KR20200115220A - Cover film - Google Patents

Abstract

A cover film having high hardness and high bending resistance is provided. The cover film according to the present invention includes a transparent base film, a buffer layer laminated on at least one side of the transparent base film, and a hard coat layer laminated on the buffer layer and formed of an ionizing radiation curable resin, wherein the thickness of the hard coat layer is 50 to 250 μm, and the thickness of the buffer layer is 5 to 75 μm.

Description

Cover film {COVER FILM}

The present invention relates to a cover film.

Recently, various cover films for protecting the surface of a touch panel display such as a smartphone have been proposed. For example, in Patent Document 1, a cover film having a film base material and a buffer layer and a hard coat layer formed on the surface thereof is proposed.

Japanese Laid-Open Patent Publication No. Hei 11-300873

In general, the hard coat layer is required to have a high hardness so as not to cause scratches or indentations due to external force. In addition, in recent years, since curved or curved displays have been proposed, a cover film that follows such a curvature or curvature and does not cause cracks in the hard coat layer is desired. The present invention has been made to solve the above problem, and an object of the present invention is to provide a cover film having high hardness and high bending resistance.

Item 1. A transparent base film,

A buffer layer laminated on at least one side of the transparent base film,

Laminated on the buffer layer and provided with a hard coat layer formed of an ionizing radiation curable resin,

The film thickness of the hard coat layer is 50 to 250 µm,

The film thickness of the buffer layer is 5 to 75 μm, the cover film.

Item 2. The cover film according to item 1, wherein the film thickness of the hard coat layer is larger than the film thickness of the buffer layer.

Item 3. The cover film according to Item 2, wherein the film thickness of the buffer layer relative to the film thickness of the hard coat layer is 3 to 70%.

Item 4. The buffer layer,

1 Hz, shear storage modulus at 25°C is 1.0 × 10 ⁵ Pa or less,

The cover film according to any one of items 1 to 3.

According to the cover film according to the present invention, while having high hardness, it is possible to increase the bending resistance.

1 is a cross-sectional view of a cover film according to an embodiment of the present invention.
2 is a diagram showing a method of a flexural test.

Hereinafter, one embodiment of the cover film according to the present invention will be described with reference to the drawings. 1 is a cross-sectional view of a cover film according to an embodiment of the present invention. As shown in FIG. 1, this cover film is, for example, attached to an image display device such as a touch panel display, and is laminated on one side of the transparent base film 1 and the base film 1 A buffer layer 2 and a hard coat layer 3 laminated on the buffer layer 2 are provided. Hereinafter, each member will be described in detail.

<1. Base film>

The base film (1) according to the present embodiment can be formed from various transparent materials, for example, cellulose acylate, cycloolefin polymer, polycarbonate, acrylate polymer, polyester, polyimide, etc. can do. In particular, polyimide is preferable because it is strong against bending and does not easily leave a mark even if it is bent. Moreover, various additives can be added to this base film 1 as needed. For example, various additives, such as a plasticizer, an antistatic agent, and an ultraviolet absorber, may be added.

The thickness of the base film 1 is, for example, preferably 250 µm or less, more preferably 200 µm or less, and still more preferably 100 µm or less. When the thickness of the base film 1 is larger than 250 µm, the flexibility of the cover film is lowered.

<2. Buffer layer>

The buffer layer 2 absorbs a stress acting on the hard coat layer 3 when the cover film is bent, and plays a role of suppressing the occurrence of cracks in the hard coat layer 3. Moreover, the buffer layer 2 also functions as an adhesive for fixing the base film 1 and the hard coat layer 3. This buffer layer (2) can be formed of, for example, an acrylic material, a urethane-based material, or a rubber-based material.As an example, it can be made by crosslinking an adhesive composition containing an acrylic acid ester copolymer as a main component and an isocyanate crosslinking agent. . Hereinafter, it demonstrates in detail.

<2-1. (Meth)acrylic acid ester copolymer>

The (meth)acrylic acid ester polymer preferably contains an alkyl (meth)acrylate having 2 to 20 carbon atoms in the alkyl group and a monomer having a reactive functional group in the molecule (reactive functional group-containing monomer) as a monomer unit.

As the (meth)acrylate alkyl ester having 2 to 20 carbon atoms in the alkyl group, the glass transition temperature (Tg) as a homopolymer is preferably -40°C or less. By containing such an alkyl (meth)acrylate as a constituent monomer unit, a buffer layer having a low shear storage modulus can be formed, and a cover film excellent in bending durability can be provided.

The (meth)acrylic acid ester polymer, by containing a reactive functional group-containing monomer as a monomer unit, reacts with a crosslinking agent to be described later through a reactive functional group derived from the reactive functional group-containing monomer, thereby forming a crosslinked structure (three-dimensional network structure). As a result, a buffer layer 2 having a desired cohesive force is obtained.

As the reactive functional group-containing monomer contained in the (meth)acrylic acid ester polymer as a monomer unit, a monomer having a hydroxyl group in the molecule (a hydroxyl group-containing monomer), a monomer having an amino group in the molecule (amino group-containing monomer), and the like are preferable. Among these, a hydroxyl group-containing monomer is particularly preferred. Many of the hydroxyl group-containing monomers have a glass transition temperature (Tg) of 0°C or less, and it is easy to set the glass transition temperature (Tg) of the main body of the buffer layer 2 according to the present embodiment to the above-described range.

The lower limit of the weight average molecular weight of the (meth)acrylic acid ester polymer is preferably 200,000 or more, preferably 300,000 or more, and particularly preferably 400,000 or more. If the lower limit of the weight average molecular weight of the (meth)acrylic acid ester polymer is above the above, problems such as leaching of the buffer layer 2 are suppressed. In addition, the weight average molecular weight in this specification is a value in terms of standard polystyrene measured by a gel permeation chromatography (GPC) method.

Moreover, it is preferable that it is 1 million or less, as for the upper limit of the weight average molecular weight of a (meth)acrylic acid ester polymer, it is more preferable that it is 900,000 or less, and it is especially preferable that it is 800,000 or less. When the upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer is below the above, the interlayer adhesion of the obtained buffer layer 2 is likely to fall into a preferred range.

<2-2. Isocyanate crosslinking agent>

When the adhesive composition according to the present embodiment is heated, the isocyanate crosslinking agent crosslinks the (meth)acrylic acid ester polymer to form a three-dimensional network structure. Thereby, the cohesive force of the obtained buffer layer 2 is improved. It does not specifically limit as an isocyanate type crosslinking agent.

<2-3. Additive>

In the buffer layer 2, if necessary, various additives commonly used in acrylic pressure-sensitive adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, antioxidants, light stabilizers, softeners, fillers, refractive index adjusters Etc. can be added, and for example, in order to adjust the shear storage modulus of the buffer layer 2 to a preferable range, it is preferable to add a rosin ester tackifier. In addition, it is assumed that the polymerization solvent and the diluted solvent described later are not included in the additive constituting the adhesive composition.

<2-4. Physical properties of the buffer layer>

<2-4-1. Buffer layer thickness>

The thickness of the buffer layer 2 is preferably 5 to 75 µm, and more preferably 10 to 50 µm. If the thickness is less than 5 µm, the buffering effect is lowered, and there is a fear that it becomes difficult to absorb stress due to bending of the hard coat layer 3. On the other hand, when the thickness exceeds 75 µm, when the cover film is pressed, since the cover film is settled, there is a fear that the pencil hardness is greatly reduced.

In particular, the thickness of the buffer layer 2 is preferably 3 to 70% of the thickness of the hard coat layer 3, more preferably 5 to 50%, and even more preferably 10 to 30%. When the thickness of the buffer layer 2 exceeds 70%, the pencil hardness may significantly decrease as described above, and when the thickness of the buffer layer 2 is less than 3%, the buffering effect by the buffer layer 2 decreases, and the hard coat layer ( 3) There is a fear that it becomes difficult to absorb the stress caused by the bending of. In addition, when the buffering effect is lowered, there is a concern that cracks may occur in the hard coat layer 3 when the cover film is bent.

<2-4-2. Shear storage modulus>

It is preferable that the buffer layer 2 according to the present embodiment has a shear storage modulus of 1.0×10 ⁵ Pa or less at 1 Hz and 25°C. The shear storage elastic modulus at 1 Hz and 25°C of the buffer layer 2 is preferably lower, more preferably 8.0×10 ⁴ Pa or less, further preferably 5.0×10 ⁴ Pa or less, and 3.0×10 ⁴ It is particularly preferable that it is Pa or less. In addition, in order to maintain the softness even at low temperatures, the storage elastic modulus at 1 Hz and -20°C of the buffer layer 2 is preferably 1.0×10 ⁵ Pa or less, more preferably 7.0×10 ⁴ Pa or less, It is particularly preferable that it is 5.5×10 ⁴ Pa or less.

In addition, the shear storage modulus at 1 Hz and 25°C can be measured by a method based on JIS K7244-6.

<3. Hard coat layer＞

Next, the hard coat layer 3 will be described. The hard coat layer 3 is obtained by curing the resin composition for a hard coat layer containing an ionizing radiation curable resin, a photoinitiator, or the like. Further, in this composition, if necessary, additives described later and fine particles such as silica may be blended.

<3-1. Ionizing radiation curable resin>

The ionizing radiation curable resin includes a radical polymerizable compound that polymerizes or crosslinks by ionizing radiation (ultraviolet or electron beam), and, for example, a compound containing at least one ethylenic unsaturated bond in a structural unit , Or a mixture of these.

As a monofunctional compound containing one unsaturated bond, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, n-butyl (meth)acrylate, and gly Cydyl (meth)acrylate, cyclohexyl (meth)acrylate, etc. are mentioned.

In addition, as a bifunctional compound containing two unsaturated bonds, for example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, butanediol di (meth) acrylate, hexanediol di (Meth)acrylate, nonanedioldi(meth)acrylate, ethoxylated hexanedioldi(meth)acrylate, propoxylated hexanedioldi(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol Di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tri Di(meth)acrylates, such as propylene glycol di(meth)acrylate and hydroxypivalate neopentyl glycol di(meth)acrylate, etc. are mentioned.

Moreover, as a polyfunctional compound containing three or more unsaturated bonds, for example, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri( Tri(meth)acrylates such as meth)acrylate, tris2-hydroxyethyl isocyanurate tri(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipenta Trifunctional (meth)acrylate compounds such as erythritol tri(meth)acrylate and ditrimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth) Acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropanepenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ditrimethylol Trifunctional or higher polyfunctional (meth)acrylate compounds such as propanehexa(meth)acrylate, and polyfunctional (meth)acrylate compounds in which some of these (meth)acrylates are substituted with an alkyl group or ε-caprolactone. (Meth)acrylate compounds are mentioned.

In addition, a urethane resin may be mixed with the (meth)acrylate compound. As the urethane resin, for example, a urethane (meth)acrylate resin can be used. Specifically, as the urethane (meth)acrylate compound, pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, pentaerythritol triacrylate toluene Diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate, toluene diisocyanate urethane prepolymer, pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer, etc. You can use

<3-2. Photopolymerization initiator>

Examples of the polymerization initiator include benzyl methyl ketals such as 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexylphenyl ketone, and 2-hydroxy-2-methyl-1-one Α-hydroxyketones such as phenylpropan-1-one, 2-methyl-1[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1 -(4-morpholinophenyl) butanone-1, such as α-amino ketones, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, such as bisacylphosphine oxides , 2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,1'-biimidazole, bis(2,4,5-triphenyl)imidazole, etc. Bisimidazoles, N-arylglycines such as N-phenylglycine, organic azides such as 4,4'-diazidechalcone, 3,3',4,4'-tetra(tert-butylperoxycar) Including organic peroxides such as benzophenone and the like, J. Photochem. Sci. Technol., 2,283 (1987). The compounds described in are mentioned.

<3-3. Additive>

Additives can be blended into the composition as needed. For example, silicone-based and fluorine-based additives (eg, leveling agents) that impart leveling, surface slip properties, high water contact arousal, and the like can be mentioned.

<3-4. Properties of the hard coat layer>

The thickness of the hard coat layer 3 is preferably 50 to 250 µm, more preferably 75 to 200 µm, and particularly preferably 100 to 150 µm. This is because if it is less than 50 µm, the surface hardness of the cover film is insufficient. On the other hand, when it is larger than 250 µm, curing shrinkage of the cover film becomes large, and the flexibility is lowered, which is not preferable.

<3-5. Tensile storage modulus>

It is preferable that the hard coat layer 3 according to the present embodiment has a tensile storage modulus of 1.0 × 10 ⁹ to 1.0 × 10 ¹⁰ Pa at 1 Hz and 25°C.

In addition, the shear storage modulus at 1 Hz and 25°C can be measured by a method based on JIS K7244-4.

<4. Manufacturing method of cover film>

Although it does not specifically limit, the manufacturing method of the cover film which concerns on this embodiment, For example, it can implement as follows.

First, the composition for a buffer layer prepared as described above is applied to one surface of the base film 1. As the coating method, a known method such as a roll coater, a reverse roll coater, a gravure coater, a knife coater, and a bar coater can be adopted. Next, the composition for a buffer layer is heated at 50 to 150°C. The heating time is 10 seconds to 10 minutes. In this way, the buffer layer 2 is formed.

Subsequently, the composition for a hard coat layer is applied onto the buffer layer (2). The application method is the same as that of the buffer layer 2. Next, the composition for a hard coat layer is dried. Although the method of drying is not particularly limited, for example, a method of passing the base film 1 coated with this composition through the inside of a dryer is mentioned. It is preferable that drying temperature at this time is 40-100 degreeC, for example. Thereafter, this composition is cured by photopolymerization. For this curing, it is preferable to use ultraviolet rays as the ionizing radiation source, and light sources such as a high pressure mercury lamp, a low pressure mercury lamp, an ultra-high pressure mercury lamp, a metal halide lamp, a carbon arc, and a xenon arc can be used. In this way, this composition is cured, and the hard coat layer 3 is formed. The cover film is completed by the above process.

Further, in order to prevent the cover film from being warped, the buffer layer 2 and the hard coat layer 3 may be laminated on both surfaces of the base film 1, respectively.

Moreover, after producing the buffer layer 2 and the hard coat layer 3 separately, the buffer layer 2 and the hard coat layer 3 can also be affixed on the base film 1 in this order. In this case, the buffer layer 2 is manufactured as a sheet material. The hard coat layer 3 can also be produced similarly to the sheet material of the buffer layer 2. That is, in addition to the release sheet, the hard coat layer 3 can be formed on a substrate such as a PET film, for example.

Alternatively, as described above, after applying the composition for a buffer layer on the base film 1 and forming the buffer layer 2 by heating, a separately manufactured hard coat layer 3 may be attached.

<5. Features>

According to the cover film according to the present embodiment, since the buffer layer 2 is formed between the base film 1 and the hard coat layer 3, for example, when the cover film is bent along the image display device. Stress can be relieved by the buffer layer 2. Therefore, when the cover film is bent, it is possible to prevent cracks from occurring in the hard coat layer 3. Moreover, since the thickness of the hard coat layer 3 is 50-250 micrometers, it can have suitable pencil hardness and bending performance.

<6. Modification Example>

The composition of the buffer layer 2 and the hard coat layer 3 described above is an example, and various materials can be used. As described above, the buffer layer 2 needs to be a material that is more flexible than the hard coat layer 3 in order to alleviate the stress acting on the hard coat layer 3 by bending. Therefore, for example, when the tensile storage modulus at 1 Hz and 25°C of the hard coat layer 3 is 1.0 × 10 ⁹ Pa to 1.0 × 10 ¹⁰ Pa, the shear storage modulus of the buffer layer 2 is 1.0 It is preferable to set it as x 10 ⁵ Pa or less.

Example

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

<1. Preparation of Examples and Comparative Examples>

Cover films according to Examples 1 to 12 and Comparative Examples 1 and 2 were prepared.

(1) base film

It was formed by polyethylene terephthalate having a thickness of 50 μm.

(2) buffer layer

With respect to 100 parts by weight of the acrylic acid ester copolymer having a weight average molecular weight of 400,000 and a hydroxyl value of 10 to 20, it was diluted with a solvent (ethyl acetate) to 35% solid content, and an isocyanate crosslinking agent (manufactured by Tosoh Corporation, model number "Colonate L-55E ") 0.13 weight part was added, and it stirred. In this way, a coating solution for the buffer layer was produced.

This coating liquid was applied on the base film using an applicator so that the film thickness after drying was as shown in Table 1. Then, it was heated and dried at 90°C for 5 min in a drying furnace (manufactured by Advantech, model number: DRD620DA) to semi-cure the coating liquid. The shear storage modulus of this buffer layer was 2.6×10 ⁴ Pa at 1 Hz and 25°C.

(3) hard coat layer

The hard coat layer is a polyfunctional urethane (meth)acrylate obtained by reacting (A) a polyisocyanate compound (except those having an alicyclic structure) and a hydroxyl group-containing (meth)acrylate, and (B) an alicyclic structure. It was prepared by the bifunctional (meth)acrylate having and the component (C) which is a photoinitiator.

First, component (A) was prepared. Specifically, as a polyisocyanate compound, an isocyanurate-type trimer (130 g) of 1,6-hexanediisocyanate was prepared. Further, as a hydroxyl group-containing (meth)acrylate, dipentaerythritol pentaacrylate (870 g) was prepared. These, 0.8 g of hydroquinone methyl ether as a polymerization inhibitor, and toluene as a solvent were put into a glass reactor equipped with a stirrer, a cooling tube, and a thermometer. The isocyanurate-type trimer of 1,6-hexanediisocyanate and the -OH group/NCO group of dipentaerythritol pentaacrylate were 1/1. Further, 0.3 g of dibutyltin dilaurate was added as a urethanization catalyst, and after reacting at 85°C for 6 hours, the solvent was distilled off to prepare a polyfunctional urethane (meth)acrylate as component (A).

In a glass container, 193.6 g of polyfunctional urethane (meth)acrylate of component (A) prepared as described above, and tricyclodecanedimethanoldi as a bifunctional (meth)acrylate having an alicyclic structure of component (B) 96.8 g of methacrylates, 677.6 g of trifunctional or higher polyfunctional polyester acrylates other than components (A) and (B), and 9.7 g of 1-hydroxycyclohexylphenyl ketone as a photoinitiator of component (C) , 0.97 g of 2-hydroxy-4-(acryloylethoxy)benzophenone as an ultraviolet absorber and 19.4 g of a thiol compound as a sensitizer were added. The mass ratio (MA)/(MB) of the mass (MA) of the component (A) and the mass (MB) of the component (B) was 66.7/33.3.

These were mixed and stirred in a glass container under conditions of 40°C and 2 hours to prepare a polymerizable composition. The viscosity of the polymerizable composition was 2700 mPa·s.

The obtained polymerizable composition was applied to the untreated surface of A4100 (manufactured by Toyobo Co., Ltd.) as a PET film (surface on which the easy-to-adhesion layer was not formed) using a bar coater manufactured by Tester Industries Co., Ltd.: ROD#38. One more sheet of A4100 was prepared and laminated on the applied polymerizable composition so that the untreated surface of A4100 was in contact with each other to prepare a laminate film having a three-layer structure. At this time, the thickness of the polymerizable composition was adjusted so that the thickness of the final hard coat layer became the thickness shown in Table 1.

The laminate film was irradiated with ultraviolet rays with an accumulated irradiation amount of 1597 mJ/cm 2 using an ultraviolet curing device (manufactured by Fusion UV Systems Japan, trade name: CV-110Q-G) to cure the polymerizable composition, and then PET The film was peeled off to obtain a hard coat layer. The tensile storage modulus of this hard coat layer was 2.5×10 ⁹ Pa at 1 Hz and 25°C.

(4) Preparation of cover film

On the buffer layer side of the base film on which the buffer layer was laminated, the hard coat layer was laminated by bonding to prepare a cover film shown in Table 1 below.

<2. Evaluation＞

(1) pencil hardness

About the hard coat layers of Examples 1-12 and Comparative Examples 1 and 2, the surface pencil hardness test based on JIS-K5600-5-4 was implemented. That is, the test was performed using a pencil (Mitsubishi UNI) of hardness H to 9H in which a load of 750 g was applied to the surface of the hard coat layer in order. Then, the change in appearance due to scratches on the surface of the hard coat layer was evaluated visually. In Table 2 below, the pencil hardness when a scratch occurred is described.

(2) flexion test

From the cover films according to Examples 1 to 12 and Comparative Examples 1 and 2, a 2 × 10 cm test piece was cut out by a laser cutting device (manufactured by GCC, SpiritGX 30W), and a bending test at room temperature (one mandrel test) Bending: JIS K5600-5-1) was implemented. In the bending test, as shown in Fig. 2, after winding the cover film so as to be folded in half on the outer peripheral surface of the cylindrical body, the original state was returned. Then, it was confirmed whether or not cracks occurred in the hard coat layer. In Table 2 below, the radius of the minimum cylindrical body in which cracks are not generated in the hard coat layer is shown. In addition, IF flexibility is a result when the hard coat layer is bent so as to contact the cylindrical body, and OF flexibility is a result when the base film is bent so as to contact the cylindrical body.

According to Table 2, as the thickness of the hard coat layer increases, the pencil hardness generally increases. In particular, as in Examples 9 to 12, when the thickness of the hard coat layer is 200 μm or more, the pencil hardness is increased regardless of the thickness of the buffer layer. On the other hand, in Comparative Example 1 in which the thickness of the hard coat layer was small, the pencil hardness was less than H. In addition, as in Examples 1 to 8, compared with Examples 9 to 12, when the thickness of the hard coat layer is not large, the pencil hardness is lowered as the thickness of the buffer layer increases. This is considered to be because, when the hard coat layer is pressed with a pencil and the thickness of the buffer layer is large, the hard coat layer becomes easy to dent.

In addition, with respect to IF flexibility, as the thickness of the hard coat layer increases, the diameter of the cylindrical body in which cracks occur increases, regardless of the thickness of the buffer layer. On the other hand, the OF flexural property can also have substantially the same tendency as the IF flexural property, but since the stress acting on the hard coat layer is greater than that of the IF flexural property, the overall flexural performance is lowered compared to the IF flexural property. In addition, as in Examples 5 to 8, when the thickness of the hard coat layer is about 100 µm, the OF flexibility is improved by the buffering effect as the thickness of the buffer layer increases. That is, the bendability in a cylindrical body having a smaller diameter is improved. On the other hand, in Comparative Example 2, since the thickness of the hard coat layer was large, the flexibility was not good in either of the IF flexibility and OF flexibility. Therefore, it was found that the cover film according to the present invention had good pencil hardness and flexural performance.

1: base film
2: buffer layer
3: hard coat layer

Claims (2)

A transparent base film,
A buffer layer laminated on at least one side of the transparent base film,
Laminated on the buffer layer and provided with a hard coat layer formed of an ionizing radiation curable resin,
The buffer layer is configured to absorb a stress acting on the hard coat layer by bending,
The film thickness of the hard coat layer is 50 to 250 µm,
The thickness of the buffer layer is 5 to 75 μm,
The cover film, wherein the thickness of the buffer layer is 3 to 50% relative to the thickness of the hard coat layer. The method of claim 1,
The buffer layer,
A cover film having a shear storage modulus of 1.0 × 10 ⁵ Pa or less at 1 Hz and 25°C.

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