Decorative film

Abstract

To provide a decorative film which is excellent in heat conductivity, toughness, heat resistance, and dimensional stability.SOLUTION: A decorative film has a film composed of a polyethylene-based thermoplastic resin composition which contains, with respect to 100 pts.wt. of a polyethylene-based thermoplastic resin (A), 1 to 60 pts.wt. of a cellulose nanofiber (B) having an average fiber diameter of 1 to 1,000 nm, and 20 to 150 pts.wt. of at least one or more kinds of heat conductive particles and / or heat conductive fibers (C) selected from the group consisting of metal, a metal oxide, a metal nitride, a metal carbide, a carbon nanotube, graphite and carbon fibers, as a structure, wherein a (thickness direction) / (plane direction) ratio by percentage of heat conductivity of the film composed of the polyethylene-based thermoplastic resin composition is 60% or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a decorative film. [Background technology]

[0002] Decorative films are films (or sheets) that have been decorated by printing, painting, vacuum deposition, coloring, etc., and are attached to the surface of a molded product, or only the design layer is transferred to the molded product. It is a film. The basic structure of the decorative film is, for example, a resin film (substrate film or sheet) / adhesive layer / decorative layer / hard coat layer / peeling layer. The main purpose of the decorative film has been to provide surface design (metallic, wood grain, embossed, mesh, grain, etc.), hard coat, anti-reflection, etc., but in recent years, new functions such as water repellency, heat insulation, heat shielding, ultraviolet shielding, near infrared shielding, heat dissipation, antibacterial and antiviral properties, electromagnetic wave shielding, inkjet printing, and 3D printer decoration have been considered. In particular, with regard to heat dissipation, the amount of heat generated by parts, equipment, devices, etc. increases with the miniaturization and high output of electric and electronic devices, semiconductors, and batteries, or the high output of power devices and power generation equipment, and there is an increasing demand for excellent heat conductive materials to suppress fires and failures. In addition, there is also an increasing demand for excellent heat conductive materials for the purpose of reducing the impact of rising temperatures due to recent climate change on the heat generated by parts, equipment, devices, etc. Methods for bonding decorative film to molded products include in-mold molding (IM-D, IM-L), in which the decorative film is inserted into a mold and then molten resin is injected to bond the film to the surface of the molded product, and out-mold molding (OMD).

[0003] On the other hand, painting has been commonly used as a method of decorating the surface of molded products, but problems have been pointed out with painting using solvents, such as low production efficiency due to manual work, low yield, dirty work sites, large carbon dioxide emissions and energy consumption in the drying process of the solvent, compliance with VOC (volatile organic compound) emission standards, and the need for measures to prevent health damage to workers. In addition, improvements have been made with powder paints and water-based paints, but there are concerns about health damage from inhalation of powder paints, and while water-based paints do not emit VOCs, they have problems such as large energy consumption in the drying process and the need for wastewater treatment. On the other hand, film decoration does not use solvents and has features such as high precision, high productivity, labor saving, and high yield, so in recent years it has been attracting attention as a paint-free method, mainly in the automotive field.

[0004] Here, cellulose nanofiber is a biomass material derived from plants, and has characteristics such as light weight, high strength, low dimensional change rate, and thixotropy, so many materials and molded products have been proposed that are composited with inks, adhesives, plastics, etc. (For example, see Patent Documents 1 to 3.) In addition, resin compositions containing thermoplastic resins, cellulose nanofibers, and thermally conductive fillers have been proposed (For example, see Patent Documents 4 to 8.) [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7248988 [Patent Document 2] Patent No. 7303015 [Patent Document 3] Patent Publication No. 2021-109911 [Patent Document 4] Patent No. 6870400 [Patent Document 5] Patent No. 6913307 [Patent Document 6] Patent No. 6795555 [Patent Document 7] Patent Publication No. 2021-143249 [Patent Document 8] Patent Publication No. 2021-50327 Summary of the Invention [Problem to be solved by the invention]

[0006] The compositions containing cellulose nanofibers proposed in Patent Documents 1 to 3 do not disclose anything about decoration. In addition, the compositions described in Patent Documents 4, 6, and 7 have a problem that their thermal conductivity is not fully satisfactory. Furthermore, the resin composition described in Patent Document 5 has a problem that its toughness is not fully satisfactory. In addition, the resin composition described in Patent Document 8 uses a curable resin, and has a problem that its productivity is low compared to decorative films using a film made of a thermoplastic resin, and recycling is also difficult.

[0007] Therefore, an object of the present invention is to provide a decorative film that is excellent in thermal conductivity, toughness, heat resistance, dimensional stability, and the like. [Means for solving the problem]

[0008] As a result of intensive research aimed at solving the above problems, the present inventors discovered that a decorative film comprising a film made of a polyethylene-based thermoplastic resin composition containing a polyethylene-based thermoplastic resin, specific cellulose nanofibers, and a specific thermally conductive filler is excellent in thermal conductivity, toughness, heat resistance, dimensional stability, etc., and thus completed the present invention.

[0009] That is, the respective aspects of the present invention are [1] to [3] shown below. [1] A decorative film comprising, as a constituent, a film made of a polyethylene thermoplastic resin composition containing, per 100 parts by weight of a polyethylene thermoplastic resin (A), 1 to 60 parts by weight of cellulose nanofibers (B) having an average fiber diameter of 1 to 1,000 nm, and 20 to 150 parts by weight of at least one type of thermally conductive particle and / or thermally conductive fiber (C) selected from the group consisting of metals, metal oxides, metal nitrides, metal carbides, carbon nanotubes, graphite, and carbon fibers, wherein the ratio of the thermal conductivity of the film made of the polyethylene thermoplastic resin composition (thickness direction) / (plane direction) as a percentage is 60% or more. [2] The decorative film according to [1], wherein the cellulose nanofiber (B) is a cellulose nanofiber (B) in which the hydroxyl groups of cellulose are acetylated or acylated. [3] The decorative film according to any one of [1] to [2], wherein the polyethylene-based thermoplastic resin composition (A) further contains 1 to 100 parts by weight of a biomass resin (D). Effect of the Invention

[0010] According to the present invention, it is possible to provide a decorative film that does not emit VOCs and has excellent thermal conductivity, toughness, heat resistance, dimensional stability, etc., for decorating the surface of a molded article with high productivity and high yield, and the industrial value of the film is extremely high. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below.

[0012] The polyethylene-based thermoplastic resin constituting the decorative film of the present invention may be, for example, a homopolymer such as high-density polyethylene, medium-density polyethylene, branched low-density polyethylene, linear low-density polyethylene, or ultra-high molecular weight polyethylene, or may be an ethylene-α-olefin copolymer. In the case of an ethylene-α-olefin copolymer, examples of the α-olefin include propylene, 1-butene, 4-methyl-1-pentene, 1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-hexadecene, and 1-octadecene. In addition, an ethylene-based copolymer may be used. In the case of ethylene-based copolymers, examples of ethylene-based copolymers include ethylene-vinyl acetate copolymers, saponified ethylene-vinyl acetate copolymers, ethylene-α,β-unsaturated carboxylic acid alkyl ester copolymers, ethylene-maleic anhydride copolymers, ethylene-α,β-unsaturated carboxylic acid alkyl ester-maleic anhydride copolymers, ethylene-α,β-unsaturated carboxylic acid glycidyl ester copolymers, ethylene-α,β-unsaturated carboxylic acid glycidyl ester-vinyl acetate copolymers, and ethylene-α,β-unsaturated carboxylic acid glycidyl ester-α,β-unsaturated carboxylic acid alkyl ester copolymers. The density of the polyethylene thermoplastic resin is not particularly limited, but is usually 0.890 to 0.975 g / cm. 3 Since it is easy to obtain mechanical strength, it is 0.910 to 0.960 g / cm 3 It is more preferable that the polyethylene thermoplastic resin is one of these. It is also possible to use these polyethylene thermoplastic resins alone or in combination.

[0013] Furthermore, the melt flow rate (MFR) of the polyethylene thermoplastic resin at 190°C under a load of 2.16 kg is not particularly limited, but is usually preferably 0.01 to 80 g / 10 min, and more preferably 0.05 to 50 g / 10 min in order to improve moldability.

[0014] The cellulose nanofiber (B) constituting the decorative film of the present invention may be any cellulose nanofiber containing material, and the cellulose that is the raw material of the cellulose nanofiber is generally known to be derived from plants such as wood, bamboo, hemp, rice, jute, kenaf, cotton, beet, oil palm, cloth, pulp, recycled pulp, waste paper, and agricultural waste such as olive oil extraction residue, or from algae, microorganisms (e.g., acetic acid bacteria) or animals (e.g., sea squirts), and any of these can be used in the present invention. Cellulose derived from plants or microorganisms is preferred, and cellulose derived from plants is more preferred. These cellulose nanofibers can be used alone or in combination. Furthermore, the cellulose nanofiber can also be used as a master batch in which it is previously incorporated into a polyethylene resin or the like.

[0015] The cellulose nanofiber (B) used in the present invention has an average fiber diameter of 1 to 1,000 nm. If the average fiber diameter of the cellulose nanofiber is less than 1 nm, the productivity of the cellulose nanofiber is low, and the production cost increases. On the other hand, if the average fiber diameter of the cellulose nanofiber exceeds 1,000 nm, the effect of improving the heat resistance and dimensional change rate by adding the cellulose nanofiber is poor, and many fish eyes are generated in the film, which deteriorates the appearance of the decorative film. The fiber length of the cellulose nanofiber is not particularly limited, but since the effect of improving the heat resistance and dimensional change rate by adding the cellulose nanofiber is particularly excellent, it is preferable that the fiber length / fiber diameter (aspect ratio) is 10 to 10,000. The average fiber diameter of the cellulose nanofiber is measured by observation with a scanning electron microscope (SEM) and calculated as the average diameter of 50 or more fibers.

[0016] Furthermore, the cellulose nanofibers can be produced by publicly known methods, for example, by mechanically opening the fibers using a twin-screw extruder, a Banbury mixer, a pressure kneader, a homogenizer, a media stirring mill, a vibration mill, a grinder, a ball mill, a high-pressure water jet, an ultrasonic dispersion processor, a beater, a disk refiner, a conical refiner, a double disk refiner, or the like.

[0017] Furthermore, the cellulose nanofiber constituting the present invention is preferably a hydrophobic cellulose nanofiber in which the hydroxyl groups of the cellulose nanofiber are acetylated or acylated, and by making the cellulose nanofiber acetylated or acylated, the dispersibility in a polyethylene-based thermoplastic resin is excellent, and a decorative film excellent in toughness, heat resistance and dimensional stability can be obtained. As a method for acetylating or acylating the hydroxyl groups of the cellulose nanofiber, a publicly known method can be used, and for example, a method of substituting the hydroxyl groups of cellulose with an acid anhydride such as acetic anhydride, propionic anhydride, butyric anhydride, pentanoic anhydride, hexanoic anhydride, decanoic anhydride, benzoic anhydride, stearic anhydride, maleic anhydride, succinic anhydride, phthalic anhydride, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, maleic anhydride-modified diene polymer, or polybasic acid anhydride can be used. The degree of substitution of the hydroxyl groups of the cellulose nanofibers with acetyl or acyl groups is optimized as appropriate depending on the type of polyethylene resin, thermally conductive particles and / or thermally conductive fibers that constitute the present invention and the target physical properties. In order to obtain a decorative film with particularly excellent thermal conductivity, toughness, heat resistance and dimensional stability, the degree of substitution is preferably 0.3 to 1, and more preferably 0.5 to 1.

[0018] The amount of the cellulose nanofiber blended is 100 parts by weight of the polyethylene thermoplastic resin. The amount of the cellulose nanofiber is less than 1 part by weight. In the case of cellulose ester, the heat resistance and dimensional stability of the decorative film are poor. If the amount of nanofibers exceeds 60 parts by weight, the toughness and moldability of the film will be poor.

[0019] The thermally conductive particles and / or thermally conductive fibers (C) constituting the decorative film of the present invention are at least one type of thermally conductive particles and / or fibers selected from the group consisting of metals, metal oxides, metal nitrides, metal carbides, carbon nanotubes, graphite, and carbon fibers. Metals include silicon, copper, aluminum, etc.; metal oxides include aluminum oxide, silicon dioxide, magnesium oxide, iron oxide, beryllium oxide, titanium dioxide, zinc oxide, etc.; metal nitrides include aluminum nitride, silicon nitride, boron nitride, gallium nitride, etc.; metal carbides include silicon carbide, titanium carbide, boron carbide, tungsten carbide, etc. Thermally conductive particles and thermally conductive fibers are classified into conductive type and insulating type, and are appropriately selected depending on the application of the parts, equipment, device, etc. in which the decorative film is used.

[0020] The amount of the thermally conductive particles and / or thermally conductive fibers is 20 to 150 parts by weight per 100 parts by weight of the polyethylene thermoplastic resin. If the amount of the thermally conductive particles and / or thermally conductive fibers is less than 20 parts by weight, the thermal conductivity, i.e., heat dissipation, of the decorative film is poor. On the other hand, if the amount of the thermally conductive particles and / or thermally conductive fibers is more than 150 parts by weight, the formability, toughness, and appearance of the film are poor. The decorative film of the present invention is characterized by using the cellulose nanofibers in combination with the thermally conductive particles and / or thermally conductive fibers. The thermally conductive particles and / or fibers interact with each other so that they are supported by the cellulose nanofibers dispersed in the polyethylene thermoplastic resin, and the thermally conductive particles and / or fibers are uniformly dispersed and oriented in the polyethylene thermoplastic resin. As a result, a thermal conduction path is efficiently formed in the polyethylene thermoplastic resin, and excellent thermal conductivity, i.e., heat dissipation, is achieved by adding a smaller amount of thermally conductive particles and / or fibers. Furthermore, since the thermally conductive particles and fibers are generally aligned in the orientation direction of the film, the thermal conductivity in the thickness direction of the film is significantly inferior to the thermal conductivity in the planar direction of the film. On the other hand, in the film made of the polyethylene thermoplastic resin constituting the present invention, the ratio of the thermal conductivity in the thickness direction to the planar direction of the film made of the polyethylene thermoplastic resin composition is 60% or more, preferably 75% or more, based on a percentage. Since the cellulose nanofibers are three-dimensionally spread throughout the polyethylene thermoplastic resin, the thermally conductive particles and thermally conductive fibers that interact with the cellulose nanofibers are also dispersed and oriented three-dimensionally, resulting in a smaller difference in thermal conductivity between the thickness direction and the plane direction of the film made of the polyethylene thermoplastic resin composition.

[0021] The polyethylene-based thermoplastic resin composition constituting the present invention may contain a biomass resin (D) useful for carbon neutrality. The biomass resin is generally classified into a type produced in a microorganism body, a type obtained by polymerizing a monomer obtained by fermenting, decomposing, and modifying biomass such as starch and fats and oils, and a type obtained by chemically modifying natural products such as polysaccharides, and examples thereof include polylactic acid, polyhydroxyalkanoate, polybutylene succinate, biomass polyethylene, biomass polypropylene, biomass polyethylene terephthalate, biomass polytrimethylene terephthalate, and biomass polyamide. The amount of the biomass resin (D) to be blended with respect to 100 parts by weight of the polyethylene-based thermoplastic resin is preferably 10 to 100 parts by weight because it is effective for carbon neutrality.

[0022] The polyethylene thermoplastic resin composition may be used by mixing various additives within the scope of the present invention, and may be one or more of conventional additives such as plasticizers such as polyalkylene oxide oligomer compounds, thioether compounds, ester compounds, and organic phosphorus compounds, slip agents, antiblocking agents, antioxidants, heat stabilizers, ultraviolet absorbers, light stabilizers, waxes, rosins, and terpenes. Furthermore, the polyethylene thermoplastic resin composition may be one or more of various thermoplastic resins such as polyester resins such as polyethylene terephthalate, polyamide resins such as polyamide 6, polyolefin resins such as polypropylene, polystyrene resins such as polystyrene, and polyurethane.

[0023] The polyethylene-based thermoplastic resin composition can be produced by feeding the polyethylene-based thermoplastic resin (A), the cellulose nanofibers (B), thermally conductive particles and / or thermally conductive fibers (C), and, if necessary, any additives and thermoplastic resins, into an extruder and extruding the resulting composition to form an image.

[0024] Examples of the method for producing the decorative film of the present invention include a method of co-extruding a film made of the polyethylene-based thermoplastic resin composition with a decorative layer, a hard coat layer, a peeling layer, etc.; a method of forming a decorative layer, a peeling layer, an adhesive layer, etc. on a film made of the polyethylene-based thermoplastic resin composition by a printing method such as gravure printing or screen printing; a method of laminating a film made of the polyethylene-based thermoplastic resin composition with a decorative layer, a hard coat layer and / or a peeling layer, etc. using an adhesive or pressure-sensitive adhesive by using a dry laminator or the like; a method of heat-sealing a film made of the polyethylene-based thermoplastic resin composition with a decorative layer, a hard coat layer, a peeling layer, etc.; a method of coating a film made of the polyethylene-based thermoplastic resin composition with a decorative layer, a hard coat layer, a peeling layer, an adhesive layer, etc. as a coating liquid; and a method of extrusion laminating the polyethylene-based thermoplastic resin composition on a film made of a decorative layer, a hard coat layer, a peeling layer, etc.

[0025] In addition, the decorative film of the present invention can also be laminated with films or membranes having functions such as ultraviolet shielding, waterproofing, water repellency, scratch resistance, abrasion resistance, sliding properties, rust prevention, stain resistance, heat shielding, electromagnetic wave shielding, antibacterial properties, antiviral properties, chemical resistance, and flame retardancy as components.

[0026] The decorative film obtained by the present invention can be suitably used for the purpose of decorating and imparting heat dissipation properties, as well as waterproofing, water repellency, scratch resistance, abrasion resistance, sliding properties, rust resistance, stain resistance, heat shielding properties, ultraviolet shielding properties, near-infrared shielding properties, electromagnetic wave shielding properties, antibacterial properties, antiviral properties, chemical resistance, flame retardancy, etc. to portable devices such as smartphones, electric devices such as home appliances and car stereos, electronic devices such as notebook computers, interior and exterior materials for automobiles, interior and exterior materials for buildings and building materials, furniture, window glass, etc. EXAMPLES

[0027] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. It is not something that is done.

[0028] The polyethylene-based thermoplastic resins used in the examples and comparative examples are shown below.

[0029] Low-density polyethylene (hereinafter referred to as PE(A-1)); manufactured by Tosoh Corporation (product name) Petrothene 212, MFR 8.0g / 10min.

[0030] Ethylene-vinyl acetate copolymer (hereinafter referred to as PE (A-2)) manufactured by Tosoh Corporation, (product name) Ultrathene 751, MFR 5.7 g / 10 min.

[0031] Saponified ethylene-vinyl acetate copolymer (hereinafter referred to as PE (A-3)) manufactured by Tosoh Corporation, (product name) Mersen H6051, MFR 5.5g / 10min.

[0032] Polylactic acid (hereinafter referred to as PLA(D)); manufactured by NatureWorks, (product name) Ingeo4032D, MFR 4g / 10min.

[0033] Polypropylene (hereinafter referred to as PP(E)); manufactured by Japan Polypropylene Corporation, (product name) Novatec FA3KM, MFR = 10 g / 10 min.

[0034] Microcellulose fiber (hereinafter referred to as MCF (B-2)); product name: ARBOCEL BC200, manufactured by Rettenmaier Co., Ltd., average fiber length 300 μm, number average fiber diameter 20 μm.

[0035] Pulp preparation example 8 kg of water-containing softwood unbleached kraft pulp (hereinafter referred to as NUKP) (solid content 5 kg) was refined and repeatedly defibrated by refinery processing until the freeness (CSF) reached 50 ml. Next, 5,000 ml of acetic anhydride was added to the refined NUKP and reacted at 80°C for 4 hours. The reaction product was then cooled to 40°C and separated from the liquid, after which acetic anhydride and acetic acid were removed at 70°C under reduced pressure. The product was then dried under reduced pressure at 60°C for 20 hours to obtain acetylated NUKP. The acetyl group substitution degree of the obtained acetylated NUKP was 0.85.

[0036] Thermally conductive particles, thermally conductive fibers Metal silicon powder (hereinafter referred to as C-1); manufactured by Kinsei Matec Co., Ltd., (product name) Metal Silicon #600; silicon content 98.5% by weight, average particle size 6 μm, irregular shape powder.

[0037] Carbon fiber (hereinafter referred to as C-2); manufactured by Mitsubishi Plastics, Inc., (product name) Dialead K223HE; fiber length 6 mm, fiber diameter 10 μm.

[0038] Scaly boron nitride powder (hereinafter referred to as C-3); manufactured by Denki Kagaku Kogyo Co., Ltd., (product name) Denka Boron Nitride SGP; average particle size 18 μm.

[0039] Carbon nanotubes (hereinafter referred to as C-4); manufactured by Hodogaya Chemical Co., Ltd., (product name) MWNT-7; average single fiber diameter 65 nm, average single fiber length 40 μm, multi-walled carbon nanotubes. <Measurement of thermal conductivity> A thermal conductivity measuring device (ULVAC, (product name) TC7000; ruby ​​laser) was used to measure by the laser flash method at 23° C. The thermal conductivity in the thickness direction was determined by a one-dimensional method to determine the heat capacity Cp and the thermal diffusivity α in the thickness direction, and the thermal conductivity in the planar direction was determined by a two-dimensional method to determine the thermal diffusivity α' in the planar direction, and the thermal conductivity was calculated from the following formula.

[0040] Thermal conductivity in the thickness direction = ρ × Cp × α Thermal conductivity in the planar direction = ρ × Cp × α' Here, the density ρ was measured according to ASTM D-792 A method (underwater displacement method). When the thermal conductivity in the thickness direction and the planar direction was 1.5 W / mK or more, the decorative film was judged to have excellent thermal conductivity. In addition, in order to evaluate the anisotropy of thermal conductivity, the ratio of thermal conductivity (thickness direction) / (planar direction) was calculated as a percentage. The closer the value is to 100%, the smaller the anisotropy is, and conversely, when the value is closer to 0% or significantly exceeds 100%, the anisotropy is considered to be large. Therefore, when the value is between 60% and 110%, the anisotropy of thermal conductivity is judged to be small. <Measurement of linear expansion coefficient of decorative film> Using a laser interference method (double-path Michaelson type), a film sample with a width of 5 mm and a length of 5 mm was used, and measurements were taken at a temperature rise rate of 2°C / min and at a measurement temperature of 0°C to 50°C. It was determined that when the linear expansion coefficient was less than 100 ppm / K, the heat resistance and dimensional stability of the decorative film were excellent, and when the linear expansion coefficient was 100 ppm / K or more, the heat resistance and dimensional stability of the decorative film were poor. <Measurement of tensile breaking stress> The measurement was performed at a pulling speed of 200 mm / min in accordance with ISO 1872-2. When the tensile breaking strength was 15 MPa or more, the decorative film was judged to have excellent strength, and when the tensile breaking strength was less than 15 MPa, the decorative film was judged to have poor strength. <Measurement of tensile elongation at break> The measurement was performed at a tensile speed of 200 mm / min in accordance with ISO 1872-2. When the tensile breaking elongation was 15% or more, the toughness of the decorative film was judged to be excellent, and when the tensile breaking elongation was less than 15%a, the toughness of the decorative film was judged to be poor.

[0041] Example 1 100 parts by weight of PE (A-1), 80 parts by weight of PE (A-2), 15 parts by weight of acetylated NUKP, and 20 parts by weight of metal silicon powder (C-1) were mixed uniformly in advance and fed into the hopper of a twin-screw extruder (manufactured by The Japan Steel Works, Ltd., (product name) TEX-25αIII, L / D=55) having four kneading zones. Meanwhile, 50 parts by weight of carbon fiber (C-2) and 10 parts by weight of carbon nanotubes (C-4) were fed from the hopper of the side feeder of the twin-screw extruder, and melt-kneaded under the condition that the cylinder temperature of the kneading zone was heated to 220°C, to produce a polyethylene-based thermoplastic resin composition in which acetylated NUKP, metal silicon powder (C-1), carbon fiber (C-2) and carbon nanotubes (C-4) were dispersed. The polyethylene thermoplastic resin composition obtained was then fed to a film forming machine with a screw diameter of 15 mmφ equipped with a T-die with a discharge port width of 100 mm, and molded into a film with a thickness of about 80 μm at a temperature of 220° C. The fiber diameter of the acetylated cellulose nanofiber (hereinafter referred to as CNF (B-1)) measured by observation with a scanning electron microscope (SEM) was 70 nm. Next, the film made of the polyethylene thermoplastic resin composition was decorated with a wood grain pattern by gravure printing. The results of each measurement and evaluation are shown in Table 1.

[0042] Examples 2 to 6 Decorative films were produced in the same manner as in Example 1, with the blending ratios of polyethylene resin (A), acetylated cellulose nanofiber (B-1), metal silicon powder (C-1), carbon fiber (C-2), scaly boron nitride powder (C-3), carbon nanotubes (C-4), and polylactic acid (D) set as shown in Table 1. They were then evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. All of the decorative films obtained were excellent in thermal conductivity, anisotropy of thermal conductivity, toughness, heat resistance, and dimensional change rate.

[0043] Comparative Examples 1 to 7 The decorative films were produced in the same manner as in Example 1 under the conditions shown in Table 2 for the blending ratios of polyethylene resin (A), acetylated cellulose nanofiber (B-1), microcellulose fiber (B-2), metal silicon powder (C-1), carbon fiber (C-2), scaly boron nitride powder (C-3), carbon nanotube (C-4), polylactic acid (D), and polypropylene (E). Then, the films were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. The decorative films obtained in Comparative Examples 1 and 3 were inferior in heat resistance and dimensional change rate. The decorative film obtained in Comparative Example 1 was inferior in strength, and the decorative films obtained in Comparative Examples 2, 4, 5, and 7 were inferior in toughness. The decorative films obtained in Comparative Examples 2, 3, 4, and 6 were inferior in thermal conductivity. The decorative films obtained in Comparative Examples 1, 3, and 4 had large anisotropy in thermal conductivity.

[0044] [Table 1]

[0045] [Table 2] [Industrial Applicability]

[0046] The present invention provides a decorative film that is excellent in thermal conductivity, toughness, heat resistance, dimensional stability, etc., and is useful for decorating and dissipating heat in portable devices such as smartphones, electric devices such as home appliances and car stereos, electronic devices such as notebook computers, interior and exterior materials for automobiles, interior and exterior materials for buildings and building materials, furniture, window glass, etc.

Claims

1. The decorative film comprises, as its constituents, a film made of a polyethylene thermoplastic resin composition containing, per 100 parts by weight of a polyethylene thermoplastic resin (A), 1 to 60 parts by weight of cellulose nanofibers (B) having an average fiber diameter of 1 to 1,000 nm, and 20 to 150 parts by weight of at least one type of thermally conductive particle and / or thermally conductive fiber (C) selected from the group consisting of metals, metal nitrides, metal carbides, carbon nanotubes, graphite, and carbon fibers, and the film made of the polyethylene thermoplastic resin composition has a (thickness direction) / (plane direction) ratio, expressed as a percentage of thermal conductivity, of 60% or more.

2. The decorative film according to claim 1 , wherein the cellulose nanofiber (B) is a cellulose nanofiber in which a hydroxyl group of cellulose is acetylated or acylated.

3. The decorative film according to any one of claims 1 to 2, wherein the polyethylene-based thermoplastic resin composition further comprises 1 to 100 parts by weight of a biomass resin (D).

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