KR20180138172A - Cover film - Google Patents

Abstract

Provided is a cover film for a bendable display, which satisfies both flex resistance and scratch resistance. The cover film for the bendable display comprises: a transparent base film; and a hard coat layer formed on at least one surface of the transparent base film. The hard coat layer is formed of an ionizing radiation curable resin, and has a thickness less than or equal to 2 μm.

Description

Cover Film {COVER FILM}

The present invention relates to a cover film.

In recent years, various cover films for protecting the surface of a display such as a smart phone have been proposed. For example, Patent Documents 1 and 2 propose a film substrate and a cover film having a hard coat layer formed on the surface thereof.

Japanese Patent Application Laid-Open No. 2008-133352 Japanese Patent Publication No. 6010992

However, recently, a curved display in which the surface of the display is curved (or curved) has been proposed. In such a display, since the cover film disposed on the surface also bends, the cover film is required to have bending resistance. That is, when the cover film is bent, it is particularly necessary that the hard coat layer does not crack. It is also necessary that the cover film is required to have scratch resistance and that it is not easily scratched on the surface. However, the hard coat films described in Patent Documents 1 and 2 did not have sufficient performance to satisfy these requirements. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a cover film for bending display that satisfies both bending resistance and scratch resistance.

Item 1. A cover film for bending display,

A transparent base film,

And a hard coat layer formed on at least one surface of the transparent base film,

The hard coat layer is formed of an ionizing radiation curable resin,

Wherein the hard coat layer has a thickness of 2 占 퐉 or less.

Item 2. A cover film for bending display,

A transparent base film,

And a hard coat layer formed on at least one surface of the transparent base film,

Wherein the base film has a thickness of 25 to 300 탆,

The hard coat layer is formed of an ionizing radiation curable resin,

Wherein the hard coat layer has a thickness of 0.5 to 1.0 mu m,

The hardness of the hard coat layer is 500 N / mm < 2 > or more,

Wherein the hardness of the hard coat layer relative to the matness hardness of the base film is 0.8 to 2.6.

Item 3. A cover film for a bend display,

A transparent base film,

And a hard coat layer formed on at least one surface of the transparent base film,

Wherein the base film has a thickness of 25 to 300 탆,

The hard coat layer is formed of an ionizing radiation curable resin,

Wherein the hard coat layer has a thickness of 2.0 占 퐉 or less,

The hardness of the hard coat layer is 500 N / mm < 2 > or more,

Wherein the hardness of the hard coat layer relative to the matness hardness of the base film is 0.8 to 2.6.

Item 4. The cover film according to any one of Items 1 to 3, wherein the hard coat layer contains a fluorine-based additive.

Item 5: The hard coat layer is formed by any one of Items 1 to 4, wherein a minimum diameter of a mandrel having cracks in the hard coat layer is less than 6 mm by a cylindrical mandrel method specified in JIS 5006-5-1 ≪ / RTI >

Item 6. The cover film according to any one of Items 1 to 5, wherein the hard coat layer is free from scratches when the steel wool # 0000 is subjected to a round trip of 3 cm / sec under a load of 60 gf / .

According to the cover film of the present invention, both bending resistance and scratch resistance can be satisfied.

Hereinafter, one embodiment of the cover film according to the present invention will be described. A cover film according to the present invention comprises a transparent base film and a hard coat layer laminated on at least one side of the base film. Hereinafter, each member will be described in detail.

<1. Base film>

The base film according to the present invention can be formed of various transparent materials and can be formed of, for example, cellulose acylate, cycloolefin polymer, polycarbonate, acrylate polymer, polyester, polyimide and the like have. Particularly, polyimide is preferable because it is resistant to bending and does not leave marks even when bent. In addition, various additives may be added to the base film, if necessary. For example, various additives such as a plasticizer, an antistatic agent, and an ultraviolet absorber may be added.

The thickness of the base film is preferably, for example, 25 占 퐉 or more and 300 占 퐉 or less, more preferably 75 占 퐉 or more and 250 占 퐉 or less. If the thickness is less than 25 mu m, sufficient scratch resistance can not be obtained on the surface of the hard coat layer, and if it is more than 300 mu m, it becomes difficult to obtain sufficient bending durability.

The base film preferably has a hardness of 200 to 600 N / mm 2 in a matence hardness test, more preferably a hardness of 250 to 500 N / mm 2, and a hardness of 300 to 450 N / Is particularly preferable. As a result, scratch resistance is improved.

The latency of the latent heat can be measured with a dynamic ultra micro hardness tester DUH-211 (Shimadzu Corporation). A triangular indenter at an inter-angle (angle of corner) of 115 degrees can be used as an indenter, and measurement can be performed under conditions of a press-in depth of 0.25 mu m and a load speed of 0.15 mN / sec. The specific matness hardness is a value calculated by the following equation.

Do tens hardness [N / ㎟] = load [μN] / (24.5 × (maximum depth hmax (㎛) ²⁾

<2. Hard coat layer>

Next, the hard coat layer will be described. The hard coat layer is obtained by curing a hard coat layer-forming resin composition containing an ionizing radiation curable resin, a photopolymerization initiator, and the like. In this composition, if necessary, additives described later may be blended.

<2-1. Ionizing radiation curable resin>

The ionizing radiation-curable resin is a compound containing a compound having radical polymerizing property that undergoes macromolecularization or crosslinking reaction by ionizing radiation (ultraviolet ray or electron beam), and includes, for example, a compound containing at least one ethylenic unsaturated bond in the structural unit , Or a mixture thereof.

Examples of the monofunctional compound having one unsaturated bond include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, n-butyl (meth) (Meth) acrylate, cyclohexyl (meth) acrylate, and the like.

Examples of the bifunctional compound containing two unsaturated bonds include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, butanediol di (meth) acrylate, hexanediol di (Meth) acrylate, diethylene glycol di (meth) acrylate, nonylene diol (meth) acrylate, ethoxylated hexanediol di (meth) acrylate, propoxylated hexanediol di Acrylates such as di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, ethoxylated neopentyl glycol di Di (meth) acrylates such as propylene glycol di (meth) acrylate and hydroxypivalic acid neopentyl glycol di (meth) acrylate.

Examples of polyfunctional compounds containing three or more unsaturated bonds include trimethylolpropane tri (meth) acrylate, ethoxylated trimethylolpropane tri (meth) acrylate, propoxylated trimethylolpropane tri Tri (meth) acrylate such as trimethylolpropane tri (meth) acrylate, tris 2-hydroxyethyl isocyanurate tri (meth) acrylate and glycerin tri (meth) acrylate, pentaerythritol tri (Meth) acrylate compounds such as trimethylolpropane tri (meth) acrylate and ditrimethylolpropane tri (meth) acrylate, trifunctional (meth) acrylate compounds such as pentaerythritol tetra Acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, ditrimethylolpropane penta (meth) acrylate, (Meth) acrylate compounds such as dipentaerythritol hexa (meth) acrylate and ditrimethylolpropane hexa (meth) acrylate, and polyfunctional (meth) acrylate compounds in which some of these (meth) (Meth) acrylate compounds such as polyfunctional (meth) acrylate compounds substituted with caprolactone.

In addition, a urethane resin may be mixed with the (meth) acrylate compound. As the urethane-based resin, for example, a urethane (meth) acrylate-based resin can be used. Specific examples of the urethane (meth) acrylate compound include 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. Can be used.

The molecular weight of the urethane resin is preferably from 1,000 to 10,000, more preferably from 2,000 to 5,000. As a method of measuring the molecular weight, a GPC method can be used.

<2-2. Photopolymerization initiator>

Examples of the polymerization initiator include benzylmethyl ketalization such as 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy- Methyl-1- [4- (methylthio) phenyl] -2-morpholinopropane-1-one, 2-benzyl-2-dimethylamino- - (4-morpholinophenyl) butanone-1, bis (2, 6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide, and other bisacylphosphine oxides , 2,2'-bis (o-chlorophenyl) -4,4 ', 5,5'-tetraphenyl-1,1'-biimidazole, bis (2,4,5-triphenyl) N-aryl glycines such as bis-imidazoles and N-phenylglycine, organic azides such as 4,4'-diazedicone, and 3,3 ', 4,4'-tetra (tert-butylperoxycar And organic peroxides such as benzophenone, as described in J. Photochem. Sci. Technol., 2, 283 (1987). And the like.

Specific examples thereof include iron complexes, trihalogenomethyl-substituted S-triazine, sulfonium salts, diazonium salts, phosphonium salts, selenonium salts, arsonium salts and iodonium salts. As the iodonium salt, Macromolecules, 10, 1307 (1977). (P-anisyl) iodonium, bis (m-nitrophenyl) iodonium, bis (p-tert-butylphenyl) iodonium, Bromide, or a boron fluoride, a hexafluorophosphate salt, a hexafluoroarsenate salt, an aromatic sulfonic acid salt or the like, or a diphenylphenazylsulfonium (n-hexafluorophosphate) salt or an iodonium salt such as bis (p- Butyl) triphenylborate, and the like.

<2-3. Additives>

Additives may be added to the resin composition for forming a hard coat layer, if necessary. For example, silicone-based or fluorine-based additives (for example, leveling agents) that impart leveling, surface slip property, low water contact arousal, and the like can be given. By blending such an additive, the scratch resistance of the surface of the hard coat layer can be improved. In the case of using ultraviolet rays at the time of photopolymerization, the curing inhibition of the resin by oxygen can be lowered by bleeding to the air interface of the above-mentioned additive. Therefore, an effective curing degree can be obtained even under a low irradiation intensity condition. The blending amount of these additives may be 0.01 to 0.5 parts by weight based on 100 parts by weight of the hard coat layer-forming resin composition.

<3. Physical Properties of Hard Coat Layer>

The thickness of the hard coat layer is preferably greater than 0.25 μm, less than 3.0 μm, more preferably 0.5 μm or more and 1.5 μm or less, and more preferably 0.75 μm or more and 1.25 μm or less. This is because if it is 0.25 탆 or less, sufficient scratch resistance performance can not be obtained, and if it is 3.0 탆 or more, it is not preferable from the viewpoint of flexibility.

The hard coat layer preferably has a hardness of 500 N / mm &lt; 2 &gt; or more, more preferably 650 N / mm &lt; 2 &gt; or more, and particularly preferably 700 N / As a result, scratch resistance is improved. On the other hand, the hardness of the hard coat layer is preferably 300 N / mm 2 or more. This also improves scratch resistance. The matence hardness can be measured by the above-described method.

In order to exhibit a high surface hardness even when the film thickness of the hard coat layer is thin, the hard coat layer needs to be equivalent to the matten hardness of the base film. From this viewpoint, the ratio of the matene hardness (the hardness of the matte of the hard coat / the hardness of the matene of the base film) is preferably 0.8 to 2.6, more preferably 1.0 to 2.5, still more preferably 1.2 to 2.4 Do.

The cover film formed by the film base material and the hard coat layer as described above was bent based on a cylindrical mandrel method (JIS K 5600-5-1), and then cracked in the hard coat layer in a cylinder having a diameter of 6 mm or more It is preferable not to occur.

<4. Method of producing cover film>

The method for producing the cover film according to the present invention is not particularly limited. For example, a resin composition for forming a hard coat layer is applied to the base film, which is then dried and then cured by photopolymerization, Can be obtained.

As a method of applying the resin composition for forming a hard coat layer to the base film, a known method such as a roll coater, a reverse roll coater, a gravure coater, a knife coater, or a bar coater can be employed.

The method of drying the coated resin composition for hard coat layer formation is not particularly limited. For example, the base film coated with the resin composition for hard coat layer formation may be passed through a dryer. The drying temperature at this time is preferably, for example, 40 to 100 ° C.

In order to cure the coating film, ultraviolet rays are preferably used as the ionizing radiation source, and a light source 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 or a xenon arc can be used.

<5. Features>

According to the cover film of the present embodiment, since the thickness of the hard coat layer is 2.5 占 퐉 or less, bending durability can be improved. That is, even when bent, it is possible to prevent cracks from being generated in the hard coat layer. Therefore, it can be preferably used as a cover film for bending display.

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 &gt;

Hereinafter, the production of a cover film related to Examples 1 to 3 and Comparative Examples 1 and 2 will be described. Examples 1 to 3 and Comparative Examples 1 and 2 have the same structure except that the thickness of the hard coat layer is different.

First, a PET film (U483, manufactured by Toray Industries, Inc.) having a thickness of 50 mu m was prepared as a base film. Next, a resin composition for forming a hard coat layer was prepared by mixing 100 parts by weight of a hard coat paint (Beam set 907 manufactured by Arakawa Chemical Co., Ltd.) and 1 part by weight of a fluorine-based additive (TEGO rad 2300 manufactured by Evonik Industries, . Then, the resin composition for forming a hard coat layer was coated on one side of the base film using a wire bar coater so as to have the following thickness. Thereafter, the resin composition for forming a hard coat layer was dried at 80 DEG C for 2 to 5 minutes by heat treatment, and then cured at a cumulative light amount of 200 mJ / cm &lt; 2 &gt; using a UV irradiator (Heraeus Co., .

The hardness hardness of the hard coat layer was 770 N / mm 2. As for the hardness of the martens, a hard coat layer was formed by applying a resin composition for forming a hard coat layer having a thickness of 10 mu m on a glass plate, and then the hardness of the martens was measured. Since the composition of the hard coat layer is the same in the examples and the comparative examples, the matences of the examples and the comparative examples are all the same.

<2. Flexibility Evaluation Test>

From the thus prepared examples and comparative examples, small pieces of 2 x 10 cm were cut out using a laser cut device (Spirit GX 30W manufactured by GCC), and based on the cylindrical mandrel method (JIS K 5600-5-1) After bending, whether or not a crack occurred in the hard coat layer was visually observed. The diameters of the cylinders used were 2 mm, 3 mm, 4 mm, 5 mm, 6 mm and 10 mm. A and no occurrence of cracks in the hard coat layer were A and B, respectively.

<3. Scratch resistance test>

Steel wool # 0000 was placed on the surfaces of the hard coat layers of Examples and Comparative Examples so that a load of 60 gf / cm 2 was applied, and the wafers were subjected to one round trip at a speed of 3 cm / sec. This was designated Test 1. Thereafter, the presence or absence of scratches at the point where the steel wool was reciprocated was visually confirmed. A and B were determined to have no scratches. Test 2, in which the test conditions were changed, was also performed. In Test 2, Steel Wool # 0000 was placed on the surfaces of the hard coat layers of Examples and Comparative Examples so that a load of 600 gf / cm 2 was applied, and one round trip was performed at a speed of 6 cm / sec. Then, as in Test 1, the presence or absence of scratches was visually confirmed and evaluated. The results are as follows.

<4. Consideration>

As described above, in the flex resistance evaluation test, no cracks were generated in the hard coat layer in the tests using the cylinders having diameters of 6 mm or more in all of the examples. Therefore, it can be seen that the cover film related to the embodiment can be preferably used also in a curved display having a curved surface with a small radius of curvature. Particularly, in Examples 2 and 3, no crack occurred in the hard coat layer even in the test using a cylinder having a diameter of 2 mm. Therefore, it was found that the bending performance was improved when the thickness of the hard coat layer was small.

In Test 1 of the scratch resistance test, no scratches were found in all of the examples. On the other hand, in the comparative example in which the thickness of the hard coat layer was small and 0.25 탆, scratches were generated. Thus, it was found that the embodiment in which the thickness of the hard coat layer is 0.5 to 2.0 占 퐉 is a cover film having both bending resistance and scratch resistance. In Test 2, which is a more severe condition, no scratches were found in Examples 1 and 2. It is preferable to use the third embodiment for the surface protection application of the device which is assumed to be used in the outdoor, etc. where dust or sand is likely to adhere.

Claims (5)

A cover film for bending display,
A transparent base film,
And a hard coat layer formed on at least one surface of the transparent base film,
Wherein the base film has a thickness of 25 to 300 탆,
The hard coat layer is formed of an ionizing radiation curable resin,
Wherein the hard coat layer has a thickness of 0.5 to 1.0 mu m,
The hardness of the hard coat layer is 500 N / mm &lt; 2 &gt; or more,
Wherein the hardness of the hard coat layer relative to the matness hardness of the base film is 0.8 to 2.6. A cover film for bending display,
A transparent base film,
And a hard coat layer formed on at least one surface of the transparent base film,
Wherein the base film has a thickness of 25 to 300 탆,
The hard coat layer is formed of an ionizing radiation curable resin,
Wherein the hard coat layer has a thickness of 2.0 占 퐉 or less,
The hardness of the hard coat layer is 500 N / mm &lt; 2 &gt; or more,
Wherein the hardness of the hard coat layer relative to the matness hardness of the base film is 0.8 to 2.6. 3. The method according to claim 1 or 2,
Wherein the hard coat layer contains a fluorine-based additive. 4. The method according to any one of claims 1 to 3,
Wherein the hard coat layer has a minimum diameter of mandrels in which cracks are generated in the hard coat layer by a cylindrical mandrel method specified in JIS 5006-5-1 of less than 6 mm. 5. The method according to any one of claims 1 to 4,
Wherein the hard coat layer is free from scratches when a steel wool # 0000 is subjected to a reciprocation of 1 cm / sec at a load of 60 gf / cm &lt; 2 &gt;.