JP3465699B2 - Silica-based composite oxide fiber and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a high-strength silica-based composite oxide fiber having an excellent photocatalytic function, electrical function and / or thermal catalytic function, and a method for producing the same. More specifically, the present invention relates to a fiber having a central portion (silica phase) that bears mechanical properties, an oxide layer of a surface layer that bears various functions, and an oxide phase of a layer in the vicinity thereof, and having a gradient composition toward the surface layer and a method for producing the same.

[0002]

2. Description of the Related Art Regarding the photocatalytic effect of semiconductors represented by titanium dioxide, 19
Much research has been done since the late 70's. Until now, when using the same catalytic function, titania crystal grains have been used by immobilizing them on the substrate, but since many problems have arisen in the bonding method, problems with immobilization have occurred in recent years. There is growing interest in titania fibers.

For example, in Japanese Unexamined Patent Publication (Kokai) No. 5-184923, a sol-like substance prepared by dissolving a titanium alkoxide and a vanadium compound in alcohol and hydrolyzing the mixture is molded into a fibrous shape and then gelled to obtain a gel at 200 to 700 ° C. A method of synthesizing a fiber composed of crystals of anatase-type titania and vanadium oxide by heat treatment in a range is disclosed. In the examples of this publication, fibers containing many silica components in addition to titania and vanadia are mainly described, and the catalytic activity as a woven fabric using these fibers is the same as that of E glass made of silica. Is only shown for a blend of only 20%.

It has been conventionally known that the titania fiber synthesized by the sol-gel method is extremely fragile, and as a study for improving the strength thereof, for example, “Ceramics Association Magazine” Vol. 94 (12), No. Pages 1243 to 1245 (1986) describe coexistence of a silica component. The method described in the above-mentioned embodiment of Japanese Patent Laid-Open No. 5-184923 is exactly the same as this method. Further, Japanese Patent Laid-Open No. 11-5036 discloses a silica-titania fiber for photocatalyst by a sol-gel method and a method for producing the same, but the fiber strength in this case is also extremely low at 0.1 to 1.0 GPa. It was a thing.

In addition to the above, the following reports have been made as a method for producing titania. For example, Journal of
In Material Science Letters 5 (1986) 402-404, hydrochloric acid is allowed to coexist in an alcohol solution of titanium alkoxide, and a colloidal product obtained by hydrolysis is spun, heated in a humidified atmosphere, and then in air. A method for synthesizing a gel-like titania fiber (anatase) by heating is described. Also, The American Ceramic Society Bul
letin, May 1998, 61-65, a viscous fluid prepared by mixing water with fine particles of titania and viscose was formed into a fibrous form, which was then heated and baked in high temperature air. A method for obtaining titania fiber has been reported.

[0006]

Since all of these fibers are made into fibers through the agglomeration process of primary particles of titania, large defects remain inside the fibers, and the photocatalytic function was recognized. However, it is extremely vulnerable, and many problems must be solved before it can be put to practical use. Further, in the system in which a silica component coexists for the purpose of improving strength, since titania and silica are present in a mixed state, it is not possible to obtain sufficient photocatalytic activity as compared with titania alone, which is also practical. It is a big problem that prevents the change.
When using photocatalyst fiber as a filter, it is naturally desirable to have a high fiber strength because it is exposed to a high-speed gas flow for a long time, and in particular, it may be applied to gas discharged from aircraft engines and automobile engines. For example, there is a strong demand for the development of fibers having a high-strength photocatalytic function or thermocatalytic function that exceeds conventional wisdom.

[0007]

The inventors of the present invention have found that a dense and high-strength silica fiber can be obtained by heat-treating a precursor fiber made of an organosilicon polymer and then firing it in air at high temperature. I found it. Then, in the same organosilicon polymer, when a low molecular weight organometallic compound or a reaction product of a low molecular weight organosilicon compound and a low molecular weight organometallic compound coexists, in the heat treatment process after spinning, A low molecular weight substance containing a metal compound component selectively migrates (bleeds out) to the fiber surface, and is fired in air after heat treatment to form an oxide layer derived from the low molecular weight substance (an oxide having a desired catalytic function). It has been found that the layer) is effectively generated on the fiber surface. It has also been found that the fibers obtained by this method are extremely dense and have high strength.

The process of forming silica from an organosilicon polymer as a starting material includes an oxidation process in which a silicon-carbon bond is converted into a silicon-oxygen bond. In this process, a volume increase of about 1.37 times is included. Is expected. This change is 6
Since it is achieved at a relatively low temperature of 00 ° C. or higher, it is considered that the dense silica-based composite fiber was effectively obtained by firing and the above-mentioned high strength could be achieved.

Accordingly, the present invention provides a fiber comprising a composite oxide phase of the oxide phase made mainly of silica component (first phase) and silica other than the metal oxide phase (second phase), the
Those in which the metal oxides that make up the two phases exert a specified function
, And the and relates silica-based composite oxide fiber characterized by existence ratio of at least one metal element of the metal oxide constituting the second phase toward the surface of the fibers is increased inclinatorily Is.

In the present invention, the oxide phase (first phase) containing a silica component as a main component may be amorphous or crystalline, and forms a solid solution or a eutectic point compound with silica. The obtained metal element or metal oxide may be contained. The metal element (A) capable of forming a solid solution with silica or the metal element (B) whose oxide can form a compound having a specific composition with silica is not particularly limited, but, for example, titanium as (A), Examples of (B) include aluminum, zirconium, yttrium, lithium, sodium, barium, calcium, boron, zinc, nickel, manganese, magnesium and iron.

This first phase forms the internal phase of the fibers obtained according to the invention and plays an important role in bearing the mechanical properties. The ratio of the first phase to the whole fiber is 9
It is preferably 8 to 40% by weight, and the target second
In order to fully express the function of the phase and also to express the high mechanical characteristics, the existence ratio of the first phase is 50 to 95.
It is preferable to control within the range of weight%.

On the other hand, the metal oxide constituting the second phase plays an important role in developing the intended function in the present invention, but is selected according to the function. For example, when a photocatalytic or thermal catalytic function is required, titania or its eutectic compound or a substitutional solid solution formed by a specific element is selected, and when piezoelectric characteristics are expected, , Lead / zirconium /
A titanium oxide or the like is selected. When the photocatalytic function or the thermal catalytic function is required, the crystal grain size of the metal oxide constituting the second phase is preferably 15 nm or less, particularly preferably 10 nm or less. The proportion of the second phase constituting the surface layer portion of the fiber varies depending on the type of oxide, but is preferably 2 to 60% by weight, and in order to sufficiently exhibit its function and also to exhibit high strength at the same time. It is preferable to control the content within the range of 5 to 50% by weight.

The abundance ratio of at least one metal element in the metal oxide forming the second phase increases in a gradient toward the surface of the fiber, and the thickness of the region where the composition gradient is clearly recognized. The thickness is preferably controlled in the range of 5 to 500 nm, but the inclined region is about 1/3 of the fiber diameter.
May extend to In the present invention, the first phase and the second phase
"Abundance ratio" of a phase means the metal oxide of the first phase and the metal oxide of the second phase, that is, the metal oxide of the first phase and the metal oxide of the second phase with respect to the whole fiber. weight%
Means

Next, a method for producing the silica-based composite oxide fiber having a graded structure obtained by the present invention will be described.
In the present invention, the general formula

[Chemical 2] (However, R in the formula represents a hydrogen atom, a lower alkyl group or a phenyl group.) Polycarbosilane having a main chain skeleton and a number average molecular weight of 200 to 10,000 is modified with an organometallic compound. The modified polycarbosilane having the above structure, or a mixture of the modified polycarbosilane and the organometallic compound is melt-spun, and after the infusibilization treatment, the silica-based composite oxide fiber is produced by firing in air or oxygen. can do.

The first step of the method of the present invention is a step of producing a modified polycarbosilane having a number average molecular weight of 1,000 to 50,000 used as a starting material for producing a silica-based composite fiber. The basic method for producing the modified polycarbosilane is very similar to that in JP-A-56-74126, but in the present invention, it is necessary to carefully control the bonding state of the functional groups described therein. is there. This is outlined below.

The modified polycarbosilane which is the starting material is
Mainly general formula (However, R in the formula represents a hydrogen atom, a lower alkyl group or a phenyl group.) A polycarbosilane having a main skeleton represented by a number average molecular weight of 200 to 10,000 and a general formula, M (OR ') n or MR''m (M is a metal element, R'is an alkyl or phenyl group having 1 to 20 carbon atoms, R'is acetylacetonate, m and n are integers greater than 1) It is derived from an organic metal compound having a structure.

Here, in order to produce the fiber having the graded composition of the present invention, the organometallic compound forms a monofunctional polymer with polycarbosilane, and only a part of the organometallic compound is polycarbosilane. It is necessary to select slow reaction conditions that form a bond with. For that purpose, it is necessary to react in an inert gas at a temperature of 280 ° C. or lower, preferably 250 ° C. or lower. Under this reaction condition, even if the organometallic compound is reacted with polycarbosilane, it is bonded (that is, pendantly bonded) as a monofunctional polymer, and a large increase in molecular weight does not occur. The modified polycarbosilane partially bonded with the organometallic compound plays an important role in improving the compatibility between the polycarbosilane and the organometallic compound.

When a large number of bifunctional or higher functional groups are bonded, a polycarbosilane bridge structure is formed and a marked increase in the molecular weight is observed. In this case, a rapid heat generation and a rise in melt viscosity occur during the reaction. On the other hand, when it is the above-mentioned monofunctional polymer and unreacted organometallic compound remains, on the contrary, a decrease in melt viscosity is observed.

In the present invention, it is desirable to select conditions under which the unreacted organometallic compound is intentionally left. In the present invention, the above modified polycarbosilane and an unreacted organometallic compound or an organometallic compound in the range of about 2-3 trimers are mainly used as a starting material, but the modified polycarbosilane alone has an extremely low molecular weight. When the modified polycarbosilane component of 1 is contained, it can be similarly used as the starting material of the present invention.

In the second step of the method of the present invention, the modified polycarbosilane obtained in the first step or a mixture of the modified polycarbosilane and a low molecular weight organometallic compound is melted to prepare a spinning solution. In some cases, this is filtered to remove substances that are harmful to the spinning, such as microgels and impurities, and this is spun by a commonly used synthetic fiber spinning device. Although the temperature of the spinning dope during spinning depends on the softening temperature of the modified polycarbosilane as the raw material,
A temperature range of 50 to 200 ° C. is advantageous. In the above spinning device, a humidification heating cylinder may be provided below the nozzle, if necessary. The fiber diameter is adjusted by changing the discharge amount from the nozzle and the winding speed of a high-speed winding device installed below the spinning machine.

In the second step of the method of the present invention, in addition to the melt spinning, the modified polycarbosilane obtained in the first step,
Alternatively, a mixture of the modified polycarbosilane and the low molecular weight organometallic compound is dissolved in, for example, benzene, toluene, xylene or another solvent capable of melting the modified polycarbosilane and the low molecular weight organometallic compound to prepare a spinning solution. In some cases, this is filtered to remove harmful substances such as macrogels and impurities during spinning, and then the spinning solution is spun by a dry spinning method using a synthetic fiber spinning device usually used to control the winding speed. The fiber can be obtained.

In these spinning steps, if necessary,
A spinning cylinder is attached to the spinning device, and the atmosphere in the cylinder is a mixed atmosphere with at least one gas of the solvents, or air, an inert gas, hot air, a heat inert gas,
By setting the atmosphere of steam, ammonia gas, hydrocarbon gas, and organosilicon compound gas, the solidification of the fibers in the spinning cylinder can be controlled.

Next, in the third step of the method of the present invention,
The spun fiber is preheated in an oxidizing atmosphere under the action of tension or no tension to infusibilize the spun fiber. In this step, the fibers do not melt during firing in the subsequent step,
In addition, the purpose is not to adhere to adjacent fibers. Treatment temperature and treatment time vary depending on the composition,
Although not particularly specified, in general, in the range of 50 to 400 ° C,
Processing conditions of several hours to 30 hours are selected. The oxidizing atmosphere may contain water, nitrogen oxides, ozone, etc. that enhance the oxidizing power of the spun fiber, and the oxygen partial pressure may be intentionally changed.

By the way, depending on the proportion of low molecular weight substances contained in the raw material, the softening temperature of the spun fiber may be lower than 50 ° C. In that case, the fiber surface is previously oxidized at a temperature lower than the above treatment temperature. In some cases, a process for promoting It is considered that, in the third step and the second step, bleeding out of the low molecular weight compound contained in the raw material to the fiber surface progresses to form an underlayer having a desired gradient composition. There is.

Next, in the fourth step of the method of the present invention,
The infusibilized fiber is subjected to 500
To 1800 ° C. in a temperature range of 1800 ° C., and is a target composite oxide of an oxide phase mainly containing a silica component (first phase) and a metal oxide phase other than silica (second phase). A silica-based composite oxide fiber that is composed of a phase and in which the abundance ratio of at least one metal element of the metal oxide that constitutes the second phase is gradually increased toward the surface layer is obtained. In this step, the organic component contained in the infusibilized fiber is basically oxidized, but it may remain in the fiber as carbon or carbide depending on the selected conditions. Even in such a state, if the intended function is not hindered, it is used as it is, but if it is hindered, further oxidation treatment is performed. At that time, the temperature and the treatment time must be selected so that the intended graded composition and crystal structure do not cause any problems.

FIG. 1 schematically shows a process of producing oxide fibers having a desired gradient composition according to the present invention.

[0027]

EXAMPLES The present invention will be described below with reference to examples. Reference Example 1 2.5 liters of anhydrous toluene and 400 g of sodium metal were placed in a 5 liter three-necked flask and heated to the boiling point of toluene under a nitrogen gas stream, and dimethyldichlorosilane 1 was added.
L was added dropwise over 1 hour. After completion of dropping, the mixture was heated under reflux for 10 hours to generate a precipitate. This precipitate is filtered,
First, it was washed with methanol and then with water to obtain 420 g of white powdery polydimethylsilane. 250 g of polydimethylsilane was charged into a three-necked flask equipped with a water-cooled reflux device, and heated and reacted at 420 ° C. for 30 hours under a nitrogen stream to obtain polycarbosilane having a number average molecular weight of 1200.

Example 1 Polycarbosilane 45 synthesized by the method of Reference Example 1
400 g xylene and tetrabutoxy titanium (TBT)
After adding 50 g and preheating at 100 ° C. for 1 hour, 1
The temperature was slowly raised to 90 ° C., xylene was distilled off, and the reaction was continued for 5 hours to synthesize modified polycarbosilane. As a result of measuring the molecular weight distribution of this modified polycarbosilane by gel permeation chromatography (GPC), it was confirmed that about 80% or more of the charged TBT remained in an unreacted monomer state.

After the modified polycarbosilane was dissolved in xylene, it was charged into a glass spinning apparatus, the inside was sufficiently replaced with nitrogen, and then the temperature was raised to distill off xylene.
Melt spinning was performed at 55 ° C. The spun fiber is heated in air stepwise to 135 ° C. to make it infusible and then 1300 ° C.
Was fired in the air for 1 hour to obtain a titania / silica fiber.

The obtained fibers (average diameter: 10 μm) are
As a result of X-ray diffraction, it consisted of amorphous silica and titania of anatase. FIG. 2 shows the result of examining the composition change from the surface to the inside of the fiber by Auger electron spectroscopy. From this, the fiber is about 60 from the surface.
It can be seen that titanium gradually increases toward the surface in the range of nm. Also, fully automatic fluorescent X made by PHILIPS
The abundance ratio of titanium oxide in the whole fiber measured by a line analyzer (PW2400) was 15% by weight. When the crystal grain size of titanium oxide on the fiber surface was measured by TEM, the average was 8 nm.

Next, the photocatalytic activity of this fiber was confirmed by examining the killing activity of E. coli as follows. To 20 ml of an aqueous solution containing 100,000 Escherichia coli per milliliter, 0.2 g of the above fiber was irradiated with 0.2 mW / cm ² of ultraviolet light using a black light to survive in the liquid. The results of measuring the number of Escherichia coli present over time are shown in FIG. In this experiment, for comparison,
The thing which irradiated only the said ultraviolet light in the state which does not insert a fiber was also investigated. From this result, it can be seen that the sterilizing effect of the product containing the same fiber is extremely excellent.

Example 2 Polycarbosilane 16 synthesized by the method of Reference Example 1
To 100 g of toluene, 100 g of toluene and 64 g of tetrabutoxytitanium were added, preheated at 100 ° C. for 1 hour, then slowly heated to 150 ° C., toluene was distilled off, the reaction was continued for 5 hours, and further heated to 250 ° C. And reacted for 5 hours to synthesize a modified polycarbosilane. To this modified polycarbosilane, 5 g of tetrabutoxytitanium was intentionally added for the purpose of allowing a low-molecular weight organometallic compound to coexist to obtain a mixture of the modified polycarbosilane and the low-molecular weight organometallic compound.

A mixture of this modified polycarbosilane and a low molecular weight organometallic compound was dissolved in toluene and charged into a glass spinning device, and the inside was sufficiently replaced with nitrogen, and then the temperature was raised to distill off the toluene. Melt spinning was performed at 180 ° C. The spun fiber was heated in air stepwise to 150 ° C. to make it infusible and then fired in air at 1200 ° C. for 1 hour to obtain a titania / silica fiber.

The obtained fibers (average diameter: 13 μm) are
As a result of X-ray diffraction, it consisted of amorphous silica and titania of anatase, and the Ti / Si (molar ratio) of the whole fiber was 0.17. Moreover, when the distribution state of constituent atoms by EPMA was examined, it was found that T
i / Si (molar ratio) = 0.87, 3 to 4 μm from the outermost periphery
In the region of Ti / Si (molar ratio) = 0.15, T in the center
It was confirmed that i / Si (molar ratio) = 0.04 and the composition was graded such that titanium increased toward the surface. The tensile strength of the fiber was 1.5 GPa, which was significantly higher than that of the anatase-type titania / silica fiber obtained by the conventional sol-gel method. Also,
The existence ratio of titanium oxide in the whole fiber measured by using a fully automatic fluorescent X-ray analyzer (PW2400) manufactured by PHILIPS is 4
It was 6% by weight. When the crystal grain size of titanium oxide on the fiber surface was measured by TEM, the average was 8 nm. The edible oil adhered to the surface of the fiber was effectively decomposed by irradiating it with ultraviolet light of 300 to 400 nm, and the photocatalytic function of the fiber could be confirmed.

Comparative Example 1 The modified polycarbosilane synthesized in the same manner as in Example 2 was dissolved in toluene and precipitated in ethanol to remove low molecular weight substances. Then, without adding the low-molecular weight organometallic compound as described in Example 2,
Melt spinning was performed at 0 ° C. This spun fiber was infusibilized in the same manner as in Example 2 and then fired in air at 1200 ° C. to obtain a titania / silica fiber.

The obtained fiber (average diameter: 13 μm) is
As a result of X-ray diffraction, it was composed of amorphous silica and titania of anatase, and the Ti / Si (molar ratio) of the whole fiber was 0.04. Moreover, when the distribution state of the constituent atoms by EPMA was examined, Ti / Si (molar ratio) = 0.05 in the region of 100 nm from the outermost periphery and 3 to 4 from the outermost periphery.
Ti / Si (molar ratio) = 0.04 in the region of μm and Ti / Si (molar ratio) = 0.05 in the central portion, showing a uniform composition distribution without a graded composition. The tensile strength of this fiber was 1.6 GPa, which was extremely high as compared with the anatase-type titania / silica fiber obtained by the conventional sol-gel method, but the amount of titania component near the surface was small. It did not show the photocatalytic function as shown in Example 2.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a production process of an oxide fiber having a target gradient composition in the present invention.

[Fig. 2] Fig. 2 is a diagram showing a result of examining a change in composition from the surface to the inside of the fiber obtained in Example 2 of the present invention by Auger electron spectroscopy.

FIG. 3 is a diagram showing the results of an Escherichia coli killing experiment on the fiber obtained in Example 2 of the present invention.

─────────────────────────────────────────────────── --- Continued from the front page (56) References JP-A 61-101427 (JP, A) JP-A 10-130962 (JP, A) JP-A 2000-192336 (JP, A) JP-A 61-28072 (JP, A) JP 11-269725 (JP, A) JP 2000-176246 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D01F 9/08-9/10 C03C 13/02 B01J 21/00-38/74

Claims (6)

(57) [Claims] 1. An oxide phase mainly comprising a silica component (first
Phase) and a metal oxide phase which is a composite oxide phase of a metal oxide phase other than silica (second phase) and which constitutes the second phase.
The compound exhibits a predetermined function, and the abundance ratio of at least one metal element of the metal oxide forming the second phase gradually increases toward the surface layer of the fiber. Silica-based composite oxide fiber. 2. The abundance ratio of the first phase to the whole fiber is 98.
The silica-based composite oxide fiber according to claim 1, wherein the silica-based complex oxide fiber has a content of the second phase of 2 to 60% by weight. 3. The gradient of the abundance ratio of at least one metal element of the metal oxide constituting the second phase is 5 to 5 from the fiber surface.
The silica-based composite oxide fiber according to claim 1, which is present at a depth of 500 nm. 4. The second-phase metal oxide is titania, which has a crystal grain size of 15 nm or less and has a photocatalytic and / or thermal catalytic function. Silica-based complex oxide fiber. 5. A general formula: (However, R in the formula represents a hydrogen atom, a lower alkyl group or a phenyl group.) Polycarbosilane having a main chain skeleton and a number average molecular weight of 200 to 10,000 is modified with an organometallic compound. The modified polycarbosilane having the above structure, or a mixture of the modified polycarbosilane and the organometallic compound is melt-spun, infusibilized, and then fired in air or oxygen. Method for producing silica-based composite oxide fiber. 6. The organometallic compound is represented by the general formula M (OR ') n or MR "m (M is a metal element, R'is a carbon atom having 1 to 20 carbon atoms).
5. The method for producing a silica-based composite oxide fiber according to claim 4, wherein the compound has a basic structure of an alkyl group or a phenyl group having R, R "is acetylacetonate, and m and n are integers greater than 1. 5.