Nonwoven fabric for electromagnetic wave shielding member

Abstract

A nonwoven fabric for an electromagnetic wave shielding member, the nonwoven fabric comprising a nonwoven fabric obtained using raw material fibers containing polyester-based drawn fibers and polyester-based undrawn fibers, wherein the blended proportion of the polyester-based undrawn fibers is 25-80 mass% of the raw material fibers, the polyester-based drawn fibers and / or the polyester-based undrawn fibers include recycled polyester fibers, the minimum blended proportion of the recycled polyester fibers is 20 mass% or more of the raw material fibers, and the nonwoven fabric has a tensile strength of 0.10-2.00 kN / m in the longitudinal direction, a Frazier air permeability of 10.0 cm3 / (cm2·s) or more, and a thickness of 5-30 µm.

Description

Nonwoven fabric for electromagnetic wave shielding

[0001] This invention relates to a nonwoven fabric for electromagnetic wave shielding materials, which is used as a base material for electromagnetic wave shielding materials.

[0002] In recent years, there has been a very strong demand for lighter and thinner materials used in industrial materials such as electromagnetic shielding materials and tape core materials for use in mobile phones, smartphones, other electrical products, automobiles, and other devices.

[0003] For example, Patent Document 1 describes a wet-laid nonwoven fabric used as an electromagnetic wave shielding material after being treated with a metal coating. By using polyester fibers with a single fiber fineness of 1.1 dtex or less as the constituent fibers, the thickness is in the range of 9 to 108 μm and the basis weight is 3 to 40 g / m². ２ It is disclosed that a nonwoven fabric can be provided.

[0004] Japanese Patent Publication No. 2024-019948

[0005] Conventional nonwoven fabrics for base materials are produced by using thin, non-recycled (new) fibers and processing them at high temperatures through thermal calendering to create thin base materials. However, in recent years, there has been a growing demand for the use of environmentally friendly materials.

[0006] However, when using resin fibers recycled through material recycling or chemical recycling (especially material-recycled fibers), there is a problem in that the softening point is not stable compared to when only non-recycled fibers are used. As a result, even when processed at the same high temperature as when only non-recycled fibers are used, the fibers stick to the heat rolls and processing becomes impossible. There is also the problem of reduced strength due to variations in molecular weight, etc.

[0007] The present invention relates to a nonwoven fabric for electromagnetic wave shielding material that, despite containing recycled fibers, exhibits excellent strength even when thinned, has excellent breathability, and good plating properties.

[0008] The present invention relates to a nonwoven fabric obtained using raw materials containing drawn polyester fibers and undrawn polyester fibers, wherein the blending ratio of undrawn polyester fibers is 25 to 80% by mass of the raw materials, at least one of the drawn polyester fibers and undrawn polyester fibers contains recycled polyester fibers, the minimum blending ratio of recycled polyester fibers is 20% by mass or more of the raw materials, the longitudinal tensile strength is 0.10 kN / m to 2.00 kN / m, and the Fragile air permeability is 10.0 cm. ３ / (cm ２ This relates to a nonwoven fabric for electromagnetic wave shielding, having a thickness of 5 μm or more and a thickness of 30 μm or less.

[0009] The nonwoven fabric for electromagnetic wave shielding materials of the present invention, while containing recycled fibers, exhibits excellent strength even when thinned, as well as superior breathability and good plating properties, thus providing excellent effects.

[0010] The nonwoven fabric for electromagnetic wave shielding material of the present invention is obtained from raw fibers containing polyester-based drawn fibers and polyester-based undrawn fibers, wherein at least one of the fibers contains recycled polyester fibers.

[0011] The polyester fiber used in this invention is not particularly limited as long as it is polyester. For example, polyester fibers made of polyethylene terephthalate (PET), polybutylene terephthalate, glycol-dicarboxylic acid polycondensate such as polyethylene succinate and polybutylene succinate, polylactides such as polyglycolic acid and polylactic acid, and polylactones can be used. From the viewpoint of heat resistance and high strength, it is more preferable that the fiber be composed solely of PET.

[0012] The recycled polyester fibers can be those recovered and prepared from used or unused products according to known methods, and may be materially recycled or chemically recycled. In the present invention, materially recycled PET fibers can be suitably used from the viewpoint of recoverability and minimal quality degradation due to recycling. Materially recycled PET fibers can be obtained, for example, by crushing and melt-kneading collected PET bottles, followed by molding and spinning.

[0013] Recycled polyester fibers exhibit variations in molecular weight and a decrease in softening and melting points. Since the softening point is important for forming nonwoven fabrics, recycled polyester fibers with a relatively high softening point may be used. Furthermore, from the standpoint of blending ratio, fineness, and strength, undrawn recycled polyester fibers can also be used. Non-recycled (new) undrawn polyester fibers can increase the strength of nonwoven fabrics because the fibers can be bonded together by heating, but undrawn recycled polyester fibers can also function as binder fibers that impart strength to the nonwoven fabric base material, similar to non-recycled undrawn fibers.

[0014] The amount of recycled polyester fiber, whether drawn or undrawn, should be such that the minimum blending ratio of the recycled polyester fiber to the total amount of fibers constituting the nonwoven fabric is 20% by mass or more, and may be 50% by mass or more. From the viewpoint of resource conservation, a higher upper limit is preferable, but it is not particularly limited and can be set appropriately depending on the balance between drawn and undrawn fibers. For example, it may be 80% by mass or less, or 60% by mass or less. If recycled fiber is included in both drawn and undrawn fibers, it is sufficient that the recycled fiber content of each satisfies 20% by mass or more, and their contents may independently fall within the above range. When multiple drawn or undrawn fibers are used as recycled polyester fibers, the recycled polyester fiber content refers to the total content of drawn recycled polyester or the total content of undrawn recycled polyester, and each total content should be 20% by mass or more. Furthermore, while the total content of recycled polyester fibers is not particularly limited, from the viewpoint of resource conservation, examples include the ranges of 20-100% by mass, 45-100% by mass, 50-100% by mass, 70-100% by mass, 75-100% by mass, and 80-100% by mass relative to the total amount of fibers constituting the nonwoven fabric.

[0015] When regenerated polyester drawn fibers are included, the blending ratio in the raw material fibers is preferably 20% by mass or more, but from the viewpoint of strength, it is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less.

[0016] The fineness and fiber length of the regenerated polyester drawn fibers are not particularly limited, with fineness ranging from 0.001 to 8.0 dtex. From the viewpoint of achieving greater strength, a fineness of 2.2 dtex or less is preferred, and 1.7 dtex or less is more preferred. The lower limit may be, for example, 0.3 dtex or more. The fiber length is not particularly limited and may be, for example, 1 to 10 mm. Since regenerated polyester itself has a lower melting point and may be inferior in terms of strength compared to non-regenerated polyester, the strength can be compensated for by making the fineness of the regenerated polyester drawn fibers thicker than that of the non-regenerated polyester drawn fibers.

[0017] When recycled polyester undrawn fibers are included, the blending ratio in the raw material fibers is preferably 20% by mass or more, but from the viewpoint of strength and air permeability, it is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. Furthermore, the proportion of recycled fibers in the total undrawn polyester fibers is not particularly limited, and from the viewpoint of resource conservation, for example, 20 to 100% by mass is exemplified. Here, a proportion of recycled fibers of 100% by mass means that all of the undrawn fibers are recycled polyester fibers.

[0018] The fineness and fiber length of the undrawn recycled polyester fibers are not particularly limited, but the fineness can range from 0.05 to 4.0 dtex. Furthermore, from the viewpoint of further improving air permeability, the fineness may be 0.2 dtex or higher, or 1.2 dtex or higher. The upper limit may be, for example, 2.2 dtex or lower. The fiber length is not particularly limited and may be, for example, 1 to 10 mm. Since recycled polyester itself has a lower melting point and may be inferior in terms of strength compared to non-recycled polyester, the strength can be compensated for by making the fineness of the undrawn recycled polyester fibers thicker than that of the undrawn non-recycled polyester fibers.

[0019] Due to molecular degradation and inconsistent molecular weights resulting from recycling, recycled polyester fibers exhibit a broad or multiple peak in their heat of fusion temperature, measured by differential scanning calorimetry (DSC). This peak is observed in 240-255°C for drawn fibers, and tends to be slightly lower, below 251°C, for undrawn fibers. Thus, materials containing recycled polyester fibers have relatively lower heat resistance, potentially leading to shrinkage or tearing during heat treatment in plating processes, requiring a reduction in the heat treatment temperature and resulting in a product with poor strength. However, in this invention, by adjusting the recycled polyester fiber content and the thickness of the resulting product, it was found that a nonwoven fabric with excellent strength and breathability could be produced without sticking to the rolls even after a thermal calendering process. Non-recycled (new) polyester fibers, similarly measured, exhibit a stable peak heat of fusion temperature around 252-255°C. The measurement conditions for DSC are not particularly limited, but for example, measurements can be performed in a nitrogen atmosphere with a heating rate of 10°C / min and a measurement temperature range of 50 to 300°C.

[0020] The non-recycled polyester drawn fibers and undrawn polyester fibers other than recycled polyester fibers are not particularly limited, and those of the above-mentioned materials can be used as appropriate. The recycled fibers and non-recycled fibers may be the same or different in material. One or more types of non-recycled polyester drawn fibers and non-recycled polyester undrawn fibers can be used in combination.

[0021] The fineness and fiber length of the non-recycled polyester-based drawn fibers are not particularly limited and can be adjusted according to known techniques. For example, the fineness may be 0.06 to 8.0 dtex, and the fiber length may be 1 to 10 mm. Also, from the viewpoint of strength and air permeability, fibers with a fineness of 0.7 dtex or less can be used, and may be 0.1 to 0.7 dtex.

[0022] The fineness and fiber length of the non-regenerated polyester undrawn fibers are not particularly limited and can be adjusted according to known techniques. For example, the fineness may be 0.1 to 2.2 dtex and the fiber length may be 1 to 10 mm.

[0023] From the viewpoint of strength, the nonwoven fabric for electromagnetic wave shielding of the present invention may contain polyester-based drawn fibers, including recycled and non-recycled fibers, in an amount of 20 to 80% by mass or 20 to 75% by mass relative to the total amount of fibers constituting the nonwoven fabric.

[0024] The nonwoven fabric for electromagnetic wave shielding of the present invention has a content of 25 to 80% by mass of polyester undrawn fibers, including recycled and non-recycled fibers, relative to the total amount of fibers constituting the nonwoven fabric, from the viewpoint of strength and air permeability. Whether recycled or non-recycled, they function as binder fibers that impart strength to the nonwoven fabric base material. A blending ratio of 25% by mass or more of polyester undrawn fibers, including recycled and non-recycled fibers, is preferable because it exhibits a strength-imparting effect through fiber bonding. Furthermore, a blending ratio of 80% by mass or less of undrawn fibers is preferable because it maintains the voids in the nonwoven fabric base material, allowing for good plating. When two or more types of undrawn fibers are included, the total blending ratio is indicated.

[0025] The ratio of drawn fibers to undrawn fibers (drawn fibers / undrawn fibers) in the nonwoven fabric for electromagnetic wave shielding material of the present invention is not particularly limited, but from the viewpoint of improving interfiber fixation and strength, 20 / 80 to 75 / 25 is preferred, and 40 / 60 to 70 / 30 is more preferred. Here, drawn fibers include both recycled and non-recycled drawn fibers, and undrawn fibers include both recycled and non-recycled undrawn fibers.

[0026] The nonwoven fabric for electromagnetic wave shielding of the present invention may contain, in addition to the fibers described above, core-sheath type composite fibers from the viewpoint of strength and air permeability. The core-sheath type composite fiber is not particularly limited as long as the fiber structure has a core-sheath structure. For example, the material of the core and sheath parts is not particularly limited, but composite fibers in which the sheath part is made of amorphous or crystalline copolymer polyester resin, or composite fibers in which the core and sheath parts are made of polyester resin can also be suitably used. Recycled fibers may be used as the material of the composite fiber.

[0027] The fineness and fiber length of the core-sheath composite fiber are not particularly limited and can be adjusted according to known techniques. For example, the fineness may be 0.5 to 2.2 dtex and the fiber length may be 1 to 10 mm.

[0028] Since core-sheath type composite fibers function as binder fibers, they can be included in the nonwoven fabric in an amount of preferably 10% by mass or more, more preferably 20% by mass or more, relative to the total amount of fibers constituting the nonwoven fabric. Furthermore, in the present invention, since plating can be performed well if the blending ratio of undrawn fibers is 80% by mass or less, core-sheath type composite fibers can be included in such a way that the total content with undrawn fibers is 80% by mass or less, from the viewpoint of achieving binder function. The total content of fibers having binder function, including core-sheath type composite fibers (i.e., the total content of core-sheath type composite fibers and undrawn fibers), is not particularly limited, but may be more than 25% by mass, 40% by mass or more, or 50% by mass or more, relative to the total amount of fibers constituting the nonwoven fabric. The upper limit is 80% by mass or less.

[0029] A preferred embodiment of the constituent fibers in the nonwoven fabric for electromagnetic wave shielding material of the present invention includes two or more types selected from (1) to (3) below, so as to include drawn fibers and undrawn fibers. For example, an embodiment including all of (1) to (3) may also be used. In the embodiment including (1) and (3), it is preferable that the fibers in (3) include at least polyester undrawn fibers other than (2) (non-recycled polyester undrawn fibers). In the embodiment including (2) and (3), it is preferable that the fibers in (3) include at least polyester drawn fibers other than (1) (non-recycled polyester drawn fibers). (1) Stretched recycled polyester (2) Undrawn recycled polyester (3) One or more fibers selected from the group consisting of polyester drawn fibers other than (1), polyester undrawn fibers other than (2), and core-sheath type composite fibers

[0030] Combinations of drawn and undrawn polyester fibers include the following embodiments (a) to (h). The aforementioned core-sheath type composite fibers may also be used in combination with these embodiments. (a) Regenerated drawn fiber / Regenerated undrawn fiber (b) Regenerated drawn fiber / Regenerated undrawn fiber / Non-regenerated drawn fiber (c) Regenerated drawn fiber / Regenerated undrawn fiber / Non-regenerated undrawn fiber (d) Regenerated drawn fiber / Regenerated undrawn fiber / Non-regenerated drawn fiber / Non-regenerated undrawn fiber (e) Regenerated drawn fiber / Non-regenerated undrawn fiber (f) Regenerated drawn fiber / Non-regenerated undrawn fiber / Non-regenerated drawn fiber (g) Non-regenerated drawn fiber / Regenerated undrawn fiber (h) Non-regenerated drawn fiber / Regenerated undrawn fiber / Non-regenerated undrawn fiber

[0031] The nonwoven fabric for electromagnetic wave shielding of the present invention preferably satisfies the following requirements from the viewpoint of strength and air permeability: (4) The blending ratio of fibers with a fineness of 1.1 dtex or less is 20 to 80% by mass of the raw material fibers. Since fibers with a fineness of 1.1 dtex or less easily penetrate the voids of the nonwoven fabric base material, stable strength can be obtained even when regenerated fibers are used. These fibers may be unregenerated and may be drawn, undrawn, or core-sheath composite fibers. A blending ratio of fibers with a fineness of 1.1 dtex or less of 20% by mass or more is preferable because it can be configured to support the voids. Furthermore, a blending ratio of fibers with a fineness of 1.1 dtex or less of 80% by mass or less is preferable because it prevents the voids from becoming too packed. As an example, an embodiment can be given in which the blending ratio of fibers with a fineness of 0.2 to 1.1 dtex is 20 to 55% by mass.

[0032] The nonwoven fabric for electromagnetic wave shielding materials of the present invention may contain synthetic fibers such as polyolefins, rayon, polyvinyl alcohol (vinylon), nylon, polyamide, and acrylic, as well as natural pulp fibers such as wood pulp, in addition to the fibers mentioned above, to the extent that they do not impair the effects of the present invention. The content of these materials can be appropriately adjusted according to known technology.

[0033] The nonwoven fabric for electromagnetic wave shielding of the present invention can be manufactured without particular limitations, as long as the recycled polyester fibers described above are used. For example, when manufacturing a wet nonwoven fabric by a wet papermaking method, the raw material fibers described above can be uniformly dispersed in water, poured onto a mesh or between belts to form a web, then squeezed with a roll and dried. If necessary, a heat calender may be performed. The temperature (metal roll surface temperature) and pressure (metal roll wire pressure) of the heat calender can be adjusted according to known technology, for example, it can be processed at 110 to 240°C and 50 to 250 kg / cm. When recycled polyester fibers are used as undrawn fibers, from the viewpoint of exhibiting a binder effect, it may be processed at 140 to 190°C and 50 to 250 kg / cm. Even if the heating temperature is around 140°C, a nonwoven fabric with sufficient strength can be obtained even when using recycled fibers by combining the raw material fibers used. Furthermore, even if the heating temperature is around 190°C, a nonwoven fabric can be obtained with sufficient moldability without sticking to the roll due to the recycled fibers.

[0034] The nonwoven fabric for electromagnetic wave shielding material of the present invention has high strength despite containing recycled polyester fibers, and preferably has a tensile strength in the longitudinal direction (MD direction; the papermaking flow direction) of 0.10 kN / m or more and 2.00 kN / m or less. If the tensile strength in the longitudinal direction is 0.10 kN / m or more, it can withstand plating, and if it is 2.00 kN / m or less, cutting after plating can be performed well. The tensile strength can be adjusted by changing the type and content of the constituent fibers used and the drying process of the nonwoven fabric. In this specification, the tensile strength is a value measured in accordance with JIS-P8113.

[0035] The nonwoven fabric for electromagnetic shielding material of the present invention is a thin film that can maintain a high porosity, and has a Frazil air permeability of 10.0 cm². ３ / (cm ２ - Preferably, the air permeability of the Fragile is 10.0 cm or higher. ３ / (cm ２・ If it is above s), since voids are formed through which the metal can penetrate internally by plating, it is preferable. The upper limit is not particularly limited, but preferably 400 cm ３ / (cm ２ ・ s) or less, more preferably 300 cm ３ / (cm ２ ・ s) or less. If the fragile air permeability is 400 cm ３ / (cm ２ ・ s) or less, it is preferable because the strength of the non-woven fabric after plating is good while containing regenerated polyester fibers with reduced plating adhesion strength. The fragile air permeability can be adjusted by changing the type and content of the constituent fibers used and the drying and heat calendering processes of the non-woven fabric. In this specification, the fragile air permeability is a value measured in accordance with Method A (fragile method) described in JIS L 1096.

[0036] The non-woven fabric for electromagnetic wave shielding material of the present invention can be made thinner because it has high strength while containing regenerated polyester fibers. From the viewpoint of workability, the thickness is preferably 5 μm or more, and from the viewpoint of making it thinner, it can be preferably 30 μm or less, more preferably 28 μm or less. The thickness can be adjusted by changing the type and content of the constituent fibers used and the drying and heat calendering processes of the non-woven fabric. In this specification, the thickness is a numerical value measured in accordance with JIS P8118.

[0037] The non-woven fabric for electromagnetic wave shielding material of the present invention can be appropriately adjusted in basis weight according to the desired thinness, lightness, etc. For example, those of 3.0 g / m ２ or more can be mentioned, and those of 20.0 g / m ２ or less, 19.0 g / m ２ or less may also be used. In this specification, the basis weight is a numerical value measured in accordance with JIS P8124.

[0038] The non-woven fabric for electromagnetic wave shielding material of the present invention preferably has a density of 0.20 g / cm ３ or more and 0.70 g / cm ３It can be adjusted as appropriate below. In this specification, the density is a numerical value measured in accordance with JIS P8118.

[0039] The non-woven fabric for an electromagnetic wave shielding material according to this embodiment can be suitably used as an electromagnetic wave shielding material by performing a metal film treatment. If necessary, an adhesive can be applied and attached to and incorporated into a final product. Examples of the metal film treatment include electroless metal plating treatment, electroplating treatment, metal vapor deposition treatment, sputtering treatment, etc. However, since recycled fibers are likely to have reduced metal fixation, the non-woven fabric for an electromagnetic wave shielding material of the present invention contains recycled polyester fibers, but can be treated without particular limitation because it is excellent in strength and air permeability. Further, since the non-woven fabric for an electromagnetic wave shielding material of the present invention contains recycled polyester fibers, it can be suitably used as a base material considering the environment.

[0040] Hereinafter, the present invention will be specifically described by examples, but the present invention is not limited by these examples.

[0041] Examples 1 to 11 and Comparative Examples 1 to 6 The combinations of fibers shown in Tables 1 to 3 were dispersed in water and poured onto a screen to obtain a web.

[0042] Next, the web obtained above was squeezed and dried with a dryer to evaporate moisture to obtain a sheet-like wet non-woven fabric. When performing a calendar process, heating and pressing treatments at the temperatures shown in Tables 1 to 3 were performed using a calendar facility composed of a combination of one set of a metal roll and an elastic (resin) roll.

[0043] The fibers used are as follows: <Recycled Fibers (Recycled PET)> Stretched fiber: Manufactured by Teijin Frontier, RA04FN, 1.7 (dtex) x 5 (mm) Unstretched fiber: Manufactured by Teijin Frontier, RA07N, 1.2 (dtex) x 5 (mm) <Non-recycled fibers> Stretched fiber: Manufactured by Teijin Frontier, TA04PN, 0.1 (dtex) x 5 (mm) Stretched fiber: Manufactured by Teijin Frontier, TA04PN, 0.3 (dtex) x 3 (mm) Stretched fiber: Manufactured by Teijin Frontier, TA04PN, 0.3 (dtex) x 5 (mm) Stretched fiber: Manufactured by Teijin Frontier, TA04N, 0.6 (dtex) x 5 (mm) Stretched fiber: Manufactured by Teijin Frontier, TA02N, 0.7 (dtex) x 5 (mm) Undrawn fiber: Teijin Frontier, TK08PN, 0.2 (dtex) x 3 (mm) Undrawn fiber: Teijin Frontier, TA07N, 1.2 (dtex) x 5 (mm) <Others> Core-sheath type composite fiber: Teijin Frontier, TJ04CN, 1.1 (dtex) x 5 (mm)

[0044] The properties of the obtained nonwoven fabric were evaluated by performing the following tests. The results are shown in Tables 1 to 3. Basis weight, thickness, density, tensile strength (MD direction, CD direction), and Frazile permeability were measured according to the following methods: Basis weight: JIS P 8124 (2011) Thickness: JIS P 8118 (2014) Density: JIS P 8118 (2014) Tensile strength: JIS P 8113 (2006) Frazile permeability: Method A (Fragile type method) as described in JIS L 1096:2010

[0045] Test Example 1 [Plating Suitability] The obtained nonwoven fabric substrate was plated with a Ni / Cu system by electroless metal plating and / or electroplating, and the degree of plating penetration was evaluated according to the following evaluation criteria. "◎" and "〇" are considered acceptable. (Evaluation Criteria) ◎: High penetration into the nonwoven fabric, resulting in excellent electromagnetic shielding performance. No fiber shedding is observed. 〇: Penetration into the nonwoven fabric is present, resulting in electromagnetic shielding performance that is acceptable for use. No fiber shedding is observed. △: Slightly low penetration into the nonwoven fabric, allowing for plating, but with slightly inferior electromagnetic shielding performance. Or, fiber shedding is observed. ×: No penetration into the nonwoven fabric, or the plating partially cracks or peels off, thus failing to meet the electromagnetic shielding performance requirements. Or, fiber shedding is observed.

[0046] Test Example 2 [Plating Process Runability] The degree of sagging, wrinkling, and tearing at both ends of the sheet during plating was evaluated according to the following evaluation criteria. "◎" and "〇" are considered acceptable. (Evaluation Criteria) ◎: The sheet has no sagging, wrinkling, or tearing, and the processing runability is good. ○: The sheet has no sagging, wrinkling, or tearing, but the efficiency of processing runability is slightly reduced. △: Sagging or wrinkling occurs at both ends of the sheet, and the processing runability is poor. ×: Sagging, wrinkling, or tearing occurs at both ends of the sheet, making plating difficult.

[0047]

[0048]

[0049]

[0050] From the above results, it can be seen that Examples 1 to 11 have excellent strength and air permeability and good plating processability compared to Comparative Examples 1 to 6. Furthermore, Example 2, with a high content of undrawn fibers at 65% by mass, obtained a material with sufficient strength for plating without the need for a thermal calendering process. Example 3, which contains a high amount of recycled polyester fibers at 70% by mass, was found to have sufficient strength for handling despite being thinned to a low basis weight. Example 4, whose constituent fibers consist solely of recycled polyester fibers, was found to have appropriate strength and voids, and was also able to be plated well.

[0051] On the other hand, in Comparative Example 1, the blending ratio of recycled undrawn polyester fibers did not meet 20% by mass, and the proportion of undrawn fibers in the raw material fibers was low, resulting in insufficient fixation between fibers and fiber shedding during plating. In Comparative Example 2, the blending ratio of recycled drawn polyester fibers did not meet 20% by mass, and the amount of undrawn fibers exceeded 80% by mass, resulting in poor strength and fiber shedding during plating, and poor plating suitability. In Comparative Example 3, even though the blending ratio of recycled polyester fibers was 20% by mass or more, the proportion of undrawn fibers in the raw material fibers was low, resulting in low Fragile air permeability and insufficient plating. Comparative Examples 4 and 5 were prepared using only non-recycled (new, virgin) polyester fibers, but Comparative Example 4 lacked sufficient strength, and while Comparative Example 5 achieved sufficient strength, its plating processability was insufficient. In Comparative Example 6, even though the blending ratio of recycled polyester fibers was 20% by mass or more, the proportion of undrawn fibers in the raw material fibers was low, and the strength was poor when the thickness reached 57 μm. Furthermore, fiber shedding occurred during the plating process, resulting in poor plating suitability.

[0052] The nonwoven fabric for electromagnetic shielding materials of the present invention is suitably used as a nonwoven fabric base material for electromagnetic shielding materials.

Claims

1. The nonwoven fabric is made using raw material fibers containing drawn polyester fibers and undrawn polyester fibers, wherein the blending ratio of the undrawn polyester fibers is 25 to 80% by mass of the raw material fibers, at least one of the drawn polyester fibers and the undrawn polyester fibers contains recycled polyester fibers, the minimum blending ratio of the recycled polyester fibers is 20% by mass or more of the raw material fibers, the longitudinal tensile strength is 0.10 kN / m or more and 2.00 kN / m or less, and the Fragile air permeability is 10.0 cm. ３ / (cm ２ - A nonwoven fabric for electromagnetic wave shielding, having a thickness of 5 μm or more and 30 μm or less, and meeting the above requirements.

2. A nonwoven fabric for electromagnetic wave shielding according to claim 1, wherein the raw material fibers include two or more types selected from (1) to (3) below: (1) Stretched recycled polyester fibers (2) Unstretched recycled polyester fibers (3) One or more fibers selected from the group consisting of stretched fibers other than (1), unstretched fibers other than (2), and core-sheath type composite fibers.

3. A nonwoven fabric for electromagnetic wave shielding according to claim 1 or 2, satisfying the following (4): (4) The blending ratio of fibers with a fineness of 1.1 dtex or less is 20 to 80% by mass of the raw fibers.

4. The nonwoven fabric for electromagnetic shielding according to claim 3, wherein the recycled polyester fibers include material recycled fibers of polyethylene terephthalate.

5. The nonwoven fabric for electromagnetic shielding material according to claim 4, wherein the lowest heat of fusion peak temperature measured by differential scanning calorimetry (DSC) of recycled polyester fibers is 251°C or less.

6. Basis weight is 20.0 g / m² ２ The nonwoven fabric for electromagnetic wave shielding material according to claim 5 is as follows:

7. The nonwoven fabric for electromagnetic wave shielding material according to claim 6, which is a wet nonwoven fabric obtained by a wet papermaking method using drawn polyester fibers and undrawn polyester fibers.

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