Molded film for electromagnetic wave shielding

Abstract

The purpose of the present invention is to provide a molded film for electromagnetic wave shielding, which has excellent electromagnetic wave shielding properties, moldability, and electromagnetic wave shielding properties after molding. A molded film for electromagnetic wave shielding, the 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 porosity in a cut surface of the conductive layer being 5-30%, and the aspect ratio of the conductive particles A being 5.0-20.0.

Description

Technical Field

[0001] This invention relates to a molded film for electromagnetic wave shielding. Background Technology

[0002] In recent years, the demand for electromagnetic wave shielding performance has been increasing in fields such as mobile phones, home appliances, and automotive parts due to the expansion of the Internet of Things (IoT) society. When resin is used in the casing, methods such as applying plating or conductive coating to the molded product are known. However, these existing methods require environmentally friendly measures regarding wastewater treatment and solvent post-treatment; therefore, various attempts have been made to improve these aspects.

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

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-297642

[0007] Patent Document 2: Japanese Patent Application Publication No. 2021-192960 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, in the technology described in Patent Document 1, when the shape of the molded body is complex, the conductive layer and the substrate film may crack or break, thus limiting the applicable shapes of the molded body. On the other hand, in the technology described in Patent Document 2, although the conductive layer can follow the shape of the molded body, there is a problem of poor electromagnetic wave shielding performance.

[0010] The purpose of this invention is to improve upon the problems of the prior art and to provide a molded film for electromagnetic wave shielding with excellent electromagnetic wave shielding properties, formability, and electromagnetic wave shielding properties after molding.

[0011] Technical means to solve the problem

[0012] In order to solve the aforementioned problems, in-depth research was conducted, and it was found that the problem was solved by the following method, thereby completing the present invention. Specifically, a preferred embodiment of the electromagnetic wave shielding molded film of the present invention adopts the following structure.

[0013] (1) A molded film for electromagnetic wave shielding, having a conductive layer on at least one side of a substrate film, the conductive layer containing conductive particles A and a thermoplastic resin, the porosity of the 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.

[0014] (2) The electromagnetic wave shielding molded film according to (1), wherein the aspect ratio of the cross-sectional shape of the void observed in the cut surface of the conductive layer is 1.0 or more and 20.0 or less.

[0015] (3) The electromagnetic wave shielding molded film according to (2), wherein the orientation angle of the gap is 0° or more and 45° or less.

[0016] (4) The electromagnetic wave shielding molded film according to any one of (1) to (3), wherein the conductive layer comprises conductive particles B with an aspect ratio of 1.0 or more and 2.0 or less.

[0017] (5) The electromagnetic wave shielding molded film according to any one of (1) to (4), wherein the area of ​​conductive particles in the cut surface of the conductive layer is 50% or more and 90% or less, and the area of ​​thermoplastic resin in the cut surface of the conductive layer is 5% or more and 45% or less.

[0018] (6) The electromagnetic wave 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° or more and 45° or less.

[0019] (7) A molded film for electromagnetic wave shielding according to any one of (1) to (6), wherein the thickness of the conductive layer is 5 μm or more and 15 μm or less.

[0020] (8) The electromagnetic wave shielding molded film according to any one of (1) to (7), wherein the release layer is located between the substrate film and the conductive layer.

[0021] The effects of the invention

[0022] This invention provides a molded film for electromagnetic wave shielding that exhibits excellent electromagnetic wave shielding properties, formability, and electromagnetic wave shielding performance after molding. Attached Figure Description

[0023] [ Figure 1 ] Figure 1 This is a schematic cross-sectional view showing an embodiment of the molded film for electromagnetic wave shielding of the present invention. Detailed Implementation

[0024] The electromagnetic wave shielding molding film of the present invention has a conductive layer on at least one side of a substrate film. The conductive layer contains conductive particles A and a thermoplastic resin. The porosity of the cross-section 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. With this configuration, the electromagnetic wave shielding molding film of the present invention exhibits excellent electromagnetic wave shielding performance, moldability, and electromagnetic wave shielding performance after molding.

[0025] The electromagnetic wave shielding molded film of the present invention will now be described in detail. Figure 1 As described above, the electromagnetic wave shielding molding film 4 has a conductive layer 1, a release layer 2, and a substrate film 3 in sequence.

[0026] (Conductive layer)

[0027] The conductive layer of this invention contains conductive particles A and a thermoplastic resin. The porosity of the cross-section 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 this configuration, the electromagnetic wave shielding performance, formability, and electromagnetic wave shielding performance after molding become excellent for electromagnetic wave shielding molding films.

[0028] The conductive particle A in this invention preferably includes one or more particles selected from the group consisting of carbon, silver, gold, copper, nickel, chromium, palladium, indium, aluminum, zinc, and platinum, all of which have a zero valence. By adopting this configuration, the resistivity of the conductive layer becomes lower, thus resulting in superior electromagnetic wave shielding performance for the molded film used for electromagnetic wave shielding. Similarly, the conductive particle A is more preferably composed of one or more particles selected from the group consisting of gold, silver, silver-plated copper powder, and alloys of silver and copper. Furthermore, "zero valence" refers not only to carbon but also to all metallic elements. Whether the conductive particle A contains a zero-valence metallic element can be determined by performing energy dispersive X-ray spectroscopy mapping (EDX mapping analysis) on a cross-section obtained by cutting the molded film for electromagnetic wave shielding, and by detecting a zero-valence metallic element in the particle portion. EDX mapping analysis can be performed, for example, using a scanning electron microscope (FEI Corporation, XL30 SFEG) including an energy-dispersive X-ray spectrometer (EDAX Corporation, NEW XL30 132-2.5), at an accelerating voltage of 20 kV and a magnification of 20,000x. Alternatively, the cutting mechanism for the electromagnetic shielding molding film can be a cross-section polisher (registered trademark) SM-09010 (JEOL Corporation), where the sample is obtained by treating it with argon gas for 10 hours at an accelerating voltage of 4 kV and a current of 70 μA. Regarding carbon particles, this refers to particles qualitatively analyzed by performing micro-Raman mapping analysis on the cross-section obtained using the same method. Micro-Raman mapping analysis can be performed, for example, using a micro-laser Raman spectrometer (Horiba Manufacturing Co., Ltd., "LabRAM" (registered trademark) HR Evolution).

[0029] In this invention, the aspect ratio of the conductive particles A is 5.0 or higher and 20.0 or lower. By setting the aspect ratio of the conductive particles A to 5.0 or higher, the overlap between particles in the molded conductive layer can be maintained, thus resulting in excellent electromagnetic wave shielding performance after molding. For the same reason, it is preferable to set it to 7.0 or higher. Furthermore, by setting the aspect ratio of the conductive particles A to 20.0 or lower, the dispersion of particles in the conductive layer can be improved, thus resulting in excellent formability and electromagnetic wave shielding performance of the molded film for electromagnetic wave shielding. For the same reason, it is preferable to set it to 15.0 or lower. The aspect ratio of the conductive particles A can be calculated using the average major axis / average minor axis of the conductive particles A. As a method for calculating the average major axis / average minor axis of conductive particles A, for example, a scanning electron microscope (FEI Corporation, XL30 SFEG) is used to observe the cross-section of the conductive layer obtained by cutting the molded film for electromagnetic wave shielding under conditions of accelerating voltage 20 kV and magnification 100,000x. Fifty particles are extracted from the obtained image and approximated as ellipses. The aspect ratio is calculated by taking the average of the longest lengths as the average major axis and the average of the shortest lengths as the average minor axis. Alternatively, as a cutting mechanism for the molded film for electromagnetic wave shielding, a manual rotary microtome (manufactured by Leica Microsystems Co., Ltd., "HistoCore BIOCUT" (registered trademark)) can be used to obtain the sample.

[0030] In this invention, the orientation angle of the conductive particles A is preferably 3° or more and 45° or less. By setting the orientation angle to 45° or less, the number of contacts between the conductive particles A in the conductive layer increases, the resistance of the conductive layer decreases, and therefore the electromagnetic wave shielding performance becomes excellent for the molded film for electromagnetic wave shielding. Following the same viewpoint, the orientation angle is more preferably set to 33° or less. Furthermore, by setting the orientation angle to 3° or more, when the conductive particles A enter the void portion during the stretching and molding of the conductive layer, the contacts between the conductive particles A can be maintained, thus the electromagnetic wave shielding performance of the molded film for electromagnetic wave shielding becomes excellent. Following the same viewpoint, the orientation angle is more preferably set to 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 in the conductive layer. In this invention, the orientation angle of the conductive particles A refers to the average angle between the length direction of the conductive layer and the length direction of the conductive particles A in the cut surface of the conductive layer. If the orientation angle is 0°, it is parallel to the length direction of the conductive layer; if the orientation angle is 90°, it is perpendicular to the length direction of the conductive layer.

[0031] The thermoplastic resin used in this invention is preferably a polyester resin, polyurethane resin, (meth)acrylic resin, polyolefin resin, ethylene-vinyl acetate copolymer resin, polyamide resin, chloroprene resin, aromatic polyamide resin, acrylate copolymer resin, or polyester urethane copolymer resin, used alone or in combination. By adopting this configuration, the dispersion of conductive particles A and conductive particles B (described later) in the conductive layer can be improved, as well as the overall moldability and flexibility of the conductive layer. For electromagnetic wave shielding molding films, the electromagnetic wave shielding performance, moldability, and post-molding electromagnetic wave shielding performance become excellent. From the same perspective, polyester resin, polyurethane resin, or polyester urethane copolymer resin is more preferably used.

[0032] The qualitative / quantitative analysis method for thermoplastic resins in this invention can be exemplified by the following method: only the conductive layer is cut from the electromagnetic wave shielding molding film, the obtained conductive layer sample is freeze-dried, and the recovered dried solids are qualitatively / quantitatively analyzed by gas chromatography-mass spectrometry (P&T-GC / MS) with a purge and trap sampler (heat desorption device).

[0033] The porosity of the cut surface of the conductive layer in this invention is 5% or more and 30% or less. By setting the porosity to 5% or more, during the stretching and molding of the conductive layer, sufficient gaps for conductive particles to enter are ensured, and cracking of the conductive layer is suppressed. Therefore, the formability and electromagnetic wave shielding performance of the molded film for electromagnetic wave shielding are excellent. Similarly, the porosity is preferably set to 7% or more. Furthermore, by setting the porosity to 30% or less, the overlap of conductive particles before molding is ensured, thus resulting in excellent electromagnetic wave shielding performance of the molded film for electromagnetic wave shielding. Similarly, the porosity is preferably set to 15% or less.

[0034] As a method for setting the porosity of the present invention to be 5% or more and 30% or less, one example is the following: A diluent organic solvent with a relative evaporation rate at least five times faster is mixed into the mixed organic solvent used in the conductive layer coating composition when the conductive layer is laminated onto the substrate film. By using this method, when heat treatment is applied after the conductive layer coating composition is coated onto the substrate film, the difference in the relative evaporation rates of the mixed organic solvent and the diluent organic solvent allows voids to form within the conductive layer due to the difference in relative evaporation rates. The relative evaporation rate based on n-butyl acetate can be determined using the evaporation rate measured according to American Society for Testing Materials (ASTM) D3539-87 (2004). Specifically, it is 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.

[0035] As the organic solvent for the mixture, 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 are preferred examples, used alone or in combination. By using such an organic solvent, the solubility with thermoplastic resins and the processability when mixing conductive resins with thermoplastic resins become excellent. Furthermore, due to the relatively slow evaporation rate, voids can be formed when the conductive coating composition is heat-treated.

[0036] Furthermore, the preferred organic solvents for dilution include, for example, ethyl methyl ketone, methyl isobutyl ketone, butyl acetate, ethyl acetate, methanol, isopropanol, cyclohexanone, and toluene, used alone or in combination. Using such solvents reduces the viscosity of the conductive layer coating composition, resulting in excellent coatability when applied to the substrate film. Furthermore, the relatively fast evaporation rate enhances the productivity of the molded film used for electromagnetic wave shielding.

[0037] In this invention, the aspect ratio of the cross-sectional shape of the voids observed in the cut surface of the conductive layer is preferably 1.0 or higher and 20.0 or lower. By setting the aspect ratio of the voids' cross-sectional shape to 1.0 or higher, during the stretching and molding of the conductive layer, gaps for conductive particles to enter can be ensured, and cracking of the conductive layer can be suppressed. Therefore, the formability and electromagnetic wave shielding performance of the molded film for electromagnetic wave shielding become excellent. Similarly, the aspect ratio of the voids' cross-sectional shape is more preferably set to 3.0 or higher. Furthermore, by setting the aspect ratio of the voids' cross-sectional shape to 20.0 or lower, the overlap of conductive particles before molding can be ensured, thus improving the electromagnetic wave shielding performance of the molded film for electromagnetic wave shielding. Similarly, the aspect ratio of the voids' cross-sectional shape is more preferably set to 15.0 or lower. The aspect ratio of the voids' cross-sectional shape can be increased 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 this invention can be calculated using the average major axis / average minor axis of the voids. As a method for calculating the average major axis / average minor axis of the voids, the same method as that used for conductive particles A can be used.

[0038] In this invention, the orientation angle of the voids is preferably 0° or higher and 45° or lower. By setting the orientation angle of the voids to 45° or lower, the contact points between conductive particles A in the conductive layer increase, the resistance value of the conductive layer decreases, and therefore the electromagnetic wave shielding performance becomes excellent for the molded film for electromagnetic wave shielding. Following the same viewpoint, the orientation angle of the voids is more preferably set to 33° or lower. Furthermore, by setting the orientation angle of the voids to 0° or higher, when conductive particles A enter the void portion during the stretching and molding of the conductive layer, the contact points between conductive particles A can be maintained, thus the electromagnetic wave shielding performance of the molded film for electromagnetic wave shielding becomes excellent. Following the same viewpoint, the orientation angle of the voids is more preferably set to 5° or higher. 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 in the conductive layer. In this invention, the orientation angle of the voids refers to the average angle between the length direction of the conductive layer and the length direction of the voids in the cut surface of the conductive layer. If the orientation angle of the void is 0°, it is parallel to the length direction of the conductive layer; if the orientation angle of the void is 90°, it is perpendicular to the length direction of the conductive layer.

[0039] As a method for measuring the porosity of the conductive layer, for example, a cross-section of the electromagnetic wave shielding molded film can be obtained by cutting the film in a direction perpendicular to the thickness using a manual rotary microtome (manufactured by Leica Microsystems, Inc., "HistoCoreBIOCUT" (registered trademark) R). The cross-section of the conductive layer is then observed using a scanning electron microscope (manufactured by FEI Corporation, XL30 SFEG) at an accelerating voltage of 20 kV and an observation magnification of 1,000x. Based on the cross-sectional photograph, the area of ​​the void portion is calculated by subtracting the unperforated portion, and the porosity is calculated in the form of the area ratio of the void portion relative to the overall area.

[0040] The conductive layer in this invention preferably comprises conductive particles B with an aspect ratio of 1.0 or higher and 2.0 or lower. By including conductive particles A and conductive particles B with an aspect ratio of 1.0 or higher and 2.0 or lower in the conductive layer, the conductive particles in the conductive layer can be densely filled. Furthermore, during the stretching and molding of the conductive layer, when conductive particles enter the gaps, the contact points between conductive particles A and B can be maintained. Therefore, the overlap between particles in the conductive layer before and after molding can be maintained, resulting in superior electromagnetic wave shielding performance for the molded film used for electromagnetic wave shielding, both before and after molding. The aspect ratio of the conductive particles B in this invention can be calculated using the same method as that for conductive particles A. The conductive particles B in this invention are preferably exemplified by comprising one or more particles selected from the group consisting of carbon, silver, gold, copper, nickel, chromium, palladium, indium, aluminum, zinc, and platinum, all with a zero valence. By adopting this configuration, the resistivity of the conductive layer becomes lower, thus resulting in superior electromagnetic wave shielding performance for the molded film used for electromagnetic wave shielding. In the same viewpoint described above, conductive particle B is more preferably one or more of the group consisting of gold, silver, silver-plated copper powder, and alloys of silver and copper.

[0041] In this invention, the area of ​​conductive particles in the cut surface of the conductive layer is 50% or more and 90% or less, and the area of ​​thermoplastic resin in the cut surface of the conductive layer is preferably 5% or more and 45% or less. The conductive particles referred to herein are conductive particles A and B in this invention. By setting the area of ​​conductive particles to 50% or more, the composition ratio of conductive particles in the conductive layer can be increased, thus improving the electromagnetic wave shielding performance and the electromagnetic wave shielding performance after molding for electromagnetic wave shielding. From the same viewpoint, it is more preferable to set it to 75% or more. Furthermore, by setting the area of ​​conductive particles to 90% or less, the composition ratio of resin in the conductive layer can be increased, thus improving the formability of the molded film for electromagnetic wave shielding. From the same viewpoint, it is more preferable to set it to 85% or less. From the same viewpoint, by setting the area of ​​thermoplastic resin to 45% or less, the composition ratio of conductive particles relative to all components constituting the conductive layer can be increased, thus improving the electromagnetic wave shielding performance and the electromagnetic wave shielding performance after molding for electromagnetic wave shielding. Regarding the same viewpoints as described above, it is more preferable to set it to 25% or less. Furthermore, by setting the area of ​​thermoplastic resin to 5% or more, the dispersion of conductive particles in the conductive layer and the overall moldability or flexibility of the conductive layer can be improved, thus resulting in excellent moldability for electromagnetic wave shielding films. Regarding the same viewpoints as described above, it is more preferable to set it to 7% or more. Moreover, here, the area of ​​conductive particles in the cross-section of the conductive layer refers to the ratio of the total area of ​​conductive particles reflected in the observation image to the total area of ​​the observation image of the cross-section of the conductive layer. Additionally, the area of ​​thermoplastic resin in the cross-section of the conductive layer refers to the ratio of the total area of ​​the thermoplastic resin portion reflected in the observation image to the total area of ​​the observation image of the cross-section of the conductive layer.

[0042] In this invention, the thickness of the conductive layer is preferably 5 μm or more and 15 μm or less. By having a conductive layer thickness of 15 μm or less, the conductive layer can be stably heated during the molding process, thus reducing in-plane deviation of the conductive layer. Therefore, for the molded film for electromagnetic wave shielding, the resulting electromagnetic wave shielding performance is excellent. From the same viewpoint, the thickness of the conductive layer is more preferably 12 μm or less. Furthermore, by having a conductive layer thickness of 5 μm or more, the particle content in the conductive layer increases, and the resistivity of the conductive layer decreases. Therefore, conductivity and electromagnetic wave shielding performance can be fully utilized, resulting in excellent electromagnetic wave shielding performance and the resulting electromagnetic wave shielding performance for the molded film for electromagnetic wave shielding. From the same viewpoint, the thickness of the conductive layer is more preferably 7 μm or more.

[0043] In addition, as a method for qualitative / quantitative analysis of thermoplastic resins, for example, only the conductive layer can be cut from the electromagnetic wave shielding molding film, the obtained conductive layer sample can be freeze-dried, and the recovered dried solids can be qualitatively / quantitatively analyzed by gas chromatography-mass spectrometry (P&T-GC / MS) with a purge trap sampler (heat desorption device).

[0044] (Substrate film)

[0045] In terms of good dimensional stability or durability, improved productivity, and excellent processability of the lamination or molding process of the release layer and conductive layer, the substrate film of the present invention preferably comprises one or more resins selected from the group consisting of polyester resins (e.g., polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), polymethyl methacrylate resin, acrylic resin, polycarbonate resin, polyethylene resin, polypropylene resin, polystyrene resin, fluoropolymer resin, triacetyl cellulose resin, polyvinyl alcohol resin, polyvinyl chloride resin, polyvinylidene chloride resin, ethylene-vinyl acetate copolymer resin, polyvinyl butyral resin, metal ion crosslinked ethylene-methacrylic acid copolymer resin, polyurethane resin, and cyclic olefin resins. For the same purpose, polyester resins are preferably used, and polybutylene terephthalate is particularly preferred.

[0046] (release layer)

[0047] The electromagnetic wave shielding molding film of the present invention can preferably be used in forms such as in-mold molding, which include processes such as placing the film in a mold and then injecting resin and / or resin precursor. Therefore, it is preferable that the release layer is located between the substrate film and the conductive layer in the present invention.

[0048] Regarding the release layer in this invention, there are no particular limitations as long as the effects of this invention are not impaired. Preferably examples include alkyd resins, polyolefin resins, resins containing long-chain alkyl groups, fluorinated resins, silicone resins, and mixtures or copolymers of organic and silicone resins. Among these, silicone resins are preferred from the viewpoint that release properties can be easily adjusted.

[0049] As for the method of laminating the release layer onto the substrate film, there are no particular limitations as long as the effect of the present invention is not compromised. It is preferred to form the release layer by coating using dip coating, roller coating, wire rod coating, gravure coating or die coating (as described in U.S. Patent No. 2,681,294). From the viewpoint of processability, gravure coating or die coating is preferred.

[0050] Example

[0051] The following examples illustrate the invention in more detail, but the invention is not limited thereto.

[0052] Furthermore, the measurement and evaluation methods in this embodiment are shown below.

[0053] (1) Thickness of the conductive layer

[0054] The thickness (μm) of the conductive layer was determined as follows: A cross-section of the electromagnetic wave shielding molding film was obtained by cutting along a direction perpendicular to the thickness using a manual rotary microtome (manufactured by Leica Microsystems, Inc., "HistoCore BIOCUT" (registered trademark) R). Subsequently, the cross-section of the electromagnetic wave shielding molding film was observed using a scanning electron microscope (manufactured by FEI, XL30 SFEG) at an accelerating voltage of 20 kV and a magnification of 100,000x. Five arbitrary points were measured based on the cross-sectional photographs, and the average value of the obtained values ​​was calculated.

[0055] (2) Aspect ratio of the cross-sectional shape of conductive particle A, conductive particle B and void

[0056] In the method of (1), 50 conductive particles and voids are extracted from the obtained scanning electron microscope image and approximated as ellipses. The aspect ratios of the cross-sectional shapes of conductive particles A, conductive particles B, and voids are calculated by taking the average of the maximum lengths as the average major axis and the average of the minimum lengths as the average minor axis. Then, for conductive particles A and B, histograms are plotted using the obtained aspect ratios at a scale of 0.1, and the peak values ​​are used as the aspect ratios of conductive particles A. In the case of two peak values, the peak with the smaller value is used as the aspect ratio of conductive particles B, and the peak with the larger value is used as the aspect ratio of conductive particles A.

[0057] (3) Orientation angle of conductive particle A and the void

[0058] In the method of (1), 20 conductive particles A and voids are extracted from the obtained scanning electron microscope image, and the orientation angles of conductive particles A and the length direction of the conductive layer relative to the length direction of the voids are calculated respectively. Then, a histogram is made using the obtained orientation angles in 1° increments, and the peak value is used as the orientation angle of conductive particles A and voids to calculate.

[0059] (4) Porosity, and the area of ​​conductive particles A, conductive particles B and thermoplastic resin.

[0060] In method (1), an image is cut from the obtained scanning electron microscope image using conductive particles A, conductive particles B, and thermoplastic resin residue. The image is analyzed using a "HALCON" (registered trademark) Ver. 10.0 manufactured by MVTec, and the void portion is calculated. The ratio of the total area of ​​the void portion to the area of ​​the entire image is used to calculate the porosity. The areas of conductive particles A, conductive particles B, and thermoplastic resin are also calculated using the same method as the porosity.

[0061] (5) Electromagnetic wave shielding effect of molded film for electromagnetic wave shielding

[0062] The electromagnetic wave shielding molded film was cut into 120 mm × 120 mm pieces, and the KEC method (electric field) was used for measurement. The electromagnetic wave shielding effect (dB) at a frequency of 300 MHz was calculated using a spectral analyzer. Regarding the results obtained, the higher the electromagnetic wave shielding effect of the molded film, the better the electromagnetic wave shielding performance.

[0063] (6) Electromagnetic wave shielding effect of the molded film for electromagnetic wave shielding when stretched by 1.6 times in length × 1.6 times in width

[0064] Electromagnetic wave shielding molded films were cut into 120 mm × 120 mm pieces and simultaneously biaxially stretched at a ratio of 1.6 times longitudinally × 1.6 times laterally using a Bruckner KARO 5.0 laboratory stretcher to prepare samples. The KEC (electric field) method was used for measurement, and the electromagnetic wave shielding effect (dB) at a frequency of 1 GHz was determined using a spectrometer. The obtained results were taken as the electromagnetic wave shielding effect at 1 GHz. A higher electromagnetic wave shielding effect indicates better electromagnetic wave shielding performance.

[0065] (7) Formability of the molded film for electromagnetic wave shielding

[0066] In the method of (6), a simultaneous biaxial extension process was performed with a length of 1.6 times the width of the sample. The sample after the simultaneous biaxial extension process was visually observed and evaluated according to the following criteria.

[0067] A: The conductive layer extends uniformly relative to the substrate film, resulting in good performance.

[0068] B: The conductive layer extends relative to the substrate film, but cracks are visible in a portion of the conductive layer. This poses no practical problem.

[0069] C: Cracks are visible throughout the conductive layer. Unusable for practical purposes.

[0070] The materials used are as described below.

[0071] (Conductive particle a)

[0072] Silver particles (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., AgC-2011, average particle diameter 2.6 μm, in flake form).

[0073] (Conductive particle b)

[0074] Silver particles (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., AgC-B, average particle diameter 4.0 μm, in flake form).

[0075] (Conductive particle c)

[0076] Silver particles (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., AgG-204B, average particle diameter 7.2 μm, in flake form).

[0077] (Conductive particle d)

[0078] Silver particles (manufactured by DOWA Electronics Co., Ltd., AG-2-1C, average particle diameter 0.8 μm, spherical).

[0079] (Conductive particle e)

[0080] Silver particles (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., AgC-222, average particle diameter 5.0 μm, kidney-shaped).

[0081] (Conductive particle f)

[0082] Silver particles (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., Ag-XF, average particle diameter 5.0 μm, in flake form).

[0083] (Conductive particle g)

[0084] Silver particles (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., AgC-251, average particle diameter 3.0 μm, kidney-shaped).

[0085] (Conductive particle h)

[0086] Silver particles (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., AgC-156, average particle diameter 1.5 μm, spherical).

[0087] (Thermoplastic resin)

[0088] Carbamate-modified polyester resin (manufactured by Toyobo Co., Ltd., "Vylon" (registered trademark) UR-4800, glass transition temperature 106°C, weight average molecular weight 25,000).

[0089] (Organic solvent a)

[0090] Diethylene glycol monoethyl ether acetate (relative evaporation rate 0.2).

[0091] (Organic solvent b)

[0092] Ethyl methyl ketone (relative evaporation rate 3.7).

[0093] [Example 1]

[0094] <Fabrication of Molded Film for Electromagnetic Wave Shielding>

[0095] The conductive layer coating composition used to obtain the conductive layer was configured as shown in Table 1. After being dispersed or dissolved in diethylene glycol monoethyl ether acetate as an organic solvent for mixing, it was kneaded using a three-roll mill. Subsequently, ethyl methyl ketone as an organic solvent for dilution was mixed and dispersed using a homogenizing disperser (manufactured by Primix Inc.) to obtain a conductive layer coating composition with a solid content of 30.0% by mass.

[0096] Using a 50 μm thick polybutylene terephthalate film (ESRM manufactured by Okura Kogyo Co., Ltd.) as the substrate film, an alkyd modified silicone resin (X-62-900B manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone and mixed and dispersed using a homogenizer (Primix Co., Ltd.). The resulting coating composition was then applied using a gravure coating method and dried at 120°C to obtain a release layer laminated substrate film with a release layer thickness of 0.05 μm.

[0097] The conductive layer coating composition is applied to the release layer laminated substrate film using a gravure coating method, dried and hardened at 120°C, and a conductive layer with a thickness of 10 μm is laminated to obtain a molded film for electromagnetic wave shielding, which is then rolled into a roll.

[0098] [Examples 2-10, Comparative Examples 1-4]

[0099] Except that the conductive particles, the organic solvent for mixing, and the organic solvent for dilution are set as described in Tables 1 to 3, the electromagnetic wave shielding molded film is made in the same manner as in Example 1.

[0100] The electromagnetic wave shielding molded films of Examples 1 to 10 all exhibit excellent electromagnetic wave shielding performance, moldability, and electromagnetic wave shielding performance after molding, in terms of electromagnetic wave shielding molded films.

[0101] On the other hand, the electromagnetic wave shielding molded films of Comparative Examples 1 and 4 have poorer moldability and electromagnetic wave shielding performance after molding compared with the electromagnetic wave shielding molded film of the embodiment.

[0102] Furthermore, the electromagnetic wave shielding molded film of Comparative Example 2 has poor electromagnetic wave shielding performance and poor electromagnetic wave shielding performance after molding compared with the electromagnetic wave shielding molded film of the embodiment.

[0103] Furthermore, compared with the electromagnetic wave shielding molded film of the embodiment, the electromagnetic wave shielding performance of the molded film of Comparative Example 3 is poor after molding.

[0104] [Table 1]

[0105] Table 1

[0106]

[0107] [Table 2]

[0108] Table 2

[0109]

[0110] [Table 3]

[0111] Table 3

[0112]

[0113] Explanation of icon numbers

[0114] 1: Conductive layer

[0115] 2: Demolding layer

[0116] 3: Substrate film

[0117] 4: Molded film for electromagnetic wave shielding

Claims

1. A molded film for electromagnetic wave shielding, wherein a conductive layer is present on at least one side of a substrate film. The conductive layer contains conductive particles A and thermoplastic resin. The porosity of the cut surface of the conductive layer is more than 5% and less than 30%. The aspect ratio of the conductive particle A is 5.0 or higher and 20.0 or lower.

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

3. The molded film for electromagnetic wave shielding according to claim 2, wherein, The orientation angle of the gap is above 0° and below 45°.

4. The molded film for electromagnetic wave shielding according to claim 1, wherein, The conductive layer contains conductive particles B with an aspect ratio of 1.0 or higher and 2.0 or lower.

5. The molded film for electromagnetic wave shielding according to claim 1, wherein, The area of ​​conductive particles in the cut surface of the conductive layer is more than 50% and less than 90%, and the area of ​​thermoplastic resin in the cut surface of the conductive layer is more than 5% and less than 45%.

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

7. The molded film for electromagnetic wave shielding according to claim 1, wherein, The thickness of the conductive layer is greater than 5 μm and less than 15 μm.

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

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