Cover film

Abstract

To provide a cover film that is excellent in abrasion resistance, surface slipperiness, flexibility, etc., and an image display device that includes the cover film.SOLUTION: There is provided a cover film comprising at least a base layer and a surface layer, wherein an elastic recovery rate of the cover film at 100% elongation is 80 to 100%, and a hysteresis loss measured at -20°C is 13 to 30%, and the base layer contains a polyurethane resin (X2), and the surface layer contains a polyurethane resin (X1) having a urea group and a polyorganosiloxane group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cover film and an image display device using the same. [Background technology]

[0002] Cover films used in flexible displays and the like are required to have a combination of scratch resistance, surface slipperiness, flexibility, and the like. Films with excellent scratch resistance and bending resistance have been proposed as cover films for displays (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-336 [Patent Document 2] Special Publication No. 2019-511386 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the demand for flexible displays has increased, making it necessary to combine scratch resistance, surface slipperiness, flexibility, etc. Currently, there are no cover films for flexible displays that satisfy all of these requirements. The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a cover film that has excellent flexibility and slipperiness (especially flexibility and slipperiness at low temperatures) and also has excellent scratch resistance and bending resistance, and an image display device that includes the cover film. [Means for solving the problem]

[0005] The present inventors have conducted extensive research to achieve the above object, and have arrived at the present invention. That is, the present invention provides a cover film having at least a base layer and a surface layer, The cover film has an elastic recovery rate of 80 to 100% when elongated to 100%, and a hysteresis loss of 13 to 30% measured at -20°C, The base layer contains a polyurethane resin (X2), and the polyurethane resin (X2) satisfies the following conditions (1-1) to (1-2): (1-1) The polyurethane resin (X2) is a reaction product of an active hydrogen component (A2) that does not contain a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group, and an isocyanate component (B2) that does not contain an aromatic ring. (1-2) The polyurethane resin (X2) has a crosslinking point concentration calculated from the following formula (1) of 0.4 mmol / g or more. Crosslinking point concentration (mmol / g) = (F-2) × (number of millimoles of trifunctional or higher functional monomers per gram of polyurethane resin) (1) (In formula (1), F represents the number of functional groups in the tri- or higher functional constituent monomer.) Fulfilling The surface layer contains a polyurethane resin (X1) having a urea group and a polyorganosiloxane group, and the polyurethane resin (X1) satisfies the following conditions (2-1) to (2-4): (2-1) The polyurethane resin (X1) is a reaction product of an active hydrogen component (A1) and an isocyanate component (B1) that does not have an aromatic ring. (2-2) The active hydrogen component (A1) contains a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group. (2-3) The weight ratio of the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group to the total amount of the active hydrogen component (A1) and the isocyanate component (B1) is 4.0 mass% or less. (2-4) The polyurethane resin (X1) has a urethane group concentration (when urea groups are present in the polyurethane resin (X1), the total concentration of urethane groups and urea groups) of 1.8 mmol / g or less. It is a cover film that satisfies the above requirements. [Effects of the Invention]

[0006] The cover film of the present invention has excellent flexibility and slipperiness at low temperatures, and also has excellent abrasion resistance and bending resistance. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing a stress-strain curve obtained by measuring hysteresis loss. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of the present invention will be described in detail below. The present invention is not limited to the following embodiment, and can be carried out by making appropriate modifications within the scope that does not impair the effects of the present invention. In this specification, the notation "to" means "greater than or equal to."

[0009] <Cover film> The cover film according to the present embodiment is a cover film having at least a base layer and a surface layer, The cover film has an elastic recovery rate of 80 to 100% when elongated to 100%, and a hysteresis loss of 13 to 30% measured at -20°C, The base layer contains a polyurethane resin (X2), and the polyurethane resin (X2) satisfies the following conditions (1-1) to (1-2): (1-1) The polyurethane resin (X2) is a reaction product of an active hydrogen component (A2) that does not contain a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group, and an isocyanate component (B2) that does not contain an aromatic ring. (1-2) The polyurethane resin (X2) has a crosslinking point concentration calculated from the following formula (1) of 0.4 mmol / g or more. Crosslinking point concentration (mmol / g) = (F-2) × (number of millimoles of trifunctional or higher functional monomers per gram of polyurethane resin) (1) (In formula (1), F represents the number of functional groups in the tri- or higher functional constituent monomer.) Fulfilling The surface layer contains a polyurethane resin (X1) having a urea group and a polyorganosiloxane group, and the polyurethane resin (X1) satisfies the following conditions (2-1) to (2-4): (2-1) The polyurethane resin (X1) is a reaction product of an active hydrogen component (A1) and an isocyanate component (B1) that does not have an aromatic ring. (2-2) The active hydrogen component (A1) contains a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group. (2-3) The weight ratio of the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group to the total amount of the active hydrogen component (A1) and the isocyanate component (B1) is 4.0 mass% or less. (2-4) The polyurethane resin (X1) has a urethane group concentration (when urea groups are present in the polyurethane resin (X1), the total concentration of urethane groups and urea groups) of 1.8 mmol / g or less. It is a cover film that satisfies the above requirements. The cover film according to this embodiment has excellent scratch resistance, mechanical properties, and optical properties, and also has excellent surface slip properties and flexibility. The cover film according to the present invention will be described in detail below.

[0010] <Surface layer> The cover film according to this embodiment has at least a base layer and a surface layer. The surface layer contains a polyurethane resin (X1) having a urethane group (urethane bond), a urea group (urea bond), and a polyorganosiloxane group in its molecule. By including the polyurethane resin (X1) having a urethane group and a urea group in its molecule, the scratch resistance of the surface layer is improved and an appropriate hardness can be achieved.

[0011] (Polyurethane resin (X1)) The polyurethane resin (X1) contained in the surface layer is a reaction product of an active hydrogen component (A1) (hereinafter also referred to as component (A1)) and an isocyanate component (B1) (hereinafter also referred to as component (B1)) that does not have an aromatic ring. The active hydrogen component (A1) contains a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group. The weight ratio of the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group to the total amount of the active hydrogen component (A1) and the isocyanate component (B1) having no aromatic ring is 4.0 mass% or less, and the urethane group concentration of the polyurethane resin (X1) (when urea groups are present in the polyurethane resin (X1), the total concentration of urethane groups and urea groups) is 1.8 mmol / g or less. When the surface layer contains the polyurethane resin (X1), scratch resistance and mechanical properties are improved.

[0012] [Active hydrogen component (A1)] The active hydrogen component (A1) contains, as an essential component, a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group.

[0013] <Compound (a1-1) Having a Polyorganosiloxane Group and an Active Hydrogen Group> The compound (a1-1) having a polyorganosiloxane group and an active hydrogen group is a compound having a polyorganosiloxane group and an active hydrogen group. By forming the surface layer from the reaction product of the active hydrogen component (A1) containing the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group and the component (B1), the scratch resistance of the surface layer is improved. The active hydrogen group contained in the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group is preferably at least one active hydrogen group selected from a hydroxyl group, an amino group, and a carboxy group, and more preferably an amino group. When the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group contains an amino group, a polyurethane resin (X1) containing a urea group in the molecule is obtained. The urea group in the polyurethane resin (X1) may be formed by reacting an active hydrogen component (A1) other than the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group with an isocyanate component (B1) that does not have an aromatic ring.

[0014] The polyorganosiloxane group contained in the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group may have a structure represented by the following general formula (I). TIFF2025177788000002.tif29170

[0015] In general formula (I), R 1 ~R 6 each independently represents a linear or branched alkyl group having 1 to 6 carbon atoms, and n represents an integer of 1 to 100. Among these, R is the most suitable from the viewpoint of improving the mechanical properties of the surface layer. 1 ~R 6 are each independently preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group. From the viewpoint of the mechanical properties of the surface layer and the haze of the cover film, n is preferably an integer of 10 to 70, more preferably an integer of 15 to 50.

[0016] The compound (a1-1) having a polyorganosiloxane group and an active hydrogen group preferably has a polyorganosiloxane group represented by the general formula (I) and has an active hydrogen group at at least one selected from one end, both ends, and a side chain of the molecular chain. Furthermore, the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group more preferably has a hydroxyl group or an amino group at at least one selected from one end and both ends of the molecular chain. Such a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group may be a commercially available product.

[0017] Commercially available compounds (a1-1) having amino groups at both ends and having a polyorganosiloxane group and an active hydrogen group include, for example, "KF-8010" (functional group equivalent weight 430 g / mol), "X-22-161A" (functional group equivalent weight 800 g / mol), "X-22-161B" (functional group equivalent weight 1,500 g / mol), "KF-8012" (functional group equivalent weight 2,200 g / mol), and "KF-8008" (functional group equivalent weight 5, 700 g / mol), "X-22-9409" (functional group equivalent 700 g / mol), "X-22-1660B-3" (functional group equivalent 2,200 g / mol) (all product names); and "BY-16-853" (functional group equivalent 650 g / mol), "BY-16-853B" (functional group equivalent 2,200 g / mol), and "BY-16-853U" (functional group equivalent 450 g / mol) (all product names) manufactured by Dow Corning Toray Co., Ltd. These may be used alone or in combination of two or more.

[0018] Examples of commercially available compounds (a1-1) having hydroxyl groups at both ends and having a polyorganosiloxane group and an active hydrogen group include "KF-6001" (functional group equivalent: 900 g / mol), "KF-6002" (functional group equivalent: 1,600 g / mol), "KF-6003" (functional group equivalent: 2,550 g / mol), and "X-22-4952" (functional group equivalent: 1,100 g / mol) (all product names) manufactured by Shin-Etsu Chemical Co., Ltd.; and "SF8427" (functional group equivalent: 930 g / mol) (product name) manufactured by Dow Corning Toray Co., Ltd. These may be used alone or in combination of two or more.

[0019] Examples of commercially available compounds (a1-1) having a hydroxyl group at one end and having a polyorganosiloxane group and an active hydrogen group include "X-22-170BX" (functional group equivalent: 2,800 g / mol), "X-22-170DX" (functional group equivalent: 4,670 g / mol), "X-22-176DX" (functional group equivalent: 1,600 g / mol), and "X-22-176F" (functional group equivalent: 6,300 g / mol) (all product names), all manufactured by Shin-Etsu Chemical Co., Ltd. These may be used alone or in combination of two or more.

[0020] Of the commercially available products described above, the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group is preferably a compound having a hydroxyl group and / or an amino group, more preferably a compound having an amino group, from the viewpoints of haze and surface slipperiness, and particularly preferably X-22-161A, BY-16-853U, and KF-8012, and most preferably BY-16-853U and KF-8012.

[0021] The weight ratio of the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group to the total amount of the active hydrogen component (A1) and the isocyanate component (B1) is 4.0 mass% or less, preferably 2.0 to 4.0 mass%, more preferably 3.0 to 4.0 mass%. When the ratio of the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group in the polyurethane resin (X1) is 4.0 mass% or less, the scratch resistance and optical properties of the cover film can be both achieved.

[0022] The polyurethane resin (X1) has a urethane group concentration (when urea groups are present in the polyurethane resin (X1), the total concentration of urethane groups and urea groups) of 1.8 mmol / g or less, preferably 1.0 to 1.8 mmol / g, and may also have a urethane group concentration of 1.0 to 1.6 mmol / g or 1.0 to 1.5 mmol / g. The urethane group concentration can be calculated from the amounts of raw materials charged. When the urethane group concentration of the polyurethane resin (X1) is within the above range, good flexibility at low temperatures is achieved.

[0023] <Other active hydrogen components (a1-2)> The active hydrogen component (A1) may contain an active hydrogen component (a1-2) other than the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group. The other active hydrogen component (a1-2) may contain, for example, at least one selected from the polymer polyols, chain extenders, and reaction terminators described in WO 2021 / 002342. Of these, from the viewpoint of scratch resistance, it is preferable to contain the polymer polyols described in WO 2021 / 002342, and it is more preferable to contain a polycarbonate polyol or a polyester carbonate polyol. The chain extender (a3) ​​may contain water, 1,4-butanediol, or the like. Furthermore, the reaction terminator (a4) may contain diethanolamine or the like. The proportion of the polymer polyol in the other active hydrogen components (a1-2) may be 50 to 100 mass % or 70 to 100 mass % based on the total mass of the other active hydrogen components (a1-2). When the proportion of the polymer polyol is within the above range, scratch resistance tends to be better.

[0024] The content of the other active hydrogen component (a1-2) in the active hydrogen component (A1) can be adjusted so that the total amount of the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group and the other active hydrogen component (a1-2) is 100 mass%.

[0025] [Isocyanate component (B1) having no aromatic ring] The isocyanate component (B1) not containing an aromatic ring reacts with the active hydrogen component (A1) to form a urethane bond (urethane group) and a urea bond (urea group). The isocyanate component (B1) not containing an aromatic ring is a polyisocyanate compound having at least two isocyanate groups and not containing an aromatic ring. That is, the isocyanate component (B1) not containing an aromatic ring is at least one isocyanate compound selected from aliphatic polyisocyanates and alicyclic polyisocyanates.

[0026] Examples of the aliphatic polyisocyanate include aliphatic diisocyanates such as ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (hereinafter referred to as "HDI"), dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethyl caproate, bis(2-isocyanatoethyl) fumarate, bis(2-isocyanatoethyl) carbonate, and 2-isocyanatoethyl-2,6-diisocyanatohexanoate. Examples of the polyisocyanate include anthracene; aliphatic triisocyanates such as 1,6,11-undecane triisocyanate; and tri- or higher functional aliphatic polyisocyanates, such as modified products of the above-mentioned aliphatic diisocyanates or aliphatic triisocyanates containing a urethane group, a carbodiimide group, an allophanate group, a urea group, a biuret group, a uretdione group, a uretoimine group, an isocyanurate group, or an oxazolidone group (for example, allophanate-modified HDI (e.g., manufactured by Tosoh Corporation, product name "CORONATE (registered trademark)-2793"), isocyanurate-modified HDI (e.g., manufactured by Asahi Kasei Corporation, product name "Duranate (registered trademark) TLA-100"), and biuret-modified HDI (e.g., manufactured by Asahi Kasei Corporation, product name "Duranate 24A-100")). These may be used alone or in combination of two or more.

[0027] Examples of alicyclic polyisocyanates include alicyclic diisocyanates such as isophorone diisocyanate (hereinafter referred to as "IPDI"), 4,4'-dicyclohexylmethane diisocyanate (hereinafter referred to as "hydrogenated MDI"), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, bis(2-isocyanatoethyl)-4-cyclohexene-1,2-dicarboxylate, and 2,5- or 2,6-norbornane diisocyanate. These may be used alone or in combination of two or more. Furthermore, an aliphatic polyisocyanate and an alicyclic polyisocyanate may be used in combination.

[0028] The isocyanate component (B1) having no aromatic ring preferably contains a tri- or higher functional isocyanate compound (b1), more preferably contains an allophanate-modified HDI or a biuret-modified HDI, and even more preferably contains an allophanate-modified HDI. By including the trifunctional or higher isocyanate compound (b1), a surface layer with better heat resistance can be obtained, which in turn makes it easier to suppress adhesion and stickiness of the film at high temperatures in flexible displays and stretchable displays to which the cover film according to this embodiment is applied. In particular, when these displays are rolled or folded, it becomes easier to prevent the films from sticking together.

[0029] The weight ratio of the tri- or higher functional isocyanate compound (b1) to the isocyanate component (B1) having no aromatic ring is more preferably 5 to 25 mass %, more preferably 10 to 25 mass %, and even more preferably 15 to 25 mass %.

[0030] The proportion of the isocyanate component (B1) having no aromatic ring in the polyurethane resin (X1) is not particularly limited as long as the effects of the present invention are achieved. In one embodiment, the molar ratio of the total number of NCO groups in the isocyanate component (B1) having no aromatic ring to the total number of active hydrogen groups in the active hydrogen component (A1) (total number of NCO groups / total number of active hydrogen groups) is preferably in the range of 1.00 to 1.30, more preferably in the range of 1.00 to 1.20. If the molar ratio is in the range of 1.00 to 1.20, scratch resistance tends to be good.

[0031] (Production method of polyurethane resin (X1)) The method for producing the polyurethane resin (X1) according to the present embodiment is not particularly limited, and examples thereof include a method (1) in which a urethane prepolymer is obtained using an active hydrogen component (A1), an isocyanate component (B1) having no aromatic ring, and, if necessary, an organic solvent, and then the urethane prepolymer is reacted with, for example, a chain extender to obtain the polyurethane resin (X1); and a method (2) in which the active hydrogen component (A1), an isocyanate component (B1) having no aromatic ring, and, if necessary, an organic solvent are all charged into a batch reaction tank, and the reaction is carried out by heating to obtain the polyurethane resin (X1). Details of method (1) and method (2) are described, for example, in International Publication No. 2021 / 002342.

[0032] (Other ingredients (C1)) The surface layer may contain other components (C1) in addition to the polyurethane resin (X1). Examples of the other components (C1) include antioxidants, ultraviolet absorbers, environmental stabilizers such as light stabilizers, plasticizers, adsorbents, fillers, release agents, and flame retardants. These may be used alone or in combination of two or more. Of these, it is preferable to include an environmental stabilizer such as an antioxidant, an ultraviolet absorber, and a light stabilizer as the other component (C1), from the viewpoint of easily suppressing deterioration of the cover film over time (discoloration, etc.) and more easily improving light resistance and heat resistance.

[0033] Examples of antioxidants include hindered phenol compounds such as pentaerythristyl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] and octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; phosphorus compounds such as tris(2,4-di-t-butylphenyl)phosphite; and sulfur compounds such as pentaerythristyl-tetrakis(3-laurylthiopropionate), dilauryl-3,3'-thiodipropionate, pentaerythristyl-tetrakis(3-laurylthiopropionate), and dilauryl-3,3'-thiodipropionate. These may be used alone or in combination of two or more.

[0034] Examples of the ultraviolet absorber include benzotriazole compounds such as 2-(3,5-di-t-amyl-2-hydroxyphenyl)benzotriazole and 2-(5-methyl-2-hydroxyphenyl)benzotriazole.

[0035] Examples of the light stabilizer include hindered amine compounds such as (bis-2,2,6,6-tetramethyl-4-piperidyl) sebacate.

[0036] The surface layer may contain one or more of the aforementioned environmental stabilizers. The content of the environmental stabilizer in the surface layer is preferably 0.5 to 5.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 1.5 to 5.0% by mass, relative to the total mass of the resin composition constituting the surface layer. When the content of the environmental stabilizer in the surface layer is 0.5% by mass or more, a cover film that is less susceptible to deterioration over time is easily obtained. Furthermore, when the content of the environmental stabilizer in the surface layer is 5.0% by mass or less, a cover film that is excellent in light resistance and heat resistance while suppressing yellowing of the film due to the environmental stabilizer is easily obtained. Note that when the surface layer is composed only of the aforementioned polyurethane resin (X1), the content of the environmental stabilizer in the surface layer is the ratio to the total amount (100% by mass) of the polyurethane resin (X1) and the environmental stabilizer. As components other than the environmental stabilizer contained in the surface layer, for example, the additives described in WO 2021 / 002342 may be used alone or in combination of two or more.

[0037] <Dynamic friction coefficient of surface layer> The dynamic friction coefficient of the surface layer is preferably greater than 1.2, and from the viewpoint of scratch resistance, is more preferably 1.3 to 2.0. The dynamic friction coefficient of the surface layer can be adjusted by the content of the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group and the concentration of the urethane group. <Method for measuring the coefficient of dynamic friction> (1) The surface layer of a cover film cut into a rectangle measuring 100 mm in length, 50 mm in width, and 400 μm in thickness is fixed on a glass plate. (2) After leaving the cover film in a room temperature-controlled at 23°C for 24 hours, measure the coefficient of dynamic friction using a Tribomaster TL-201s (manufactured by Trinity Labs) and a tactile contactor under the following conditions: temperature 23°C, load 30 g, speed 50 mm / s, and travel distance 50 mm.

[0038] <Base material layer> In the cover film according to this embodiment, the substrate layer contains a polyurethane resin (X2) having a urethane bond in the molecule, which is a reaction product of an active hydrogen component (A2) that does not contain the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group, and an isocyanate component (B2) that does not contain an aromatic ring. By including the polyurethane resin (X2), the base layer becomes soft and has a large restoring force, which improves the mechanical properties of the cover film, particularly the pencil hardness.

[0039] (Polyurethane resin (X2)) The polyurethane resin (X2) contained in the base layer is a reaction product of an active hydrogen component (A2) that does not contain a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group, and an isocyanate component (B2) that does not contain an aromatic ring. The crosslinking point concentration of the polyurethane resin (X2) calculated from the following formula (1) is 0.4 mmol / g or more, preferably 0.4 to 0.6 mmol / g, and more preferably 0.4 to 0.5 mmol / g. If the crosslinking point concentration of the polyurethane resin (X2) is 0.4 mmol / g or more, the mechanical properties of the cover film, particularly the pencil hardness, are improved. Crosslinking point concentration (mmol / g) = (F-2) × (number of millimoles of trifunctional or higher functional monomers per gram of polyurethane resin) (1) (In formula (1), F represents the number of functional groups in the tri- or higher functional constituent monomer.)

[0040] <Active hydrogen component (A2)> The active hydrogen component (A2) is an active hydrogen component that does not contain a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group. The active hydrogen component (A2) preferably has an active hydrogen group at at least one selected from one end, both ends, and a side chain of the molecular chain, and the active hydrogen group contained in the active hydrogen component (A2) is preferably at least one active hydrogen group selected from a hydroxyl group, an amino group, and a carboxy group.

[0041] Particularly preferably, the active hydrogen component (A2) contains a polymer polyol component (a2-1). The polymer polyol component (a2-1) is a polyol having a number average molecular weight (Mn) of 500 or more, preferably 500 to 5,000, and more preferably 700 to 4,000, and examples thereof include the polymer polyols described in WO 2021 / 002342. Among these, from the viewpoint of easily adjusting the crosslinking point concentration in the polyurethane resin (X2) to 0.4 mmol / g or more, the polymer polyol component (a2-1) preferably contains a polyol in which an alkylene oxide is added to a tetrafunctional to octafunctional polyhydric alcohol such as pentaerythritol, sorbitol, mannitol, sorbitan, diglycerin, and dipentaerythritol, and more preferably contains a polyol in which an alkylene oxide is added to a hexafunctional to octafunctional polyhydric alcohol such as sorbitol, mannitol, sorbitan, and dipentaerythritol. The polymer polyol component (a2-1) may be used alone or in combination of two or more types. The polymer polyol component (a2-1) may also contain a polyether polyol. Examples of polyether polyols include compounds in which alkylene oxide is added to a polyol having an Mn or a chemical formula weight of less than 500. The polyether polyols may be used alone or in combination of two or more.

[0042] Examples of the alkylene oxide include alkylene oxides having 2 to 12 carbon atoms such as ethylene oxide, 1,2- or 1,3-propylene oxide, 1,2-, 1,3- or 2,3-butylene oxide, tetrahydrofuran, 3-methyltetrahydrofuran, styrene oxide, α-olefin oxide, and epichlorohydrin. Of these, ethylene oxide and 1,2- or 1,3-propylene oxide are preferred from the viewpoint of scratch resistance. In one embodiment, the polymer polyol component (a2-1) may include 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 polyhydric alcohol selected from sorbitol, mannitol, sorbitan, and dipentaerythritol. In one embodiment, the polymer polyol component (a2-1) may contain polytetramethylene ether glycol (PTMG) having an Mn of 500 to 2,500.

[0043] The proportion of the polymer polyol component (a2-1) in the active hydrogen component (A2) is preferably 70 to 100 mass%, more preferably 75 to 100 mass%, and even more preferably 80 to 100 mass%, based on the total mass of the active hydrogen component (A2). When the proportion of the polymer polyol (a2-1) is within the above range, scratch resistance tends to be good.

[0044] In this specification, Mn can be measured by gel permeation chromatography, for example, under the following conditions. Apparatus: "Waters Alliance 2695" (manufactured by Waters) Column: "Guardcolumn Super HL" (1 piece), "TSKgel SuperH2000, TSKgel SuperH3000, TSKgel Sup erH4000 (both manufactured by Tosoh Corporation) connected together Sample solution: 0.25 mass% THF solution Solution injection volume: 10μL Flow rate: 0.6mL / min Measurement temperature: 40℃ Detector: Refractive index detector Reference material: Standard polyethylene glycol

[0045] <Other active hydrogen components (a2-2)> The active hydrogen component (A2) may contain an active hydrogen component (a2-2) other than the high molecular weight polyol (a2-1). The active hydrogen component (a2-2) other than the polymer polyol (a2-1) may include, for example, at least one selected from the chain extenders and reaction terminators described in WO 2021 / 002342. Among these, from the viewpoint of scratch resistance, it is preferable to include 1,4-butanediol or ethylene glycol, and it is more preferable to include 1,4-butanediol. The proportion of 1,4-butanediol and / or ethylene glycol in the other active hydrogen components (a2-2) other than the polymer polyol (a2-1) may be 50 to 100 mass% or 70 to 100 mass% based on the total mass of the other active hydrogen components (a2-2) other than the polymer polyol (a2-1). If the proportion of 1,4-butanediol and / or ethylene glycol is within the above range, scratch resistance tends to be better.

[0046] [Isocyanate component (B2) having no aromatic ring] The isocyanate component (B2) having no aromatic ring reacts with the active hydrogen component (A2) to form a urethane bond. Examples of the isocyanate component (B2) having no aromatic ring include the same polyisocyanates as the isocyanate component (B1) having no aromatic ring. Among these, from the viewpoint of scratch resistance, the isocyanate component (B2) having no aromatic ring preferably contains HDI or IPDI. The content of HDI and IPDI in the isocyanate component (B2) having no aromatic ring is more preferably 80 to 100 mass%, more preferably 90 to 100 mass%, based on the total mass of the isocyanate component (B2) having no aromatic ring.

[0047] The proportion of the isocyanate component (B2) having no aromatic ring in the polyurethane resin (X2) is not particularly limited as long as the effects of the present invention are achieved. In one embodiment, the molar ratio of the total number of NCO groups in the isocyanate component (B2) having no aromatic ring to the total number of active hydrogen groups in the active hydrogen component (A2) (total number of NCO groups / [total number of active hydrogen groups]) is preferably in the range of 0.95 to 1.20, more preferably in the range of 1.00 to 1.15. If the molar ratio is in the range of 1.00 to 1.20, scratch resistance tends to be good.

[0048] The urethane group concentration in the polyurethane resin (X2) is preferably 1.5 to 2.5 mmol / g, more preferably 1.7 to 2.2 mmol / g. If the urethane group concentration is within the above range, scratch resistance and pencil hardness tend to be good.

[0049] (Method for producing polyurethane resin (X2)) The method for producing the polyurethane resin (X2) according to this embodiment is not particularly limited, and the polyurethane resin (X2) can be produced by the same method as that for the polyurethane resin (X1), except that an active hydrogen component (A2) and an isocyanate component (B2) not having an aromatic ring are used.

[0050] (Other ingredients (C2)) The substrate layer may contain other components (C2) in addition to the polyurethane resin (X2). Examples of the other components (C2) include the same components as the aforementioned other components (C1). Among these, from the viewpoints of easily suppressing deterioration over time (discoloration, etc.) of the cover film and more easily improving light resistance and heat resistance, it is preferable that the other components (C2) contain environmental stabilizers such as antioxidants, ultraviolet absorbers, and light stabilizers.

[0051] The content of the environmental stabilizer in the base layer is preferably 0.5 to 5.0 mass %, more preferably 1.0 to 5.0 mass %, and even more preferably 1.5 to 5.0 mass %, relative to the total mass of the resin composition constituting the base layer. When the content of the environmental stabilizer in the base layer is 0.5 mass % or more, a cover film that is less susceptible to deterioration over time can be obtained. Furthermore, by setting the content of the environmental stabilizer in the substrate layer to 5.0% by mass or less, it becomes easier to obtain a cover film that is excellent in light resistance and heat resistance while suppressing yellowing of the film caused by the environmental stabilizer. Note that when the substrate layer is composed only of the aforementioned polyurethane resin (X2), the content of the environmental stabilizer in the substrate layer is the ratio to the total amount (100% by mass) of the polyurethane resin (X2) and the environmental stabilizer. In one embodiment, the total amount of component (C1) and other component (C2) contained in the cover film may be 0.5 to 5.0 mass%, 1.0 to 5.0 mass%, or 1.5 to 5.0 mass%, based on the total mass of all resin compositions constituting the cover film. By keeping the total amount of other component (C1) and other component (C2) contained in the cover film within the above range, it becomes easier to obtain a cover film that is less susceptible to deterioration over time.

[0052] [Cover film manufacturing method] The method for producing the cover film according to this embodiment is not particularly limited. In one preferred embodiment, the cover film can be produced by a method including, for example, preparing a prepolymer for polyurethane resin (X1) and a prepolymer for polyurethane resin (X2) (step (i)), applying the prepolymer for polyurethane resin (X1) to a release film or the like to form a surface layer having a predetermined thickness (step (ii)), and applying the prepolymer for polyurethane resin (X2) to a predetermined thickness on the surface layer to form a base layer (step (iii)). The production method including the above steps (i) to (iii) will be described below.

[0053] <Process (i)> Step (i) is a step of preparing a prepolymer for polyurethane resin (X1) and a prepolymer for polyurethane resin (X2). The prepolymer for polyurethane resin (X1) is a compound having a terminal hydroxyl group, and can be prepared by reacting an active hydrogen component (A1) with an isocyanate component (B1) having no aromatic ring, if necessary, in an organic solvent. The hydroxyl value of the prepolymer for polyurethane resin (X1) is preferably 0.5 to 2.0 mgKOH / g in a composition containing an organic solvent.

[0054] The prepolymer for polyurethane resin (X2) is a compound having an isocyanate group at its terminal, and can be prepared by reacting an active hydrogen component (A2) with an isocyanate component (B2) having no aromatic ring, if necessary, in an organic solvent. The amount of isocyanate residues in the prepolymer for polyurethane resin (X2) is preferably 2.0 to 6.0% in the composition excluding the organic solvent.

[0055] In producing the polyurethane resin (X1) and the polyurethane resin (X2), a catalyst may be added, if necessary, to promote the reaction. Specific examples of the catalyst include organometallic compounds (dibutyltin dilaurate, dioctyltin dilaurate, bismuth carboxylate, bismuth alkoxide, and chelate compounds of bismuth with a compound having a dicarbonyl group, etc.), inorganic metal compounds (bismuth oxide, bismuth hydroxide, bismuth halides, etc.), tertiary amines (triethylamine, triethylenediamine, 1,8-diazabicyclo[5.4.0]-7-undecene, etc.), and combinations of two or more of these.

[0056] The reaction temperature when preparing the urethane prepolymer for the polyurethane resin (X1) or the polyurethane resin (X2) may be 50 to 140° C. or 70 to 100° C. The reaction time may be 1 to 10 hours or 2 to 8 hours.

[0057] <Process (ii)> Step (ii) is a surface layer forming step. In step (ii), a urethane prepolymer for polyurethane resin (X1) or an organic solvent solution thereof is mixed with the aliphatic polyisocyanate and other component (C1) as needed, and then coated onto a release film to a predetermined thickness to form a surface layer. From the viewpoints of scratch resistance and optical properties, the thickness of the surface layer is preferably 10 μm or less, more preferably 1 to 8 μm. When an organic solvent solution of a prepolymer for polyurethane resin (X1) is used, step (ii) may include a step of drying the organic solvent. The drying temperature may be 30 to 160°C, or may be 100 to 150°C. The drying time may be 10 seconds to 5 minutes, or may be 20 to 60 seconds.

[0058] <Step (iii)> Step (iii) is a base layer formation step. In step (ii), a urethane prepolymer for polyurethane resin (X2) or an organic solvent solution thereof is mixed with component (a2-2) such as the chain extender and component (C2) such as an environmental stabilizer, as needed, and then coated to a predetermined film thickness on the surface layer obtained in step (ii) to form a base layer. Step (iii) is preferably a step of coating a prepolymer for polyurethane resin (X2) or an organic solvent solution thereof on the surface layer and then heat-curing the coated prepolymer. The curing temperature may be 60 to 150°C, or 80 to 120°C. The curing time may be 1 to 8 hours, or 2 to 6 hours. When an organic solvent solution of the prepolymer for polyurethane resin (X2) is used, step (iii) may include a step of drying the organic solvent. The step of drying the organic solvent may be carried out simultaneously with the above-mentioned curing. From the viewpoint of mechanical properties, the thickness of the substrate layer is preferably 150 μm or more, more preferably 150 to 450 μm.

[0059] The cover film according to this embodiment can be produced by a production method including the above steps (i) to (iii).

[0060] The elastic recovery rate of the cover film when stretched to 100% as measured by the method described below is 80 to 100%, and more preferably 90 to 100%. If the elastic recovery rate of the cover film at 100% elongation is within the above range, the scratch resistance tends to be good.

[0061] <Method for measuring elastic recovery at 100% elongation> (1) Cut the cover film into a strip measuring 100 mm in length, 5 mm in width, and 400 μm in thickness, and mark it with a mark 25 mm from both ends of the long side to create a test piece. (2) This test piece is placed in an Instron tensile testing machine at 23°C with a chuck distance of 50 mm and a pulling rate of 300 mm / min. The cover film is stretched until the gauge length is 100 mm (stretching process), and then the chuck distance is returned to 50 mm (return process). (3) The stress at 50% elongation during the elongation process is M1, and the stress at 50% elongation during the return process is M2. The following formula is the elastic recovery rate. Elastic recovery rate (%) = (M2 / M1) x 100

[0062] The hysteresis loss of the cover film measured at −20° C. by the method described below is 13 to 30%, and more preferably 13 to 25%. If the hysteresis loss of the cover film measured at -20°C is within the above range, the flexibility at low temperatures tends to be good.

[0063] <Method of measuring hysteresis loss> (1) Cut the cover film into a strip measuring 100 mm in length, 15 mm in width, and 400 μm in thickness, and mark it with a mark 15 mm from both ends of the long side to create a test piece. (2) This test piece is placed in an Instron tensile testing machine at -20°C with a chuck distance of 70 mm and a pulling speed of 300 mm / min. The cover film is stretched until the gauge length is 105 mm, and then the chuck distance is returned to 70 mm. (3) The value calculated using the following formula from the area A (area of ​​part A in Figure 1) and area B (area of ​​part B in Figure 1) of the obtained stress-strain curve is the hysteresis loss. Hysteresis loss (%) = {A / (A+B)} x 100

[0064] The total light transmittance of the cover film measured by the method described below is preferably 85% or more, and more preferably 90% or more. The haze of the cover film, measured by the method described below, is preferably 2% or less, and more preferably 1% or less. As mentioned above, the cover film is used as a surface protection material for the image display device, and therefore must also have excellent transparency. If the cover film has a total light transmittance of 90% or more when stretched 50% and a haze of 1% or less, the transparency of the cover film is unlikely to decrease even when an image display device equipped with the cover film according to this embodiment is stretched, folded, or expanded.

[0065] [Image display device] The image display device according to this embodiment is characterized in that the cover film, the image display element, and a stretchable substrate or a flexible substrate are laminated in this order. The image display device according to this embodiment is equipped with a cover film that has excellent scratch resistance, mechanical properties, and optical properties, as well as excellent stretchability, and therefore can be used as a flexible display and / or a stretchable display. In other words, the image display device according to this embodiment may be flexible and / or stretchable.

[0066] <Image display element> In this specification, the term "image display element" refers to an element having a display medium whose contrast, brightness, reflectance, transmittance, etc. change due to electrical or magnetic action. Examples of display elements include EL (electroluminescence) elements, LED chips (white LED chips, red LED chips, green LED chips, blue LED chips, etc.), liquid crystal elements, etc.

[0067] <Stretchable substrate> As used herein, the term "stretchable substrate" refers to a substrate that can be stretched and contracted. In one embodiment, the stretchable substrate may be, but is not limited to, a silicone rubber such as polydimethylsiloxane; polyurethane; or an elastic polymer such as PTFE (Polytetrafluoroethylene).

[0068] <Flexible PCB> As used herein, the term "flexible substrate" refers to a substrate that can be bent, folded, rolled up, etc. In one embodiment, the flexible substrate may be made of a resin material such as polyimide, polyethylene terephthalate, polyethylene naphthalate, or polycarbonate, but is not limited thereto.

[0069] <Other configurations> The image display device according to this embodiment may include a touch panel and a sensor element.

[0070] [Manufacturing method for image display device] The image display device according to this embodiment may include a step of directly attaching the cover film according to this embodiment onto the image display element. [Example]

[0071] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to these examples in any way.

[0072] <Production Example 1> [Production of urethane prepolymer for polyurethane resin (X1-1) used in surface layer] In a container equipped with a stirrer and a temperature controller, the type and amount (parts by weight) of a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group, other active hydrogen components (a1-2), an isocyanate component (B1) without an aromatic ring, a chain extender (a3), and an organic solvent were charged and reacted at 80 ° C. for 3 hours, followed by the addition of a reaction terminator (a4) and reacting at 80 ° C. for 1 hour to obtain a urethane prepolymer for polyurethane resin (X1-1) used in the surface layer. The hydroxyl value of the resulting organic solvent solution of the urethane prepolymer for polyurethane resin (X1-1) used in the surface layer was 1.22 mg KOH / g.

[0073] <Production Examples 2 to 5 and Comparative Production Examples 1 and 2> [Production of urethane prepolymers for polyurethane resins (X1-2) to (X1-5) and (X1'-1) to (X1'-2) used in surface layer] Urethane prepolymers for polyurethane resins (X1-2) to (X1-5) used in the surface layer and urethane prepolymers for polyurethane resins (X1'-1) to (X1'-2) used in the surface layer for comparison were obtained in the same manner as in Production Example 1, except that the raw materials used and their amounts (parts by weight) were changed to those shown in Table 1.

[0074] [Table 1]

[0075] <Production Example 6> [Production of urethane prepolymer for polyurethane resin (X2-1) used in base layer] A vessel equipped with a stirrer and a temperature controller was charged with the types and amounts (parts by weight) of high molecular weight polyol (a2-2) and polyisocyanate component (B1) not having an aromatic ring shown in Table 2, and reacted at 80°C for 3 hours to obtain a urethane prepolymer for polyurethane resin (X2-1). The NCO content of the obtained urethane prepolymer for polyurethane resin (X2-1) used in the substrate layer was 4.04%.

[0076] <Production Examples 7 to 9 and Comparative Production Examples 3 and 4> [Production of urethane prepolymers for polyurethane resins (X2-2) to (X2-4) and (X2'-1) to (X2'-2) used in base layer] Urethane prepolymers for polyurethane resins (X2-2) to (X2-4) used in the base layer and urethane prepolymers for polyurethane resins (X2'-1) to (X2'-2) used in the base layer for comparison were obtained in the same manner as in Production Example 6, except that the urethane prepolymers used and the amounts (parts by weight) thereof were changed to those shown in Table 2.

[0077] [Table 2]

[0078] Example 1 The other component (C1) was added to and mixed with an organic solvent solution of the prepolymer for the polyurethane resin (X1-1) used for the surface layer, and then coated onto a release film to a thickness of 5 μm. This was then dried at 90°C for 2 minutes to form a semi-cured surface layer. The other component (C2) was added to and mixed with the prepolymer for the polyurethane resin (X2-1) used for the base layer, and then coated onto the semi-cured surface layer so that the total thickness of the cover film was 400 μm. The base layer and surface layer were cured by heating at 140°C for 2 hours, producing a cover film 1 in which the base layer and surface layer were chemically bonded. The compositions of the polyurethane resin (X1-1) constituting the surface layer of the obtained cover film 1 and the polyurethane resin (X2-1) constituting the base layer are as shown in Tables 1, 2, and 3. The proportion of the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group relative to the total amount of the active hydrogen component (A1) and the isocyanate component (B1) not having an aromatic ring in the polyurethane resin (X1) was 2.5 mass%. The proportions of the other components (C1) and (C2) in the surface layer and the base layer were as shown in Table 3.

[0079] <Examples 2 to 13 and Comparative Examples 1 to 4> Cover films of Examples 2 to 13 and Comparative Examples 1 to 4 were obtained in the same manner as in Example 1, except that the polyurethane resin for the surface layer and the polyurethane resin for the base layer were changed to the combinations shown in Table 3.

[0080] The contents of the various raw materials listed in Table 1 are as follows: <Urethane prepolymer material for polyurethane resin> [Compound (a1-1) having a polyorganosiloxane group and an active hydrogen group] BY-16-853U: Amino group-modified silicone oil manufactured by Toray Dow Corning Co., Ltd. [Mn=920, R in general formula (1)] 1 ~R 6 = methyl group, n = 12] KF-8012: Amino group-modified silicone oil manufactured by Shin-Etsu Chemical Co., Ltd. [Mn=2200, R in general formula (1)] 1 ~R 6 = methyl group, n = 57] KF-6001: hydroxyl-modified silicone oil manufactured by Shin-Etsu Chemical Co., Ltd. [Mn=1800, R in general formula (1)] 1 ~R 6 = methyl group, n = 23] KF-6002: hydroxyl-modified silicone oil manufactured by Shin-Etsu Chemical Co., Ltd. [Mn=3200, R in general formula (1)] 1 ~R 6 = methyl group, n = 42] [Other active hydrogen components (a1-2)] ETERNACALL UHC50-100: Polyester carbonate polyol (Mn=1000) manufactured by UBE Corporation ETERNACALL UHC40-200: Polyester carbonate polyol (Mn=2000) manufactured by UBE Corporation G3450J: Polycarbonate polyol (Mn=800) manufactured by Asahi Kasei Corporation G3452: Polycarbonate polyol (Mn=2000) manufactured by Asahi Kasei Corporation [High molecular weight polyol component (a2-2)] PTMG-3000: Polytetramethylene ether glycol, Mn=3000, manufactured by Mitsubishi Chemical Corporation PTMG-2000: Polytetramethylene ether glycol, Mn=2000, manufactured by Mitsubishi Chemical Corporation PTMG-1000: Polytetramethylene ether glycol, Mn=1000, manufactured by Mitsubishi Chemical Corporation Plaxel L220AL: Polycaprolactone polyol (Mn=2000) manufactured by Daicel Corporation Sannix SP-750: Polyoxypropylene sorbitol ether manufactured by Sanyo Chemical Industries, Ltd. [Chain extender (a3)] 1,4-BG: Fujifilm Wako Pure Chemical Industries, Ltd. [Reaction stopper (a4)] Diethanolamine: Fujifilm Wako Pure Chemical Industries, Ltd. [Alicyclic isocyanate] Desmodur W: Hydrogenated MDI manufactured by Sumika Covestro Urethane Co., Ltd. [Aliphatic polyisocyanate] CORONATE-2793: Allophanate-containing polyisocyanate (average functionality = 5.1) manufactured by Tosoh Corporation Duranate 50M: HDI manufactured by Asahi Kasei Corporation [Other ingredients (C1) and other ingredients (C2)] Irganox 245: BASF Japan Ltd., 3,6-dioxaoctamethylene bis[3-(tert-butyl-4-hydroxy-5-methylphenyl)]propionate Tinuvin 144: BASF Japan Ltd., bis(1,2,2,6,6-pentamethyl-4-piperidyl) 2-(3,5-di-tert-butyl-4-hydroxybenzyl)-2-n-butylmalonate Tinuvin 329: BASF Japan Ltd., 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)

[0081] <Method for measuring hysteresis loss at -20°C> (1) Cut the cover film into a strip measuring 100 mm in length, 15 mm in width, and 400 μm in thickness, and mark it with a mark 15 mm from both ends of the long side to create a test piece. (2) This test piece is placed in an Instron tensile testing machine at -20°C with a chuck distance of 70 mm and a pulling speed of 300 mm / min. The cover film is stretched until the gauge length is 105 mm, and then the chuck distance is returned to 70 mm. (3) The value calculated using the following formula from the area A (area of ​​part A in Figure 1) and area B (area of ​​part B in Figure 1) of the obtained stress-strain curve is the hysteresis loss. Hysteresis loss (%) = {A / (A+B)} x 100

[0082] <Method for measuring flexibility at low temperatures> (1) A cover film cut into a strip measuring 50 mm in length, 15 mm in width, and 400 μm in thickness is wrapped around a glass rod with a diameter of 10 mm and fixed in place. (2) The test piece is left standing at -20°C for 24 hours. (3) After 24 hours, the cover film was removed from the glass rod, and while kept at -20°C, it was placed on a flat surface with the bent inside facing down and visually inspected. <Evaluation criteria> ◎: The sample is not deformed, or even if it is deformed, the maximum height of the lift when placed horizontally is less than 3 mm. ○: The sample was deformed, and when placed horizontally, the maximum floating height was 3 mm or more and less than 5 mm. ×: The sample was deformed and when placed horizontally, the maximum height of the lift was 5 mm or more.

[0083] <Method for measuring elastic recovery at 100% elongation> (1) Cut the cover film into a strip measuring 100 mm in length, 15 mm in width, and 400 μm in thickness, and mark it with a mark 15 mm from both ends of the long side to create a test piece. (2) This test piece was set in the chuck of an Instron-type tensile testing machine (Shimadzu Corporation, product name "Autograph") and stretched at a constant rate of 500 mm / min in an atmosphere of 25°C until the distance between the gauge lines reached 100%, and then immediately returned to the distance between the chucks before stretching at the same rate. (3) The stress (M1) at 50% elongation during the elongation process and the stress (M2) at 50% elongation during the return process were measured, and the elastic recovery was calculated using the following formula (2). Elastic recovery rate (%) = M2 / M1 × 100 (2)

[0084] <Method for measuring pencil hardness> The cover film was fixed on a glass substrate with the surface layer facing up, and a pencil lead was pressed against the surface layer of the cover film with a load of 750 gf. In this state, the pencil was moved at a speed of 300 mm / min, and the scratch hardness of the cover film was evaluated by the hardness of the pencil lead. The cover film was fixed on the glass substrate without any adhesive.

[0085] <Method for measuring bending resistance> For the cover films obtained in the Examples and Comparative Examples, samples measuring 50 mm in the width direction (direction of the folded portion) and 100 mm in the machine direction (bending direction) were prepared. Using a no-load U-shaped stretch tester (Yuasa System Co., Ltd., DLDMLH-FS), the sample was bent 50,000 times at a rate of 1 bend / second with a bending radius of 3 mm. The sample was fixed at 10 mm positions on both ends of the long side, and the bending area was 50 mm x 80 mm. After the bending process, the sample was placed on a flat surface with the inside of the bend facing down and visually inspected. <Evaluation criteria> ◎: The sample is not deformed, or even if it is deformed, the maximum height of the lift when placed horizontally is less than 3 mm. ○: The sample was deformed, and when placed horizontally, the maximum floating height was 3 mm or more and less than 5 mm. ×: The sample has creases or the maximum height of the sample when placed horizontally is 5 mm or more.

[0086] <Method for measuring total light transmittance and haze> The total light transmittance and haze of the cover films obtained in the examples and comparative examples were measured using a spectrophotometer (manufactured by Konica Minolta, Inc., product name "CM3600A").

[0087] <Method for measuring the coefficient of dynamic friction> (1) The surface layer of a cover film cut into a rectangle measuring 100 mm in length, 50 mm in width, and 400 μm in thickness is fixed on a glass plate. (2) After leaving the cover film in a room temperature-controlled at 23°C for 24 hours, measure the coefficient of dynamic friction using a Tribomaster TL-201s (manufactured by Trinity Labs) and a tactile contactor under the following conditions: temperature 23°C, load 30 g, speed 50 mm / s, and travel distance 50 mm.

[0088] [Table 3] [Industrial Applicability]

[0089] The cover film of the present invention is excellent in abrasion resistance, surface slipperiness, flexibility, etc., and is therefore suitable as a surface protective film for optical members, particularly as a surface protective film for image display devices.

Claims

1. A cover film having at least a base layer and a surface layer, The cover film has an elastic recovery rate of 80 to 100% when elongated to 100%, and a hysteresis loss of 13 to 30% measured at −20° C. The base material layer contains a polyurethane resin (X2), and the polyurethane resin (X2) satisfies the following conditions (1-1) to (1-2): (1-1) The polyurethane resin (X2) is a reaction product of an active hydrogen component (A2) that does not contain a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group, and an isocyanate component (B2) that does not contain an aromatic ring. (1-2) The polyurethane resin (X2) has a crosslinking point concentration calculated from the following formula (1) of 0.4 mmol / g or more. Crosslinking point concentration (mmol / g)=(F−2)×(number of millimoles of tri- or higher functional monomers per gram of polyurethane resin) (1) (In formula (1), F represents the number of functional groups in the tri- or higher functional constituent monomer.) Fulfilling The surface layer contains a polyurethane resin (X1) having a urea group and a polyorganosiloxane group, and the polyurethane resin (X1) satisfies the following conditions (2-1) to (2-4): (2-1) The polyurethane resin (X1) is a reaction product of an active hydrogen component (A1) and an isocyanate component (B1) having no aromatic ring. (2-2) The active hydrogen component (A1) contains a compound (a1-1) having a polyorganosiloxane group and an active hydrogen group. (2-3) The weight ratio of the compound (a1-1) having a polyorganosiloxane group and an active hydrogen group to the total amount of the active hydrogen component (A1) and the isocyanate component (B1) is 4.0 mass% or less. (2-4) The polyurethane resin (X1) has a urethane group concentration (when urea groups are present in the polyurethane resin (X1), the total concentration of urethane groups and urea groups) of 1.8 mmol / g or less. Meet, cover film.

2. The cover film according to claim 1 , wherein the active hydrogen component (A1) has at least an amino group as an active hydrogen group.

3. An image display device comprising the cover film according to claim 1 or 2, an image display element, and a stretchable or flexible substrate laminated in this order.

4. The image display device according to claim 3 , which has flexibility and / or stretchability.

Images