Nonwoven fabric for electromagnetic wave shielding material and electromagnetic wave shielding material

Abstract

To provide a nonwoven fabric substrate for an electromagnetic shielding material, and an electromagnetic shielding material, which are capable of exhibiting excellent electromagnetic shielding properties.SOLUTION: A nonwoven fabric for an electromagnetic wave shielding material, which is a wet nonwoven fabric, contains stretched polyester staple fibers and unstretched polyester staple fibers having a melting point of 220°C or higher and 250°C or lower, and a peel strength (in a longitudinal direction) of the nonwoven fabric is 2.0 N / m or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nonwoven fabric for an electromagnetic wave shielding material, which is excellent in web transportability and exhibits excellent electromagnetic wave shielding properties, and to an electromagnetic wave shielding material. [Background technology]

[0002] Electronic devices generate electromagnetic waves. Electromagnetic wave shielding materials are used to prevent the electromagnetic waves from leaking outside the electronic device and to prevent the electronic device from malfunctioning due to the electromagnetic waves. Examples of electromagnetic wave shielding materials include sheet metal, metal-containing paint, metal mesh, and metal foam. Furthermore, an electromagnetic wave shielding material has been disclosed in which a nonwoven fabric made of polyester staple fibers is subjected to a metal plating treatment (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1 discloses an electromagnetic wave shielding material in which a continuous metal conductive layer is attached by wet plating to the outer periphery and all around the intersections of fibers of a woven, knitted, or nonwoven fabric made of non-conductive fibers. It describes that polyester fibers and polypropylene fibers are preferable as chemical fibers because the base material itself has excellent tensile strength and elongation properties and can prevent deterioration of properties during pre-plating treatment steps.

[0004] Patent Document 2 discloses an electromagnetic wave shielding material made by subjecting a wetlaid nonwoven fabric to a metal coating treatment, characterized in that the electromagnetic wave shielding material contains polyester fibers with a single fiber fineness of 1.1 dtex or less and has a thickness within the range of 10 to 30 μm.

[0005] With the recent trend toward smaller electronic devices, higher frequencies, and higher performance, there is a demand for thinner electromagnetic wave shielding materials with high electromagnetic wave shielding properties. Specifically, there is a demand for electromagnetic wave shielding materials with a thickness of 15 μm or less that exhibit excellent electromagnetic wave shielding properties over a wide frequency range from 100 MHz to 10 GHz.

[0006] When a metal film treatment such as metal plating is applied to a nonwoven fabric as in Patent Documents 1 and 2, the processing is carried out by roll-to-roll, which has good productivity, but there is a problem that wrinkles occur in the nonwoven fabric during transportation, which makes it difficult to transport.

[0007] In addition, in the examples of Patent Document 2, a wetlaid nonwoven fabric containing polyester drawn fibers with a single fiber fineness of 0.1 dtex and undrawn binder fibers with a single fiber fineness of 0.2 dtex has a paper weight of 8 g / m 2 The weight of the electromagnetic wave shielding material is 19 g / m 2 and a thickness of 12 μm. However, as thinner electromagnetic shielding materials are desired, the electromagnetic shielding material of Patent Document 2 has the problem of not being able to ensure sufficient electromagnetic shielding properties. Also, there is a problem that the metal coating may peel off.

[0008] Furthermore, in electromagnetic wave shielding materials in which nonwoven fabrics are subjected to metal plating, it is required that the polyester staple fibers and the metal coating formed by the metal plating treatment are in close contact with each other. For this purpose, it is known that the polyester staple fibers are subjected to an alkali treatment as a pre-plating treatment step.

[0009] Patent Document 1 describes that polyester fibers can prevent deterioration of properties during pre-plating treatment. However, alkali treatment of nonwoven fabrics is usually a wet treatment, and fibers can fall off into the water tank, significantly reducing operability. Furthermore, the fallen fibers can reattach to the nonwoven fabric, causing defects during the metal plating process. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Utility Model Application Publication No. 48-40800 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-75485 Summary of the Invention [Problem to be solved by the invention]

[0011] A first object of the present invention is to provide a nonwoven fabric for an electromagnetic wave shielding material that has excellent transportability and exhibits excellent electromagnetic wave shielding properties, and an electromagnetic wave shielding material that uses the nonwoven fabric for an electromagnetic wave shielding material.

[0012] A second object of the present invention is to provide a nonwoven fabric for an electromagnetic wave shielding material that is thin and exhibits excellent electromagnetic wave shielding properties, and in which the metal coating is not easily peeled off, and an electromagnetic wave shielding material using the nonwoven fabric for an electromagnetic wave shielding material.

[0013] A third object of the present invention is to provide a nonwoven fabric for electromagnetic shielding materials that exhibits high strength and reduces fiber shedding during alkali treatment, which is a pre-plating treatment step for electromagnetic shielding materials, and to provide an electromagnetic shielding material using the nonwoven fabric for electromagnetic shielding materials. [Means for solving the problem]

[0014] As a result of extensive research into solving the above problems, the present inventors have discovered the following invention.

[0015] <1> A nonwoven fabric for use as an electromagnetic wave shielding material, which is a wet-laid nonwoven fabric, characterized in that the wet-laid nonwoven fabric contains, as essential components, two or more types of stretched polyester staple fibers with different fiber diameters selected from stretched polyester staple fibers with fiber diameters of 3 μm or more and less than 12 μm, and unstretched polyester staple fibers with fiber diameters of 3 μm or more and 5 μm or less.

[0016] <2> A wet-laid nonwoven fabric for use as an electromagnetic wave shielding material contains, as essential components, stretched polyester staple fibers with a fiber diameter of less than 3 μm and unstretched polyester staple fibers with a fiber diameter of 3 μm to 5 μm, and has a basis weight of 7 g / m. 2 and the density is 0.5 to 0.8 g / cm 3 A nonwoven fabric for use as an electromagnetic wave shielding material, characterized in that:

[0017] <3> A wet-laid nonwoven fabric for use as an electromagnetic wave shielding material, characterized in that it contains stretched polyester staple fibers and unstretched polyester staple fibers having a melting point of 220°C or higher and 250°C or lower, and the peel strength (longitudinal direction) of the nonwoven fabric is 2.0 N / m or higher.

[0018] <4> the above <1> ~ <3> 1. An electromagnetic wave shielding material, comprising the nonwoven fabric for an electromagnetic wave shielding material according to any one of the above items 1 to 5, which is subjected to a metal coating treatment.

[0019] <5> The metal film treatment is one or more treatments selected from the group consisting of electroless metal plating treatment, electroplating treatment, metal vapor deposition treatment and sputtering treatment. <4> The electromagnetic wave shielding material described above.

[0020] <6> The metal coating treatment is characterized in that it includes a treatment of forming a nickel coating by sputtering, a treatment of forming a copper coating by electroplating, and a treatment of forming a nickel coating by electroplating in this order. <4> The electromagnetic wave shielding material described above.

[0021] <7> The thickness of the electromagnetic wave shielding material is 15 μm or less, and the surface resistance of the electromagnetic wave shielding material is 0.03 Ω / □ or less. <4> ~ <6> 10. The electromagnetic wave shielding material according to claim 9, wherein [Effects of the Invention]

[0022] A first effect of the present invention is to provide a nonwoven fabric for an electromagnetic wave shielding material that has excellent transportability and exhibits excellent electromagnetic wave shielding properties, and an electromagnetic wave shielding material using the nonwoven fabric for an electromagnetic wave shielding material.

[0023] A second effect of the present invention is to provide a nonwoven fabric for an electromagnetic wave shielding material that is thin and exhibits excellent electromagnetic wave shielding properties, and in which the metal coating is not easily peeled off, and an electromagnetic wave shielding material using the nonwoven fabric for an electromagnetic wave shielding material.

[0024] A third effect of the present invention is to provide a nonwoven fabric for an electromagnetic shielding material that exhibits high strength and reduces fiber shedding in an alkali treatment, which is a pre-plating treatment step for the electromagnetic shielding material, and an electromagnetic shielding material using the nonwoven fabric for the electromagnetic shielding material. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 2 is a schematic diagram showing the state of a nonwoven fabric for an electromagnetic wave shielding material when measuring peel strength. DETAILED DESCRIPTION OF THE INVENTION

[0026] The nonwoven fabric for an electromagnetic wave shielding material and the electromagnetic wave shielding material of the present invention will be described in detail below.

[0027] -Nonwoven fabric for electromagnetic wave shielding <1> - The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <1> is a wetlaid nonwoven fabric containing, as essential components, two or more types of stretched polyester staple fibers with different fiber diameters selected from stretched polyester staple fibers with a fiber diameter of 3 μm or more and less than 12 μm, and unstretched polyester staple fibers with a fiber diameter of 3 μm or more and 5 μm or less.

[0028] Generally, tension is applied to the nonwoven fabric in the MD (machine direction) during transport in roll-to-roll processing, causing the nonwoven fabric to stretch and resulting in wrinkles. <1> The nonwoven fabric for electromagnetic wave shielding material of the present invention contains as essential components two or more types of stretched polyester staple fibers with different fiber diameters selected from stretched polyester staple fibers with a fiber diameter of 3 μm or more and less than 12 μm, and unstretched polyester staple fibers with a fiber diameter of 3 μm or more and less than 5 μm. Therefore, compared to a nonwoven fabric containing as essential components one type of stretched polyester staple fiber with the same fiber diameter selected from stretched polyester staple fibers with a fiber diameter of 3 μm or more and less than 12 μm, and unstretched polyester staple fibers with a fiber diameter of 3 μm or more and less than 5 μm, it is less likely to stretch and therefore less likely to wrinkle during transport. Furthermore, when a nonwoven fabric containing stretched polyester staple fibers with a large fiber diameter of 12 μm or more is used, it is difficult to obtain a thin electromagnetic wave shielding material. <1> By including stretched polyester staple fibers with a fiber diameter of less than 12 μm and unstretched polyester staple fibers with a fiber diameter of 3 μm or more and 5 μm or less, the effect of being thin and having excellent transportability can be achieved.

[0029] Generally, electromagnetic wave shielding properties are achieved by absorption reflection loss, reflection loss, and multiple reflection loss of electromagnetic waves. <1> In the electromagnetic wave shielding material, by using two or more types of drawn polyester staple fibers with different fiber diameters selected from drawn polyester staple fibers with a fiber diameter of 3 μm or more and less than 12 μm, electromagnetic waves that have penetrated the electromagnetic wave shielding material are more likely to be reflected repeatedly within the electromagnetic wave shielding material, and excellent electromagnetic wave shielding properties can be obtained by improving multiple reflection loss.

[0030] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <1> In the nonwoven fabric, the mass ratio of the stretched polyester staple fibers to the unstretched polyester staple fibers is preferably 10:90 to 90:10, more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30. If the content of the unstretched polyester staple fibers is less than 10% by mass of the total fibers constituting the wetlaid nonwoven fabric, the strength required for the nonwoven fabric as an electromagnetic wave shielding material may not be achieved. On the other hand, if the content of the unstretched polyester staple fibers exceeds 90% by mass, uniformity may be impaired.

[0031] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <1> In the above, drawn polyester staple fibers other than drawn polyester staple fibers having a fiber diameter of 3 μm or more and less than 12 μm may be used. Also, undrawn polyester staple fibers other than undrawn polyester staple fibers having a fiber diameter of 3 μm or more and less than 5 μm may be used. That is, drawn polyester staple fibers having a fiber diameter of less than 3 μm, drawn polyester staple fibers having a fiber diameter of 12 μm or more, undrawn polyester staple fibers having a fiber diameter of less than 3 μm, and undrawn polyester staple fibers having a fiber diameter of more than 5 μm may be used. These may be used alone, or fibers having two or more different fiber diameters may be used in combination.

[0032] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <1> In the case of drawn polyester staple fibers having a fiber diameter of 3 μm or more and less than 12 μm, the mass content thereof is preferably 1 to 100 mass%, and more preferably 3 to 100 mass%, of the total drawn polyester staple fibers contained. If the content of drawn polyester staple fibers having a fiber diameter of 3 μm or more and less than 12 μm is less than 1 mass%, it may not be possible to obtain a thin electromagnetic wave shielding material with excellent transportability.

[0033] The nonwoven fabric for electromagnetic wave shielding material of the present invention <1> In the nonwoven fabric, the mass content of unstretched polyester staple fibers having a fiber diameter of 3 μm or more and 5 μm or less is preferably 1 to 100 mass%, and more preferably 2 to 100 mass%, of the total unstretched polyester staple fibers contained. If the content of unstretched polyester staple fibers having a fiber diameter of 3 μm or more and 5 μm or less is less than 1 mass%, depending on the diameter of the fibers used in combination, the specific surface area may be small, making it difficult to achieve excellent electromagnetic wave shielding properties. In addition, it may be difficult for the wetlaid nonwoven fabric to achieve sufficient strength.

[0034] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <1> For the purpose of use in electronic devices, the thickness is preferably 7 to 30 μm, and more preferably 15 μm or less. The basis weight is 5 to 30 g / m 2 It is preferable that the thickness is 15 g / m 2 It is more preferable that the weight per unit area is 5 g / m or less. 2 If the thickness is less than this, it becomes difficult to obtain uniformity, and the electromagnetic wave shielding effect is likely to vary.

[0035] -Nonwoven fabric for electromagnetic wave shielding <2> - The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <2> contains as essential components stretched polyester staple fibers with a fiber diameter of less than 3 μm and unstretched polyester staple fibers with a fiber diameter of 3 μm to 5 μm, and has a basis weight of 7 g / m 2 and the density is 0.5 to 0.8 g / cm 3 The wet-laid nonwoven fabric is characterized by:

[0036] Generally, when a wetlaid nonwoven fabric is subjected to a metal coating treatment, if the specific surface area (surface area per unit volume) of the fibers forming the wetlaid nonwoven fabric is small, the amount of metal attached per unit volume will be small, and there are cases where excellent electromagnetic wave shielding properties cannot be achieved. <2> is a wetlaid nonwoven fabric that contains, as essential components, stretched polyester staple fibers with a fiber diameter of less than 3 μm and unstretched polyester staple fibers with a fiber diameter of 3 μm to 5 μm, thereby increasing the specific surface area and exhibiting excellent electromagnetic wave shielding properties. A wetlaid nonwoven fabric consisting solely of stretched polyester staple fibers with a fiber diameter of 3 μm or more and unstretched polyester staple fibers with a fiber diameter of more than 5 μm would not exhibit excellent electromagnetic wave shielding properties. Unstretched polyester staple fibers with a fiber diameter of less than 3 μm are difficult to obtain. Furthermore, the fiber diameter of stretched polyester staple fibers with a fiber diameter of less than 3 μm is preferably 0.1 μm or more. Fiber diameters of less than 0.1 μm may result in insufficient strength.

[0037] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <2> In the wetlaid nonwoven fabric, the mass ratio of the stretched polyester staple fibers to the unstretched polyester staple fibers is preferably 20:80 to 80:20, more preferably 30:70 to 70:30, and even more preferably 40:60 to 60:40. If the content of unstretched polyester staple fibers is less than 20% by mass of the total fibers constituting the wetlaid nonwoven fabric, the strength required for the nonwoven fabric as an electromagnetic wave shielding material may not be achieved. On the other hand, if the content of unstretched polyester staple fibers exceeds 80% by mass, uniformity may be impaired.

[0038] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <2> In the above, fibers other than drawn polyester staple fibers having a fiber diameter of less than 3 μm and undrawn polyester staple fibers having a fiber diameter of 3 μm to 5 μm may be used. That is, drawn polyester staple fibers having a fiber diameter of 3 μm or more, undrawn polyester staple fibers having a fiber diameter of less than 3 μm, and undrawn polyester staple fibers having a fiber diameter of more than 5 μm may be used. These may be used alone, or two or more fibers having different fiber diameters may be used in combination.

[0039] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <2> In the above, the content of drawn polyester staple fibers having a fiber diameter of less than 3 μm is preferably 1 to 100 mass %, and more preferably 3 to 100 mass %, of the total drawn polyester staple fibers. If the content of drawn polyester staple fibers having a fiber diameter of less than 3 μm is less than 1 mass %, depending on the diameter of the fibers used in combination, the specific surface area may become small, making it difficult to achieve excellent electromagnetic wave shielding properties.

[0040] The nonwoven fabric for electromagnetic wave shielding material of the present invention <2> In the nonwoven fabric, the content of unstretched polyester staple fibers having a fiber diameter of 3 μm or more and 5 μm or less is preferably 1 to 100 mass %, and more preferably 2 to 100 mass %, of the total unstretched polyester staple fibers. If the content of unstretched polyester staple fibers having a fiber diameter of 3 μm or more and 5 μm or less is less than 1 mass %, depending on the diameter of the fibers used in combination, the specific surface area may become small, making it difficult to achieve excellent electromagnetic wave shielding properties or excellent wetlaid nonwoven fabric strength.

[0041] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <2> In this case, the basis weight of the wet nonwoven fabric is 7 g / m 2 less than 5 g / m 2 More preferably, it is 4 g / m or less. 2 It is more preferable that the weight is 7 g / m or less. 2 If the thickness exceeds 15μm, the thickness will be even thicker after metal coating treatment, and the thickness of the electromagnetic wave shielding material may exceed 15μm, which may make it unusable for electronic devices, communication devices, electrical appliances, etc. Also, the basis weight of wet-laid nonwoven fabrics is 3g / m 2 The basis weight was measured by the method described in JIS P8124:2011.

[0042] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <2> In this case, the density of wet-laid nonwoven fabric is 0.5-0.8g / cm 3 and 0.55 to 0.65 g / cm 3 It is more preferable that the density is 0.8 g / cm 3By keeping the density below 0.5 g / cm, the specific surface area increases, which increases the amount of metal film formed by metal film treatment, improving the electromagnetic wave shielding properties. In addition, the metal film is less likely to peel off. 3 When the density is above this level, the strength of the wetlaid nonwoven fabric is increased, defects are less likely to occur during metal coating treatment, and the metal coating is less likely to peel off. The density was measured by the method described in JIS P8118:2014.

[0043] -Nonwoven fabric for electromagnetic wave shielding <3> - The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <3> is a wet-laid nonwoven fabric containing stretched polyester staple fibers and unstretched polyester staple fibers having a melting point of 220°C or higher and 250°C or lower. <3> The peel strength (longitudinal direction) is 2.0 N / m or more.

[0044] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <3> In the present invention, the peel strength (longitudinal direction) of the nonwoven fabric for electromagnetic shielding material is 2.0 N / m or more, more preferably 2.5 N / m or more, and even more preferably 3.0 N / m or more. If the peel strength (longitudinal direction) is less than 2.0 N / m, the adhesion between the fibers is too weak, so that many fibers fall off from the nonwoven fabric for electromagnetic shielding material during alkali treatment, causing fibers to accumulate on the transport rolls, necessitating periodic cleaning and reducing operability, and the fallen fibers reattach to the nonwoven fabric for electromagnetic shielding material, causing defects in the metal plating process. Nonwoven fabric for electromagnetic shielding material of the present invention <3> In the above, the peel strength (longitudinal direction) of the nonwoven fabric for electromagnetic shielding material is preferably 10.0 N / m or less. If it exceeds 10.0 N / m, the fusion of the nonwoven fabric for electromagnetic shielding material will proceed too much, causing the surface of the nonwoven fabric for electromagnetic shielding material to turn into a film, which may make it impossible to maintain its shape.

[0045] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <3> In the above, the fiber diameter of the drawn polyester staple fiber is preferably 1 to 10 μm, and more preferably 2 to 8 μm. The drawn polyester staple fiber may contain two or more types of drawn polyester staple fibers with different fiber diameters. When the drawn polyester staple fiber has a fiber diameter of 10 μm or less, it is easy to provide a thin electromagnetic wave shielding material. Furthermore, it is preferable that the drawn polyester staple fiber contains, as an essential component, a polyester staple fiber with a fiber diameter of 3 μm or less. By containing polyester staple fibers with a fiber diameter of 3 μm or less, the electromagnetic wave shielding property is further improved.

[0046] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <3> In the above, the fiber diameter of the unstretched polyester staple fiber is preferably 1 to 8 μm, and more preferably 3 to 5 μm. When the fiber diameter is within this range, it becomes easy to provide a thin electromagnetic wave shielding material while increasing the strength of the wetlaid nonwoven fabric. The unstretched polyester staple fiber may contain two or more types of unstretched polyester staple fibers with different fiber diameters.

[0047] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <3> In the nonwoven fabric for electromagnetic wave shielding material of the present invention, the mass ratio of the stretched polyester staple fibers to the unstretched polyester staple fibers is preferably 20:80 to 80:20. If the content of unstretched polyester staple fibers is less than 20% by mass of the total fibers constituting the wetlaid nonwoven fabric, the strength required for the nonwoven fabric for electromagnetic wave shielding material may not be achieved. On the other hand, if the content of unstretched polyester staple fibers exceeds 80% by mass, uniformity may be impaired. Furthermore, in order to improve the electromagnetic wave shielding property, it is more preferable that the content of stretched polyester staple fibers having a fiber diameter of 3 μm or less is 5 to 80% by mass of the total fibers constituting the wetlaid nonwoven fabric. Nonwoven fabric for electromagnetic wave shielding material of the present invention <3> In the above, the most preferred fiber blend is 20 to 80 mass% of unstretched polyester staple fibers, 0 to 75 mass% of stretched polyester staple fibers having a fiber diameter of more than 3 μm and not more than 10 μm, and 5 to 80 mass% of stretched polyester staple fibers having a fiber diameter of 3 μm or less.

[0048] The nonwoven fabric for use as an electromagnetic wave shielding material of the present invention <3> For the purpose of use in electronic devices, the thickness is preferably 5 to 30 μm, more preferably 20 μm or less. The basis weight is 3 to 30 g / m 2 It is preferable that the thickness is 15 g / m 2 It is more preferable that the weight per unit area is 3 g / m or less. 2 If the thickness is less than this, it becomes difficult to obtain uniformity, the electromagnetic wave shielding effect is likely to vary, it becomes difficult to maintain the strength of the nonwoven fabric for electromagnetic wave shielding material itself, and workability is poor.

[0049] -Polyester staple fiber- In the present invention, the drawn polyester staple fibers are the main fibers that are resistant to melting or softening even when subjected to a heat calendaring treatment and form the skeleton of the wetlaid nonwoven fabric.

[0050] In the present invention, the unstretched polyester staple fibers are melted or softened by heat calendering and function as binder fibers that increase the strength of the wetlaid nonwoven fabric. The melting point of the unstretched polyester staple fibers is preferably 220° C. to 250° C. The nonwoven fabric for electromagnetic wave shielding material of the present invention <3> In the above, the melting point of the unstretched polyester staple fiber is 220°C or higher and 250°C or lower. If the melting point of the unstretched polyester staple fiber is lower than 220°C, the wetlaid nonwoven fabric may stick to the heat roll during the heat calendering treatment, and may not form a sheet. If the melting point is higher than 250°C, the fibers may not adhere and the wetlaid nonwoven fabric may not exhibit its strength. The melting point of the unstretched polyester staple fiber is more preferably 225°C or higher and 250°C or lower.

[0051] The melting point of the unstretched polyester staple fiber is the peak temperature when the fiber is heated from 25°C to 300°C at a heating rate of 10°C / min in a nitrogen atmosphere using a differential scanning calorimeter.

[0052] In the examples of the present invention, the fiber diameter of the polyester staple fiber is the fiber diameter before the nonwoven fabric is produced. The fiber diameter of the polyester staple fiber can be measured by taking a 3000x magnification photograph of the cross section of the wetlaid nonwoven fabric or electromagnetic wave shielding material with a microscope, measuring the cross-sectional area of ​​the polyester staple fiber, and calculating the diameter assuming that the cross-sectional shape of the fiber is a perfect circle. In this case, it is preferable to calculate the arithmetic average value of 10 or more fibers having approximately the same cross-sectional area.

[0053] The fiber length of the polyester staple fiber is preferably 1 to 20 mm, more preferably 1 to 10 mm, and even more preferably 2 to 8 mm. If the fiber length of the polyester staple fiber is less than 1 mm, it may be difficult to achieve the strength required for a wetlaid nonwoven fabric. If the fiber length of the polyester staple fiber is more than 20 mm, uniformity may be impaired.

[0054] In the present invention, examples of polyester include polyethylene terephthalate, polyethylene isophthalate, polytrimethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, and polybutylene naphthalate. Polyester staple fibers are preferred because they can be made smaller in diameter to reduce the thickness of the electromagnetic wave shield, are easy to make into paper, and are dimensionally stable during wet alkali treatment in plating. Polyester staple fibers may be used alone or in combination of two or more types.

[0055] -Wet-processed non-woven fabric- Methods for forming fibers into a sheet include various manufacturing methods such as spunbonding, meltblowing, electrospinning, and wet methods. The nonwoven fabric for an electromagnetic wave shielding material of the present invention is a wet-laid nonwoven fabric formed into a sheet by a wet method (papermaking), and is a nonwoven fabric with excellent strength and high uniformity. Methods for bonding fibers include various methods such as chemical bonding and heat fusion. Among these, the heat fusion method is preferred because it is excellent in durability and strength and produces a smooth surface for the nonwoven fabric.

[0056] As a heat fusion method in a wet process, a method can be used in which a sheet obtained by a papermaking process is heat-fused when it is thermally dried in a dryer used after papermaking, such as a multi-cylinder dryer, Yankee dryer, or air-through dryer. Also usable is a method of heat fusion by heat calendering using a heat calendering device having a combination of rolls such as a metal heat roll / metal heat roll, a metal heat roll / elastic roll, or a metal heat roll / cotton roll. The heat drying or heat calendering causes the binder component to thermally melt and heat fusion occurs.

[0057] The conditions for the thermal calendering can be exemplified below, but are not limited to these. The temperature of the thermal roll in the thermal calendering treatment is preferably 200°C or higher and 215°C or lower. If the temperature of the thermal roll is lower than 200°C, the fibers may not bond together, resulting in a problem of insufficient strength. Conversely, if the temperature of the thermal roll is higher than 215°C, the wet nonwoven fabric may stick to the thermal roll, resulting in a problem of not being able to form a sheet. The temperature of the thermal roll is more preferably 203°C or higher and 210°C or lower, and even more preferably 205°C or higher. The nonwoven fabric for an electromagnetic wave shielding material of the present invention <3> In order to increase the peel strength of the nonwoven fabric for use as an electromagnetic shielding material, it is preferable to subject a wetlaid nonwoven fabric containing oriented polyester staple fibers and unoriented polyester staple fibers having a melting point of 220°C or higher and 250°C or lower to a thermal calendering treatment using a heated roll having a temperature of 200°C or higher and 215°C or lower. The heated roll temperature is more preferably 203°C or higher and 210°C or lower.

[0058] To achieve sufficient strength, the pressure (linear pressure) in the thermal calendering treatment is preferably 50 to 250 kN / m, and more preferably 80 to 150 kN / m. If the pressure is less than 50 kN / m, the surface smoothness may be impaired, and the thickness may not be reduced unless the speed is reduced. If the pressure is more than 250 kN / m, the sheet may not be able to withstand the pressure and may break. The thermal calendering speed is preferably 1 to 300 m / min. A processing speed of 1 m / min or more improves work efficiency. A processing speed of 300 m / min or less facilitates heat conduction to the wetlaid nonwoven fabric, making it easier to achieve effective heat fusion. The number of nip passes in the thermal calendering is not particularly limited as long as heat can be conducted to the wetlaid nonwoven fabric. However, when using a combination of a metal heat roll and an elastic roll, nipping may be performed two or more times to conduct heat from both sides of the wetlaid nonwoven fabric.

[0059] -Electromagnetic wave shielding material- The electromagnetic shielding material of the present invention is characterized in that the nonwoven fabric for electromagnetic shielding of the present invention has been subjected to a metal coating treatment, i.e., the electromagnetic shielding material of the present invention comprises the nonwoven fabric for electromagnetic shielding of the present invention and a metal coating.

[0060] In the present invention, examples of metal coating treatments include electroless metal plating, electroplating, metal vapor deposition, and sputtering. One or more treatments selected from these treatments can be performed. Among these, sputtering is preferably performed followed by electroplating, as this allows for a thinner film, tends to lower the surface resistance, and makes the metal coating less likely to peel off. The metal coating may be a single layer or a multilayer film consisting of two or more layers.

[0061] Examples of metals used in the metal coating treatment include gold, silver, copper, zinc, aluminum, nickel, tin, and alloys thereof. Among these, one or more metals selected from the group consisting of gold, silver, copper, aluminum, nickel, and tin are preferred, and copper and nickel are more preferred in terms of conductivity and production costs.

[0062] In the present invention, it is more preferable that the metal coating treatment includes, in this order, a treatment of forming a nickel coating by sputtering, a treatment of forming a copper coating by electroplating, and a treatment of forming a nickel coating by electroplating. First, a metal coating is formed on a wetlaid nonwoven fabric by sputtering. The metal used in the sputtering treatment is preferably nickel. After the sputtering treatment, a metal coating is laminated by electroplating. The metal used in the electroplating is preferably copper. Furthermore, for rust prevention, a metal with good rust prevention properties, such as nickel, may be laminated on the outer layer. The lamination method is preferably electroplating.

[0063] The thickness of the electromagnetic shielding material of the present invention is preferably 15 μm or less, more preferably 13 μm or less, and even more preferably 12 μm or less. If the thickness of the electromagnetic shielding material is greater than 15 μm, it may not be usable in electronic devices, communication devices, electrical appliances, etc. Furthermore, the thickness of the electromagnetic shielding material is preferably 7 μm or more. The thickness was measured using the method described in JIS P8118:2014.

[0064] The surface resistance of the electromagnetic shielding material of the present invention is preferably 0.03 Ω / □ or less, and more preferably 0.01 Ω / □ or less. The electromagnetic shielding property at 40 MHz to 18 GHz is preferably 50 dB or more. Furthermore, the electromagnetic shielding property at 40 MHz to 10 GHz is preferably 60 dB or more. Furthermore, the electromagnetic shielding property at 40 MHz to 1 GHz is preferably 70 dB or more. [Example]

[0065] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Examples 1 to 10 are reference examples, and in the examples, % and parts are all by mass unless otherwise specified.

[0066] <Nonwoven fabric for electromagnetic wave shielding material of the present invention <1> Examples of related examples

[0067] [Example 1] 30 parts by mass of stretched polyethylene terephthalate (PET) staple fibers with a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers with a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, and 40 parts by mass of unstretched PET staple fibers with a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm were dispersed in water using a pulper to prepare a uniform papermaking slurry with a concentration of 1% by mass. This papermaking slurry was passed through a pulp machine with an air permeability of 275 cm 3 / cm 2 / sec, on an inclined paper machine equipped with a papermaking wire with a structure [upper mesh: plain weave, lower mesh: ribbed weave], the paper was made using the wet method, and a cylinder dryer at 135°C was used to heat-seal the unstretched PET short fibers to develop strength, resulting in a basis weight of 10 g / m 2 This wet-laid nonwoven fabric was then subjected to a thermal calendering treatment using a single-nip thermal calendering device consisting of a dielectric heating jacket roll (metallic heated roll) and an elastic roll, under conditions of a heat roll temperature of 200°C, a linear pressure of 100 kN / m, and a processing speed of 30 m / min, to produce a nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm.

[0068] [Example 2] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 17 μm was produced in the same manner as in Example 1, except that the blend consisted of 10 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 50 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, and 40 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm.

[0069] [Example 3] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 16 μm was produced in the same manner as in Example 1, except that the mixture was 50 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 10 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, and 40 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm.

[0070] [Example 4] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 16 μm was produced in the same manner as in Example 1, except that the mixture was 45 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 45 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, and 10 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm.

[0071] [Example 5] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 14 μm was produced in the same manner as in Example 1, except that the mixture was 30 parts by mass of stretched PET staple fibers having a fineness of 0.1 dtex (fiber diameter 3.0 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, and 40 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm.

[0072] [Example 6] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 14 μm was produced in the same manner as in Example 1, except that the blend consisted of 10 parts by mass of stretched PET staple fibers having a fineness of 0.1 dtex (fiber diameter 3.0 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, and 30 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm.

[0073] [Example 7] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 16 μm was produced in the same manner as in Example 1, except that the blend consisted of 30 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, 10 parts by mass of stretched PET staple fibers having a fineness of 1.7 dtex (fiber diameter 12.0 μm) and a fiber length of 5 mm, and 30 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm.

[0074] [Example 8] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 14 μm was produced in the same manner as in Example 1, except that the blend consisted of 10 parts by mass of stretched PET staple fibers having a fineness of 0.06 dtex (fiber diameter 2.4 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, and 30 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm.

[0075] [Example 9] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 16 μm was produced in the same manner as in Example 1, except that the blend consisted of 30 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, 30 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm, and 10 parts by mass of unstretched PET staple fibers having a fineness of 1.2 dtex (fiber diameter 10.5 μm) and a fiber length of 5 mm.

[0076] [Example 10] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 14 μm was produced in the same manner as in Example 1, except that the mixture was 15 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 15 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, and 70 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm.

[0077] [Comparative Example 1] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 17 μm was produced in the same manner as in Example 1, except that the mixture was 30 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, and 40 parts by mass of unstretched PET staple fibers having a fineness of 1.2 dtex (fiber diameter 10.5 μm) and a fiber length of 5 mm.

[0078] Comparative Example 2 A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 15 μm was produced in the same manner as in Example 1, except that 60 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm and 40 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm were used.

[0079] Comparative Example 3 A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 21 μm was produced in the same manner as in Example 1, except that the mixture was 30 parts by mass of stretched PET staple fibers having a fineness of 1.7 dtex (fiber diameter 12.0 μm) and a fiber length of 5 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 3.3 dtex (fiber diameter 17.5 μm) and a fiber length of 5 mm, and 40 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm.

[0080] Comparative Example 4 A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 18 μm was produced in the same manner as in Example 1, except that 60 parts by mass of stretched PET staple fibers having a fineness of 1.7 dtex (fiber diameter 12.0 μm) and a fiber length of 5 mm and 40 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm were used.

[0081] Comparative Example 5 A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 15 μm was produced in the same manner as in Example 1, except that 60 parts by mass of stretched PET staple fibers having a fineness of 0.1 dtex (fiber diameter 3.0 μm) and a fiber length of 3 mm and 40 parts by mass of unstretched PET staple fibers having a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm were used.

[0082] The nonwoven fabrics for electromagnetic wave shielding materials prepared in the examples and comparative examples were covered with a nickel film by electroless plating, and then a copper film and a nickel film were laminated in this order by electroplating to prepare electromagnetic wave shielding materials.

[0083] <Evaluation> [Transportability] The nonwoven fabric for electromagnetic wave shielding material was conveyed with a constant tension, and the occurrence of wrinkles at that time was evaluated according to the following criteria.

[0084] "○": No wrinkles and very easy to transport. "△": Wrinkles appear in some parts of the nonwoven fabric for electromagnetic wave shielding material, but there is no problem with transportability. "X": The entire nonwoven fabric for electromagnetic shielding material was wrinkled to the extent that processing was not possible, and transportability was poor.

[0085] [Electromagnetic wave shielding (electric field)] Measurements were made based on the electromagnetic wave shielding properties (electric field) using the coaxial tube method. In the frequency range of 40 MHz to 3 GHz, measurements were made using the coaxial tube method 39D, and in the frequency range of 500 MHz to 18 GHz, measurements were made using the coaxial tube method GPC7. In the frequency range of 500 MHz to 3 GHz, measurements were made using both the coaxial tube method 39D and the coaxial tube method 7, but the lower value was used.

[0086] The higher the numerical value given for the electromagnetic wave shielding property, the better the electromagnetic wave shielding property.

[0087] [Table 1]

[0088] The nonwoven fabrics for electromagnetic shielding materials of Examples 1 to 10 are wetlaid nonwoven fabrics containing, as essential components, two or more types of stretched polyester staple fibers with different fiber diameters selected from stretched polyester staple fibers with a fiber diameter of 3 μm or more and less than 12 μm, and unstretched polyester staple fibers with a fiber diameter of 3 μm or more and 5 μm or less, and therefore have excellent transportability and electromagnetic shielding properties. The nonwoven fabric for electromagnetic shielding materials of Example 4 showed a slight decrease in strength, but there were no problems with transportability and the electromagnetic shielding properties were also excellent.

[0089] In contrast, the nonwoven fabrics for electromagnetic shielding materials of Comparative Examples 1, 2, 3, and 4, which did not contain, as essential components, two or more types of drawn polyester staple fibers with different fiber diameters selected from drawn polyester staple fibers with a fiber diameter of 3 μm or more and less than 12 μm, and undrawn polyester staple fibers with a fiber diameter of 3 μm or more and 5 μm or less, were inferior in electromagnetic shielding properties. That is, it is believed that the multiple reflection loss was reduced in the nonwoven fabric for an electromagnetic shielding material of Comparative Example 1, in which the fiber diameter of the unstretched polyester staple fiber exceeds 5 μm; the nonwoven fabric for an electromagnetic shielding material of Comparative Example 3, which contains two types of stretched polyester staple fibers with different fiber diameters selected from stretched polyester staple fibers with a fiber diameter of 12 μm or more; the nonwoven fabric for an electromagnetic shielding material of Comparative Example 4, in which the stretched polyester staple fiber has a fiber diameter of 12 μm; and the nonwoven fabric for an electromagnetic shielding material of Comparative Example 2, which contains stretched polyester staple fibers with a fiber diameter of 3 μm or more but less than 12 μm, but only one type of stretched polyester staple fiber (fiber diameter 5.3 μm) with the same fiber diameter.

[0090] Furthermore, the nonwoven fabric for an electromagnetic shielding material of Comparative Example 5, which contains only one type of stretched polyester staple fiber with the same fiber diameter (fiber diameter 3.0 μm) although it contains stretched polyester staple fibers with a fiber diameter of 3 μm or more and less than 12 μm, wrinkles occur during web transport and transportability is poor. It is believed that the inclusion of only the stretched polyester staple fibers with a small fiber diameter makes the web flexible, easy to stretch, and prone to wrinkles.

[0091] <Nonwoven fabric for electromagnetic wave shielding material of the present invention <2> Examples of related examples

[0092] <Evaluation> (1) Surface resistance Measured according to MIL DTL 83528C.

[0093] (2) Electromagnetic wave shielding (electric field) Measurements were made based on the electromagnetic wave shielding properties (electric field) using the coaxial tube method. In the frequency range of 40 MHz to 3 GHz, measurements were made using the coaxial tube method 39D, and in the frequency range of 500 MHz to 18 GHz, measurements were made using the coaxial tube method GPC7. In the frequency range of 500 MHz to 3 GHz, measurements were made using both the coaxial tube method 39D and the coaxial tube method GPC7, but the lower value was used.

[0094] (3) Peel evaluation Adhesive tape (Nitto (registered trademark) 31B tape, manufactured by Nitto Denko Corporation) was attached to an electromagnetic wave shielding material sample measuring 25 mm wide and 150 mm long, and the tape was rolled 10 times at a speed of 300 mm / min with a 2 kg roll. The tape and the sample were then at an angle of 180 degrees and peeled off at a speed of 1000 mm / min. Evaluation was based on the following criteria.

[0095] <Standards> ○: Measurement was performed three times, and there was no breakage of the sample or adhesion of metal powder to the tape. △: Measurement was carried out three times, and the sample broke and metal powder adhered to the tape once or twice. ×: Measurement was carried out three times, and the sample broke and metal powder adhered to the tape three times.

[0096] [Example 11] 20 parts by mass of oriented polyethylene terephthalate (PET) staple fibers with a fineness of 0.06 dtex (fiber diameter 2.4 μm) and a fiber length of 3 mm, 40 parts by mass of oriented PET staple fibers with a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, and 40 parts by mass of unoriented PET staple fibers for a single-component binder with a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm were dispersed in water using a pulper to prepare a uniform papermaking slurry with a concentration of 1% by mass. This papermaking slurry was then passed through a pulp machine with an air permeability of 275 cm 3 / cm2 The nonwoven fabric was made by a wet method using an inclined papermaking machine equipped with a papermaking wire with a weave of [upper wire: plain weave, lower wire: rib weave] at 1 / sec, and the unstretched PET short fibers used as a binder were heat-fused using a cylinder dryer at 135°C to develop strength, resulting in a wetlaid nonwoven fabric. This wetlaid nonwoven fabric was then thermally calendered using a single-nip thermal calender consisting of a dielectric heating jacket roll (metallic heated roll) and an elastic roll, under conditions of a heat roll temperature of 200°C, a linear pressure of 100 kN / m, and a processing speed of 100 m / min, resulting in a basis weight of 6.5 g / m. 2 , density 0.50g / cm 3 We have produced a nonwoven fabric for use as an electromagnetic wave shielding material.

[0097] Next, the nonwoven fabric for electromagnetic wave shielding material was covered with a nickel film by electroless plating, and then a copper film and a nickel film were laminated in that order by electroplating to perform metal film treatment, thereby obtaining an electromagnetic wave shielding material with a thickness of 17.5 μm.

[0098] [Example 12] A wetlaid nonwoven fabric was obtained in the same manner as in Example 11, except that the fiber blend was 40 parts by mass of stretched PET staple fibers with a fineness of 0.06 dtex (fiber diameter 2.4 μm) and a fiber length of 3 mm, 20 parts by mass of stretched PET staple fibers with a fineness of 0.3 dtex (fiber diameter 3.0 μm) and a fiber length of 3 mm, and 40 parts by mass of unstretched PET staple fibers for a single-component binder with a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm. This wetlaid nonwoven fabric was subjected to a heat calendering treatment in the same manner as in Example 11, except that the treatment speed was changed to 50 m / min, to obtain a fabric with a basis weight of 6.5 g / m. 2 , density 0.63g / cm 3 Then, a metal film treatment was carried out in the same manner as in Example 11 to obtain an electromagnetic wave shielding material having a thickness of 16.0 μm.

[0099] [Example 13] A wetlaid nonwoven fabric was obtained in the same manner as in Example 11, except that the fiber blend was 60 parts by mass of stretched PET staple fibers with a fineness of 0.06 dtex (fiber diameter 2.4 μm) and a fiber length of 3 mm, and 40 parts by mass of unstretched PET staple fibers for a single-component binder with a fineness of 0.2 dtex (fiber diameter 4.3 μm) and a fiber length of 3 mm. This wetlaid nonwoven fabric was subjected to a heat calendering treatment in the same manner as in Example 11, except that the conditions were a linear pressure of 125 kN / m and a processing speed of 40 m / min, to obtain a fabric with a basis weight of 6.5 g / m. 2 , density 0.80g / cm 3 Then, a metal film treatment was carried out in the same manner as in Example 11 to obtain an electromagnetic wave shielding material having a thickness of 15.5 μm.

[0100] [Example 14] Weight 5.0g / m 2 A wetlaid nonwoven fabric was obtained in the same manner as in Example 11, except that the density of the wetlaid nonwoven fabric was 0.80 g / cm. This wetlaid nonwoven fabric was subjected to a heat calendering treatment in the same manner as in Example 13. 3 Next, the nonwoven fabric for an electromagnetic wave shielding material was covered with a nickel film by sputtering, and then a copper film and a nickel film were laminated in this order by electroplating to perform a metal film treatment, thereby obtaining an electromagnetic wave shielding material with a thickness of 8.5 μm.

[0101] [Example 15] Weight 5.0g / m 2 A wetlaid nonwoven fabric was obtained in the same manner as in Example 12, except that the density of the wetlaid nonwoven fabric was 0.50 g / cm. This wetlaid nonwoven fabric was subjected to a heat calendering treatment in the same manner as in Example 11. 3 The nonwoven fabric for an electromagnetic wave shielding material was then subjected to a metal film treatment in the same manner as in Example 14 to obtain an electromagnetic wave shielding material having a thickness of 12.0 μm.

[0102] [Example 16] Weight 5.0g / m 2 A wetlaid nonwoven fabric was obtained in the same manner as in Example 13, except that the density was 0.63 g / cm. This wetlaid nonwoven fabric was subjected to a heat calendering treatment in the same manner as in Example 12. 3Then, a metal film treatment was carried out in the same manner as in Example 14 to obtain an electromagnetic wave shielding material having a thickness of 10.0 μm.

[0103] [Comparative Example 11] A 10.0 g / m2 woven fabric was prepared in the same manner as in Example 11, except that the fiber blend was 60 parts by mass of oriented PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 5 mm, and 40 parts by mass of unoriented PET staple fibers for a single-component binder having a fineness of 1.2 dtex (fiber diameter 10.7 μm) and a fiber length of 5 mm. 2 This wetlaid nonwoven fabric was subjected to a heat calendering treatment in the same manner as in Example 11, except that the conditions were a linear pressure of 135 kN / m and a treatment speed of 40 m / min, to obtain a wetlaid nonwoven fabric having a density of 0.85 g / cm. 3 Then, a metal film treatment was carried out in the same manner as in Example 14 to obtain an electromagnetic wave shielding material having a thickness of 16.0 μm.

[0104] [Comparative Example 12] The same procedure as in Comparative Example 11 was carried out except that the conditions were a line pressure of 100 kN / m and a processing speed of 50 m / min, and a basis weight of 10.0 g / m 2 , density 0.63g / cm 3 Then, a metal film treatment was carried out in the same manner as in Comparative Example 11 to obtain an electromagnetic wave shielding material having a thickness of 20.0 μm.

[0105] [Comparative Example 13] The same procedure as in Comparative Example 11 was carried out except that the conditions were a line pressure of 90 kN / m and a processing speed of 100 m / min, and a basis weight of 10.0 g / m was obtained. 2 , density 0.45g / cm 3 Then, a metal film treatment was carried out in the same manner as in Comparative Example 11 to obtain an electromagnetic wave shielding material having a thickness of 26.0 μm.

[0106] [Comparative Example 14] In the same manner as in Comparative Example 11, a basis weight of 10.0 g / m 2 , density 0.85g / cm 3Then, a metal film treatment was carried out in the same manner as in Example 11 to obtain an electromagnetic wave shielding material having a thickness of 16.0 μm.

[0107] [Comparative Example 15] In the same manner as in Comparative Example 12, a basis weight of 10.0 g / m 2 , density 0.63g / cm 3 Then, a metal film treatment was carried out in the same manner as in Comparative Example 14 to obtain an electromagnetic wave shielding material having a thickness of 20.0 μm.

[0108] [Comparative Example 16] In the same manner as in Comparative Example 13, a basis weight of 10.0 g / m 2 , density 0.45g / cm 3 Then, a metal film treatment was carried out in the same manner as in Comparative Example 14 to obtain an electromagnetic wave shielding material having a thickness of 26.0 μm.

[0109] [Table 2]

[0110] It contains as essential components stretched polyester staple fibers with a fiber diameter of less than 3 μm and unstretched polyester staple fibers with a fiber diameter of 3 μm to 5 μm, and has a basis weight of 7 g / m 2 and the density is 0.5 to 0.8 g / cm 3 Examples 11 to 16, which are electromagnetic shielding materials obtained by subjecting a wetlaid nonwoven fabric for electromagnetic shielding to a metal coating treatment, achieved excellent electromagnetic shielding properties and made the metal coating less likely to peel off. Furthermore, it can be seen that the electromagnetic shielding materials of Examples 14 to 16, in which the metal coating treatment included a process of forming a nickel coating by sputtering, a process of forming a copper coating by electroplating, and a process of forming a nickel coating by electroplating, in that order, and which had a thickness of 15 μm or less and a surface resistance of 0.03 Ω / □ or less, had better electromagnetic shielding properties and made the metal coating less likely to peel off, compared to the electromagnetic shielding materials of Examples 11 to 13.

[0111] Comparative Examples 11 to 16 contain stretched PET short fibers with a fiber diameter of 3 μm or more and unstretched PET short fibers with a fiber diameter of more than 5 μm, and have a basis weight of 7 g / m 2 The electromagnetic shielding material is obtained by subjecting a wetlaid nonwoven fabric for use as an electromagnetic shielding material, which is a nonwoven fabric having a resistance to high temperature, to a metal coating treatment. Comparative Examples 11 and 13, in which the metal coating treatment involved, in this order, a process of forming a nickel coating by sputtering, a process of forming a copper coating by electroplating, and a process of forming a nickel coating by electroplating, showed poor results in the electromagnetic shielding property and peel evaluation. The electromagnetic shielding material of Comparative Example 12 showed good results in the electromagnetic shielding property and peel evaluation, but the thickness of the electromagnetic shielding material was 20.0 μm and could not be made thinner. Comparative Examples 14 to 16, in which a nickel coating was formed by electroless plating, and then a copper coating and a nickel coating were laminated in this order by electroplating, were subjected to the metal coating treatment. The peel evaluation results were good, but the electromagnetic shielding property was poor.

[0112] <Nonwoven fabric for electromagnetic wave shielding material of the present invention <3> Examples of related examples

[0113] [Example 21] 30 parts by mass of stretched polyethylene terephthalate (PET) staple fibers with a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 5 mm, 30 parts by mass of stretched PET staple fibers with a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, and 40 parts by mass of unstretched PET staple fibers for single-component binders with a fineness of 0.2 dtex (fiber diameter 4.3 μm), a fiber length of 3 mm, and a melting point of 246°C were dispersed in water using a pulper to prepare a uniform papermaking slurry with a concentration of 1% by mass. This papermaking slurry was then passed through a pulp machine with an air permeability of 275 cm 3 / cm 2 / sec, on an inclined paper machine equipped with a papermaking wire with a structure [upper mesh: plain weave, lower mesh: ribbed weave], the paper was made using the wet method, and the unstretched PET short fibers used as binders were heat-fused in a cylinder dryer at 135°C to develop strength, resulting in a basis weight of 10 g / m 2This wetlaid nonwoven fabric was then subjected to a thermal calendering treatment using a single-nip thermal calendering device consisting of a dielectric heating jacket roll (metallic thermal roll) and an elastic roll, under conditions of a thermal roll temperature of 202°C, a linear pressure of 100 kN / m, and a processing speed of 40 m / min, to produce a nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 2.1 N / m.

[0114] [Example 22] A nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 3.1 N / m was prepared in the same manner as in Example 21, except that the heat roll temperature was set to 208°C.

[0115] [Example 23] A nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 4.2 N / m was prepared in the same manner as in Example 21, except that the heat roll temperature was set to 205°C.

[0116] [Example 24] A nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 3.5 N / m was produced in the same manner as in Example 23, except that the blend of stretched polyester staple fibers was changed to 30 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 3 mm, and 30 parts by mass of stretched PET staple fibers having a fineness of 0.1 dtex (fiber diameter 3.0 μm) and a fiber length of 3 mm.

[0117] [Example 25] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 3.7 N / m was produced in the same manner as in Example 23, except that the blend of stretched polyester staple fibers was changed to 30 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 3 mm, and 30 parts by mass of stretched PET staple fibers having a fineness of 0.06 dtex (fiber diameter 2.4 μm) and a fiber length of 3 mm.

[0118] [Example 26] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 3.4 N / m was produced in the same manner as in Example 23, except that the blend of stretched polyester staple fibers was changed to 30 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, and 30 parts by mass of stretched PET staple fibers having a fineness of 0.1 dtex (fiber diameter 3.0 μm) and a fiber length of 3 mm.

[0119] [Example 27] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 3.3 N / m was produced in the same manner as in Example 23, except that the blend of stretched polyester staple fibers was changed to 30 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, and 30 parts by mass of stretched PET staple fibers having a fineness of 0.06 dtex (fiber diameter 2.4 μm) and a fiber length of 3 mm.

[0120] [Example 28] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 3.5 N / m was produced in the same manner as in Example 23, except that the blend of stretched polyester staple fibers was changed to 30 parts by mass of stretched PET staple fibers having a fineness of 0.1 dtex (fiber diameter 3.0 μm) and a fiber length of 3 mm, and 30 parts by mass of stretched PET staple fibers having a fineness of 0.06 dtex (fiber diameter 2.4 μm) and a fiber length of 3 mm.

[0121] [Comparative Example 21] A nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 1.8 N / m was prepared in the same manner as in Example 21, except that the hot roll temperature was set to 198°C.

[0122] [Comparative Example 22] A nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 1.0 N / m was prepared in the same manner as in Example 21, except that the heat roll temperature was set to 195°C.

[0123] [Comparative Example 23] A nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 1.5 N / m was prepared in the same manner as in Example 24, except that the hot roll temperature was set to 198°C.

[0124] [Comparative Example 24] A nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 1.0 N / m was prepared in the same manner as in Example 25, except that the heat roll temperature was set to 198°C.

[0125] [Comparative Example 25] A nonwoven fabric for an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 0.2 N / m was prepared in the same manner as in Example 23, except that the fiber blend was 30 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.3 dtex (fiber diameter 5.3 μm) and a fiber length of 3 mm, 30 parts by mass of stretched PET staple fibers having a fineness of 0.1 dtex (fiber diameter 3.0 μm) and a fiber length of 3 mm, and 10 parts by mass of unstretched PET staple fibers for a single-component binder having a fineness of 0.2 dtex (fiber diameter 4.3 μm), a fiber length of 3 mm, and a melting point of 246°C.

[0126] [Comparative Example 26] A nonwoven fabric for use as an electromagnetic wave shielding material having a thickness of 15 μm and a peel strength of 1.8 N / m was prepared in the same manner as in Example 23, except that the fiber blend was changed to 10 parts by mass of stretched PET staple fibers having a fineness of 0.6 dtex (fiber diameter 7.4 μm) and a fiber length of 3 mm, and 90 parts by mass of unstretched PET staple fibers for use as a single-component binder having a fineness of 0.2 dtex (fiber diameter 4.3 μm), a fiber length of 3 mm, and a melting point of 246°C.

[0127] The nonwoven fabrics for electromagnetic wave shielding materials prepared in the examples and comparative examples were subjected to alkali treatment as a pre-plating treatment, and then subjected to metal plating treatment with copper and nickel by electroless plating to prepare electromagnetic wave shielding materials.

[0128] <Evaluation> [Peel strength] The nonwoven fabric for electromagnetic wave shielding was cut into 25 mm x 200 mm pieces, and double-sided tape (Nichiban, product name: NW-R25, Nicetack (registered trademark), low adhesive type) was attached to a backing (Mitsubishi Paper Mills, product name: N Pearl Card (registered trademark), FSC certified-MX (450.0 g / m 2)), and then a nonwoven fabric for electromagnetic shielding was placed on top of that, and packaging tape (manufactured by Kamoi Kogyo, product name: No. 220W) was attached to the top of that, and a peel test was carried out in the format shown in Figure 1 to measure the peel strength. For the peel test, a digital force gauge FGC-2B manufactured by SHIMPO (Nidec Shimpo) was used, with a jig distance of 1.8 cm, with the nonwoven fabric for electromagnetic shielding placed in the center of that distance, and measurements were taken at a speed of 100 mm / min.

[0129] [Fiber shedding resistance] A nonwoven fabric for use as an electromagnetic wave shielding material was collected and cut into a piece of 25 mm x 200 mm. Using a Gakushin-type friction fastness tester, the nonwoven fabric for use as an electromagnetic wave shielding material was rubbed five times back and forth with a Billiken Moss (registered trademark) cloth with a 500 gf weight placed on it, and the rub resistance was evaluated according to the following criteria.

[0130] "◎" Fibers do not adhere to the Billiken Moss cloth. "○": Almost no fibers adhere to the Billiken Moss fabric. "△": Some fibers adhere to the Billiken Moss cloth, but this does not cause any problems in practical use. "X": Fibers adhere to the Billiken Moss cloth, and in some cases the substrate breaks.

[0131] [Fault frequency] The frequency of defects per 1000m was confirmed when metal plating was performed on nonwoven fabric for electromagnetic wave shielding material that had been subjected to alkali treatment, which is a pre-plating treatment.

[0132] "◎" 0 pieces / 1000m. "○" 1 piece / 1000m. "△" 2 pieces / 1000m. "×" 3 or more pieces / 1000m.

[0133] [Electromagnetic wave shielding (electric field)] Measurements were made based on the electromagnetic wave shielding properties (electric field) using the coaxial tube method. In the frequency range of 40 MHz to 3 GHz, measurements were made using the coaxial tube method 39D, and in the frequency range of 500 MHz to 18 GHz, measurements were made using the coaxial tube method GPC7. In the frequency range of 500 MHz to 3 GHz, measurements were made using both the coaxial tube method 39D and the coaxial tube method 7, but the lower value was used.

[0134] The higher the numerical value given for the electromagnetic wave shielding property, the better the electromagnetic wave shielding property.

[0135] [Table 3]

[0136] The nonwoven fabrics for electromagnetic shielding materials of Examples 21 to 28 had higher peel strength and therefore better resistance to fiber shedding than the nonwoven fabrics for electromagnetic shielding materials of Comparative Examples 21 to 26, and also had a lower frequency of defects, resulting in good yield and excellent electromagnetic shielding properties.

[0137] Comparing Examples 21 to 23, Example 23, in which the heat roll temperature was 205° C., had the highest peel strength and improved resistance to fiber shedding. On the other hand, in Comparative Examples 21 to 24, the heat roll temperature was lower than 200° C., so the nonwoven fabrics for electromagnetic shielding materials had low peel strength, poor resistance to fiber shedding, and a very high frequency of defects.

[0138] In Comparative Examples 25 and 26, the content of unstretched polyester staple fiber was less than 20 mass% or more than 80 mass% of the total fibers constituting the nonwoven fabric for electromagnetic shielding material, which was outside the preferred range. Therefore, even though the heat roll temperature was 205°C, which was within the preferred range, the nonwoven fabric for electromagnetic shielding material had low peel strength and poor resistance to fiber shedding. [Industrial Applicability]

[0139] The nonwoven fabric for electromagnetic shielding and the electromagnetic shielding material of the present invention are suitable for use in electronic devices, communication devices, electrical appliances, etc. These devices and products include devices such as mobile phones, smartphones, mobile phones, personal computers, and mobile devices, as well as cases for storing these devices, and electrical appliances such as televisions and washing machines. In particular, the electromagnetic shielding material of the present invention is suitable for use by being fixed to plastic housings, flexible printed circuit boards, electric wire cables, connector cables, etc. by adhesion, crimping, fusion bonding, winding, etc.

Claims

1. A nonwoven fabric for an electromagnetic wave shielding material, which is a wet-laid nonwoven fabric, comprises stretched polyester staple fibers and unstretched polyester staple fibers having a melting point of 220°C or higher and 250°C or lower, and the peel strength (longitudinal direction) between the fibers of the nonwoven fabric is 2.0 N / m or higher.

2. 2. An electromagnetic wave shielding material, comprising the nonwoven fabric for use as an electromagnetic wave shielding material according to claim 1, which is subjected to a metal coating treatment.

3. 3. The electromagnetic wave shielding material according to claim 2, wherein the metal film treatment is one or more treatments selected from the group consisting of electroless metal plating, electroplating, metal vapor deposition, and sputtering.

4. 3. The electromagnetic wave shielding material according to claim 2, wherein the metal coating treatment includes a treatment of forming a nickel coating by sputtering, a treatment of forming a copper coating by electroplating, and a treatment of forming a nickel coating by electroplating, in this order.

5. 4. The electromagnetic wave shielding material according to claim 2, wherein the thickness of the electromagnetic wave shielding material is 15 μm or less and the surface resistance of the electromagnetic wave shielding material is 0.03 Ω / □ or less.

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