阅读说明：本技术 层叠薄膜 (Laminated film ) 是由 谷山弘行 小西敦子 加藤刚司 于 2020-02-25 设计创作，主要内容包括：一种层叠薄膜,其特征在于,具备在基材薄膜的表面依次层叠有固化树脂层(A)和固化树脂层(B)的构成,关于根据微小硬度计测定(JIS Z 2255)而测得的弹性模量,固化树脂层(B)的弹性模量大于固化树脂层(A)的弹性模量、且固化树脂层(B)的弹性模量与固化树脂层(A)的弹性模量之差大于0(MPa)且小于220(MPa)。(A laminated film having a structure in which a cured resin layer (A) and a cured resin layer (B) are laminated in this order on the surface of a base film, wherein the cured resin layer (B) has an elastic modulus measured by a microhardness tester (JIS Z2255) which is higher than that of the cured resin layer (A) and the difference between the elastic modulus of the cured resin layer (B) and that of the cured resin layer (A) is greater than 0(MPa) and less than 220 (MPa).)

1. A laminated film characterized by having a structure in which a cured resin layer (A) and a cured resin layer (B) are laminated in this order on the surface of a base film,

regarding the elastic modulus measured according to the microhardness meter measurement (JIS Z2255), the elastic modulus of the cured resin layer (B) is larger than the elastic modulus of the cured resin layer (a), and the difference between the elastic modulus of the cured resin layer (B) and the elastic modulus of the cured resin layer (a) is larger than 0(MPa) and smaller than 220 (MPa).

2. The laminate film according to claim 1, wherein the cured resin layer (a) has an elastic modulus of 10(MPa) or more.

3. The laminated film according to claim 1 or 2, wherein the pencil hardness of the surface of the cured resin layer (B) is 2H or more.

4. The laminated film according to any one of claims 1 to 3, which can be bent 20 ten thousand or more times in the repeated bendability evaluation (under the condition of R2.5).

5. A laminated film according to any one of claims 1 to 4, wherein the film haze is 5.0% or less.

6. The laminated film according to any one of claims 1 to 5, wherein the tensile modulus (JIS K7161) of the base film is 2.0GPa or more.

7. A laminated film according to any one of claims 1 to 6, wherein the base film is a polyester film.

8. The laminate film according to any one of claims 1 to 7, wherein the substrate film is a polyethylene naphthalate (PEN) film.

9. The laminate film according to any one of claims 1 to 7, wherein the base film is a polyethylene terephthalate (PET) film.

10. The laminate film according to any one of claims 1 to 7, wherein the base film is a Polyimide (PI) film.

11. The laminated film according to any one of claims 1 to 10, wherein a difference in refractive index between the cured resin layer (A) and the cured resin layer (B) is 0.15 or less.

12. The laminated film according to any one of claims 1 to 11, wherein a total thickness of the cured resin layer (a) and the cured resin layer (B) is 6.0 μm or less.

13. A laminated film according to any one of claims 1 to 12 for surface protection.

14. A laminated film according to any one of claims 1 to 12, which is used for a display.

15. A laminated film according to any one of claims 1 to 12, which is used for a front panel.

16. A method for producing a laminated film according to any one of claims 1 to 12,

the cured resin layer (A) is characterized by being formed by applying a curable composition onto a base film and curing the composition, wherein the mass average molecular weight of the curable composition is in the range of 1000 to 500000.

Technical Field

The present invention relates to a laminated film having excellent surface hardness and repeated bending characteristics.

Background

In recent years, with the miniaturization and weight reduction of electronic devices and the like, flexible substrates and flexible printed circuits tend to be used. In addition, with this trend, there is a tendency that the demand for flexibility is increased in display applications. Further, in the surface protective film for display screens used in such applications, not only surface protective properties such as high hardness, scratch resistance, stain resistance, abrasion resistance and the like are required, but also high durability is required for the bendability, and further improvement in performance is desired.

Therefore, in recent years, many surface protection films have been proposed for the purpose of maintaining scratch resistance while having high hardness and improving flexibility and bendability.

For example, patent document 1 discloses a technique related to a hard coat film in which, in a hard coat layer formed of a laminated structure, the elastic modulus is increased by increasing the elastic modulus of an intermediate layer to be higher than that of a surface layer, thereby improving the surface hardness, preventing damage to the hard coat film due to stress concentration, and making it less likely to be scratched.

Patent document 2 discloses a hard coat layer having a laminated structure in which a radical material is used for a surface layer and a cation material is used for an intermediate layer, and which has good interlayer adhesion.

Patent document 3 discloses the following technical contents: the elastic modulus of the hard coat coating film is controlled by including silica particles in the coating film.

Patent document 4 discloses a technique relating to a hard coat film having excellent abrasion resistance and flexibility in a hard coat layer formed of a laminated structure, in which the elastic modulus of the surface layer is made larger than that of the intermediate layer, and the elongation of the cured coating film is made within a specific range.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 4574766

Patent document 2: japanese patent No. 4160217

Patent document 3: japanese patent No. 5320848

Patent document 4: japanese patent No. 4569807

Disclosure of Invention

Problems to be solved by the invention

As described above, in recent years, development of flexible portable terminals capable of folding or folding an image display screen (display) has been advanced, and surface protective films used for such image display screens are required to have excellent surface hardness and durability such that the films can be folded repeatedly in practice, specifically, for example, can be folded repeatedly 20 ten thousand times or more.

However, none of the inventions described in patent documents 1 to 4 assumes the use of repeated bending, and it is sometimes difficult to cope with this.

Therefore, the present invention intends to propose: a novel laminated film which has not only excellent surface hardness but also excellent practical repeated bending characteristics.

Means for solving the problems

The present invention provides a laminated film characterized by comprising a substrate film and, laminated on the surface thereof in this order, a cured resin layer (A) and a cured resin layer (B),

regarding the elastic modulus measured according to the microhardness meter measurement (JIS Z2255), the elastic modulus of the cured resin layer (B) is larger than the elastic modulus of the cured resin layer (a), and the difference between the elastic modulus of the cured resin layer (B) and the elastic modulus of the cured resin layer (a) is larger than 0(MPa) and smaller than 220 (MPa).

The present invention provides a method for producing a laminated film, wherein the cured resin layer (a) is formed by applying a curable composition having a mass average molecular weight in the range of 1000 to 500000 to a base film and curing the composition, as an example of the method for producing a laminated film.

ADVANTAGEOUS EFFECTS OF INVENTION

The laminated film provided by the invention has the following characteristics: the film is provided with a structure in which a cured resin layer (A) and a cured resin layer (B) are sequentially laminated on the surface of a base film, and the difference ((B) - (A)) between the elastic modulus of the cured resin layer (B) and the elastic modulus of the cured resin layer (A) is greater than 0(MPa) and less than 220 (MPa). Therefore, the practical repeated bending characteristics can be improved while maintaining the surface hardness, and specifically, excellent repeated bending characteristics without any problem can be obtained even if the bending is repeated 20 ten thousand or more times.

Detailed Description

Next, the present invention will be described based on embodiment examples. However, the present invention is not limited to the embodiments described below.

< the laminated film >

A laminated film (referred to as "present laminated film") according to an embodiment of the present invention is a laminated 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 (referred to as "present base film").

The present laminated film may have any other layer as long as it has the above-described structure.

< present substrate film >

The base film is not limited in material and composition as long as it has sufficient rigidity and repeated bendability.

The base film may be a single-layer structure or a multilayer structure.

When the base film has a multilayer structure, the base film may have 4 or more layers, as long as the base film does not exceed the gist of the present invention, in addition to 2 or 3 layers.

The base film may be a single layer or a multilayer, and the main component resin of each layer is preferably polyester or Polyimide (PI). Such films are referred to as "polyester films" or "polyimide films".

In this case, the "main component resin" refers to a resin having the highest content of the resins constituting the base film, and is, for example, a resin that accounts for 50% by mass or more, particularly 70% by mass or more, and 80% by mass or more (including 100% by mass) of the resins constituting the base film.

Each layer constituting the base film may contain a resin other than polyester or polyimide or a component other than a resin as long as the main component resin is polyester or polyimide.

(polyester)

The polyester (referred to as "present polyester") as the main component resin constituting each layer of the base film may be a homopolyester or a copolyester.

When the present polyester is formed of a homopolyester, it is preferably obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic diol.

Examples of the aromatic dicarboxylic acid include: terephthalic acid, 2, 6-naphthalenedicarboxylic acid, and the like.

Examples of the aliphatic diol include: ethylene glycol, diethylene glycol, 1, 4-cyclohexanedimethanol, and the like.

On the other hand, when the present polyester is a copolyester, examples of the dicarboxylic acid component include: 1 or 2 or more species selected from isophthalic acid, phthalic acid, terephthalic acid, 2, 6-naphthalenedicarboxylic acid, sebacic acid, etc. On the other hand, examples of the diol component include: ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1, 4-cyclohexanedimethanol, neopentyl glycol, and the like.

Specific examples of the representative polyester include, for example: polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polybutylene naphthalate (PBN), polyethylene furan dicarboxylate (PEF), and the like. Among them, PET and PEN are preferable in terms of handling.

When the main component resin of each layer constituting the base film is, for example, polyethylene terephthalate, the film is referred to as a "polyethylene terephthalate film". The same applies to the case where other resins are the main component resin.

(polyimide)

The base film is suitably a polyimide film in addition to the polyester film. The imidization of the polyimide can be exemplified by, for example, the following methods: diamine and dianhydride, especially aromatic dianhydride and aromatic diamine are mixed in a ratio of 1: 1 equivalent ratio was used for imidization after polymerization of polyamic acid.

Examples of the aromatic dianhydride include: 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 4- (2, 5-dioxotetrahydrofuran-3-yl) -1,2,3, 4-tetrahydronaphthalene-1, 2-dicarboxylic acid dianhydride (TDA), pyromellitic dianhydride (1,2,4, 5-benzenetetracarboxylic dianhydride, PMDA), Benzophenone Tetracarboxylic Dianhydride (BTDA), biphenyl tetracarboxylic dianhydride (BPDA), biscarboxyphenyldimethylsilane dianhydride (SiDA), and the like. These may be used alone, or 2 or more of them may be used in combination.

Further, as the aforementioned aromatic diamine, there may be exemplified: oxydianiline (ODA), p-phenylenediamine (pPDA), m-phenylenediamine (mPDA), p-methylenedianiline (pMDA), m-methylenedianiline (mMDA), bistrifluoromethylbenzidine (TFDB), cyclohexanediamine (13CHD, 14CHD), bisaminohydroxyphenylhexafluoropropane (DBOH), and the like. These may be used alone, or 2 or more of them may be used in combination.

(other resin component)

Each layer constituting the base film may be made of a resin other than polyester and polyimide as a main component resin. Examples of the main component resin in this case include: epoxy, polyarylate, polyethersulfone, polycarbonate, polyetherketone, polysulfone, polyphenylene sulfide, polyester-based liquid crystal polymer, cellulose triacetate, cellulose derivative, polypropylene, polyamide, polycycloolefin, and the like.

(particle)

The base film may contain particles for the purpose of imparting slidability to the film surface and for the main purpose of preventing scratches in the respective steps.

The kind of the particles is not particularly limited as long as the particles can impart slidability. Examples thereof include: inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, alumina, and titanium oxide, organic particles such as acrylic resins, styrene resins, urea resins, phenol resins, epoxy resins, and benzoguanamine resins, and the like. These can be used alone in 1, also can be combined with more than 2 and use.

In the polyester production step, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst may be used.

The shape of the particles is not particularly limited. For example, the shape may be spherical, massive, rod-like, or flat.

Further, the hardness, specific gravity, color, and the like of the above particles are also not particularly limited. These series of particles may be used in combination of 2 or more kinds as necessary.

The average particle diameter of the particles is preferably 5 μm or less, more preferably 0.01 μm or more or 3 μm or less, and still more preferably 0.5 μm or more or 2.5 μm or less. When the thickness exceeds 5 μm, the surface roughness of the base film becomes too rough, and there may be a case where a cured resin layer formed from various cured compositions is formed in a subsequent step.

The content of the particles is preferably 5% by mass or less of the base film, more preferably 0.0003% by mass or less or 3% by mass or less, and further preferably 0.01% by mass or more or 2% by mass or less.

When the average particle diameter of the particles is within the above range, the surface roughness of the base material film does not become excessively rough, and therefore, defects occurring in the case of forming a cured resin layer formed of various cured compositions in a subsequent step and the like can be suppressed.

The method for adding the particles to the base film is not particularly limited, and conventionally known methods can be used. For example, it can be added at an arbitrary stage in the production of a raw material resin such as polyester. In the case of a polyester, it is preferably added after the completion of the esterification or transesterification reaction.

(other Components)

The base film may contain, as other components, for example, conventionally known antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, ultraviolet absorbers, and the like, as necessary.

(thickness)

The thickness of the base film is, for example, preferably 9 μm to 125 μm, more preferably 12 μm or more or 100 μm or less, and still more preferably 20 μm or more or 75 μm or less, from the viewpoint of obtaining the desired and sufficient rigidity and repeated bendability.

(preparation method)

The base film can be formed, for example, by forming the resin composition into a film shape by a melt film-forming method or a solution film-forming method. In the case of a multilayer structure, coextrusion may be carried out.

Further, the film may be uniaxially stretched or biaxially stretched, and a biaxially stretched film is preferable in view of rigidity.

(characteristics of the base film)

The tensile modulus (JIS K7161) of the base film is preferably 2.0GPa or more, more preferably 9.0GPa or less, particularly 3.0GPa or more or 8.0GPa or less, and particularly 3.0GPa or more or 7.0GPa or less, from the viewpoint of obtaining the required and sufficient rigidity and repeated bendability.

< cured resin layers (A) (B) >

The laminated film has a laminated structure comprising: a cured resin layer (A) is provided on at least one surface of the base film, and a cured resin layer (B) is further provided on the surface side.

The crosslinked resin layer refers to a layer having a crosslinked resin structure. Whether or not the crosslinked resin structure is present can be judged by analyzing the crystal structure with an apparatus such as TOFSIMS or IR. But is not limited to such a method.

(modulus of elasticity of each layer)

The cured resin layers (a) and (B) are both layers containing a cured resin, in other words, a resin having a crosslinked structure, and the modulus of elasticity of the cured resin layer (a) is preferably lower than that of the cured resin layer (B).

Further, regarding the elastic modulus measured by microhardness measurement (JIS Z2255), it is preferable that the difference between the elastic modulus of the cured resin layer (B) and the elastic modulus of the cured resin layer (a) (the elastic modulus of the cured resin layer (B) — the elastic modulus of the cured resin layer (a)) is more than 0(MPa) and less than 220 (MPa).

When only the cured resin layer (B) is present on at least one surface of the base film, the laminated film is not resistant to deformation when an external force is applied to the laminated film, and the surface of the laminated film is damaged or irreversibly crazed. In contrast, by making the elastic modulus of the cured resin layer (a) lower than that of the cured resin layer (B) and making the difference between the elastic modulus of the cured resin layer (B) and that of the cured resin layer (a) greater than 0(MPa) and less than 220(MPa), stress concentration can be avoided, and further, the cured resin layer (a) can be deformed to absorb external force. Therefore, a laminated film having excellent repeated folding characteristics can be formed.

Among them, from the viewpoint of the bendability, the difference in the elastic modulus between the cured resin layer (B) and the cured resin layer (a) is more preferably 50MPa or more, still more preferably 100MPa or more, particularly 150MPa or more. On the other hand, from the viewpoint of surface hardness, the difference is preferably 210MPa or less, more preferably 200MPa or less, and further more preferably 190MPa or less.

Further, the modulus of elasticity measured by the microhardness measurement (JIS Z2255) is preferably not less than 10MPa for the cured resin layer (B) > the cured resin layer (A).

When only the cured resin layer (B) is present on at least one surface of the base film, the laminated film is not resistant to deformation when an external force is applied to the laminated film, and the surface of the laminated film is damaged or irreversibly crazed. In contrast, in the present laminated film, by the presence of the cured resin layer (a) satisfying the conditions that the cured resin layer (B) > the cured resin layer (a) ≥ 10MPa as a lower layer of the cured resin layer (B), stress concentration can be avoided. Further, the external force can be absorbed by the deformation of the cured resin layer (a). Therefore, a laminated film having excellent repeated folding characteristics can be formed.

From the above-mentioned viewpoint, the modulus of elasticity of the cured resin layer (a) is more preferably 20MPa or more, still more preferably 50MPa or more, particularly 100MPa or more. On the other hand, as for the upper limit, 495MPa or less, further preferably 400MPa or less, among them 350MPa or less, is preferable.

On the other hand, from the viewpoint of surface hardness, the modulus of elasticity of the cured resin layer (B) is preferably 100MPa or more, more preferably 200MPa or more, and even more preferably 300MPa or more. On the other hand, it is preferably 900MPa or less, more preferably 800MPa or less among them, and 700MPa or less among them.

(method of adjusting modulus of elasticity of each layer)

The elastic modulus of the cured resin layer (a) and the cured resin layer (B) can be adjusted by changing the thickness and the particle content of each layer, the selection of the curable monomer, the composition ratio of the curable monomer, the content ratio of the crosslinkable monomer, the crosslinking density (molecular weight between crosslinking points), the molecular weight of the base polymer forming each layer, the molecular weight of the cured resin composition forming each layer, and the like. But is not limited to these methods.

In the present invention, the "base polymer" refers to the resin having the highest mass ratio among the resins constituting each layer.

(thickness of each layer)

By changing the thickness of each of the cured resin layers (a) and (B), not only the elastic modulus of the cured resin layers (a) and (B) can be adjusted, but also the surface hardness can be improved. For example, by making the thickness of the cured resin layer (B) larger than that 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%, more preferably 20% or more or 200% or less, and even more preferably 30% or more or 100% or less of the thickness of the cured resin layer (B).

In addition to satisfying the above relationship, the thickness of the cured resin layer (A) is preferably 1.0 μm or more and 30.0 μm or less. If the thickness is 1.0 μm or more, insufficient curing due to oxygen inhibition or the like can be prevented when the cured resin layer (A) is cured by ultraviolet ray irradiation, for example. On the other hand, if it is 30.0 μm or less, the surface smoothness of the present laminated film can be easily ensured, and the transparency can be easily ensured. From the above viewpoint, the thickness of the layer is preferably 1.0 μm or more and 30.0 μm or less, of these, 20.0 μm or less, more preferably 10.0 μm or less, of these, particularly 5.0 μm or less.

On the other hand, the thickness of the cured resin layer (B) is preferably 1.0 μm or more and 30.0 μm or less, more preferably 20.0 μm or less, further preferably 10.0 μm or less, particularly 5 μm or less.

From the viewpoint of bendability, the total thickness of the cured resin layer (a) and the cured resin layer (B) may be 20.0 μm or less, preferably 10.0 μm or less, more preferably 8.0 μm or less, particularly 6.0 μm or less, and further 5.0 μm or less.

(particle content of each layer)

The cured resin layer (a) contains no particles, the cured resin layer (B) contains particles, or the particle content of the cured resin layer (a) is made smaller than the particle content of the cured resin layer (B), and the elastic modulus of the cured resin layer (B) can be adjusted to be higher than that of the cured resin layer (a).

As a specific example of the latter, the elastic modulus of each layer can be adjusted by setting the particle content of the cured resin layer (a) to 1 to 20 mass% and the particle content of the cured resin layer (B) to 20 to 60 mass%.

In this case, the content of the particles in the cured resin layer (a) is more preferably 1 mass% or more, particularly 2 mass% or more, particularly 5 mass% or more, and on the other hand, is more preferably 20 mass% or less, particularly 15 mass% or less, particularly 10 mass% or less.

On the other hand, the content of the particles in the cured resin layer (B) is more preferably 20 mass% or more, 25 mass% or more, and 30 mass% or more, and on the other hand, 60 mass% or less, 55 mass% or less, and 50 mass% or less.

The types of particles contained in the cured resin layer (a) and the cured resin layer (B) are as follows.

(surface condition of each layer)

The surface of the cured resin layer (a) may be uneven or flat. Among them, from the viewpoint of appearance (surface gloss), it is preferably flat.

On the other hand, the surface of the cured resin layer (B) may be uneven or flat. Among them, from the viewpoint of appearance (surface gloss), it is preferably flat.

(optical Properties of Each layer)

In consideration of optical use, the cured resin layers (a) and (B) are preferably transparent.

Among these, in order to improve the 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.

When the difference in refractive index between the cured resin layer (a) and the cured resin layer (B) is 0.15 or less, the visibility can be improved. Specifically, when the film is viewed at an angle inclined by 45 degrees with respect to the film surface, the outline derived from the cured resin layer (a) becomes less visible.

From the above viewpoint, the difference in refractive index between the cured resin layer (a) and the cured resin layer (B) is preferably 0.15 or less, more preferably 0.10 or less, and still more preferably 0.05 or less. The lower limit of the refractive index difference is 0.

< method for producing laminated film >)

Both the cured resin layer (a) and the cured resin layer (B) can be formed by curing a curable composition, i.e., a composition having curable properties.

More specifically, the present laminated film can be produced by applying a curable composition to at least one surface of the base film and curing the composition to form a cured resin layer (a), and then applying a curable composition to the cured resin layer (a) and curing the composition to form a cured resin layer (B). In this case, the curing of the cured resin layer (a) and the cured resin layer (B) may be performed simultaneously.

After the cured resin layer (a) is formed, the film may be once wound into a roll, and then the film may be unwound again to apply the curable composition to the cured resin layer (a) and cured to form the cured resin layer (B), or after the cured resin layer (a) is formed on the surface of the base film, the curable composition may be continuously applied and cured to form the cured resin layer (B). The method for producing the present laminated film is not limited to the above method.

< curable composition >

The curable composition for forming the cured resin layer (a) and the cured resin layer (B) preferably contains, in addition to the curable monomer, a photopolymerization initiator, a solvent, particles, a crosslinking agent, and other components as necessary. Hereinafter, each will be described.

The mass average molecular weight of the curable monomer as the base polymer forming the cured resin layer (a) or the mass average molecular weight of the curable resin composition forming the cured resin layer (a) is larger than the mass average molecular weight of the curable monomer as the base polymer forming the cured resin layer (B) or the mass average molecular weight of the curable resin composition forming the cured resin layer (B), whereby the elastic modulus of the cured resin layer (B) can be adjusted to be higher than the elastic modulus of the cured resin layer (a).

Among these, from the viewpoint of reducing the total thickness of the cured resin layers (a) and (B), for example, making the total thickness of the cured resin layers (a) and (B) 30 μm or less, 20 μm or less, and 10 μm or less, maintaining the surface hardness, and improving the repetitive bending property, the elastic modulus of the cured resin layer (B) can be adjusted to be higher than the elastic modulus of the cured resin layer (a) by making the mass average molecular weight of the base polymer forming the cured resin layer (a) or the mass average molecular weight of the curable resin composition forming the cured resin layer (B) 1-digit number or more, that is, 10 times or more the mass average molecular weight of the base polymer forming the cured resin layer (B) or the mass average molecular weight of the curable resin composition forming the cured resin layer (B).

From the above-mentioned viewpoint, the mass average molecular weight of the curable monomer as the base polymer forming the cured resin layer (a) or the mass average molecular weight of the curable resin composition forming the cured resin layer (a) is preferably 1000 or more, more preferably 3000 or more, and further preferably 5000 or more. On the other hand, 500000 or less, more preferably 400000 or less, and still more preferably 250000 or less, are preferable.

On the other hand, the mass average molecular weight of the curable monomer which is the base polymer forming the cured resin layer (B) or the mass average molecular weight of the curable resin composition forming the cured resin layer (B) is preferably 100 or more, more preferably 200 or more, among them 400 or more. On the other hand, 500000 or less, more preferably 400000 or less, and still more preferably 250000 or less, are preferable.

(curable monomer)

The curable monomer may be a compound that can be cured. Among them, from the viewpoint of satisfying both excellent surface hardness and repeated bendability, it is preferable to contain 1 or more selected from the group consisting of crosslinkable monomers, acrylates, and methacrylates.

Among them, from the viewpoint of handling, ease of industrial availability, and cost, a blend of at least 2 or more selected from crosslinkable monomers and (meth) acrylic esters, or a mixture of at least 2 or more selected from methacrylic esters and vinyl monomers is preferable.

As described above, when 2 kinds of monomers (a/b) are used, the compounding ratio (a/b) is preferably in the range of 90/10 to 10/90, more preferably in the range of 80/20 to 40/60, and may be 70/30 to 40/60, among others, in terms of mass ratio.

In the present invention, the expression "(meth) acrylic acid" is used to mean either one or both of "acrylic acid" and "methacrylic acid". The same applies to "(meth) acrylate" and "(meth) acryloyl group". In addition, "(poly) propylene glycol" means either or both of "propylene glycol" and "polypropylene glycol". The same applies to "(poly) ethylene glycol".

From these mixtures, it is preferable that each main component is selected so that at least the aforementioned elastic modulus and refractive index can be satisfied for each of the cured resin layer (a) and the cured resin layer (B).

Among them, the curable monomer used in the curable composition for forming the cured resin layer (a) is preferably selected so as to satisfy the above-mentioned elastic modulus and refractive index.

On the other hand, the curable monomer used in the curable composition for forming the cured resin layer (B) is preferably selected so as to satisfy the aforementioned elastic modulus and refractive index.

(crosslinkable monomer)

The crosslinkable monomer is a monomer having 1 or 2 or more polymerizable functional groups in one molecule.

Examples of the crosslinkable monomer include: allyl acrylate, allyl methacrylate, 1-acryloxy-3-butene, 1-methacryloxy-3-butene, 1, 2-diacryloyloxy-ethane, 1, 2-dimethacryloxy-ethane, 1, 2-diacryloyloxy-propane, 1, 3-diacryloyloxy-propane, 1, 4-diacryloyloxy-butane, 1, 3-dimethacryloxy-propane, 1, 2-dimethacryloxy-propane, 1, 4-dimethacryloxy-butane, triethylene glycol dimethacrylate, polyethylene glycol diacrylate, 1, 6-hexanediol dimethacrylate, 1, 9-nonanediol dimethacrylate, mixtures thereof, and mixtures thereof, Triethylene glycol diacrylate, 1, 6-hexanediol diacrylate, 1, 9-nonanediol diacrylate, 1, 4-pentadiene, trimethylolpropane triacrylate, etc.

Examples of the hydroxyl group-containing (meth) acrylate compound include: hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-hydroxyhexyl (meth) acrylate, 2-hydroxyethylacryloyl phosphate, and 2- (meth) acryloyloxyethyl-2-hydroxypropyl phthalate, (meth) acrylate-based compounds having 1 ethylenically unsaturated group such as caprolactone-modified 2-hydroxyethyl (meth) acrylate, dipropylene glycol (meth) acrylate, fatty acid-modified glycidyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, and 2-hydroxy-3- (meth) acryloyloxypropyl (meth) acrylate; (meth) acrylate compounds containing 2 ethylenically unsaturated groups such as glycerol di (meth) acrylate and 2-hydroxy-3-acryloyl-oxypropyl methacrylate; and (meth) acrylate compounds containing 3 or more ethylenically unsaturated groups, such as pentaerythritol tri (meth) acrylate, caprolactone-modified pentaerythritol tri (meth) acrylate, ethylene oxide-modified pentaerythritol tri (meth) acrylate, dipentaerythritol penta (meth) acrylate, caprolactone-modified dipentaerythritol penta (meth) acrylate, and ethylene oxide-modified dipentaerythritol penta (meth) acrylate.

Examples of the crosslinkable monomer having a vinyl group include: glycidyl (meth) acrylate, beta-methylglycidyl (meth) acrylate, o-vinylbenzyl glycidyl ether, m-vinylbenzyl glycidyl ether, p-vinylbenzyl glycidyl ether, alpha-methyl-o-vinylbenzyl glycidyl ether, alpha-methyl-m-vinylbenzyl glycidyl ether, alpha-methyl-p-vinylbenzyl glycidyl ether, among which, among others, mention may be made of: o-vinylbenzyl glycidyl ether, m-vinylbenzyl glycidyl ether, p-vinylbenzyl glycidyl ether, 3, 4-epoxycyclohexylmethyl (meth) acrylate. These may be used alone, or 2 or more of them may be used in combination.

(acrylic esters)

As the above-mentioned acrylates, for example: acyclic alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, pentadecyl acrylate, and dodecyl acrylate; cyclic alkyl acrylates such as cyclohexyl acrylate and isobornyl acrylate; aryl acrylates such as phenyl acrylate and naphthyl acrylate; and non-cyclic alkyl acrylates having functional groups such as 2-hydroxyethyl acrylate, 2-methoxyethyl acrylate, and glycidyl acrylate.

(methacrylic acid esters)

Examples of the above-mentioned methacrylates include: acyclic alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, pentadecyl methacrylate, and dodecyl methacrylate; cyclic alkyl methacrylates such as cyclohexyl methacrylate and isobornyl methacrylate; aryl methacrylates such as phenyl methacrylate; and acyclic alkyl methacrylates having a functional group such as 2-hydroxyethyl methacrylate, 2-methoxyethyl methacrylate, and glycidyl methacrylate. These may be used alone, or 2 or more of them may be used in combination.

(photopolymerization initiator)

When the curable composition is photocured, a photopolymerization initiator is preferably blended.

The photopolymerization initiator is not particularly limited, and examples thereof include: ketone-based photopolymerization initiators, amine-based photopolymerization initiators, and the like. Specifically, examples thereof include: benzophenone, micheli ketone, 4 '-bis (diethylamino) benzophenone, xanthone, thioxanthone, isopropyl xanthone, 2, 4-diethylthioxanthone, 2-ethylanthraquinone, acetophenone, 2-hydroxy-2-methylpropiophenone, 2-hydroxy-2-methyl-4' -isopropylphenylacetone, 1-hydroxycyclohexylphenyl ketone, isopropylbenzoin ether, isobutylbenzoin ether, 2-diethoxyacetophenone, 2-dimethoxy-2-phenylacetophenone, camphorquinone, benzanthrone, 2-methyl-1- [4- (methylthio) phenyl ] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1-one Ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 4,4 '-di (tert-butylperoxycarbonyl) benzophenone, 3,4, 4' -tri (tert-butylperoxycarbonyl) benzophenone, 3 ', 4, 4' -tetra (tert-hexylperoxycarbonyl) benzophenone, 3 '-di (methoxycarbonyl) -4, 4' -di (tert-butylperoxycarbonyl) benzophenone, 3,4 '-di (methoxycarbonyl) -4, 3' -di (tert-butylperoxycarbonyl) benzophenone, 4,4 '-di (methoxycarbonyl) -3, 3' -di (tert-butylperoxycarbonyl) benzophenone, benzophenone, {1- [4- (phenylthio) -2- (O-benzoyloxime) ] }1, 2-octanedione, 2- (4 ' -methoxystyryl) -4, 6-bis (trichloromethyl) -s-triazine, 2- (3 ', 4 ' -dimethoxystyryl) -4, 6-bis (trichloromethyl) -s-triazine, 2- (2 ' -methoxystyryl) -4, 6-bis (trichloromethyl) -s-triazine, 2- (4 ' -pentyloxyphenylvinyl) -4, 6-bis (trichloromethyl) -s-triazine, 2-phenylthiopropionic acid, 4-bis (trichloromethyl) -s-triazine, 2-phenylthiopropionic acid, 4-bis (trichloromethyl) -s-triazine, 2-methylpropionic acid, 4-bis (trichloromethyl) -s-triazine, 2-methyl-triazine, 2-methyloxy-4, 6-bis (trichloromethyl) -s-triazine, 2-methyloxy-methyl, 4- [ p-N, N-bis (ethoxycarbonylmethyl) ] -2, 6-bis (trichloromethyl) -s-triazine, 1, 3-bis (trichloromethyl) -5- (2 ' -chlorophenyl) -s-triazine, 1, 3-bis (trichloromethyl) -5- (4 ' -methoxyphenyl) -s-triazine, 2- (p-dimethylaminostyryl) benzoxazole, 2- (p-dimethylaminostyryl) benzothiazole, 2-mercaptobenzothiazole, 3 ' -carbonylbis (7-diethylaminocoumarin), 2- (o-chlorophenyl) -4,4 ', 5,5 ' -tetraphenyl-1, 2 ' -biimidazole, 2 ' -bis (2-chlorophenyl) -4,4 ', 5,5 ' -tetrakis (4-ethoxycarbonylphenyl) -1,2 ' -biimidazole, 2 ' -bis (2, 4-dichlorophenyl) -4,4 ', 5,5 ' -tetraphenyl-1, 2 ' -biimidazole, 2 ' -bis (2, 4-dibromophenyl) -4,4 ', 5,5 ' -tetraphenyl-1, 2 ' -biimidazole, 2 ' -bis (2,4, 6-trichlorophenyl) -4,4 ', 5,5 ' -tetraphenyl-1, 2 ' -biimidazole, 3- (2-methyl-2-dimethylaminopropionyl) carbazole, 3, 6-bis (2-methyl-2-morpholinopropionyl) -9-n-dodecylcarbazole, 1-hydroxycyclohexyl phenyl ketone, bis (. eta.5-2, 4-cyclopentadien-1-yl) -bis (2, 6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium, phenylbis (2,4, 6-trimethylbenzoyl) phosphine oxide, diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide, and the like. These photopolymerization initiators may be used in only 1 kind, or may be used in 2 or more kinds.

In addition, a sensitizer may be used in combination with the photo-curing initiator as necessary. Specific examples of the sensitizer include: aliphatic amines such as n-butylamine, triethylamine and ethyl p-dimethylaminobenzoate, and aromatic amines.

The content of the photopolymerization initiator is preferably in the range of 1 to 10 parts by mass per 100 parts by mass of the curable composition. More preferably, it is in the range of 1 to 5 parts by mass.

The content of the photopolymerization initiator is 1 part by mass or more, whereby a desired polymerization initiating effect can be obtained, and the content of the photopolymerization initiator is 10 parts by mass or less, whereby yellowing of the resin layer can be suppressed. The photo-curing initiator and the sensitizer are preferably used in a proportion of 20% by mass or less based on the solid content of the photocurable composition.

(solvent)

As the aforementioned solvent, for example, there can be exemplified: ketone solvents such as methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, diacetone alcohol, and acetone; alcohol solvents such as pentanol, hexanol, heptanol, and octanol; ether solvents such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, and propylene glycol monomethyl ether acetate; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, methoxybutyl acetate, amyl acetate, propyl acetate, ethyl lactate, methyl lactate, and butyl lactate; and organic solvents such as hydrocarbon solvents including toluene, xylene, solvent naphtha, hexane, cyclohexane, ethylcyclohexane, methylcyclohexane, heptane, octane, and decane. These organic solvents may be used alone, or 2 or more of them may be used in combination.

(particle)

The curable composition may contain a predetermined amount of particles for improving slidability and blocking and for adjusting the elastic modulus of each layer.

Examples of the particles include: inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, alumina, and titanium oxide, organic particles such as acrylic resins, styrene resins, urea resins, phenol resins, epoxy resins, and benzoguanamine resins, and the like. These can be used alone in 1, also can be combined with more than 2 and use.

Further, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst in a polyester production process may be used.

The shape of the particles is not particularly limited. For example, the shape may be spherical, massive, rod-like, or flat.

Further, the hardness, specific gravity, color, and the like of the above particles are also not particularly limited. These series of particles may be used in combination of 2 or more kinds as necessary.

If the average particle size of the particles is too large, the surface roughness becomes too coarse, and there may be a case where a problem occurs when a cured resin layer formed from various cured compositions is formed in a subsequent step, and if it is too small, the effect of adding the particles is reduced, and therefore, it is preferably 5 μm or less, more preferably 0.01 μm or more or 3 μm or less, and further more preferably 0.5 μm or more or 2.5 μm or less.

(crosslinking agent)

From the viewpoint of improving chemical resistance or improving elastic modulus, it is preferable to blend a crosslinking agent. The crosslinking agent herein means other than the crosslinkable monomer.

Examples of the crosslinking agent include: oxazoline compounds, isocyanate compounds, epoxy compounds, melamine compounds, carbodiimide compounds, and the like. Among them, from the viewpoint of improving the adhesiveness, it is more preferable to use at least 1 of the oxazoline compound or the isocyanate compound.

(oxazoline compound)

The oxazoline compound used in the crosslinking agent is a compound having an oxazoline group in a molecule, and particularly preferably an oxazoline group-containing polymer can be produced by polymerizing an addition-polymerizable oxazoline group-containing monomer alone or with another monomer.

Examples of the addition-polymerizable oxazoline group-containing monomer include: 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, and the like, and mixtures of 1 or 2 or more of them may be used. Among them, 2-isopropenyl-2-oxazoline is also industrially available and suitable.

The other monomer is not limited as long as it is a monomer copolymerizable with the addition-polymerizable oxazoline group-containing monomer, and examples thereof include: (meth) acrylates such as alkyl (meth) acrylates (alkyl is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, 2-ethylhexyl, cyclohexyl); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid and salts thereof (sodium salt, potassium salt, ammonium salt, tertiary amine salt, etc.); unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated amides such as (meth) acrylamide, N-alkyl (meth) acrylamide, and N, N-dialkyl (meth) acrylamide (alkyl groups include methyl, ethyl, N-propyl, isopropyl, N-butyl, isobutyl, tert-butyl, 2-ethylhexyl, and cyclohexyl); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α -olefins such as ethylene and propylene; halogen-containing α, β -unsaturated monomers such as vinyl chloride and vinylidene chloride; and α, β -unsaturated aromatic monomers such as styrene and α -methylstyrene, and 1 or 2 or more of these monomers can be used.

From the viewpoint of improving the adhesion, the oxazoline group amount of the oxazoline compound is preferably 0.5 to 10mmol/g, more preferably 1mmol/g or more and 9mmol/g or less, still more preferably 3mmol/g or more and 8mmol/g or less, particularly preferably 4mmol/g or more and 6mmol/g or less.

(isocyanate Compound)

The isocyanate compound used in the crosslinking agent is, for example, an isocyanate or a compound having an isocyanate derivative structure represented by a blocked isocyanate.

Examples of the isocyanate include: aromatic isocyanates such as toluene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate and naphthalene diisocyanate, aliphatic isocyanates having an aromatic ring such as α, α, α ', α' -tetramethylxylylene diisocyanate, aliphatic isocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate and hexamethylene diisocyanate, and alicyclic isocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylene bis (4-cyclohexyl isocyanate) and isopropylidene dicyclohexyl diisocyanate. In addition, there can be mentioned: polymers and derivatives such as biuretized products, isocyanurate products, uretdione products and carbodiimide-modified products of these isocyanates. These may be used alone or in combination of two or more. Among the above isocyanates, aliphatic isocyanates or alicyclic isocyanates are suitable as measures against yellowing caused by ultraviolet irradiation.

When used in the state of blocking isocyanate, examples of the blocking agent include: bisulfite, phenol compounds such as phenol, cresol and ethylphenol, alcohol compounds such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol and ethanol, active methylene compounds such as methyl isobutyrylacetate, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate and acetylacetone, thiol compounds such as butyl mercaptan and dodecyl mercaptan, lactam compounds such as epsilon-caprolactam and delta-valerolactam, amine compounds such as diphenylaniline, aniline and ethyleneimine, acid amide compounds such as acetanilide and acetic amide, and oxime compounds such as formaldehyde, acetaldoxime, acetoxime, methyl ethyl ketoxime and cyclohexanone oxime, and these may be used alone or in combination of 2 or more.

The isocyanate compound may be used alone or as a mixture or a combination with various polymers. In order to improve the dispersibility and the crosslinkability of the isocyanate compound, a mixture or a combination of the isocyanate compound with a polyester resin or a urethane resin is preferably used.

(epoxy compound)

The epoxy compound used in the crosslinking agent is a compound having an epoxy group in a molecule, and examples thereof include: the condensate of epichlorohydrin with a hydroxyl group or an amino group such as ethylene glycol, polyethylene glycol, glycerin, polyglycerin, or bisphenol a includes: polyepoxy compounds, diepoxy compounds, monoepoxy compounds, glycidylamine compounds, and the like.

Examples of the above-mentioned polyepoxides include: sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris (2-hydroxyethyl) isocyanate, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, and examples of the diepoxy compound include: neopentyl glycol diglycidyl ether, 1, 6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, and monoepoxy compounds include, for example: allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether, and examples of the glycidyl amine compound include: n, N' -tetraglycidyl-m-xylylenediamine, 1, 3-bis (N, N-diglycidylamino) cyclohexane, and the like. From the viewpoint of improving the adhesion, polyether-based epoxy compounds are preferable. The amount of the epoxy group is preferably a polyfunctional polyepoxide having 3 or more functions as compared with 2 functions.

(Melamine Compound)

The above melamine compound used in the crosslinking agent is a compound having a melamine skeleton in the compound, and for example: an alkylolated melamine derivative, a compound which is partially or completely etherified by reacting an alkylolated melamine derivative with an alcohol, and a mixture thereof.

As the alcohol used for the etherification, methanol, ethanol, isopropanol, n-butanol, isobutanol, and the like are suitably used. The melamine compound may be a monomer, a dimer or higher polymer, or a mixture thereof. Further, a catalyst may be used in combination for improving the reactivity of the melamine compound, such as a type in which a part of melamine is co-condensed with urea.

The content of the crosslinking agent is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and further preferably 25 parts by mass or more, based on 100 parts by mass of the curable monomer, from the viewpoint of obtaining good coating film strength. On the other hand, from the viewpoint of obtaining good adhesion between the films, the amount is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and further preferably 40 parts by mass or less.

(carbodiimide Compound)

The carbodiimide compound used in the crosslinking agent is a compound having a carbodiimide structure, and has 1 or more carbodiimide structures in a molecule. For better adhesion and the like, a polycarbodiimide compound having 2 or more carbodiimide structures in the molecule is more preferable.

The carbodiimide compound can be synthesized by a conventionally known technique, and a condensation reaction of a diisocyanate compound is generally used. The diisocyanate compound is not particularly limited, and any of aromatic and aliphatic compounds can be used, and specific examples thereof include: toluene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, benzene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, trimethyl hexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, dicyclohexylmethane diisocyanate, and the like.

The content of the carbodiimide group contained in the carbodiimide compound is preferably 100 to 1000, more preferably 250 or more and 800 or less, and even more preferably 300 or more and 700 or less, in terms of carbodiimide equivalent (weight [ g ] of the carbodiimide compound for providing 1mol of carbodiimide groups). When the amount is in the above range, the durability of the coating film is improved.

(other Components)

(polyol-based Compound)

Examples of the polyol compound include: ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1, 2-butanediol, 1, 3-butanediol, 2, 3-butanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 3-methyl-1, 5-pentanediol, 1, 8-octanediol, 1, 9-nonanediol, 2-dimethylolheptane, trimethylene glycol, 1, 4-tetramethylene glycol, dipropylene glycol, 1, 3-tetramethylene glycol, 2-methyl-1, 3-trimethylene glycol, 2, 4-diethyl-1, 5-pentamethylene glycol, hydrogenated bisphenol A, hydroxyalkylated bisphenol A, 1, 4-cyclohexanedimethanol, 1, 4-cyclohexanediol, hydrogenated bisphenol A, and mixtures thereof, Low molecular weight diols such as 2,2, 4-trimethyl-1, 3-pentanediol and N, N-bis- (2-hydroxyethyl) dimethylhydantoin; high molecular weight polyols such as polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, polybutadiene polyols, (meth) acrylic polyols, polycaprolactone polyols, polysiloxane polyols, and polyurethane polyols.

Examples of the polyether polyol include: polyether polyols having an oxyalkylene structure such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and polyhexamethylene glycol, and random or block copolymers of these polyalkylene glycols.

Among these, polyether polyols having an oxyalkylene structure are preferable, and the number of carbon atoms in the alkylene structure is preferably 2 to 6, particularly preferably 2 to 4, and further preferably 4.

Examples of the polyester polyol include: condensation polymers of polyols and polycarboxylic acids; ring-opening polymers of cyclic esters (lactones); reactants based on 3 components of polyhydric alcohol, polycarboxylic acid and cyclic ester, and the like.

Examples of the polyol include: the aforementioned low molecular weight diols, and the like.

Examples of the polycarboxylic acid include: aliphatic dicarboxylic acids such as malonic acid, maleic acid, fumaric acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; alicyclic dicarboxylic acids such as 1, 4-cyclohexanedicarboxylic acid; aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 2, 6-naphthalenedicarboxylic acid, p-phenylene dicarboxylic acid, and trimellitic acid.

Examples of the cyclic ester include: propiolactone, beta-methyl-delta-valerolactone, epsilon-caprolactone and the like.

Examples of the polycarbonate polyol include: reactants of polyols with phosgene; transesterification reactants of carbonates and polyols, and the like.

Examples of the polyol include: examples of the alkylene carbonate include the low molecular weight diol mentioned above: ethylene carbonate, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, and the like.

The polycarbonate polyol may have both a carbonate bond and an ester bond as long as it has a carbonate bond in the molecule and a hydroxyl group at the terminal.

< curable composition for Forming cured resin layers (A) and (B) >

Examples of the curable composition for forming the cured resin layers (a) and (B) include: urethane (meth) acrylate compounds obtained by combining a hydroxyl group-containing (meth) acrylate compound with an isocyanate compound or by combining a hydroxyl group-containing (meth) acrylate compound with an isocyanate compound and a polyol compound.

In addition, it is possible to exemplify: a combination of an acrylate and a crosslinkable monomer having a vinyl group, a combination of a methacrylate and a crosslinkable monomer having a vinyl group, a combination of an acrylate and a hydroxyl group-containing (meth) acrylate compound, a combination of a methacrylate and a hydroxyl group-containing (meth) acrylate compound, and the like. But is not limited thereto.

The viscosity at 25 ℃ of the curable composition for forming the cured resin layers (A) and (B) is preferably 10 to 60 mPas, more preferably 30 mPas or less, even more preferably 20 mPas or less, even more preferably 15 mPas or less, even more preferably 12 mPas or less, as measured with an E-type viscometer, in order to improve coatability.

< method for Forming cured resin layer (A) >

The cured resin layer (a) is preferably formed, for example, as follows: the curable composition is applied by a conventionally known application method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, or inkjet coating, and then cured by light irradiation, for example, ultraviolet irradiation.

< method for Forming cured resin layer (B) >

The method of providing the cured resin layer (B) is preferably formed, for example, as follows: the curable composition is applied by a conventionally known application method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, or inkjet coating, and then cured by light irradiation, for example, ultraviolet irradiation.

< Properties of laminated film >)

(Pencil hardness)

The present laminated film having the above-described configuration can be such that the surface hardness of the film, specifically, the pencil hardness of the surface of the cured resin layer (B) is 2H or more, and in particular, 3H or more.

(repeated bendability)

In the present laminated film having the above-described configuration, the cured resin layer (a) is provided on the surface of the base film, and the elastic modulus of the cured resin layer (a) is set to be lower than that of the cured resin layer (B), whereby the practical repetitive characteristics can be further improved.

This laminated film can be bent 20 ten thousand or more times under repeated bendability evaluation (under the condition of R2.5), and can also have durability without generating cracks.

(haze of film)

When the present laminated film is used for optical applications, the haze of the film is preferably 5.0% or less, more preferably 4.0% or less, particularly 3.0% or less.

< characteristics and uses of the laminated film >)

As a result of the experiments conducted by the present inventors and examples, the use of the present laminated film can achieve both a high level of surface hardness (for example, 2H or more in evaluation of pencil hardness) and repeated bendability (capable of being bent 20 ten thousand times under a condition of R2.5).

Presume that: by adjusting the thicknesses of the cured resin layer (a) located in the first layer and the cured resin layer (B) located in the second layer, it is possible to reduce the propagation of stress into the cured resin layer (B) that is applied when the present laminated film is bent. Therefore, in the conventional method (full-surface coating formulation based on a single-layer structure), a resin component composed of an acrylic monomer which is difficult to use can be used, and there is an advantage that the degree of freedom in designing a laminated film is increased. Further, by forming the two-layer structure of the cured resin layer (a) and the cured resin layer (B), it is also expected that the stress is dispersed in the thickness direction, and therefore, it is estimated that the two-layer structure is advantageous for further improvement of the bending durability.

In addition, it is known that: by setting the elastic modulus of the cured resin layer (a) to be lower than that of the cured resin layer (B), it is possible to achieve both surface hardness (for example, 2H or more in pencil hardness evaluation) and repeated bendability (capable of being bent 20 ten thousand times under the condition of R being 2.5) at a high level. In contrast, it is also known that: by simply forming the above-described two-layer structure (comparative examples 3 to 5), it is difficult to achieve both desired hard coatability and repeated bendability.

In addition, it is known that: if the cured resin layer (a) and the cured resin layer (B) are formed as two layers, the tensile modulus of the base film to be used cannot be extremely increased.

Conventionally, in a laminated film having a surface layer with a high surface hardness, when the target surface hardness is designed to be a desired level (for example, 2H or more), re-evaluation is performed as necessary from the structural design of the raw material constituting the base film to be used, and the tensile modulus must be further increased.

On the other hand, if the above-described two-layer structure of the cured resin layer (a) and the cured resin layer (B) is used, a general-purpose substrate film that is distributed on the market can be appropriately selected, and there is an advantage that the degree of freedom in selecting the substrate film is increased.

The laminated film has excellent surface hardness and practical repeated bending property, and further can obtain transparency, so that the laminated film can be used for surface protection, display, particularly front panel and other applications. For example, the film can be suitably used as a surface protective film, a surface protective film for a display, or a surface protective film for a flexible display. However, the use of the present laminated film is not limited to these uses.

< < description of terms >)

In the present invention, the term "film" includes "sheet" and the term "film" includes "sheet".

In the present invention, when "X to Y" (X, Y is an arbitrary number), the meaning of "X or more and Y or less" and the meaning of "preferably more than X" or "preferably less than Y" are included at the same time unless otherwise specified.

In addition, the meaning of "preferably more than X" is included when the symbol "X" is not more than X (X is an arbitrary number), and the meaning of "preferably less than Y" is included when the symbol "Y" is not more than Y (Y is an arbitrary number).

Examples

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples.

The measurement method and the evaluation method used in the present invention are as follows.

(1) Method for measuring film thickness of cured resin layer

Each laminate film was bonded to a glass slide glass by "Aronalpha series" manufactured by Toyo Synthesis Co., Ltd to prepare a sample for SAICS (SAICAS). The obtained sample for SAICS was mounted on SAICAS (Daipla Wintes Co., Ltd., DN-01 model by Ltd.), and a notch 300 μm wide and 1 μm deep was cut in advance with a diamond blade. Notching was performed using a single crystal diamond blade with a V-angle dimension of 80 °, a rake angle of 5 °, and a relief angle of 5 °. The assay was as follows: a borax cutting blade having a width of 300 μm was attached to the sample having the notch having a width of 300 μm, and the film thickness of each cured resin layer was measured at an arbitrary depth, a horizontal speed of 1 μm/s, and a vertical speed of 0.5 μm/s. For the measurement, a boron nitride plain cutter having a cutter width of 0.3mm, a rake angle of 20 ° and a relief angle of 10 ° was used. The material strength was measured from the vertical displacement position and the cutting force, and the thickness of each layer was confirmed.

(2) Film haze (transparency)

The film haze of each laminated film was measured according to JIS K7136 using a haze meter HM-150 manufactured by color technical research on village.

(criteria for determination)

A (good): less than 5%

B (poor): more than 5 percent

(3) Pencil hardness (hard coating)

The pencil hardness was evaluated by a pencil hardness tester (manufactured by Anthras Seisakusho K.K.) under a load of 750g in accordance with JIS K5600-5-4. Based on the result, the determination is performed according to the following determination criterion.

(criteria for determination)

A (good): the pencil hardness is more than 3H.

B (slightly better): the pencil hardness is more than 2H and less than 3H.

C (poor): the pencil hardness is lower than 2H.

(4) Repeated bendability

The test was performed using a bending tester (Yuasa System Equipment co., ltd., DLDMLH-FS) so that the cured resin layer side of the laminated film was the outer surface, and the presence or absence of crack generation in the cured resin layer on the outer surface was visually confirmed.

Then, the number of repeated bending times is measured together with the minimum radius (R) at which no crack occurs, and based on the result, determination is made based on the following criteria.

(criteria for determination)

A (good): r is 2.5 or less and the number of times of repeated bending can be 20 ten thousand.

B (slightly better): more than 2.5, or the number of repeated bending is more than 1 ten thousand and less than 20 ten thousand

C (poor): more than 2.5, or less than 1 ten thousand times of repeated bending.

(5) Evaluation based on bending direction (In/Out) designation

The cured resin layer on the inner surface (In) or the outer surface (Out) of the laminated film was tested by a bending tester (Yuasa System Equipment co., ltd., DLDMLH-FS) so that the cured resin layer side became the inner surface (In) or the outer surface (Out), and the presence or absence of crack generation In the cured resin layer on the inner surface (In) or the outer surface (Out) was visually confirmed.

Then, the minimum radius (R) at which no crack occurs is measured, and based on the result, the determination is performed according to the following criteria.

(criteria for determination)

A (good): Out/In is R1.5 or more and less than 2.0

B (slightly better): out is R2.0 or more and less than R2.5

C (poor): out is R2.5 or more

(6) Modulus of elasticity of the cured resin layer (A) and the cured resin layer (B)

The elastic modulus (MPa) was determined in accordance with JIS Z2255 using a dynamic ultramicro hardness tester (DUH-W201, manufactured by Shimadzu corporation).

At this time, the sample temperature was 25 ℃, the test force was 4mN, the load speed was 0.7mN/S, and the holding time was 5 seconds.

(7) Refractive index of the cured resin layer (A) and the cured resin layer (B)

The refractive index of each layer was determined by abbe measurement. Based on the result, the determination is performed according to the following determination criterion.

(criteria for determination)

A (good): the difference in refractive index between the cured resin layer (A) and the cured resin layer (B) is 0.15 or less. B (poor): the difference in refractive index between the cured resin layer (A) and the cured resin layer (B) is more than 0.15.

(8) Adhesion between the cured resin layer (A) and the cured resin layer (B)

The adhesion between the cured resin layer (A) and the cured resin layer (B) was evaluated according to JIS K5600-5-6 by the cross cut method (100 cells of 10X 10). Based on the result, the determination is performed according to the following determination criterion.

(criteria for determination)

A (good): good sealing property (sealing area: 100%)

B (slightly better): and (4) partially stripping.

(sealing area: 50% or more but less than 100%)

C (poor): partial peeling or peeling of the entire surface.

(area of seal: less than 50%)

(9) Comprehensive evaluation

The laminated films obtained in examples and comparative examples were evaluated according to the following criteria.

(criteria for determination)

A (good): all of the items of transparency, hard coat property, repeated bendability, bending directionality, refractive index difference between the cured resin layer (a) and the cured resin layer (B), and adhesion between the cured resin layer (a) and the cured resin layer (B) are a.

B (slightly better): regarding each item of transparency, hard coat property, repeated bendability, bending directionality, refractive index difference between the cured resin layer (a) and the cured resin layer (B), and adhesion between the cured resin layer (a) and the cured resin layer (B), at least one is B, and the remainder is a.

C (poor): regarding each item of transparency, hard coating property, repeated bendability, bending directionality, refractive index difference between the cured resin layer (a) and the cured resin layer (B), and adhesion between the cured resin layer (a) and the cured resin layer (B), at least one of the hard coating property, the repeated bendability, and the bending directionality is C, and the remaining one is a or B.

Various materials used in examples and comparative examples were prepared as follows.

< base film F1>

Mitsubishi chemical corporation: biaxially stretched polyethylene terephthalate film (product name "DIAFOIL T612 type"), thickness: 50 μm, tensile modulus (JIS K7161) 4.3 GPa.

< base film F2>

The imperial product is manufactured: polyethylene naphthalate biaxially stretched film (grade name "Teonex W51"), thickness: 50 μm, tensile modulus (JIS K7161) 6.4 GPa.

< base film F3>

Manufactured by Kolon: polyimide film (product name "C50"), thickness: 50 μm, tensile modulus (JIS K7161) 6.9 GPa.

< acrylic ester (A) >

Into a reactor equipped with a stirrer, a reflux condenser and a thermometer, 98 parts by mass of glycidyl methacrylate ("Acryester G" manufactured by Mitsubishi chemical corporation), 1 part by mass of methyl methacrylate ("Acryester M" manufactured by Mitsubishi chemical corporation), 1 part by mass of ethyl acrylate (manufactured by Mitsubishi chemical corporation), 1.9 parts by mass of mercaptopropyltrimethoxysilane ("KBM 803" manufactured by shin-Etsu chemical corporation) and 157.3 parts by mass of propylene glycol monomethyl ether (PGM) were charged, and after the start of stirring, the inside of the system was replaced with nitrogen, and the temperature was raised to 55 ℃. To this was added 1 part by mass of 2, 2' -azobis (2, 4-dimethylvaleronitrile) (Fuji film and Wako pure chemical industries, Ltd. "V-65"), the inside of the system was heated to 65 ℃ and stirred for 3 hours, and further V-650.5 parts by mass was added and stirred for 3 hours at 65 ℃. The temperature in the system was raised to 100 ℃ and stirred for 30 minutes, then, 0.45 part by mass of p-methoxyphenol (manufactured by Fuji film and Wako pure chemical industries, Ltd.) and 138.1 parts by mass of PGM were added to the mixture, and the temperature in the system was raised to 100 ℃ again. Subsequently, 3.1 parts by mass of triphenylphosphine (manufactured by fuji film & Wako pure chemical industries, Ltd.) was added, 50.7 parts by mass of acrylic acid (manufactured by Mitsubishi chemical Co., Ltd.) was added, the temperature was raised to 110 ℃, and the mixture was stirred for 6 hours to obtain a solution of an acrylate (A) having a (meth) acryloyl group in a side chain. The composition of the reaction solution was 30/70 (mass ratio) X/PGM.

[ example 1]

On the above base film F2, a curable composition a prepared as described below was applied at 25 ℃ with a bar coater so that the applied thickness (after drying) became 2.0. mu.m, and dried by heating at 90 ℃ for 1 minute.

Next, a curable composition b prepared as described below was applied by a bar coater so that the thickness of the applied layer (after drying) became 3.0. mu.m so as to cover the cured resin layer (A), heated at 90 ℃ for 1 minute to dry the layer, and then the applied layer was dried to obtain a cumulative light amount of 400mJ/cm²The cured resin layers (a) and (B) were cured by the ultraviolet irradiation of (2) to obtain a laminated film having a laminated structure of the base film F2/cured resin layer (a)/cured resin layer (B).

(curable composition a)

A curable composition a was prepared by adding 5 parts by mass of a photopolymerization initiator to 100 parts by mass of the acrylate (a). The mass average molecular weight of the curable composition a was 15000, and the refractive index of the cured resin layer (a) was 1.53.

(curable composition b)

A curable composition b was prepared by adding 67 parts by mass of silica particles (MEK-AC-2140Y, manufactured by Mitsubishi chemical corporation) and 5 parts by mass of a photopolymerization initiator to 100 parts by mass of urethane acrylate (Violet light "UT-5670, manufactured by Mitsubishi chemical corporation). The mass average molecular weight of the curable composition B was 10500, and the refractive index of the cured resin layer (B) was 1.50.

[ example 2]

A laminated film was produced in the same manner as in example 1, except that the thicknesses of the cured resin layer (a) and the cured resin layer (B) were changed in example 1.

[ example 3]

A laminated film was produced in the same manner as in example 1, except that the curable composition b in example 1 was changed to the following curable composition b 1.

(curable composition b1)

To 100 parts by mass of the acrylic ester (a), 67 parts by mass of alumina particles (CIK Nanotech co., ALTPGDA, ltd.) and 5 parts by mass of a photopolymerization initiator were added to prepare a curable composition b 1. The mass average molecular weight of the curable composition B1 was 15000, and the refractive index of the cured resin layer (B) was 1.54.

[ example 4]

A laminated film was produced in the same manner as in example 1, except that the base film F2 was changed to the base film F1 in example 1.

[ example 5]

A laminated film was produced in the same manner as in example 1, except that the base film F2 was changed to the base film F3 in example 1.

Comparative example 1

On the base film F2, similarly to example 1, the curable composition a was applied at 25 ℃ by a bar coater so that the applied thickness (after drying) became 5.0. mu.m, heated at 90 ℃ for 1 minute so as to be dried, and then irradiated with a cumulative light quantity of 400mJ/cm²The cured resin layer (A) was formed to a thickness (after drying) of 5.0. mu.m by the ultraviolet ray of (2) to obtain a laminated film. At this time, the cured resin layer (B) was not formed.

Comparative example 2

On the base film F2, similarly to example 1, the curable composition b was applied by a bar coater so that the applied thickness (after drying) was uniformly 5.0 μm, dried by heating at 90 ℃ for 1 minute, and then irradiated with a cumulative light amount of 400mJ/cm²Ultraviolet ray of (2)A cured resin layer (B) having a thickness (after drying) of 5.0 μm was formed to obtain a laminated film. At this time, the cured resin layer (a) was not formed.

Comparative example 3

A laminated film was obtained in the same manner as in example 1, except that in example 1, the curable composition a was changed to the following curable composition a1, and the curable composition b was changed to the following curable composition b 2.

(curable composition a1)

To 100 parts by mass of urethane acrylate (ultraviolet light "UV-6640B" manufactured by mitsubishi chemical corporation), 5 parts by mass of a photopolymerization initiator was added to prepare a curable composition a 1. The mass average molecular weight of the curable composition a1 was 5000, and the refractive index of the cured resin layer (a) was 1.51.

(curable composition b2)

100 parts by mass of urethane acrylate (ultraviolet "UV-1700B", Mitsubishi chemical corporation) were added with 5 parts by mass of a photopolymerization initiator and DPHA80 parts by mass to prepare a curable composition B2. The mass average molecular weight of the curable composition B2 was 2000, and the refractive index of the cured resin layer (B) was 1.51.

DPHA: aronix M-404 (dipentaerythritol hexaacrylate/dipentaerythritol pentaacrylate) manufactured by Toyo synthetic Co., Ltd

Comparative example 4

A laminated film was obtained in the same manner as in example 1, except that the order of applying the curable composition a and the curable composition b was reversed in example 1.

Comparative example 5

A laminated film was obtained in the same manner as in example 1, except that in example 1, the curable composition a was changed to the following curable composition a2, and the curable composition b was changed to the following curable composition b 3.

(curable composition a2)

100 parts by mass of the DPHA thus obtained was combined with 100 parts by mass of 6mol EO-modified DPHA, 200 parts by mass of silica particles (MEK-AC-2140Y, manufactured by Nissan chemical Co., Ltd.), and 5 parts by mass of a photopolymerization initiator to prepare a curable composition a 2. The mass average molecular weight of the curable composition a2 was 790, and the refractive index of the cured resin layer (a) was 1.50.

(curable composition b3)

100 parts by mass of pentaerythritol triacrylate and 5 parts by mass of a photopolymerization initiator were added to 100 parts by mass of urethane acrylate (UV-7650B, Mitsubishi chemical corporation) to prepare curable composition B3. The mass average molecular weight of the curable composition B3 was 2300, and the refractive index of the cured resin layer (B) was 1.51.

Comparative example 6

A laminated film was obtained in the same manner as in example 1, except that in example 1, the curable composition a was changed to the following curable composition a3, and the curable composition b was changed to the following curable composition b 4.

(curable composition a3)

To 100 parts by mass of the following (meth) acrylic polymer solution, 6 parts by mass of the following polyisocyanate and 23 parts by mass of the above DPHA were added to prepare a curable composition a 3. The mass average molecular weight of the curable composition a3 was 15000, and the refractive index of the cured resin layer (a) was 1.50.

((meth) acrylic acid polymer solution)

283 parts by mass of methyl isobutyl ketone, 149 parts by mass of glycidyl methacrylate, 276 parts by mass of methyl methacrylate, and 25 parts by mass of t-butyl peroxy (2-ethylhexanoate) (product name: Perbutyl O, manufactured by Nippon emulsifier Co., Ltd.) were synthesized to obtain a precursor, and 76 parts by mass of acrylic acid was added thereto and synthesized to obtain 1000 parts by mass of a methyl isobutyl ketone solution of a (meth) acrylic polymer (nonvolatile content: 50.0 mass%).

The properties of the (meth) acrylic acid polymer were as follows.

Weight average molecular weight (Mw): 15000.

theoretical acryloyl equivalent weight converted to solid content: 478g/eq,

Hydroxyl value: 117 mgKOH/g.

(polyisocyanate)

BURNOCK DN-950 (adduct type polyisocyanate) manufactured by DIC K.K.)

(curable composition b4)

To 100 parts by mass of the following (meth) acrylic polymer solution, 6 parts by mass of the following polyisocyanate and 8 parts by mass of the above DPHA were added to prepare a curable composition b 4. The mass average molecular weight of the curable composition B4 was 40000, and the refractive index of the cured resin layer (B) was 1.52.

((meth) acrylic acid polymer solution)

In a reaction apparatus equipped with a stirrer, a condenser, a dropping funnel and a nitrogen gas inlet tube, 229 parts by mass of methyl isobutyl ketone was charged, the temperature in the system was raised to 110 ℃ while stirring, and then a mixed solution of 309 parts by mass of glycidyl methacrylate, 34 parts by mass of methyl methacrylate and 10 parts by mass of t-butyl peroxy (2-ethylhexanoate) (product name: Perbutyl O, manufactured by Nippon emulsifier Co., Ltd.) was added dropwise from the dropping funnel over 3 hours, and the mixture was held at 110 ℃ for 15 hours. Subsequently, the temperature of the mixed solution was decreased to 90 ℃, 0.1 part by mass of p-methoxyphenol and 157 parts by mass of acrylic acid were added, 3 parts by mass of triphenylphosphine was added, the temperature was increased to 100 ℃, the mixture was maintained for 8 hours, and the mixture was diluted with methyl isobutyl ketone to obtain 1000 parts by mass (50.0 mass% nonvolatile content) of a methyl isobutyl ketone solution of (meth) acrylic polymer (a 1).

The property values of the (meth) acrylic acid polymer (a1) are as follows.

Weight average molecular weight (Mw): 40000.

theoretical acryloyl equivalent weight converted to solid content: 230g/eq, and,

Hydroxyl value: 244 mgKOH/g.

(polyisocyanate)

Barnock DN-980S (isocyanurate type polyisocyanate) manufactured by DIC K.K

< evaluation results >

The properties of each of the laminated films obtained in the examples and comparative examples are shown in table 1 below.

[ Table 1]

[ Table 2]

< examination >

From the above examples and the results of the tests carried out by the inventors up to this point, it is clear that: the elastic modulus of the resin composition has a structure in which a cured resin layer (a) and a cured resin layer (B) are sequentially laminated on the surface of a base film, and is characterized in that: the cured resin layer (B) > the cured resin layer (a), and the difference ((B) - (a)) between the elastic modulus of the cured resin layer (B) and the elastic modulus of the cured resin layer (a) is greater than 0(MPa) and less than 220(MPa), so that the cured resin layer (a) can be bent 20 ten thousand times with a high level of surface hardness (for example, 2H or more in pencil hardness evaluation) and repeated bendability (R is 2.5).

In contrast, it is known that: as in comparative examples 3 to 6, it is difficult to achieve both desired hard coat properties and repeated bendability by merely forming two layers.

It is presumed that such a difference is caused by the difference ((B) - (a)) between the elastic modulus of the cured resin layer (B) and the elastic modulus of the cured resin layer (a) being greater than 0(MPa) and less than 220(MPa), and therefore, stress propagation into the cured resin layer (B) that is applied when the laminated film is bent can be reduced, and further, stress in the thickness direction is dispersed, which is advantageous for improving bending durability.

At this time, it was confirmed that: the respective elastic moduli of the cured resin layers (a) and (B) can be adjusted by adjusting the respective thicknesses and compositions, for example, the particle contents of the cured resin layers (a) and (B). Therefore, the conventional method (full-surface coating formulation based on a single-layer structure) can use a resin component made of an acrylic monomer which is difficult to use, and has an advantage of increasing the degree of freedom in designing a laminated film.

Note that, it is also known that: the difference ((B) - (a)) between the elastic modulus of the cured resin layer (B) and the elastic modulus of the cured resin layer (a) may be greater than 0(MPa) and less than 220(MPa), and the tensile modulus of the base film to be used does not need to be extremely increased.

Conventionally, in a laminated film having a surface layer with a high surface hardness, when the surface hardness to be a target is designed to be a desired level (for example, 2H or more), re-evaluation is performed as necessary from the structural design of a raw material constituting a base film to be used, and it is necessary to further increase the tensile modulus.

On the other hand, if the cured resin layer (a) and the cured resin layer (B) are formed in two layers, a general-purpose substrate film that is distributed on the market can be selected appropriately, and there is an advantage that the degree of freedom in selecting the substrate film is increased.

In the above examples, the case where the cured resin layer (a) has an elastic modulus of 330MPa as measured by a microhardness tester (JIS Z2255) was examined. For example, from the viewpoint of excluding an extremely soft layer such as a pressure-sensitive adhesive layer, it is estimated that the same effect can be obtained as long as the elastic modulus of the cured resin layer (a) is 10MPa or more.

Industrial applicability

The laminated film of the present invention is excellent in high-level hard coatability (for example, 2H or more in pencil hardness evaluation) and repeated bendability (capable of being bent 20 ten thousand times under a condition of R being 2.5), and can be applied to various surface protection applications. Among them, the resin composition is particularly suitable for optical applications such as display members (surface protective films and the like) which require flexibility.