JP2004060096A - Nonwoven fabric and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonwoven fabric constituted of a silicon carbide-based inorganic fiber and produced by a melt blowing method; and to provide its production method. <P>SOLUTION: The nonwoven fabric produced by the melt blowing method is constituted of the silicon-carbide-based inorganic fiber. The nonwoven fabric is obtained by using the melt blowing method, melting an organosilicon polymer, extruding the melted product from a spinning nozzle, jetting heated nitrogen gas from surroundings of the spinning nozzle to spin the organosilicon polymer, gathering the spun fiber on a receiver arranged at the lower part of the spinning nozzle to form a nonwoven fabric, subjecting the nonwoven fabric to infusible treatment, and heating and firing the treated nonwoven fabric. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nonwoven fabric made of a silicon carbide-based inorganic fiber and manufactured by a melt blow method, and a method for manufacturing the same. More specifically, the present invention relates to a nonwoven fabric composed of silicon carbide-based inorganic fibers having high tensile strength of 2N or more and excellent workability, and a method for producing the same.
[0002]
[Prior art]
Conventionally, as interest in environmental conservation has increased, there has been a demand for catalysts and filters for purifying harmful substances such as nitrogen oxides generated from automobiles and industrial plants, and filters made of silicon carbide inorganic fibers have been put into practical use. I have.
However, when a nonwoven fabric is to be produced from the silicon carbide-based inorganic fiber by the needle punch method, a problem occurs that a nonwoven fabric having sufficient strength cannot be obtained due to the breakage of the fiber or a non-uniform basis weight. was there. In particular, when a nonwoven fabric is processed into a filter or the like, excellent workability is required.
On the other hand, conventionally, the silicon carbide-based inorganic fiber has been produced by melt spinning, and its fiber diameter is about 8 to 15 μm, and it has been difficult to produce a finer fiber by a conventional method.
This is because in the melt spinning method, the spinning polymer is discharged from a nozzle and wound at a high speed to reduce the fiber size.However, the strength of the spun fiber itself is low, and as the diameter becomes smaller, the fiber becomes thinner. The strength per one becomes extremely small. On the other hand, the tension at the time of spinning increases as the fiber diameter becomes thinner, that is, as the winding speed increases, so that the tension eventually exceeds the strength of the fiber and yarn breakage occurs, so that stable spinning cannot be performed. .
[0003]
[Problems to be solved by the invention]
An object of the present invention is to solve the above problems and to provide a nonwoven fabric made of a silicon carbide-based inorganic fiber having a fiber diameter of 8 μm or less produced by a melt blow method and having excellent workability, and a method for producing the same. And
[0004]
[Means for Solving the Problems]
That is, the present invention relates to a nonwoven fabric produced by a melt blow method, wherein the nonwoven fabric is composed of silicon carbide-based inorganic fibers.
[0005]
In addition, the present invention uses a melt blow method to melt the organosilicon polymer, discharge the melt from a spinning nozzle, and spout by blowing heated nitrogen gas from around the spinning nozzle to spin the lower portion of the spinning nozzle. A nonwoven fabric is formed by collecting spun fibers in a receiver arranged in a nonwoven fabric, and then the nonwoven fabric is infusibilized and then heated and fired.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
The nonwoven fabric in the present invention is constituted by silicon carbide based inorganic fibers.
Examples of the silicon carbide-based inorganic fiber include, for example, Si-CO fiber represented by Nicalon (registered trademark, manufactured by Nippon Carbon) or Si-Ti represented by tyrano fiber (registered trademark, manufactured by Ube Industries) or A silicon carbide-based inorganic fiber having the same composition as the Zr-CO fiber is exemplified.
[0007]
Further, the silicon carbide-based inorganic fiber in the present invention is selected from the group consisting of Group 2, Group 3, and Group 4 metal atoms, and the temperature at which the free energy change in the carbon reduction reaction of the oxide becomes a negative value, Use of a silicon carbide fiber containing a metal element whose temperature is higher than the temperature at which the free energy change in the carbon reduction reaction of silicon oxide becomes negative and having an oxygen content in the range of 1 to 13% by weight. You can also. Since the silicon carbide fiber has excellent heat resistance, it is suitable when the nonwoven fabric is used at a high temperature.
[0008]
The weight ratio of the constituent elements in the silicon carbide fiber is such that oxygen atoms are 1 to 13%, silicon atoms are usually 35 to 70%, and carbon atoms are usually 20 to 40%. Examples of the metal atom include Be, Mg, Ca, Sr, Ba, Sc, Y, Th, U, Al, Zr and Hf.
[0009]
The content ratio of the metal atom depends on the coordination number of the metal, but is preferably an amount capable of capturing at least 5% or more of the oxygen contained in the fiber. The method for calculating the amount of metal atoms in this ratio will be described below.
M is a metal atom, and its coordination number is W,
When Si: C: O: M = a: b: c: d (molar ratio), the amount of metal atoms sufficient to capture at least 5% or more of the total amount of oxygen in the fiber can be calculated by the following equation. it can.
d ≧ c × 0.05 / W (however, d ≦ c / W)
Here, assuming that the atomic weight of M is m, the weight ratio of M is represented by the following equation.
M (% by weight) = (d × m) / (a × 28.09 + b × 12.01 + c × 16.00 + d × m)
[0010]
Since the silicon carbide-based inorganic fiber in the present invention is manufactured by a melt blow method, the average fiber diameter is 1 to 20 μm, preferably 1 to 8 μm, more preferably 2 to 6 μm, and is manufactured by a conventional melt spinning method. Can be made thinner than the fibers to be made. As a result, the surface area of the fiber becomes larger than that of the conventional fiber, so that when used as a filter, the collection efficiency increases.
[0011]
Furthermore, since the nonwoven fabric of the present invention is manufactured by the melt blow method, the fibers are compared with those obtained by forming a nonwoven fabric by a needle punch method from short fibers having a length of about 40 to 50 μm manufactured by a conventional melt spinning method. It will be long. As a result, the nonwoven fabric has high strength and has sufficient pleating workability when processed into a filter or the like. Specifically, the nonwoven fabric obtained by the needle punch method has a tensile strength of at most about 1N, whereas the nonwoven fabric of the present invention has a high tensile strength of 2N or more.
The tensile strength is obtained by performing a tensile test in a length direction on a test piece having a width of 5 cm and a length of 20 cm, and measuring a load until the nonwoven fabric is broken.
[0012]
Next, a method for producing the nonwoven fabric of the present invention will be described.
In the present invention, using a melt blow method, the organosilicon polymer is melted, and the melt is discharged from a spinning nozzle, and heated nitrogen gas is spouted from around the spinning nozzle to spin. A nonwoven fabric is formed by collecting the spun fibers in an arranged receiver, and then infusifying the nonwoven fabric, followed by heating and firing to obtain a nonwoven fabric.
[0013]
The organosilicon polymer (hereinafter referred to as a precursor polymer) is not particularly limited, and polycarbosilane, polysilazane, polysiloxane, polysilastyrene, methylchloropolysilane, and the like are used. Further, the organosilicon polymer may contain a metal element such as boron, titanium, zirconium, and aluminum.
[0014]
For example, the temperature at which the free energy change in the carbon reduction reaction of the oxide is selected to be a negative value is selected from the group consisting of the above-described Group 2, Group 3, and Group 4 metal atoms. In the case of a silicon carbide fiber containing a metal element having a higher temperature than the temperature at which the energy change becomes negative, and having an oxygen content in the range of 1 to 13% by weight, the precursor polymer is as follows: It is manufactured as follows.
[0015]
The organosilicon polymer can be prepared by adding 15 parts by weight or less of phenyl group-containing polyborosiloxane to 100 parts by weight of polysilane in an inert gas, or heating the polysilane as it is, usually for 2 to 25 hours. The heating temperature is usually in the range of 250 to 500 ° C., and the organosilicon polymer is mainly composed of a carbosilane (—Si—CH ₂ —) bonding unit and a polysilane (—Si—Si—) bonding unit, and has a silicon side chain. Has a group selected from the group consisting of a hydrogen atom, a lower alkyl group, an aryl group, a phenyl group and a silyl group. The ratio of carbosilane units to polysilane units in the organosilicon polymer is usually from 100: 5 to 2,000. The number average molecular weight of the organosilicon polymer is usually from 200 to 10,000.
[0016]
The above-mentioned polysilane is, for example, a chain or cyclic polymer obtained by subjecting one or more kinds of dichlorosilane to a dechlorination reaction with sodium according to the method described in "Chemistry of Organosilicon Compounds" by Kagaku Dojin (1972). It is. The number average molecular weight of the polysilane is usually from 300 to 1,000. In the present specification, the polysilane includes a polysilane partially having a carbosilane bond, which is obtained by heating the above-mentioned chain or cyclic polysilane to a temperature in the range of 400 to 700 ° C.
[0017]
The phenyl group-containing polyborosiloxane is prepared, for example, by a dehydrochlorination condensation reaction between boric acid and one or more diorganochlorosilanes according to the methods described in JP-B-53-42330 and JP-B-53-50299. Can be. The number average molecular weight of the phenyl group-containing polyborosiloxane is generally from 500 to 10,000.
[0018]
To the organosilicon polymer, one or more compounds selected from the above-mentioned metal alkoxides, acetylacetoxy compounds, carbonyl compounds, cyclopentadienyl compounds and amine compounds are added, and heated and reacted in an inert gas. Prepare a precursor polymer. Those skilled in the art can easily determine the amount of the metal compound to be added based on the above-mentioned calculation formula. The heating temperature is usually from 250 to 350C, and the heating time is generally from 1 to 10 hours.
[0019]
In the present invention, a spun fiber is obtained from the precursor polymer by a melt blow method.
That is, the precursor polymer is melted by a melt-blowing method, and the melt is discharged from a spinning nozzle, and heated nitrogen gas is spouted from the periphery of the spinning nozzle to spin the fiber, and then spun into a receiver arranged below the spinning nozzle. A nonwoven fabric is formed by collecting the fibers.
[0020]
The diameter of the spinning nozzle is usually about 100 to 500 μm. The nitrogen gas ejection speed is about 30 to 300 m / s, and the higher the speed, the thinner the fibers. The heating temperature of the nitrogen gas is not particularly limited as long as a desired spun fiber is obtained, but the nitrogen gas heated to about 500 ° C. is usually blown out.
Conventionally, in a general melt blow method, air is used as a jet gas, but nitrogen must be used to spin the precursor polymer of the present invention. By using nitrogen as the jet gas, spinning can be stably performed.
[0021]
Further, in the present invention, when the precursor polymer is spun and the spun fibers are collected in a receiver arranged below the spinning nozzle, suction is performed from the lower side of the receiver using a suctionable receiver. It is preferable to perform while performing. By suction, the fibers are effectively entangled, and a high-strength nonwoven fabric is obtained. The suction speed is preferably in the range of about 2 to 10 m / s.
[0022]
Next, the obtained spun fiber is infusibilized to prepare an infusible fiber.
The infusibilization treatment is usually performed in an oxygen-containing atmosphere. Examples of the gas constituting the oxygen-containing atmosphere include air, oxygen, and ozone. The infusibilization temperature is 50 to 300 ° C., and the infusibilization time depends on the infusibilization temperature, but is usually several minutes to 30 hours.
Further, an infusibilization method using an electron beam or γ-ray may be employed.
[0023]
Next, the infusibilized fiber is preheated in an inert atmosphere to prepare a preheated fiber. Examples of the gas constituting the inert atmosphere include nitrogen and argon. The heating temperature is usually from 150 to 800 ° C., and the heating time is from several minutes to 20 hours. Preheating the infusibilized fiber in an inert atmosphere prevents the incorporation of oxygen into the fiber, further promotes the crosslinking reaction of the polymer constituting the fiber, and maintains excellent elongation of the infusibilized fiber. The sintering in the final step can be stably performed with good workability.
[0024]
Finally, the pre-heated fiber is subjected to heat treatment in an inert gas atmosphere such as argon or a reducing gas atmosphere such as hydrogen at a temperature in the range of 1000 to 1900 ° C. Is obtained.
[0025]
Although there is no particular limitation on the basis weight and thickness of the nonwoven fabric of the present invention, a nonwoven fabric having a basis weight of 50 to 500 g / m ² and a thickness of 0.5 to ²⁰ mm is usually used. May be laminated.
Since the nonwoven fabric of the present invention has a high tensile strength of 2N or more and has sufficient pleating property when processed into a filter or the like, it can be formed into a desired shape. The nonwoven fabric of the present invention is used, for example, as a filter for removing harmful substances. The filtration performance can be adjusted by adjusting the basis weight of the nonwoven fabric. The filter shape may be a flat shape, or may be various shapes such as a cylindrical shape, an envelope shape, and a conical shape.
[0026]
【Example】
Hereinafter, the present invention will be described with reference to examples.
Reference Example 1
2.5 L of anhydrous toluene and 400 g of metallic sodium were placed in a 5 L three-necked flask, heated to the boiling point of toluene under a nitrogen gas stream, and 1 L of dimethyldichlorosilane was added dropwise over 1 hour. After completion of the dropwise addition, the mixture was heated under reflux for 10 hours to produce a precipitate. This precipitate was filtered, washed first with methanol, and then washed with water to obtain 420 g of white powdery polydimethylsilane.
Reference Example 2
By heating 750 parts of diphenyldichlorosilane and 124 parts of boric acid at 100 to 120 ° C. in n-butyl ether under a nitrogen gas atmosphere, and further heating the resulting white resinous material at 400 ° C. in vacuum for 1 hour. And 530 parts of a phenyl group-containing polyborosiloxane.
[0027]
Example 1
To 100 parts of the polydimethylsilane obtained in Reference Example 1, 1 part of the phenyl group-containing polyborosiloxane obtained in Reference Example 2 was added, and thermally condensed at 380 ° C. for 10 hours in a nitrogen gas atmosphere to obtain a number average molecular weight of 1700. Was obtained. 10 parts of tetrabutoxytitanium was added to a xylene solution in which 100 parts of the organosilicon polymer was dissolved, and a cross-linking reaction was performed at 320 ° C. under a nitrogen gas stream to obtain polytitanocarbosilane.
This polytitanopolycarbosilane was charged into a spinning apparatus, melted at 225 ° C., discharged from a spinning nozzle having a diameter of 300 μm, and nitrogen gas heated to 500 ° C. from the periphery of the spinning nozzle at about 50 m / s. The spun fibers were spouted at a high speed and spun, and a spun fiber was collected in a receiver arranged below the spinning nozzle while sucking the spun fibers from the lower side of the receiver at a suction speed of about 5 m / s to form a nonwoven fabric.
The obtained nonwoven fabric was heat-treated at 170 ° C. for 1 hour in the air to make it infusible, and further heated at 300 ° C. for 10 hours in nitrogen for preheating, and then heat-treated at 1300 ° C. in nitrogen. A nonwoven fabric made of silicon carbide based inorganic fibers was obtained.
[0028]
The chemical composition of the inorganic fibers (average diameter: 5 μm) constituting the obtained nonwoven fabric is as follows: Si: 54%, C: 31%, O: 12.6%, Ti: 2%. Si: C: O: Ti = 1: 1.34: 0.41: 0.02.
The basis weight of the obtained nonwoven fabric was 100 g / m ² , and the thickness was 1 mm. A test piece having a width of 5 cm and a length of 20 cm was cut out from this nonwoven fabric, and a tensile test was performed in the length direction. As a result, the tensile strength was 5N.
[0029]
Comparative Example 1
After melt-spinning the polytitanocarbosilane obtained in Example 1 at 225 ° C., it is heat-treated in air at 170 ° C. for 1 hour to prepare an infusible fiber. C. for 10 hours to obtain preheated fibers. This preheated fiber was heat-treated at 1300 ° C. in nitrogen to prepare an inorganic fiber.
[0030]
The chemical composition of the obtained inorganic fiber (average diameter: 10 μm) is Si: 54%, C: 31%, O: 12.6%, Ti: 2%. O: Ti = 1: 1.34: 0.41: 0.02.
[0031]
The obtained inorganic fibers were converted into short fibers having a length of 50 mm, and then needle punched to obtain a nonwoven fabric made of inorganic fibers having a basis weight of 100 g / m ² and a thickness of 1 mm.
A test piece having a width of 5 cm and a length of 20 cm was cut out from this nonwoven fabric and subjected to a tensile test in the length direction. As a result, the tensile strength was 1N.
[0032]
Example 2
To 100 parts of the polydimethylsilane obtained in Reference Example 1, 10 parts of the phenyl group-containing polyborosiloxane obtained in Reference Example 2 was added, and thermally condensed at 350 ° C. in a nitrogen gas atmosphere to obtain a carbosilane unit and a siloxane unit. And an organosilicon polymer having a ratio of 100: 0.93 was obtained. 3.5 parts of zirconium (tetravalent) acetylacetonate was added to a xylene solution in which 100 parts of the organosilicon polymer was dissolved, and a cross-linking reaction was carried out at 320 ° C. under a stream of nitrogen gas to convert polyzirconocarbosilane. Prepared.
This polyzirconocarbosilane is charged into a spinning apparatus, melted at 240 ° C., discharged from a spinning nozzle having a diameter of 300 μm, and nitrogen gas heated to 500 ° C. from the periphery of the spinning nozzle at a speed of about 50 m / s. , And spun, and a spun fiber was collected in a receiver arranged below the spinning nozzle while sucking the spun fiber from the lower side of the receiver at a suction speed of about 5 m / s to form a nonwoven fabric.
The obtained nonwoven fabric was heat-treated at 160 ° C. for 1 hour in the air to make it infusible, then further preheated by heating at 300 ° C. for 10 hours in nitrogen, and then heat-treated at 1450 ° C. in nitrogen. A nonwoven fabric made of silicon carbide based inorganic fibers was obtained.
[0033]
The chemical composition of the inorganic fibers (average diameter: 5 μm) constituting the obtained nonwoven fabric was Si: 55.5%, O: 9.8%, C: 34.1%, and Zr: 0.6%. .
The basis weight of the obtained nonwoven fabric was 100 g / m ² , and the thickness was 1 mm. A test piece having a width of 5 cm and a length of 20 cm was cut out from this nonwoven fabric, and a tensile test was performed in the length direction. As a result, the tensile strength was 5N.
[0034]
Comparative Example 2
The polyzirconocarbosilane obtained in Example 2 was melt-spun at 240 ° C., and then heat-treated at 160 ° C. for 1 hour in air to prepare infusible fibers. C. for 10 hours to obtain preheated fibers. This preheated fiber was heat-treated at 1450 ° C. in nitrogen to prepare an inorganic fiber.
[0035]
The chemical composition of the obtained inorganic fibers (average diameter: 10 μm) was 55.5% for Si, 9.8% for O, 34.1% for C, and 0.6% for Zr.
[0036]
The obtained inorganic fibers were converted into short fibers having a length of 50 mm, and then needle punched to obtain a nonwoven fabric made of inorganic fibers having a basis weight of 100 g / m ² and a thickness of 1 mm.
A test piece having a width of 5 cm and a length of 20 cm was cut out from this nonwoven fabric and subjected to a tensile test in the length direction. As a result, the tensile strength was 1N.
[0037]
Example 3
To a xylene solution of 100 parts of an organosilicon polymer obtained in the same manner as in Example 2, 8 parts of aluminum tributoxide was added, and a crosslinking reaction was carried out at 290 ° C. under a stream of nitrogen gas to obtain polyaluminocarbosilane.
This polyzirconocarbosilane is charged into a spinning apparatus, melted at 255 ° C., discharged from a spinning nozzle having a diameter of 300 μm, and nitrogen gas heated to 500 ° C. from the periphery of the spinning nozzle at a speed of about 50 m / s. , And spun, and a spun fiber was collected in a receiver arranged below the spinning nozzle while sucking the spun fiber from the lower side of the receiver at a suction speed of about 5 m / s to form a nonwoven fabric.
The obtained nonwoven fabric was heat-treated at 160 ° C. for 1 hour in the air to make it infusible, then further preheated by heating at 300 ° C. for 10 hours in nitrogen, and then heat-treated at 1300 ° C. in nitrogen. A nonwoven fabric made of silicon carbide based inorganic fibers was obtained.
[0038]
The chemical composition of the inorganic fibers (average diameter: 5 μm) constituting the obtained nonwoven fabric was Si: 55.2%, O: 9.8%, C: 34.3%, and Al: 0.55%. .
The basis weight of the obtained nonwoven fabric was 100 g / m ² , and the thickness was 1 mm. A test piece having a width of 5 cm and a length of 20 cm was cut out from this nonwoven fabric, and a tensile test was performed in the length direction. As a result, the tensile strength was 5N.
[0039]
【The invention's effect】
Since the nonwoven fabric of the present invention is manufactured by a melt-blowing method, the length of the fiber is longer than that of a nonwoven fabric manufactured by a conventional melt spinning method and having a length of about 40 to 50 μm as a nonwoven fabric by a needle punch method. It becomes. As a result, the nonwoven fabric has a high tensile strength of 2N or more and has excellent workability when processed into a filter or the like, so that it can be formed into a desired shape.
Further, since the silicon carbide-based inorganic fibers constituting the nonwoven fabric of the present invention are manufactured by a melt blow method, the average fiber diameter is 1 to 8 μm, which is thinner than fibers manufactured by a conventional melt spinning method. can do. As a result, the surface area of the fiber becomes larger than that of the conventional fiber, so that when used as a filter, the collection efficiency increases.
[Brief description of the drawings]
FIG. 1 is a schematic view of a spinning apparatus used for producing a nonwoven fabric by a melt blow method in the present invention.

Claims (7)

What is claimed is: 1. A nonwoven fabric produced by a melt blow method, wherein the nonwoven fabric is constituted by silicon carbide based inorganic fibers. The nonwoven fabric according to claim 1, wherein the nonwoven fabric has a tensile strength of 2N or more. 3. The nonwoven fabric according to claim 1, wherein the average fiber diameter of the silicon carbide inorganic fibers is 1 to 8 [mu] m. The temperature at which the silicon carbide-based inorganic fiber is selected from the group consisting of metal atoms belonging to Group 2, Group 3, and Group 4 and whose free energy change in the carbon reduction reaction of the oxide is negative is determined by the carbon reduction of silicon oxide. A silicon carbide fiber containing a metal element whose temperature is higher than the temperature at which the free energy change in the reaction becomes negative, and having an oxygen content in the range of 1 to 13% by weight. Item 4. The nonwoven fabric according to any one of Items 1 to 3. Using a melt blow method, the organosilicon polymer is melted, and the melt is discharged from a spinning nozzle, and heated nitrogen gas is spouted from the periphery of the spinning nozzle for spinning. The nonwoven fabric according to claim 1, which is obtained by forming a nonwoven fabric by collecting spun fibers, then subjecting the nonwoven fabric to an infusibilization treatment, and then heating and firing the resulting nonwoven fabric. Using a melt blow method, the organosilicon polymer is melted, and the melt is discharged from a spinning nozzle, and heated nitrogen gas is spouted from the periphery of the spinning nozzle for spinning. The method for producing a nonwoven fabric according to claim 1, wherein the nonwoven fabric is formed by collecting the spun fibers, and then the nonwoven fabric is infusibilized and then heated and fired. 7. The method for producing a nonwoven fabric according to claim 6, wherein when collecting the spun fibers in the receiver, suction is performed from below the receiver.

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