Decorative film

Abstract

To provide a decorative film which is excellent in toughness, heat resistance and dimensional stability, and is useful for decoration of portable devices such as smart phones, electric devices such as household electric appliances and car stereos, electronic devices such as notebook computers, interior materials and exterior materials of automobiles, interior materials and exterior materials of buildings and building materials, furniture and window glass.SOLUTION: A decorative film has, as a component, a film composed of a polyethylene-based thermoplastic resin composition containing 1 to 60 pts.wt. of a cellulose nanofiber (B) having an average fiber diameter of 1 to 1,000 nm with respect to 100 pts.wt. of a polyethylene-based thermoplastic resin (A).SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Decorative films are films (or sheets) decorated by printing, painting, vacuum deposition, coloring, etc., which are then attached to the surface of a molded product, or only the design layer is transferred to the molded product. The basic structure of decorative films is, for example, a resin film (substrate film or sheet) / adhesive layer / decorative layer / hard coat layer / peeling layer. The main purpose of decorative films has traditionally been to provide surface designs (metallic, wood grain, embossed, mesh, grain, etc.), hard coats, and anti-reflection, but in recent years, new functions such as water repellency, heat insulation, heat shielding, UV shielding, near infrared shielding, heat dissipation, antibacterial and antiviral properties, electromagnetic wave shielding, inkjet printing, and 3D printer decoration have been considered. The methods of attaching decorative films 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 attach 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, decorative films containing thermoplastic resins and cellulose nanofibers have been proposed (For example, see Patent Documents 4 to 6.) [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7248988 [Patent Document 2] Patent No. 7303015 Publication [Patent Document 3] Patent Publication No. 2021-109911 [Patent Document 4] JP 2019-142110 A [Patent Document 5] JP 2010-6031 A [Patent Document 6] JP 2005-342977 A 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 decorative film described in Patent Document 4 has a problem that the toughness is not sufficiently satisfactory. Furthermore, the decorative film described in Patent Document 5 is a film in which a mixture of cellulose microfibrils attached to the surface of a resin material is integrated with the decorative film in a mold, and the decorative film does not contain cellulose nanofibers, so that the characteristics of the cellulose nanofibers are not easily utilized in the decorative film. In addition, the decorative film described in Patent Document 6 has a problem that the number of cellulose fibers contained in the film is significantly smaller than that of cellulose nanofibers because the fiber diameter of the cellulose fibers is 1 to 100 μm, so that the characteristics of the cellulose fibers are not easily utilized in the decorative film, and further, there is a problem that many fish eyes are generated in the film.

[0007] Therefore, an object of the present invention is to provide a decorative film that is excellent in 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-mentioned 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 and specific cellulose nanofibers has excellent 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 a film made of a polyethylene thermoplastic resin composition containing 100 parts by weight of a polyethylene thermoplastic resin (A) and 1 to 60 parts by weight of cellulose nanofibers (B) having an average fiber diameter of 1 to 1,000 nm. [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 [1] or [2], wherein the polyethylene-based thermoplastic resin composition further contains 1 to 100 parts by weight of a biomass resin (C). 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 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. 3Since 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 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 nanofiber with acetyl or acyl groups is optimized as appropriate depending on the type of polyethylene resin constituting the present invention and the target physical properties. However, a degree of substitution of 0.5 to 1 is particularly preferred, as this results in a decorative film with particularly excellent toughness, heat resistance, and dimensional stability.

[0018] The amount of the cellulose nanofiber is 1 to 60 parts by weight based on 100 parts by weight of the polyethylene thermoplastic resin. If the amount of the cellulose nanofiber is less than 1 part by weight, the heat resistance and dimensional stability of the decorative film will be poor. On the other hand, if the amount of the cellulose nanofiber is more than 60 parts by weight, the toughness and moldability of the film will be poor.

[0019] The polyethylene-based thermoplastic resin composition may contain a biomass resin (C) that is 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.

[0020] 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.

[0021] The polyethylene-based thermoplastic resin composition can be produced by putting the polyethylene-based thermoplastic resin (A), the cellulose nanofibers (B), and, if necessary, any additives and thermoplastic resins into an extruder, and applying an image by extrusion molding.

[0022] 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.

[0023] In addition, the decorative film of the present invention can also be laminated with films or membranes having functions such as waterproofing, water repellency, scratch resistance, abrasion resistance, sliding properties, rust resistance, stain resistance, heat dissipation, heat shielding, ultraviolet shielding, near-infrared shielding, electromagnetic wave shielding, antibacterial properties, antiviral properties, chemical resistance, and flame retardancy as components.

[0024] The decorative film obtained by the present invention can be suitably used for the purpose of decorating 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., as well as for the purpose of imparting waterproofing, water repellency, scratch resistance, abrasion resistance, sliding properties, rust resistance, stain resistance, heat dissipation, heat insulation, ultraviolet shielding, near-infrared shielding, electromagnetic wave shielding, antibacterial properties, high virus resistance, chemical resistance, flame retardancy, etc. EXAMPLES

[0025] 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.

[0026] The polyethylene-based thermoplastic resins used in the examples and comparative examples are shown below. Low-density polyethylene (hereinafter referred to as PE(A-1)); manufactured by Tosoh Corporation (product name) Petrothene 212, MFR 8.0g / 10min. 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. Saponified ethylene-vinyl acetate copolymer (hereinafter referred to as PE (A-3)) manufactured by Tosoh Corporation, (product name) Mersen H6051, MFR 5.5g / 10min. Polylactic acid (hereinafter referred to as PLA(C)); manufactured by NatureWorks, (product name) Ingeo4032D, MFR 4g / 10min. Polypropylene (hereinafter referred to as PP(D)); manufactured by Japan Polypropylene Corporation, (product name) Novatec FA3KM, MFR = 10 g / 10 min. Microcellulose fiber (hereinafter referred to as MCF (B-2)); manufactured by Rettenmaier Co., Ltd., (product name) ARBOCEL BC200, average fiber length 300 μm, number average fiber diameter 20 μm.

[0027] Pulp preparation example 8 kg (5 kg solids) of moist softwood unbleached kraft pulp (NUKP) was refined and repeatedly defibrated until the freeness (CSF) reached 50 ml. 5,000 ml of acetic anhydride was then added to the refined NUKP and reacted at 80°C for 4 hours. The reaction mixture 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 mixture 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. <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%, the toughness of the decorative film was judged to be poor. <Film fisheye evaluation> A composition containing a polyethylene resin and cellulose nanofibers was fed to a film extrusion machine with a screw diameter of 15 mm and a T-die with a discharge opening width of 100 mm at the tip of the extruder, and formed into a film. A fluorescent lamp was irradiated from below the obtained film, and the film was observed visually or with a magnifying glass to determine the thickness of the film. 2 The number of fisheyes with a diameter of 1 mm or more observed per film was counted, and a film with fewer than 100 fisheyes was judged to have excellent appearance, whereas a film with 100 or more fisheyes was judged to have poor appearance.

[0028] Example 1 100 parts by weight of PE (A-1), 80 parts by weight of PE (A-2), and 15 parts by weight of acetylated NUKP were mixed uniformly in advance and fed into the hopper of a twin-screw extruder (manufactured by Japan Steel Works, Ltd., (product name) TEX-25αIII, L / D=55) having four kneading zones. Then, melt-kneading was performed under the condition that the cylinder temperature of the kneading zone was heated to 210°C, and a polyethylene-based thermoplastic resin composition in which acetylated NUKP was dispersed was produced. The polyethylene-based thermoplastic resin composition obtained was then fed into a film forming machine having a screw diameter of 15 mmφ and equipped with a T-die having a discharge port width of 100 mm, and formed into a film having a thickness of about 50 μm at a temperature of 210°C. The number of fish eyes was measured, and it was 8, and the appearance of the film was excellent. In addition, the average fiber diameter of the acetylated cellulose nanofibers (hereinafter referred to as CNF (B-1)) measured by observation with a scanning electron microscope (SEM) was 80 nm. Next, a 50 μm thick acrylic film decorated with a wood grain pattern by gravure printing and the obtained polyethylene thermoplastic resin composition film were laminated using a dry laminator with a two-liquid curing type urethane adhesive. The results of the measurements and evaluations for each are shown in Table 1.

[0029] Examples 2 to 6 A decorative film was produced in the same manner as in Example 1, with the blending ratios of the polyethylene resin (A), the acetylated cellulose nanofiber (B-1), and the polylactic acid (C) set as shown in Table 1. The film was then evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. All of the resulting decorative films were excellent in toughness, heat resistance, dimensional change rate and appearance.

[0030] Comparative Examples 1 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), microcellulose fiber (B-2), polylactic acid (C), and polypropylene (D) set as shown in Table 2. 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, 3, and 5 were inferior in heat resistance and dimensional change rate. The decorative films obtained in Comparative Examples 1 and 5 were inferior in strength, and the decorative films obtained in Comparative Examples 2, 4, and 6 were inferior in toughness. The decorative films obtained in Comparative Examples 2, 3, and 4 were inferior in appearance.

[0031] [Table 1]

[0032] [Table 2] [Industrial Applicability]

[0033] The present invention provides a decorative film that is excellent in toughness, heat resistance, dimensional stability, etc., and is useful for decorating portable devices such as smartphones, electrical 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 a constituent, a film made of a polyethylene thermoplastic resin composition containing 100 parts by weight of a polyethylene thermoplastic resin (A) and 1 to 60 parts by weight of cellulose nanofibers (B) having an average fiber diameter of 1 to 1,000 nm.

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 claim 1 or 2, wherein the polyethylene-based thermoplastic resin composition further comprises 1 to 100 parts by weight of a biomass resin (C).

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