JP2003089547A - Inorganic fiber soluble in physiological saline solution, and production method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain amorphous inorganic fibers which are soluble in physiological saline solution in spite of the fact that they have heat resistance equal to that of alumina silica based ceramic fibers, and maintain high solubility in the physiological saline solution even after the application of a heat history. SOLUTION: The inorganic fibers consist of MgO, SrO, CaO and SiO2 as essential components, and the vacuum-formed preform of the fibers exhibits a coefficient of linear construction of <=3.5% before and after heating at 1,260 deg.C for 24 hr. The inorganic fibers contain SiO2 of >=70.0 wt.%, SrO of 0.5 to 15.0 wt.%, SrO of 0.5 to 15.0 wt.%, and CaO of 0.5 to 15.0 wt.%. The dissolution rate in physiological saline solution is >=1%. Even after the inorganic fibers have a heat history, the dissolution rate in physiological saline solution is kept >=1%. In the method where the raw material consisting of MgO, CaO and SiO2 as essential components is melted, and is made into fibers, SrO is added as the raw material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inorganic fiber having high heat resistance equivalent to that of ceramic fiber and having high solubility in physiological saline, and a method for producing the same.

[0002]

The use of inorganic fibers is widespread as an industrial material. For example, it is widely used as a heat insulating material and sound absorbing material in the form of bulk, felt, and blanket, as a vacuum molded body such as boards and papers for the purpose of fireproof insulation, and as a reinforcing material for building materials and vehicle brakes. .

Although asbestos is a natural inorganic fiber, one form thereof is deeply associated with respiratory diseases such as asbestosis and further cancer of lungs and surrounding tissues. On the other hand, regarding artificial inorganic fiber, although there is no clear evidence of respiratory disease due to inhalation, from studies such as animal experiments,
The risk of disease development has been pointed out.

Through experimental studies on the toxicity of inorganic fibers in animals such as rats, there are three important factors that are largely related to the development of diseases caused by inhalation of inorganic fibers, particularly cancer: 1) inhalation of fibers Quantities are listed, 2) inhaled fiber size, 3) fiber persistence in the lung.
In recent years, in particular, 3) of these, attention has been focused on the persistence of fibers in the lung. As one of the means for reducing the sustainability of fibers in the lung, there is a method of increasing the solubility of fibers in body fluids. That is, if the inhaled fiber is easily dissolved in the body fluid, it can be considered that toxicity of the fiber to the human body by inhalation is reduced. From such a background, inorganic fibers having high solubility in body fluids, that is, physiological saline are desired.

The German dangerous goods regulation adopts an index value called KI value calculated from its chemical composition as the solubility of the fiber as a criterion for determining the biosolubility and hence the safety to the human body. The KI value is defined by the following formula.

KI value = Na ₂ O + K ₂ O + CaO + MgO
+ BaO + B ₂ O ₃ -2Al ₂ O ₃ (wt%) That is, Na ₂ O, K among the chemical composition of the inorganic fiber.
_The KI value (carcinogenicity index) is the value obtained by subtracting the double Al ₂ O ₃ component concentration from the total of the ₂ O, CaO, MgO, BaO, and B ₂ O ₃ component concentrations (wt%).

According to this classification, if the KI straight is greater than 40, the fiber does not require warning of health effects. If the KI value is 30-40, a warning is required. If the KI value is less than 30, a stricter warning is required. However, it is obvious that it is difficult to provide an inorganic fiber having a KI value of more than 40 while maintaining the same high heat resistance as the ceramic fiber represented by the alumina-silica fiber. Also,
It has been pointed out that it is difficult to uniformly define carcinogenicity by such a simple calculation method.

Japanese Unexamined Patent Publication No. 10-324542 and Japanese Unexamined Patent Publication No. 2
Japanese Patent Publication No. 000-220037 discloses an inorganic fiber having a carcinogenicity index KI value of 40 or more and having low durability in the body. However, although the heat resistance of this inorganic fiber exceeds the level of conventional rock wool, it does not have heat resistance comparable to that of alumina-silica ceramic fibers.

Inorganic fibers having heat resistance similar to that of conventional alumina-silica ceramic fibers and having low durability in physiological saline are, for example, CaO-MgO-SiO.
A fiber having a composition of ₂ is disclosed in JP-A-8-506561, and a fiber having a composition of MgO—SiO ₂ —ZrO ₂ is disclosed in JP-A-10-512232. However, it goes without saying that when the inorganic fibers are dusted in the working environment and inhaled by the human body, the durability of the fibers in the lungs is required to be as short as possible. That is, there is a demand for an inorganic fiber having the same level of heat resistance as that of the alumina-silica ceramic fiber and having a high solubility in physiological saline.

Further, the evaluation of the durability of the inorganic fiber in the living body was made mainly from the viewpoint of the solubility in the physiological salt solution in the state where the fiber has no heat history. . However, assuming that the inorganic fiber-based material is used as a refractory heat insulating material and the working environment is dismantled, even after the inorganic fiber has a thermal history,
It goes without saying that it is required to exhibit high solubility in physiological saline. In particular, when the inorganic fiber is amorphous, it is expected that the inorganic fiber is crystallized after having a heat history and its solubility is significantly changed from that before having a heat history.

[0011]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
CaO-MgO-S disclosed in Japanese Patent No. 06561
Fibers composed of iO ₂ and special table 10-512232
The fiber having the composition of MgO—SiO ₂ —ZrO ₂ disclosed in the publication is inferior in heat resistance.

Therefore, the present invention has the same level of heat resistance as alumina-silica-based ceramic fibers, but is soluble in physiological saline and further has a physiological salt solution even after having a heat history. The object is to provide an amorphous inorganic fiber that maintains high solubility.

[0013]

When the solution means of the present invention is exemplified, it is the inorganic fiber described in claims 1 to 6 and the method for producing the same.

For example, the preferred inorganic fiber of the present invention is S
iO ₂ is 70.0% by weight or more, and MgO is 5.
0 to 20.0 wt% and SrO 0.5 to 15.0
% By weight, and CaO has a composition of 0.5 to 15.0% by weight.

By using SiO ₂ and MgO as main components and introducing SrO and CaO as essential components into them, it is possible to maintain high heat resistance at the same level as that of alumina-silica ceramic fibers, It has high solubility.

Furthermore, the preferred inorganic fibers of the present invention have high solubility in physiological saline even after having a heat history.

An example of a method for producing this inorganic fiber will be described.
To do. MgO, CaO and SiO ₂Hara whose main component is
In the method of manufacturing the fiber that melts the material
Then, SrO is added to the raw material to manufacture.

Another aspect of the present invention is that when a raw material containing SiO ₂ as a main component is melted and made into fibers, Sr is used.
The use of O as a viscosity modifier.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described in detail.

The inorganic fibers provided by the present invention can be obtained, for example, by mixing raw materials based on a predetermined composition, electrically melting the raw materials, and then blowing the melt to form fibers.

When the melt is blown to form fibers, the viscosity of the melt is important. That is, there is an optimum melt viscosity range for fiberization. Since the viscosity of the melt tends to increase as the temperature decreases, when the fiber is industrially produced by the above method, the change in the viscosity of the melt due to the temperature drop may be insensitive. desirable. If the change in viscosity of the melt due to temperature change is insensitive, the temperature range in which fiber formation is possible becomes wider. The change in viscosity of the melt due to temperature drop depends largely on the chemical composition of the melt.

The present inventors have found that MgO-CaO-SiO ₂
It has been found that, in the case of a melt having a system composition, by introducing SrO into the system, the change in viscosity of the melt due to temperature change becomes insensitive, and the temperature range in which fiber formation is possible becomes wide. . That is, SrO is MgO-CaO.
It has been found that in a melt having a —SiO ₂ composition, it functions as a “viscosity modifier” for fiberization.

The concentration of SrO is 0.5 to 15.0% by weight.
Is desirable. If the SrO concentration is less than 0.5% by weight, the effect as the above-mentioned "viscosity modifier" may be reduced. Moreover, as a raw material of the SrO component,
When the carbonate is used, gas is generated at the time of melting, and the electric current fluctuates during electric melting. For these reasons, SrO is preferably 15.0% by weight or less.

The SiO ₂ content is preferably 70.0% by weight or more. The more SiO _2, the higher the heat resistance of the fiber. 7
If it is less than 0.0% by weight, rapid shrinkage may occur with an increase in temperature.

MgO improves biosolubility and reduces heat resistance. When MgO is too small, it has poor biosolubility, and when it is too large, it has poor heat resistance. CaO has the same characteristics as MgO, and a part of MgO can be replaced with CaO. For this reason, MgO is 5.0-20.0% by weight.
And CaO is preferably 0.5 to 15.0% by weight.

Conventional CaO-MgO-SiO ₂ type inorganic fibers cannot maintain heat resistance at temperatures higher than 1200 ° C.
This is because the SiO ₂ concentration is lower than that of the inorganic fiber of the present invention. If the SiO ₂ concentration can be increased, the heat resistance of the CaO—MgO—SiO ₂ composition fiber will be improved. However, SiO
₂ Increasing the concentration leads to an increase in the viscosity of the melt and, as a result, tends to make fiber formation difficult.

The inorganic fiber of the present invention solves this problem by increasing the SiO ₂ content and adding the SrO component as a viscosity modifier for the melt to function.

Next, the biosolubility of the inorganic fiber was evaluated. The essence of body fluids is saline. Therefore, physiological saline was used as a physiological salt solution for evaluating biosolubility.

The method for evaluating biosolubility is as follows. First, 1 g of a fiber sample crushed until it passes through a sieve of 200 mesh (opening 0.075 mm) is precisely weighed.
Take it in a 300 ml conical beaker, add 150 ml of physiological saline and stopper. It is placed in a constant temperature water bath having a temperature of 40 ° C. and horizontally shaken at a speed of 120 rotations per minute for 50 hours. Then, filtration with a glass filter and drying are performed, and the insoluble fiber is precisely weighed to determine the amount of fiber lost due to dissolution. The weight loss rate calculated from the fiber weight loss is taken as the physiological saline solution rate of the fiber.

Table 1 shows the chemical composition (mol%) and the physiological saline dissolution rate of the inorganic fibers for which the biosolubility was evaluated. Further, the relationship between the (SrO + CaO) / MgO molar concentration ratio of the inorganic fiber and the physiological saline dissolution rate is shown in FIG.

[0031]

[Table 1] From FIG. 1, it can be seen that the physiological saline dissolution rate tends to increase as the concentration ratio of (SrO + CaO) to MgO increases. Further, if the alkaline earth metal oxide introduced into the inorganic fiber is only MgO, the dissolution rate in physiological saline solution is low.

However, the present inventors have found that the inorganic fiber contains an alkaline earth metal oxide component other than MgO, that is,
It has been found that when SrO and CaO are introduced, the dissolution rate in physiological saline increases, and the inorganic fibers exhibit excellent biosolubility.

The biosolubility of the inorganic fiber is required to be as high as possible. At least the physiological saline dissolution rate is preferably 1% or more.

Further, as will be described later, the inorganic fiber of the present invention exhibits a high physiological saline dissolution rate even after having a heat history, and maintains excellent biosolubility.

Further, the inorganic fiber of the present invention has the same excellent heat resistance as the alumina-silica ceramic fiber.

In this way, an inorganic fiber having both excellent biosolubility before and after having a heat history and high heat resistance equivalent to that of a ceramic fiber was completed.

[0037]

EXAMPLES The present invention will be further clarified below with reference to Examples and Comparative Examples.

As raw materials, silica stone, magnesia clinker, strontium carbonate and wollastonite were used. The above raw materials are mixed in a predetermined amount. After electrically melting it, the melt was blown into fibers to form fibers, and cotton was collected to obtain fibers having the chemical composition shown in Table 2.

The heat resistance and physiological saline solubility of the obtained fiber were evaluated by the following methods.

[Heat resistance] 200 g of each of the obtained inorganic fibers is stirred and dispersed in 10 liters of a 0.04% starch solution and then molded by a dehydration molding machine. After being sufficiently dried at 110 ° C., it is cut into a predetermined size to prepare a preform for heat resistance evaluation. This was heated at a predetermined temperature for 24 hours, and the linear shrinkage ratio before and after heating was obtained. The heat resistance evaluation temperatures were 1200 ° C and 1260 ° C.

[Solubility in physiological saline] The weight loss rate of the obtained fiber was determined in the same manner as in the above-mentioned biosolubility evaluation method and used as the physiological saline solubility rate of the fiber. The solubility was evaluated for unheated fibers and fibers heated at 1100 ° C. for 24 hours.

This heating temperature of 1100 ° C. is lower than 1200 ° C. or 1260 ° C. which is the heat resistance evaluation temperature.

However, the solubility evaluation is a valuable evaluation even if the heating temperature in the solubility test is low because of the following reasons.

When using fibers as a heat insulating material, for example, in the case where such an inorganic fiber heat insulating material is usually used as a furnace material, a heat insulating material having a considerably large thickness is used. It At this time, when the furnace inner surface, that is, the furnace inner surface of the heat insulating material is 1200 ° C. or 1260 ° C., the thickness is usually 250 to 300 mm, and the temperature from the furnace inner side, that is, the high temperature side to the furnace outer side, that is, the low temperature side is the temperature. There is a gradient, and the temperature outside the furnace is about 100 ° C. From this, most of the heat insulating material is 1200 ° C. or 1260 ° C. or less, and the temperature range of 1100 ° C. or less occupies approximately 2/3 to 3/4 in the thickness direction of the heat insulating material. Therefore, the progress of the solubility of the fiber heated to 1100 ° C in the physiological saline solution can be a great evaluation for improving the health of the human body.

Table 2 shows the evaluation results of heat resistance and biosolubility of Examples and Comparative Examples.

[0046]

[Table 2] Examples 1 to 3 are MgO-SrO-C according to the present invention.
It is an inorganic fiber of aO-SiO ₂ system. Examples 1 to 3
Has a heating linear shrinkage ratio of 3% or less at 1260 ° C., Comparative Examples 1 and 2 are 4.5% and 7.9%, respectively. When these are compared, all of Examples 1 to 3 are heated. The linear shrinkage ratio is greatly improved.

That is, according to the present invention, the heat resistance of the MgO-SiO ₂ fiber and the CaO-SiO ₂ fiber of Comparative Examples 1 and 2 is greatly improved. % Or less is almost at the same level as the heat resistance of the Al ₂ O ₃ —SiO ₂ fiber that is most often used in the high temperature region.

In Japanese Patent Publication No. 10-504272, Ca is disclosed.
There is a description that MgO and SrO do not match in the fiber of O-MgO-SrO-SiO ₂ system composition. This is described from the heat resistance, that is, the value of the shrinkage rate by heating, but the evaluated fiber has an SiO ₂ concentration of 5
It is in the range of 0 to 67 mol%, and fibers having a composition having a SiO ₂ concentration higher than this range are not described. The present inventors have found that the heat resistance of fibers having a CaO—MgO—SrO—SiO ₂ composition is dramatically improved by setting the SiO ₂ concentration of the fibers to 70% by weight or more (Table 2). Examples 1 and 2 shown are in weight percent.
These are # 307 and # 306 in Table 1 in mol% notation.
(Each of which has a SiO ₂ component concentration of 70 mol% or more).

The dissolution rate of the fiber in physiological saline is 4 to 5% without heating, showing excellent biosolubility. This is due to the addition of SrO and CaO components. As can be seen from FIG. 1, in the MgO-SiO ₂ based inorganic fiber, it is possible to increase the biosolubility of the fiber by adding an alkaline earth metal oxide component other than MgO, that is, SrO and CaO. . Also, 1
Even after being baked at 100 ° C. for 24 hours, it shows a dissolution rate of about 1 to 2%, and it can be seen that the fiber has excellent biosolubility even after having a heat history.

Comparative Example 1 is a MgO-SiO ₂ type inorganic fiber which is commercially available because of its excellent biosolubility.
In the unheated state, this inorganic fiber shows a dissolution rate of about 2% in physiological saline solution, but in the state after being baked at 1100 ° C. for 24 hours, the dissolution rate in physiological saline solution is 1% or less. It can be seen that the biosolubility is almost lost.

Therefore, judging from this point, Comparative Example 1
It appears that there was no improvement in saline solubility when heated to 1100 ° C. and therefore no improvement in health effects. Regarding heat resistance, Comparative Example 1
Has a large shrinkage rate as compared with Examples 1 to 3 of the present invention, and shows a shrinkage rate of about 5% after heating at 1260 ° C. for 24 hours, which is generally considered to be not practical. ing.

Comparative Example 2 is a CaO-MgO-SiO ₂ type inorganic fiber which is commercially available as having excellent biosolubility. In the unheated state, this fiber has a dissolution rate of about 7% in physiological saline, which shows that it has excellent biosolubility. Further, the dissolution rate shows a value of about 1% even after being baked at 1100 ° C. for 24 hours. However, regarding the heat resistance, at 1200 ° C., although the heating linear shrinkage ratio is as small as about 1%, the heating linear shrinkage ratio at 1260 ° C. reaches up to 8%. Therefore, 12
It can be seen that when the temperature becomes higher than 00 ° C., the heat shrinkage rate rapidly increases and it is difficult to maintain heat resistance.

When manufacturing fibers, it is an important operation to fiberize the molten raw material. At this time, there is a preferable melt viscosity range for forming a fiber. Fibrosis involves the process of instantly cooling the melt while stretching it with air. There is a preferred melt viscosity range for drawing. The viscosity range depends on the composition and temperature of the melt. A composition capable of maintaining a preferable viscosity range for a long time while being cooled is preferable.
That is, a composition in which the change in viscosity is insensitive to the change in temperature is desired.

On the other hand, the composition determines the heat resistance of the fiber.
In order to make the composition capable of efficiently obtaining the heat-resistant fiber, it is effective to add a viscosity modifier to the composition, which can obtain the insensitivity to the viscosity while maintaining the heat resistance. In the present invention, SrO is used as the viscosity modifier.
I found

In order to confirm the effect of SrO as a viscosity modifier, the effect was tested by changing the amount of SrO based on the composition of Example 1.

The results are shown in Table 3 as Experimental Examples 1 to 3.

[0057]

[Table 3] The fiberization rate is the value obtained when the raw material is melted, sprinkled and fiberized.
The number obtained by dividing the weight of the obtained fiber by the weight of the blown melt is shown.

Experimental Example 1 is an example in which SrO was not contained at all, and the fiberization rate was 0.4. In contrast, Experimental Examples 2 and 3, which are within the scope of the present invention, contain SrO in an amount of 5.2% by weight and 9.8% by weight, respectively. As a result, the fiberization rate was increased to 0.7 and 0.8, respectively. That is, the addition of SrO increases the temperature range suitable for fiber formation and, as a result, exhibits the effect as a viscosity modifier.

[0059]

INDUSTRIAL APPLICABILITY As described above, the inorganic fiber of the present invention has high heat resistance comparable to that of the conventional ceramic fiber and excellent biosolubility which the conventional ceramic fiber does not have. Furthermore, the inorganic fiber of the present invention,
Maintains excellent biosolubility even after having a thermal history.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the (SrO + CaO) / MgO molar ratio of inorganic fibers and the physiological saline dissolution rate.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Omiya, Osamu             4-4 Nihonbashi Hisamatsucho, Chuo-ku, Tokyo Itoshige             Building Toshiba Monoflux Co., Ltd. (72) Inventor, Koji Nemoto             4-4 Nihonbashi Hisamatsucho, Chuo-ku, Tokyo Itoshige             Building Toshiba Monoflux Co., Ltd. (72) Inventor Masaru Sugiyama             4-4 Nihonbashi Hisamatsucho, Chuo-ku, Tokyo Itoshige             Building Toshiba Monoflux Co., Ltd. (72) Inventor Kimio Hirata             4-4 Nihonbashi Hisamatsucho, Chuo-ku, Tokyo Itoshige             Building Toshiba Monoflux Co., Ltd. F-term (reference) 4G062 AA05 BB01 DA07 DA08 DB01                       DC01 DD01 DE01 DF01 EA01                       EB01 EC01 ED03 ED04 EE02                       EE03 EE04 EF02 EF03 EF04                       EG01 FA01 FA10 FB01 FC01                       FD01 FE01 FF01 FG01 FH01                       FJ01 FK01 FL01 GA01 GA10                       GB01 GC01 GD01 GE01 HH01                       HH03 HH05 HH07 HH09 HH11                       HH13 HH15 HH17 HH20 JJ01                       JJ03 JJ05 JJ07 JJ10 KK01                       KK03 KK05 KK07 KK10 MM01                       NN40

Claims (6)

[Claims] 1. MgO, SrO, CaO and SiO ₂
An inorganic fiber containing as an essential component, wherein the vacuum forming preform of the fiber exhibits a linear shrinkage of 3.5% or less before and after being heated at 1260 ° C. for 24 hours. 2. SiO ₂ is 70.0% by weight or more,
MgO is 5.0 to 20.0% by weight, and SrO is 0.
5 to 15.0% by weight, and CaO is 0.5 to 15.0
Inorganic fiber, characterized in that it is wt%. 3. The inorganic fiber according to claim 1, which has a physiological saline dissolution rate of 1% or more. 4. The physiological saline dissolution rate is 1% or more even after the inorganic fiber has a heat history.
The inorganic fiber according to any one of items 1 to 3. 5. A method for producing an inorganic fiber, which comprises adding SrO as a raw material in a method of melting and fibrating a raw material containing MgO, CaO and SiO ₂ as essential components. 6. Use of SrO as a viscosity modifier in the case of melting a raw material containing SiO ₂ as a main component to form a fiber.