JP2007023440A - Method for producing conductive nonwoven fabric - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a conductive nonwoven fabric which is a nonwoven fabric consisting essentially of synthetic fibers, having ≤10% mixing ratio of carbon fibers and usable for detecting water leakage sites of waterstop sheets in industrial waste disposal sites in a usual production process of nonwoven fabrics. <P>SOLUTION: The method for producing the conductive nonwoven fabric is carried out as follows. Chopped fibers of the carbon fibers are mixed with general-purpose synthetic fiber staples in (1/99) to (10/90) mass ratio and opened and a plurality of the resultant card webs are laminated and pre-punched by a needle punching method. A plurality of pre-punched laps obtained by the previous punching are further laminated and then subjected to finish punching by the needle punching method. In the method, electrical resistance between two points separated by a prescribed distance is measured on the pre-punched laps prepared by the previous punching and the pre-punched laps having the measured value within a prescribed range are fed to the next step and subjected to the finish punching in the method for producing the conductive nonwoven fabric. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for producing a conductive nonwoven fabric in which a small amount of carbon fiber is mixed into a synthetic fiber. The obtained conductive nonwoven fabric is used by being sandwiched between, for example, a waterproof sheet laid in a waste disposal site. Used to detect water leakage due to sheet damage.

As a water leakage detection system for a waste disposal site, the following Patent Document 1 discloses that a plurality of water leakage detection electrodes are arranged at a predetermined interval between two upper and lower water shielding sheets. It is disclosed that a semiconductive material sandwiched or encased in contact is sandwiched, and as this semiconductive material, a conductive non-woven fabric or cushion material, or a conductive cloth made of a metal-plated fiber is used. Illustrated.
JP 2000-202392 A

On the other hand, as a conductive nonwoven fabric, it is known to mix conductive carbon fibers or copper-plated fibers into general-purpose fibers such as polyester fibers and polypropylene fibers. For example, Patent Document 2 below discloses a conductive nonwoven fabric composed of 75 to 97% by mass of polyacrylonitrile-based carbon fibers and 25 to 3% by mass of cellulose. However, the nonwoven fabric sandwiched between the water-impervious sheets at the industrial waste disposal site can withstand long-term use in an industrial waste disposal site where the conditions of use are severe, so that the basis weight is 1 kg / m ² and the thickness is about 10 mm. It is not economically allowed to mix more than 10% of expensive carbon fiber because it is required to be durable and has a large use area of 10,000 square meters or more per laying.
JP 2004-353124 A

And it is necessary to uniformly disperse the carbon fiber in the nonwoven fabric, and to uniformly arrange the conductivity of the nonwoven fabric in each part, but the commercially available carbon fibers are in the form of strands of thousands to tens of thousands of synthetic fiber filaments Since it is carbonized and then hardened with a sizing agent, it is difficult to open the fiber even if it is cut into a length of about 50 mm for a non-woven fabric to make a chopped fiber. Therefore, the mixing amount is set to 10% or less. In some cases, uniform dispersion became more difficult. In addition, in Patent Document 3 below, in order to uniformly disperse the carbon fiber, it is disclosed that the carbon fiber and the polypropylene fiber are separately opened, then both are mixed, and then the second opening is performed. However, this method cannot be used for a conductive nonwoven fabric for detecting a water leakage location because the carbon fiber breaks and shortens when the chopped fiber of the carbon fiber is opened alone, resulting in a decrease in conductivity.
JP 2004-43985 A

The present invention is a non-woven fabric mainly composed of synthetic fibers and having a carbon fiber mixing ratio of 10% or less, and the carbon fibers are uniformly dispersed and the electric conductivity is uniform in each part. For example, in an industrial waste disposal site It is possible to manufacture a conductive nonwoven fabric that can be used for detecting a water leakage location of a water shielding sheet in a normal nonwoven fabric manufacturing process.

The process for producing a conductive nonwoven fabric according to the present invention is obtained by mixing chopped fibers of carbon fibers and staples of general-purpose synthetic fibers such as polyester fibers and polypropylene fibers at a mass ratio of 1/99 to 10/90 and opening the fibers. A conductive nonwoven fabric in which a plurality of card webs are laminated, subjected to preliminary punching by a needle punch method, and finish punching is performed by needle punching on one or a plurality of laminates of pre-pan wrap obtained by this preliminary punching In this manufacturing method, the electrical resistance between two points separated by a predetermined distance on the pre-bread wrap obtained by the preliminary punch is measured, and the pre-bread wrap whose measured value is within the predetermined range is sent to the next process and finished. It is characterized by punching.

The carbon fiber used in the present invention has a fiber diameter of 5 to 10 μm and a length of 30 to 80 mm, and is used in the form of a commercially available chopped fiber in which thousands to tens of thousands of fibers are hardened with a sizing agent. This chopped fiber is easy to open depending on the quality and amount of sizing agent used by the manufacturer and application. At this stage, by measuring the electric resistance of the plastic pan wrap, the conductivity of the product nonwoven fabric obtained by finish punching can be predicted, and at the same time, it can be known whether or not the fiber opening is sufficient. In other words, when the chopped fiber is easy to disperse and its opening is easy, the carbon fiber is uniformly dispersed in the non-woven fabric to improve the conductivity of the non-woven fabric. When it is difficult, the chopped fiber is left unopened sufficiently, and the carbon fiber is biased to reduce the conductivity of the product nonwoven fabric.

Therefore, chopped fibers and general-purpose synthetic fiber staples are supplied onto a lattice conveyor at a predetermined mixing ratio, opened to produce a card web, and a plurality of the obtained card webs are laminated and pre-punched. A non-woven fabric having a desired conductivity can be obtained by measuring the electrical resistance of the pre-pan wrap and using the pre-pan wrap having a measured value in a predetermined range and applying a finishing punch to the pre-pan wrap. . And the needle density of the needle punch in the pre-pan wrap is remarkably low compared to the one subjected to the finish punch only for the preliminary punch, so the pre-pan wrap whose electric resistance is out of the predetermined range is It is possible to return to the previous process, perform re-fibering, process it into a card web again, and laminate it to make a pre-pan wrap. On the other hand, after the finishing punch is applied, the finishing punch is added to the preliminary punch, and the finishing punch is performed from both the front and back surfaces, the needle density is greatly increased, and the fibers are strongly entangled. Even if the conductivity is insufficient, even if it is returned to the previous process and resumed, the carbon fiber is damaged more and the conductivity is further reduced. Therefore, reuse by the resumed fiber is impossible. .

In the present invention, the mixing ratio of the carbon fiber and the general-purpose fiber is set to 1/99 to 10/90, preferably 1/99 to 5/95 by mass ratio. If this mass ratio is less than 1/99, the conductivity is insufficient, and if it exceeds 10/90, the conductivity tends to be excessive, and it is not economical for detecting a leaking point in a waste disposal site. Then, the carbon fiber and the general-purpose fiber are mixed by feeding on the lattice conveyor at the above ratio, and then opened by a normal opening device, preferably a normal opening device using a fair note. Then, it is sent to a card via a hopper feeder to form a card web, and 20 to 40 card webs are stacked, and a preliminary punch is applied by a needle punch method to obtain a pre-pan wrap. The basis weight of the pre-pan wrap is preferably 150 to 400 g / m ² , and the needle density of the preliminary punch is preferably 10 to 30 / cm ² .

In the present invention, as described above, the electrical resistance of the pre-pan wrap is measured, and the pre-pan wrap selected by the measured value is sent to the next process, and one of them is used or a predetermined number of layers are laminated, and then the needle Finished by punching and commercialized. In this case, the basis weight of the nonwoven fabric to be the product is set as appropriate according to the use, but the basis weight for the purpose of detecting the water leakage location of the water shielding sheet is preferably 0.3 to ² kg / m ^2. The thickness is preferably 3 to 20 mm. The finishing punch is preferably performed at a needle density of 10 to 30 needles / cm ² from both the front and back sides. When the needle density is insufficient, the nonwoven fabric is insufficient in strength. Cause damage. And as mentioned above, when a pre-pan wrap having an electric resistance of 100 to 1500 Ω is selected and one sheet is used, or a plurality of sheets are laminated and finished punched to produce a product, the resulting conductive nonwoven fabric is obtained. It was confirmed that when the electrical resistance was measured by a method similar to that of pre-pan wrap, the measured value was within a desired resistance value of 50 to 900 Ω and satisfied the market demand.

In addition, the commercially available chopped fiber can be used by selecting a fiber that is easy to open, in which case the occurrence rate of pre-pan wrap that is insufficient in opening and insufficient in conductivity is greatly reduced, Prepan wrap productivity is improved. However, it is not necessary to use only chopped fibers that pass this selection criterion, and even chopped fibers that deviate from this selection criterion can be mixed within the limits where the electrical resistance of the pre-pan wrap falls within a predetermined range.

The method for selecting the chopped fiber that is easy to open is arbitrary, and a chopped fiber, that is, a rod-like carbon fiber bundle in which several thousand to several tens of thousands of carbon fiber staples are aligned in parallel and hardened with a sizing agent, is fingered. A method of judging by the spread width by pinching and rolling, a method of overlapping round bars on chopped fibers placed on a flat plate, rolling them while applying a predetermined pressure, and judging by the spread width Or, a predetermined amount of the chopped fiber of carbon fiber is put into a container of a predetermined volume, the compressed air of a predetermined pressure is blown from a pipe of a predetermined size for a predetermined time, and the fiber is made into a cotton to increase the apparent volume, The method of judging from this apparent volume is exemplified, but according to the experiment of the present inventors, the method of blowing compressed air has few errors due to individual differences, Preferable from the viewpoint of excellent current property.

As a method of blowing the compressed air, 2 g of carbon fiber chopped fiber is put into a 1 L flask, and a pipe having an inner diameter of 4 mm and a length of 30 cm is inserted into the flask. Is preferably sprayed onto the chopped fiber for 1 second to disperse the chopped fiber, and the fiber is opened to increase the apparent volume, and the determination based on the apparent volume (hereinafter referred to as “determination method A”) is preferable. The apparent volume selection criterion is set to 50 cc or more, preferably 80 cc or more, and most preferably 100 cc or more. When the apparent volume is less than 50 cc, sufficient opening cannot be performed in a normal opening process. Therefore, when processed into a pre-pan wrap, desired conductivity cannot be obtained at a carbon fiber mixing ratio of 10% or less.

In the present invention, the electrical resistance between two points separated by a predetermined distance is measured on the pre-pan wrap obtained by the preliminary punch, and the pre-pan wrap whose measured value is within the predetermined range is selected and used. To do. Specifically, the above pre-pan wrap is overlaid on an insulating plate, two plate-like electrodes are placed on the pre-pan wrap at a predetermined interval, and the electrical resistance between the two electrodes is measured. If the area is small, the variation in the length of the carbon fibers cannot be covered, and the measurement error becomes large. On the other hand, if the area is large, the electrode plate becomes heavy and handling becomes inconvenient. In addition, when the surface is light, the surface contact with the nonwoven fabric is insufficient, the measured value is not stable, and when it is heavy, handling is inconvenient. If the distance between the electrode plates is narrow, the variation in the measured value becomes large. On the other hand, if the distance is wide, the sample becomes large and wasted.

In particular, for the purpose of detecting the leak location of a water shielding sheet laid in an industrial waste disposal site, an electrode having a diameter of 100 mm and a mass of 600 g made of a stainless steel plate is used as the above electrode, and the distance between the two electrodes is set to be the same. A method of setting to 1 m (hereinafter referred to as “determination method B”) is preferable. In this case, there is little variation in measured values, and determination is easy. Further, the stainless steel plate is preferable in that the surface hardly rusts and the measurement variation is small. And the criterion based on the electrical resistance of the pre-pan wrap used for the above purpose is set to 100 to 1500Ω, preferably 200 to 900Ω. When the electrical resistance is less than 100Ω or more than 1500Ω, it is difficult to obtain a product nonwoven fabric that satisfies market requirements.

The method for producing a conductive nonwoven fabric according to the present invention is suitable for detecting a leak location of a water shielding sheet in an industrial waste disposal site while using a commercially available chopped fiber as a carbon fiber and reducing the mixing ratio to 1 to 10%. A conductive non-woven fabric can be produced. In addition, since the pre-pan wrap excluded in the measurement of the electrical resistance of the pre-pan wrap can be returned to the previous step and resumed and used, there is no waste of fiber raw materials including carbon fibers. In particular, in the invention according to claim 2, the generation ratio of the pre-pan wrap whose conductivity is insufficient due to insufficient opening is greatly reduced, and the productivity of the pre-pan wrap is improved. Moreover, the invention which concerns on Claim 3 can manufacture an electroconductive nonwoven fabric, determining the opening property of the said chopped fiber efficiently and correctly. Moreover, the invention which concerns on Claim 4 can manufacture an electroconductive nonwoven fabric, determining the electroconductivity required in order to detect the water leak location of the water shielding sheet in an industrial waste disposal site efficiently.

A chopped fiber having a good opening property is selected from the commercially available chopped fibers composed of thousands to tens of thousands of carbon fibers (fiber diameter: 5 to 10 μm, length: 30 to 80 mm) by the determination method A. Then, the chopped strand and the polyester fiber or polypropylene fiber staple (fineness of 1 to 10 d, fiber length of 30 to 100 mm) that have passed this judgment method A are 1/99 to 10/90, preferably 1/99 to 5/95. Is supplied to a lattice conveyor at a mass ratio of 1, through a normal opening process using a fair note, supplied to a card via a hopper feeder, 20 to 40 obtained card webs are stacked, and needles are formed by a needle punch method. A preliminary punch with a density of 10 to 30 pieces / cm ² is applied to prepare a pre-pan wrap with a basis weight of 150 to 400 g / m ² . Next, the electrical resistance of the pre-pan wrap is measured by the above-described determination method B, and one of the pre-pan wraps that has passed the determination method B is supplied directly to the needle punch machine, or 2 to 6 sheets are stacked. A finish punch having a needle density of 10 to 30 / cm ² is applied from the front and back, respectively, to produce a conductive nonwoven fabric having a basis weight of 0.3 to 2.0 kg / m ² and a thickness of 3 to 20 mm.

Example 1
A sample is collected from a commercially available chopped fiber consisting of 12,000 acrylic carbon fibers (fiber diameter: 7 μm, fiber length: 50 mm) at a rate of 2 g per lot, and the openability of this sample is determined according to the above-described determination method. Tested with A, a lot with an apparent volume of 110 cc was selected. The obtained chopped fiber of carbon fiber and polyester fiber staple (fineness: 3d, fiber length: 51 mm) are supplied onto a lattice conveyor at a mass ratio of 2/98, and passed through a normal opening process including a fair note. The resulting card web was put on a card machine via a hopper feeder, 28 sheets were laminated, and pre-punched with a needle density of 28 needles / cm ² by a needle punch machine to make a pre-pan wrap with a basis weight of 340 g / m ² . When the electrical resistance of this pre-pan wrap was measured by the above-mentioned determination method B, the resistance value was 480Ω.

Next, four pre-pan wraps were overlaid, and a finish punch having a needle density of 22 / cm ² was applied from the front and back surfaces by the needle punch method, to obtain a nonwoven fabric having a basis weight of 1.2 kg / m ² and a thickness of 12 mm. When the electrical resistance of this nonwoven fabric was measured by the above-mentioned determination method B, the resistance value was 85Ω, which was within the product standard of 50 to 900Ω for a water leakage point detection system in an industrial waste disposal site.

Example 2
In Example 1 described above, the nonwoven fabric of Example 2 was manufactured in the same manner as Example 1 except that a chopped fiber of carbon fiber having an apparent volume of 55 cc after 1 second according to Determination Method A was used. In Example 2, the electrical resistance of the pre-pan wrap according to the determination method B was 620Ω, and the resistance value of the product nonwoven fabric was 140Ω, which passed the product standard.

Comparative Example 1
In the above Example 1, a nonwoven fabric of Comparative Example 1 was produced in the same manner as in Example 1 except that a carbon fiber chopped fiber having an apparent volume of 20 cc after 1 second according to the determination method A was used. In Comparative Example 1, the electrical resistance of the pre-pan wrap according to the determination method B was remarkably large as 3680Ω, and the resistance value of the product nonwoven fabric was 1030Ω, which exceeded the product standard.

Comparative Example 2
In Example 1 above, the same fiber as in Example 1 except that a garnet type is used for the opening process in order to obtain good opening, and the card web is manufactured by opening the fiber while applying a strong force to the fiber. The nonwoven fabric of Comparative Example 2 was produced by the method. In this case, breakage of the carbon fiber occurred at the time of opening, so that the electric resistance according to the determination method B was 4450Ω, significantly exceeding the predetermined range, and the electric resistance of the nonwoven fabric was 1140Ω, which also exceeded the product standard.

Claims (4)

A chopped fiber of carbon fiber and staples of general-purpose synthetic fibers such as polyester fiber and polypropylene fiber are mixed at a mass ratio of 1/99 to 10/90, and a plurality of card webs obtained by opening are laminated and needles In the manufacturing method of a conductive nonwoven fabric, a preliminary punch is applied by a punch method, and a finish punch is applied by a needle punch method to one or a plurality of laminates of the pre-pan wrap obtained by the preliminary punch. A conductive nonwoven fabric characterized by measuring electrical resistance between two points separated by a predetermined distance on a pre-prepared wrap and sending a pre-pun wrap having the measured value within a predetermined range to the next process to perform a finishing punch The manufacturing method. Prior to mixing the chopped fiber of carbon fiber and the staple of general-purpose synthetic fiber, the above-mentioned carbon fiber chopped fiber that is easy to open is selected, and the carbon fiber chopped fiber obtained by this selection is combined with the above-mentioned general-purpose synthesis The process for producing a conductive nonwoven fabric according to claim 1, wherein the conductive nonwoven fabric is mixed with fiber staples. A means for selecting a carbon fiber chopped fiber that can be easily opened is charged into a container of a predetermined volume with a predetermined amount of the above-mentioned carbon fiber chopped fiber, and compressed air of a predetermined pressure is sprayed from a pipe of a predetermined size for a predetermined time. The method for producing a conductive nonwoven fabric according to claim 2, comprising increasing the apparent volume and measuring the apparent volume. The electrical resistance of the pre-pan wrap was measured by placing two electrodes of 100 mm in diameter and 600 g in mass on the pre-pan wrap stacked on the insulating plate at an interval of 1 m, and this measured value was 100-1500Ω. The method for producing a conductive nonwoven fabric according to any one of claims 1 to 3, wherein the pre-pan wrap is sent to the next step.