Electromagnetic wave-shielding molded film

Abstract

The purpose of the present invention is to provide an electromagnetic wave-shielding molded film having excellent electromagnetic wave shielding properties, moldability, and electromagnetic wave shielding properties after molding. This electromagnetic wave-shielding molded film has at least a conductive layer on one surface of a substrate film, wherein: the conductive layer contains conductive particles A and a thermoplastic resin; the porosity of the conductive layer on a cut surface is 5-30%; and the aspect ratio of the conductive particles A is 5.0-20.0.

Description

Electromagnetic wave shielding molding film

[0001] The present invention relates to a molded film for electromagnetic wave shielding.

[0002] In recent years, with the expansion of the IoT society, there has been an increasing demand for electromagnetic wave shielding performance in fields such as mobile phones, electrical appliances, and automobile parts. When using resin for housings, known methods include plating or conductive coating of molded products. However, these conventional methods require environmental measures such as wastewater treatment and post-treatment of solvents, and various attempts have been made to improve this aspect.

[0003] For example, Patent Document 1 discloses a technique related to an in-mold transfer molding film having a conductive layer made of metal or conductive polymer resin, and Patent Document 2 discloses a technique for in-mold transfer molding a molding film having a conductive layer containing resin and conductive fine particles.

[0004] JP 2006-297642 A JP 2021-192960 A

[0005] However, the technology described in Patent Document 1 is limited in terms of the shape of the object to be molded, since cracks or tears may occur in the conductive layer and the base film when the molded object has a complex shape. On the other hand, the technology described in Patent Document 2 has a problem in that, although the conductive layer can conform to the shape of a molded object with a complex shape, the electromagnetic wave shielding performance is inferior.

[0006] The present invention aims to overcome the problems of the prior art and to provide a molded film for electromagnetic wave shielding that is excellent in electromagnetic wave shielding properties, moldability, and electromagnetic wave shielding properties after molding.

[0007] As a result of extensive research aimed at solving the above-mentioned problems, the present inventors have found the following solution, and have arrived at the present invention. That is, one preferred embodiment of the electromagnetic shielding molded film of the present invention has the following configuration. (1) An electromagnetic shielding molded film having a conductive layer on at least one surface of a base film, the conductive layer containing conductive particles A and a thermoplastic resin, the conductive layer having a porosity of 5% to 30% in a cut surface of the conductive layer, and the conductive particles A having an aspect ratio of 5.0 to 20.0. (2) The electromagnetic shielding molded film according to (1), in which the aspect ratio of the cross-sectional shape of the voids observed in the cut surface of the conductive layer is 1.0 to 20.0. (3) The electromagnetic shielding molded film according to (2), in which the orientation angle of the voids is 0° to 45°. (4) The electromagnetic shielding molded film according to any one of (1) to (3), in which the conductive layer contains conductive particles B having an aspect ratio of 1.0 to 2.0. (5) The electromagnetic shielding molded film according to any one of (1) to (4), wherein the area of ​​the conductive particles in the cut surface of the conductive layer is 50% to 90% and the area of ​​the thermoplastic resin in the cut surface of the conductive layer is 5% to 45%. (6) The electromagnetic shielding molded film according to any one of (1) to (5), wherein the orientation angle of the conductive particles A in the cut surface of the conductive layer is 3° to 45°. (7) The electromagnetic shielding molded film according to any one of (1) to (6), wherein the thickness of the conductive layer is 5 μm to 15 μm. (8) The electromagnetic shielding molded film according to any one of (1) to (7), wherein a release layer is located between the base film and the conductive layer.

[0008] According to the present invention, it is possible to provide an electromagnetic wave shielding molded film that is excellent in electromagnetic wave shielding properties, moldability, and electromagnetic wave shielding properties after molding.

[0009] FIG. 1 shows a schematic cross-sectional view of one embodiment of the electromagnetic wave shielding molded film of the present invention.

[0010] The electromagnetic wave shielding molded film of the present invention has a conductive layer on at least one surface of a base film, the conductive layer containing conductive particles A and a thermoplastic resin, the porosity at a cut surface of the conductive layer being 5% or more and 30% or less, and the aspect ratio of the conductive particles A being 5 or more and 20 or less. By adopting such an embodiment, the electromagnetic wave shielding molded film of the present invention is excellent in electromagnetic wave shielding property, moldability, and electromagnetic wave shielding property after molding.

[0011] The electromagnetic wave shielding molded film of the present invention will be specifically described below. Here, as shown in Figure 1, the electromagnetic wave shielding molded film 4 has a conductive layer 1, a release layer 2, and a base film 3 in this order.

[0012] (Conductive Layer) The conductive layer in the present invention contains conductive particles A and a thermoplastic resin, and the porosity at the cut surface of the conductive layer is 5% or more and 30% or less, and the aspect ratio of the conductive particles A is 5 or more and 20 or less. By adopting such a configuration, the electromagnetic wave shielding molding film has excellent electromagnetic wave shielding properties, moldability, and electromagnetic wave shielding properties after molding.

[0013] Preferred examples of the conductive particles A in the present invention include particles containing one or more elements selected from the group consisting of zero-valent carbon, silver, gold, copper, nickel, chromium, palladium, indium, aluminum, zinc, and platinum. Such a configuration reduces the resistivity of the conductive layer, resulting in excellent electromagnetic wave shielding properties for the electromagnetic wave shielding molded film. From the same perspective as above, it is more preferable that the conductive particles A contain one or more elements selected from the group consisting of gold, silver, silver-plated copper powder, and a silver-copper alloy. Note that "zero-valent" refers not only to the first carbon but also to all metal elements. Whether or not the conductive particles A contain a zero-valent metal element can be determined by performing energy dispersive X-ray spectroscopy mapping analysis (hereinafter referred to as EDX mapping analysis) on a cross section obtained by cutting the electromagnetic wave shielding molded film, and determining whether or not a zero-valent metal element is detected in the particle portion. EDX mapping analysis can be performed, for example, using a scanning electron microscope (FEI, XL30 SFEG) equipped with an energy dispersive X-ray spectrometer (EDAX, NEW XL30 132-2.5) under conditions of an acceleration voltage of 20 kV and a magnification of 20,000 times. Furthermore, the means for cutting the electromagnetic wave shielding molded film can be a "Cross Section Polisher" (registered trademark) SM-09010 (JEOL), or the like. When using this device, a sample is obtained by treating with argon gas at an acceleration voltage of 4 kV and a current value of 70 μA for 10 hours. Furthermore, carbon particles refer to particles that have been qualitatively analyzed by performing microscopic Raman mapping analysis on a cross section obtained by the same method as above. Microscopic Raman mapping analysis can be performed, for example, using a microscopic laser Raman spectrometer (HORIBA, Ltd., "LabRAM" (registered trademark) HR Evolution).

[0014] The aspect ratio of the conductive particles A in the present invention is 5.0 or more and 20.0 or less. By making the aspect ratio of the conductive particles A 5.0 or more, overlap between particles in the molded conductive layer can be maintained, resulting in excellent electromagnetic wave shielding properties after molding. From the same viewpoint as above, it is preferably 7.0 or more. Furthermore, by making the aspect ratio of the conductive particles A 20.0 or less, it is possible to improve the dispersibility of the particles in the conductive layer, resulting in excellent moldability as an electromagnetic wave shielding molded film and excellent electromagnetic wave shielding properties after molding. From the same viewpoint, it is preferably 15.0 or less. The aspect ratio of the conductive particles A can be calculated by the average major axis / average minor axis of the conductive particles A. The average major axis / average minor axis of the conductive particles A can be calculated, for example, by using a scanning electron microscope (XL30 SFEG, manufactured by FEI) to observe the cross section of the conductive layer obtained by cutting the electromagnetic wave shielding molded film under conditions of an acceleration voltage of 20 kV and a magnification of 100,000 times, extracting 50 particles from the obtained image, approximating each to an ellipse, and calculating the aspect ratio by taking the average value of the maximum length as the average major axis and the average value of the minimum length as the average minor axis. Furthermore, as a means for cutting the electromagnetic wave shielding molded film, for example, a manual rotary microtome (HistoCore BIOCUT® R, manufactured by Leica Microsystems) can be used to obtain a sample.

[0015] The orientation angle of the conductive particles A in the present invention is preferably 3° or more and 45° or less. An orientation angle of 45° or less increases the number of contact points between the conductive particles A in the conductive layer, reducing the resistance of the conductive layer and resulting in an excellent electromagnetic wave shielding molded film. From the same viewpoint as above, the orientation angle is more preferably 33° or less. Furthermore, an orientation angle of 3° or more allows the contact points between the conductive particles A to be maintained when the conductive particles A enter voids during molding in which the conductive layer is stretched, resulting in an excellent electromagnetic wave shielding molded film after molding. From the same viewpoint as above, the orientation angle is more preferably 5° or more. The orientation angle of the conductive particles A can be reduced by increasing the area and aspect ratio of the conductive particles A in the conductive layer. On the other hand, the orientation angle of the conductive particles A can be reduced by increasing the porosity of the conductive layer. The orientation angle of the conductive particles A in the present invention refers to the average angle of the length direction of the conductive layer relative to the length direction of the conductive particles A at the cross section of the conductive layer. An orientation angle of 0° means that the direction is parallel to the length of the conductive layer, and an orientation angle of 90° means that the direction is perpendicular to the length of the conductive layer.

[0016] The thermoplastic resin in the present invention is preferably a polyester resin, a polyurethane resin, a (meth)acrylic resin, a polyolefin resin, an ethylene-vinyl acetate copolymer resin, a polyamide resin, a chloroprene resin, an aramid resin, an acrylic urethane copolymer resin, or a polyester urethane copolymer resin, used alone or in combination. By adopting such a form, the dispersibility of the conductive particles A and the conductive particles B described below in the conductive layer, as well as the moldability and flexibility of the entire conductive layer, can be improved, resulting in an electromagnetic wave shielding molded film with excellent electromagnetic wave shielding properties, moldability, and electromagnetic wave shielding properties after molding. From the same viewpoint as above, it is more preferable to use a polyester resin, a polyurethane resin, or a polyester urethane copolymer resin.

[0017] The qualitative and quantitative analysis method for the thermoplastic resin in the present invention may, for example, be a method in which only the conductive layer is scraped off from the electromagnetic wave shielding molded film, the obtained sample of the conductive layer is freeze-dried, and the recovered dried product is subjected to qualitative and quantitative analysis by gas chromatography mass spectrometry (P&T-GC / MS) equipped with a purge and trap sampler (thermal desorption device).

[0018] The porosity of the cut surface of the conductive layer in the present invention is 5% or more and 30% or less. By making the porosity 5% or more, gaps into which the conductive particles can enter can be secured during molding when the conductive layer is stretched, and the occurrence of cracks in the conductive layer can be suppressed, resulting in an electromagnetic wave shielding molded film with excellent formability and electromagnetic wave shielding properties after molding. From the same viewpoint as above, it is preferable that the porosity be 7% or more. Furthermore, by making the porosity 30% or less, it is possible to ensure the overlap of the conductive particles before molding, resulting in an electromagnetic wave shielding molded film with excellent electromagnetic wave shielding properties. From the same viewpoint as above, it is preferable that the porosity be 15% or less.

[0019] In the present invention, a method for achieving a void ratio of 5% to 30% can be exemplified by mixing a dilution organic solvent having a relative evaporation rate at least 5 times faster than the mixing organic solvent used in the conductive layer coating composition when laminating a conductive layer on a substrate film. By using this method, when the conductive layer coating composition is applied to a substrate film and then subjected to heat treatment, voids can be formed in the conductive layer due to the difference in the relative evaporation rates of the mixing organic solvent and the dilution organic solvent. The relative evaporation rate based on n-butyl acetate can be determined by the evaporation rate measured in accordance with ASTM D3539-87 (2004). Specifically, it is a value defined as the relative value of the evaporation rate based on the time required for 90% by mass of n-butyl acetate to evaporate under dry air.

[0020] Examples of the organic solvent for mixing include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, butyl carbitol, hexyl carbitol, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, ethylene glycol mono-n-propyl ether, diacetone alcohol, tetrahydrofurfuryl alcohol, and propylene glycol monomethyl ether acetate, which may be used alone or in combination. The use of such organic solvents results in excellent solubility with the thermoplastic resin and excellent processability when mixing the conductive resin and thermoplastic resin. Furthermore, since the relative evaporation rate is slow, voids can be formed when the conductive layer coating composition is subjected to heat treatment.

[0021] In addition, as the dilution organic solvent, for example, ethyl methyl ketone, methyl isobutyl ketone, butyl acetate, ethyl acetate, methanol, isopropanol, cyclohexanone, toluene, preferably used alone or in combination.By using such solvent, the viscosity of the conductive layer coating composition can be reduced, and the conductive layer coating composition is excellent in coating property when being applied to the substrate film.Furthermore, since the relative evaporation rate is fast, the productivity of the molding film for electromagnetic wave shielding is excellent.

[0022] In the present invention, the aspect ratio of the cross-sectional shape of the voids observed on a cut surface of the conductive layer is preferably 1.0 or more and 20.0 or less. By setting the aspect ratio of the cross-sectional shape of the voids to 1.0 or more, gaps into which the conductive particles can enter can be secured during molding when the conductive layer is stretched, and cracking of the conductive layer can be suppressed, resulting in an electromagnetic wave shielding molded film with excellent formability and electromagnetic wave shielding properties after molding. From the same viewpoint as above, it is more preferable that the aspect ratio of the cross-sectional shape of the voids be 3.0 or more. Furthermore, by setting the aspect ratio of the cross-sectional shape of the voids to 20.0 or less, overlapping of the conductive particles before molding can be ensured, resulting in an electromagnetic wave shielding molded film with excellent electromagnetic wave shielding properties. From the same viewpoint as above, it is more preferable that the aspect ratio of the cross-sectional shape of the voids be 15.0 or less. The aspect ratio of the cross-sectional shape of the voids can be improved by increasing the area of ​​the conductive particles in the conductive layer and the aspect ratio of the conductive particles. On the other hand, by increasing the porosity in the conductive layer, the aspect ratio of the cross-sectional shape of the voids can be reduced. The aspect ratio of the cross-sectional shape of the voids in the present invention can be calculated by the average major axis / average minor axis of the voids. The average major axis / average minor axis of the voids can be calculated by the same method as for the conductive particles A.

[0023] In the present invention, the orientation angle of the voids is preferably 0° or more and 45° or less. By setting the orientation angle of the voids to 45° or less, the number of contact points between the conductive particles A in the conductive layer increases, reducing the resistance value of the conductive layer, resulting in an electromagnetic wave shielding molded film with excellent electromagnetic wave shielding properties. From the same viewpoint as above, the orientation angle of the voids is more preferably 33° or less. Furthermore, by setting the orientation angle of the voids to 0° or more, contact points between the conductive particles A can be maintained when the conductive particles A enter the void portions during molding in which the conductive layer is stretched, resulting in an electromagnetic wave shielding molded film with excellent electromagnetic wave shielding properties after molding. From the same viewpoint as above, the orientation angle of the voids is more preferably 5° or more. The orientation angle of the voids can be reduced by increasing the area and aspect ratio of the conductive particles in the conductive layer. On the other hand, the orientation angle of the voids can be reduced by increasing the porosity of the conductive layer. The orientation angle of the voids in the present invention refers to the average angle of the length direction of the conductive layer relative to the length direction of the voids in the cut surface of the conductive layer. If the orientation angle of the voids is 0°, they are parallel to the length direction of the conductive layer, and if the orientation angle of the voids is 90°, they are perpendicular to the length direction of the conductive layer.

[0024] The porosity of the conductive layer can be measured, for example, by using a manual rotary microtome ("HistoCore BIOCUT" (registered trademark) R, manufactured by Leica Microsystems) to cut the electromagnetic shielding molded film in a direction perpendicular to the thickness to obtain a cross section of the electromagnetic shielding molded film, and then observing the cross section of the conductive layer using a scanning electron microscope (XL30 SFEG, manufactured by FEI) at an acceleration voltage of 20 kV and an observation magnification of 1,000 times.The area of ​​the void parts is calculated by subtracting the non-perforated parts from the cross section photograph, and the porosity can be calculated as the area ratio of the void parts to the total area.

[0025] The conductive layer in the present invention preferably contains conductive particles B having an aspect ratio of 1.0 or more and 2.0 or less. By including conductive particles B having an aspect ratio of 1.0 or more and 2.0 or less in addition to conductive particles A in the conductive layer, the conductive particles in the conductive layer are closely packed. Furthermore, when the conductive particles enter voids during molding, in which the conductive layer is stretched, contact points between conductive particles A and B can be maintained. This maintains the overlap between particles in the conductive layer before and after molding, resulting in an electromagnetic wave shielding molded film with even better electromagnetic wave shielding properties, both before and after molding. The aspect ratio of conductive particles B in the present invention can be calculated in the same manner as for conductive particles A. Preferred examples of conductive particles B in the present invention are particles containing one or more elements selected from the group consisting of zero-valent carbon, silver, gold, copper, nickel, chromium, palladium, indium, aluminum, zinc, and platinum. Such a configuration reduces the resistivity of the conductive layer, resulting in an electromagnetic wave shielding molded film with excellent electromagnetic wave shielding properties. From the same viewpoint as above, it is more preferable that the conductive particles B contain at least one kind selected from the group consisting of gold, silver, silver-plated copper powder, and silver-copper alloys.

[0026] In the present invention, the area of ​​the conductive particles in the cut surface of the conductive layer is preferably 50% to 90%, and the area of ​​the thermoplastic resin in the cut surface of the conductive layer is preferably 5% to 45%. The conductive particles referred to here refer to conductive particles A and conductive particles B in the present invention. By making the area of ​​the conductive particles 50% or more, the proportion of the conductive particles in the conductive layer can be increased, resulting in an electromagnetic wave shielding molded film with excellent electromagnetic wave shielding properties and excellent electromagnetic wave shielding properties after molding. From the same perspective, it is more preferable to make it 75% or more. Furthermore, by making the area of ​​the conductive particles 90% or less, the proportion of the resin in the conductive layer can be increased, resulting in an electromagnetic wave shielding molded film with excellent moldability. From the same perspective, it is more preferable to make it 85% or less. From the same perspective, by making the area of ​​the thermoplastic resin 45% or less, the proportion of the conductive particles relative to all components constituting the conductive layer can be increased, resulting in an electromagnetic wave shielding molded film with excellent electromagnetic wave shielding properties and excellent electromagnetic wave shielding properties after molding. From the same perspective, it is more preferable to make it 25% or less. Furthermore, by making the area of ​​the thermoplastic resin 5% or more, the dispersibility of the conductive particles in the conductive layer and the moldability and flexibility of the entire conductive layer can be improved, resulting in an excellent moldability as a molded film for electromagnetic wave shielding. From the same viewpoint as above, it is more preferable to make it 7% or more. Here, the area of ​​the conductive particles in the cut surface of the conductive layer means the ratio of the total area of ​​the conductive particles reflected in the observed image to the entire area of ​​the observed image of the cut surface of the conductive layer. Furthermore, the area of ​​the thermoplastic resin in the cut surface of the conductive layer means the ratio of the total area of ​​the thermoplastic resin portions reflected in the observed image to the entire area of ​​the observed image of the cut surface of the conductive layer.

[0027] The thickness of the conductive layer in the present invention is preferably 5 μm or more and 15 μm or less. When the thickness of the conductive layer is 15 μm or less, the conductive layer is stably heated during the molding process, thereby reducing in-plane variations in the conductive layer, and the resulting molded film for electromagnetic shielding has excellent electromagnetic shielding properties after molding. From the same perspective, the thickness of the conductive layer is more preferably 12 μm or less. Furthermore, when the thickness of the conductive layer is 5 μm or more, the particle content in the conductive layer increases and the resistivity of the conductive layer decreases, allowing the conductive layer to fully exhibit conductivity and electromagnetic shielding properties, resulting in the resulting molded film for electromagnetic shielding having excellent electromagnetic shielding properties and excellent electromagnetic shielding properties after molding. From the same perspective, the thickness of the conductive layer is more preferably 7 μm or more.

[0028] As a method for qualitatively and quantitatively analyzing a thermoplastic resin, for example, the conductive layer alone can be scraped off from an electromagnetic wave shielding molded film, the obtained sample of the conductive layer is freeze-dried, and the recovered dried product can be subjected to qualitative and quantitative analysis using gas chromatography mass spectrometry (P&T-GC / MS) equipped with a purge and trap sampler (thermal desorption device).

[0029] (Substrate Film) In the present invention, the substrate film is preferably composed of one or more selected from the group consisting of polyester resins (e.g., polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polymethyl methacrylate resins, acrylic resins, polycarbonate resins, polyethylene resins, polypropylene resins, polystyrene resins, fluororesins, triacetyl cellulose resins, polyvinyl alcohol resins, polyvinyl chloride resins, polyvinylidene chloride resins, ethylene-vinyl acetate copolymer resins, polyvinyl butyral resins, metal ion-crosslinked ethylene-methacrylic acid copolymer resins, polyurethane resins, and cyclic olefin resins, from the viewpoints of good dimensional stability and durability, improved productivity, and excellent processability in the lamination and molding steps of the release layer and conductive layer. From the same viewpoints as above, polyester resins are preferably used, and polybutylene terephthalate is particularly preferably used.

[0030] (Release layer) The electromagnetic wave shielding molded film of the present invention is preferably used in an embodiment that includes a step of placing the film in a mold, such as in-mold molding, and then injecting a resin and / or a resin precursor. Therefore, it is preferable that a release layer be located between the base film and the conductive layer in the present invention.

[0031] The release layer in the present invention is not particularly limited as long as it does not impair the effects of the present invention, and preferred examples include alkyd resins, polyolefin resins, long-chain alkyl group-containing resins, fluorine-based resins, silicone resins, mixed or copolymer resins of organic and silicone resins, etc. Among these, silicone resins are preferred from the viewpoint of easily adjusting the release properties.

[0032] The method for laminating the release layer onto the base film is not particularly limited as long as it does not impair the effects of the present invention. However, it is preferable to form the release layer by coating using a method such as dip coating, roller coating, wire bar coating, gravure coating, or die coating (U.S. Pat. No. 2,681,294), and from the viewpoint of processability, gravure coating or die coating is more preferable.

[0033] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to these examples.

[0034] The measurement and evaluation methods used in the present examples are as follows.

[0035] (1) Thickness of the Conductive Layer The thickness (μm) of the conductive layer was determined by cutting the electromagnetic shielding molded film in a direction perpendicular to the thickness using a manual rotary microtome (HistoCore BIOCUT® R, manufactured by Leica Microsystems K.K.) to obtain a cross section of the electromagnetic shielding molded film. Next, the cross section of the conductive layer of the cross section of the electromagnetic shielding molded film was observed using a scanning electron microscope (XL30 SFEG, manufactured by FEI) at an accelerating voltage of 20 kV and an observation magnification of 100,000 times, and measuring any five points on the cross section photograph, and calculating the average value of the obtained values.

[0036] (2) Aspect ratios of the cross-sectional shapes of conductive particles A, conductive particles B, and voids In the method of (1), 50 conductive particles and voids were extracted from the obtained scanning electron microscope image, and each was approximated to an ellipse. The aspect ratios of the cross-sectional shapes of conductive particles A, conductive particles B, and voids were calculated using the average value of the maximum length as the average major axis and the average value of the minimum length as the average minor axis. Next, a histogram was created in increments of 0.1 using the obtained aspect ratios for conductive particles A and conductive particles B, and the peak value was calculated as the aspect ratio of conductive particle A. When there were two peaks, the peak with the smaller value was taken as the aspect ratio of conductive particle B, and the peak with the larger value was taken as the aspect ratio of conductive particle A.

[0037] (3) Orientation angle of conductive particles A and voids In the method of (1), 20 conductive particles A and 20 voids were extracted from the obtained scanning electron microscope image, and the orientation angle of each of them in the longitudinal direction of the conductive layer relative to the longitudinal direction of the conductive particles A and the voids was calculated. Next, a histogram was created in 1° increments using the obtained orientation angles, and the peak value was calculated as the orientation angle of the conductive particles A and the voids.

[0038] (4) Porosity and Area of ​​Conductive Particles A, Conductive Particles B, and Thermoplastic Resin In the method of (1), the image was cut out from the obtained scanning electron microscope image so that conductive particles A, conductive particles B, and thermoplastic resin remained, and image analysis was performed using "HALCON" (registered trademark) Ver. 10.0 manufactured by MVTec Corporation to calculate the void area, and the ratio of the total area of ​​the void area to the area of ​​the entire image was calculated as the void rate. The areas of conductive particles A, conductive particles B, and thermoplastic resin were also calculated in the same manner as the void rate.

[0039] (5) Electromagnetic Wave Shielding Effect of Electromagnetic Wave Shielding Molded Film The electromagnetic wave shielding molded film was cut into a piece of 120 mm x 120 mm, and was measured using the KEC method (electric field), and the electromagnetic wave shielding effect (dB) at a frequency of 300 MHz was calculated using a spectrum analyzer. The obtained results indicate that the higher the electromagnetic wave shielding effect of the electromagnetic wave shielding molded film, the better the electromagnetic wave shielding properties.

[0040] (6) Electromagnetic wave shielding effect of electromagnetic wave shielding molded film when stretched 1.6 times vertically and 1.6 times horizontally The electromagnetic wave shielding molded film was cut into a size of 120 mm x 120 mm and subjected to simultaneous biaxial stretching treatment at 1.6 times vertically and 1.6 times horizontally using a Bruckner KARO 5.0 laboratory stretcher to obtain a sample, which was measured using the KEC method (electric field) and the electromagnetic wave shielding effect (dB) at a frequency of 1 GHz was measured using a spectrum analyzer, and the obtained result was taken as the electromagnetic wave shielding effect at a frequency of 1 GHz. A higher electromagnetic wave shielding effect indicates better electromagnetic wave shielding properties.

[0041] (7) Moldability of Electromagnetic Wave Shielding Molded Films In the method of (6), simultaneous biaxial stretching was performed at 1.6 times the longitudinal and 1.6 times the transverse magnification, and the samples after simultaneous biaxial stretching were visually observed and evaluated according to the following criteria: A: The conductive layer was uniformly stretched relative to the substrate film, resulting in a good result. B: The conductive layer was stretched relative to the substrate film, but cracks were observed in some parts of the conductive layer. No practical problems. C: Cracks were observed throughout the conductive layer. Not suitable for practical use.

[0042] The materials used are as follows:

[0043] (Conductive particles a) Silver particles (manufactured by Fukuda Metal Foil and Powder Co., Ltd., AgC-2011, average particle diameter 2.6 μm, flake shape).

[0044] (Conductive particles b) Silver particles (manufactured by Fukuda Metal Foil and Powder Co., Ltd., AgC-B, average particle size 4.0 μm, flake shape).

[0045] (Conductive particles c) Silver particles (manufactured by Fukuda Metal Foil and Powder Co., Ltd., AgG-204B, average particle size 7.2 μm, flake shape).

[0046] (Conductive particles d) Silver particles (manufactured by DOWA Electronics Co., Ltd., AG-2-1C, average particle diameter 0.8 μm, spherical).

[0047] (Conductive particles e) Silver particles (manufactured by Fukuda Metal Foil and Powder Co., Ltd., AgC-222, average particle size 5.0 μm, kidney-shaped).

[0048] (Conductive particles f) Silver particles (manufactured by Fukuda Metal Foil and Powder Co., Ltd., Ag-XF, average particle size 5.0 μm, flake shape).

[0049] (Conductive particles g) Silver particles (manufactured by Fukuda Metal Foil and Powder Co., Ltd., AgC-251, average particle diameter 3.0 μm, kidney-shaped).

[0050] (Conductive particles h) Silver particles (manufactured by Fukuda Metal Foil and Powder Co., Ltd., AgC-156, average particle diameter 1.5 μm, spherical).

[0051] (Thermoplastic Resin) Urethane-modified polyester resin (manufactured by Toyobo Co., Ltd., "Vylon" (registered trademark) UR-4800, glass transition temperature 106° C., weight average molecular weight 25,000).

[0052] (Organic solvent a) Diethylene glycol monoethyl ether acetate (relative evaporation rate 0.2).

[0053] (Organic solvent b) Ethyl methyl ketone (relative evaporation rate 3.7).

[0054] [Example 1] <Preparation of a molded film for electromagnetic wave shielding> A conductive layer coating composition for obtaining a conductive layer was prepared using the composition shown in Table 1, and was dispersed or dissolved in diethylene glycol monoethyl ether acetate as an organic solvent for mixing, and then kneaded using a three-roll mill. Next, ethyl methyl ketone was mixed and dispersed as an organic solvent for dilution using a Homodisper (manufactured by Primix Corporation), thereby obtaining a conductive layer coating composition with a solids content of 30.0 mass %.

[0055] A 50 μm thick polybutylene terephthalate film (ESRM manufactured by Okura Kogyo Co., Ltd.) was used as the substrate film, and an alkyd-modified silicone resin (X-62-900B manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone, and the resulting coating composition was mixed and dispersed using a Homodisper (manufactured by Primix Corporation). The coating composition was applied by gravure coating, and the film was dried at 120°C, resulting in a release layer-laminated substrate film having a release layer with a thickness of 0.05 μm.

[0056] The conductive layer coating composition was applied to the release layer-laminated substrate film by gravure coating, dried at 120°C, and cured to laminate a conductive layer having a thickness of 10 μm, thereby obtaining a molded film for electromagnetic wave shielding, which was then wound into a roll.

[0057] [Examples 2 to 10, Comparative Examples 1 to 4] Electromagnetic wave shielding molded films were produced in the same manner as in Example 1, except that the conductive particles, the organic solvent for mixing, and the organic solvent for dilution were as shown in Tables 1 to 3.

[0058] The electromagnetic wave shielding molded films of Examples 1 to 10 all had excellent electromagnetic wave shielding properties, moldability, and electromagnetic wave shielding properties after molding as electromagnetic wave shielding films.

[0059] On the other hand, the electromagnetic wave shielding molded films of Comparative Examples 1 and 4 were inferior to the electromagnetic wave shielding molded films of the Examples in terms of moldability and electromagnetic wave shielding properties after molding.

[0060] Furthermore, the electromagnetic wave shielding molded film of Comparative Example 2 was inferior to the electromagnetic wave shielding molded films of Examples in electromagnetic wave shielding properties and in electromagnetic wave shielding properties after molding.

[0061] Furthermore, the electromagnetic wave shielding molded film of Comparative Example 3 was inferior in electromagnetic wave shielding properties after molding to the electromagnetic wave shielding molded films of Examples.

[0062]

[0063]

[0064]

[0065] 1: Conductive layer 2: Release layer 3: Base film 4: Electromagnetic wave shielding molded film

Claims

1. A molded film for electromagnetic shielding, comprising a conductive layer on at least one side of a base film, the conductive layer containing conductive particles A and a thermoplastic resin, the void ratio at a cut surface of the conductive layer being 5% or more and 30% or less, and the aspect ratio of the conductive particles A being 5.0 or more and 20.0 or less.

2. The electromagnetic wave shielding molded film according to claim 1, wherein the aspect ratio of the cross-sectional shape of the voids observed on a cut surface of the conductive layer is 1.0 or more and 20.0 or less.

3. The electromagnetic wave shielding molded film according to claim 2, wherein the orientation angle of the voids is from 0° to 45°.

4. The electromagnetic wave shielding molded film according to claim 1, wherein the conductive layer contains conductive particles B having an aspect ratio of 1.0 or more and 2.0 or less.

5. A molded film for electromagnetic shielding as described in claim 1, wherein the area of ​​conductive particles on the cut surface of the conductive layer is 50% or more and 90% or less, and the area of ​​thermoplastic resin on the cut surface of the conductive layer is 5% or more and 45% or less.

6. The electromagnetic wave shielding molded film according to claim 1, wherein the orientation angle of the conductive particles A on the cut surface of the conductive layer is 3° or more and 45° or less.

7. The electromagnetic wave shielding molded film according to claim 1, wherein the conductive layer has a thickness of 5 μm or more and 15 μm or less.

8. The electromagnetic wave shielding molded film according to claim 1, wherein a release layer is located between the base film and the conductive layer.

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