JP4535101B2 - Alumina fiber assembly - Google Patents

Description

  The present invention relates to an alumina fiber assembly.

  Alumina fiber aggregates are processed into alumina fiber brackets and the like and are used as heat insulating materials, taking advantage of their excellent heat resistance. Such an alumina fiber bracket can be manufactured, for example, by the following method.

  That is, a spinning solution containing basic aluminum chloride, a silicon compound, an organic polymer and water is spun by a blowing method, and an aggregate (laminated sheet) of the obtained alumina short fiber precursor is subjected to needling as necessary. After application, it is fired. And in a baking process, while volatile matter is removed, crystallization of an alumina and a silica advances and it converts into an alumina fiber. As a result, an alumina fiber aggregate composed of short alumina fibers is obtained. Such a manufacturing method is generally called a precursor fiberizing method.

  By the way, when the diameter of the alumina short fiber is small, the alumina short fiber is likely to be scattered, the handling property is deteriorated, and it is not preferable from the viewpoint of the working environment. That is, it has been pointed out that fibers having a diameter of several μm or less tend to enter the human alveoli through breathing.

  The present invention has been made in view of such circumstances, and an object of the present invention is an alumina fiber assembly composed of alumina short fibers, and the diameter of the alumina short fibers is increased to suppress scattering of the alumina short fibers. It is an object to provide an alumina fiber assembly and a method for producing the same.

  As a result of intensive studies, the inventors have changed the diameter of the short alumina fiber depending on the properties of the spinning solution used, and by using a spinning solution having a specific property and optimizing the spinning conditions, The knowledge that an alumina short fiber having a large diameter and a small fiber diameter distribution can be obtained was obtained, and the present invention was completed.

  The present invention has been completed based on the above findings, and the gist thereof consists of short alumina fibers having an average fiber diameter of 4.0 to 10.0 μm and a minimum fiber diameter of 3.0 μm or more. It exists in the alumina fiber assembly characterized by this.

  According to the present invention, there is provided an alumina fiber aggregate composed of alumina short fibers, in which the diameter of the alumina short fibers is increased and scattering of the alumina short fibers is suppressed. Such an alumina fiber aggregate is excellent in terms of handleability and work environment sanitation due to less scattering of fibers during handling. Therefore, the industrial value of the present invention is remarkable.

  Hereinafter, the present invention will be described in detail. First, for the convenience of explanation, a method for producing an alumina fiber assembly according to the present invention will be described.

  The production method of the present invention is a method in which a spinning solution containing basic aluminum chloride, a silicon compound, an organic polymer and water is spun by a blowing method, and an aggregate of the obtained alumina short fiber precursor is fired (precursor). Fiberizing method). And it mainly comprises a spinning solution preparation step, a spinning step, and a firing step, and a needling step is provided between the spinning step and the firing step as necessary.

<Process for preparing spinning solution>
Basic aluminum _{chloride; Al (OH) 3-X} Cl x , for example, can be prepared by dissolving metallic aluminum in hydrochloric acid or aluminum chloride solution. The value of X in the above chemical formula is usually 0.45 to 0.54, preferably 0.50 to 0.53. Silica sol is preferably used as the silicon compound, but other water-soluble silicon compounds such as tetraethyl silicate and water-soluble siloxane derivatives can also be used. As the organic polymer, for example, water-soluble polymer compounds such as polyvinyl alcohol, polyethylene glycol, and polyacrylamide are preferably used. These polymerization degrees are 1000-3000 normally.

In the present invention, as the spinning solution of the ratio of aluminum and silicon is in terms of the weight ratio of _Al 2 _{O 3} and SiO ₂ 99: 1~65: 35, the concentration of A aluminum 180-200 g / L, It is important to use a spinning solution having an organic polymer concentration of 20 to 40 g / L.

When the amount of the silicon compound is less than the above range, the alumina constituting the short fiber is easily converted to α-alumina, and the short fiber is easily embrittled due to the coarsening of the alumina particles. On the other hand, when the amount of the silicon compound is larger than the above range, the amount of silica (SiO ₂ ) produced together with mullite (3Al ₂ O ₃ .2SiO ₂ ) increases and the heat resistance decreases. The ratio of aluminum to silicon in terms of the weight ratio of Al ₂ O ₃ and SiO ₂ is usually 99: 1 to 65:35, preferably 99: 1 to 70:30, more preferably 98: 2 to 72:28. is there.

The concentration of A aluminum is the concentration or if the organic polymer is less than 180 g / L in the case of less than 20 g / L, both, the fiber diameter decreases without proper viscosity is obtained. That is, as a result of too much free water in the spinning solution, the drying speed during spinning by the blowing method is slow, the drawing proceeds excessively, the fiber diameter of the spun precursor fiber changes, the fiber diameter is large and the fiber Short fibers with a small diameter distribution cannot be obtained. Moreover, if the concentration of A aluminum is less than 180 g / L, productivity is lowered. On the other hand, if the concentration or if the organic polymer concentration of A aluminum exceeds 200 g / L more than 40 g / L, both, not a spinning solution viscosity is too high. The preferred concentration of A aluminum is 185~195g / L, preferably the concentration of the organic polymer is 30 to 40 g / L.

  The spinning solution is prepared by adding a silicon compound and an organic polymer to a basic aluminum chloride aqueous solution, and concentrating the basic aluminum chloride and the organic polymer so that the concentrations are within the above ranges. The viscosity of the spinning solution at normal temperature is usually 1 to 1000 poise, preferably 10 to 100 poise.

<Spinning>
Spinning (fiber formation of the spinning solution) is performed by a blowing method in which the spinning solution is supplied into a high-speed spinning airflow, and thereby an alumina short fiber precursor having a length of several tens to several hundreds of millimeters is obtained.

  The structure of the spinning nozzle used in the above spinning is not particularly limited. For example, the spinning nozzle is blown out from an air nozzle as described in European Patent No. 495466 (Japanese Patent No. 2602460). It is preferable that the air flow and the spinning liquid flow extruded from the spinning liquid supply nozzle are parallel flows, and that the parallel air flow is sufficiently rectified to come into contact with the spinning liquid. In this case, the diameter of the spinning nozzle is usually 0.1 to 0.5 mm, and the liquid amount per spinning liquid supply nozzle is usually 1 to 120 ml / h, preferably 3 to 50 ml / h. The gas flow rate per slit is usually 40 to 200 m / s.

  According to the spinning nozzle as described above, the spinning solution extruded from the spinning solution supply nozzle is sufficiently stretched without being sprayed (mist) and difficult to fuse between fibers, so that the spinning conditions are optimized. By doing so, a uniform alumina fiber precursor with a narrow fiber diameter distribution can be obtained.

  In spinning, it is preferable that a sufficiently stretched fiber is first formed from the spinning solution under conditions where moisture evaporation and spinning solution decomposition are suppressed, and then the fiber is dried quickly. . For this purpose, it is preferable to change the atmosphere from a state in which the evaporation of moisture is promoted to a state in which the evaporation of moisture is promoted in the process from the formation of fibers from the spinning solution to the arrival of the fiber collector. Therefore, it is preferable that the temperature in the vicinity of the spinning solution to start contact with the air flow is 10 to 200 ° C, the temperature of the air flow in the vicinity of the fiber collector is 40 to 50 ° C, and the relative humidity is less than 30%.

  If the temperature of the atmosphere is too high at the stage where sufficiently stretched fibers are to be formed from the spinning solution, it is difficult to form sufficiently stretched fibers due to rapid evaporation of moisture or the like, and the formed fibers Inorganic oxide fibers finally obtained due to defects are weakened. On the other hand, when fibers are formed from the spinning solution in a low-temperature or high-humidity atmosphere to suppress evaporation, the fibers remain in the same atmosphere after the fibers are formed. This is not preferable because it tends to cause shots.

  The aggregate of short alumina fiber precursors is installed with an endless belt made of wire mesh so as to be substantially perpendicular to the spinning airflow, and the spinning airflow containing the alumina short fiber precursor collides with this while rotating the endless belt. It can collect | recover as a continuous sheet (thin layer sheet) with the stacking apparatus of the structure to make.

  The thin-layer sheet collected from the stacking device is continuously drawn out, sent to the folding device, folded into a predetermined width and stacked, and continuously moved in a direction perpendicular to the folding direction into a laminated sheet. I can do it. Thereby, since the both ends of the width direction of a thin layer sheet are arrange | positioned inside the laminated sheet formed, the fabric weight of a laminated sheet becomes uniform over the whole sheet | seat. As the above folding device, the one described in European Patent Publication No. 971057 (Japanese Patent Publication No. 2000-80547) can be used.

<Needling process>
By applying needling to an aggregate (laminated sheet) of alumina short fiber precursors, an alumina fiber aggregate with high mechanical strength that is also oriented in the thickness direction can be obtained. Needling strikes are usually 1 to 50 strikes / cm ² , and generally the larger the number of strikes, the greater the bulk density and peel strength of the resulting alumina fiber aggregate.

<Baking process>
Firing is usually performed at a temperature of 500 ° C. or higher, preferably 700 to 1400 ° C. When the firing temperature is less than 500 ° C., crystallization is insufficient, so that only weak short alumina fibers with low strength can be obtained. When the firing temperature exceeds 1400 ° C., the crystal growth of the fiber crystals proceeds and the strength is increased. Only small brittle alumina short fibers can be obtained.

  Next, the alumina short fiber aggregate of the present invention will be described. The alumina fiber aggregate of the present invention is obtained, for example, by the production method as described above, and is structurally composed of short alumina fibers. And the fiber diameter of the alumina short fiber which comprises an alumina fiber aggregate is large, and fiber diameter distribution is small. That is, the alumina fiber assembly of the present invention is characterized in that the average fiber diameter of the short alumina fibers is 4.0 to 10.0 μm and the minimum fiber diameter is 3.0 μm or more. The lower limit of the average fiber diameter of the short alumina fibers is preferably 4.0 μm, more preferably 5.0 μm. The average fiber diameter of the short alumina fibers is preferably 5.0 to 8.0 μm, more preferably 6.0 to 8.0 μm.

  If the number of fibers having a small fiber diameter increases, the fibers are likely to be scattered, the handleability is deteriorated, and work hygiene is undesirable. In addition, if the fiber diameter is too large, the heat insulating property and elasticity of the aggregate of short alumina fibers are generally not preferable. The above frequency distribution means the value measured according to the fiber diameter distribution measuring method described later. In addition, the length of the alumina short fiber obtained here is 10-500 mm normally.

  Since the alumina fiber aggregate of the present invention has the above-described characteristics, for example, when it is handled in the manufacturing process of an alumina fiber blanket, there is little scattering of fibers, and it is excellent in terms of handleability and work environment hygiene. .

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded. Moreover, in the following examples, the measurement of the fiber diameter distribution of the alumina single fiber was performed according to the following procedure.

<Measurement method of fiber diameter distribution>
(1) About 1 cup of fiber is picked from the alumina fiber mat with tweezers.
(2) Place the fibers picked up in the above (1) on the carbon conductive tape affixed to the scanning electron microscope (SEM) observation sample stage so as not to overlap as much as possible.
(3) A platinum-palladium film is vapor-deposited with a thickness of 1 to 3 nm on the surface of the sample so that the fiber surface of (2) has conductivity.
(4) The deposited analysis sample is put into a SEM measurement chamber, observed at a magnification suitable for measuring the fiber diameter, and the observed image is photographed. As the apparatus, a scanning electron microscope “JSM-6320F” manufactured by JEOL Ltd. was used, and the observation conditions were an acceleration voltage of 15 KV and a work distance (WD) of 15 mm. Moreover, it selected suitably from the range of 1000-3000 magnification.
(5) Measure from the SEM photograph taken in (4) above to the nearest 0.1 mm with a caliper or straight ruler. And a total of 100 fiber diameters are measured arbitrarily.
(6) The average fiber diameter is calculated by the following formula. At this time, the calculated value is rounded to the first decimal place by rounding off the two decimal places.
(7) Here, in the case where the lower limit fiber diameter is in doubt in view of the tendency of the fiber diameter frequency distribution, the measurement is normally repeated 2 to 4 times, and the frequency distribution is the minimum fiber having an average diameter of 1% or more. The diameter.

[Equation 1]
Average fiber diameter (μm) = {total measured value of 100 points / (100 × observation magnification)} × 1,000

Example 1
<Preparation of spinning solution>
First, a basic aluminum chloride having an aluminum concentration of 165 g / L; 606 g of a 20 wt% silica sol solution per 1.0 L of an aqueous solution of Al (OH) _{3 -X} Cl _x (X = 0.51), 5 wt% polyvinyl alcohol (polymerization) Degree 1700) 608 g of aqueous solution was added and mixed, and then concentrated under reduced pressure at 50 ° C. to obtain a spinning solution. The viscosity of the spinning solution 60 poise (measured by a rotational viscometer at 25 ° C.), the ratio of aluminum and silicon (Al ₂ O ₃ and the weight ratio of SiO ₂₎ is 72.0: 28.0, the concentration of A aluminum is The concentration of 190 g / L and the organic polymer was 35.0 g / L.

<Spinning>
The above spinning solution was spun by a blowing method. As the spinning nozzle, a spinning nozzle having the same structure as that described in FIG. 6 of European Patent No. 495466 (Japanese Patent No. 2602460) was used. Spinning is performed by using a spinning liquid supply nozzle with a diameter of 0.3 mm, a liquid amount per spinning liquid supply nozzle of 5 ml / h, an air flow rate (slit portion of the air nozzle): 54 m / s (pressure: 2 kg / cm ² , (Temperature: 18 ° C., relative humidity 40%). In collecting cotton, hot air at 150 ° C. dried in parallel with high-speed air flow was introduced into the screen to adjust the air flow in the vicinity of the fiber collector to a temperature of 40 ° C. and a relative humidity of 20%. Then, an endless belt made of a wire mesh is installed so as to be substantially perpendicular to the spinning airflow, and the continuous sheet is rotated by an accumulating device having a structure in which the spinning airflow containing the alumina short fiber precursor collides with the endless belt. It was recovered as a (thin layer sheet).

  The thin layer sheet collected from the stacking device was continuously drawn out, sent to a folding device, folded into a predetermined width and stacked, and continuously moved in a direction perpendicular to the folding direction to form a laminated sheet. As the folding device, a folding device having the same structure as that described in European Patent No. 971057 (Japanese Published Patent No. 2000-80547) was used.

<Manufacture of alumina fiber assembly>
The above laminated sheet (aggregate of short alumina fiber precursors) was subjected to needling and then fired in air at 1250 ° C. for 1 hour to obtain an alumina fiber aggregate. The needling was performed by punching 8 times / cm ² with a needle punching machine. Table 1 shows the measurement results of the fiber diameter distribution of the constituent alumina short fibers of the obtained alumina fiber aggregate. The average fiber diameter was 6.9 μm, and the minimum fiber diameter was 5.2 μm.

Example 2
<Preparation of spinning solution>
First, a basic aluminum chloride having an aluminum concentration of 165 g / L; 606 g of a 20 wt% silica sol solution per 1.0 L of an aqueous solution of Al (OH) _{3 -X} Cl _x (X = 0.51), 5 wt% polyvinyl alcohol (polymerization) Degree 1700) 608 g of aqueous solution was added and mixed, and then concentrated under reduced pressure at 50 ° C. to obtain a spinning solution. The viscosity of the spinning solution 40 poise (measured by a rotational viscometer at 25 ° C.), the ratio of aluminum and silicon _(Al 2 _{O 3} and the weight ratio of SiO ₂₎ is 72.0: 28.0, the concentration of A aluminum is The concentration of the organic polymer was 180 g / L, and the concentration was 33.2 g / L.

<Spinning and production of alumina fiber assembly>
The same operation as in Example 1 was performed. Table 1 shows the measurement results of the fiber diameter distribution of the constituent alumina short fibers of the obtained alumina fiber aggregate. The average fiber diameter was 4.9 μm, and the minimum fiber diameter was 3.3 μm.

Comparative Example 1
<Preparation of spinning solution>
Basic aluminum chloride having an aluminum concentration of 75 g / L; 276 g of 20 wt% silica sol solution per 1.0 L of an aqueous solution of Al (OH) _{3 -X} Cl _x (X = 0.56), 5 wt% polyvinyl alcohol (degree of polymerization 1700 ) After adding and mixing 315 g of an aqueous solution, the solution was concentrated under reduced pressure at 50 ° C. to obtain a spinning solution. The viscosity of the spinning solution 40 poise (measured by a rotational viscometer at 25 ° C.), the ratio of aluminum and silicon _(Al 2 _{O 3} and the weight ratio of SiO ₂₎ is 72.0: 28.0, the concentration of A aluminum is The concentration of the organic polymer was 160 g / L, and the concentration was 33.6 g / L.

<Spinning and production of alumina fiber assembly>
The same spinning nozzle as in Example 1 was used. Spinning is performed by using a spinning liquid supply nozzle with a diameter of 0.3 mm, a liquid amount per spinning liquid supply nozzle of 5 ml / h, an air flow rate (slit portion of the air nozzle): 54 m / s (pressure: 2 kg / cm ² , (Temperature: 18 ° C., relative humidity 40%). In collecting cotton, hot air at 90 ° C. dried in parallel with high-speed air flow was introduced into the screen to adjust the air flow near the fiber collector to a temperature of 35 ° C. and a relative humidity of 30%. And it collect | recovered as a continuous sheet (thin layer sheet | seat) with the same cotton collecting apparatus and the accumulation apparatus as Example 1. Table 1 shows the measurement results of the fiber diameter distribution of the constituent alumina short fibers of the obtained alumina fiber aggregate. The average fiber diameter was 6.6 μm, and the minimum fiber diameter was 2.2 μm.

Comparative Example 2
<Preparation of spinning solution>
Basic aluminum chloride having an aluminum concentration of 165 g / L; 606 g of a 20 wt% silica sol solution per 1.0 L of an aqueous solution of Al (OH) _{3 -X} Cl _x (X = 0.51), 5 wt% polyvinyl alcohol (degree of polymerization 1700) ) After adding and mixing 260 g of an aqueous solution, the solution was concentrated under reduced pressure at 50 ° C. to obtain a spinning solution. Spinning solution viscosity is 8 poises (measured by a rotational viscometer at 25 ° C.), the ratio of aluminum and silicon _(Al 2 _{O 3} and the weight ratio of SiO ₂₎ is 72.0: 28.0, the concentration of A aluminum is The concentration of the organic polymer was 190 g / L and 15.0 g / L.

<Spinning and production of alumina fiber assembly>
The same operation as in Example 1 was performed. Table 1 shows the measurement results of the fiber diameter distribution of the constituent alumina short fibers of the obtained alumina fiber aggregate. The average fiber diameter was 2.3 μm, and the minimum fiber diameter was 0.4 μm.

Comparative Example 3
<Preparation of spinning solution>
Basic aluminum chloride having an aluminum concentration of 165 g / L; 606 g of a 20 wt% silica sol solution per 1.0 L of an aqueous solution of Al (OH) _{3 -X} Cl _x (X = 0.51), 5 wt% polyvinyl alcohol (degree of polymerization 1700) ) after adding and mixing an aqueous solution 550 g, concentrated under reduced pressure at 50 ° C., the aluminum and silicon ratio (the weight ratio of _Al 2 _{O 3} and SiO ₂₎ 72.0: 28.0, 210g concentration of a aluminum / L, the concentration of the organic polymer was adjusted to 35.0 g / L. However, the obtained composition exhibited a solidified state at the concentration stage and did not become a spinning solution.

Comparative Example 4
<Preparation of spinning solution>
Basic aluminum chloride having an aluminum concentration of 165 g / L; 606 g of a 20 wt% silica sol solution per 1.0 L of an aqueous solution of Al (OH) _{3 -X} Cl _x (X = 0.51), 5 wt% polyvinyl alcohol (degree of polymerization 1700) ) after adding and mixing an aqueous solution 868 g, concentrated under reduced pressure at 50 ° C., the aluminum and silicon ratio (the weight ratio of _Al 2 _{O 3} and SiO ₂₎ 72.0: 28.0, the concentration of a aluminum 190g / L, the concentration of the organic polymer was adjusted to 50.0 g / L. However, the viscosity of the obtained composition became too high at the concentration stage, and it was impossible to appropriately measure the viscosity with a rotational viscometer, so that the properties could not be spun.

Reference example 1:
The average fiber diameter of conventional alumina fibers is generally 2 to 5 μm, but analysis was performed on commercially available alumina fibers from three companies. The results were as shown in Table 2.

Claims (6)

  An alumina fiber assembly comprising alumina short fibers having an average fiber diameter of 4.0 to 10.0 μm and a minimum fiber diameter of 3.0 μm or more.   The alumina fiber assembly according to claim 1, comprising alumina short fibers having a minimum fiber diameter of 4.0 µm or more.   The alumina fiber assembly according to claim 1, comprising alumina short fibers having a minimum fiber diameter of 5.0 μm or more.   The alumina fiber aggregate according to any one of claims 1 to 3, comprising alumina short fibers having an average fiber diameter of 5.0 to 8.0 µm.   The alumina fiber aggregate according to any one of claims 1 to 3, comprising alumina short fibers having an average fiber diameter of 6.0 to 8.0 µm. Alumina composition of the short fibers, Al ₂ O ₃ and SiO ₂ in a weight ratio of 99: 1 to 65: alumina fiber aggregate according to any one of claims 1 to 5 is 35.