JP7739753B2 - Laminated Sheet - Google Patents

Description

The present invention relates to a laminate sheet with excellent electromagnetic wave shielding properties.

With advances in communications technology, electromagnetic waves of various frequency bands are now being used and flying through the atmosphere, including meter waves in the hundreds of MHz to several GHz range, which are primarily used for mobile phones and wireless communications; centimeter waves in the several GHz to tens of GHz range, 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 hundreds of GHz range, which are primarily used for automobile collision prevention radar.

Electromagnetic waves of an appropriate frequency band are selected depending on the amount of information, transmission distance, and application. However, 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, development of communication technologies that use electromagnetic waves in the GHz frequency band has accelerated in order to achieve high-speed, high-capacity communications, and there is a demand for electromagnetic wave shielding materials that can block electromagnetic waves in this frequency band.

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; greater effectiveness can be achieved by combining reflection and absorption.

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. Generally, electromagnetic wave shielding over a wide frequency range can be achieved by coating or laminating a material with very low resistance, such as metal (copper), on the surface of the substrate (Patent Document 1). Meanwhile, electromagnetic wave shielding by absorption involves incorporating conductive and/or magnetic particles into the substrate, which absorbs the electromagnetic waves that enter the interior as induced currents, thereby dissipating the electromagnetic wave energy. Absorption performance is achieved by incorporating metal particles such as carbon particles or ferrite into dielectric polymers such as rubber (Patent Documents 2-4).

Special Publication No. 2011-502285 Japanese Patent Application Laid-Open No. 2003-158395 Japanese Patent Application Laid-Open No. 2017-118073 Japanese Patent Application Laid-Open No. 2019-057730

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, leading to issues such as short circuits in electronic and communication devices and reduced durability.

Furthermore, among the electromagnetic wave shielding materials that utilize absorption, such as those described in Patent Documents 2 to 4, many of these materials 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, uneven 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 with a high concentration of conductive particles, the resin's melt viscosity changes during extrusion (thixotropy) become significant. This can lead 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.

The present invention aims to solve the above problems and provide a laminated sheet that is thin yet has both electromagnetic wave shielding properties and formability.

In order to solve the above problems, the present invention has the following configuration. That is, it 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 or more and 10,000 or less, at least one of the A layers and the B layers contains the conductive particles X.

The present invention makes it possible to provide a laminated sheet that is thin yet combines electromagnetic wave shielding properties with formability.

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. 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. FIG. 2 is a schematic diagram of a layer containing conductive particles X. FIG. 2 is a schematic diagram of a layer containing conductive particles X and conductive particles Y. This is a plot in which the vertical axis represents the degree and the horizontal axis represents the logarithm of the aspect ratio.

The laminate sheet of the present invention will be 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 or more and 10,000 or less, at least one of the A layers and the B layers contains the conductive particles X.

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

Specifically, the compositions of the layers can be considered to be different 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) using 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 value differs by 3°C or more or 10% or more. (5) When the cross section is observed at the desired magnification (500-20,000 times) using a transmission electron microscope (TEM) or scanning electron microscope (SEM), an interface can be confirmed. Here, "an interface can be confirmed" means that the brightness of adjacent layers differs. Specifically, brightness is measured at 1,000 points for each layer. Next, the average brightness and the standard deviation of the brightness for each layer are calculated. If the difference between the average brightness of two adjacent layers is greater than the standard deviation of the brightness of each layer, the brightness is determined 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 measured by 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 perspective of film-forming properties and preventing conductive particle shedding.

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. Furthermore, while thermally crystallized films become brittle, the present invention reduces thermal crystallization by thinning each layer, thereby reducing defects such as cracking during molding. Furthermore, while resins are subject to significant deformation during molding, it is desirable for the laminate sheet to be resistant to post-molding impacts and scratches (small deformations). The interfacial layers between the layers retain their shape in response to small deformations, but large deformations cause microfractures and slippage at the interfaces. Therefore, the multilayer structure provides excellent formability and allows the sheet to adequately 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. There is no upper limit to the number of layers in the alternating unit, but from the perspective of film formation stability, the maximum number is approximately 2,000.

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 and B layers 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. A single type of conductive particle X may be used, or multiple types may be used in combination. In the latter case, the content of conductive particles X is calculated based on the total content of all components. For example, organic carbon-based particles, inorganic particles, and metal-based particles may be used alone or in combination as conductive particles X. However, organic carbon-based particles are preferred because of their small primary particle size and suitability for melt extrusion. Note that using only metal-based particles to produce a laminate sheet using an extruder can result in problems such as material pulverization and damage to the device due to friction between the device and the metal of the conductive particles X. Therefore, it is preferable that at least one type of conductive particle X contains organic carbon-based particles or inorganic particles primarily composed of carbon.

Examples of inorganic or metal particles suitable for use as conductive particles X include titanium oxides such as titanium dioxide and lower 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 particles in contact with each other expand in the plane, forming stronger conductive paths in the plane and improving electromagnetic wave absorption. Furthermore, because the area of the particles is larger when viewed from the surface of the laminated sheet, electromagnetic wave leakage through gaps between particles can be reduced.

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

In particular, the conductive particle X is preferably made of carbon nanotubes, flat carbon, carbon fiber, 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 particle X due to the effect of the conductive particle arrangement in the plane direction of the laminated structure, and to form a stronger conductive path in the plane direction. It is more preferable that the conductive particle X is carbon nanotubes or carbon fiber. On the other hand, if the aspect ratio is too high, the interaction between the resin and the conductive particle may become too strong, resulting in poor moldability. From the above perspective, the aspect ratio of the conductive particle X is preferably 20 or more and 5000 or less, and more preferably 30 or more and 3000 or less.

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. The use of organic carbon-based particles increases the hydrocarbon weight fraction. However, from the perspective of forming conductive paths by connecting organic carbons together, the hydrocarbon weight fraction of the entire particle 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 particle can be measured by dissolving the sample in triethylene glycol at 90°C, filtering the particles using a metal filter, and analyzing the result using an organic trace elemental analyzer (the apparatus and conditions are described below).

Aligning the conductive particles in a specific direction and stacking them side by side promotes the formation of conductive paths, improving the electromagnetic wave shielding performance of the laminate sheet. To achieve this, it is preferable that the total contact area between the conductive particles and the resin is large, so the finer the conductive particles, the better. 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 or more and 1000 nm or less, and more preferably 5 nm or more and 500 nm or less. The average particle size of each particle can be measured using the method described in the Examples from observation images of the longitudinal and width cross sections of the laminate sheet.

Generally, to improve the electromagnetic wave absorption properties of a laminate sheet, it is necessary to increase the content of conductive particles X; however, if there is an excess of conductive particles X, film-forming properties and processability may be impaired in exchange for high conductivity. Conversely, if there is an insufficient amount of conductive particles X, the electromagnetic wave absorption effect may not be fully achieved. From the above perspective, it is preferable that at least one of Layer A and Layer B contains 1 vol% to 90 vol% of conductive particles X, more preferably 5 vol% to 65 vol%, and even more preferably 10 vol% to 50 vol%.

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 observing the image 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 is anisotropic, 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 the method for identifying conductive particles X by observing the image, are shown in the Examples.

If the longitudinal or width direction is unknown, the elongation at break is measured every 30° from any direction of the sample, and the direction with the smallest elongation at break is considered to be the longitudinal direction (the same applies hereinafter to each parameter that requires specifying the longitudinal or width direction for measurement). The method for measuring elongation at break is described below.

The aspect ratio of conductive particles can be determined by approximating each conductive particle to an ellipse and calculating the value obtained by dividing the major axis by the minor axis. One method for measuring the aspect ratio of conductive particles in a laminate 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 portion is extracted and approximated as an ellipse, and the major and minor axes are measured and their ratios are calculated. When cutting the cross section, methods that minimize particle damage, such as freezing or resin embedding, may be used as needed. Furthermore, during observation, metal sputtering, such as platinum, may be performed as needed to minimize charge buildup. Examples of image analysis software include ImageJ and Mac-View, 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 of 5 or greater and 10,000 or less correspond to conductive particles X.

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 any 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 made thinner in order to thin the layer containing a large amount of conductive particles X, this will lead to a decrease in the electromagnetic wave absorption performance of the laminate sheet. However, by using the laminate structure described above, 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.

From the viewpoint of achieving both 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 approximately 1000 dB/mm.

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 at 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, we found that a good return loss can be consistently achieved if the value obtained by dividing the electromagnetic wave attenuation by the thickness of the laminate sheet is within the above range.

The thickness of a laminate sheet can be measured using a known dial gauge. Return loss, expressed in decibels (dB), represents the amount of electromagnetic wave loss during a round-trip within a laminate sheet. Specifically, using the coaxial waveguide method or free-space method, electromagnetic waves are irradiated onto a laminate sheet with a metal reflector (e.g., aluminum) attached to the backside. 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. The return loss peak with the largest peak intensity (attenuation) is the focus of our analysis. The "peak top" here refers to the point where the slope of the tangent to the return loss spectrum changes sign (slope) 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 used as the reference. Note that since the example in Figures 1 and 2 has 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.

Of the reflection loss peaks of the laminate sheet of the present invention, the peak with the largest reflection loss is preferably present in the frequency band of 1 to 100 GHz. When the laminate sheet of the present invention is used for electromagnetic wave shielding purposes, 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.

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 sheet's dielectric constant 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 combining conductive particles with high and low aspect ratios (conductive particles X and conductive particles Y, described below) so that the volume concentration of conductive particles Y is 0.1 or greater and less than 10 when the volume concentration of conductive particles X is 1, increasing the volume concentration of conductive particles X, or multiplying the sheet to an appropriate thickness for each layer to promote the alignment of conductive particles X.

In the laminate sheet of the present invention, when conductive particles Y are conductive particles with an aspect ratio of 1 or more and less than 5, at least one of layer A and layer B 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 configuration are explained below with reference to the drawings. Figure 3 is a schematic diagram of a layer containing conductive particles X, and Figure 4 is a schematic diagram of a layer containing conductive particles X and conductive particles Y. In Figures 3 and 4, the reference numerals 3 to 5 represent resin, conductive particles X, and conductive particles Y, respectively.

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 help prevent a decrease in attenuation due to electromagnetic wave leakage. However, arranging 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 even 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%.

The conductive particles Y can be made of the same material as the conductive particles X. From the perspective of the connection between the conductive particles, it is preferable to use a similar material. Specifically, if 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.

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 X and Y 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 will increase, causing surface reflection of electromagnetic waves, which may reduce the electromagnetic wave absorption effect of the conductive particles.

For example, in the case of a laminate sheet having repeating units 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 that are not surface layers. In other words, if A layers are surface layers and B layers are not 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.

From the viewpoint of achieving high electromagnetic wave absorption and reducing unevenness in electromagnetic wave absorption, the laminate sheet of the present invention preferably has a particle orientation degree of 10 to 10,000 in both the longitudinal and width cross sections, 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 in a plane parallel to the longitudinal and thickness directions, and the width cross section refers to a cross section of the laminate sheet cut in a plane parallel to the width and thickness directions. Furthermore, the term "particles" refers to all conductive particles contained in the laminate sheet. When the laminate sheet contains only conductive particle X, this refers to conductive particle X. When the laminate sheet contains both conductive particles X and Y, this refers to both particles. By setting each orientation degree within the above range, it is possible to effectively connect the conductive particles to each other and achieve high electromagnetic wave absorption. Methods for achieving each degree of orientation within this range include using conductive particles with a high aspect ratio, using a laminated structure to reduce the thickness of each layer, aligning the conductive particles using shear force during extrusion, and aligning the conductive particles by stretching.

The laminated sheet of the present invention can eliminate unevenness in electromagnetic wave absorption depending on the direction of incidence 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 particle orientation in the longitudinal cross section to that in the width cross section is 0.50 or more and 2.00 or less, 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 or more and 1.25 or less. On the other hand, when the ratio of particle orientation in the longitudinal cross section to that 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 requiring the absorption of only electromagnetic waves include electromagnetic wave absorption around ETCs. 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 the value obtained by dividing the degree of particle orientation in the longitudinal cross section by the degree of particle orientation in the width cross section. The degree of particle orientation 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 provided in the examples.

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 greater the stretching ratio, the greater the degree of orientation in each direction. Another method is to increase the degree of orientation in the longitudinal direction by lowering the particle concentration and increasing the shear force experienced by each particle during extrusion. Furthermore, when molding by extrusion 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.

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, as determined by leakage electric field analysis obtained by EFM (Electric Force Microscope) measurement, is preferably 100 or more and 100,000 or less. 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, achieving high electromagnetic wave absorption. On the other hand, an electrical orientation degree of 100,000 or less suppresses excessive formation of conductive paths, reducing the decrease in electromagnetic wave absorption caused by electromagnetic waves being reflected rather than absorbed.

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

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 both the longitudinal cross section and the width cross section is preferably 0° to 30°, more preferably 0° to 10°, and even more preferably 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 to the plane direction, the area of the particles increases when observed from the surface of the laminate sheet, enabling more efficient absorption of electromagnetic waves.

The angle between the particle's long axis and the plane direction can be determined by analyzing images of the longitudinal and width cross sections using image analysis software. Details of the image analysis software and analysis methods are provided in the Examples.

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

In the laminate sheet of the present invention, it is preferable that the standard deviation of the angle between the long axis of the particles and the plane direction is 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 long 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.

The standard deviation of the angle between the particle's long axis and the plane direction can be determined by analyzing images of the longitudinal and width cross sections using image analysis software. Details of the image analysis software and analysis method are provided in the Examples.

The same method for setting the standard deviation of the angle between the long axis of the particles and the surface direction within this range can be used as for setting the average value of the angle between the long axis of the particles and the surface direction within a preferred range. However, since the thickness of each layer has a stronger effect than the average value of the angle between the long axis of the particles 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 particles and the surface direction may not be small.

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

Methods for keeping the lowest cooling-down crystallization temperature within the above range, or for preventing the cooling-down crystallization temperature from being observed, include, for example, using a resin with low crystallinity. The cooling-down crystallization temperature can also be lowered by creating a multilayer structure for the laminate sheet, thereby reducing the thickness of each layer and inhibiting crystal growth above a certain size. Furthermore, increasing the amount of particles can cause crystallization to progress due to the ordered structure of the particle surface, which can increase the cooling-down crystallization temperature. Therefore, in the laminate sheet of the present invention, the cooling-down crystallization temperature can also be lowered by using conductive particles with a high aspect ratio (conductive particles X) to reduce the total amount of particles added.

In the laminate sheet of the present invention, the resins constituting each layer may be, for example, polyolefin resins such as polyethylene, polypropylene, poly(1-butene), poly(4-methylpentene), polyisobutylene, polyisoprene, polybutadiene, polyvinylcyclohexane, polystyrene, poly(α-methylstyrene), poly(p-methylstyrene), polynorbornene, and polycyclopentene; polyamide resins such as nylon 6, nylon 11, nylon 12, and nylon 66; vinyl monomer copolymer resins such as 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 such as 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 resins that can be used alone or in combination include polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, polyacetal, polyglycolic acid, polycarbonate, polyketone, polyethersulfone, polyetheretherketone, modified polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide, polysiloxane, tetrafluoroethylene resin, trifluoroethylene resin, trichloroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinylidene fluoride. It is also preferable to use a compound in which two or more resins are mixed in at least one layer from the perspective of improving moldability.

From the perspective of improving formability, 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 with a chain structure promotes molecular chain movement originating from the chain structure during heat molding, improving formability. From this perspective, 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 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. There is no particular upper limit on the number of carbon atoms in the chain alkane units, but from the perspective of feasibility, it is set to approximately 100,000.

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 of the laminate sheet opposite the electromagnetic wave incident surface, the electromagnetic waves are reflected back and forth within the laminate sheet, thereby increasing the electromagnetic wave absorption efficiency. On the other hand, if a reflector is placed on the front surface, it is also possible to have a certain amount of electromagnetic waves reflected by the reflector surface and a portion of the transmitted electromagnetic waves 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.

The reflector may be made of any material that can reflect electromagnetic waves. Examples of materials 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 tailored to the material being used, but it can be flat, curved, hemispherical, or other plate-like shapes.

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, or plate; composite reflectors in which metal, alloy, or carbon is dispersed within a polymer film, sheet, or plate; and composite reflectors containing a mesh made of metal or alloy within a polymer film, sheet, or plate. Furthermore, when combined with the laminate sheet of the present invention, supports, housings, etc. in various applications that contain metal, alloy, or carbon can also be used as reflectors as they are.

The electronic device of the present invention comprises the laminate sheet of the present invention. It is preferable for the electronic device (including communications equipment) to have the laminate sheet of the present invention or an electromagnetic wave shielding body 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 Intelligent Transport Systems (ITS) radar, reducing unnecessary electromagnetic wave radiation from electronic devices installed inside the housings of computers, mobile phones, radios, medical devices, vehicle bumpers, etc., and preventing malfunctions of devices due to radiation from adjacent devices. In addition, any electronic device that uses frequencies in the GHz band can be suitably used by incorporating the laminate sheet of the present invention, without being limited to the above.

The laminated sheet of the present invention can also be suitably used for transportation such as vehicles, aircraft, and ships; the walls of structures such as buildings, tunnels, guardrails, highways, bridges, and steel towers; communication facilities such as telegraph and telephone facilities; and transportation means such as drones and unmanned vehicles.

The building material of the present invention comprises 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 another sheet, shielding plate, panel, etc. A method of molding it together with a support material in a single batch is also preferred for building materials for local 5G. Additionally, the laminate sheet of the present invention can also be used as a wall or window material for shielded rooms to protect against the effects of external electromagnetic jamming noise.

The method for producing a laminate sheet of the present invention will be described below using specific examples, but the present invention is not limited to the following aspects.

First, we will explain the process using an example of a laminate sheet that uses rubber or a thermoplastic elastomer as the base polymer. First, a predetermined amount of the desired conductive particles is blended with the base polymer and kneaded 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. Next, the prepared sheets corresponding to Layer A and Layer B are alternately stacked in a total of five or more layers 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.

Next, we will explain an example of a manufacturing method for 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.

The thermoplastic resin compositions that make up 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 above the melting point of the thermoplastic resin. The extrusion rate is then equalized using a gear pump or similar device, and the thermoplastic resin composition is discharged, with foreign matter and denatured thermoplastic resin removed using a filter or similar device.

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 extruded from the die is extruded onto a cooling body such as a casting drum, and cooled and solidified to form a cast sheet. Because the cast sheet itself is conductive, it is preferable to use a method in which air is blown from a slit-shaped, spot-shaped, or planar device to bring the sheet into close contact with a cooling body such as a casting drum and rapidly cool and solidify it, or a method in which the sheet is brought into close contact with a cooling body using nip rolls and rapidly cool and solidify it.

Multi-manifold dies, feed blocks, static mixers, and other devices can be used as multi-layer lamination devices. However, to efficiently obtain the multi-layer laminate of the present invention, it is preferable to use a feed block with fine slits. The use of such a feed block prevents the device from becoming excessively large, reduces the amount of foreign matter generated due to thermal degradation of the resin, and enables high-precision lamination even when an extremely large number of layers are used. Furthermore, lamination precision in the width direction is significantly improved compared to conventional technology. Further advantages of this device include the ability to adjust the thickness of each layer by the shape (length and width) of the slits, making it easy to achieve any desired layer thickness, and the ability to easily orient conductive particles in the direction of the laminate sheet surface during the lamination process due to the effect of resin flow.

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

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, the sheet may be further stretched in the longitudinal and/or transverse directions as needed.

First, we will explain sequential biaxial stretching, in which the sheet is stretched first in the longitudinal direction and then in the transverse direction. Here, longitudinal stretching refers to uniaxial stretching to impart longitudinal molecular orientation to the sheet, typically achieved by varying the peripheral speed of the rolls. This stretching can be performed in a single step or in multiple steps using multiple pairs of rolls. The stretching ratio varies depending on the type of resin, but typically 1.1 to 7.0 times is preferred, with 1.5 to 4.0 times being particularly preferred. Furthermore, the stretching temperature is preferably set within the glass transition temperature range to the glass transition temperature + 100°C and below the melting point for all resins making up the sheet. The uniaxially stretched laminate sheet obtained in this manner can be optionally subjected to surface treatments such as corona treatment, flame treatment, or plasma treatment, followed by the formation of a primer layer 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, both sides simultaneously, or one side at a time.

Stretching in the width direction refers to stretching to impart widthwise orientation to a sheet. This is typically done 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 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 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 making up the sheet. The biaxially stretched laminate sheet is then heat-treated in the tenter at a temperature above the stretching temperature and below the melting point, and then uniformly annealed to room temperature before being wound up. If necessary, relaxation treatments, such as those in the longitudinal and/or width directions, may be used during annealing to impart a low orientation angle and thermal dimensional stability to the sheet.

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 imparted 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.

The cast sheet is then introduced into a simultaneous biaxial tenter, where it is conveyed while being held at both ends with clips, and simultaneously and/or stepwise stretched 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 arbitrary adjustment of the stretch ratio and allow relaxation treatment at any location. The stretch 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 speed may be the same or different in the longitudinal and transverse directions. The stretching temperature is preferably within the range of the glass transition temperature to the glass transition temperature + 120°C for all resins making up the alternating laminate unit.

To impart flatness and dimensional stability to the sheet that has been simultaneously biaxially stretched in this manner, 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 that make up the sheet. During this heat-treatment, to suppress distribution of the main orientation axis in the width direction, it is preferable to instantaneously relax the sheet in the longitudinal direction immediately before and/or immediately after entering the heat-treatment zone. After heat-treatment in this manner, the laminated sheet is uniformly cooled slowly, then cooled to room temperature and wound up. If necessary, relaxation may also be performed in the longitudinal and/or width directions during the slow cooling from the heat treatment. It can also be instantaneously relaxed in the longitudinal direction immediately before and/or immediately after entering the heat-treatment zone.

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 create a laminate sheet that more strongly blocks 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 the reflection of electromagnetic waves 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 this is a laminate sheet in which the concentration of the electromagnetic wave suppression material added to the layer exhibiting a high dielectric constant is constant, by continuously reducing the thickness of the layer exhibiting a high dielectric constant from the surface to the interior, the conductive particles become more densely connected in the inner layers, 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.

The present invention will be explained below using examples, but the present invention is not limited to these examples. Each item was evaluated using the following methods.

(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 (IB-19520CCP, manufactured by JEOL Ltd.). 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 (IB-3, manufactured by Eiko Engineering Co., Ltd.). 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 (JSM-6700F, manufactured by JEOL Ltd.). 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>
Acceleration voltage: 3 kV
Objective aperture: 4
Secondary electron detection: ON
Mode: LEI
Emission: 10 μA
Magnification: 10,000x Tilt: None Then, using the Analyze Particles function of ImageJ (1.52e manufactured by NIH), the regions of individual particles were extracted from each cross-sectional image, and the Mean (average diameter), Major (long diameter), and Minor (short diameter) were calculated when the area of each region was approximated to an ellipse using Fit Ellipse. Furthermore, the value obtained by dividing the Major by the Minor of each particle was used as the aspect ratio of each particle, calculated 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 particles X, and the average value of the Mean values for particles with an aspect ratio of 1 to less than 5 was used as the average particle size of conductive particles Y. Measurement of the average particle size was performed for one sample in both the longitudinal and width directions (n = 7 each), and the average values of the average particle sizes for 10 measurements excluding the maximum and minimum values for each were used as the average particle sizes of conductive particles X and Y. In this case, particles showing a Minor of 0 were excluded from the analysis as abnormal values.

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, calculated in the same manner, was taken as the volume concentration of conductive particles Y in the observation image. Seven measurements were made for each sample in the longitudinal and width directions, and the average values of the area ratios for 10 measurements, excluding the maximum and minimum values, were taken as the volume concentrations of conductive particles X and Y, respectively.

Furthermore, as shown in Figure 5, the aspect ratios of the particles in the observed image were plotted with the vertical axis representing frequency and the horizontal axis representing the logarithm of the aspect ratio. Among the maximum values, those in the aspect ratio range of 5 to 10,000 and those in 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. Analysis was performed on n=7 1.5 μm x 12 μm rectangles within the layer in both the longitudinal and transverse directions, and the average of five points was calculated after excluding the maximum and minimum values for each. The larger of the obtained average values in the longitudinal and transverse directions was used as the aspect ratio of conductive particle X and the aspect ratio of conductive particle Y. Note that reference numeral 6 in Figure 5 denotes a logarithmic graph of aspect ratio.

(3) Thickness: Measured using a dial gauge (Mitutoyo 2019S-10) and a dial gauge stand (Mitutoyo 7002-10). Measurements were made 5 times, and the average value was taken as the thickness of the laminated sheet.

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

(4-1) 1 GHz to 40 GHz frequency band: The attenuation of the sample was measured using a vector network analyzer (E8361A) manufactured by Agilent Technologies, Inc. The 0.5 GHz to 18 GHz frequency band was measured using a donut-shaped coaxial waveguide with an outer diameter of 7 mm and an inner diameter of 3.04 mm, the 18 to 26.5 GHz frequency band was measured using a rectangular waveguide with a rectangular shape of 4.32 mm x 10.67 mm, and the 26.5 to 40 GHz frequency band was measured using a rectangular waveguide with an internal shape of 3.56 mm x 7.11 mm. The longitudinal attenuation was measured when the electric field direction in the waveguide was parallel to the longitudinal direction of the sample, and the widthwise attenuation was measured when the widthwise direction was parallel. The measurement interval was set so that 200 measurements could be taken for each frequency band. A 3 mm aluminum metal plate was placed on the back of the sample, so that incident electromagnetic waves would be totally reflected when there was no electromagnetic wave absorption by the sample. The difference in S11, which represents the intensity ratio of reflected electromagnetic waves to incident electromagnetic waves, between with and without the sample was taken as the attenuation, and the absolute value of the average of the attenuation in the longitudinal and width directions was taken as the return loss. In addition, the average of the frequencies that showed the maximum return loss in the longitudinal and width directions 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 lens antenna type oblique incidence type electromagnetic wave absorber (electromagnetic wave absorbing material) and return loss measurement device LAF-26.5B manufactured by Keycom Corporation, electromagnetic waves were irradiated at an oblique incidence angle of 15° in accordance with JIS R 1679 (2007), and the return loss was measured for each frequency band 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. This measurement method also measures values from 33 to 40 GHz, but the return loss in the frequency band of 33 GHz or higher and lower than 40 GHz was measured using the measurement data in (4-1). The return loss and absorption frequency were then determined in the same manner as in (4-1).

(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 (1.52e manufactured by NIH) and OrientationJ (2.0.5 manufactured by Daniel Sage). A 1.5 μm thick and 12 μm in planar direction was cut out from the cross-sectional image to create a 100 × 400 pixel image. The image was subjected to image vector analysis using OrientationJ Distribution to determine the degree of 0° (planar 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.

(6) Electrical Orientation Degree After embedding the laminated sheet in epoxy resin and polishing, the longitudinal cross section and the width cross section were each subjected to surface polishing using an ion mill (IB-19520CCP manufactured by JEOL Ltd.). At this time, the acceleration voltage was 4 kV and the processing temperature was -120°C. Then, measurements were performed at room temperature in a high-purity argon gas atmosphere (H ₂ O = 0.1 ppm, O ₂ = 0.1 ppm) using an electric force microscope (NanoScopeV Dimension Icon Glovebox manufactured by Bruker) under the following measurement 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 portion with a brightness of 0 to 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 of 0° (plane direction). The analysis conditions were as follows:
<Analysis conditions>
Local Window: σ2Pixel
Gradient:Cubic Spline
Measurements were made for one sample in the longitudinal direction and the width direction, n = 3, and the average values were used as the orientation degrees in the longitudinal direction and the width direction.

(7) Particle angle, standard deviation A cross-sectional image was obtained in the same manner as when measuring the volume concentration of conductive particles. After binarization using image analysis software ImageJ (1.52e manufactured by NIH), 200 particles were selected from the binarized cross-sectional image in ascending order of proximity to the center of the field of view, and the angle between the long axis of each particle and the surface direction was measured using the image analysis software. The average of the obtained values was used as the particle angle. In addition, the standard deviation was also calculated from the obtained values. However, when particles overlapped, only the particle at the forefront was analyzed.

(8) Temperature-Down Crystallization Temperature Evaluation was performed using a differential scanning calorimeter (Seiko Instruments Inc. DSC6220) 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 temperature increase rate of 20°C/min, and then held in that state for 5 minutes. Measurement was then performed by lowering the temperature from 290°C to 25°C at a temperature decrease rate of 20°C/min. In the differential scanning calorimeter chart obtained during temperature decrease, the peak top temperature of the crystallization peak was taken as the temperature-down crystallization temperature. When there were multiple crystallization peaks, the lower temperature was taken as the temperature-down crystallization temperature.

(9) Elongation at Break The sample was cut into a size of 1 cm x 20 cm along the longitudinal or width 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., 5 cm between chucks, 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 width directions of each sample, and the average value was used as the elongation at break.

(10) Weight Fraction of Hydrocarbons A sample was dissolved in triethylene glycol at 90°C, and particles were filtered off using a metal filter. The obtained particles were washed with ethanol, dried at 150°C for 90 minutes, and then 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 of the obtained C and H atoms was divided by the total weight to obtain the weight fraction of hydrocarbons.
Sample amount: 10 mg
Sample decomposition furnace: 950°C
Reduction furnace: 500°C
Helium flow rate: 200 ml/min.

(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.

(12) Absorption Performance Unevenness/Polarization Selectivity With regard to absorption performance unevenness, when the difference in return loss between the longitudinal direction and the width direction is 5 dB or less, it is evaluated as no absorption performance unevenness (A), and when it is more than 5 dB, it is evaluated as absorption performance unevenness (B). When absorption performance unevenness is A, it is possible to absorb electromagnetic waves regardless of the polarization of the electromagnetic waves. Furthermore, with regard to polarization selectivity, when the difference in return loss between the longitudinal direction and the width direction is more than 10 dB, it is evaluated as polarization selectivity (A), and when it is 10 dB or less, it is evaluated as no polarization selectivity (B). When polarization selectivity is A, it is possible to selectively absorb a specific polarized wave.

(13) Molding followability Molding was performed using a vacuum molding machine (300X manufactured by Seiko Sangyo Co., Ltd.) under the following conditions. Heating was performed using an infrared heater, and the temperature was determined by attaching a heat label (6R-99 manufactured by Micron Co., Ltd.) to the sample. Molding tests were performed three times for each sample.
<Molding conditions>
Heating time: 30 seconds Heating temperature: 110℃
Vacuum pump pressure: 0.17 MPa
Shape of the mold: Box shape, 5cm wide, 7.5cm long, 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 have no wrinkles.
B: One or two samples have spaces remaining on the sides or air remaining near the vertices, causing wrinkles.
C: All three samples have spaces on the sides or air remaining near the vertices, causing wrinkles.

(Particles and resins used in manufacturing the laminated sheet)
The particles and resins used in the production of the laminated sheet are as shown in Tables 1 and 2.

(Examples 1 to 8, 13 to 22, Comparative Examples 1 and 2)
First, the resin composition for Layer B was prepared into conductive master pellets by kneading in a twin-screw extruder to obtain the compositions listed 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, melted at 270°C, and kneaded. 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 listed 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. Thickness was adjusted by adjusting the discharge rate of each extruder and the rotation speed of the casting drum.

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. For 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.

The "second resin" content (wt%) in Table 4 is calculated assuming that the total resin in Layer B is 100 wt%. 100 - second resin content (wt%) is the "resin" content shown in Table 4. The same applies to Table 5.

The present invention provides a laminate sheet that is thin yet has high electromagnetic wave absorption properties 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.

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

Claims (16)

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 . The laminate sheet of claim 1, wherein, when the return loss is measured for each frequency, the electromagnetic wave attenuation at the peak top with the largest return loss divided by the thickness of the laminate sheet is 5 dB/mm or more. The laminate sheet according to claim 1 or 2, 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% to 90 vol% of the conductive particles X and 1 vol% to 90 vol% of the conductive particles Y. The laminate sheet according to any one of claims 1 to 3, wherein the degree of electrical orientation of particles in both the longitudinal cross section and the width cross section, as measured by electric force microscopy (EFM), is 1,000 or more and 100,000 or less. A laminate sheet according to any one of claims 1 to 4, in which 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. A laminate sheet according to any one of claims 1 to 5, in which 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. A laminate sheet according to any one of claims 1 to 5, in which 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. A laminate sheet according to any one of claims 1 to 7, wherein the average angle between the major axis of the particles and the plane direction is 0° or more and 30° or less in both the longitudinal cross section and the width cross section. A laminate sheet according to any one of claims 1 to 8, wherein the standard deviation of the angle between the major axis of the particles and the plane direction in both the longitudinal and width cross sections is 0° or more and 30° or less. A laminate sheet according to any one of claims 1 to 9, characterized in that the lowest temperature-decreasing crystallization temperature is between 70°C and 200°C, or no temperature-decreasing crystallization temperature is observed. A laminate sheet according to any one of claims 1 to 10, wherein the resin component contains 1 mol % to 99 mol % of at least one 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. A laminate sheet according to any one of claims 1 to 11, in which the weight fraction of hydrocarbons in the entire particle is 85% or more and 100% or less. 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. An electronic device using the laminate sheet described in any one of claims 1 to 13. Furniture made using the laminate sheet described in any one of claims 1 to 13. A building material using the laminate sheet described in any one of claims 1 to 13.