JP7750082B2 - Laminated Film - Google Patents

Description

The present invention relates to a laminated film.

Laminated films, in which a cured resin layer is provided on at least one side of a base film, are used in a variety of fields, including industrial materials, optical materials, electronic component materials, and battery packaging materials (see, for example, Patent Documents 1 and 2). Polyethylene terephthalate (PET) film, a typical polyester film, and biaxially oriented PET film in particular, are widely used as the base film for laminated films due to their excellent transparency, mechanical strength, heat resistance, flexibility, etc.

In recent years, as display panels have become thinner and more functional, there has been a technological trend toward thinner components. One such component is the polarizing plate. Polarizing plates are typically constructed by laminating triacetyl cellulose to a polarizer via an adhesive layer. However, in response to technological trends, active development is underway to coat a polymerizable liquid crystal composition onto a substrate film to obtain a thin liquid crystal polarizing film, which is then incorporated into a display.

For example, when forming a liquid crystal polarizing film by applying an alignment film composition and a polymerizable liquid crystal composition in that order onto a substrate film, even the slightest coating defect, such as a tiny air bubble, directly affects the quality of the display, so it is necessary to minimize coating defects. Furthermore, because the liquid crystal polarizing film is incorporated into the display, the substrate film itself must also be extremely smooth.

Japanese Patent Application Laid-Open No. 2019-18392 Japanese Patent Application Laid-Open No. 2020-34622

However, it has been difficult to achieve high levels of both coatability of a liquid crystal polarizing film composition such as an alignment film composition and a polymerizable liquid crystal composition and film flatness with general-purpose substrate films.
Therefore, an object of the present invention is to provide a laminated film that has few coating defects, yet suppresses the occurrence of heat wrinkles and has good flatness, for applications that particularly require a high degree of smoothness on the film surface, such as supports for forming liquid crystal polarizing films, terminal devices equipped with (high-speed) communication functions (components such as smartphones and I-Pads, film mirrors, etc.).

As a result of extensive research, the present inventors have found that the above-mentioned problems can be easily solved by using a laminated film in which two cured resin layers of specific configurations are provided on a base film and the surface roughness is controlled within a specific range, and have completed the present invention as described below.
That is, the present invention provides the following [1] to [20].
[1] A laminate film having a configuration in which a cured resin layer (A) and a cured resin layer (B) are sequentially laminated on at least one surface of a base film, and which satisfies all of the following (1) to (3):
(1) The average surface roughness (Sa) of the cured resin layer (B) is 5.0 nm or less.
(2) The shortest interphase distance (Sal) on the surface of the cured resin layer (B) is 15 μm or more.
(3) Both the cured resin layer (A) and the cured resin layer (B) are cured products of a curable resin composition containing (a) a (meth)acrylate.
[2] The laminated film according to the above [1], wherein the maximum peak height (Sp) of the surface of the cured resin layer (B) is 45 nm or less.
[3] The laminated film according to the above [1] or [2], wherein the number of protrusions of 10 nm or more on the surface of the cured resin layer (B) is 10/(237.65 μm×178.25 μm) or less.
[4] The laminated film according to any one of the above [1] to [3], wherein the base film is a polyester film.
[5] The laminated film according to any one of the above [1] to [4], wherein the base film is a polyethylene terephthalate (PET) film.
[6] The laminated film according to any one of the above [1] to [5], wherein the base film has at least two layers.
[7] The laminated film according to any one of the above [4] to [6], wherein the layer of the polyester film in contact with the cured resin layer (A) contains particles having an average particle size of 0.1 to 5 μm.
[8] The laminate film according to any one of the above [1] to [7], wherein the thickness of the base film is 12 to 125 μm.
[9] The laminate film according to any one of the above [1] to [8], wherein the total thickness of the cured resin layer (A) and the cured resin layer (B) is 10 μm or less.
[10] The laminate film according to any one of [1] to [9], wherein the cured resin layer (A) and the cured resin layer (B) are each formed by curing a curable resin composition containing (a) a (meth)acrylate, (b) a photoinitiator, and (c) a solvent.
[11] The laminated film according to the above [10], wherein the (a) (meth)acrylate includes a polyfunctional (meth)acrylate.
[12] The method for producing a laminate film according to any one of the above [1] to [11], wherein a curable composition is applied to at least one surface of a base film and cured to form a cured resin layer (A), and then a curable composition is applied thereon and cured to form a cured resin layer (B).
[13] The method for producing a laminated film according to the above [12], wherein the cured resin layer (B) is provided within 5 minutes after the cured resin layer (A) is provided.
[14] A metal laminated film obtained by laminating a metal layer on the cured resin layer (B) of the laminated film according to any one of [1] to [11] above.
[15] The metal laminated film according to [14] above, wherein the metal layer is a patterned metal layer.
[16] The laminated film according to any one of [1] to [11] above, which is for use in a communication terminal device.
[17] The metal laminated film according to [14] or [15] above, which is for use in a communication terminal device.
[18] The laminated film according to any one of the above [1] to [11], which is for optical use.
[19] The metal laminated film according to [14] or [15] above, which is for optical use.
[20] The laminated film according to the above [18], which is for forming a liquid crystal polarizing film.

The present invention makes it possible to provide a laminated film that is highly smooth and yet prevents the occurrence of heat wrinkles and other problems, resulting in good film flatness. The laminated film of the present invention can be suitably used for optical applications such as supports for forming liquid crystal polarizing films, components for terminal devices (smartphones, iPads, etc.) equipped with (high-speed) communication functions, film mirrors, and the like.

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

<Laminated film>
The laminate film of the present invention is characterized in that it has a configuration in which a cured resin layer (A) and a cured resin layer (B) are sequentially laminated on at least one surface of a base film, the surface roughness of the cured resin layer (B) is controlled within a specific range, and both the cured resin layer (A) and the cured resin layer (B) are cured products of a curable resin composition containing (a) (meth)acrylate.
The cured resin layer (A) and the cured resin layer (B) are preferably formed by curing a curable resin composition (hereinafter, sometimes referred to as the "curable resin composition of the present invention") containing (a) a (meth)acrylate, (b) a photoinitiator, and (c) a solvent.
The curable resin composition of the present invention is applied to a substrate such as a substrate film, and then dried and cured to form a cured resin layer. Hereinafter, the present invention will be described with reference to an embodiment of a laminate film in which a cured resin layer formed by curing the curable resin composition is provided on a substrate film.
Each member will be described in more detail below, but first each member constituting the laminated film will be described in more detail.

[Base film]
The material of the substrate film constituting the laminate film of the present invention (hereinafter sometimes referred to as "the present laminate film") is not particularly limited as long as it is film-like. For example, it may be made of paper, resin, metal, etc. Among these, it is preferably made of resin from the viewpoint of mechanical strength and flexibility.

Examples of resin substrate films include resin films made from polymers such as polyethylene, polypropylene, cycloolefin polymer (COP), polyester, polystyrene, acrylic resin, polycarbonate, polyurethane, triacetyl cellulose (TAC), polyvinyl chloride, polyethersulfone, polyamide, polyimide, and polyamideimide, formed into a membrane. Furthermore, as long as they can be formed into a film, they may also be mixtures of these materials (polymer blends) or composites of their constituent units (copolymers).

Among the films exemplified above, polyester films are particularly preferred because of their excellent physical properties such as heat resistance, flatness, optical properties, and strength. The polyester films may be single-layer or multi-layer films (i.e., laminated films) having two or more layers with different properties. Here, the polyester film is a film containing polyester as a main resin component.
The polyester film may be a non-stretched film (sheet) or a stretched film. Among these, a uniaxially or biaxially stretched film is preferred. Among these, a biaxially stretched film is more preferred from the viewpoint of balance of mechanical properties and flatness. Therefore, a biaxially stretched polyester film is even more preferred.

The polyester that is the main component resin of the polyester film may be either a homopolyester or a copolymer polyester. The term "main component resin" refers to the resin that makes up the film with the largest mass percentage, and may account for 50% or more, 75% or more, 90% or more, or 100% by mass of the resin that makes up the film.

The homopolyester is preferably one obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, with terephthalic acid being preferred. Examples of the aliphatic glycol include ethylene glycol, diethylene glycol, 1,4-butanediol, and 1,4-cyclohexanedimethanol, with ethylene glycol being preferred.
Typical examples of homopolyester include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

On the other hand, when the polyester is a copolymer polyester, it is preferable that the copolymer contains 30 mol % or less of a third component.
Examples of the dicarboxylic acid component of the copolymer polyester include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, etc., and examples of the glycol component include one or more of ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, etc. Preferably, the copolymer polyester contains terephthalic acid as the dicarboxylic acid, ethylene glycol as the glycol component, and a third component other than these.
Among these, the substrate in the present laminate film is preferably polyethylene terephthalate (PET) in which 60 mol % or more, preferably 80 mol % or more, of the ethylene terephthalate unit is an ethylene terephthalate unit.

Particles can also be blended into the base film of this laminate film, primarily for the purposes of imparting slipperiness and preventing scratches during each process. When particles are blended, the type of particles to be blended is not particularly limited as long as they are capable of imparting slipperiness. Specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin. Furthermore, in the case of polyester films, precipitated particles formed by precipitating and finely dispersing a portion of a metal compound such as a catalyst during the polyester manufacturing process can also be used.

On the other hand, the shape of the particles to be used is not particularly limited, and any of spherical, blocky, rod-like, flat, etc. may be used. Furthermore, there are no particular limitations on the hardness, specific gravity, color, etc. Two or more types of these particles may be used in combination as needed.
The average particle size of the particles used is preferably 5 μm or less, more preferably in the range of 0.1 to 3 μm. By using particles with an average particle size in the above range, an appropriate surface roughness can be imparted to the film, ensuring good slipperiness and smoothness.
When particles are blended, it is preferable to provide a surface layer and an intermediate layer and incorporate the particles in the surface layer, for example. In this case, it is more preferable to form a multilayer structure having, in this order, a surface layer containing particles, an intermediate layer, and a surface layer containing particles.

Furthermore, the particle content in the substrate film is preferably 5% by mass or less, more preferably in the range of 0.0003 to 3% by mass. By setting the particle content within this range, the substrate film can be easily imparted with slipperiness while ensuring the transparency of the substrate film. However, the substrate film does not necessarily need to contain substantially any particles.
In this specification, the phrase "substantially free of particles" means that particles are not intentionally contained, and specifically refers to a particle content (particle mass concentration) of 200 ppm by mass or less, more preferably 150 ppm by mass or less, relative to the member or layer (here, the substrate film). Similar terms used below have similar meanings.
In addition, when the substrate film does not substantially contain particles or the content is small, the transparency of the substrate film is high, a film with a good appearance is obtained, and the smoothness of the surface of the cured resin layer is likely to be high. On the other hand, the slipperiness of the laminated film may be insufficient. Therefore, in such a case, the slipperiness may be improved by blending particles into the cured resin layer, or by providing a slippery layer containing particles as described below.

The thickness of the substrate film is preferably 12 to 125 μm, more preferably 12 to 75 μm, and even more preferably 20 to 60 μm. Substrate films within this range can be suitably used in a variety of fields, including industrial materials, optical components, electronic components, and battery packaging.

(Laminated structure of base film)
The substrate film may have a single layer or a laminate structure of two or more layers, but from the viewpoint of imparting lubricity and transparency to the substrate film, it is preferable that the substrate film has at least a two-layer structure. By disposing particles only in the surface layer, it is possible to impart lubricity with a small particle content and ensure transparency.
When the substrate film has a laminate structure having two or more layers, preferred are a three-layer structure of B/A/C consisting of a base layer A, a surface layer B, and a surface layer C, and a B/A/B consisting of a base layer A and a surface layer B. When the substrate film has a laminate structure having two or more layers, the main component resin constituting each layer is preferably polyester, as described above.

In the three-layer structure of B/A/C and B/A/B, the surface layer B and the surface layer C preferably contain particles to ensure ease of handling.
In the above-mentioned three-layer structures of B/A/C and B/A/B, it is particularly preferable that the surface layer B and the surface layer C each contain particles having a narrow particle size distribution and a substantially uniform average particle size (so-called monodispersity).

Surface layer B preferably contains particles with an average particle size of 0.1 to 5 μm, more preferably 0.1 to 3 μm, and even more preferably 0.1 to 0.5 μm. Surface layer C preferably contains particles with an average particle size of 0.01 to 3 μm, and even more preferably 0.05 to 0.2 μm, and even more preferably 0.05 to 0.1 μm.

In the present invention, it is preferable that the polyester film (substrate film) on the side in contact with the cured resin layer (A) contains particles with an average particle size of 0.1 to 5 μm. When the polyester film is a laminate of two or more layers, it is preferable that the layer in contact with the cured resin layer (A) contains the particles. This makes the laminate film of the present invention easier to handle during the manufacturing process. Furthermore, when the polyester film is a single layer, this means that the particles are contained throughout the entire polyester film.

The average particle size of particles can be determined by measuring the diameters of 10 or more particles using a scanning electron microscope (SEM) and taking the average value. In the case of non-spherical particles, the average of the longest and shortest diameters can be measured as the diameter of each particle.

The base film contains the particles in a mass proportion of, for example, 900 ppm or more, preferably 2000 to 10000 ppm, more preferably 2500 ppm to 9500 ppm, and even more preferably 3000 ppm to 9000 ppm. The mass proportion referred to here refers to the proportion of particles in each surface layer.

It is particularly preferable that the surface layer C contains the particles in a mass ratio of 900 ppm to 6000 ppm.
When the surface layer C contains particles in this range, the handling properties of the film can be improved.

Furthermore, it is particularly preferable that the surface layer B contains the particles at a mass ratio of less than 5000 ppm, and most preferably at a mass ratio of 2000 ppm to 4000 ppm.

The base layer A preferably functions as the thickest main layer, and in order to reduce costs, it preferably contains substantially no particles or at least a lower concentration of particles than the surface layer B.

<Cured resin layer (A)/(B)>
The present laminate film has a laminated structure in which a cured resin layer (A) is provided on at least one surface of the present substrate film, and a cured resin layer (B) is further provided on the surface of the cured resin layer (A).

(Thickness of each layer)
By changing the thickness of each of the cured resin layers (A) and (B), it is possible to adjust the elastic modulus of the cured resin layers (A) and (B) and also to improve the surface hardness. For example, by making the thickness of the cured resin layer (B) larger than the thickness of the cured resin layer (A), the surface hardness can be improved.
The thickness of the cured resin layer (A) is preferably 10 to 300% of the thickness of the cured resin layer (B), more preferably 20% or more or 200% or less, and even more preferably 30% or more or 100% or less.

While satisfying the above relationship, the thickness of the cured resin layer (A) is preferably 0.5 μm or more and 5 μm or less. If it is 0.5 μm or more, extreme insufficient curing due to oxygen inhibition, etc. can be prevented when curing the cured resin layer (A) by, for example, irradiating it with ultraviolet light. On the other hand, if it is 5 μm or less, it becomes easier to ensure the surface smoothness of the present laminate film, and transparency can be easily ensured. From this viewpoint, the layer thickness is preferably 0.5 μm or more and 3 μm or less, and more preferably 0.5 μm or more and 2 μm or less.
On the other hand, the thickness of the cured resin layer (B) is preferably 0.5 μm to 5 μm, more preferably 0.5 μm to 3 μm, and even more preferably 0.5 μm to 2 μm.

In order to ensure high smoothness, the total thickness of the cured resin layer (A) and the cured resin layer (B) is preferably 10 μm or less, more preferably 6 μm or less, even more preferably 4 μm or less, and especially 2 μm or less. On the other hand, the total thickness of the cured resin layer (A) and the cured resin layer (B) is preferably 0.5 μm or more, more preferably 0.7 μm or more, and even more preferably 1 μm or more.

When the total thickness of the cured resin layers is at or above these lower limits, the cured resin layers can be cured and have a highly smooth surface. Furthermore, when the thickness of the cured resin layers is at or below these upper limits, curling and heat wrinkles can be prevented in laminate structures having cured resin layers, such as laminate films, and good flatness can be ensured.

(Surface condition of each layer)
The surface of the cured resin layer (A) is preferably flat from the viewpoint of appearance (surface gloss), whereas the surface of the cured resin layer (B) must be highly smooth.

(Optical properties of each layer)
In consideration of optical applications, it is preferable that both the cured resin layers (A) and (B) have low haze and are transparent.

In particular, in order to achieve excellent visibility at a high level, the difference in refractive index between the cured resin layer (A) and the cured resin layer (B) is preferably 0.15 or less.
If the refractive index difference between the cured resin layer (A) and the cured resin layer (B) is 0.15 or less, visibility can be improved. Specifically, when viewed from a 45-degree angle with respect to the film surface, the contour derived from the cured resin layer (A) becomes difficult to see. From this viewpoint, the refractive index difference between the cured resin layer (A) and the cured resin layer (B) is preferably 0.10 or less, and more preferably 0.05 or less. The lower limit of the refractive index difference is 0.

<Cured resin layer>
The cured resin layer (A) and the cured resin layer (B) are each formed by curing a curable resin composition and are provided on a substrate film. The cured resin layers (A) and (B) may be provided on only one side of the substrate film or on both sides.
The cured resin layers (A) and (B) have the function of protecting, for example, optical components. The curable resin composition contains a component that becomes a polymer upon polymerization. Specifically, it may contain either a photopolymerizable compound or a thermally polymerizable compound. However, it is preferable that the curable resin composition contains a photopolymerizable compound and is a photocurable resin composition. By using a photocurable resin composition, there is no need to perform heat treatment at high temperatures to cure the curable resin composition, so that the generation of impurities due to heat treatment and the occurrence of thermal shrinkage can be prevented. In addition, examples of the polymerizable compound include monomers having one or more polymerizable functional groups in one molecule.
The curable resin compositions for forming the cured resin layer (A) and the cured resin layer (B) may be the same or different.
Even if the cured resin layer (A) and the cured resin layer (B) are formed using the same curable resin composition, they can be distinguished as different layers by forming each layer using the manufacturing method described below. As a means for distinguishing, a cross-sectional observation method using an electron microscope such as a SEM can be used.

The curable resin composition of the present invention comprises (a) a (meth)acrylate, (b) a photoinitiator, and (c) a solvent. In the curable resin composition, component (a) is a photopolymerizable compound.
In the present invention, when the expression "(meth)acrylate" is used, it means one or both of "acrylate" and "methacrylate". When the expression "(meth)acryloyl" is used, it means one or both of "acryloyl" and "methacryloyl". When the expression "(meth)acrylic" is used, it means one or both of "acrylic" and "methacrylic", and the same applies to other similar expressions.
The (meth)acryloyl group concentration of the (meth)acryloyl group-containing compound used in the present invention may be expressed as the (meth)acryloyl group equivalent (g/eq). The (meth)acryloyl group equivalent is the average molecular weight per (meth)acryloyl group. For example, if a (meth)acrylate compound with a number average molecular weight of 10,000 contains 10 (meth)acryloyl groups per molecule, the (meth)acryloyl group equivalent is 10,000/10 = 1,000 g/eq.

((a) (meth)acrylate)
The curable resin composition of the present invention, containing (a) (meth)acrylate, tends to have a good effect of suppressing bleed-out of the ultraviolet absorber in the layer (cured resin layer) formed by curing the curable resin composition, and also tends to have improved scratch resistance and adhesion to a substrate film.
Specific examples of (a) (meth)acrylates include those having three ethylenically unsaturated groups, such as trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris-2-hydroxyethyl isocyanurate tri(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ditrimethylolpropane hexa(meth)acrylate. modified products of polyfunctional (meth)acrylate compounds in which a portion of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone; polyfunctional (meth)acrylates having a nitrogen atom-containing heterocyclic structure such as polyfunctional (meth)acrylates having an isocyanurate structure; polyfunctional (meth)acrylates having a multi-branched resinous structure such as polyfunctional (meth)acrylates having a dendrimer structure and polyfunctional (meth)acrylates having a hyperbranched structure; urethane (meth)acrylates in which a (meth)acrylate having a hydroxyl group, such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, or dipentaerythritol penta(meth)acrylate, is added to a polyisocyanate such as diisocyanate or triisocyanate, or a trimer (isocyanurate) thereof. The (meth)acrylate having a hydroxyl group is preferably polyfunctional having two or more ethylenically unsaturated groups.

Specifically, from the viewpoint of compatibility with the (meth)acrylic polymer, the (meth)acrylate is preferably a polyfunctional (meth)acrylate of pentaerythritol or dipentaerythritol, such as pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, or dipentaerythritol hexa(meth)acrylate. Furthermore, from the viewpoints of the scratch resistance and weather resistance of the coating film and the effect of suppressing bleed-out of the ultraviolet absorber, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, urethane (meth)acrylate which is a reaction product of pentaerythritol tri(meth)acrylate and hexamethylene diisocyanate, urethane (meth)acrylate which is a reaction product of pentaerythritol tri(meth)acrylate and isophorone diisocyanate, urethane (meth)acrylate which is a reaction product of dipentaerythritol penta(meth)acrylate and hexamethylene diisocyanate, and urethane (meth)acrylate which is a reaction product of dipentaerythritol penta(meth)acrylate and isophorone diisocyanate are preferred. In particular, urethane (meth)acrylate is preferred for the above reasons.
The above compounds may be used alone or in combination of two or more.

Among the above, trifunctional to hexafunctional polyfunctional (meth)acrylates, or urethane (meth)acrylates in which a polyfunctional (e.g., trifunctional to pentafunctional) (meth)acrylate having a hydroxyl group is added to a polyisocyanate, are more preferred, and it is also preferred to use the above-mentioned polyfunctional (meth)acrylates in combination with urethane (meth)acrylates. Furthermore, it is even more preferred that the polyisocyanate used in the urethane (meth)acrylate is a diisocyanate.

The mass average molecular weight of the (a) (meth)acrylate is, for example, from 250 to 8000, preferably from 300 to 7000, more preferably from 400 to 5000, and particularly preferably from 500 to 3000. By satisfying this range, good coatability onto the substrate film can be ensured.
The weight average molecular weight is a value measured by gel permeation chromatography (GPC) and calculated in terms of standard polystyrene.

The (meth)acryloyl group equivalent of the (a) (meth)acrylate is, for example, preferably 80 g/eq or more and less than 150 g/eq, more preferably 85 g/eq or more and less than 135 g/eq, and even more preferably 90 g/eq or more and less than 120 g/eq. By ensuring that the (meth)acryloyl group equivalent of the (A) (meth)acrylate is within the above range, curability can be appropriately controlled.

In addition, in the curable resin composition, component (a) is the main component and may account for 50% by mass or more, preferably 70% by mass or more and 99% by mass or less, and more preferably 80% by mass or more and 97% by mass or less, of the total solid content of the curable resin composition.

(b) Photoinitiator When the curable resin composition is a photocurable resin composition, the curable resin composition preferably contains a photoinitiator to improve curability. The photoinitiator is a photopolymerization initiator, and known ones can be used. Examples of the photopolymerization initiator include a photoradical generator and a photoacid generator.

Among the photopolymerization initiators that can be used in the curable resin composition, examples of photoradical generators include benzoin and its alkyl ethers, such as benzoin, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether; acetophenone, 2,2-dimethoxy-2-phenylacetophenone [e.g., trade name "Omnirad (registered trademark) 651", manufactured by IGM RESINS], 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxycyclohexyl phenyl ketone [e.g., trade name "Omnirad (registered trademark) 184", manufactured by IGM RESINS], 2-hydroxy-2-methyl-1-phenylpropan-1-one [e.g., trade name "Omnirad (registered trademark) 1173", manufactured by IGM RESINS], and the like. IGM RESINS], 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one [for example, trade name "Omnirad (registered trademark) 127, IGM RESINS], 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one [for example, trade name "Omnirad (registered trademark) 2959, IGM RESINS], 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one [for example, trade name "Omnirad (registered trademark) 907, IGM RESINS], alkylphenones such as 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone; phosphine oxides such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide [for example, trade name "Omnirad (registered trademark) TPO", manufactured by IGM RESINS] and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide [for example, trade name "Omnirad (registered trademark) 819", manufactured by IGM RESINS]; anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, and 2-amylanthraquinone; benzophenone and various derivatives thereof; and formic acid derivatives such as methyl benzoylformate and ethyl benzoylformate. These may be used alone or in combination of two or more.

Among these photoradical generators, from the viewpoint of light resistance of the cured product, alkylphenones, phosphine oxides, and formic acid derivatives are preferred, with 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and methyl benzoylformate being particularly preferred, with 1-hydroxycyclohexyl phenyl ketone and 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methylpropan-1-one being particularly preferred.

While known photoacid generators can be used, diaryliodonium salts and triarylsulfonium salts are preferred from the standpoint of curability, acid generation efficiency, and the like. Specific examples include anion salts of di(alkyl-substituted)phenyliodonium (specifically, PF6 salt, SbF5 salt, tetrakis(perfluorophenyl)borate salt, etc.). A particularly preferred example of anion salts of (alkyl-substituted)phenyliodonium is PF6 salt of dialkylphenyliodonium [trade name "Omniad (registered trademark) 250", manufactured by IGM RESINS]. These photoacid generators may be used alone or in combination of two or more.

The content of the photoinitiator is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and particularly preferably 1 part by mass or more, relative to a total of 100 parts by mass of compounds having a (meth)acryloyl group in the curable resin composition, from the viewpoint of improving curability. On the other hand, from the viewpoint of maintaining the stability of the coating liquid when the curable resin composition is made into a solution and from the viewpoint of the flatness of the cured coating film, the content is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and particularly preferably 4 parts by mass or less.

(c) Solvent The curable resin composition may be diluted with a (c) solvent to form a coating liquid. The curable resin composition may be applied to a substrate film as a liquid coating liquid, dried, and cured to form a cured resin layer. Each component constituting the curable resin composition (such as component (a)) may be dissolved in a solvent or dispersed in a solvent. The curable resin composition contains a (c) solvent, and drying and curing the coating liquid may cause wrinkles, curls, etc. However, in the present invention, the combination with the above-mentioned component (a) and the two-layer structure of the cured resin layer prevent wrinkles and curls from occurring.
The solvent is preferably an organic solvent. Specific examples of the organic solvent include aromatic solvents such as toluene and xylene; ketone solvents such as methyl ethyl ketone (MEK), acetone, methyl isobutyl ketone (MIBK), cyclohexanone, and diisobutyl ketone; ether solvents such as diethyl ether, isopropyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether (PGM), anisole, and phenetole; ester solvents such as ethyl acetate, butyl acetate, isopropyl acetate, and ethylene glycol diacetate; amide solvents such as dimethylformamide, diethylformamide, dimethylacetamide, and N-methylpyrrolidone; cellosolve solvents such as methyl cellosolve, ethyl cellosolve, and butyl cellosolve; alcohol solvents such as methanol, ethanol, propanol, isopropanol, and butanol; and halogenated solvents such as dichloromethane and chloroform. These organic solvents may be used alone or in combination of two or more. Among these organic solvents, ester solvents, ether solvents, alcohol solvents and ketone solvents are preferably used.

There are no particular restrictions on the amount of organic solvent used, and it is determined appropriately taking into consideration the coatability of the curable resin composition to be prepared, the viscosity and surface tension of the liquid, and the compatibility of the solids. The curable resin composition is prepared using the aforementioned solvent as a coating liquid with a solids concentration of preferably 15 to 80% by mass, more preferably 20 to 70% by mass. Note that the "solids" in the curable resin composition refers to the components excluding the solvent, which is a volatile component, and includes not only solid components but also semi-solid and viscous liquid substances.

(d) Other Components Various additives may be blended into the curable resin composition as needed within the scope of the present invention. Examples of additives that may be used in combination include ultraviolet absorbers, antioxidants, antistatic agents, organic pigments, organic particles, inorganic particles, flame retardants, leveling agents, dispersants, thixotropy-imparting agents (thickeners), and antifoaming agents.

The cured resin layer formed from the curable resin composition of the present invention contains an acrylic resin obtained by polymerizing a (meth)acrylate as component (a), but any other resin may be used as long as it does not impair the gist of the present invention.
However, the cured resin layer is preferably an acrylic resin layer whose main component resin is an acrylic resin. The main component resin means the resin with the largest mass ratio among the resins constituting the cured resin layer, and may account for 50 mass % or more, 75 mass % or more, 90 mass % or more, or 100 mass % of the resins constituting the cured resin layer.

<Method for forming cured resin layer>
As described above, the cured resin layer can be obtained by applying a curable resin composition to the surface of a substrate film, drying the composition to form a coating layer, and curing the coating layer.

More specifically, the present laminate film can be produced by applying a curable composition to at least one surface of the present substrate film and curing it to form a cured resin layer (A), and then applying a curable composition thereon and curing it to form a cured resin layer (B). In this case, curing of the cured resin layer (A) and the cured resin layer (B) may be carried out simultaneously.
Alternatively, after forming the cured resin layer (A), the film may be temporarily wound into a roll and then unwound again, and a curable resin composition may be applied to the cured resin layer (A) and cured to form the cured resin layer (B). Alternatively, after forming the cured resin layer (A) on the surface of the substrate film, a curable composition may be continuously applied and cured to form the cured resin layer (B). The method for producing the present laminate film is not limited to such a method.
In the present invention, as will be described later, in the process of laminating the cured resin layer (A) and the cured resin layer (B), the cured resin layer (B) can be laminated on the semi-cured cured resin layer (A). By employing such a method, a laminate film having an extremely smooth and even surface can be obtained without conforming to the uneven shape of the base film.

Furthermore, the time between forming the cured resin layer (A) and providing the cured resin layer (B) is preferably within 5 minutes, more preferably within 3 minutes, and most preferably within 1 minute. By satisfying these conditions, a laminated film with a highly smooth surface can be obtained.

Examples of a method for applying the curable resin composition include air doctor coating, blade coating, rod coating, bar coating, knife coating, squeeze coating, impregnation coating, reverse roll coating, transfer roll coating, gravure coating, kiss roll coating, cast coating, spray coating, curtain coating, calendar coating, and extrusion coating.
Examples of combinations of coating methods for the cured resin layer (A) and the cured resin layer (B) include bar coating + bar coating, bar coating + gravure coating, and gravure coating + gravure coating.
The drying conditions are not particularly limited, and the drying may be carried out at around room temperature or by heating, for example, at about 25 to 120° C., preferably 50 to 100° C., and more preferably 60 to 90° C. The drying time is not particularly limited as long as the (c) solvent can be sufficiently evaporated, and is, for example, about 10 seconds to 30 minutes, and preferably about 15 seconds to 10 minutes.

The curing method of the curable resin composition may be appropriately selected depending on the curing mechanism of the curable resin composition, and if the curable resin composition is a thermosetting resin composition, it may be cured by heating, or if it is a photocurable resin composition, it may be cured by irradiating it with energy rays.
In the laminated film of the present invention, active energy rays that can be used to cure the curable resin composition include ultraviolet rays, electron beams, X-rays, infrared rays, and visible light. Of these active energy rays, ultraviolet rays and electron beams are preferred from the viewpoints of curability and prevention of resin deterioration.
Among these, the curing method of the curable resin composition is preferably curing by energy ray irradiation, from the viewpoints of molding time and productivity, and of preventing thermal shrinkage and thermal degradation of each member due to heating, etc. The energy ray irradiation may be performed from either side, or may be performed from the substrate film side or the opposite side of the substrate film.

When producing the laminate film of the present invention, if the curable resin composition is cured by ultraviolet irradiation, various ultraviolet irradiation devices can be used, and the light source can be a xenon lamp, a high-pressure mercury lamp, a metal halide lamp, an LED-UV lamp, etc. The ultraviolet irradiation dose (unit: mJ/cm ² ) is usually 50 to 3,000 mJ/cm ² , and from the viewpoints of the curability of the curable resin composition and the flexibility of the cured product (cured film), it is preferably 100 to 1,000 mJ/cm ² , and from the viewpoint of the flatness of the laminate film, it is more preferably in the range of 100 to 500 mJ/cm ² , and is appropriately determined depending on the reaction rate of the (meth)acryloyl group required in each curing step.

Furthermore, when producing the laminated film of the present invention, if the curable resin composition is cured by electron beam irradiation, various electron beam irradiation devices can be used. The electron beam irradiation dose (Mrad) is typically 0.5 to 20 Mrad, and is preferably in the range of 1 to 15 Mrad from the standpoints of the curability of the curable resin composition, flexibility of the cured product, and prevention of damage to the substrate, and is determined appropriately depending on the reaction rate of the (meth)acryloyl group required in each curing step.

<Easy adhesive layer>
The laminated film of the present invention may have an easy-adhesion layer on the surface of the base film. The easy-adhesion layer is preferably provided on one side of the base film on which the above-mentioned cured resin layer is provided, and the above-mentioned cured resin layer is preferably formed on the surface of the easy-adhesion layer.
The adhesive layer is formed from an adhesive layer composition containing a binder resin and a crosslinking agent, and the adhesive layer can be easily bonded to the substrate film.

Examples of binder resins include polyester resins, acrylic resins, urethane resins, polyvinyl resins such as polyvinyl alcohol, polyalkylene glycols, polyalkyleneimines, methyl cellulose, hydroxycellulose, and starches. Among these, polyester resins, acrylic resins, and urethane resins are preferred from the viewpoint of improving adhesion to the cured resin layer, with polyester resins and acrylic resins being more preferred. These binder resins may be used alone or in combination of two or more. The content of the binder resin in the adhesion layer composition is, for example, 20 to 90% by mass, preferably 30 to 80% by mass, based on the solids content.

As the crosslinking agent, various known crosslinking agents can be used, for example, oxazoline compounds, melamine compounds, epoxy compounds, isocyanate compounds, carbodiimide compounds, silane coupling compounds, etc. The oxazoline compound may be an acrylic polymer having an oxazoline group.
Among these, melamine compounds, oxazoline compounds, and epoxy compounds are preferred. These crosslinking agents may be used alone or in combination of two or more.
The content of the crosslinking agent in the adhesive layer composition is, for example, 5 to 50 mass %, preferably 10 to 40 mass %, based on the solid content.

The adhesion layer composition may contain particles for the purpose of improving blocking resistance and slippage. The particles may be any of those described in the slip layer section below. However, it is preferable that the adhesion layer composition (i.e., the adhesion layer) does not substantially contain particles. By substantially not containing particles, the smoothness of the cured resin layer surface can be increased.
The adhesive layer composition may further contain a component for promoting crosslinking, such as a crosslinking catalyst. Furthermore, the adhesive layer composition may contain a defoaming agent, a coating property improver, a thickener, an organic lubricant, an antistatic agent,
It is also possible to use ultraviolet absorbers, antioxidants, foaming agents, dyes, pigments, etc. in combination.

The easy-adhesion layer composition is generally preferably diluted with water, an organic solvent, or a mixture thereof. The easy-adhesion layer can be formed by coating the surface of the substrate film with a diluted solution of the easy-adhesion layer composition as a coating liquid and drying it. Coating can be performed using a conventionally known method. The thickness of the easy-adhesion layer is usually in the range of 0.003 to 1 μm, preferably 0.005 to 0.6 μm, and more preferably 0.01 to 0.4 μm. A thickness of 0.003 μm or more ensures sufficient adhesion. Furthermore, a thickness of 1 μm or less can reduce the risk of deterioration in appearance and blocking.

<Easy slip layer>
The laminate film of the present invention may have a lubrication layer. The lubrication layer is preferably provided on the surface of the substrate film opposite to the surface on which the cured resin layer is provided. The lubrication layer is preferably provided on the surface of the substrate film. By having the lubrication layer, the laminate film has good slip properties. Therefore, as described above, even if the smoothness of the surface of the laminate film on which the cured resin layer is provided is increased, the roll winding property and handling property of the laminate film are improved.

The lubrication layer is formed from a lubrication layer composition containing, for example, a binder resin, a crosslinking agent, and particles. Compounds that can be used for the binder resin and the crosslinking agent are as described above for the binder resin and the crosslinking agent used in the adhesion layer.
The content of the binder resin in the lubrication layer composition is, for example, 20 to 90 mass %, preferably 30 to 80 mass %, based on the solid content. The content of the crosslinking agent in the lubrication layer composition is, for example, 5 to 50 mass %, preferably 10 to 40 mass %, based on the solid content.

Specific examples of particles used in the lubrication layer include silica, alumina, kaolin, calcium carbonate, and organic polymer particles. Of these, silica is preferred from the standpoint of transparency. The average particle size of the particles is preferably 0.005 to 1.0 μm, more preferably 0.01 to 0.8 μm, and even more preferably 0.01 to 0.6 μm, from the standpoint of improving lubrication without impairing the surface smoothness of the polyester film. The particle content in the lubrication layer composition is, for example, 1 to 20% by mass, preferably 3 to 15% by mass, based on the solids content. The particles used in the lubrication layer may be of one type alone or two or more types in combination.

The lubrication layer composition is generally preferably diluted with water, an organic solvent, or a mixture thereof, and the lubrication layer may be formed by coating the diluted lubrication layer composition as a coating liquid on the surface of the substrate film and drying it. Coating may be performed by a conventionally known method.
The thickness of the lubrication layer is usually in the range of 0.003 to 1 μm, preferably 0.005 to 0.6 μm, and more preferably 0.01 to 0.4 μm. By making the thickness 0.003 μm or more, the particles contained in the lubrication layer can be sufficiently retained and lubrication can be imparted. Furthermore, by making the thickness 1 μm or less, deterioration of appearance and blocking can be made less likely to occur.

A coating can be applied to the surface of the base film as needed, and the aforementioned easy-adhesion layer and easy-lubrication layer can be formed by coating. Coating can be performed inline, offline, or a combination of both, but inline is preferred. Inline coating is performed by applying the coating to the base film on the base film production line. For example, if the base film is a biaxially stretched film, a coating liquid for forming at least one of the easy-adhesion layer and the easy-lubrication layer can be applied after longitudinal stretching is completed, and the coating liquid can then be dried, cured, etc. during the subsequent base film production process.

<Physical properties of laminated film>
(1) Average surface roughness (Sa) of cured resin layer (B)
The average surface roughness (Sa) of the cured resin layer (B) is 5.0 nm or less, and preferably in the range of 1 to 5 nm.
If the average surface roughness (Sa) of the cured resin layer surface is greater than 5.0 nm, the fine irregularities on the cured resin layer surface will easily cause defects such as pinholes when used as a support for resin coating. On the other hand, if the average surface roughness (Sa) is 1 nm or more, the film surface will not be too flat and will be less susceptible to scratches.
In order to prevent pinholes when the present film is used as a support for resin coating, the average surface roughness (Sa) of the cured resin layer surface (B) is preferably 2 to 5 nm.

The average surface roughness (Sa) is one of the surface roughness parameters (ISO 25178), and is a three-dimensional extension of the two-dimensional Ra. It is obtained by dividing the volume of the area enclosed by the surface shape curved surface and the average surface by the measured area, and can be calculated using the following formula (1):
When the surface is the XY plane and the height direction is the Z axis, A is the defined area (the entire image), and Z(x, y) is the height of the image point (x, y) from the surface at height 0, it can be expressed as follows.

(2) Maximum peak height (Sp) of the surface of the cured resin layer (B)
In the present laminate film, from the viewpoint of suppressing pinholes, the maximum peak height (Sp) of the cured resin layer surface (B) is preferably 45 nm or less, more preferably 40 nm or less. The lower limit of the maximum peak height (Sp) of the cured resin layer surface is not particularly limited, but from the viewpoint of film handleability, it is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more.

The maximum peak height (Sp) is one of the surface roughness parameters (ISO 25178) and represents the maximum value of the height from the mean plane of the surface, and is expressed by the following formula (2):

(3) Shortest self-interphase distance (Sal) on the surface of the cured resin layer
The shortest interphase distance (Sal) of the cured resin layer surface (B) must be 15 μm or more. Sal is an index indicating the degree of smoothness of the surface irregularities, and the larger this value, the gentler the irregularities. Therefore, if Sal is less than 15 μm, sufficient surface smoothness cannot be obtained. Sal is preferably 20 μm or more.

(4) Number of protrusions of 10 nm or more on the surface of the cured resin layer (B) The number of protrusions of 10 nm or more on the surface of the cured resin layer (B) is preferably 10 or less/(237.65 μm×178.25 μm), more preferably 5 or less (237.65 μm×178.25 μm), particularly 1 or less/(237.65 μm×178.25 μm), and most preferably 0/(237.65 μm×178.25 μm).
By satisfying the above range, the resin sheet is suitable as a support for molding a resin sheet having an extremely smooth surface, such as for forming a liquid crystal polarizing film.

In the present invention, during the process of laminating cured resin layer (A) and cured resin layer (B), cured resin layer (B) is laminated just before cured resin layer (A) is completely cured. This results in a laminated film with an extremely smooth and even surface that does not conform to the uneven shape of the base film as in conventional cases. The mechanism is unknown, but it is thought that this is because, in an incompletely cured state, cured resin layer (A) itself maintains its smoothness without conforming to the uneven shape of the base film.

<Metal laminated film>
In one preferred embodiment, the laminate film of the present invention is used as a metal laminated film by laminating a metal layer on its surface. The metal layer is preferably laminated on the surface of the laminate film on the side of the cured resin layer (B). By having the metal layer, the metal laminated film has metallic luster and can improve its design properties.
Since the surface on the side of the cured resin layer (B) is smooth as described above, the metal layer provided on that surface is also smooth and has little graininess.

The thickness of the metal layer is not particularly limited, but is preferably 5 to 900 nm, and more preferably 10 to 300 nm. When the thickness of the metal layer is equal to or greater than the lower limit, the metal layer is less prone to cracking and is strong. On the other hand, when the thickness of the metal layer is equal to or less than the upper limit, the metal layer can be formed in a short time. Furthermore, by keeping the thickness within the above range, sufficient metallic luster can be imparted.
The metal layer may be provided on the entire surface of the cured resin layer (B) or may be patterned.

The metal layer can be formed by a conventionally known method, specifically by one or more methods selected from vapor deposition, sputtering, and ion plating, but from the viewpoint of ease of production, sputtering is particularly preferred.
The sputtering method involves placing a laminated film in a vacuum chamber, introducing an inert gas such as argon, applying a DC voltage, causing the ionized inert gas to collide with a target metal, and using the metal that is ejected to form a metal layer on the surface of the laminated film.

[Application]
The curable resin composition and laminate film of the present invention can be used in various fields such as industrial materials, optical components, electronic components, and battery packaging materials, but are preferably used for optical purposes such as various displays, lenses, mirrors, and window glass.
The laminated film of the present invention is preferably used in applications requiring particularly high surface smoothness, and is useful, for example, as a support for forming a liquid crystal polarizing film. It is also preferably used in electronic devices, particularly in communication terminal devices compatible with high-speed communication. Furthermore, when used in electronic device applications, such as around housings and displays, the surface smoothness ensures the smoothness of the metal layer, even when the metal layer is laminated thereon, making it useful for communication terminal devices and offering enhanced designability.
The laminated film of the present invention maintains a low haze value, and therefore, even when used in optical components, the performance of the optical components is not impaired.
The laminate film may also be used as a decorative sheet, and a design layer that imparts design to the laminate film may be provided on the cured resin layer of the laminate film. The design layer may be a resin layer, a metal layer, a printed layer, or the like. In the present invention, the surface smoothness of the cured resin layer can be increased, so that the design layer can also have high surface smoothness. Therefore, combined with the increased flatness of the laminate film, it is possible to achieve a high design.

<Explanation of terms, etc.>
In the present invention, the term "film" includes the term "sheet", and the term "sheet" includes the term "film".
In the present invention, when it is described as "X to Y" (X and Y are any numbers), unless otherwise specified, it means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y".
Furthermore, when it is stated that the amount is "X or more" (X is any number), it also means that the amount is "preferably greater than X" unless otherwise specified, and when it is stated that the amount is "Y or less" (Y is any number), it also means that the amount is "preferably smaller than Y" unless otherwise specified.

Next, the present invention will be explained in more detail using examples. However, the present invention is not limited to the examples described below.

<Evaluation method>
The methods for measuring and evaluating various physical properties and characteristics are as follows.

(1) Intrinsic viscosity (IV)
1 g of polyester was precisely weighed, dissolved in 100 ml of a mixed solvent of phenol/tetrachloroethane = 50/50 (mass ratio), and measured at 30°C.

(2) Average particle size of particles The powder was observed using a scanning electron microscope (manufactured by HITACHI, "S3400N").
The size of each particle was measured from the obtained image data, and the average value of 10 points was taken as the average particle size.

(3) Number average molecular weight (Mn)
Measurements were performed using a gel permeation chromatography (GPC) "HLC-8120" (manufactured by Tosoh Corporation). The column used was a TSKgel G5000HXL*GMHXL-L (manufactured by Tosoh Corporation). A calibration curve was created using standard polystyrenes F288/F80/F40/F10/F4/F1/A5000/A1000/A500 (manufactured by Tosoh Corporation) and styrene. Measurements were performed at a column oven temperature of 40°C using 100 μl of a solution prepared by dissolving the polymer in tetrahydrofuran to a concentration of 0.4%. The number average molecular weight (Mn) was calculated in terms of standard polystyrene.

(4) Average Surface Roughness (Sa), Maximum Peak Height (Sp), Self-Phase Distance (Sal), and Number of Protrusions of 10 nm or More The surfaces of the resin layer (A) side of the polyester film in the polyester film rolls of Examples and Comparative Examples were measured using a surface roughness measuring device (Ametec Co., Ltd., "NewView" (registered trademark)), and the average surface roughness Sa value, maximum peak height Sp value, self-phase distance (Sal), and number of protrusions of 10 nm or more were determined from the obtained surface profile curves.

(5) Thickness of cured resin layer (after curing)
The thickness (d) of the cured resin layers (A) and (B) was measured by cross-sectional observation using an SEM.

(6) Film Flatness (Wrinkle) Evaluation A sample film wound into a roll was unwound and the occurrence of wrinkles in the film was visually observed under a fluorescent lamp using reflection light.
(Evaluation criteria)
○...No wrinkles visible.
△: Disappears when removed by hand or only a small amount remains.
×...It does not disappear even when pulled by hand.

The raw materials of the laminated films in the examples and comparative examples are as follows.
(Base film)
<Polyester (A)>
100 mol% dimethyl terephthalate, 100 mol% ethylene glycol, and 100 parts by mass of the monomers were placed in a reactor, and 0.07 parts by mass of calcium acetate monohydrate was added. The mixture was heated and the methanol was distilled off to carry out a transesterification reaction. After the start of the reaction, the temperature was raised to 230°C over approximately four and a half hours, at which point the transesterification reaction was essentially complete. Next, 0.04 parts by mass of phosphoric acid and 0.035 parts by mass of antimony trioxide were added, and polymerization was carried out according to a conventional method. That is, the reaction temperature was gradually increased to a final temperature of 280°C, while the pressure was gradually reduced to a final temperature of 0.05 mmHg. After 4 hours, the reaction was terminated, and the mixture was chipped according to a conventional method to obtain polyester (A). The intrinsic viscosity of the resulting polyester (A) was 0.63.
<Polyester (B)>
Silica particles having an average particle size of 2 μm were added to the polyester (A) to obtain a polyester (B) containing 0.2% by mass of silica particles. The intrinsic viscosity was 0.65.

(Curable resin composition)
(a) (meth)acrylate (curable resin)
(a1) Pentaerythritol triacrylate (PETA)
(a2) Dipentaerythritol hexaacrylate (DPHA)
(b) Photoinitiator: Omnirad 127, manufactured by IGM Resins
(c) Solvent: a mixed solvent of methyl ethyl ketone (MEK) and propylene glycol monomethyl ether (PGM) (mixed so that the solvent ratio of MEK to PGM in the coating liquid is 3:7)

[Example 1]
A mixed raw material obtained by mixing polyesters (A) and (B) at a ratio of 90% by mass and 10% by mass was used as the raw material for the outermost layer (surface layer), and polyester (A) alone was used as the raw material for the intermediate layer. The materials were fed into two extruders, melted at 285 ° C., and then co-extruded onto a cooling roll set at 40 ° C. in a layer structure of two types and three layers (surface layer / intermediate layer / surface layer = 1 / 8 / 1 discharge rate (mass ratio)), cooled and solidified to obtain an unstretched sheet. The film was then stretched 3.4 times in the longitudinal direction at a film temperature of 85 ° C. using the roll peripheral speed difference, introduced into a tenter, stretched 4.3 times in the transverse direction at 110 ° C., heat-treated at 235 ° C., and then relaxed 2% in the transverse direction to obtain a polyester film (substrate film) with a thickness of 50 μm.

Onto the above polyester film, a curable resin composition (A) prepared according to the following formulation was applied by bar coating to a thickness (after curing) of 0.75 μm, dried at 80° C. for 30 seconds, and then irradiated with ultraviolet light (cumulative light dose of 200 mJ/cm ² ) to form a cured resin layer (A). Next, 1 minute after forming the cured resin layer (A), a curable resin composition (B) prepared according to the following formulation was applied by bar coating to a thickness (after curing) of 0.75 μm, dried at 80° C. for 30 seconds, and then irradiated with ultraviolet light (cumulative light dose of 200 mJ/cm ² ) to form a cured resin layer (B) on the cured resin layer (A), thereby obtaining a laminated film having a configuration of polyester film/cured resin layer (A)/cured resin layer (B).
The obtained sample was evaluated, and the evaluation results are shown in Table 1.
(Formulation conditions for curable resin (A) composition)
a1/b/c=100/3/309 (parts by mass)
(Formulation conditions for curable resin (B) composition)
a1/b/c=100/3/309 (parts by mass)

[Examples 2 and 3, and Comparative Examples 1 to 3]
A laminated film was obtained in the same manner as in Example 1, except that the curable resin in the curable resin composition for forming each of the cured resin layers (A) and (B) was changed as shown in Table 1.

[Reference Examples 1 and 2]
The surface characteristics of the base film (PET film) are shown. Reference Example 1 shows the surface characteristics of polyester (B), and Reference Example 2 shows the surface characteristics of polyester (A).

PETA: Pentaerythritol triacrylate DPHA: Dipentaerythritol hexaacrylate

(Consideration)
It was found that Examples 1 to 3 were extremely smooth and had good film planarity. On the other hand, Comparative Examples 1 to 3 were cured resin layers (single layer configuration) made from the same resin composition, but the resulting surface shape was insufficient in smoothness, possibly because the cured resin composition followed the uneven shape of the base film.
In particular, it was found that it was difficult to obtain a high degree of smoothness by simply applying a thick cured resin layer as in Comparative Example 3.
Furthermore, Reference Example 1 describes the surface roughness (Sa) of the substrate film used in Examples 1 to 3. As in Examples 1 to 3, even when the total thickness (after curing) of the cured resin layer was as thin as 1.5 μm, the unevenness of the substrate film surface was reduced, and a high degree of smoothness was obtained.
It was also found that the level of surface smoothness could be made even higher than that of the highly transparent film shown in Reference Example 2.

In the present invention, during the process of laminating cured resin layer (A) and cured resin layer (B), by laminating cured resin layer (B) just before cured resin layer (A) is fully cured (semi-cured), it is possible to obtain a laminated film with an extremely smooth and even surface without conforming to the unevenness of the substrate film as in conventional methods. While the mechanism is unclear, it is presumed that in the semi-cured state, where the curing reaction of cured resin layer (A) is not complete, cured resin layer (A) itself does not conform to the unevenness of the substrate film surface, but rather reduces the unevenness of the surface, thereby maintaining smoothness. Furthermore, it is believed that the active energy rays irradiated when curing the second cured resin layer (B) also contribute to the curing reaction of the underlying cured resin layer (A), and therefore the curing reaction is presumed to be complete in the finished two-layer structure.

The laminate film of the present invention has few coating defects, is highly smooth, and prevents the occurrence of heat wrinkles and other problems, resulting in excellent film flatness. Therefore, the laminate film of the present invention can be suitably used for optical applications such as supports for forming liquid crystal polarizing films, components for terminal devices equipped with high-speed communication functions such as smartphones and iPads, film mirrors, etc.

Claims (18)

A laminate film having a structure in which a cured resin layer (A) and a cured resin layer (B) are laminated in this order on at least one surface of a base film, the base film being a polyester film, the layer of the polyester film on the side in contact with the cured resin layer (A) containing particles having an average particle size of 0.1 to 5 μm, and satisfying all of the following (1) to (3):
(1) The average surface roughness (Sa) of the cured resin layer (B) is 5.0 nm or less.
(2) The shortest interphase distance (Sal) on the surface of the cured resin layer (B) is 15 μm or more.
(3) Both the cured resin layer (A) and the cured resin layer (B) are cured products of a curable resin composition containing (a) a (meth)acrylate. The laminate film according to claim 1, wherein the maximum peak height (Sp) of the surface of the cured resin layer (B) is 45 nm or less. The laminated film according to claim 1 or 2 , wherein the number of protrusions having a size of 10 nm or more on the surface of the cured resin layer (B) is 10/(237.65 μm×178.25 μm) or less. The laminated film according to any one of claims 1 to 3 , wherein the base film is a polyethylene terephthalate (PET) film. The laminated film according to any one of claims 1 to 4 , wherein the base film has a structure of at least two layers. The laminated film according to any one of claims 1 to 5 , wherein the thickness of the substrate film is 12 to 125 µm. The laminated film according to any one of claims 1 to 6 , wherein the total thickness of the cured resin layer (A) and the cured resin layer (B) is 10 µm or less. The laminate film according to any one of claims 1 to 7, wherein the cured resin layer (A) and the cured resin layer (B) are each formed by curing a curable resin composition containing (a) a (meth)acrylate, ( b ) a photoinitiator, and (c) a solvent. The laminate film according to claim 8 , wherein the (meth)acrylate (a) comprises a polyfunctional (meth)acrylate. The method for producing a laminated film according to any one of claims 1 to 9, wherein a curable composition is applied to at least one surface of a substrate film and cured to form a cured resin layer (A), and then a curable composition is applied thereon and cured to form a cured resin layer (B). The method for producing a laminated film according to claim 10 , wherein the cured resin layer (B) is provided within 5 minutes after the cured resin layer (A) is provided. A metal laminated film obtained by laminating a metal layer on the cured resin layer (B) of the laminated film according to any one of claims 1 to 9 . The metal laminate film of claim 12 , wherein the metal layer is a patterned metal layer. The laminate film according to any one of claims 1 to 9, which is used in communication terminal equipment. The metal laminated film according to claim 12 or 13 , which is for use in a communication terminal device. The laminated film according to any one of claims 1 to 9 , which is for optical use. The metal laminated film according to claim 12 or 13 , which is for optical use. The laminated film according to claim 16 , which is used to form a liquid crystal polarizing film.