CN117488576A

CN117488576A - Sheet nonwoven fabric

Info

Publication number: CN117488576A
Application number: CN202310857953.9A
Authority: CN
Inventors: 山本大昭; 豊田纯也
Original assignee: Daio Paper Corp
Current assignee: Daio Paper Corp
Priority date: 2022-08-01
Filing date: 2023-07-13
Publication date: 2024-02-02
Also published as: JP7219364B1; TW202407186A; JP2024019948A; KR20240017742A

Abstract

The present invention aims to provide a sheet-like nonwoven fabric which tends to have a low basis weight and which has good secondary processability. The above problems can be solved by the following sheet-like nonwoven fabric. A sheet nonwoven fabric is a nonwoven fabric of polyester staple fibers, and is composed of wet nonwoven fabric, wherein the fineness is 0.1 d-3.3 d, and the fiber length is 3-10 mm; the polyester staple fiber comprises a core-sheath polyester fiber and at least one of a drawn polyester fiber and an undrawn polyester fiber; the basis weight of the non-woven fabric is 3-40 g/m ² The reduced air permeability in a state of overlapping 40 sheets is 6.0 seconds or less, and the tensile strength is highRatio [ (tensile strength in MD direction + tensile strength in CD direction)/basis weight]Is 0.035 kN/m/(g/m) ² ) The above.

Description

Sheet nonwoven fabric

Technical Field

The present invention relates to a sheet nonwoven fabric.

Background

In order to prevent malfunction of the electronic device due to electromagnetic waves, an electromagnetic wave shielding material is used. As an electromagnetic wave shielding material, a substrate for an electromagnetic wave shielding material has been disclosed, which is obtained by using a nonwoven fabric formed of polyester staple fibers as a substrate and subjecting the substrate to a metal plating treatment (patent document 1).

On the other hand, a technique for producing polyester staple fibers to obtain an adhesive base material is known (patent document 2).

With the increase in density, thickness, and the like of electronic devices, even in industrial applications such as in the automotive field, it is desired that such a substrate, though being thin, exhibits a desired strength and is excellent in secondary processability including a high plating adhesion amount at the time of plating processing and permeability of an adhesive or the like at the time of adhesive processing, and suitability as a final product thereafter, due to demands for electronic control, safety, compactness, and the like.

[ Prior Art literature ]

(patent literature)

Patent document 1: japanese patent No. 6669940

Patent document 2: japanese patent No. 6009843

Disclosure of Invention

[ problem to be solved by the invention ]

Accordingly, the main object of the present invention is to provide a sheet-like nonwoven fabric which tends to have a low basis weight and which is excellent in secondary processability.

[ means of solving the problems ]

The sheet-like nonwoven fabric which solves the above problems has the following aspects.

A sheet nonwoven fabric, characterized in that:

the nonwoven fabric is made of polyester staple fibers, and is made of wet nonwoven fabric, the fineness is 0.1 d-3.3 d, and the fiber length is 3-10 mm;

the polyester staple fiber comprises a core-sheath polyester fiber and at least one of a drawn polyester fiber and an undrawn polyester fiber;

the basis weight of the non-woven fabric is 3-40 g/m ² ，

The converted air permeability in a state of overlapping 40 sheets is 6.0 seconds or less,

tensile strength ratio [ (tensile strength in MD direction + tensile strength in CD direction)/basis weight]Is 0.035 kN/m/(g/m) ² ) The above.

(effects of the invention)

According to the present invention, a sheet-like nonwoven fabric having a low basis weight and excellent secondary processability can be obtained.

Detailed Description

The present invention will be described below with reference to the embodiments. The following embodiments are examples only, and the invention is apparent from the description of the claims.

The sheet-like nonwoven fabric of the present invention is expected to be, for example, the following embodiments: after the plating process, an adhesive is applied in various forms, and the adhesive is applied to an industrial application (hereinafter, a sheet-like nonwoven fabric may be referred to as an "industrial substrate") to be attached to a final product and assembled. In this embodiment, it is assumed that tension is applied not only in the MD direction but also in the CD direction perpendicular thereto, and when the basis weight is reduced, the present inventors focused on increasing the total strength in the MD direction+cd direction per unit basis weight to a predetermined value or more, and completed the present invention.

The present invention relates to a wet nonwoven fabric based on a papermaking method.

As a typical example of the papermaking method, short fibers, which are a raw material of nonwoven fabric, are uniformly dispersed in water, and then poured onto a wire or between belts to form a fabric. Then, the resultant sheet was squeezed by a roller and dried by a drying means (dryer) to evaporate the water, thereby obtaining a uniform sheet. Thereafter, the adhesion between fibers is improved by a thermal casting process. The wet method facilitates the formation of a film of the wet nonwoven fabric, and the wet nonwoven fabric is excellent in uniformity, durability, strength, and porosity (void ratio).

As described above, the wet nonwoven fabric is used as a substrate for an electromagnetic wave shielding material and a substrate for an adhesive tape, and these substrates are thin in thickness, but in addition to the high (tensile) strength, the former substrate is often required to be sufficiently fixed for plating, and the latter substrate is often required to be sufficiently impregnated with an adhesive. In addition, since the electromagnetic wave shielding material is used by coating an adhesive on one side or both sides after plating processing, adhesive permeability may be required even in the electromagnetic wave shielding material application.

In general, drawn fibers are used in combination with undrawn polyester fibers. In general, only undrawn fibers are used, and the thickness is easily adjusted by collapsing the fibers during the thermal calendering treatment, and the void ratio is adjusted by controlling the thickness of the drawn fibers, thereby obtaining a thin nonwoven fabric.

However, when a hot-calendering treatment is performed on an undrawn polyester fiber in order to obtain a high-strength nonwoven fabric, the fiber tends to collapse due to the high heat and high pressure treatment, and the void ratio tends to be low.

In the embodiment of the present invention, the core-sheath polyester fiber is used as an essential component. The core (core) of the core-sheath polyester fiber has a high melting point of about 260 ℃ and the sheath (sheath) has a low melting point of about 110 to 150 ℃.

As a result, since the sheath portion is melted and the core portion is not melted by the hot-calendering treatment at a temperature exceeding 110 ℃, the fiber shape can be ensured, and as a result, a nonwoven fabric having a high void ratio and high strength can be obtained.

Therefore, the wet nonwoven fabric according to the embodiment is useful as an electromagnetic wave shielding material, an industrial base material such as an adhesive tape or an adhesive sheet, and the like. Further, an embodiment of a conductive sheet formed by adhering an industrial substrate subjected to plating processing can also be employed.

< polyester fiber >

In an aspect of the present invention, a polyester staple fiber (hereinafter, also referred to as "polyester fiber") includes a core-sheath polyester fiber and at least one of a drawn polyester fiber and an undrawn polyester fiber.

Therefore, there are cases where one of the drawn polyester fiber and the undrawn polyester fiber is contained and both are contained. These fibers, when compared to the core-sheath structure, may also be referred to as single structure fibers. Further, dtex (dtex) of the fineness is also sometimes abbreviated as "d".

The material of the embodiment is not particularly limited as long as it is a polyester, and for example, a polyester fiber composed of polyethylene terephthalate, polybutylene terephthalate, polyethylene glycol succinate, a polyethylene glycol-dicarboxylic acid polycondensation system such as polybutylene succinate, polylactic acids such as polylactic acid and polylactic acid, and polylactates can be used. Among these materials, polyethylene terephthalate having excellent balance between various functional surfaces such as heat resistance and weather resistance and price surfaces is particularly preferable.

Drawn polyester staple fibers have a high melting point and vary considerably in thickness from 0.06 to 8.0 d. By using drawn fibers, the fibers are not deformed during heat treatment such as wet papermaking and hot-press-ironing, and therefore, the high void ratio can be maintained, and the thickness can be controlled by the combination of the fibers.

The undrawn polyester fiber, which is pressed and bonded to each other at the time of heat treatment, is advantageous in terms of thickness reduction because the fiber is easily deformed.

Conversely, when an undrawn polyester fiber is blended to a high degree for obtaining high strength or is subjected to a heat treatment at a high temperature and high pressure, permeability is impaired, and there is a limit to specific development in terms of an industrial substrate such as a substrate for electromagnetic wave shielding material and an adhesive tape substrate.

According to the embodiments, as described below, the main advantages of using a core-sheath polyester fiber having a core portion and a thermoplastic sheath portion as a sheet are presented.

(1) The core-sheath structure is such that the outer sheath portion thereof melts by heat, thereby exhibiting adhesiveness. Therefore, the core-sheath structure is welded and hardened in the paper-making step, whereby the fibers can be strongly adhered to each other. Further, since the core of the fiber remains without melting, the tensile strength can be improved while maintaining the fiber shape and the gaps between the fibers.

(2) The sheet thickness is difficult to decrease, and the density becomes comparatively low.

Since many gaps exist, in the case of a substrate as an electromagnetic wave shielding material, plating is likely to penetrate into the interior, and a large amount of coating film can be formed, and thus the conductivity is improved (particularly in electroless plating, gaps are increased, and the penetration is increased, which is preferable).

(3) The strength is determined by melting the core and sheath, and exhibits high strength and fiber-fixing properties as compared with the non-drawn polyester fiber which is softened and pressed. Therefore, even in the low basis weight type, the papermaking can be performed while maintaining the void ratio, and in the high basis weight type, even in the low density state, the heat treatment temperature is lowered, and high strength can be obtained.

(4) Since the melting point of the sheath portion is low, the thickness can be adjusted by hot rolling even after plating.

That is, the thickness may be adjusted to a desired thickness by the user by performing the hot-pressing process after the plating process.

(5) Since the core-sheath polyester fiber has very good adhesion and a portion that becomes the skeleton of the core, it can be made into paper without stretching the polyester fiber.

(6) Since the melting point of the sheath portion of the core-sheath fiber is very low at 110 ℃, a high-strength sheet can be produced even without hot rolling, and the fiber is less likely to be dehaired. In the hot-press-ironing, a very wide range of temperatures from 110 ℃ or higher of the sheath melting point to less than 260 ℃ or lower of the core melting point can be selected for the machining, and the hot-press-ironing is preferable because the density and strength can be easily adjusted. In general, since the undrawn fiber has a softening temperature of 150 ℃ or more and a melting point of 230 to 260 ℃, a temperature of 150 ℃ or more is required, whereas in order to improve strength by press bonding, a higher temperature and pressure are required, and thus the void ratio decreases inversely. The hot-dip casting may be performed after the plating process.

The polyester staple fiber in the embodiment preferably has a fineness of 0.1d to 3.3d (d=dtex) and a fiber length of 3 to 10mm.

The same type of polyester fiber among the polyester-based short fibers can be blended with 2 or 3 or more different types of polyester fibers for at least one of fineness and fiber length.

Among them, the undrawn polyester fiber is particularly preferably one having a fineness of 0.2d to 1.4d and a fiber length of 3 to 5mm.

The drawn polyester fiber is particularly preferably one having a fineness of 0.1d to 3.3d and a fiber length of 3 to 10mm.

In contrast, the core-sheath polyester fiber is particularly preferably one having a fineness of 0.2d to 3.3d and a fiber length of 3 to 10mm. Further preferably, the fineness is 1.1d to 1.7d, and the fiber length is 3 to 5mm.

The core-sheath polyester fiber mainly determines the fiber structure of the nonwoven fabric, in particular, the void ratio and the air permeability.

The blending ratio of the core-sheath polyester fiber, the drawn polyester fiber and the undrawn polyester fiber can be set in the following range.

[ core-sheath polyester fibers: drawn and/or undrawn polyester fibers ] = preferably 10:90 to 90:10, particularly preferably 30:70 to 60:40.

The undrawn polyester fiber is preferably 0% to less than 50%. If the blending amount is too high, the gap collapses during heat treatment, and the void fraction decreases. However, when an undrawn polyester fiber is blended, the elongation and heat resistance of the fiber sheet are improved, and the fiber sheet is hardly broken during the heating process in the secondary processing.

The basis weight of the nonwoven fabric of the embodiment is preferably 3.0 to 40.0g/m ² Particularly preferably 5.0 to 15.0g/m ² . Except for low basis weight 3.0-10.0 g/m ² In addition to the nonwoven fabric of (2), the high basis weight is 12.0-40.0 g/m ² The nonwoven fabric of (a) can be easily produced.

As the thickness, a suitable nonwoven fabric can be used, for example, a nonwoven fabric having a thickness of 7 to 120 μm can be obtained, based on the relationship between the application and the basis weight.

The converted air permeability in a state of 40 sheets being stacked is 6.0 seconds or less, and particularly preferably 2.0 seconds or less. The lower limit of the air permeability is preferably 0.10 seconds.

The core-sheath polyester fiber will be further described.

As described above, the core-sheath polyester fiber is particularly preferably one having a fineness of 0.2d to 3.3d and a fiber length of 3 to 10mm. Further preferably, the fineness is 1.1d to 1.7d, and the fiber length is 3 to 5mm.

When the fineness of the core-sheath structure is smaller (lower) than the above range, the void ratio between fibers becomes low, and there is a possibility that the permeability of the plating or adhesive may be lowered. Conversely, when the fineness of the core-sheath structure dimension exceeds the above range, the winding of the fibers becomes small, the strength becomes low, or the papermaking property is deteriorated, and there is a possibility that the papermaking cannot be performed.

The length of the core-sheath structure is preferably 3mm to 10mm, more preferably 3mm to 5mm. When the length of the core-sheath structure dimension is less than the above range, the tensile strength is lowered because the fibers become shorter. In contrast, when the fineness of the core-sheath structure is more than the above range, the dispersibility of the core-sheath structure in water may be lowered, and there is a possibility that the strength may be lowered due to twisting and poor molding.

The melting point of the sheath portion in the dimension of the core-sheath structure is preferably 110℃or more and 150℃or less. When the melting point of the sheath portion is less than (less than) the above range, the fibers may adhere to the dryer during paper making of the base material, and productivity may be lowered. Conversely, if the melting point of the sheath portion exceeds the above range, the sheath portion does not melt and the fibers are not adhered in the drying step at the time of papermaking of the base material, and therefore the base material may not have sufficient tensile strength.

The core of the core-sheath structure may be made of the same material as that of the drawn fiber, and has a melting point of about 230 to 260 ℃. When the melting point of the core is less than the above range, the core-sheath structure is melted in its entirety in the heat treatment step of the base material, and there is a possibility that the tensile strength of the base material is lowered or the base material becomes film-like and voids between fibers are reduced, so that the permeability of the adhesive is deteriorated.

In an embodiment, the thermal bonding may be performed by wet papermaking or a thermal calendering process. The adhesive component is thermally melted by a thermal drying or thermal calendering process to produce thermal adhesion.

The conditions of hot rolling can be exemplified as follows, but are not limited to these conditions.

The temperature of the heating roller in the thermal casting treatment is preferably 110 ℃ or higher and 260 ℃ or lower. When the temperature of the heating roller is less than 110 ℃, there is a problem that the adhesion of the fibers to each other is insufficient and the strength is not developed. In contrast, when the temperature of the heating roll exceeds 260 ℃, the wet nonwoven fabric may adhere to the hot calender roll, and thus the sheet may not be formed.

The temperature of the hot rolling is more preferably 120 ℃ or more and 230 ℃ or less.

In the production method using the hot-calendering, the hot-calendering is performed under conditions of a temperature equal to or higher than the melting point of the sheath portion of the core-sheath polyester fiber and equal to or lower than the melting point of the drawn/undrawn fiber.

In order to develop strength, the pressure (line pressure) in the hot-press-casting treatment is preferably 0 to 250kg/cm, more preferably 80 to 200kg/cm. When the pressure exceeds 250kg/cm, the sheet collapses excessively, and the void fraction decreases. The processing speed is 5m/min or more, thereby improving the working efficiency. The treatment speed is set to 200m/min or less, whereby heat is easily conducted to the wet nonwoven fabric to obtain the actual effect of heat bonding. The number of times of pinching (nip) by heat rolling is not particularly limited as long as it is capable of conducting heat to the wet nonwoven fabric, but in the combination of the metal heating roller and the elastic roller, it may be pinched 2 times or more in order to conduct heat from the front surface and the back surface of the wet nonwoven fabric.

The base material in the embodiment may contain, as a raw material, a fiber including at least one of a core-sheath polyester fiber, a drawn polyester fiber, and an undrawn polyester fiber, or may contain a fiber other than these as a raw material. As the fibers, for example, synthetic fibers such as rayon, polyvinyl alcohol (vinylon), nylon, polyamide, polyolefin, and acrylic ester, and natural pulp fibers such as wood pulp can be used in addition to polyester. The content of the fibers other than the polyester fibers is, for example, 40 mass% or less, and particularly preferably 30 mass% or less.

The definitions in this specification are as follows.

So-called "basis weight (unit: g/m) ² ) The term "is a value measured in accordance with Japanese JIS-P8124.

The "fineness (unit: dtex)" is a value measured in accordance with Japanese JIS-L1095.

The "thickness (unit: μm)" is a value measured in accordance with Japanese JIS-P8118.

The "air permeability (unit: seconds)" is a value measured according to the method described in Japanese JIS-P8117. However, in the case of 1 sheet, the measurement time is short and measurement cannot be performed, and therefore, measurement is performed in a state of 40 sheets being stacked.

The "tensile strength (unit: kN/m)" is a value measured in accordance with Japanese JIS-P8113.

The "void fraction" is a value calculated as 100- (density/polyester density (=1.38))%.

The air permeability of the base material in the embodiment is preferably 6.0 seconds or less, more preferably 2.0 seconds or less. The lower limit of the air permeability is preferably 0.10 seconds. If the air permeability is above the above range, the air permeability is poor, and there is a possibility that the plating and adhesive permeability may deteriorate. The air permeability can be adjusted by adjusting the basis weight, the type of the raw material fiber, fineness, blending amount, temperature and pressure during the calendering process, and the like.

For example, considering the application to the "industrial substrate" described above, or breakage in the step of producing a sheet-like nonwoven fabric until the final product, it is desirable that both the MD direction and CD direction have high tensile strength and a tensile strength ratio [ (tensile strength in MD direction+tensile strength in CD direction)/basis weight]Is 0.035 kN/m/(g/m) ² ) The above is particularly preferably 0.040 kN/m/(g/m) ² ) Above and 0.20 kN/m/(g/m) ² ) The following is given.

For example, the tensile strength ratio is less than 0.035 kN/m/(g/m) ² ) In the case of (2), the workability is low. If the tensile strength ratio is low, not only the sheet will move due to the tension during the plating processIn the moving direction, there is a possibility that shrinkage occurs in the width direction to cause dimensional change. In the case of using the adhesive after the plating process in the "industrial substrate" described above, it is necessary to suppress the dimensional change, and it is necessary to set the desired strength ratio in consideration of the strength in the longitudinal direction and the transverse direction.

The MD direction (machine direction) tensile strength of the sheet-like nonwoven fabric substrate is preferably 0.15kN/m or more and 2.0kN/m or less, more preferably 0.20kN/m or more and 1.3kN/m or less. When the tensile strength is less than the above range, the substrate tends to stretch and break easily, and the processability and handleability are lowered. Conversely, when the tensile strength of the base material exceeds the above range, the density becomes high, and there is a possibility that the permeability of the plating and the adhesive may be lowered.

The CD direction (transverse direction) tensile strength of the sheet-like nonwoven fabric substrate is preferably 0.03kN/m or more and 1.8kN/m or less, more preferably 0.03kN/m or more and 1.8kN/m or less. When the tensile strength is less than the above range, there is a possibility that dimensional change occurs in the plating process and the adhesive coating step or in use after coating. Conversely, when the tensile strength of the base material exceeds the above range, the base material may become thicker and there is a concern that the strength in the machine direction may be lowered. The cross direction alignment is a case of assuming strength or more, the basis weight becomes too high, and the paper thickness becomes high. It is also considered that the fiber alignment is a cause of the side face, and there is a possibility that the strength in the longitudinal direction is lowered.

The MD (machine direction) tensile strength of the sheet-like nonwoven fabric substrate and the CD (transverse direction) tensile strength of the sheet-like nonwoven fabric substrate can be adjusted by adjusting the basis weight, the type of raw material fiber, fineness, length, adjustment of the amount of the raw material fiber, adjustment of the temperature and pressure during the calendering process, and the like.

Examples (example)

The effects of the present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples.

Polyester fibers obtained from Di human Fu Rui Ten Co., ltd were used as raw materials for the preparation shown in Table 1 to produce wet nonwoven fabrics. Also, a part of the wet nonwoven fabric was treated at the hot-calendering temperature shown in table 2.

TABLE 1

Examples and comparative examples include examples in which one of the undrawn polyester fiber and the undrawn polyester fiber is not used.

In the comparative example, the effect of the present invention is clearly shown by comparison with the example not including the core-sheath polyester fiber.

For each example, the evaluations shown in table 2 were carried out.

In consideration of the use of the electromagnetic wave shielding material, ni/Cu-based plating was performed in electroless plating and electrolytic plating, and electromagnetic wave shielding properties were evaluated based on the permeability of the plating. The evaluation criteria are shown below.

(evaluation criterion)

Good electromagnetic wave shielding performance can be obtained by judging that the permeability into the substrate and the workability are high.

Delta, it was determined that the permeability into the substrate and workability were slightly low, and the electromagnetic wave shielding property was poor.

It was determined that the permeability into the substrate and the workability were low, and the electromagnetic wave shielding performance was not satisfied.

In addition to the adhesive tape application, the electromagnetic wave shielding material application is also required to be related to the penetrability of the plating solution and the penetrability of the adhesive. The substrate of the electromagnetic wave shielding material is assembled by applying Ni/Cu plating to a wet nonwoven fabric substrate, and then applying an adhesive to the plated substrate to form a single-sided or double-sided adhesive tape. Since the permeability evaluation by the adhesive also becomes a permeability evaluation of the plating, the permeability evaluation is performed by the adhesive described below.

A propylene-based adhesive (product name: corponil 5411 manufactured by Japanese synthetic chemical industry Co., ltd.) was coated on the film at a thickness of 100. Mu.m,then, the coated base material was placed on the adhesive coated surface of the film, and the film having no adhesive applied thereto was placed on the surface of the coated base material opposite to the film having the adhesive applied thereto, thereby forming a test body. The test body was sandwiched by glass plates and measured by a micrometer at 50kg/m ² The thickness of the test piece after the press-bonding was evaluated for adhesive permeability by the following criteria.

(evaluation criterion)

Permeability = [ thickness of test body before pressing (film thickness of upper and lower 2 sheets + thickness of base material paper + thickness of adhesive coating) -thickness of test body after pressing ]/thickness of base material paper × 100% (v/v)

The permeability is 40% or more.

The permeability is 20% or more and less than 40%.

The permeability was not more than 20%.

The results are shown in table 2. Further, comparative example 6 shows an example in which paper cannot be made.

TABLE 2

From the results shown in table 2, it is found that the test pieces of the examples were sheet-like nonwoven fabrics, which tended to have low basis weights and good secondary processability.

In each of examples and comparative examples, fibers composed of 2 or 3 types of core-sheath PET (polyethylene terephthalate) fibers, and drawn PET fibers and undrawn PET fibers were dispersed in water by a attritor (pulper) and adjusted to a slurry having a concentration of 0.5 to 1.0%. The slurry is wet (cylinder or inclined wire) and dried using a yankee dryer (about 110-130 ℃) and the fibers are welded to each other. The sheet is processed by hot-pressing at 110-230 ℃ under a line pressure of 80-200 kg/cm and a speed of 5-200 m/min to obtain an industrial substrate.

[ Industrial applicability ]

The present invention relates to a sheet-like nonwoven fabric, which is usually used as a base material (i.e., as a main body), and is subjected to a plating treatment and an adhesion treatment, and further subjected to other treatments or combined with other materials as needed. Therefore, the sheet-like nonwoven fabric of the present invention may be used as a secondary processing or may be used in combination with other materials to form a composite.

Claims

1. A sheet nonwoven fabric, characterized in that:

the basis weight of the non-woven fabric is 3-40 g/m ² ，

2. The sheet-like nonwoven fabric according to claim 1, wherein the polyester staple fibers comprise core-sheath polyester fibers, and stretched polyester fibers and unstretched polyester fibers.

3. The sheet-like nonwoven fabric according to claim 1, wherein the amount of the core-sheath polyester fiber blended is 10 mass% or more.

4. The sheet-like nonwoven fabric according to any one of claims 1 to 3, wherein the sheet-like nonwoven fabric is used as an electromagnetic wave shielding material.

5. The sheet-like nonwoven fabric according to any one of claims 1 to 3, wherein the industrial substrate is an adhesive sheet material.