Laminated Sheet

Abstract

To provide a laminate sheet having enhanced electromagnetic wave shielding properties and excellent moldability even though being a thin film.SOLUTION: A laminate sheet includes an alternate laminate unit of five or more alternately laminated A-layers and B-layers that are different from each other. At least one of the A-layer and the B-layer contains conductive particles whose aspect ratio is 10 to 10000.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminate sheet having excellent electromagnetic wave shielding properties. [Background technology]

[0002] With advances in communications technology, electromagnetic waves of various frequency bands are now being used and flying around in the atmosphere. These include meter waves in the hundreds of MHz to several GHz band, which are primarily used for mobile phones and other wireless communications; centimeter waves in the several GHz to several tens of GHz band, which are primarily used for mobile communications such as 4G and 5G and wireless LAN (Wi-Fi) communications; and millimeter waves in the tens to several hundred GHz band, which are primarily used for automobile collision prevention radar.

[0003] Electromagnetic waves of an appropriate frequency band are selected depending on the amount of information, the distance to be transmitted, and the application, but because electromagnetic waves of similar frequency bands are used in a variety of devices and applications, there is a growing need for electromagnetic wave shielding materials that block electromagnetic waves to prevent device malfunctions, communication disruptions, information leaks, and the effects on the human body, which is sensitive to electromagnetic waves. In particular, in recent years, the development of communication technology that uses electromagnetic waves in the GHz frequency band has accelerated in order to achieve high-speed, large-capacity communications, and there is a demand for electromagnetic wave shielding materials that can block electromagnetic waves in this frequency band.

[0004] Electromagnetic waves are waves made up of two components, an electric field and a magnetic field, which propagate through space while vibrating against each other. Electromagnetic shielding materials that block electromagnetic waves are materials that reflect electromagnetic waves on their surface or inside the material, or absorb them inside the material, thereby losing or attenuating electromagnetic wave energy; a combination of reflection and absorption can increase the effect.

[0005] For example, the surface reflection of electromagnetic waves can be enhanced by the difference in electrical resistance (impedance) between the air interface and the interface of the electromagnetic wave shielding material, and electromagnetic wave shielding properties can generally be obtained over a wide frequency band by coating or laminating a material with very low resistance, such as metal (copper), on the surface of the substrate (Patent Document 1).On the other hand, electromagnetic wave shielding by absorption involves incorporating conductive particles and / or magnetic particles into the substrate, which absorbs the electromagnetic waves that enter the interior as induced currents, thereby causing a loss of electromagnetic wave energy, and absorption performance is achieved by incorporating metal particles such as carbon particles or ferrite into dielectric polymers such as rubber (Patent Documents 2 to 4). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2011-502285 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-158395 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-118073 [Patent Document 4] Japanese Patent Application Publication No. 2019-057730 Summary of the Invention [Problem to be solved by the invention]

[0007] Electromagnetic wave shielding materials that utilize reflection, such as those described in Patent Document 1, use techniques such as metal sputtering, vacuum deposition, and coating the outermost layer with a paste material containing conductive and / or magnetic particles. However, peeling of the coating material can reduce the electromagnetic wave shielding properties, which can lead to short circuits in electronic and communication devices and reduced durability, which can be problematic.

[0008] Furthermore, among the electromagnetic wave shielding materials that utilize absorption, as described in Patent Documents 2 to 4, many of them provide uniform electromagnetic wave shielding across a wide frequency range. In order to increase the absolute value of electromagnetic wave attenuation (to improve electromagnetic wave shielding properties), it is necessary to thicken the substrate or increase the conductive particle content. However, increasing the substrate thickness increases the stiffness of the electromagnetic wave shielding material, making it difficult to apply to applications requiring formability, such as wrapping cables or housings with complex irregular shapes. Furthermore, considering the formability and production efficiency of electromagnetic wave shielding materials, continuous sheeting by melt extrusion using thermoplastic resins is preferable to press-processed products using thermoplastic resins. However, when forming a single-layer sheet containing a high concentration of conductive particles, the resin's melt viscosity changes during extrusion (thixotropy) become significant. This leads to problems such as uneven extrusion during sheet molding, making it difficult to form a sheet of uniform thickness, and the resulting sheet becomes brittle and prone to cracking.

[0009] The present invention aims to solve the above problems and to provide a laminated sheet that is thin yet has both electromagnetic wave shielding properties and formability. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention has the following configuration: A laminate sheet including an alternating laminate unit in which five or more different A layers and B layers are alternately laminated, wherein, when conductive particles X have an aspect ratio of 5 or more and 10,000 or less, at least one of the A layers and the B layers contains the conductive particles X. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a laminate sheet that is thin but has both electromagnetic wave shielding properties and formability. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 10 is a diagram showing an example of the peak top of the peak with the largest return loss when plotted with the return loss on the vertical axis and the frequency on the horizontal axis. [Figure 2] FIG. 10 is a diagram showing an example of the peak top of the peak with the largest return loss when plotted with the return loss on the vertical axis and the frequency on the horizontal axis. [Figure 3] 2 is a schematic diagram of a layer containing conductive particles X. FIG. [Figure 4] 1 is a schematic diagram of a layer containing conductive particles X and conductive particles Y. FIG. [Figure 5] This is a plot in which the vertical axis represents the degree and the horizontal axis represents the logarithm of the aspect ratio. DETAILED DESCRIPTION OF THE INVENTION

[0013] The laminate sheet of the present invention is described in detail below. The laminate sheet of the present invention is a laminate sheet including an alternating laminate unit in which five or more different A layers and B layers are alternately laminated, and is characterized in that, when conductive particles X have an aspect ratio of 5 to 10,000, at least one of the A layers and the B layers contains the conductive particles X.

[0014] The laminated sheet of the present invention is characterized by including an alternating laminate unit in which a total of five or more layers of different A layers and B layers are alternately laminated. Here, "different from each other" refers to the fact that the composition of at least one of the resin and particles constituting each layer is different. If it is difficult to identify the composition of each layer, it can be confirmed by the following method.

[0015] Specifically, the layers can be considered to have different compositions in any of the following cases (1) to (5): (1) The elastic modulus of the film cross section is evaluated using dynamic viscoelasticity measurement (AFM-DMA) with an atomic force microscope, and the ratio of the average elastic modulus of the two layers is 1.1 or greater. (2) The surface potential is evaluated using an electric force microscope (EFM), and the ratio of the average surface potential of the two layers is 1.1 or greater. (3) The concentration of each atom is evaluated using energy dispersive X-ray spectroscopy (SEM-EDX), and the ratio of the mole fraction (or weight fraction) of each atom in the two layers is 1.1 or greater. (4) The two layers can be peeled off, and the density, glass transition temperature, melting point, decomposition temperature, and ash content after decomposition are evaluated, and at least one of these values ​​differs by 3°C or more or 10% or more. (5) The interface can be confirmed by observing the cross section at the desired magnification (500 to 20,000 times) with a transmission electron microscope (TEM) or a scanning electron microscope (SEM). Here, being able to see the interface means that the brightness between adjacent layers is different. Specifically, first, the brightness is measured at 1,000 points for each layer. Next, the average brightness for each layer and the standard deviation of the brightness for each layer are calculated. If the difference between the average brightnesses of two adjacent layers is greater than either of the standard deviations of the brightness of each layer, the brightness is deemed to be different. Which of the two layers is designated as layer A and layer B can be determined by selecting the layer with the higher surface potential in EFM as layer B. Furthermore, if conductive particles X are added to layer B, it is preferable to designate layer A as the outermost layer from the viewpoints of film formation and preventing the conductive particles from falling off.

[0016] The laminate sheet of the present invention has five or more alternating layers, with the layers with excellent formability acting as support layers, improving elongation at break and reducing defects such as tears and holes during molding. Thermally crystallized films become brittle, but the present invention reduces thermal crystallization by thinning each layer, thereby reducing defects such as cracking during molding. Furthermore, while resins are subject to large deformation during molding, it is desirable for the laminate sheet to be resistant to impacts and scratches (small deformations) after molding. The interfacial layers between the layers retain their shape against small deformations, but large deformations cause minor fractures and slippage at the interfaces. Therefore, the multilayer structure provides good formability and allows the sheet to fully conform to recesses that are relatively difficult to mold. From this perspective, the number of layers in the alternating laminate unit is preferably 11 or more, more preferably 51 or more, and particularly preferably 201 or more. While there is no upper limit on the number of layers in the alternating unit, a maximum of approximately 2000 layers is recommended from the perspective of film formation stability.

[0017] In the laminate sheet of the present invention, when conductive particles X are defined as conductive particles having an aspect ratio of 5 to 10,000, at least one of the A layer and the B layer contains the conductive particles X. Here, "contains" refers to a content of 0.1 vol% or more in the particle volume concentration measurement described below. The conductive particles X may be of one type or a combination of multiple types. In the latter case, the content of the conductive particles X is calculated by combining all components. For example, organic carbon-based particles, inorganic particles, and metal-based particles can be used alone or in combination as the conductive particles X. However, organic carbon-based particles are preferably selected as the conductive particles X because of their small primary particle size and suitability for melt extrusion. Note that when a laminate sheet is produced using an extruder using only metal-based particles, friction between the device and the metal of the conductive particles X can cause problems such as material pulverization and device damage. Therefore, it is preferable that at least one type of the conductive particles X be organic carbon-based particles or inorganic particles primarily composed of carbon.

[0018] Examples of inorganic or metal particles suitable for use as the conductive particles X include titanium oxides such as titanium dioxide and low-order titanium oxides; perovskite-type oxides such as barium titanate, strontium titanate, and calcium titanate; metal-coated inorganic particles such as antimony oxide-doped tin-coated mica, nickel-coated mica particles, and copper-coated mica; and carbon monoxide complexes such as carbonyl iron and carbonyl nickel. These particles must have a high aspect ratio structure, such as a needle, disk, spindle, fiber, or bead shape. Such a structure allows the conductive particles X to be more tightly aligned in the plane when stacked. As a result, the connections between the particles in contact with each other expand in the plane, forming stronger conductive paths in the plane and improving electromagnetic wave absorption. Furthermore, the area of ​​the particles present when viewed from the surface of the laminated sheet is increased, thereby reducing electromagnetic wave leakage through gaps between the particles.

[0019] Examples of organic carbon particles that can be suitably used as the conductive particles X include carbon black (spherical carbon) such as acetylene black, channel black, lamp black, thermal black, ketjen black, and furnace black; carbon nanotubes, which are cylindrical carbon such as single-walled nanotubes, multi-walled nanotubes, and cup-stacked nanotubes; flat carbon such as graphite, graphene, and others; cylindrical graphite, carbon microcoils, and carbon fibers (long fibers and short fibers).

[0020] In particular, the conductive particles X are preferably carbon nanotubes, flat carbon, carbon fibers, or the like, which have a uniform structure and a high aspect ratio, in order to improve the conductivity of the layer containing the conductive particles X by arranging the conductive particles in the plane direction due to the laminated structure, and to form a stronger conductive path in the plane direction. It is more preferable that the conductive particles X are carbon nanotubes or carbon fibers. On the other hand, if the aspect ratio is too high, the interaction between the resin and the conductive particles becomes too strong, which may result in poor moldability. From the above viewpoint, the aspect ratio of the conductive particles X is preferably 20 or more and 5000 or less, and more preferably 30 or more and 3000 or less.

[0021] One method for evaluating the components of the conductive particles used in the laminate sheet is to dissolve the resin of each layer in a solvent, filter the particles, and then burn the resulting particles to measure the amounts of carbon dioxide, water, nitrogen oxides, and ash. While the use of organic carbon particles increases the hydrocarbon weight fraction, from the viewpoint of forming conductive paths by connecting organic carbons to each other, the hydrocarbon weight fraction of the entire particles in the laminate sheet of the present invention is preferably 85% to 100%, and more preferably 90% to 100%. The hydrocarbon weight fraction of the entire particles can be measured by dissolving the sample in triethylene glycol at 90°C, filtering the particles using a metal filter, and analyzing them using an organic trace element analyzer (the equipment and conditions are described below).

[0022] Furthermore, arranging the conductive particles in a uniform direction and stacking them side by side promotes the formation of conductive paths, thereby improving the electromagnetic wave shielding performance of the laminate sheet. To achieve this, it is preferable to have a large total contact area between the conductive particles and the resin, so fine conductive particles are preferred. On the other hand, if the conductive particles are too fine, aggregation of the conductive particles can cause uneven return loss and reduced moldability, or the resin can thicken, making lamination difficult. From this perspective, specifically, the average particle size of at least one of the conductive particles X and conductive particles Y (described below) is preferably 5 nm to 1000 nm, more preferably 5 nm to 500 nm. The average particle size of each particle can be measured using observation images of the longitudinal and transverse cross sections of the laminate sheet using the method described in the Examples.

[0023] Generally, to improve the electromagnetic wave absorption of a laminate sheet, it is necessary to increase the content of conductive particles X. However, if the conductive particles X are excessive, film-forming properties and processability may be impaired in exchange for high conductivity. Conversely, if the conductive particles X are insufficient, the electromagnetic wave absorption effect may not be sufficiently obtained. From the above viewpoint, at least one of the A layer and the B layer preferably contains conductive particles X in an amount of 1 vol% to 90 vol%, more preferably 5 vol% to 65 vol%, and even more preferably 10 vol% to 50 vol%.

[0024] One method for measuring the content of conductive particles X in each layer of a laminate sheet is to cut the cross section using a microtome or ion milling, extract the conductive particle X portion by image observation with a scanning electron microscope, and measure the area ratio of the conductive particle X portion in the layer. If there is a possibility that the laminate sheet has anisotropy, similar measurements are made on cross sections in both the longitudinal and transverse directions, and the average of the obtained values ​​is used. Note that detailed measurement procedures, including a method for identifying conductive particles X by image observation, are shown in the Examples.

[0025] Furthermore, if the longitudinal direction or width direction is unknown, the elongation at break is measured at 30° intervals from any direction of the sample, and the direction with the smallest elongation at break is taken as the longitudinal direction (hereinafter, the same applies to each parameter that requires specifying the longitudinal direction or width direction for measurement). The method for measuring the elongation at break will be described later.

[0026] The aspect ratio of conductive particles can be determined by approximating each conductive particle to an ellipse and calculating the ratio of the long axis to the short axis. One method for measuring the aspect ratio of conductive particles in a laminated sheet involves first cutting the cross section using ion milling or a microtome, then observing the cross section with a scanning electron microscope (SEM) or transmission electron microscope (TEM) to obtain an image. Using image analysis software, the conductive particle area is extracted and approximated as an ellipse, and the long and short axes are measured and calculated to determine their ratio. When cutting the cross section, methods that minimize particle damage, such as freezing or resin embedding, may be used as needed. Furthermore, metal sputtering, such as platinum, may be performed during observation to prevent charge buildup. Image analysis software such as ImageJ or Mac-View may be used, and binarization and brightness adjustment may be performed as appropriate. If anisotropy is suspected within the sheet, similar measurements are performed on both longitudinal and transverse cross sections, and the larger aspect ratio is used. Conductive particles with an aspect ratio between 5 and 10,000 correspond to conductive particle X.

[0027] By using conductive particles (conductive particles X) with a high aspect ratio as described above, connections between the conductive particles X are more likely to occur, improving electromagnetic wave absorption performance. In particular, by thinning the layer containing a large amount of conductive particles X, the conductive particles X are aligned in the plane direction, strengthening the connections between the conductive particles and arranging the conductive particles without gaps. This suppresses electromagnetic wave leakage when the laminate sheet is formed, leading to improved electromagnetic wave absorption. On the other hand, if the entire laminate sheet is thinned in order to thin the layer containing a large amount of conductive particles X, the electromagnetic wave absorption performance of the laminate sheet will decrease. However, by using the above-mentioned laminate structure, it is possible to make each layer containing a large amount of conductive particles X thinner while maintaining the thickness of the entire laminate sheet.

[0028] From the viewpoint of compatibility between application to high-frequency electromagnetic waves and electromagnetic wave absorption performance, when the return loss of the laminate sheet of the present invention is measured for each frequency, it is preferable that the value obtained by dividing the electromagnetic wave attenuation at the peak top with the largest return loss by the thickness of the laminate sheet is 5 dB / mm or more. From the above viewpoint, the electromagnetic wave attenuation at the peak top is preferably 10 dB / mm or more, more preferably 20 dB / mm or more, even more preferably 25 dB / mm or more, and most preferably 29 dB / mm or more. There is no particular upper limit to the value obtained by dividing the electromagnetic wave attenuation at the peak top by the thickness of the laminate sheet, but from the viewpoint of performance stability and feasibility, it should be at most about 1000 dB / mm.

[0029] Typically, the thinner the laminate sheet is designed, the more it can absorb higher frequency electromagnetic waves, but it is more likely to have the drawback of fluctuations in return loss with small changes in thickness. On the other hand, thicker laminate sheets have stable return loss, but are inferior in absorbing high frequency electromagnetic waves. After extensive research into a laminate sheet that can stably absorb electromagnetic waves in the centimeter to millimeter wave band, it was discovered that a good return loss can be stably obtained if the value obtained by dividing the electromagnetic wave attenuation by the thickness of the laminate sheet is within the above range.

[0030] The thickness of a laminate sheet can be measured using a known dial gauge. Return loss is a value expressed in decibels (dB) that represents the amount of electromagnetic wave loss during a round-trip within a laminate sheet when an electromagnetic wave of a specific frequency is incident on the laminate sheet and reflected back by the laminate sheet. Specifically, using the coaxial waveguide method or the free-space method, an electromagnetic wave is irradiated onto a laminate sheet with a metal reflector plate (e.g., aluminum) attached to the back surface, and the intensity of the electromagnetic wave reflected by the metal plate and traveling back and forth within the laminate sheet is measured and calculated. Return loss is measured by sweeping the frequency, and a return loss spectrum is plotted with return loss on the vertical axis and frequency on the horizontal axis. Multiple peaks may be observed, but we focus on the return loss peak with the largest peak intensity (attenuation). The "peak top" here refers to the position where the sign (slope) of the tangent to the return loss spectrum changes from positive to negative or from negative to positive. When there is a single peak top as shown in Figures 1 and 2, the attenuation of the return loss peak is expressed as the difference in attenuation between the peak top and the baseline for the frequency at which the peak top is located, with the baseline of that peak as the reference. Note that since the examples in Figures 1 and 2 have a single peak top, reference numeral 1 in the figures indicates the peak with the largest return loss, and reference numeral 2 indicates the return loss at the peak top of the peak with the largest return loss.

[0031] Of the reflection loss peaks of the laminate sheet of the present invention, the peak with the largest reflection loss is preferably present in a frequency band of 1 to 100 GHz. When the laminate sheet of the present invention is used for electromagnetic wave shielding, it is usually necessary to shield the GHz frequency band, so it is preferable that the peak with the largest reflection loss be present in this region.

[0032] Methods for keeping the value obtained by dividing the electromagnetic wave attenuation at the peak top of the peak with the greatest return loss by the thickness of the laminate sheet within the above range include, for example, adjusting the type and concentration of conductive particles in the sheet to set the dielectric constant of the sheet within an appropriate range, or adjusting the thickness during manufacturing. More specifically, the value obtained by dividing the electromagnetic wave attenuation at the peak top of the peak with the greatest return loss by the thickness of the laminate sheet can be increased by using conductive particles with high and low aspect ratios (conductive particles X and conductive particles Y, described below) in combination so that the volume concentration of conductive particles Y is 0.1 or more and less than 10 when the volume concentration of conductive particles X is 1, increasing the volume concentration of conductive particles X, or forming multiple layers with appropriate thicknesses to promote the alignment of conductive particles X.

[0033] In the laminate sheet of the present invention, when conductive particles Y are conductive particles having an aspect ratio of 1 or more and less than 5, at least one of the A layer and the B layer preferably contains 1 vol% to 90 vol% of conductive particles X and 1 vol% to 90 vol% of conductive particles Y. The advantages of this embodiment will be explained below with reference to the drawings. Fig. 3 is a schematic diagram of a layer containing conductive particles X, and Fig. 4 is a schematic diagram of a layer containing conductive particles X and conductive particles Y. In Figs. 3 and 4, the reference numerals 3 to 5 respectively represent a resin, conductive particles X, and conductive particles Y.

[0034] As shown in Figure 3, when conductive particles with a high aspect ratio (conductive particles X) are included in a layer, the conductive particles are more likely to be closer together than when only conductive particles with a low aspect ratio are used, contributing to the formation of conductive paths. Furthermore, the reduced gaps also reduce the reduction in attenuation due to electromagnetic wave leakage. However, arranging the conductive particles X so that their major axes are parallel to the surface direction leaves room for improvement in the formation of conductive paths in the thickness direction. Therefore, as shown in Figure 4, the use of conductive particles with a low aspect ratio (conductive particles Y) in combination expands the conductive paths in the thickness direction, achieving higher electromagnetic wave absorption. From the above perspective, the content of conductive particles Y in a layer containing 1 vol% to 90 vol% of conductive particles X is preferably 10 vol% to 75 vol%, more preferably 20 vol% to 60 vol%.

[0035] The conductive particles Y can be made of the same material as the conductive particles X. From the viewpoint of the connection between the conductive particles, it is preferable to use a similar material. Specifically, when an organic carbon material such as carbon nanotubes or carbon fibers is used as the conductive particles X, it is preferable to use conductive carbon black or graphite.

[0036] In the laminate sheet of the present invention, conductive particles X and conductive particles Y may be contained in only one of layers A and B, or in both layers A and B. Furthermore, when conductive particles are contained in both layers A and B, each layer may contain different conductive particles, or the same conductive particles may be contained in different amounts. However, if both layers A and B are highly conductive, the laminate sheet as a whole will exhibit an effect similar to that of a single-film electromagnetic wave shielding material, and the desired steep electromagnetic wave absorption may not be achieved. Furthermore, the conductivity and dielectric constant of the surface layer may increase, causing surface reflection of electromagnetic waves, which may reduce the electromagnetic wave absorption effect of the conductive particles.

[0037] Therefore, for example, in a laminate sheet having a repeating unit of A(BA)n, in other words, a laminate sheet in which A layers and B layers are alternately laminated and A layers are the outermost layers on both sides, it is preferable that the content of conductive particles in the surface layers be lower than the content of conductive particles in the layers other than the surface layers. In other words, when A layers are the surface layers and B layers are the layers other than the surface layers, it is preferable that the amount of conductive particles contained in A layers be lower than the amount of conductive particles contained in B layers. More specifically, it is preferable that the total content of conductive particles contained in A layers be less than 10 vol% of the entire A layers, and that the total content of conductive particles contained in B layers be 10 vol% or more of the entire B layers.

[0038] From the viewpoint of realizing high electromagnetic wave absorption and reducing unevenness in electromagnetic wave absorption, the laminate sheet of the present invention preferably has a particle orientation degree in both the longitudinal cross section and the width cross section of 10 to 10,000, more preferably 100 to 5,000, and even more preferably 300 to 2,000. Here, the longitudinal cross section refers to a cross section of the laminate sheet cut along a plane parallel to the longitudinal and thickness directions, and the width cross section refers to a cross section of the laminate sheet cut along a plane parallel to the width and thickness directions. Furthermore, the term "particle" refers to all conductive particles contained in the laminate sheet. When the laminate sheet contains only conductive particle X, it refers to conductive particle X. When the laminate sheet contains both conductive particles X and Y, it refers to both particles. By setting each orientation degree within the above range, the conductive particles can be effectively connected to each other, thereby achieving high electromagnetic wave absorption. Methods for achieving each degree of orientation within the range include using conductive particles with a high aspect ratio, thinning the thickness of each layer by forming a laminated structure, aligning the conductive particles by shear force during extrusion, and aligning the orientation of the conductive particles by stretching.

[0039] The laminate sheet of the present invention can eliminate unevenness in electromagnetic wave absorption depending on the direction of incidence of electromagnetic waves by eliminating bias in particle orientation between the longitudinal and width directions, or conversely, can selectively absorb electromagnetic waves by creating a large difference in particle orientation. Specifically, when the ratio of the particle orientation in the longitudinal cross section to the particle orientation in the width cross section is 0.50 to 2.00, it can be used as an electromagnetic wave shielding material with minimal unevenness in electromagnetic wave absorption depending on the direction of incidence. For such applications, this ratio is more preferably 0.80 to 1.25. On the other hand, when the ratio of the particle orientation in the longitudinal cross section to the particle orientation in the width cross section is 0.1 or less or 10 or more, it becomes possible to selectively absorb only polarized electromagnetic waves. Examples of applications that require the absorption of only electromagnetic waves include electromagnetic wave absorption around ETCs. The ratio of the particle orientation degree in the longitudinal cross section to the particle orientation degree in the width direction cross section is the value obtained by dividing the particle orientation degree in the longitudinal cross section by the particle orientation degree in the width direction cross section. The particle orientation degree can be determined by analyzing images of the longitudinal cross section and the width direction cross section using image analysis software, and details of the image analysis software and analysis method will be shown in the examples.

[0040] One method for independently controlling the degree of particle orientation in the longitudinal and transverse directions is stretching using rolls or clips in a tenter. In this case, the degree of orientation in each direction can be increased by increasing the stretch ratio. Another method for increasing the degree of orientation in the longitudinal direction is to lower the particle concentration and increase the shear force that each particle experiences during extrusion. Furthermore, when extruding and molding onto a cooling body such as a casting drum, a method can also be used in which the speed of the cooling body is increased to slightly stretch the particles in the longitudinal direction during casting, thereby increasing the degree of orientation in the longitudinal direction.

[0041] In the laminate sheet of the present invention, the degree of electrical orientation of the particles in both the longitudinal cross section and the width cross section is preferably 100 or more and 100,000 or less, as determined by leakage electric field analysis obtained by EFM (Electric Force Microscope) measurement. It is more preferably 1,000 or more and 100,000 or less. An electrical orientation degree of 100 or more ensures sufficient formation of conductive paths, thereby achieving high electromagnetic wave absorption. On the other hand, an electrical orientation degree of 100,000 or less prevents excessive formation of conductive paths, thereby reducing the decrease in electromagnetic wave absorption due to electromagnetic waves being reflected rather than absorbed.

[0042] Methods for increasing the degree of electrical orientation include using highly conductive particles, increasing the amount of conductive particles added, reducing the thickness of each layer by using a laminated structure, aligning conductive particles using shear force during extrusion, and aligning the orientation of conductive particles by stretching. The degree of electrical orientation can be determined by analyzing images measured by EFM using image analysis software, and details of the image analysis software and analysis methods are shown in the examples.

[0043] In the laminate sheet of the present invention, from the viewpoint of efficiently absorbing electromagnetic waves, the average angle between the major axis of the particles and the plane direction in each of the longitudinal cross section and the width cross section is preferably from 0° to 30°, more preferably from 0° to 10°, and even more preferably from 0° to 5°. In particular, when conductive particles with a high aspect ratio are oriented in the plane direction or in a direction with a small angle with the plane direction, the area of ​​the particles when observed from the surface of the laminate sheet becomes larger, enabling more efficient absorption of electromagnetic waves.

[0044] The angle between the long axis of the particle and the plane direction can be determined by analyzing images of the longitudinal cross section and the width cross section using image analysis software. Details of the image analysis software and analysis method are shown in the Examples.

[0045] Methods for keeping the average value of the angle between the long axis of the particle and the surface direction within this range include using a multilayer laminate structure or reducing the thickness of the entire laminate sheet to reduce the thickness of each layer relative to the long axis of the conductive particles, stretching the conductive particles to orient them in the stretching direction, and increasing the particle concentration to strengthen the interaction between the conductive particles.

[0046] In the laminate sheet of the present invention, the standard deviation of the angle between the major axis of the particles and the plane direction is preferably 0° or more and 30° or less in both the longitudinal cross section and the width cross section. By suppressing the variation in the angle between the major axis of each conductive particle and the plane direction, stable electromagnetic wave absorption properties can be achieved throughout the laminate sheet. From the above perspective, the standard deviation is more preferably 0° or more and 20° or less, and even more preferably 0° or more and 10° or less.

[0047] The standard deviation of the angle between the long axis of the particle and the plane direction can be determined by analyzing images of the longitudinal cross section and the width cross section using image analysis software. Details of the image analysis software and analysis method will be described in the Examples.

[0048] As a method for setting the standard deviation of the angle between the long axis of the particle and the surface direction within the range, a method similar to the method for setting the average value of the angle between the long axis of the particle and the surface direction within a preferred range can be used. However, since the effect of the thickness of each layer is stronger than the average value of the angle between the long axis of the particle and the surface direction, if the thickness of each layer is not small even in a multilayer laminate structure, the standard deviation of the angle between the long axis of the particle and the surface direction may not be small.

[0049] In the laminate sheet of the present invention, the lowest temperature-decreasing crystallization temperature is preferably 70°C or higher and 200°C or lower, or no temperature-decreasing crystallization temperature is observed. A temperature-decreasing crystallization temperature of 200°C or lower suppresses the crystallinity of the laminate sheet, thereby reducing cracking and deterioration of conformability during post-processing such as molding. Furthermore, a temperature-decreasing crystallization temperature of 70°C or higher reduces deterioration of durability and deformation during use at high temperatures. From the above perspective, if a temperature-decreasing crystallization temperature is observed, the lowest temperature is preferably 90°C or higher and 190°C or lower, more preferably 110°C or higher and 180°C or lower, and particularly preferably 110°C or higher and 165°C or lower. The temperature-decreasing crystallization temperature can be evaluated using a differential scanning calorimeter in accordance with JIS K-7121 (1987) and JIS K-7122 (1987), and details are provided in the Examples.

[0050] Examples of methods for keeping the lowest temperature-drop crystallization temperature within the above range and preventing the temperature-drop crystallization temperature from being observed include using a resin with low crystallinity. The temperature-drop crystallization temperature can also be lowered by forming a laminate sheet with a multilayer structure, thereby reducing the thickness of each layer and inhibiting crystal growth beyond a certain size. Furthermore, increasing the particle amount can sometimes cause crystallization to progress due to the ordered structure of the particle surface, raising the temperature-drop crystallization temperature. Therefore, in the laminate sheet of the present invention, the temperature-drop crystallization temperature can also be lowered by using conductive particles (conductive particles X) with a high aspect ratio to reduce the total amount of particles added.

[0051] In the laminate sheet of the present invention, examples of the resin constituting each layer include polyolefin resins typified by polyethylene, polypropylene, poly(1-butene), poly(4-methylpentene), polyisobutylene, polyisoprene, polybutadiene, polyvinylcyclohexane, polystyrene, poly(α-methylstyrene), poly(p-methylstyrene), polynorbornene, and polycyclopentene; polyamide resins typified by nylon 6, nylon 11, nylon 12, and nylon 66; copolymer resins of vinyl monomers typified by ethylene / propylene copolymer, ethylene / vinylcyclohexane copolymer, ethylene / vinylcyclohexene copolymer, ethylene / alkyl acrylate copolymer, ethylene / acrylic methacrylate copolymer, ethylene / norbornene copolymer, ethylene / vinyl acetate copolymer, propylene / butadiene copolymer, isobutylene / isoprene copolymer, and vinyl chloride / vinyl acetate copolymer; and acrylic resins typified by polyacrylate, polymethacrylate, polymethyl methacrylate, polyacrylamide, and polyacrylonitrile. Resins, polyester resins such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate; polyether resins such as polyethylene oxide, polypropylene oxide, and polyacrylene glycol; cellulose ester resins such as diacetyl cellulose, triacetyl cellulose, propionyl cellulose, butyryl cellulose, acetylpropionyl cellulose, and nitrocellulose; biodegradable polysimilar resins such as polylactic acid and polybutyl succinate. Other examples of the polymer that can be used alone or in combination include polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, polyacetal, polyglycolic acid, polycarbonate, polyketone, polyether sulfone, polyether ether ketone, modified polyphenylene ether, polyphenylene sulfide, polyether imide, polyimide, polysiloxane, tetrafluoroethylene resin, trifluoroethylene resin, trifluorochloroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinylidene fluoride.It is also preferable to use a compound in which two or more types of resins are mixed in at least one layer from the viewpoint of improving moldability.

[0052] From the viewpoint of improving moldability, the laminate sheet of the present invention preferably contains at least one unit selected from the group consisting of cycloalkane units, chain alkane units having 5 or more carbon atoms, and polyethylene glycol units having a molecular weight of 20,000 or less in an amount of 1 mol% to 99 mol% of the total resin components constituting the laminate sheet. Adding molecular chains having a chain structure promotes molecular chain movement originating from the chain structure during heat molding, thereby improving moldability. From the above viewpoint, it is even more preferable that the resin component contains at least two units selected from the group consisting of cycloalkane units, chain alkane units having 5 or more carbon atoms, and polyethylene glycol units having a molecular weight of 20,000 or less, each in an amount of 1 mol% to 40 mol%. The chain alkane units preferably have 7 or more carbon atoms, and particularly preferably 9 or more. While there is no particular upper limit on the number of carbon atoms in the chain alkane units, it is preferably approximately 100,000 from the viewpoint of feasibility.

[0053] A preferred embodiment of the laminate sheet of the present invention is an electromagnetic wave shield comprising the laminate sheet of the present invention and a reflector. By combining a reflector on the surface opposite to the electromagnetic wave incident surface of the laminate sheet, the electromagnetic wave is reflected back and forth within the laminate sheet, thereby improving the electromagnetic wave absorption efficiency. On the other hand, when a reflector is placed on the front surface, it is also possible to have a certain amount of electromagnetic wave reflected by the reflector surface and a portion of the transmitted electromagnetic wave sharply shielded within the laminate sheet. To fully utilize the electromagnetic wave absorption properties of the laminate sheet of the present invention, the former configuration is more preferable.

[0054] The reflector may be made of any material that can reflect electromagnetic waves. Examples of the material include metals such as aluminum, copper, iron, and gold, alloys such as stainless steel, and carbon films. The shape and thickness of the reflector are also not limited. The shape should be in accordance with the material to be used, but it may be, for example, a flat, curved, or hemispherical plate.

[0055] Examples of reflectors include plate reflectors containing metal, alloy, or carbon, laminated reflectors in which a film made of metal, alloy, or carbon is formed on the surface of a polymer film, sheet, plate, etc., composite reflectors in which metal, alloy, or carbon is dispersed inside a polymer film, sheet, plate, etc., and composite reflectors containing a mesh made of metal or alloy inside a polymer film, sheet, plate, etc. In addition, when combined with the laminated sheet of the present invention, if a support, housing, etc. in each application contains a metal, alloy, carbon, etc., it can also be used as a reflector as is.

[0056] The electronic device of the present invention is equipped with the laminate sheet of the present invention. For purposes such as preventing false images caused by electromagnetic waves used in 4G / 5G communications, wireless LAN, and ITS radar, reducing unwanted electromagnetic radiation from electronic devices installed inside the housings of computers, mobile phones, radios, medical devices, vehicle bumpers, and the like, and preventing malfunctions due to radiation from adjacent devices, the laminate sheet of the present invention or an electromagnetic wave shielding body equipped with the laminate sheet is preferably used as the electronic device (including communications devices). In addition, any electronic device that uses frequencies in the GHz band can be suitably equipped with the laminate sheet of the present invention, without being limited to the above.

[0057] The laminated sheet of the present invention can also be suitably used for transportation such as vehicles, aircraft, and ships, wall surfaces of structures such as buildings, tunnels, guardrails, highways, bridges, and steel towers, communication facilities such as telegraphs and telephones, and transportation means such as drones and unmanned vehicles.

[0058] The building material of the present invention includes the laminate sheet of the present invention. The laminate sheet can be applied by attaching it to structures such as floors, ceilings, walls, windows, and pillars directly via an adhesive or via other sheets, shielding plates, panels, etc. A method of molding it together with a support material in a single batch is also preferred for building materials for local 5G. The laminate sheet of the present invention can also be used as a wall or window material for shielded rooms to protect against external electromagnetic jamming noise.

[0059] The method for producing a laminate sheet of the present invention will be described below with reference to specific examples, but the present invention is not limited to the following embodiments.

[0060] First, we will explain a laminate sheet using rubber, thermoplastic elastomer, or the like as the base polymer of the substrate. First, a predetermined amount of desired conductive particles is blended with the base polymer and kneaded and incorporated using a known device such as a kneader, Banbury mixer, mill mixer, roll mill, jet mill, or ball mill to obtain a conductive particle-containing base polymer mixture. The base polymer alone, or the prepared conductive particle-containing base polymer, is rolled using a batch press or melt extruded to form a sheet of the desired thickness. Then, a total of five or more layers of the prepared sheets corresponding to Layer A and Layer B are alternately stacked and pressed or laminated to obtain a laminate sheet. The fusion temperature during this process varies depending on the type of polymer used, but is preferably 150°C to 400°C, more preferably 250°C to 380°C.

[0061] Next, we will explain the manufacturing method of a laminate sheet using a flexible thermoplastic resin, which is a preferred resin in this invention, in which only Layer B contains conductive particles and Layer A does not. First, the thermoplastic resin prepared in pellet form and a predetermined amount of conductive particles are kneaded in a twin-screw extruder and extruded into a gut shape. This is then cooled in a water tank and cut with a chip cutter to form a master pellet containing conductive particles. In this case, the conductive particles may be dry-blended with the thermoplastic resin and then metered and fed from a hopper, or they may be side-fed into the molten thermoplastic resin using a side feeder from any position in the extruder. The feeding method is not limited to the above and can be selected appropriately depending on the specific gravity and shape of the conductive particles used.

[0062] The thermoplastic resin compositions constituting Layer A and Layer B are then dried in hot air or under vacuum, and then fed into separate extruders, where they are heated and melted to a temperature equal to or higher than the melting point of the thermoplastic resin. The extrusion rate is then made uniform using a gear pump or the like, and the thermoplastic resin composition is discharged, and foreign matter, modified thermoplastic resin, etc. are removed using a filter or the like.

[0063] Next, these thermoplastic resin compositions are laminated in a multi-layer lamination device capable of laminating the desired number of layers, molded into the desired shape using a die, and extruded into a sheet. The sheet-like material extruded from the die is extruded onto a cooling body such as a casting drum and cooled and solidified to form a cast sheet. In this case, since the cast sheet itself exhibits electrical conductivity, it is preferable to use a method in which air is blown from a slit-shaped, spot-shaped, or planar device to bring the cast sheet into close contact with a cooling body such as a casting drum and rapidly solidify it, or a method in which the cast sheet is brought into close contact with a cooling body using a nip roll and rapidly solidify it.

[0064] Multi-layer lamination devices such as multi-manifold dies, feed blocks, and static mixers can be used. However, to efficiently obtain the multilayer laminate of the present invention, it is particularly preferable to use a feed block with fine slits. The use of such a feed block minimizes the device's excessive size, reducing the amount of foreign matter generated due to thermal degradation of resins and enabling highly accurate lamination even when a large number of layers are stacked. Furthermore, the lamination accuracy in the width direction is significantly improved compared to conventional technologies. Furthermore, this device has the advantages of easily achieving any layer thickness by adjusting the shape (length and width) of the slits, and of easily orienting conductive particles in the direction of the laminate sheet surface during the lamination process due to the effect of resin flow.

[0065] When using a slit-type feedblock to produce laminated sheets, the thickness and distribution of each layer can be adjusted by adjusting the length and width of the slits to achieve a proper pressure balance. The slit length refers to the length of the comb-like portion that forms the flow path for alternately flowing layers A and B through the slit plate. Another suitable method for increasing the number of layers is to form a laminate in the feedblock, then stack the layers in a static mixer to double the number of layers.

[0066] The resulting cast sheet can be biaxially stretched in the longitudinal and transverse directions as needed. When biaxial stretching is performed, the stretching may be performed sequentially or simultaneously. Furthermore, if necessary, the sheet may be further stretched again in the longitudinal and / or transverse directions.

[0067] First, we will explain sequential biaxial stretching, in which a sheet is stretched first in the longitudinal direction and then in the transverse direction. Here, stretching in the longitudinal direction refers to uniaxial stretching to impart molecular orientation to the sheet in the longitudinal direction, and is usually performed by varying the peripheral speed of rolls. This stretching can be performed in a single stage or in multiple stages using multiple pairs of rolls. The stretching ratio varies depending on the type of resin, but is usually preferably 1.1 to 7.0 times, with 1.5 to 4.0 times being particularly preferred. Furthermore, the stretching temperature is preferably set within the range of the glass transition temperature to the glass transition temperature + 100°C for all resins constituting the sheet, but below the melting point. The uniaxially stretched laminate sheet obtained in this manner can be subjected to surface treatment such as corona treatment, flame treatment, or plasma treatment, as necessary, and then a primer layer can be formed to improve adhesion with the film to be laminated on top. In the in-line coating process, the primer layer can be applied to one side, or both sides simultaneously, or one side at a time.

[0068] Width-direction stretching refers to stretching to impart width-direction orientation to a sheet. This is typically performed using a tenter, with both ends of the sheet held by clips while being conveyed. The stretching ratio varies depending on the type of resin, but is typically preferably 1.1 to 7.0 times, with 1.5 to 5.0 times being particularly preferred. Stretching reduces variations in return loss and prevents a decrease in electromagnetic wave attenuation after molding. Furthermore, the stretching temperature is preferably within the range of the glass transition temperature to the glass transition temperature + 120°C for all resins constituting the sheet. The biaxially stretched laminate sheet is then heat-treated in a tenter at a temperature above the stretching temperature and below the melting point, uniformly annealed, cooled to room temperature, and wound up. If necessary, relaxation treatments, etc., may be performed in the longitudinal and / or width directions during annealing to impart a low orientation angle and thermal dimensional stability to the sheet.

[0069] Next, simultaneous biaxial stretching will be described. In the case of simultaneous biaxial stretching, the obtained cast sheet may be subjected to a surface treatment such as corona treatment, flame treatment, or plasma treatment as necessary, and then provided with properties such as easy slippage, easy adhesion, and antistatic properties by in-line coating. In the in-line coating process, the coating layer may be applied to one side of the sheet, or to both sides simultaneously or one side at a time.

[0070] The cast sheet is then introduced into a simultaneous biaxial tenter, where it is conveyed while being held at both ends with clips and stretched simultaneously and / or stepwise in the longitudinal and transverse directions. Simultaneous biaxial stretching machines (tenters) include pantograph, screw, drive motor, and linear motor types. Drive motor or linear motor types are preferred, as they allow for variable stretching ratios and relaxation treatment at any desired location. The stretching ratio varies depending on the type of resin, but an area ratio of 2.0 to 50 times is generally preferred, with 4.0 to 20 times being more preferred. The stretching speeds may be the same or different in the longitudinal and transverse directions. The stretching temperature is preferably within a range from the glass transition temperature to the glass transition temperature + 120°C for all resins constituting the alternating laminate unit.

[0071] To impart flatness and dimensional stability to the sheet thus simultaneously biaxially stretched, it is preferable to subsequently heat-treat the sheet in a tenter at a temperature above the stretching temperature but below the melting point of all resins constituting the sheet. During this heat-treatment, it is preferable to instantly relax the sheet in the longitudinal direction immediately before and / or immediately after entering the heat-treatment zone to suppress the distribution of the main orientation axis in the width direction. After the heat-treatment, the laminated sheet is uniformly and slowly cooled, then cooled to room temperature, and wound up. If necessary, relaxation treatment may be performed in the longitudinal and / or width directions during the slow cooling from the heat treatment. The sheet may also be instantly relaxed in the longitudinal direction immediately before and / or immediately after entering the heat-treatment zone.

[0072] Furthermore, the laminate sheet of the present invention can be combined with an electromagnetic wave reflective layer capable of blocking a wide frequency band to provide stronger shielding for only certain frequencies. Alternatively, a new layer exhibiting a low dielectric constant can be provided on the outermost surface of the laminate sheet to further reduce electromagnetic wave reflection at the surface, resulting in a laminate sheet with enhanced electromagnetic wave absorption. In addition to the latter, it is also preferable for the layer exhibiting a high complex dielectric constant to exhibit a layer thickness distribution in which the layer thickness continuously decreases from the surface to the interior of the sheet. Because the concentration of the EMI suppression material added to the layer exhibiting a high dielectric constant is constant, the thickness of the layer exhibiting a high dielectric constant can be continuously reduced from the surface to the interior, resulting in a state in which the conductive particles are more densely connected in the inner layer, resulting in a gradual increase in the dielectric constant. This allows electromagnetic waves to be taken into the interior of the laminate sheet without inadvertently reflecting them, thereby enhancing the electromagnetic wave absorption effect. [Example]

[0073] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Evaluation of each item was carried out by the following methods.

[0074] (Methods for measuring characteristics and evaluating effects) (1) Average particle size, volume concentration, and aspect ratio of conductive particles The longitudinal and width cross sections of the laminated sheet were embedded in epoxy resin and polished, and then the surface was polished using an ion mill (JEOL Ltd., IB-19520CCP). The acceleration voltage was 4 kV and the processing temperature was -120°C. Pt-Pd was then vapor-deposited at 2 mA for 3.75 minutes using a sputtering device (Eiko Engineering, IB-3). In this way, processed samples of the thickness-width cross section and the thickness-longitudinal cross section of each sample were obtained. Next, observations were performed using a scanning electron microscope (JEOL Ltd., JSM-6700F). Light was irradiated parallel to the thickness direction of the processed sample, and cross-sectional images were obtained under the following observation conditions. <Observation conditions> Accelerating voltage: 3 kV Objective aperture: 4 Secondary electron detection: ON Mode: LEI Emission: 10μA Magnification: 10000x Inclination: None The Analyze Particles function in ImageJ (NIH 1.52e) was then used to extract the area of ​​each particle from each cross-sectional image. The area of ​​each area was then approximated to an ellipse using Fit Ellipse to calculate the Mean (average diameter), Major (major axis), and Minor (minor axis). Furthermore, the aspect ratio of each particle was calculated by dividing the Major by the Minor, to three significant digits. The average value of the Mean values ​​for particles with an aspect ratio of 5 to 10,000 was used as the average particle size of conductive particle X, and the average value of the Mean values ​​for particles with an aspect ratio of 1 to 5 but less than 5 was used as the average particle size of conductive particle Y. Measurements of the average particle size were performed seven times in each of the longitudinal and transverse directions for each sample, and the average values ​​of the 10 average particle sizes, excluding the maximum and minimum values, were used as the average particle sizes of conductive particle X and Y. Note that particles with a Minor value of 0 were excluded from the analysis as outliers.

[0075] The ratio of the area occupied by particles with an aspect ratio of 5 or more and 10,000 or less in the entire observation image was taken as the volume concentration of conductive particles X in the observation image, and the ratio of the area of ​​particles with an aspect ratio of 1 or more and less than 5, determined in the same manner, was taken as the volume concentration of conductive particles Y in the observation image. Measurements were performed for one sample with n=7 in each of the longitudinal and width directions, and the average values ​​of the area ratios for 10 measurements excluding the maximum and minimum values ​​for each were taken as the volume concentrations of conductive particles X and Y, respectively.

[0076] Furthermore, the aspect ratios of the particles in the observed images were plotted as shown in Figure 5, with the vertical axis representing frequency and the horizontal axis representing the logarithm of the aspect ratio. The maximum values ​​within the aspect ratio range of 5 to 10,000 and the maximum values ​​within the aspect ratio range of 1 to less than 5 were designated as the aspect ratios of conductive particle X and conductive particle Y in the observed region, respectively. The analysis was performed on seven 1.5 μm × 12 μm rectangles within the layer in both the longitudinal and transverse directions, and the average values ​​of five points were calculated after excluding the maximum and minimum values. The larger of the average values ​​obtained in the longitudinal and transverse directions was used as the aspect ratios of conductive particle X and conductive particle Y. Reference numeral 6 in Figure 5 denotes a logarithmic graph of aspect ratio.

[0077] (3) Thickness Measurements were taken using a dial gauge (Mitutoyo 2019S-10) and a dial gauge stand (Mitutoyo 7002-10). Measurements were taken five times and the average value was used as the thickness of the laminated sheet.

[0078] (4) Return loss Measurements were carried out by changing the measurement unit as follows according to the measurement frequency band.

[0079] (4-1) 1GHz to 40GHz frequency band The attenuation of the samples was measured using an Agilent Technologies Vector Network Analyzer (E8361A). A donut-shaped coaxial waveguide with an outer diameter of 7 mm and an inner diameter of 3.04 mm was used for the 0.5 GHz to 18 GHz frequency band, a rectangular waveguide with a rectangular shape of 4.32 mm x 10.67 mm for the 18 to 26.5 GHz frequency band, and a rectangular waveguide with an internal shape of 3.56 mm x 7.11 mm for the 26.5 to 40 GHz frequency band. The longitudinal attenuation was measured when the electric field direction in the waveguide was parallel to the length of the sample, and the width attenuation was measured when the electric field direction was parallel to the width of the sample. The measurement interval was set to allow 200 measurements for each frequency band. A 3 mm aluminum metal plate was placed on the back of the sample, ensuring total reflection of the incident electromagnetic wave when there was no electromagnetic wave absorption by the sample. The difference between the S11 values, which represent the intensity ratio of the reflected electromagnetic wave to the incident electromagnetic wave, and the S11 values ​​without the sample was taken as the attenuation, and the absolute value of the average value of the attenuation in the longitudinal direction and the width direction was taken as the return loss. In addition, the average value of the frequency that showed the maximum return loss in the longitudinal direction and the width direction was taken as the absorption frequency. (4-2) 40 to 110 GHz frequency band A measurement sample was prepared by attaching an aluminum metal plate to the back of a 150 mm square sample. Using a Keycom Corporation lens antenna type oblique incidence electromagnetic wave absorber (electromagnetic wave absorbing material) return loss measurement device LAF-26.5B, electromagnetic waves were irradiated at an oblique incidence angle of 15° in accordance with JIS R 1679 (2007). The return loss was measured in the frequency bands of 33 to 50 GHz (WR-22), 50 to 75 GHz (WR-15), and 75 to 110 GHz (WR-10). The longitudinal attenuation was measured when the sample was placed parallel to the electric field direction, and the widthwise attenuation was measured when the sample was placed parallel to the electric field direction. While this measurement method also measures values ​​from 33 to 40 GHz, the return loss in the frequency band above 33 GHz and below 40 GHz was measured using the data measured in (4-1). The return loss and absorption frequency were then calculated in the same manner as in (4-1).

[0080] (5) Degree of orientation A cross-sectional image was obtained in the same manner as when measuring the volume concentration of conductive particles. Analysis was performed using ImageJ (NIH 1.52e) and OrientationJ (Daniel Sage 2.0.5). A 1.5 μm section in the thickness direction and 12 μm in the plane direction was cut out from the cross-sectional image to create a 100 × 400 pixel image. Image vector analysis of the image was performed using OrientationJ Distribution to determine the degree of 0° (plane direction). The analysis conditions were as follows: Local Window: σ2Pixel Gradient: Cubic Spline Measurements were made for one sample in the longitudinal direction and the width direction, n=7, and the average values ​​of the five points excluding the maximum and minimum values ​​were taken as the orientation degrees in the longitudinal direction and the width direction.

[0081] (6) Electrical orientation The longitudinal and width cross sections of the laminated sheet were embedded in epoxy resin and polished, and then the surface was polished using an ion mill (JEOL IB-19520CCP). The acceleration voltage was 4 kV and the processing temperature was -120°C. Measurements were then performed at room temperature in a high-purity argon gas atmosphere (HO = 0.1 ppm, O = 0.1 ppm) using an electric force microscope (Bruker NanoScope V Dimension Icon Glovebox) under the following conditions: <Measurement conditions> EFM scanning: Tapping AFM mode EFM probe: PtIr coated silicon cantilever Measurement range: 10 x 10 μm Frequency range: ±3Hz Next, ImageJ (NIH 1.52e) was used to divide the overall brightness into 255 levels, and the area with a brightness between 0 and 125 was extracted and binarized. Next, image vector analysis was performed using OrientationJ Distribution in OrientationJ (Daniel Sage 2.0.5) to determine the frequency at 0° (plane direction). The analysis conditions were as follows: <Analysis conditions> Local Window: σ2Pixel Gradient: Cubic Spline Measurements were made for one sample in both the longitudinal and transverse directions (n ​​= 3) and the average values ​​were used as the orientation degrees in the longitudinal and transverse directions.

[0082] (7) Particle angle, standard deviation Cross-sectional images were obtained in the same manner as when measuring the volume concentration of conductive particles. After binarization using the image analysis software ImageJ (NIH 1.52e), 200 particles were selected from the binarized cross-sectional image in ascending order of their center of view. The image analysis software was used to measure the angle between the long axis of each particle and the surface direction, and the average of the obtained values ​​was used as the particle angle. The standard deviation was also calculated from the obtained values. However, if particles overlapped, only the particle at the forefront was analyzed.

[0083] (8) Cooling down crystallization temperature Evaluation was performed using a differential scanning calorimeter (DSC6220, manufactured by Seiko Instruments Inc.) in accordance with JIS K-7121 (1987) and JIS K-7122 (1987). Five mg of sample was weighed into a sample pan, heated from 25°C to 290°C at a heating rate of 20°C / min, and then held at that temperature for 5 minutes. Measurements were then performed by lowering the temperature from 290°C to 25°C at a cooling rate of 20°C / min. The temperature at the top of the crystallization peak in the differential scanning calorimeter chart obtained during cooling was taken as the cooling crystallization temperature. When there were multiple crystallization peaks, the lower temperature was taken as the cooling crystallization temperature.

[0084] (9) Elongation at break The sample was cut into a size of 1 cm x 20 cm along the longitudinal or transverse direction, and the elongation at break was measured using an automatic film strength and elongation measuring device (Orientec Co., Ltd. "Tensilon" (registered trademark) AMF / RTA-100) at 90 °C, a chuck distance of 5 cm, and a pulling rate of 300 mm / min. The measurement was performed according to the methods described in JIS K-7161 (2014) and JIS K-7127 (1999). The measurement was performed five times in each of the longitudinal and transverse directions of each sample, and the average value was used as the elongation at break.

[0085] (10) Weight fraction of hydrocarbons The sample was dissolved in triethylene glycol at 90°C, and the particles were filtered off using a metal filter. The resulting particles were washed with ethanol and dried at 150°C for 90 minutes, after which they were analyzed using an organic trace elemental analyzer (PerkinElmer 2400II) under the following conditions. The combustion residue was considered to be inorganic and metallic substances unrelated to organic matter, and the weight fraction of hydrocarbons was determined by dividing the amount of C and H atoms obtained by the total weight. Sample amount: 10 mg Sample decomposition furnace: 950℃ Reduction furnace: 500℃ Helium flow rate: 200ml / min.

[0086] (11) Electromagnetic wave absorption performance When the return loss is 30 dB or more, it is rated as A, when it is 25 dB or more but less than 30 dB, it is rated as B, when it is 20 dB or more but less than 25 dB, it is rated as C, and when it is less than 20 dB, it is rated as D. If it is C or more, it can be used as an electromagnetic wave absorber.

[0087] (12) Absorption performance unevenness and polarization selectivity Regarding uneven absorption performance, if the difference in return loss between the lengthwise and widthwise directions is 5 dB or less, it is evaluated as no uneven absorption performance (A), and if it is more than 5 dB, it is evaluated as uneven absorption performance (B). If the uneven absorption performance is A, it is possible to absorb electromagnetic waves regardless of the polarization of the electromagnetic waves. Furthermore, regarding polarization selectivity, if the difference in return loss between the lengthwise and widthwise directions is more than 10 dB, it is evaluated as having polarization selectivity (A), and if it is 10 dB or less, it is evaluated as not having polarization selectivity (B). If the polarization selectivity is A, it is possible to selectively absorb specific polarized waves.

[0088] (13) Molding conformability Molding was performed using a vacuum molding machine (Seiko Sangyo Co., Ltd. 300X) under the following conditions. Heating was performed using an infrared heater, and the temperature was determined by attaching a heat label (Micron Co., Ltd. 6R-99) to the sample. Molding tests were performed three times for each sample. <Molding conditions> Heating time: 30 seconds Heating temperature: 110℃ Vacuum pump pressure: 0.17MPa Shape of the mold: Box shape, 5cm wide, 7.5cm long and 2cm deep. Thereafter, the appearance after molding was visually inspected and evaluated as follows. <Evaluation criteria> A: All samples are tightly adhered to the edges and vertices and are wrinkle-free. B: One or two samples have air pockets on the edges or wrinkles near the vertices. C: All three samples have air spaces around the edges or wrinkles near the vertices.

[0089] (particles and resins used in manufacturing laminated sheets) The particles and resins used in the production of the laminated sheet are shown in Tables 1 and 2.

[0090] [Table 1]

[0091] [Table 2]

[0092] (Examples 1 to 8, 13 to 22, Comparative Examples 1 and 2) First, the resin composition for Layer B was kneaded in a twin-screw extruder to form conductive master pellets, with the composition shown in Tables 3 to 5. Next, the resin for Layer A and the conductive master pellets for Layer B were each fed into separate twin-screw extruders, where they were melted and kneaded at 270°C. The kneading conditions were set so that the screw rotation speed relative to the discharge rate was 0.7. Next, the two were merged in a multi-manifold feed block with the number of layers shown in Tables 3 to 5, and alternately laminated at a lamination ratio of 1.0. The resulting molten alternating laminate was then extruded into a sheet form from a die onto a casting drum with a surface temperature of 25°C, which was then cooled and solidified to obtain an unstretched laminate sheet. The evaluation results are shown in Tables 3 to 5. The thickness was adjusted by adjusting the discharge rate of each extruder and the rotation speed of the casting drum.

[0093] Examples 9 to 12 Unstretched laminate sheets were obtained by the methods described in Examples 1 to 8, 13 to 22, and Comparative Examples 1 and 2, and then stretched in the machine direction at 95°C to the ratios shown in Table 4. In Example 12, the sheets were further stretched in the width direction at 105°C to the ratios shown in Table 4 to obtain uniaxially or biaxially stretched laminate sheets. The evaluation results are shown in Table 4. Note that the thicknesses listed in Table 4 for Examples 9 to 12 are values ​​after stretching.

[0094] [Table 3]

[0095] [Table 4]

[0096] The content (wt%) of the "second resin" in Table 4 is a value calculated assuming that the entire resin in layer B is 100 wt%. In addition, 100 - the content (wt%) of the second resin is the content of the "resin" shown in Table 4. The same applies to Table 5.

[0097] [Table 5] [Industrial Applicability]

[0098] The present invention provides a laminate sheet that is thin but has high electromagnetic wave absorption performance and excellent formability. Because the laminate sheet of the present invention has the above-mentioned excellent properties, it can be suitably used in electronic devices, transportation, building materials, furniture, etc. [Explanation of symbols]

[0099] 1: Peak with the largest return loss 2: Return loss at the peak top with the largest return loss 3: Resin 4: Conductive particles 5: Conductive particle Y 6: Logarithmic aspect ratio graph

Claims

1. 1. A laminated sheet including an alternating laminate unit in which different A layers and B layers are alternately laminated in 13 to 249 layers, wherein at least one of the A layers and the B layers contains conductive particles X, where X is a conductive particle having an aspect ratio of 5 to 10,000, and the conductive particles X are carbon nanotubes or carbon fibers, and the laminated sheet has an overall thickness of 3.0 mm or less.

2. 2. The laminate sheet according to claim 1, wherein when the return loss is measured for each frequency, the value obtained by dividing the electromagnetic wave attenuation at the peak top of the peak with the largest return loss by the thickness of the laminate sheet is 5 dB / mm or more.

3. 3. The laminate sheet according to claim 1, wherein when conductive particles Y are conductive particles having an aspect ratio of 1 or more and less than 5, at least one of the A layer and the B layer contains 1 vol% or more and 90 vol% or less of the conductive particles X and 1 vol% or more and 90 vol% or less of the conductive particles Y.

4. 4. The laminate sheet according to claim 1, wherein the degree of electrical orientation of particles in both the longitudinal cross section and the width cross section measured by electric force microscope (EFM) is 1,000 or more and 100,000 or less.

5. 5. The laminate sheet according to claim 1, wherein the degree of particle orientation in both the longitudinal cross section and the width cross section is 10 or more and 10,000 or less.

6. 6. The laminate sheet according to claim 1, wherein the ratio of the degree of particle orientation in the longitudinal cross section to the degree of particle orientation in the width cross section is 0.50 or more and 2.00 or less.

7. 6. The laminate sheet according to claim 1, wherein the ratio of the degree of particle orientation in the longitudinal cross section to the degree of particle orientation in the width cross section is 0.1 or less or 10 or more.

8. 8. The laminate sheet according to claim 1, wherein the average value of the angle formed between the major axis of the particle and the plane direction in each of the longitudinal cross section and the width cross section is 0° or more and 30° or less.

9. 9. The laminate sheet according to claim 1, wherein the standard deviation of the angle formed between the major axis of the particle and the plane direction in each of the longitudinal cross section and the width cross section is 0° or more and 30° or less.

10. 10. The laminate sheet according to claim 1, wherein the lowest crystallization temperature upon cooling is 70° C. or more and 200° C. or less, or no crystallization temperature upon cooling is observed.

11. The laminate sheet according to any one of claims 1 to 10, wherein the resin component contains at least one unit selected from the group consisting of a cycloalkane unit, a chain alkane unit having 5 or more carbon atoms, and a polyethylene glycol unit having a molecular weight of 20,000 or less in an amount of 1 mol% to 99 mol%.

12. 12. The laminate sheet according to claim 1, wherein the weight fraction of hydrocarbons in the whole particles is 85% or more and 100% or less.

13. 4. The laminate sheet according to claim 3, wherein at least one of the conductive particles X and the conductive particles Y has an average particle size of 5 nm or more and 1000 nm or less.

14. An electronic device using the laminate sheet according to any one of claims 1 to 13.

15. Furniture using the laminate sheet according to any one of claims 1 to 13.

16. A building material using the laminate sheet according to any one of claims 1 to 13.

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