JPH0544149A - Non-oriented nonwoven fabric and its production - Google Patents

Abstract

PURPOSE:To provide a non-oriented nonwoven fabric having excellent properties as a sound-absorbing material and electromagnetic wave-absorbing material. CONSTITUTION:Short fibers of <=20mm long are subjected to wet paper-making process to obtain a nonwoven fabric. In the above process, the slurry is frothed, the paper-making process is carried out in a state containing the short fibers dispersed on the surface of the bubble and the produced paper-like sheet is defoamed and dehydrated. Since the obtained nonwoven fabric is almost free from steric orientation, there is no directivity of the sound absorption and electromagnetic wave absorption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a non-oriented non-woven fabric (hereinafter abbreviated as NWF) which is particularly excellent as a sound absorbing material for a music hall, a sound absorbing material for a speaker box, or an electromagnetic wave absorbing material. Regarding

[0002]

2. Description of the Related Art As a NWF manufacturing method, as a dry method, long fibers are put into a carding machine or a garnet machine to form webs, which are stacked in parallel or intersecting each other, or an irregularly arranged web using air flow. Generally, the method of manufacturing by dipping or spraying this in an adhesive solution, drying, and heat treatment is used.However, the orientation of the fibers cannot be partially biased, and the orientation (fiber orientation in the plane direction) is inevitable. Therefore, when a non-oriented NWF is required, the wet papermaking method is often used.

This method mainly uses short fibers of about 20 mm or less, and disperses the short fibers in an aqueous solution of sodium acrylate, carboxymethyl cellulose, Trolo mallow, etc.
Known methods include papermaking, dehydration, drying and heat treatment, or a method in which a water-soluble polymer is dissolved or thermosoftening fibers are mixed and heat-treated to fix. Although this method can overcome the partial deviation of the fiber orientation found in the dry method, the planar orientation is still dominant,
A non-oriented NWF could not be obtained in three dimensions.

[0004]

In the NWF obtained by the conventional wet papermaking method, short fibers are randomly oriented in a plane, which is a great improvement over the dry method, but in the vertical direction. Since it has almost no orientation, it still retains its directionality when used as an absorber of sound waves and electromagnetic waves.
Since it is inevitable that sound absorption and electromagnetic wave absorption are greatly affected depending on the incident angle, the development of NWF having no orientation in three dimensions has been required.

The present invention is an electromagnetic wave absorber for a car, a personal computer, a word processor, a television, a cordless telephone (including a car telephone), a computer-controlled machine tool, etc. which itself generate electromagnetic waves and are affected by the electromagnetic waves. The purpose of the present invention is to develop an efficient manufacturing method of NWF in which fibers that are preferable as a sound absorbing material such as a shield material, a music hall, and a speaker are three-dimensionally non-oriented.

[0006]

The present invention has a length of about 20 m.
In developing NWF, which is characterized in that short fibers of m or less are arranged in a non-oriented state in the plane direction and the vertical direction, and further, in producing NWF by a wet papermaking method, short fibers are contained. By developing a method for producing a three-dimensionally non-oriented NWF by foaming a papermaking liquid, dispersing the short fibers on the surface of the air bubbles, papermaking this, and defoaming and dehydrating the same, Achieved

The short fibers used in the present invention include N
The type and thickness of the material differ depending on the intended use of the WF.
Generally speaking, non-oriented NWF such as simple soundproofing material, sound absorbing material, and cushioning material is preferable, as well as filter cloth, vinyl leather or artificial leather base cloth, wall material for industrial use, diapers, napkins. NWF used in ordinary fields such as household NWF such as sheets and sheets is made of organic or inorganic short fibers. Of these, different materials should be selected as a matter of course, when it is not hygroscopic and when hygroscopicity is required. Short fibers made of a synthetic resin having a low melting point and having a property as a binder can be used as a mixed paper material.

Further, when NWF is used as an electromagnetic wave absorber or shield, it is necessary to mix metallized fibers or metal fibers with at least a portion of the short fibers. In this case, the metalization of the fibers is carried out by electroless plating, sputtering, coating or the like of inorganic material fibers or organic material fibers, but electroless plated fibers have the best performance and are easy to manufacture.

As can be seen from the above, the fibers used in the method of the present invention are not particularly limited in terms of material, and examples of organic materials include polyolefins such as polyethylene and polypropylene, polyesters, polyamides, vinyl chloride, polyacrylonitrile. , Fibers from thermoplastic resins such as polyvinyl chloride and aramid, fibers from thermosetting resins such as kinol, natural fibers such as cotton and wool, and semi-synthetic fibers. Examples of the inorganic type include glass fiber and carbon fiber. Metal fibers include iron, copper, stainless steel, steel and the like. As the metallized fibers, there are those obtained by electrolessly plating synthetic resin-based, inorganic material-based, etc. short fibers, and further, a combination of these short fibers, especially for electromagnetic wave shielding, metal fibers or metallized fibers are essential components. In this, a blend of organic and inorganic short fibers is used.

The short fibers that can be used have a length of about 20 mm or less, preferably about 5 mm, in order to maintain the non-oriented nature of the NWF. Although not critical, when staple fibers longer than 20 mm are used, they tend to be oriented in the plane direction in the papermaking process, the vertical orientation is small, and non-orientation (randomness) is reduced. When the length is too short, the randomness tends to improve, but since the properties as NWF are lost, short fibers of about 5 mm are preferable.

Water is used as a medium in the papermaking liquid of the present invention. Anionic surfactants such as alkylbenzene sulfonates and alkyl sulfonates as a foaming agent, cationic surfactants which are quaternary ammonium compounds, and polyoxyethylene nonyl which is an adduct of ethylene oxide. Although it is operationally advantageous to use a nonionic surfactant such as phenyl ether or poly (oxyethylene-oxypropylene) copolymer, an anionic surfactant is preferable from the viewpoint of cost and foaming property. It is not necessary to limit the type because it defoams during papermaking.

Further, in order to improve the stability of the foam, polyvinyl alcohol, carboxymethyl cellulose, trolooi, water-dispersible polymer emulsion, water-soluble thermosetting resin prepolymer or the like is used as a thickener (also as a binder in some cases). Add and use.

Polyvinyl alcohol and water-soluble thermosetting resins (prepolymers such as phenol resin, melamine resin, urea resin) are used to melt or fuse short fibers in a heat treatment process of NWF. Carboxymethylcellulose, Troloois, etc. exhibit adhesive strength just by drying and can be used as a binder.

In the present invention, a papermaking liquid containing a filler having a diameter larger than the short fiber diameter and having a particle diameter of 1/2 or less, preferably 1/10 or less, of the target NWF thickness. It is that the non-orientation property of the short fibers can be further enhanced by mixing and using

The material of the filler is NW, as is the case with short fibers.
The material can be widely changed depending on the purpose of use of F, but when it is desired to use it as a binder, polyethylene having a low melting point, ethylene-vinyl acetate copolymer, vinyl chloride or the like can be used for the purpose of bulkiness. Examples thereof include a crushed product or a cut product of a foam of a thermoplastic or thermosetting resin, or a simple crushed product of a resin. When it is a non-equipment, it is possible to use aerated lightweight aggregate such as pearlite perlite and vermiculite, and crushed products such as anti-fire stone or sand. These fillers need to be dispersed on the surface of the bubbles together with the short fibers when the foaming liquid is foamed, and thus help the non-orientation of the three-dimensional structure of the short fibers by uniformly dispersing them in the short fibers, When used as a binder, it has the function of adhering short fibers.

The amount of the filler mixed depends on the type and shape of the short fibers used, the type and amount of the foaming agent, the thickener, the binder, the filler, etc., the desired properties of the NWF, etc. However, in the case of a property that is well compatible with short fibers, an amount exceeding about 10 times by weight can be blended, but in some cases, there is a limit of about 5 times by weight. Although this limit can be confirmed by a simple experiment, it can greatly affect the properties of the target NWF and should be appropriately selected depending on the application.

A papermaking liquid consisting of water, short fibers, surfactants, thickeners and optionally fillers is then foamed. As a foaming method, any method such as blowing air into the liquid or stirring may be used, but it is preferable to use both of them together. By appropriately selecting the short fibers, the surfactant and the thickener, the short fibers and the filler can be dispersed on the cell surface.

This bubble portion is transferred onto a cloth or the like and left to wait for defoaming, or defoaming is performed by using pressure such as pressurization or suction to obtain a short fiber laminate. It can be pressed, dehydrated and dried to be bonded with a room temperature adhesive such as carboxymethyl cellulose, troloy mallow, polyvinyl alcohol to obtain NWF, or a low melting point thermoplastic resin (polyethylene, ethylene-vinyl acetate copolymer,
When mixed with fibers or fillers (such as polyvinyl), it may be heated to a temperature above its melting point to bond, or, if a water-soluble thermosetting resin is mixed, at a temperature above its curing temperature. You may heat-process and adhere.

Alternatively, after making a laminate not containing these adhesives and impregnating it with a water-soluble thermosetting resin, latex emulsion, thermoplastic resin emulsion, etc., heat treatment or heat treatment with a low melting point is carried out. It is also possible to laminate by laminating with a plastic film, followed by heat treatment and adhesion, or by laminating a molten resin by pressing, press-fitting or the like.

No matter which binder is used for the adhesion method, when the short fibers are dispersed on the cell surface and then the paper is made into paper, a NWF produced by a usual papermaking method from a papermaking liquid in which the short fibers are dispersed is used. In comparison, the orientation in the three-dimensional direction is small, and a more uniform NWF can be obtained.

[0021]

In order to produce a non-oriented NWF which is desired as a sound absorbing material, an electromagnetic wave absorbing material or an electromagnetic wave shielding material, fibers are suspended and dispersed on the surface of bubbles, the bubbles are scooped, and then the bubbles are defoamed and laminated. It has been found that by forming a body, NWF can be obtained in which the fibers are not only oriented in the plane direction but also three-dimensionally. In this method, the randomness of the orientation is high as compared with the case where the papermaking liquid is scooped up (may be sprinkled) on the filtration surface.

Further, the filler used for enhancing the non-orientation property (in some cases, the effects such as bulkiness and adhesiveness can be expected) has the effect of facilitating the orientation of the short fibers in the thickness direction, Further, the filler remains even when the laminate is press-molded, and the three-dimensional structure of the fiber is easily maintained around the filler. Furthermore, since there is a filler, when a binder such as a water-soluble thermosetting resin, rubber latex, or resin emulsion is impregnated, it is effective in impregnating a large amount of binder.

[0023]

【Example】

Example 1 Acrylic short fibers having a thickness of 16 μm and a length of 5 mm were degreased at 80 ° C. with a dilute hydrochloric acid aqueous solution and then with a dilute caustic soda aqueous solution at the same temperature, washed with water and dried. 5g of this at 95 ℃
/ L of hydrochloric acid-acidic stannous chloride solution for 10 minutes for sensitizing treatment, and then 0.1% palladium chloride at the same temperature.
The activation treatment was performed by immersing in a g / l aqueous solution for 10 minutes.
This pretreated acrylic short fiber is an electroless plating bath (pH 5, nickel acetate hexahydrate 30 g / l, sodium acetate 10 g / l, sodium hypophosphite 10 g / l).
Bath temperature 90 ℃), nickel plating layer thickness 0.3
A metal-plated short fiber having a thickness of 0.5 μm (not a plate having a uniform thickness) was obtained.

10 g of this nickel-plated short fiber, 1000 g of water, sodium alcohol sulfonate (Riboran PJ 400; Lion Corporation) as a surfactant, and polyvinyl alcohol were mixed in the proportions shown in Table 1 to prepare a papermaking solution. , Stir this to make it foam, and have a basis weight of 10
A bubble portion was transferred onto the cloth with a target of 0 g / m ² and left to defoam. Then, scissors with 60 mesh wire mesh, pressure 3
It was pressed at Kg / cm ² and dehydrated to obtain a nonwoven fabric (1).
Next, this non-woven fabric (1) is heated at 120 ° C. and a pressure of 50 Kg / cm.
^It was hot pressed at ² for 20 minutes to obtain a nonwoven fabric (2) (electromagnetic wave shielding material). The orientation structure of the short fibers of the non-woven fabric was obtained by observing the cut surface and the non-woven fabric surface under a microscope. This sheet was tested for electromagnetic wave shielding properties using a TR4131 electromagnetic shielding test device manufactured by Advantest. The electromagnetic wave shield test was carried out by wrapping the sample with a polypropylene sheet and wrapping the sample with a metal copper foil and grounding the measuring device. The results are shown in Table 1.

[0025]

The short fibers of the non-woven fabric (1) and non-woven fabric (2) to which a foaming agent and a thickener are added are randomly oriented not only in the plane direction but also in the direction perpendicular thereto (three-dimensional direction). There is. That is, in Experiment Nos. 1 and 5, the short fibers are random in the plane direction when viewed from the upper surface, but it is found that the cut fibers are hardly oriented in the vertical direction when the cut surface is observed. On the other hand, it is understood that the nonwoven fabrics of Experiment Nos. 2 to 4 are not only random in the plane direction, but also the short fibers are sufficiently randomized in the cut surface. Although it is not clear how it will be affected by the electromagnetic wave shielding test, it is not oriented when the measuring instrument is completely insulated with a polypropylene sheet and when the measuring instrument contact part is wrapped in copper foil and electrically connected to the measuring instrument. The non-woven fabric of No. 2 had almost no difference in the electromagnetic wave shielding effect, whereas the two-dimensionally randomly oriented non-woven fabric showed a large difference in the shielding effect.

Example 2 In 1000 g of water, 10 g of the nickel-plated acrylic short fibers used in Example 1, 0.5 g of ribolane PJ 400, 5 g of polyvinyl alcohol and Niijima anti-firestone (Neosand 6 as a filler) were used.
No. 32 to 150 mesh) in the proportions shown in Table 2, and in the same manner as in Example 1, a nonwoven fabric (1) and a nonwoven fabric (2) were produced. The electromagnetic wave shield test was conducted in an insulating state wrapped with a polypropylene sheet.

[0028]

By incorporating the filler, the structure of the non-woven fabric becomes more three-dimensionally non-oriented. This effect is recognized when the mixing time of the papermaking liquid is short. This is presumed to be effective when it is difficult to uniformly stir using a large tank.

(Example 3) Synthetic pulp (polyethylene, SWP-E790, fiber length) of linter pulp, glass fiber (20 μmφ, length about 15 mm) and metal fiber (material, thickness 5 μmφ, length 15 mm) were used as short fibers. 1.6
mm, manufactured by Mitsui Petrochemical Co., Ltd.) with an equal weight of 10 g,
Polyvinyl alcohol 5g, Ribolane PJ400
Disperse and dissolve 0.5 g of water in 1000 g of water, and add 1 part of ethylene-vinyl acetate copolymer (EVA) as a filler.
What was crushed after foaming 0 times (200 μm or less)
And anti-fire stone (Neosand 6) were blended, and sufficiently foamed in the same manner as in Example 1 and paper-made to obtain a nonwoven fabric (2). The tactile sensation at this time and the apparent specific gravity by cutting out and measuring the weight were measured.

[0031]

From the above results, it cannot be determined that the filler is in an appropriate amount (the kind of the fiber, the material of the filler, etc., so that it cannot be determined, but the filler is equal weight or more to the fiber, 5 to 1).
It can be seen that a non-oriented NWF having a porous and excellent tactile sensation is obtained when it is blended (weight of 0 times or less).

[0033]

The NWF produced by the method of the present invention is
Almost no fiber orientation is recognized, and there is no difference in sound absorption, electromagnetic wave absorption, and electromagnetic wave shieldability depending on the incident angle by selecting the material, so conventionally there is no choice but to design based on the minimum value depending on the incident angle. However, since it is almost homogeneous and has high performance, it has an advantage that the shield wall thickness can be thin. Of course, it is an excellent NWF that can be used for conventional NWF applications.

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Claims (6)

[Claims] 1. A non-woven fabric characterized in that short fibers having a length of about 20 mm or less are arranged in a non-oriented state in the plane direction and the vertical direction. 2. When producing a non-woven fabric by a wet papermaking method, a papermaking liquid containing short fibers is foamed, the short fibers are dispersed on the surface of the bubbles, and the paper is made into paper, defoamed and dehydrated. Non-oriented non-
Woven fabric manufacturing method. 3. The non-oriented paper according to claim 2, wherein a papermaking liquid containing a short fiber and a filler having a diameter larger than the diameter of the short fiber and not more than ½ of the thickness of the target non-woven fabric is used. Non-woven fabric manufacturing method. 4. A method for producing a non-oriented non-woven fabric, wherein a non-woven fabric having a binder of a thermoplastic resin or a thermosetting resin produced by the method of claim 2 is welded or fused by hot pressing. .. 5. A non-aligned non-woven fabric produced by impregnating and / or welding or fusing a non-woven fabric produced by the method according to claim 2 with a binder of a thermoplastic resin or a thermosetting resin. Method. 6. A non-oriented non-oriented paper according to claim 2, which is a papermaking liquid containing at least short fibers, a foaming agent and a thickening agent.
Woven fabric manufacturing method.