Nonwoven fabric for electromagnetic wave shielding

Abstract

This invention relates to a nonwoven fabric for electromagnetic wave shielding that, despite containing recycled fibers, exhibits excellent strength even when thinned, has excellent breathability, and good plating properties. [Solution] The nonwoven fabric is made from raw materials 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 materials, 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 materials, 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 Nonwoven fabric for electromagnetic wave shielding, having a thickness of 5 μm or more and a thickness of 30 μm or less.

Description

[Technical Field]

[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. [Background technology]

[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 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. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-019948 [Overview of the project] [Problems that the invention aims to solve]

[0005] Conventional nonwoven fabrics for base materials are produced by using thin, non-recycled (new) fibers and processing them at high temperatures through heat 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. [Means for solving the problem]

[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. [Effects of the Invention]

[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. [Modes for carrying out the invention]

[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 glycol-dicarboxylic acid polycondensate systems such as polyethylene terephthalate (PET), polybutylene terephthalate, 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 recycled polyester fiber content, whether drawn or undrawn, should be such that the minimum blending ratio of the recycled polyester fibers 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 fibers are 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 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 stretched 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 containing undrawn fibers of recycled polyester, the blending ratio in the raw material fibers is preferably 20% by mass or more, but from the viewpoints of strength and air permeability, it is preferably 80% by mass or less, more preferably 70% by mass or less, still more preferably 60% by mass or less. Also, the ratio of the recycled fibers in the whole of the polyester-based undrawn fibers is not particularly limited, and from the viewpoint of resource protection, for example, 20 to 100% by mass is exemplified. Here, the ratio of the recycled fibers being 100% by mass means that all of the undrawn fibers are recycled polyester fibers.

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

[0019] Recycled polyester fibers tend to have a broad melting heat temperature peak measured by differential scanning calorimetry (DSC) at 240 to 255 °C or multiple peaks in the case of drawn fibers, or slightly lower than 251 °C in the case of undrawn fibers due to molecular degradation and uneven molecular weight during recycling. Thus, when containing recycled polyester fibers, the heat resistance is relatively low, so there is a risk that the fibers may shrink or break during the heat treatment in plating, and the heat treatment temperature needs to be lowered, resulting in poor strength. However, in the present invention, by adjusting the content of recycled polyester fibers and the thickness of the obtained product, it was found that a non-woven fabric excellent in strength and air permeability can be produced without sticking to the roll even after passing through the heat calender process. Note that for non-recycled (new) polyester fibers, the melting heat peak temperature measured in the same manner is stable around 252 to 255 °C. The measurement conditions of DSC are not particularly limited, but for example, the measurement can be carried out at a heating rate of 10 °C / min and a measurement temperature range of 50 to 300 °C in a nitrogen atmosphere.

[0020] The drawn and undrawn polyester fibers other than recycled polyester fibers (non-recycled) are not particularly limited, and those of the above-described materials can be appropriately used. The materials of the recycled fibers and non-recycled fibers may be the same or different. The non-recycled drawn polyester fibers and non-recycled undrawn polyester fibers can be used alone or in combination of two or more.

[0021] The fineness and fiber length of the non-recycled drawn polyester 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 viewpoints of strength and air permeability, those with a fineness of 0.7 dtex or less can be used, and it 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 aforementioned fibers, core-sheath composite fibers from the viewpoint of strength and air permeability. The core-sheath 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 is not particularly limited, but composite fibers in which the sheath is made of amorphous or crystalline copolymer polyester resin, or composite fibers in which the core and sheath are made of polyester resin, can also be suitably used. Regenerated 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 of undrawn fibers and core-sheath type composite 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 fibers (2) Unstretched recycled polyester fibers (3) One or more fibers selected from the group consisting of polyester drawn fibers other than those in (1), polyester undrawn fibers other than those in (2), and core-sheath type composite fibers.

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

[0031] The nonwoven fabric for electromagnetic shielding material of the present invention meets the following requirements from the viewpoint of strength and breathability: (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. It is preferable to satisfy the following conditions. 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. It is preferable that the blending ratio of fibers with a fineness of 1.1 dtex or less is 20% by mass or more, as this allows for a structure that supports the voids. It is also preferable that the blending ratio of fibers with a fineness of 1.1 dtex or less is 80% by mass or less, as this 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] In addition to the aforementioned fibers, 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, 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 at a heating temperature of 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 at a heating temperature of around 190°C, a nonwoven fabric with sufficient moldability can be obtained without sticking to the roll due to the recycled fibers.

[0034] The non-woven fabric for electromagnetic wave shielding material of the present invention contains recycled polyester fibers, yet has high strength, and preferably has a tensile strength in the longitudinal direction (MD direction; the papermaking flow direction of the paper) 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 have the strength to withstand plating processing, and if it is 2.00 kN / m or less, cutting processing after plating processing 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 non-woven fabric. In this specification, the tensile strength is a value measured in accordance with JIS-P8113.

[0035] The non-woven fabric for electromagnetic wave shielding material of the present invention can maintain a high porosity while being a thin film, and the Gurley air permeability is 10.0 cm 3 / (cm 2 ·s) or more, which is preferable. If the Gurley air permeability is 10.0 cm 3 / (cm 2 ·s) or more, it is preferable because voids are formed through which the metal can penetrate inside by plating processing. The upper limit is not particularly limited, but preferably it is 400 cm 3 / (cm 2 ·s) or less, more preferably 300 cm 3 / (cm 2 ·s) or less. If the Gurley air permeability is 400 cm 3 / (cm 2 ·s) or less, it is preferable because the strength of the non-woven fabric after plating processing is good while containing recycled polyester fibers with reduced plating adhesion strength. The Gurley 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 Gurley air permeability is a value measured in accordance with Method A (Gurley method) described in JIS L 1096.

[0036] The nonwoven fabric for electromagnetic shielding materials of the present invention can be made thin due to its high strength despite containing recycled polyester fibers. From the viewpoint of workability, the thickness is preferably 5 μm or more, and from the viewpoint of thinning, 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 process of the nonwoven fabric. In this specification, the thickness is a value measured in accordance with JIS P8118.

[0037] The nonwoven fabric for electromagnetic shielding according to the present invention allows for appropriate adjustment of the basis weight according to the desired thinness, lightness, etc. For example, 3.0 g / m² 2 The above are some examples, and the price is 20.0 g / m². 2 Below, 19.0g / m 2 The following may also be used. In this specification, basis weight is a value measured in accordance with JIS P8124.

[0038] The nonwoven fabric for electromagnetic wave shielding of the present invention preferably has a density of 0.20 g / cm³, depending on the desired thinness, lightness, etc. 3 More than 0.70g / cm 3 The following adjustments may be made as appropriate. In this specification, density is a value measured in accordance with JIS P8118.

[0039] The nonwoven fabric for electromagnetic shielding according to this embodiment can be suitably used as an electromagnetic shielding material after undergoing a metal coating treatment. If necessary, an adhesive can be applied and the fabric can be attached to and incorporated into the final product. Examples of metal coating treatments include electroless metal plating, electroplating, metal vapor deposition, and sputtering. While recycled fibers tend to have reduced metal adhesion, the nonwoven fabric for electromagnetic shielding according to the present invention, despite containing recycled polyester fibers, has excellent strength and breathability, so it can be treated without particular limitations. Furthermore, because the nonwoven fabric for electromagnetic shielding according to the present invention contains recycled polyester fibers, it can be suitably used as an environmentally friendly base material. [Examples]

[0040] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way by these examples.

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

[0042] Next, the web obtained above was squeezed and dried with a dryer to evaporate the moisture, thereby obtaining a sheet-like wet nonwoven fabric. When performing the calendering process, a calendering system consisting of a combination of metal rolls and elastic (resin) rolls was used, and heating and pressurizing treatment was performed at the temperatures shown in Tables 1 to 3.

[0043] The fibers used are as follows: <Recycled Fiber (Recycled PET)> Stretched fiber: Manufactured by Teijin Frontier, RA04FN, 1.7 (dtex) x 5 (mm) Unstretched fiber: Teijin Frontier Co., Ltd., RA07N, 1.2 (dtex) x 5 (mm) <Non-recycled fiber> 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: Teijin Frontier Co., Ltd., TA04N, 0.6 (dtex) x 5 (mm) Stretched fiber: Teijin Frontier Co., Ltd., TA02N, 0.7 (dtex) x 5 (mm) Undrawn fiber: Teijin Frontier Co., Ltd., TK08PN, 0.2 (dtex) x 3 (mm) Unstretched fiber: Teijin Frontier Co., Ltd., TA07N, 1.2 (dtex) x 5 (mm) <Other> Core-sheath type composite fiber: Teijin Frontier Co., Ltd., 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 Fragile air permeability were measured according to the method described below. Basis weight: JIS P 8124(2011) Thickness: JIS P 8118 (2014) Density: JIS P 8118(2014) Tensile strength: JIS P 8113 (2006) Fragile air 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) ◎: It has high penetration into the nonwoven fabric, resulting in excellent electromagnetic shielding performance. Furthermore, no fiber shedding is observed. ○: It penetrates into the nonwoven fabric, providing sufficient electromagnetic shielding performance for use. Furthermore, no fiber shedding is observed. △: The penetration into the nonwoven fabric is somewhat low, and while plating is possible, the electromagnetic shielding performance is slightly inferior. Alternatively, fiber shedding may occur. ×: The material does not penetrate into the nonwoven fabric, or the plating partially cracks or peels off, thus failing to meet the electromagnetic shielding performance requirements. Alternatively, fiber shedding may occur.

[0046] Test Example 2 [Plating Process Runability] The degree of sagging, wrinkling, and tearing at both ends of the sheet during the plating process was evaluated according to the following criteria. A score of "◎" or "〇" indicates a pass. (Evaluation Criteria) ◎: The seat is free from sagging, wrinkles, and tears, and its handling and drivability are excellent. ○: The seat is free from sagging, wrinkles, and tears, but the efficiency of processing and driving is slightly reduced. △: Sagging and wrinkles occur at both ends of the sheet, resulting in poor processing and running performance. ×: The sheet has sagging, wrinkles, or tears at both ends, making plating difficult.

[0047] [Table 1]

[0048] [Table 2]

[0049] [Table 3]

[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. [Industrial applicability]

[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. It consists of a nonwoven fabric obtained using raw material fibers containing drawn polyester fibers and undrawn polyester fibers. The blending ratio of the aforementioned undrawn polyester fibers is 25 to 80% by mass of the aforementioned raw fibers. The stretched polyester fiber and the unstretched polyester fiber include at least one of the stretched polyester fiber, 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. Fragile breathability is 10.0 cm ３ / (cm ２ ・s) is greater than or equal to, Nonwoven fabric for electromagnetic wave shielding, with a thickness of 5 μm or more and 30 μm or less.

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

3. A nonwoven fabric for electromagnetic shielding material 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 material 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: 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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