Base material for electromagnetic wave shielding and electromagnetic wave shielding material that comprise wet-laid nonwoven fabric

Abstract

To provide a base material for electromagnetic wave shielding and an electromagnetic wave shielding material that comprise a wet-laid nonwoven fabric with good air permeability, high strength and heat resistance.SOLUTION: The problem is solved by, e.g., a base material for electromagnetic wave shielding which comprises a wet-laid nonwoven fabric having a drawn polyester-based fiber and an undrawn polyester-based fiber. The undrawn polyester-based fiber has: a first undrawn polyester-based fiber having a melting point of 245°C or more and 265°C or less and a fineness of 0.7 dtex or more and 1.7 dtex or less; and a second undrawn polyester-based fiber having a melting point of 245°C or more and 265°C or less and a fineness of 0.1 dtex or more and 0.6 dtex or less. A content of the drawn polyester-based fiber is between 20 mass% and 80 mass% based on the total amount of the fibers constituting the wet-laid nonwoven fabric, and a content of the undrawn polyester-based fiber is between 80 mass% and 20 mass% based on the total amount of the fibers constituting the wet-laid nonwoven fabric.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an electromagnetic shielding substrate and an electromagnetic shielding material that contain a wetlaid nonwoven fabric. [Background technology]

[0002] Electromagnetic shielding materials are used to prevent electronic devices from malfunctioning due to electromagnetic waves. As an electromagnetic shielding material, a substrate for an electromagnetic shielding material, which is made of a nonwoven fabric made of polyester staple fibers and is subjected to a metal plating treatment, has been disclosed (Patent Document 1). It is also known to obtain an adhesive substrate by papermaking polyester staple fibers (Patent Document 2).

[0003] Substrates for electromagnetic wave shielding materials are used in mobile phones, smartphones, other electrical products, automobiles, etc., and in recent years there has been a strong demand for them to be lighter and thinner.

[0004] However, the promotion of making the substrate lighter and thinner leads to a decrease in the strength of the nonwoven fabric. To address this issue, for example, a method of densifying the substrate by using relatively fine fibers can be considered. Although such a densification of the substrate improves the strength of the nonwoven fabric, it also causes a new problem of deteriorating the air permeability.

[0005] It may seem that this problem can be solved by using, for example, sheath-core fibers. Although the use of sheath-core fibers can certainly prevent the substrate from becoming excessively dense, it also reduces heat resistance, raising concerns that the nonwoven fabric may shrink or tear during heat treatment in the plating process. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2022-43131 [Patent Document 2] Patent Publication No. 2022-83165 Summary of the Invention [Problem to be solved by the invention]

[0007] In light of this background, a primary object of the present invention is to provide an electromagnetic shielding substrate and an electromagnetic shielding material that contain a wetlaid nonwoven fabric that has good air permeability, high strength, and heat resistance. [Means for solving the problem]

[0008] The inventors of the present invention used two types of unstretched polyester fibers with different fineness as the material for the substrate in order to prevent the substrate from becoming excessively dense and thus deteriorating in air permeability, and to increase the strength of the substrate. In addition, the inventors of the present invention have completed the present invention by focusing on the use of unstretched polyester fibers having a melting point within a specific range to give the substrate heat resistance and to prevent excessive densification. The aspects of the completed invention are as follows.

[0009] (First aspect) A substrate for electromagnetic shielding comprising a wetlaid nonwoven fabric having stretched polyester fibers and unstretched polyester fibers, The undrawn polyester fiber includes a first undrawn polyester fiber having a melting point of 245° C. or more and 265° C. or less and a fineness of 0.7 dtex or more and 1.7 dtex or less, and a second undrawn polyester fiber having a melting point of 245° C. or more and 265° C. or less and a fineness of 0.1 dtex or more and 0.6 dtex or less, The unstretched polyester fiber is contained in an amount of 20% by mass or more and 80% by mass or less based on the total amount of fibers constituting the wetlaid nonwoven fabric, The content ratio of the first unstretched polyester fiber to the second unstretched polyester fiber is 30:70 to 95:5. A wetlaid nonwoven fabric comprising an electromagnetic wave shielding substrate.

[0010] In this embodiment, since the unstretched polyester fibers have different finenesses in the above range, the voids formed between the fibers are not excessively large, and the fibers are not too dense, so that voids of an appropriate size are formed, resulting in good air permeability. The voids of this size are easy to plate, and the plating has excellent permeability and processing suitability. In addition, since the stretched polyester fibers and the unstretched polyester fibers having a relatively high melting point are contained in the above range, the electromagnetic shielding substrate includes a wet-laid nonwoven fabric having excellent heat resistance and high strength.

[0011] In addition to the first embodiment, the following embodiment is also preferred.

[0012] (Second aspect) The drawn polyester fiber has a melting point of 245°C or more and 265°C or less, and a fineness of 0.1 dtex or more and 1.7 dtex or less. Electromagnetic wave shielding substrate comprising the sheet-like nonwoven fabric of the first embodiment.

[0013] By setting the melting point of the stretched polyester fiber in the above range in addition to the melting point of the unstretched polyester fiber, the heat resistance becomes excellent, which is preferable.

[0014] (Third aspect) The thermal shrinkage rate in the MD direction is 0.01% or more and 3.8% or less. Electromagnetic wave shielding substrate comprising the sheet-like nonwoven fabric of the first embodiment.

[0015] If the heat shrinkage rate in the MD direction of the electromagnetic shielding substrate containing the sheet-like nonwoven fabric is within the above range, even if processing is performed by applying heat, the thermal deformation is small, and the substrate has excellent processing suitability.

[0016] (Fourth aspect) When 40 sheets are stacked, the converted air permeability is 0.5 seconds or more and 9.0 seconds or less. Electromagnetic wave shielding substrate comprising the sheet-like nonwoven fabric of the first embodiment.

[0017] If the converted air permeability when 40 sheets are stacked is within the above range, the nonwoven fabric is not excessively densified and can be easily plated.

[0018] (Fifth aspect) the sum of the content of the first unstretched polyester fiber and the content of the second unstretched polyester fiber relative to the total amount of fibers constituting the wetlaid nonwoven fabric is 20% by mass or more and 80% by mass or less; Electromagnetic wave shielding substrate comprising the sheet-like nonwoven fabric of the first embodiment.

[0019] When the total content is within the above range, the nonwoven fabric is not excessively dense and the gaps formed in the nonwoven fabric are unlikely to be excessively large, making it easy to carry out plating processing.

[0020] (Sixth aspect) The tensile strength in the MD direction is 0.2 kN / m or more and 3.0 kN / m or less. Electromagnetic wave shielding substrate comprising the sheet-like nonwoven fabric of the first embodiment.

[0021] If the tensile strength is within the above range, the sheet is less likely to break during the production of the electromagnetic wave shielding substrate, and the sheet has sufficient strength as an electromagnetic wave shielding material.

[0022] (Seventh aspect) The wet-laid nonwoven fabric has a basis weight of 3.0 g / m 2 More than 25.0g / m 2 Below is the Electromagnetic wave shielding substrate comprising the sheet-like nonwoven fabric of the first embodiment.

[0023] If the basis weight is within the above range, the sheet can be easily handled as an electromagnetic wave shielding substrate.

[0024] (Eighth aspect) An electromagnetic wave shielding material comprising a wetlaid nonwoven fabric having stretched polyester fibers and unstretched polyester fibers, The wet-laid nonwoven fabric is The undrawn polyester fiber includes a first undrawn polyester fiber having a melting point of 245° C. or more and 265° C. or less and a fineness of 0.7 dtex or more and 1.7 dtex or less, and a second undrawn polyester fiber having a melting point of 245° C. or more and 265° C. or less and a fineness of 0.1 dtex or more and 0.6 dtex or less, The unstretched polyester fiber is contained in an amount of 20% by mass or more and 80% by mass or less based on the total amount of fibers constituting the wetlaid nonwoven fabric, The content ratio of the first unstretched polyester fiber to the second unstretched polyester fiber is 30:70 to 95:5; The plated nonwoven fabric is Electromagnetic wave shielding material comprising a wetlaid nonwoven fabric.

[0025] This provides an electromagnetic shielding material that exhibits the same effects as the first aspect. Effect of the Invention

[0026] According to the present invention, it is possible to obtain an electromagnetic shielding substrate and an electromagnetic shielding material that contain a wetlaid nonwoven fabric that has good air permeability, high strength, and heat resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The present invention will be described below with reference to the embodiments. The following embodiments are merely examples, and the present invention will be clarified by the claims.

[0028] The electromagnetic shielding substrate and electromagnetic shielding material including the wetlaid nonwoven fabric of the present invention are expected to be in an embodiment (hereinafter also referred to as "industrialized form") in which, for example, a pressure-sensitive adhesive is applied to a plated nonwoven fabric, and the plated nonwoven fabric is attached to a final product in various forms and incorporated therein. This embodiment is a wetlaid nonwoven fabric including stretched polyester fibers and unstretched polyester fibers, and the unstretched polyester fibers include a first unstretched polyester fiber having a melting point of 245°C to 265°C and a fineness of 0.7 dtex to 1.7 dtex, and a second unstretched polyester fiber having a melting point of 245°C to 265°C and a fineness of 0.1 dtex to 0.6 dtex. The wetlaid nonwoven fabric can be a sheet-shaped nonwoven fabric including a vacuum deposition plating process, and is characterized in that it can be used as an electromagnetic shielding material including the nonwoven fabric.

[0029] From the classification of nonwoven fabrics based on the manufacturing method, the papermaking method is selected, and the present invention targets wet-laid nonwoven fabrics made by this method. In a typical papermaking method, short fibers, which are the raw material of nonwoven fabrics, are uniformly dispersed in water and poured onto a screen or between belts to form a web. The web is then squeezed with a roll and dried with a drying means (dryer) to evaporate the water, thereby obtaining a uniform sheet. Then, a thermal calendar treatment is performed to improve the fixation between the fibers. Wet-laid nonwoven fabrics obtained by this wet papermaking method are easy to form thin films and have excellent uniformity, durability, strength, and porosity (void ratio).

[0030] As mentioned above, wetlaid nonwoven fabrics are used as substrates for electromagnetic shielding materials, and are often required to have a thin thickness yet a (tensile) strength suitable for the application, and often require sufficient adhesion of plating. In addition, for electromagnetic shielding materials, pressure sensitive adhesive is applied to one or both sides after plating, so pressure sensitive adhesive permeability may be required.

[0031] In the technical field of nonwoven fabrics for electromagnetic shielding materials, as disclosed in Patent Document 2, nonwoven fabrics manufactured by combining stretched polyester fibers and unstretched polyester fibers are sometimes used as electromagnetic shielding materials. The document states that a lightweight nonwoven fabric can be obtained by combining two types of polyester fibers and adjusting the gaps between the fibers. However, the nonwoven fabric manufactured from the polyester fibers described in the document is made of polyester fibers with a relatively low melting point, and therefore the fibers may shrink or break due to heat when heat-treated in plating processing, and the product may become too dense, resulting in a decrease in plating performance (permeability of plating solution and processability) and a lack of strength.

[0032] <Polyester fiber> In the embodiment of the present invention, the nonwoven fabric contains unstretched polyester fibers, which have a relatively high melting point, and therefore can withstand the heat treatment in the plating process. Next, the polyester fibers used in the embodiment of the present invention will be described.

[0033] In the embodiment, the essential components are stretched polyester fibers and unstretched polyester fibers. These polyester fibers are preferably short fibers. In addition, the embodiment may contain fibers other than polyester fibers, such as acrylic fibers and polypropylene fibers.

[0034] Regarding the material of the embodiment, the polyester-based fiber is not particularly limited as long as it is polyester-based, and for example, polyester-based fibers made of glycol-dicarboxylic acid polycondensation such as polyethylene terephthalate, polybutylene terephthalate, polyethylene succinate, polybutylene succinate, polylactides such as polyglycolic acid and polylactic acid, polylactones, etc. can be used. Among these, polyethylene terephthalate is particularly preferable because it has a good balance between functions such as heat resistance and high strength and price.

[0035] <Unstretched polyester fiber> The embodiment according to the present invention includes two types of unstretched polyester fibers (i.e., a first unstretched polyester fiber and a second unstretched polyester fiber thinner than the first unstretched polyester fiber). By using two types of unstretched polyester fibers, the papermaking properties are improved when manufacturing the embodiment according to the present invention, and the roughness (porosity) and strength of the nonwoven fabric can be easily adjusted.

[0036] The fiber length of the unstretched polyester fiber is preferably 2 mm or more, more preferably 3 mm or more, and is preferably 10 mm or less, more preferably 7 mm or less. If the fiber length of the unstretched polyester fiber is within this range, the papermaking property is good and the nonwoven fabric has relatively high strength, which is preferable. If the fiber length is less than the above range, the fibers become shorter and the tensile strength decreases. Conversely, if the fiber length exceeds the above range, the dispersion of the fibers during papermaking may decrease, causing a decrease in strength due to poor bundling and formation.

[0037] The first unstretched polyester fiber preferably has a melting point of 245°C to 265°C and a fineness of 0.7 dtex to 1.7 dtex, more preferably a melting point of 250°C to 260°C and a fineness of 1.0 dtex to 1.4 dtex. If the melting point of the first unstretched polyester fiber is less than 245°C, the fiber may shrink significantly during the heat treatment in the deposition plating process. If the fineness of the first unstretched polyester fiber is less than 0.7 dtex, there is no significant difference between the fineness of the first unstretched polyester fiber and the fineness of the second unstretched polyester fiber, making it difficult to easily adjust the roughness and strength of the nonwoven fabric. On the other hand, if the melting point of the first unstretched polyester fiber exceeds 265°C, the fiber may be highly crystallized, and if the fineness of the first unstretched polyester fiber exceeds 1.7 dtex, the porosity of the nonwoven fabric may be large, and sufficient strength may not be obtained.

[0038] The second unstretched polyester fiber preferably has a melting point of 245°C to 265°C and a fineness of 0.1 dtex to 0.6 dtex, more preferably a melting point of 245°C to 255°C and a fineness of 0.2 dtex to 0.3 dtex. If the melting point of the second unstretched polyester fiber is less than 245°C, the fiber may shrink during the heat treatment in the deposition plating process. If the fineness of the second unstretched polyester fiber exceeds 0.6 dtex, there is no significant difference between the fineness of the second unstretched polyester fiber and the fineness of the first unstretched polyester fiber, making it difficult to easily adjust the roughness and strength of the nonwoven fabric. On the other hand, if the fineness of the second unstretched polyester fiber is less than 0.1 dtex, the nonwoven fabric becomes dense and plating is difficult.

[0039] The content of the unstretched polyester fiber relative to the total amount of fibers constituting the nonwoven fabric according to the embodiment of the present invention is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 60% by mass or less. The total content of the first unstretched polyester fiber and the second unstretched polyester fiber relative to the total amount of fibers constituting the nonwoven fabric according to the embodiment of the present invention is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 60% by mass or less. The blending ratio of the first unstretched polyester fiber to the second unstretched polyester fiber is preferably in the range of 30:70 to 95:5. If the ratio of the first unstretched polyester fiber is smaller than the above blending ratio and the ratio of the second unstretched polyester fiber is larger than the above blending ratio, the nonwoven fabric may become dense and the plating processability may decrease. In addition, the heat shrinkage rate may also deteriorate due to the increase in the ratio of the relatively thin unstretched polyester fiber. On the other hand, if the ratio of the second unstretched polyester fiber is smaller than the above-mentioned blend ratio, the strength of the sheet-like nonwoven fabric will decrease, and when used in an embodiment with a low basis weight, the processing suitability of the nonwoven fabric may decrease.

[0040] The nonwoven fabric according to the embodiment of the present invention contains unstretched polyester fibers as well as stretched polyester fibers and other fibers. The content of stretched polyester fibers is preferably 20% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 75% by mass or less, based on the total amount of fibers constituting the nonwoven fabric.

[0041] <Other fibers> Stretched polyester fibers have a high melting point and are available in a wide variety of thicknesses. By using stretched polyester fibers, the fibers are less likely to melt or soften during heat treatments such as wet papermaking and heat calendaring, and therefore the void ratio can be maintained high, and the thickness of the nonwoven fabric can be controlled by the combination of fibers.

[0042] The stretched polyester fiber included in the embodiment of the present invention preferably has a melting point of 245°C to 265°C and a fineness of 0.1 dtex to 1.7 dtex, more preferably a melting point of 250°C to 260°C and a fineness of 0.3 dtex to 1.5 dtex. If the melting point of the stretched polyester fiber is less than 245°C, the fiber may shrink during the heat treatment in the deposition plating process. If the fineness of the stretched polyester fiber exceeds 1.7 dtex, the nonwoven fabric becomes thick and the strength decreases. On the other hand, if the fineness of the stretched polyester fiber is less than 0.1 dtex, the nonwoven fabric becomes dense and plating process becomes difficult.

[0043] Examples of the other fibers that can be used include synthetic fibers such as polypropylene, rayon, polyvinyl alcohol (vinylon), nylon, polyamide, polyolefin, and acrylic, and natural pulp fibers such as wood pulp. Of these, acrylic fibers and polypropylene fibers are preferred.

[0044] In the above-mentioned conventional technique, Patent Document 2, the melting point of the fiber used is lower than that of the present invention. Unstretched polyester fibers with a relatively low melting point tend to be easily thermally deformed even at low processing temperatures when subjected to thermal calendaring, and the fibers may be crushed, resulting in an excessive decrease in porosity. On the other hand, the unstretched polyester fibers used in the present invention have a higher melting point than the fibers used in Patent Document 2, the conventional technique, and therefore are less likely to thermally deform and be crushed even in high-temperature thermal calendaring. Therefore, processing by thermal calendaring is easy.

[0045] Although the unstretched polyester fibers used in the present invention are crushed by the thermal calendaring process to a certain extent, the degree of crushing is extremely small, so that it is possible to obtain a nonwoven fabric with high heat resistance while maintaining air permeability. In addition, by using fibers with different fineness as the unstretched fibers, that is, by combining relatively thick unstretched polyester fibers with thin unstretched polyester fibers, when a heat treatment is performed, the thin unstretched polyester fibers (second unstretched polyester fibers) adhere (fix) to other fibers, and increase the number of contact points between the fibers, so that it is possible to obtain high strength as well. The fixing of the fibers to each other can be achieved not only by the thermal calendaring process, but also by wet papermaking heat, heat drying, etc.

[0046] <Nonwoven fabric> The basis weight of the nonwoven fabric of the embodiment is 3.0 g / m 2 More than 25.0g / m 2 Below, especially 5.0g / m 2 More than ~20.0g / m 2 Within the above-mentioned basis weight range, a low basis weight of 3.0 to 5.0 g / m 2 In addition to those with a high basis weight of 20.0 to 25.0 g / m 2 It is also easy to manufacture.

[0047] The thickness of the nonwoven fabric of the embodiment can be appropriately selected depending on the application and the above-mentioned basis weight, but preferably it is 10 to 50 μm, and more preferably it is 14 to 30 μm.

[0048] The converted air permeability when 40 sheets are stacked is preferably 9.0 seconds or less, more preferably 6.0 seconds or less. The lower limit of the converted air permeability is preferably 0.5 seconds or more. If the converted air permeability is within the above range, plating can easily penetrate into the inside of the nonwoven fabric, and the plating process suitability is excellent. If the converted air permeability exceeds the above range, the air permeability decreases, and the penetration of plating and adhesives may deteriorate. The converted air permeability can be adjusted by adjusting the basis weight, the type, fineness, and amount of raw fiber, and the temperature and pressure during calendaring.

[0049] Next, the thermal calendaring process will be described, but this is an example and is not limited thereto. The temperature of the thermal roll in the thermal calendaring process is preferably 140°C or more and 235°C or less, more preferably 160°C or more and 220°C or less. If the temperature of the thermal roll is less than 140°C, the adhesion between the fibers may be insufficient, and the strength may not be developed. On the other hand, if the temperature of the thermal roll exceeds 235°C, the wet nonwoven fabric may stick to the thermal roll, and the sheet may not be formed.

[0050] In order to develop strength, the pressure (linear pressure) in the thermal calendaring is preferably 0 to 250 kg / cm, more preferably 80 to 200 kg / cm. If the pressure exceeds 250 kg / cm, the sheet is crushed too much, resulting in a decrease in porosity. If the processing speed is 5 m / min or more, the work efficiency is good. If the processing speed is 200 m / min or less, heat is conducted to the wet nonwoven fabric, and the effect of heat fusion is easily obtained. The number of nips in the thermal calendaring is not particularly limited as long as heat can be conducted to the wet nonwoven fabric, but if the roll combination is a metal heat roll / elastic (resin) roll, nipping may be performed two or more times to conduct heat from the front and back of the wet nonwoven fabric.

[0051] In this specification, the definitions are as follows: "Basis weight (unit: g / m 2 ) is a value measured in accordance with JIS-P8124. "Fineness (unit: dtex)" is a value measured in accordance with JIS-L1095. "Thickness (unit: μm)" is a value measured in accordance with JIS-P8118. "Air permeability (unit: seconds)" is a value measured using the method described in JIS-P8117. However, since the measurement time is too short to measure with a single sheet, the measurement is performed with 40 sheets stacked. "Tensile strength (unit: kN / m)" is a value measured in accordance with JIS-P8113. "Heat shrinkage rate (150℃, 10 minutes)" is the value calculated by cutting a sheet-shaped nonwoven fabric into a sample of 200 mm in the longitudinal direction (MD) × 200 mm in the transverse direction (CD), heating it in a dryer at 150℃ for 10 minutes, measuring the length in the MD (or CD) at the center of the sample after heating to the nearest 0.5 mm, and using the following formula (Equation 1). [Number 1] Heat shrinkage rate (%) = {length of sample before heating (mm) - length of sample in the same direction after heating (mm)} / length of sample before heating (mm) x 100 When warping or curling occurred in the sheet-like nonwoven fabric, the warped or curled portion was flattened out to obtain the length of the sample. "Melting point (℃)" is the temperature at the endothermic peak top measured using differential scanning calorimetry (DSC) at a temperature rise rate of 10℃ / min in a nitrogen atmosphere over a measurement temperature range of 50 to 300℃.

[0052] The tensile strength (MD direction (length direction)) of the nonwoven fabric substrate is preferably 0.15 kN / m to 3.0 kN / m, more preferably 0.15 kN / m to 2.0 kN / m, and even more preferably 0.20 kN / m to 1.3 kN / m. If the tensile strength is below the above range, the substrate will be easily stretched and easily torn, resulting in reduced processability and handling. Conversely, if the tensile strength of the substrate exceeds the above range, the density will be high, which may reduce the permeability of plating or adhesive.

[0053] The tensile strength (in the CD (cross grain)) of the nonwoven fabric substrate is preferably 0.03 kN / m or more and 1.8 kN / m or less. If the tensile strength is less than the above range, dimensional changes may occur during plating or adhesive application processes or when used after application. Conversely, if the tensile strength of the substrate exceeds the above range, the substrate may become thick and strength in the longitudinal direction may decrease. If the transverse orientation exceeds the expected strength, the basis weight becomes excessively high and the paper thickness increases. In this case, it is also possible that the fiber orientation is crosswise, which may cause a decrease in strength in the longitudinal direction, etc.

[0054] The tensile strength in the MD (vertical grain direction) and the tensile strength in the CD (cross grain direction) of the nonwoven fabric substrate can be adjusted by adjusting the basis weight, the type, fineness, length and amount of raw fiber, and the temperature and pressure during calendaring.

[0055] The nonwoven fabric substrate is expected to be coated with an adhesive after plating, and then attached to the final product in various forms. In this embodiment, tension is expected to be applied not only in the MD direction but also in the opposing CD direction, and the optimal embodiment can be achieved by reducing the basis weight by setting the tensile strength ratio (%) per unit basis weight in the nonwoven fabric substrate [(tensile strength (CD) / tensile strength (MD)) × 100] to 5.0% or more and 21.0% or less.

[0056] The nonwoven fabric of the embodiment has a main fiber with a relatively high melting point, so that the fibers are unlikely to shrink even when heat is applied, and has excellent heat resistance. That is, the heat shrinkage rate of the nonwoven fabric of the embodiment is relatively low. The heat shrinkage rate of the nonwoven fabric is preferably 3.8% or less in the MD direction (vertical grain direction), more preferably 2.5% or less. The heat shrinkage rate of the nonwoven fabric is preferably 5.7% or less in the CD direction (cross grain direction), more preferably 2.5% or less. If the heat shrinkage rate exceeds 3.8% in the MD direction and 5.7% in the CD direction, strong shrinkage or breakage may occur during heat processing such as vapor deposition plating or heat calendering. The lower limit of the heat shrinkage rate of the nonwoven fabric is not particularly limited, but it is preferable that it is close to 0% in both the MD and CD directions, for example, it is preferable that it is more than 0.01%.

[0057] In an embodiment, the heat shrinkage rate of the nonwoven fabric can be adjusted by the content and basis weight of the unstretched polyester fiber.

[0058] Considering application to the "industrialized form" mentioned above, or breakage during the manufacturing process of the sheet-like nonwoven fabric up to the final product, it is also desirable for the tensile strength to be high in both the MD and CD directions.

[0059] The wetlaid nonwoven fabric according to the embodiment is useful as an industrial substrate such as an electromagnetic wave shielding material, an adhesive tape or sheet, etc. Also, it can be embodied as a conductive sheet in which the nonwoven fabric is adhered to a plated industrial substrate. EXAMPLES

[0060] Next, the effects of the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. A wetlaid nonwoven fabric was produced using polyester fibers as raw materials with the composition shown in Table 1. The fibers used were available from Teijin Frontier Co., Ltd., etc., and stretched PET fibers with different finenesses were used as stretched polyester fibers. All of these stretched PET fibers have a melting point of 245°C or higher, and for example, fibers manufactured by Teijin Frontier Co., Ltd. (TA04PN, 0.3 dtex x 5 mm, melting point 255°C) were used. As unstretched polyester fibers, unstretched PET fibers (TA07N, 1.2 dtex x 5 mm, melting point 254°C) and unstretched PET fibers (TK08PN, 0.2 dtex x 3 mm, melting point 247°C) were used. As other fibers, acrylic fibers (1.3 dtex x 3 mm), polypropylene fibers (0.8 dtex x 8 mm), and core-sheath PET / PET fibers (1.0 dtex x 5 mm, melting point 150°C or less) were used.

[0061] [Table 1]

[0062] The combination of fibers shown in Table 1 was dispersed in water and poured onto a net to obtain a web. The web was squeezed with a roll and dried with a dryer to evaporate the water, and then subjected to a thermal calendaring process to obtain a sheet-like wet-laid nonwoven fabric. The obtained wet-laid nonwoven fabrics were used as Examples, Comparative Examples, and Reference Examples.

[0063] The wetlaid nonwoven fabric thus obtained was measured for basis weight, thickness, density, tensile strength and air permeability. The results are shown in Table 2.

[0064] The obtained wet nonwoven fabric was plated as follows. The wet nonwoven fabric was plated in three stages. First, the wet nonwoven fabric was preheated by aging at 160°C or less, and then nickel plating was performed by vacuum deposition plating in the first stage to obtain a plated nonwoven fabric consisting of one layer of plating. Copper plating was performed by electroless plating in the second stage on this plated nonwoven fabric consisting of one layer of plating, to obtain a plated nonwoven fabric consisting of two layers of plating. Furthermore, nickel plating was performed by vacuum deposition plating in the third stage on this plated nonwoven fabric consisting of two layers of plating, to obtain a plated nonwoven fabric consisting of three layers of plating.

[0065] In the vacuum deposition plating method, nickel plating is performed at a base material temperature of 200°C or less, so the extent to which the wet-laid nonwoven fabric, which is the object of plating, shrinks due to heat becomes an issue in manufacturing electromagnetic wave shielding material.

[0066] (Plating coverage and plating penetration) Considering the use of the obtained wetlaid nonwoven fabric substrate as an electromagnetic shielding material, the heat shrinkage rate, electromagnetic shielding performance (specifically, the electromagnetic shielding performance was evaluated based on covering property and permeability) and processability were evaluated when the above-mentioned three-stage plating process (vacuum deposition method and electroless Ni / Cu plating) was performed. The results are shown in Table 2. The evaluation criteria are as follows. <Electromagnetic wave shielding performance> ⊚: It is judged that the coating property and permeability to the wetlaid nonwoven fabric substrate are high, and excellent electromagnetic wave shielding performance is obtained. ◯: It is judged that the wetlaid nonwoven fabric substrate has covering and permeability, and electromagnetic wave shielding performance is obtained. Δ: Coverage and permeability to the wetlaid nonwoven fabric substrate is somewhat low, and it is judged that the electromagnetic wave shielding property is poor. ×: The covering property and permeability to the wetlaid nonwoven fabric substrate are low, and it is judged that the electromagnetic wave shielding performance is not satisfied.

[0067] <Plating process suitability> Specifically, the plating suitability was evaluated according to the following criteria, taking into consideration the occurrence of sheet breakage and heat shrinkage during plating and adhesive processing after plating. ◎: There is no sheet breakage or heat shrinkage during plating and adhesive processing, and it is judged that excellent processing suitability is obtained. ◯: There was little sheet breakage or heat shrinkage during plating and adhesive processing, and the processing suitability was judged to be sufficient. △: There was a lot of sheet breakage and heat shrinkage during plating and adhesive processing, and it was determined that the processing suitability was poor. ×: The sheet broke frequently during plating and adhesive processing, or the heat shrinkage was very large, so that the processing suitability could not be evaluated.

[0068] [Table 2] [Industrial Applicability]

[0069] The electromagnetic shielding substrate and electromagnetic shielding material of the present invention include a sheet-like nonwoven fabric, but usually the sheet-like nonwoven fabric is used as the basic material (i.e., the main body), which is subjected to plating treatment, adhesive processing, etc., and is further treated with other treatments or combined with other materials as necessary. Therefore, the electromagnetic shielding substrate of the present invention includes not only the sheet-like nonwoven fabric itself, but also secondary processed products or products combined with other materials.

Claims

1. An electromagnetic wave shielding substrate comprising a wetlaid nonwoven fabric, The wetlaid nonwoven fabric is The fabric contains drawn polyester fibers and two types of undrawn polyester fibers with different finenesses, The heat shrinkage rate in the MD direction is 3.8% or less, The thermal shrinkage rate in the CD direction is 5.7% or less, When 40 sheets are stacked, the converted air permeability is 9.0 seconds or less, The tensile strength in the MD direction is 0.15 kN / m or more and 3.0 kN / m or less, The tensile strength in the CD direction is 0.03 kN / m or more and 1.8 kN / m or less. Electromagnetic wave shielding substrate characterized by:

2. The unstretched polyester fiber is The fiber length is 2 mm or more and 10 mm or less, The fabric comprises first unstretched polyester fibers having a predetermined fineness and second unstretched polyester fibers that are thinner than the first unstretched polyester fibers. The electromagnetic wave shielding substrate according to claim 1 .

3. The stretched polyester fiber has a melting point of 245°C or more and 265°C or less, and a fineness of 0.1 dtex or more and 1.7 dtex or less, The wetlaid nonwoven fabric contains the stretched polyester fibers in an amount of 20% by mass or more and 80% by mass or less based on the total amount of fibers. The electromagnetic wave shielding substrate according to claim 1 .

4. The wet-laid nonwoven fabric has a basis weight of 3.0 g / m 2 or more and 25.0 g / m 2 or less and a thickness of 10 to 50 μm. The electromagnetic wave shielding substrate according to claim 1 .