same method as that of the 1 st resin.

When the 2 nd resin is formed into a film having a thickness of 100 μm, the water vapor transmission rate measured under the conditions of a temperature of 40 ℃ and a humidity of 90% RH is preferably low in accordance with JIS K7129B (1992). Specifically, the water vapor transmission rate is preferably 5 g/(m)²Day) or less, more preferably 4.5 g/(m)²Day) or less, more preferably 4 g/(m)²Day) below. By making the 2 nd resin have such low moisture permeability, the water vapor barrier ability of the laminated film can be effectively improved, and therefore, in the case of using the laminated film as a polarizer protective film, the polarizer can be effectively protected from moisture. The lower limit of the water vapor transmission rate is preferably zero, and may be 0.1 g/(m)²Day).

The water vapor transmission rate of the 2 nd resin can be measured by the same method as the water vapor transmission rate of the 1 st resin.

The 2 nd resin preferably has a high ultraviolet blocking ability. Such high ultraviolet blocking ability can be achieved by using a resin containing an ultraviolet absorber as the 2 nd resin. By using the 2 nd resin having a high ultraviolet blocking ability, the laminated film can also have a high ultraviolet blocking ability. Therefore, in the case where the laminated film is used as a polarizer protective film, the polarizer can be protected from ultraviolet rays.

As described above, the thickness of the 2 nd layer may be set so that the ratio of the sum of the thickness of the 1 st layer and the thickness of the 3 rd layer to the thickness of the 2 nd layer falls within a predetermined range. Therefore, the thickness of the 2 nd layer may be set so that the ratio of the thicknesses falls within the above range. Specifically, the thickness of the 2 nd layer is preferably 10 μm or more, more preferably 13 μm or more, particularly preferably 15 μm or more, preferably 25 μm or less, more preferably 23 μm or less, and particularly preferably 20 μm or less. When the thickness of the 2 nd layer is not less than the lower limit of the above range, the properties of the laminate, such as heat resistance and bending resistance, can be effectively improved by the action of the 2 nd layer. On the other hand, by setting the thickness of the 2 nd layer to the upper limit value or less of the above range, the laminated film can be made thin.

[4. layer 3]

The 3 rd layer is formed of the 3 rd resin. As the 3 rd resin, a resin containing a polymer and optionally further containing an optional component may be used. The polymer can be used alone in 1, also can be used in any ratio of more than 2.

As described above, in the laminated film, a resin containing an alicyclic structure-containing polymer is used as one or both of the 1 st resin and the 3 rd resin (requirement (iv)). Therefore, in the case where the 1 st resin contains a polymer having an alicyclic structure, the 3 rd resin may or may not contain the polymer having an alicyclic structure. Further, in the case where the 1 st resin does not contain a alicyclic structure-containing polymer, the 3 rd resin contains an alicyclic structure-containing polymer. However, from the viewpoint of effectively improving the heat resistance and the bending resistance of the laminated film, it is preferable that both the 1 st resin and the 3 rd resin contain the alicyclic structure-containing polymer.

As the 3 rd resin, those in the range described as the 1 st resin can be arbitrarily used. Thus, the same effects as those of the layer 1 can be obtained by the layer 3. The 1 st resin and the 3 rd resin may be different from each other, but are preferably the same from the viewpoint of suppressing the production cost of the laminated film and suppressing curling.

The 3 rd resin preferably has low moisture permeability. Specifically, when the 3 rd resin is formed into a film having a thickness of 100 μm, the water vapor transmission rate measured in accordance with JIS K7129B (1992) is preferably in the same range as the water vapor transmission rate of the 1 st resin. By making the 3 rd resin have low moisture permeability, the same effects as those of the 1 st resin can be obtained.

The water vapor transmission rate of the 3 rd resin can be measured by the same method as the water vapor transmission rate of the 1 st resin.

The 3 rd resin preferably has a high flexural modulus of elasticity. Specifically, the flexural modulus of the film of the 3 rd resin having a thickness of 4mm is preferably in the same range as that of the 1 st resin. By providing the 3 rd resin with a high flexural modulus, the same effects as those of the 1 st resin can be obtained. In particular, by providing both the 1 st resin and the 3 rd resin with a flexural modulus in the above range, the bending resistance of the laminated film can be extremely effectively improved.

The flexural modulus of the 3 rd resin can be measured by the same method as that of the 1 st resin.

The glass transition temperature of the 3 rd resin is preferably in the same range as that of the 1 st resin. This can provide the same effects as those of the 1 st resin.

As described above, the thickness of the 3 rd layer may be set so that the ratio of the sum of the thickness of the 1 st layer and the thickness of the 3 rd layer to the thickness of the 2 nd layer falls within a predetermined range. Therefore, the thickness of the 3 rd layer may be set so that the ratio of the thicknesses falls within the above range. Specifically, the thickness of the 3 rd layer is preferably in the same range as the range of the thickness of the 1 st layer. By setting the thickness of the 3 rd layer within the above range, the same effects as those of the 1 st layer can be obtained. The thickness of the 1 st layer and the thickness of the 3 rd layer may be different, but are preferably the same from the viewpoint of effectively suppressing curling of the laminated film.

[5. optional layers ]

The laminate film may have any layer as necessary to be combined with the above-described 1 st, 2 nd and 3 rd layers. For example, the laminated film may have any layer at a position such as a 1 st layer side opposite to the 2 nd layer, a 3 rd layer side opposite to the 2 nd layer, and the like. Examples of the optional layer include a hard coat layer, a low refractive index layer, an antistatic layer, and a refractive index matching layer. However, from the viewpoint of making the laminated film thin, the laminated film is preferably a film having a 3-layer structure without any arbitrary layer.

[6. Properties and thickness of laminated film ]

The laminated film has excellent heat resistance. Therefore, the laminated film can suppress deterioration of the surface condition under a high-temperature environment. For example, in one embodiment, when the laminated film is left in an environment of 140 ℃ for 10 minutes without applying tension to the laminated film, it is possible to suppress the occurrence of irregularities on both surfaces of the laminated film.

Further, since the laminated film has the 1 st layer or the 3 rd layer containing the alicyclic structure-containing polymer, it generally has excellent dimensional stability even under an extremely high temperature and high humidity environment. In particular, when the alicyclic structure-containing polymer having crystallinity is used, the above-described effects can be remarkably obtained.

The laminated film has excellent bending resistance. Therefore, even if the laminated film is repeatedly bent, the occurrence of cracks, creases, and white turbidity can be suppressed. For example, in one embodiment, even when the sheet is repeatedly bent 10 ten thousand times by the bending resistance test described in the examples below, the occurrence of cracks, creases, and white turbidity can be suppressed.

In the laminated film, the formation of bubbles is suppressed. Therefore, in general, the laminated film has a small number of bubbles inside it, and preferably has no bubbles inside it.

The light transmittance of the laminated film at a wavelength of 380nm is preferably low. The low light transmittance at a wavelength of 380nm means that the ultraviolet-blocking ability is excellent. When the laminated film having excellent ultraviolet-blocking ability is used as a polarizer protective film, the polarizer can be protected from ultraviolet rays. Further, organic components contained in an organic EL display device are generally very likely to be deteriorated by ultraviolet rays having a long wavelength. Therefore, when the laminated film is provided in an organic EL display device, degradation of organic components can be effectively suppressed.

From the viewpoint of using the laminated film as an optical film, the laminated film preferably has a high total light transmittance. The specific total light transmittance of the laminate film is preferably 85% to 100%, more preferably 87% to 100%, and particularly preferably 90% to 100%. The total light transmittance can be measured in a range of a wavelength of 400nm to 700nm using a commercially available spectrophotometer.

From the viewpoint of improving the image clarity of an image display device incorporating the laminate film, the laminate film is preferably low in haze. The haze of the laminate film is preferably 1% or less, more preferably 0.8% or less, and particularly preferably 0.5% or less. The haze can be measured according to JIS K7361-1997 using a haze meter.

The thickness of the laminated film is preferably 20 μm or more, more preferably 25 μm or more, particularly preferably 30 μm or more, preferably 50 μm or less, more preferably 47 μm or less, and particularly preferably 45 μm or less. By setting the thickness of the laminated film to be equal to or more than the lower limit of the above range, heat resistance and rigidity required for optical film applications can be ensured, and by setting the thickness of the laminated film to be equal to or less than the upper limit of the above range, lightweight properties and space saving properties required for optical film applications can be ensured.

[7. method for producing laminated film ]

The laminated film can be produced by a production method including the steps of: a step of drying the 2 nd resin; and forming a 1 st layer, a 2 nd layer and a 3 rd layer from the 1 st resin, the dried 2 nd resin and the dried 3 rd resin.

In the drying step of the resin 2, the drying temperature is preferably 40 ℃ or higher, more preferably 45 ℃ or higher, and particularly preferably 50 ℃ or higher. Drying can be rapidly performed by setting the drying temperature to be not lower than the lower limit of the above range. The upper limit of the drying temperature is not particularly limited. However, from an industrial point of view, since the 2 nd resin drying step is performed on a production line, the drying step is often performed while the 2 nd resin is being conveyed. The 2 nd resin preferably conveyed in such a manner can suppress melt adhesion due to heat. Therefore, the drying temperature is preferably 100 ℃ or lower, more preferably 80 ℃ or lower, and particularly preferably 70 ℃ or lower, from the viewpoint of stably suppressing melt adhesion.

In the drying step of the 2 nd resin, the drying time is preferably 180 minutes or more, more preferably 210 minutes or more, particularly preferably 240 minutes or more, preferably 720 minutes or less, more preferably 660 minutes or less, and particularly preferably 600 minutes or less. By setting the drying time to be equal to or more than the lower limit of the above range, the moisture content of the 2 nd resin can be effectively reduced. Further, by setting the drying time to be equal to or less than the upper limit of the above range, deterioration of the resin can be suppressed, the production time of the laminated film can be shortened, and the production efficiency can be improved.

After the 2 nd resin is dried, the 1 st layer, the 2 nd layer and the 3 rd layer are formed from the 1 st resin, the dried 2 nd resin and the dried 3 rd resin, thereby producing a laminated film. There is no limitation on the formation method of the 1 st, 2 nd and 3 rd layers. For example, the 1 st, 2 nd and 3 rd layers can be formed by a forming method including a step of forming the 1 st, 2 nd and 3 rd resins into a film shape. Examples of the molding method include a co-extrusion method and a co-casting method. Among these molding methods, the coextrusion method is preferable because it is excellent in production efficiency and it is difficult to cause volatile components to remain in the laminate film.

The co-extrusion method includes a step of co-extruding the 1 st resin, the 2 nd resin and the 3 rd resin. In the coextrusion method, the 1 st, 2 nd and 3 rd resins are extruded in a molten state into layers, respectively, to form the 1 st, 2 nd and 3 rd layers. In this case, examples of the method for extruding each resin include a co-extrusion T-die method, a co-extrusion inflation molding method, a co-extrusion lamination method, and the like. Among them, the coextrusion T die method is preferable. In the co-extrusion T-die method, there are a block feeding system and a multi-manifold system, and the multi-manifold system is particularly preferable in terms of reducing the thickness unevenness.

The method for producing a laminated film may further include any step in combination with the above-described steps. For example, the method for producing a laminated film may include a stretching step of subjecting the laminated film to a stretching treatment. By performing the stretching treatment in this way, the laminated film can be made thin, the mechanical strength of the laminated film can be improved, and the laminated film can exhibit desired optical characteristics.

[8. polarizing plate ]

The laminated film can be used in a wide range of applications as an optical film such as a retardation film, a polarizer protective film, and a polarization compensation film. Among them, the laminated film is preferably used as a polarizer protective film.

The polarizing plate according to one embodiment of the present invention includes a polarizer and the laminated film described above. The laminated film may be provided only on a single side of the polarizer, or may be provided on both sides of the polarizer. In this polarizing plate, since the laminated film has excellent heat resistance, deterioration of performance in a high-temperature environment can be suppressed. In addition, in the polarizing plate, since the laminated film has excellent bending resistance, the polarizing plate itself also has excellent bending resistance. Therefore, the polarizing plate can be applied to a flexible display such as an organic EL display device.

As the polarizer, a film which transmits one of two linearly polarized lights having vibration directions perpendicular to each other, absorbs or reflects the other can be used. The vibration direction of the linearly polarized light refers to the vibration direction of the electric field of the linearly polarized light. Specific examples of the polarizer include polarizers obtained by subjecting a film of a vinyl alcohol polymer such as polyvinyl alcohol or partially formalized polyvinyl alcohol to appropriate treatments such as dyeing treatment with a dichroic substance such as iodine or a dichroic dye, stretching treatment, and crosslinking treatment in an appropriate order and manner. Particularly preferred is a polarizer comprising polyvinyl alcohol. Further, the thickness of the polarizer is usually 5 μm to 80 μm.

The polarizing plate can be manufactured by bonding a laminated film to a polarizer. When bonding them, an adhesive may be used as needed.

The polarizing plate may further have any layer to be combined with the polarizer and the laminated film. For example, the polarizing plate may have an arbitrary protective film layer other than the laminated film to protect the polarizer. Further, examples of the optional layer include a hard coat layer, a low refractive index layer, an antistatic layer, and a refractive index matching layer.

The polarizing plate obtained in the above manner can be used for an image display device such as an organic EL display device.