Cover film and image display device including the same

Abstract

The cover film according to the present disclosure includes a substrate layer; and a surface layer chemically bonded to the substrate layer, wherein the surface layer includes a polyurethane resin X1 containing urethane bonds and urea bonds and a polyorganosiloxane group in the molecule, and the polyurethane resin X1 is a reaction product of a non-yellowing isocyanate component B1 and an active hydrogen component A1 including compound a1-1; the substrate layer includes a polyurethane resin X2 having a urethane bond in the molecule, and the polyurethane resin X2 is a reaction product of a non-yellowing isocyanate component B2 and an active hydrogen component A2 that does not include the compound a1-1, and has a certain crosslinking point concentration and a certain elastic recovery rate.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Japanese Patent Application No. 2022-088915 filed in the Japan Intellectual Property Office on May 31, 2022, which is hereby incorporated by reference herein in its entirety. Technical Field

[0003] The present disclosure relates to a cover film and an image display device including the cover film. Background Art

[0004] In addition to image display devices having flexibility (bendability, foldability, or rollability), image display devices showing stretchability are recently being developed as portable image display devices such as smartphones, tablet computers, and the like (Patent Documents 1, 2, and the like).

[0005] This type of image display device has a cover window configured to protect an image display element such as an organic EL display, an LED display, a liquid crystal display, and the like. In recent years, many portable image display devices have been using a cover window comprising a glass substrate. However, since the glass substrate is easily broken by external impact and is not flexible, the glass substrate is not suitable for a flexible image display device (hereinafter also referred to as a "flexible display") or a stretchable image display device (hereinafter also referred to as a "stretchable display"). Therefore, research is underway to replace the glass substrate with a resin film (i.e., a cover film) instead of a glass substrate, and image display devices using a transparent polyimide-based film as a cover film are already known.

[0006] When using a cover film as a surface protection material for an image display device, in addition to transparency, the cover film is also required to have appropriate lubricity (scratch resistance) and mechanical properties (hardness). In addition, when the cover film has a smaller radius of curvature in a flexible display, it is desired that the cover film has greater flexibility. At the same time, when the surface protection material is used as a cover film for a stretchable display, it is also necessary to have excellent stretchability. Since traditional polyimide-based films do not have stretchability, it is difficult to apply polyimide-based films to stretchable displays. For this challenge, for example, Patent Document 3 discloses the use of an elastomer that exhibits stretchability as a cover film.

[0007] However, there is a problem with the stretchable cover film, that is, it does not have sufficient scratch resistance. In order to improve the scratch resistance, it is known to apply a hard coating with a lubricating material, but even by this method, it is impossible to meet the scratch resistance required for a flexible display or a stretchable display. Another problem is that the film will break when the image display device is stretched. In addition, there are new problems in the technology for coating the surface of such a film, such as coating (electroplating) or close adhesion to the film used as a substrate.

[0008] [Related Literature]

[0009] [Patent Document]

[0010] Patent Document 1: Japanese Patent Laid-Open No. 2015-152922

[0011] Patent Document 2: Japanese Patent Unexamined Publication No. 2020-102065

[0012] Patent Document 3: Japanese Patent Unexamined Publication No. 2020-042981 Summary of the Invention

[0013] Accordingly, embodiments of the present disclosure are directed to a cover film and an image display device including the same that substantially obviate one or more problems associated with limitations and disadvantages of the related art.

[0014] An object of the present disclosure is to provide a cover film having excellent anti-scratch performance, mechanical properties, and optical properties and having excellent stretchability, and an image display device including the cover film.

[0015] Additional features and aspects will be set forth in the following description, some of which will be apparent from the description, or may be learned by practice of the disclosure provided herein. Other features and aspects of the present disclosure may be realized and attained by the structure particularly pointed out in the written description or derived therefrom, and in the claims and drawings of the present disclosure.

[0016] To achieve these and other advantages according to the purposes of embodiments of the present disclosure, as described herein, one aspect of the present disclosure is a cover film comprising: a substrate layer; and a surface layer mounted on at least one surface of the substrate layer; wherein the substrate layer and the surface layer are chemically bonded to each other; wherein the surface layer comprises a polyurethane resin X1 having urethane units and urea units and polyorganosiloxane groups, wherein the polyurethane resin X1 is a reaction product of a non-yellowing-type isocyanate component B1 and an active hydrogen component A1; wherein the active hydrogen component A1 comprises a compound a1-1 containing a polyorganosiloxane group and an active hydrogen group, and the compound a1-1 reacts with the active hydrogen component A1 and the non-yellowing-type The ratio of the total amount (100 wt%) of the isocyanate component B1 is less than or equal to 4.0 wt%; wherein the substrate layer includes a polyurethane resin X2 having a urethane unit, wherein the polyurethane resin X2 is a reaction product of a non-yellowing isocyanate component B2 and an active hydrogen component A2 excluding the compound a1-1; wherein the crosslinking point concentration of the polyurethane resin X2 calculated from the following equation 1 is greater than or equal to 0.4 mmol / g, [Equation 1] Crosslinking point concentration (mmol / g) = (F-2) × (mmol of trifunctional or higher functional group constituent monomers in 1 g of the polyurethane resin), wherein in the equation 1, F represents the number of functional groups in the trifunctional or higher functional group constituent monomer, and wherein the elastic recovery rate of the covering film when stretched by 100% is 80% to 100%.

[0017] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the inventive concepts as claimed. DETAILED DESCRIPTION

[0018] Hereinafter, exemplary embodiments of the present disclosure will be described in detail. The present disclosure is not limited to the following embodiments and can be implemented in various forms without departing from the scope of the present disclosure.

[0019] In this specification, the symbol "~" represents the term "to".

[0020] [Cover film]

[0021] The cover film according to this embodiment includes a substrate layer and a surface layer disposed (installed) on at least one surface of the substrate layer. The substrate layer and the surface layer are chemically bonded to each other. The surface layer includes a polyurethane resin X1 (e.g., a first polyurethane resin) having a urethane bond (unit), a urea bond, and a polyorganosiloxane group in the molecule, and the polyurethane resin X1 is a reaction product of a non-yellowing isocyanate component B1 (e.g., a first non-yellowing isocyanate component) and an active hydrogen component A1 (e.g., a first active hydrogen component). The active hydrogen component A1 includes a compound a1-1 containing a polyorganosiloxane group and an active hydrogen group, and the ratio of the compound a1-1 to the total of the active hydrogen component A1 and the non-yellowing isocyanate component B1 (100% by weight) is 4.0% by weight or less. The substrate layer includes a polyurethane resin X2 (e.g., a second polyurethane resin) having a urethane bond in the molecule. The polyurethane resin X2 is a reaction product of a non-yellowing isocyanate component B2 (e.g., a second non-yellowing isocyanate component) and an active hydrogen component A2 (e.g., a second active hydrogen component), wherein the active hydrogen component A2 does not include compound a1-1. The crosslinking point concentration of the polyurethane resin X2, as calculated from the following equation 1, is 0.4 mmol / g or higher, and the elastic recovery rate of the cover film at 100% stretching ranges from 80% to 100%.

[0022] [Equation 1]

[0023] Cross-linking point concentration (mmol / g) = (F-2) × (mmol of trifunctional or more functional group-constituting monomers in 1g of polyurethane resin)

[0024] The cover film according to the present embodiment has excellent scratch resistance, mechanical properties, and optical properties, and also has excellent stretchability. Hereinafter, the cover film according to the present disclosure will be described in detail.

[0025] <Surface layer>

[0026] The covering film according to the present embodiment comprises a substrate layer and a surface layer provided on at least one surface of the substrate layer. The surface layer comprises a polyurethane resin X1 having a urethane bond, a urea bond and a polyorganosiloxane group in its molecules. The surface layer will be chemically bonded to the substrate layer as described below. Here, the term "chemical bonding" refers to a state in which the components constituting the surface layer and the components constituting the substrate layer chemically react with each other, causing them to be chemically connected to each other at their interface. Since the covering film has such a structure, when stress is applied to the covering film, delamination between the layers is difficult. Therefore, the scratch resistance and mechanical properties are improved. Moreover, when the surface layer comprises a polyurethane resin X1 containing a urethane bond and a urea bond in its molecules, the scratch resistance of the surface layer can be improved and appropriate hardness can also be exhibited.

[0027] (Polyurethane resin x1)

[0028] The polyurethane resin X1 included in the surface layer is a reaction product of a non-yellowing isocyanate component B1 (hereinafter referred to as component B1) and an active hydrogen component A1 (hereinafter referred to as component A1). In this specification, "non-yellowing-type isocyanate" and "non-yellowing isocyanate" refer to isocyanate compounds that do not include an aromatic component.

[0029] Active hydrogen component A1 includes compound a1-1 containing a polyorganosiloxane group and an active hydrogen group. The ratio of compound a1-1 to the total of component A1 and component B1 (100% by weight) is 4.0% by weight or less. When the surface layer includes polyurethane resin X1, scratch resistance and mechanical properties are improved.

[0030] [Active hydrogen component A1]

[0031] The active hydrogen component A1 is an essential component, which includes a compound a1-1 containing a polyorganosiloxane group and an active hydrogen group (hereinafter referred to as compound a1-1).

[0032] <Compound a1-1>

[0033] Compound a1-1 is a compound having a polyorganosiloxane group and an active hydrogen group. When the reaction product of component B1 and component A1 including compound a1-1 is used in the surface layer, the scratch resistance of the surface layer is enhanced.

[0034] The active hydrogen group included in compound a1-1 may include at least one active hydrogen group selected from a hydroxyl group, an amino group, and a carboxyl group, preferably an amino group. When compound a1-1 contains an amino group having an active hydrogen group, a polyurethane resin X1 containing a urea bond in the molecule can be easily obtained. Furthermore, the urea bond in polyurethane resin X1 can be formed by reacting component B1 with a component included in component A1 other than compound a1-1.

[0035] The polyorganosiloxane group of compound a1-1 may have a structure represented by the following formula (I).

[0036] [Formula (I)]

[0037]

[0038] In formula (I), R 1 to R 6 Each is independently selected from the group consisting of C1 to C6 linear alkyl groups and C1 to C6 branched alkyl groups, and n is an integer from 1 to 100.

[0039] In one aspect of the present disclosure, R 1 to R 6 Each of the C1 to C3 straight-chain alkyl groups may be a C1 to C3 straight-chain alkyl group, preferably a methyl group, to improve the mechanical properties of the surface layer. Furthermore, n may be an integer from 10 to 70, preferably an integer from 15 to 50, to improve the mechanical properties of the surface layer and the haze value of the cover film. The "C1 to C10 straight-chain alkyl group" may be a methyl group, an ethyl group, or an n-propyl group.

[0040] Compound a1-1 may have a polyorganosiloxane group represented by formula (I) and may also have an active hydrogen group at one or more side ends and side chains of the molecular chain. Furthermore, compound a1-1 may more preferably have a hydroxyl group or an amino group at one or more of one or both side ends of the molecular chain. Commercially available products may be used as compound a1-1.

[0041] For example, commercially available products of compound a1-1 having amino groups at both side ends thereof may include at least one selected from the group consisting of: products of Shin-Etsu Chemical Co., Ltd., such as “KF-8010” (functional group equivalent: 430 g / mol), “X-22-161A” (functional group equivalent: 800 g / mol), “X-22-161B” (functional group equivalent: 1500 g / mol), “KF-8012” (functional group equivalent: 2200 g / mol), “KF-8008” (functional group equivalent: 5700 g / mol), “X-22-9409” (functional group equivalent: 700 g / mol), and “X-22-1660B-3” (functional group equivalent: 2200 g / mol) (all trade names); and Toray Dow Corning Co., Ltd. Co., Ltd.), such as "BY-16-853U" (functional group equivalent: 460 g / mol), "BY-16-853" (functional group equivalent: 650 g / mol), and "BY-16-853B" (functional group equivalent: 2200 g / mol) (all trade names). These commercially available products can be used alone or in combination of two or more.

[0042] For example, commercially available products of compound a1-1 having a hydroxyl group at both side ends thereof may include at least one selected from the group consisting of: products of Shin-Etsu Chemical Co., Ltd., such as "KF-6001" (functional group equivalent: 900 g / mol), "KF-6002" (functional group equivalent: 1600 g / mol), "KF-6003" (functional group equivalent: 2550 g / mol), and "X-22-4952" (functional group equivalent: 1100 g / mol) (all trade names); and products of Toray Dow Corning Co., Ltd., such as "SF8427" (functional group equivalent: 930 g / mol) (trade name). These commercially available products may be used alone or in combination of two or more.

[0043] For example, commercially available products of compound a1-1 having a hydroxyl group at one side end may include at least one selected from the group consisting of: products of Shin-Etsu Chemical Co., Ltd., such as "X-22-170BX" (functional group equivalent: 2,800 g / mol), "X-22-170DX" (functional group equivalent: 4670 g / mol), "X-22-176DX" (functional group equivalent: 1600 g / mol), and "X-22-176F" (functional group equivalent: 6300 g / mol) (all trade names). These commercially available products may be used alone or in combination of two or more.

[0044] Among the commercially available products, X-22-161A, BY-16-853U, and KF-8012 are preferably used as compound a1-1, and BY-16-853U and KF-8012 are more preferably used as compound a1-1.

[0045] The proportion of compound a1-1 in polyurethane resin X1 is less than or equal to 4.0% by weight, preferably in the range of 1.0 to 3.0% by weight, and more preferably in the range of 1.5 to 2.0% by weight, relative to the total of component A1 and component B1 (100% by weight). When the proportion of compound a1-1 in polyurethane resin X1 is less than or equal to 4.0% by weight, the cover film may not have both scratch resistance and optical properties.

[0046] In the conventional cover film described in patent document 3, the technology of applying hard coating is adopted to improve the anti-scratch performance of film.The coating of hard coating improves the hardness of film, strengthens the anti-scratch performance of film, but makes the stretchability of film worse.Therefore, it is difficult to apply conventional cover film to stretchable display.The inventors of the present disclosure have studied the lubricity rather than hardness of cover film, and found that by mixing a predetermined amount of compound a1-1 into the surface layer of cover film, a resin with slightly high hardness and excellent lubricity and stretchability is obtained. In addition, they also found that by using a resin with a high crosslinking point concentration (as described below) to the substrate layer and providing a structure in which the substrate layer and the surface layer are chemically bonded to each other to improve the lubricity of the surface layer and the restoring force of the substrate layer, the pencil hardness is enhanced.

[0047] <Other active hydrogen components a1-2>

[0048] In addition to compound a1-1, component A1 may further include an active hydrogen component a1-2 (hereinafter referred to as component a1-2). For example, component a1-2 may include at least one selected from a polymer polyol, a chain extender, and a reaction terminator, as disclosed in International Publication No. 2021 / 002342. Preferably, component a1-2 may be a polymer polyol disclosed in International Publication No. 2021 / 002342, more preferably a polycarbonate polyol, to improve scratch resistance. In addition, component a1-2 may further include at least one selected from water, 1,4-diol, such as 1,4-butanediol, and the like as a chain extender. In addition, component a1-2 may further include diethanolamine and the like as a reaction terminator.

[0049] The proportion of the polymer polyol in component a1-2 can be in the range of 50 to 100 wt %, or in the range of 70 to 100 wt %, relative to the total mass of component a1-2. When the proportion of the polymer polyol is within this range, the scratch resistance can be greatly improved.

[0050] The content of the component a1-2 in the component A1 may be adjusted so that the sum of the compound a1-1 and the component a1-2 becomes 100% by weight relative to the total weight of the component A1.

[0051] [Non-yellowing isocyanate component B1]

[0052] The non-yellowing isocyanate component B1 is an isocyanate compound that does not contain an aromatic component. Component B1 reacts with component A1 to provide a urethane bond and a urea bond. Component B1 is a polyisocyanate compound having at least two isocyanate groups and does not contain an aromatic component. Specifically, component B1 is at least one isocyanate compound selected from aliphatic polyisocyanate compounds and alicyclic polyisocyanate compounds.

[0053] For example, the aliphatic polyisocyanate compound may be: an aliphatic diisocyanate compound, for example, ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (hereinafter referred to as "HDI"), dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanate-methylhexanoate, bis(2-isocyanate-ethyl)fumarate, bis(2-isocyanate-ethyl)carbonate or 2-isocyanate-ethyl-2,6-diisocyanate; an aliphatic triisocyanate compound, for example, 1,6,11-undecane triisocyanate; or a trifunctional or higher-functional aliphatic polyisocyanate compound, for example, a urethane containing the above aliphatic diisocyanate compound or the above aliphatic triisocyanate compound. In one aspect of the present disclosure, the aliphatic polyisocyanate compound may be an allophanate-modified HDI (e.g., product name: "CORONATE (registered trademark) -2793", available from Tosoh Corporation), an isocyanurate-modified HDI (e.g., product name: "DURANATE (registered trademark) TLA-100", available from Asahi Kasei Corporation), or a biuret-modified HDI (e.g., product name: "DURANATE 24A-100", available from Asahi Kasei Corporation). The aliphatic polyisocyanate compound may be used alone or in combination of two or more of the aliphatic polyisocyanate compounds.

[0054] For example, the alicyclic polyisocyanate compound may be an alicyclic diisocyanate compound such as isophorone diisocyanate (hereinafter referred to as "IPDI"), 4,4'-dicyclohexylmethane diisocyanate (hereinafter referred to as "hydrogenated MDI"), cyclohexene diisocyanate, methylcyclohexene diisocyanate, bis(2-isocyanate-ethyl)-4-cyclohexene-1,2-dicarboxylate, 2,5- or 2,6-norbornene diisocyanate, and the like. The alicyclic polyisocyanate compound may be used alone or in combination of two or more of the alicyclic polyisocyanate compounds.

[0055] The non-yellowing isocyanate component B1 preferably includes a trifunctional or higher functional isocyanate compound B1 (hereinafter referred to as compound b1), more preferably includes an allophanate-modified HDI or a biuret-modified HDI, and preferably further includes an allophanate-modified HDI. When component B1 includes compound b1, a surface layer with excellent heat resistance can be easily obtained. Therefore, it is easy to control the adhesion or bonding of the film in a flexible display or a stretchable display to which the cover film according to this embodiment is applied at high temperatures. In particular, when these displays are folded or rolled, it is easy to control the adhesion between the films.

[0056] The content of compound b1 in component B1 is preferably in the range of 0.5 to 10 wt %, more preferably in the range of 0.5 to 7.5 wt %, and further preferably in the range of 0.5 to 5.0 wt %, relative to the total mass of component B1.

[0057] As long as component B1 has the effects according to the present disclosure, the proportion of component B1 in the polyurethane resin X1 is not particularly limited. On the one hand, the molar ratio of the total amount of NCO groups in component B1 to the total amount of active hydrogen groups in component A1 (total amount of NCO groups / total amount of active hydrogen groups) is preferably in the range of 1.00 to 1.10, more preferably in the range of 1.0 to 1.05. When this molar ratio is in the range of 1.00 to 1.10, scratch resistance can be enhanced.

[0058] The crosslinking point concentration of polyurethane resin X1, calculated from the following equation 1, is preferably in the range of 0.02 to 0.10 mmol / g, more preferably in the range of 0.04 to 0.08 mmol / g. The crosslinking point concentration of polyurethane resin X1 may be lower than that of polyurethane resin X2. When the crosslinking point concentration is within this range, the scratch resistance is easily improved:

[0059] [Equation 1]

[0060] Cross-linking point concentration (mmol / g) = (F-2) × (mmol of trifunctional or more functional group-constituting monomers in 1g of polyurethane resin)

[0061] In Formula 1, F represents the number of functional groups in the trifunctional or higher functional group-constituting monomer.

[0062] The concentration of the sum of urethane and urea bonds in the polyurethane resin X1 is preferably in the range of 1.6 to 2.4 mmol / g, more preferably in the range of 1.8 to 2.2 mmol / g. When the concentration of the sum of urethane and urea bonds is within this range, scratch resistance is easily improved. Furthermore, the concentration of the sum of urethane and urea bonds in the polyurethane resin X1 can be calculated based on the raw material amounts of the active hydrogen component A1 and the non-yellowing isocyanate component B1.

[0063] (Method for preparing polyurethane resin X1)

[0064] The method for preparing the polyurethane resin X1 according to the present embodiment is not particularly limited and may be i) Method 1: After obtaining a urethane prepolymer using component A1, component B1, and optionally an organic solvent, a chain extender is reacted with the urethane prepolymer to obtain the polyurethane resin X1, or ii) Method 2: After jointly preparing component A1, component B1, and optionally an organic solvent in a batch-type reactor, they are reacted by heating to obtain the polyurethane resin X1.

[0065] For example, details of Method 1 and Method 2 include those described in International Publication No. 2021 / 002342.

[0066] The elastic recovery rate of the polyurethane resin X1 at 100% elongation, as measured by the method described later, is preferably in the range of 40 to 100%, more preferably in the range of 50 to 100%. When the elastic recovery rate of the polyurethane resin X1 at 100% elongation is within this range, the scratch resistance is easily improved.

[0067] (Other components C1)

[0068] In addition to the polyurethane resin X1, the surface layer may further include other components C1 (hereinafter referred to as component C1). For example, component C1 may include an environmental stabilizer (such as an antioxidant, an ultraviolet absorber or a light stabilizer), a plasticizer, an adsorbent, a filler, a release agent, a flame retardant, and the like. These materials may be used alone or in combination of two or more.

[0069] Among them, in order to easily control the deterioration of the cover film with the passage of time (discoloration and the like) and further improve the light resistance and heat resistance, it is preferable to include an environmental stabilizer as component C1.

[0070] As mentioned above, environmental stabilizers include antioxidants, ultraviolet absorbers, and light stabilizers.

[0071] Examples of antioxidants may include hindered phenol compounds, such as pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], or octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; phosphorus compounds, such as tris(2,4-di-t-butylphenyl)phosphite; phenyl)phosphite); sulfur compounds, for example, pentaerythrityl-tetrakis(3-laurylthiopropionate), pentaerythrityl-tetrakis(3-laurylthiopropionate), or dilauryl-3,3'-thiodipropionate. These materials can be used alone or in combination of two or more.

[0072] Examples of the ultraviolet absorber may include benzotriazole compounds, for example, 2-(3,5-di-tert-amyl-2-hydroxyphenyl)benzotriazole or 2-(5-methyl-2-hydroxyphenyl)benzotriazole.

[0073] Examples of the light stabilizer may include hindered amine compounds, for example, (bis-2,2,6,6-tetramethyl-4-piperidyl) sebacate.

[0074] The surface layer can include one or two or more of the above-mentioned environmental stabilizers. Relative to the gross mass of the resin composition constituting the surface layer, the content of the environmental stabilizer in the surface layer is preferably in the range of 0.5 to 5.0 weight %, more preferably in the range of 1.0 to 5.0 weight %, and further preferably in the range of 1.5 to 5.0 weight %. When the content of the environmental stabilizer in the surface layer is greater than or equal to 0.5 weight %, a covering film with less thermal degradation over time can be easily obtained. In addition, when the content of the environmental stabilizer in the surface layer is less than or equal to 5.0 weight %, the yellowing effect of the environmental stabilizer on the film can be suppressed, so that the covering film has excellent light resistance and heat resistance.

[0075] When the surface layer consists of the polyurethane resin X1 and the environmental stabilizer without containing the component C1, the content of the environmental stabilizer in the surface layer is a ratio relative to the sum of the polyurethane resin X1 and the environmental stabilizer (100 wt %).

[0076] The surface layer may further include one or more additives described in International Publication No. 2021 / 002342.

[0077] <Base Material Layer>

[0078] In the cover film according to this embodiment, the substrate layer includes a polyurethane resin X2 having urethane bonds in the molecule. The polyurethane resin X2 is a reaction product of a non-yellowing isocyanate component B2 and an active hydrogen component A2 that does not include compound a1-1. The polyurethane resin X2 has a crosslinking point concentration of 0.4 mmol / g or greater, as calculated from the following equation 1, and exhibits an elastic recovery rate at 100% stretching ranging from 80% to 100%. When the substrate layer includes this polyurethane resin X2 having an elastic recovery rate ranging from 80% to 100%, the substrate layer becomes a soft layer with high resilience. Consequently, the mechanical properties (particularly pencil hardness) of the cover film are improved.

[0079] (Polyurethane resin x2)

[0080] The polyurethane resin X2 included in the substrate layer is a reaction product of a non-yellowing isocyanate component B2 (hereinafter referred to as component B2) and an active hydrogen component A2 (hereinafter referred to as component A2) that does not contain compound a1-1. The crosslinking point concentration of the polyurethane resin X2, as calculated from the following equation 1, is greater than or equal to 0.4 mmol / g, preferably within the range of 0.4 to 0.6 mmol / g, and more preferably within the range of 0.4 to 0.5 mmol / g. When the crosslinking point concentration of the polyurethane resin X2 is greater than or equal to 0.4 mmol / g according to equation 1, the mechanical properties (particularly pencil hardness) of the cover film are improved:

[0081] [Equation 1]

[0082] Cross-linking point concentration (mmol / g) = (F-2) × (mmol of trifunctional or more functional group-constituting monomers in 1g of polyurethane resin)

[0083] In Formula 1, F represents the number of functional groups in the trifunctional or higher functional group-constituting monomer in the polyurethane resin X2.

[0084] [Active hydrogen component A2]

[0085] The active hydrogen component A2 does not include the compound a1-1, and includes a high molecular weight polyol a2-1 (hereinafter referred to as the component a2-1) as an essential component.

[0086] Component a2-1 includes a polyol having a number average molecular weight (Mn) of 500 or more, preferably 500 to 5,000, and more preferably 800 to 4,000. For example, International Publication No. 2021 / 002342 describes a high molecular weight polyol for high molecular weight polyol a2-1. Wherein, in terms of ease of adjusting the crosslinking point concentration in the polyurethane resin X2 to 0.4 mmol / g or higher, the high molecular weight polyol a2-1 preferably includes adding oxyalkylene to a polyvalent alcohol having a tetrafunctional group to an octafunctional group, for example, pentaerythritol, sorbitol, mannitol, sorbitan, diglycerol or dipentaerythritol, and more preferably includes adding oxyalkylene to a polyvalent alcohol having a hexafunctional group to an octafunctional group, for example, sorbitol, mannitol, sorbitan or dipentaerythritol. The high molecular weight polyol a2-1 can be used alone or in combination with two or more of the high molecular weight polyols.

[0087] In addition, polyether polyols may be included as the polymer polyol a2-1. For example, the polyether polyol may be a compound obtained by adding alkylene oxide to a polyol having a number average molecular weight (Mn) or a chemical formula weight of less than 500. The polyether polyols may be used alone or in combination of two or more.

[0088] In addition, for example, the alkylene oxide may be a C2 to C12 alkylene oxide, such as ethylene oxide, 1,2-propylene oxide, 1,3-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide or 2,3-butylene oxide, tetrahydrofuran, 3-methyltetrahydrofuran, styrene oxide, α-epoxy olefin or epichlorohydrin. Among them, ethylene oxide and 1,2-propylene oxide or 1,3-propylene oxide may be preferred in terms of scratch resistance.

[0089] In one aspect of the present disclosure, the polymer polyol a2-1 may be a polyol obtained by adding at least one alkylene oxide selected from ethylene oxide, 1,2-propylene oxide, and 1,3-propylene oxide to at least one polyvalent alcohol selected from sorbitol, mannitol, sorbitan, and dipentaerythritol.

[0090] In one aspect of the present disclosure, the polymer polyol a2-1 may include polytetramethyl ether glycol (PTMG) having an Mn of 500 to 2,500.

[0091] The proportion of component a2-1 in component A2 is preferably in the range of 70 to 100 wt %, more preferably in the range of 75 to 100 wt %, and even more preferably in the range of 75 to 90 wt %, relative to the total mass of component A2. When the proportion of high molecular weight polyol a2-1 is within this range, scratch resistance is easily improved.

[0092] Furthermore, in this specification, "Mn" may be, for example, measured by gel permeation chromatography under the following conditions.

[0093] Apparatus: Waters Alliance 2695 (commercially available from Waters)

[0094] Chromatographic column: Guardcolumn Super HL (1 column) and TSKgel SuperH2000, TSKgelSuperH3000, and TSKgel SuperH4000 (all commercially available from Tosoh Corporation)

[0095] Sample solution: 0.25 wt% THF solution

[0096] Solution injection volume: 10 μL

[0097] Flow rate: 0.6 mL / min

[0098] Measurement temperature: 40℃

[0099] Detection device: Refractive index detector

[0100] Reference material: Standard polyethylene glycol

[0101] <Other active hydrogen components a2-2>

[0102] In addition to component a2-1, component A2 may include an active hydrogen component a2-2 (hereinafter referred to as component a2-2). For example, component a2-2 may include at least one of the chain extenders and reaction terminators described in International Publication No. 2021 / 002342. Component A2 may include 1,4-butanediol or ethylene glycol, with 1,4-butanediol being preferred for its scratch resistance.

[0103] The proportion of 1,4-butanediol and / or ethylene glycol in component a2-2 can be in the range of 50 to 100 wt %, or in the range of 70 to 100 wt %, relative to the total mass of component a2-2. When the proportion of 1,4-butanediol and / or ethylene glycol is within this range, scratch resistance can be further enhanced.

[0104] [Non-yellowing isocyanate component B2]

[0105] Non-yellowing isocyanate component B2 is an isocyanate compound that does not include an aromatic component. Component B2 reacts with component A2 to form a urethane bond. The example of component B2 can include the polyisocyanates identical to component B1. With regard to scratch resistance, component B2 preferably includes HDI or IPDI. Relative to the gross mass of component B2, the content of HDI and isophorone diisocyanate (IPDI) is preferably in the range of 80 to 100 % by weight, more preferably in the range of 90 to 100 % by weight among the component B2.

[0106] As long as component B2 has the effects according to the present disclosure, the proportion of component B2 in the polyurethane resin X2 is not particularly limited. On the one hand, the molar ratio of the total amount of NCO groups of component B2 to the total amount of active hydrogen groups in component A2 (total molar amount of NCO groups of component B2 / total molar amount of active hydrogen groups in component A2) is preferably in the range of 1.00 to 1.10, more preferably in the range of 1.0 to 1.05. When this molar ratio is in the range of 1.00 to 1.10, scratch resistance can be enhanced.

[0107] (Method for preparing polyurethane resin X2)

[0108] The method for preparing the polyurethane resin X2 according to the present embodiment is not particularly limited, and the polyurethane resin X2 can be prepared in the same manner as the method described for the polyurethane resin X1, except that the component A2 and the component B2 are used.

[0109] The polyurethane resin X2 has an elastic recovery rate at 100% stretching of 80 to 100% as measured by the method described later. When the polyurethane resin X2 has an elastic recovery rate at 100% stretching of 80 to 100% within this range, a substrate layer having a high recovery force can be obtained, and the pencil hardness of the cover film can be increased.

[0110] In this embodiment, the elastic recovery rate at 100% stretching can be measured using the following method.

[0111] <Method for measuring elastic recovery at 100% stretch>

[0112] (1) A sheet with a film thickness of approximately 2 mm was prepared using polyurethane resin X1 or polyurethane resin X2. The sheet was cut into elongated rectangular specimens measuring 100 mm x 5 mm (width x length), and scales were displayed on the sheet so that the distance between scales was 50 mm.

[0113] (2) The specimen was placed in the fixture of an Instron tensile testing machine (product name: "Autograph", commercially available from Shimadzu Corporation), and stretched at a constant rate of 500 mm / min in an atmosphere of 25°C until the distance between the scales reached 100%, and immediately an operation was performed to return the distance between the scales to the distance before stretching.

[0114] (3) The stress (M1) at 50% stretching in the stretching process and the stress (M2) at 50% stretching in the return process when this operation is performed are measured to calculate the elastic recovery rate from the following equation 2.

[0115] [Equation 2]

[0116] Elastic recovery rate (%) = M2 / M1×100

[0117] (Other components (C2))

[0118] In addition to the polyurethane resin X2, the base material layer may include another component C2 (hereinafter referred to as component C2). For example, component C2 may include the same components as component C1 described above. However, it is preferable to include an environmental stabilizer as component C2 in order to easily control the deterioration of the cover film over time (discoloration and the like) and further improve light resistance and heat resistance.

[0119] The content of the environmental stabilizer in the substrate layer is preferably in the range of 0.5 to 5.0 wt %, more preferably in the range of 1.0 to 5.0 wt %, and further preferably in the range of 1.5 to 5.0 wt %, relative to the total mass of the resin composition constituting the substrate layer. When the content of the environmental stabilizer in the substrate layer is greater than or equal to 0.5 wt %, a covering film that is less susceptible to thermal degradation over time can be easily obtained. In addition, when the content of the environmental stabilizer in the substrate layer is less than or equal to 5.0 wt %, the yellowing effect of the environmental stabilizer on the film can be suppressed, so that the covering film has excellent light resistance and heat resistance. In addition, when the substrate layer is composed of the above-mentioned polyurethane resin X2 and the environmental stabilizer without containing component C2, the content of the environmental stabilizer in the substrate layer is the ratio relative to the sum of the polyurethane resin X2 and the environmental stabilizer (100 wt %).

[0120] In one aspect of the present disclosure, the total amount of component C1 and component C2 in the cover film may be in the range of 0.5 to 5.0 wt %, 1.0 to 5.0 wt %, or 1.5 to 5.0 wt %, relative to the total mass of the entire resin composition constituting the cover film. When the total amount of component C1 and component C2 included in the cover film is within this range, a cover film that is less susceptible to thermal degradation over time can be readily obtained.

[0121] [Method for producing cover film]

[0122] The method for preparing the covering film according to the present embodiment is not particularly limited. In a preferred embodiment, the covering film according to this embodiment can be, for example, prepared using the following method, the method comprising: preparing a prepolymer for polyurethane resin X1 and a prepolymer for polyurethane resin X2 (process (i)), coating (electroplating) the prepolymer for polyurethane resin X1 on a release film to form a surface layer with a predetermined film thickness (process (ii)), and coating the prepolymer for polyurethane resin X2 on the surface layer to form a substrate layer with a predetermined film thickness (process (iii)). Hereinafter, the preparation method including processes (i) to (iii) will be described.

[0123] <Step (i)>

[0124] The step (i) is a step of preparing a prepolymer for the polyurethane resin X1 and a prepolymer for the polyurethane resin X2.

[0125] The prepolymer for the polyurethane resin X1 is a compound having a hydroxyl group at its terminal and can be prepared by reacting component A1 including compound a1-1 and component B1 in an organic solvent as appropriate. The hydroxyl value of the prepolymer for the polyurethane resin X1 is preferably in the range of 2.5 to 10.0 mgKOH / g of the composition from which the solvent is removed.

[0126] The prepolymer for the polyurethane resin X2 is a compound having an isocyanate group at its terminal and can be prepared by reacting component A2 and component B2 in an organic solvent as appropriate. The amount of isocyanate residue in the prepolymer for the polyurethane resin X2 is preferably in the range of 2.0 to 6.0% based on the composition from which the solvent is removed.

[0127] When preparing polyurethane resins X1 and X2, a catalyst may be used to promote the reaction as appropriate. Specific examples of catalysts include: organic metal compounds such as dibutyltin dilaurate, dioctyltin dilaurate, bismuth carboxylates, bismuth alkoxides, or chelate compounds of bismuth and a compound having a dicarbonyl group; inorganic metal compounds such as bismuth oxide, bismuth hydroxide, or bismuth halide; and tertiary amines such as triethylamine, triethylenediamine, or 1,8-diazacyclo[5.4.0]-7-undecene. Two or more catalysts may be used in combination.

[0128] When preparing the urethane prepolymer for the polyurethane resin X1 or X2, the reaction temperature may be in the range of 50 to 140° C., or in the range of 70 to 100° C. The reaction time may be in the range of 1 to 10 hours, or in the range of 2 to 8 hours.

[0129] <Step (ii)>

[0130] Step (ii) is a step for forming a surface layer. In step (ii), the surface layer is formed by mixing a urethane prepolymer for polyurethane resin X1 or, if appropriate, an organic solvent solution, with the above-mentioned high molecular weight polyol, the above-mentioned components a1-2 such as chain extenders and the like, and the above-mentioned component C1 such as environmentally friendly stabilizers and the like, and applying (electroplating) the resulting mixture to a predetermined film thickness on a release film. In terms of scratch resistance and optical properties, the thickness of the surface layer is preferably less than or equal to 10 μm, more preferably in the range of 3 to 8 μm. In addition, when an organic solvent solution of the prepolymer for polyurethane resin X1 is used, step (ii) may further include a step of drying the organic solvent. The drying temperature may be in the range of 30 to 160°C, or in the range of 100 to 150°C. The drying time may be in the range of 10 seconds to 5 minutes, or in the range of 20 to 60 seconds.

[0131] <Step (iii)>

[0132] Step (iii) is a step of forming a substrate layer. In step (iii), the substrate layer is formed by mixing a urethane prepolymer for the polyurethane resin X2, or optionally an organic solvent solution thereof, with the aforementioned component a2-2, such as a chain extender and the like, and the aforementioned component C2, such as an environmentally friendly stabilizer and the like, and applying (electroplating) the resulting mixture to a predetermined film thickness on the surface layer obtained in step (ii). Step (iii) may further include a heat curing step after applying (electroplating) the urethane prepolymer for the polyurethane resin X2 or its organic solvent solution on the surface layer. The curing temperature may be in the range of 60 to 150°C, or in the range of 80 to 120°C. The curing time may be in the range of 1 to 8 hours, or in the range of 2 to 6 hours.

[0133] In addition, when an organic solvent solution of the prepolymer for the polyurethane resin X2 is used, step (iii) may further include a step of drying the organic solvent. The step of drying the organic solvent may be performed together with the curing step.

[0134] In terms of mechanical properties, the thickness of the substrate layer is preferably greater than or equal to 150 μm, more preferably in the range of 150 to 450 μm.

[0135] The cover film according to this embodiment can be produced using a production method including steps (i) to (iii).

[0136] The cover film according to this embodiment preferably has a total light transmittance of 85% or greater, more preferably 90% or greater, when stretched to 50%. Furthermore, the cover film preferably has a haze value of 5% or less, more preferably 1% or less. As mentioned above, since the cover film is used as a surface protective film for image display devices, it requires high transparency. When the cover film has a total light transmittance of 90% or greater when stretched to 50% and a haze value of 1% or less, the transparency of the cover film is unlikely to decrease even when the image display device having the cover film according to this embodiment is stretched or folded.

[0137] The cover film according to this embodiment preferably has a hysteresis loss rate of 12% or less, more preferably 10% or less, and further preferably 8% or less, as measured according to Japanese Industrial Standard (JIS) K 6400-2. A hysteresis loss rate of 12% or less facilitates enhanced responsiveness and durability when the image display device having the cover film according to this embodiment is deformed.

[0138] [Image Display Device]

[0139] The image display device according to the present embodiment includes a cover film, an image display element and a substrate, such as a stretchable substrate or a flexible substrate. The image display element is arranged between the cover film and the substrate. In other words, the image display device according to the present embodiment is characterized in that the cover film, the image display element, the stretchable substrate or the flexible substrate are stacked in sequence. The image display device according to the present embodiment can be used as a flexible display and / or a stretchable display because the image display device has excellent scratch resistance, mechanical properties, optical properties and stretchability. That is, the image display device according to the present embodiment can have flexibility and / or stretchability.

[0140] <Image Display Component>

[0141] In this specification, the term "image display element" refers to a display element having a display medium whose contrast, brightness, reflectivity, transmittance, and the like can be changed by electrical or magnetic action. Examples of the display element include an electroluminescent (EL) element, an LED chip (a white LED chip, a red LED chip, a green LED chip, a blue LED chip, and the like), a liquid crystal element, and the like.

[0142] <Flexible Substrate>

[0143] In this specification, the term "flexible substrate" refers to a substrate that is bendable, foldable, rollable, and the like. In one aspect, the flexible substrate can be composed of a resin material such as polyimide, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, and the like, but the present disclosure is not limited thereto.

[0144] <Stretchable Substrate>

[0145] In this specification, the term "stretchable substrate" refers to a stretchable substrate. In one aspect, the stretchable substrate may include silicone rubber such as polydimethylsiloxane and the like, or elastomers such as polyurethane, polytetrafluoroethylene (PTFE), and the like, but the present disclosure is not limited thereto.

[0146] <Other Configuration>

[0147] The image display device according to this embodiment may further include a touch panel or a sensor element.

[0148] [Method for producing an image display device]

[0149] The method of manufacturing the image display device according to the present embodiment may include a process of directly attaching the cover film according to the present embodiment to the image display element.

[0150] Example

[0151] Hereinafter, the present disclosure will be described in further detail with reference to exemplary embodiments thereof, but the present disclosure is not limited to these exemplary embodiments.

[0152] The materials used in each of the Examples and Comparative Examples are as follows.

[0153] [Polyurethane resin X1: PU-X1]

[0154] <Active Hydrogen Component A1>

[0155] (Compound a1-1)

[0156] - A compound having a polyorganosiloxane group and an amino group as a skeleton structure at both ends of its molecular chain (product name: "BY-16-853U", commercially available from Dow Corning Toray Co., Ltd., or product name: "KF-8012", commercially available from Shin-Etsu Chemical Co., Ltd.).

[0157] (Component a1-2)

[0158] - High molecular weight polyol: polycarbonate diol (product name: "DURANOL T4671", commercially available from Asahi Kasei Corporation).

[0159] -Chain extenders: 1,4-butanediol and water.

[0160] -Reaction terminator: diethanolamine.

[0161] <Non-yellowing polyisocyanate component B1>

[0162] -Alicyclic polyisocyanate (hydrogenated MDI)

[0163] - Compound b1: Allophanate-modified HDI (product name: "CORONATE-2793", commercially available from Tosoh Corporation).

[0164] [Polyurethane resin X2: PU-X2]

[0165] <Active Hydrogen Component A2>

[0166] (Compound a2-1)

[0167] - Polytetramethyl ether glycol (product name: "PTMG-2000", commercially available from Mitsubishi Chemical Corporation; Mn = 2000).

[0168] - Polytetramethyl ether glycol (product name: "PTMG-1000", commercially available from Mitsubishi Chemical Corporation; Mn = 1000).

[0169] - Polyoxypropylene sorbitol ether (product name: "SANNIX (registered trademark) SP-750", commercially available from Sanyo Chemical Industries, Ltd.).

[0170] (Component a2-2)

[0171] -Chain extender: 1,4-butanediol

[0172] <Non-yellowing polyisocyanate component B2>

[0173] -Hexamethylene diisocyanate

[0174] [PU-1]

[0175] A polyurethane resin obtained by reacting a main material including the following lubricant with a curing agent.

[0176] Main material: A prepolymer which is a reaction product of a polyisocyanate and a polyol (including polycarbonate polyol) and has a hydroxyl group at its terminal.

[0177] Lubricant: Silicone compound.

[0178] Curing agent: polyisocyanate compound.

[0179] [PU-2]

[0180] Two-component curing polyurethane resin.

[0181] [PU-3]

[0182] A polyurethane resin obtained by reacting a main material including the following lubricant with a curing agent.

[0183] Main material: A prepolymer which is the reaction product of polyisocyanate and polyol and has hydroxyl groups at its terminals.

[0184] Lubricant: Silicone compound.

[0185] Curing agent: polyisocyanate compound.

[0186] [PDMS]

[0187] A polydimethylsiloxane copolymer obtained by reacting α and β reagents in a 1:1 ratio and having one siloxane bond in the molecule.

[0188] α-reagent: includes vinyl-containing polydimethylsiloxane with a platinum catalyst.

[0189] β-reagent: A composition comprising vinyl-containing polydimethylsiloxane, a curing agent and a reaction inhibitor.

[0190] [Component C1]

[0191] Environmental stabilizer: A UV absorber (benzotriazole compound (product name: "TINUVIN (registered trademark) 329", commercially available from BASF Japan Ltd.)), an antioxidant (hindered phenol compound (product name: "Irganox (registered trademark) 245", commercially available from BASF Japan Ltd.)), and a light stabilizer (hindered amine compound (product name: "TINUVIN 144", commercially available from BASF Japan Ltd.)) are mixed in a ratio of 1:4:16.

[0192] [Component C2]

[0193] Environmental stabilizer: A UV absorber (benzotriazole compound (product name: "TINUVIN (registered trademark) 329", commercially available from BASF Japan Ltd.)), an antioxidant (hindered phenol compound (product name: "Irganox (registered trademark) 245", commercially available from BASF Japan Ltd.)), and a light stabilizer (hindered amine compound (product name: "TINUVIN 144", commercially available from BASF Japan Ltd.)) are mixed in a ratio of 1:11:45.

[0194] Example 1

[0195] Component C1 is added to the organic solvent solution of the prepolymer of the polyurethane resin X1 and mixed. The mixture is coated (electroplated) on a release film so that the thickness of the mixture is 5 μm. Then, the release film is dried at 145°C for 5 minutes to form a semi-cured surface layer. Component C2 is added to the prepolymer for the polyurethane resin X2 and mixed. The mixture is coated (electroplated) on the semi-cured surface layer so that the total thickness of the covering film is 400 μm. The substrate layer and the surface layer are cured at 145°C for 2 hours and then cured at 80°C for 24 hours to make a covering film in which the substrate layer and the surface layer are chemically bonded to each other. The composition of the polyurethane resin (X1: PU-X1) constituting the surface layer of the covering film and the composition of the polyurethane resin (X2: PU-X2) constituting the substrate layer of the covering film are shown in Table 1. In PU-X1, the ratio of compound a1-1 to the sum of component A1 and component B1 is 1.75% by weight. In addition, the ratios of component C1 and component C2 in the surface layer and the base material layer are shown in Table 2.

[0196] Furthermore, the elastic recovery rates of PU-X1 and PU-X2 at 100% stretching, measured under the following conditions, were 63% and 85%, respectively.

[0197] <Method for measuring elastic recovery at 100% stretch>

[0198] (1) A sheet with a film thickness of 2 mm was prepared using polyurethane resin X1 or polyurethane resin X2. The sheet was cut into elongated rectangular specimens measuring 100 mm x 5 mm (width x length), and scales were displayed on the sheet so that the distance between scales was 50 mm.

[0199] (2) This specimen is placed in the jig of an Instron type tensile testing machine (product name: "Autograph", commercially available from Shimadzu Corporation), stretched at a constant rate of 500 mm / min in an atmosphere of 25°C until the distance between the scales reaches 100%, and immediately an operation is performed to return the distance between the scales to the distance before stretching.

[0200] (3) The stress (M1) at 50% stretching in the stretching process and the stress (M2) at 50% stretching in the return process when this operation is performed are measured to calculate the elastic recovery rate from the following equation 2.

[0201] [Equation 2]

[0202] Elastic recovery rate (%) = M2 / M1×100

[0203] The adhesive properties, texture, optical properties, fracture properties, scratch resistance, mechanical properties, and environmental properties (deterioration over time) of the cover film obtained in Example 1 were evaluated under the following conditions. The results are shown in Table 2.

[0204] <Adhesion properties and texture of cover film>

[0205] (Adhesion performance)

[0206] A surface tack of less than or equal to 0.01 N is considered satisfactory when tested according to ASTM D2979.

[0207] (Texture)

[0208] The contact angle scale was slid against the surface layer of a cover film having a size of 15 mm × 10 mm using a static / dynamic friction measuring machine (product name: “TL201Tt”, commercially available from Trinity-Lab) at a load of 20 gf and a speed of 1 mm / s to measure the dynamic friction coefficient and the static friction coefficient, which were then evaluated according to the following evaluation criteria.

[0209] (Evaluation Criteria)

[0210] Acceptable: The dynamic friction coefficient and the static friction coefficient are less than or equal to the measured values ​​of water-white glass (product name: "Eagle XG (registered trademark)", commercially available from Corning Incorporated).

[0211] Unacceptable: The dynamic friction coefficient and the static friction coefficient are greater than the measured values ​​of water-white glass (product name: "Eagle XG (registered trademark)", commercially available from Corning Incorporated).

[0212] <Optical Properties: Measurement of Total Light Transmittance and Haze Value>

[0213] The total light transmittance and haze value of the resulting cover film were measured using a spectrocolorimeter (product name: "CM3600A," commercially available from Konica Minolta, Inc.) at 0% stretch (unstretched), 50% stretch, and release. The expression "at 50% stretch" refers to the value measured when the sample of the resulting cover film was stretched 1.5 times. Furthermore, the expression "at release" refers to the value measured immediately after the cover film was released after being stretched 50%.

[0214] <Breakage performance: measurement of hysteresis and hysteresis loss rate]

[0215] The hysteresis and hysteresis loss rate of the obtained cover film were measured in accordance with JIS K 6400-2.

[0216] <Scratch resistance: Steel wool test>

[0217] On one side of the surface layer of the cover film, 75 gf / cm 2The steel wool #0000 was reciprocated with a pressure of 1000 and a speed of 40 mm / s to evaluate the degree of friction of the covering film (whether there are scars or sliding tracks) according to the following evaluation criteria. In addition, the number of reciprocations below indicates the number of reciprocations that do not produce scars or sliding tracks on the covering film.

[0218] (Evaluation Criteria)

[0219] S: The number of reciprocating motions is greater than or equal to 1000 times.

[0220] A: The number of reciprocating times is 500 or more and less than 1000 times.

[0221] B: The number of reciprocating times is 250 times or more and less than 500 times.

[0222] C: The number of reciprocating times is 50 times or more and less than 250 times.

[0223] D: The number of reciprocating times is less than 50 times.

[0224] <Mechanical properties: pencil hardness>

[0225] The cover film was fixed to a glass substrate, and the surface layer of the cover film was pushed down with a pencil lead at a load of 750 gf. The pencil was moved at a speed of 300 mm / min in this state to evaluate the scratch hardness of the cover film as a function of the pencil lead hardness. Furthermore, the cover film was fixed to the glass substrate without any adhesive and then evaluated.

[0226] <Stretchability: Heat resistance test>

[0227] The paper was stacked on the cover film, rolled up to adhere to the surface layer of the cover film, and then stored at 95° C. for 300 hours. The cover film was then cooled to room temperature, and adhesion of the paper to the surface layer of the cover film was visually inspected and evaluated according to the following evaluation criteria.

[0228] (Evaluation Criteria)

[0229] Acceptable: The paper does not fall off when the covering film returns to its original shape, nor does it adhere to the surface layer of the covering film.

[0230] Unacceptable: When the cover film returns to its original shape, the paper is torn and adheres to the surface layer of the cover film.

[0231] Comparative Examples 1 to 3

[0232] The resins listed in Table 2 were used to prepare the covering film. In Comparative Example 1, a covering film was also prepared in the same manner as in Example 1, except that the resins shown in Table 2 were used. In Comparative Example 3, the α agent and the β agent were mixed in a ratio of 1: 1, the mixture was coated on a release film, and the coated release film was cured at 130°C for 5 minutes to prepare a covering film (PDMS film) consisting only of a surface layer. In Comparative Example 2, the PDMS film of Comparative Example 3 was corona discharge treated, coated with PU-3, and then cured at 80°C for 1 hour to prepare a covering film. Then, in the same manner as in Example 1, the adhesion properties, texture, optical properties, fracture properties, scratch resistance, mechanical properties and stretchability of the covering films of each comparative example were evaluated according to the following conditions. The results are listed in Table 2.

[0233] Reference example 1

[0234] For the covering film of Example 1, samples were prepared in which the contents of component C1 and component C2 in the surface layer and the substrate layer were 0% by weight (excluding components C1 and C2), 1.5% by weight, 3% by weight, and 5% by weight, respectively, relative to the resin composition constituting each layer, and environmental tests were performed according to the following conditions. As a result, the ΔY1 (yellowing index) of the sample with a content of 0% by weight of components C1 and C2 was greater than 10, and the film turned yellow. At the same time, in the samples including 1.5 to 5% by weight of components C1 and C2, ΔY1 was in the range of about 1.2 to 2.4, and the film did not change color. From these results, it can be confirmed that by incorporating predetermined amounts of components C1 and C2 (environmental stabilizers) into the surface layer and the substrate layer, it is easy to suppress the deterioration of the covering film over time.

[0235] <Environmental testing>

[0236] At a power density of 830W / m 2 The cover film sample was stored under a metal halide lamp at a temperature of 65°C and a humidity of 60% RH for 240 hours. After storage, the ΔY1 (yellowing index) of the cover film was measured using a spectrocolorimeter (product name: "CM3600A", commercially available from Konica Minolta).

[0237] [Table 1]

[0238]

[0239] [Table 2]

[0240]

[0241]

[0242] The symbol "-" in Table 1 and Table 2 indicates that the corresponding component (or exemplary bond) is not included.

[0243] As shown in Table 2, the cover film of Example 1, which meets the requirements of this embodiment, has excellent scratch resistance, mechanical properties, and optical properties, and has good stretchability. Meanwhile, the cover films of Comparative Examples 1 to 3, which do not meet the requirements of this embodiment, have poor scratch resistance, mechanical properties, optical properties, and stretchability. These results confirm that the cover film according to this embodiment has excellent scratch resistance, mechanical properties, and optical properties, as well as excellent stretchability. Furthermore, in the image display device having the cover film according to this embodiment, the film does not crack or break even when the device is stretched or folded.

[0244] According to the present disclosure, it is possible to provide a cover film having excellent anti-scratch properties, mechanical properties, and optical properties and having excellent stretchability, and an image display device including the cover film.

[0245] A few embodiments have been described above. However, it will be appreciated that various modifications may be made. For example, suitable results may be achieved by performing the described techniques and / or by combining components of the described systems, architectures, devices, or circuits in a different order and / or by replacing or supplementing them with other components or their equivalents. Therefore, other implementations are within the scope of the following claims.

Claims

1. A covering film comprising: substrate layer; and a surface layer disposed on at least one surface of the substrate layer; wherein the substrate layer and the surface layer are chemically bonded to each other by a reaction between components in the surface layer and components in the substrate layer at least at an interface between the substrate layer and the surface layer; wherein the surface layer comprises a polyurethane resin X1 having urethane units and urea units and polyorganosiloxane groups; wherein the polyurethane resin X1 is the reaction product of a non-yellowing isocyanate component B1 and an active hydrogen component A1; wherein the active hydrogen component A1 comprises a compound a1-1 containing a polyorganosiloxane group and an active hydrogen group, and the ratio of the compound a1-1 to the sum of 100 wt % of the active hydrogen component A1 and the non-yellowing isocyanate component B1 is less than or equal to 4.0 wt %; The substrate layer includes a polyurethane resin X2 having a urethane unit; wherein the polyurethane resin X2 is a reaction product of a non-yellowing isocyanate component B2 and an active hydrogen component A2 excluding the compound a1-1; wherein the non-yellowing isocyanate component B1 comprises a tri- or more functional isocyanate compound b1, and wherein the non-yellowing isocyanate component B2 comprises a tri- or more functional isocyanate compound b2, wherein the crosslinking point concentration of the polyurethane resin X1 calculated from the following equation 1 is in the range of 0.02 to 0.1 mmol / g, and the crosslinking point concentration of the polyurethane resin X2 calculated from the following equation 1 is greater than or equal to 0.4 mmol / g, [Equation 1] Cross-linking point concentration (mmol / g) = (F-2) × (mmol of trifunctional or more functional group-constituting monomers in 1g of polyurethane resin) wherein in the formula 1, F represents the number of functional groups in the monomer consisting of trifunctional groups or more, and The elastic recovery rate of the covering film when stretched 100% is 80% to 100%. 2 . The cover film according to claim 1 , wherein the active hydrogen component A1 contains at least one group selected from a hydroxyl group, an amino group, and a carboxyl group as the active hydrogen group. 3 . The cover film according to claim 1 , wherein each of the surface layer and the base material layer includes an environmental stabilizer, and a ratio of the environmental stabilizer in each of the surface layer and the base material layer is in a range of 0.5 to 5.0 wt %. 4 . The cover film according to claim 1 , wherein the non-yellowing isocyanate component B1 comprises a tri- or higher functional isocyanate compound b1. 5 . The cover film according to claim 1 , wherein the surface layer has a thickness of 10 μm or less, and the base material layer has a thickness of 150 μm or more.

6. The cover film according to claim 1, wherein the cover film has a total light transmittance of 85% or more and a haze value of 5% or less when stretched by 50%. 7 . The cover film according to claim 1 , wherein the cover film has a hysteresis loss rate measured in accordance with JIS K 6400-2 of 12% or less.

8. The cover film according to claim 1, wherein the non-yellowing isocyanate component B1 is an isocyanate that does not include an aromatic component. 9 . The covering film according to claim 1 , wherein the content of the compound b1 in the non-yellowing isocyanate component B1 is in the range of 0.5 to 10% by weight.

10. An image display device, comprising: The covering film defined in claim 1; an image display element disposed below the cover film; and A stretchable substrate or a flexible substrate is provided below the image display element. 11 . The image display device according to claim 10 , wherein the active hydrogen component A1 contains at least one group selected from a hydroxyl group, an amino group, and a carboxyl group as the active hydrogen group. 12 . The image display device according to claim 10 , wherein each of the surface layer and the base material layer includes an environmental stabilizer, and a ratio of the environmental stabilizer in each of the surface layer and the base material layer is in a range of 0.5 to 5.0% by weight. 13 . The image display device according to claim 10 , wherein the non-yellowing isocyanate component B1 comprises a tri- or higher functional isocyanate compound b1. 14 . The image display device according to claim 10 , wherein the surface layer has a thickness of 10 μm or less, and the base material layer has a thickness of 150 μm or more.

15. The image display device of claim 10, wherein the cover film has a total light transmittance of 85% or more and a haze value of 5% or less when stretched by 50%. 16 . The image display device according to claim 10 , wherein a hysteresis loss rate of the cover film measured according to JIS K6400-2 is 12% or less.

17. The image display device according to claim 10, wherein the image display device has flexibility and / or stretchability.

18. The image display device according to claim 10, wherein the non-yellowing isocyanate component B1 is an isocyanate that does not include an aromatic component.

19. The image display device according to claim 10, wherein the content of the compound b1 in the non-yellowing type isocyanate component B1 is in the range of 0.5 to 10 wt%.

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