JPH05148720A - Polysilazane fiber, its production and ceramic fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber useful for reinforcing material, etc., having a ratio of weight-average molecular weight and number-average molecular weight of >= a given value and high ceramics yield by controlling a reaction time of hexamethylcyclosilazane and trichloromethylsilane, forming an oligomer and heat-treating. CONSTITUTION:By controlling a reaction time of hexamethylcyclcosilazane and trichloromethylsilane, chlorosilazane oligomer is formed, subjected to ammonolysis, further heat-treated to form a polysilzane. The polysilazane is made to have a ratio Mw/Mn of weight-average molecular weight and number- average molecular weight of >=7, subjected to melt spinning to give the objective fiber. The fiber is heated in vacuum or in an inert gas atmosphere at >=800 deg.C and thermally decomposed to give ceramic fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preceramic polymer, a method for producing the same, and a ceramic fiber obtained from the preceramic polymer. More specifically, the present invention relates to a polysilazane fiber which becomes a silicon nitride ceramic by heating.
The present invention relates to a method for producing the polysilazane fiber and a ceramic fiber obtained by pyrolyzing the polysilazane fiber.

[0002]

[Prior Art and Problems to be Solved by the Invention]

Silicon nitride ceramics have excellent heat resistance,
It has high strength, high hardness, and is relatively lightweight, so
It has been highlighted as an alternative material to metal materials. Since this silicon nitride ceramics is generally difficult to sinter, a powder of a sintering aid such as Y ₂ O ₃ or Al ₂ O ₃ or other additive powder is added to the silicon nitride powder to obtain a slip cast method. The molded body was first manufactured and then sintered.

However, when a ceramic molded body is produced by the slip casting method or the like, the bonding strength between the ceramic powder particles is not necessarily large even if the ceramic powder is mixed with a binder and the like, so that the mechanical strength is not large. There is a high risk of damage. Further, in the slip casting method, the ceramic molded body shrinks due to dehydration drying in a gypsum mold, and cracks easily occur. Therefore, it has been difficult to manufacture a thin-walled molded product or a molded product having a complicated shape without fear of damage or cracks.

Therefore, for example, in the production of silicon nitride ceramics, a proposal has been made to increase the strength of a (green) compact by adding a sintering aid such as Al ₂ O ₃ into a raw material and adding it to the raw material. ing. However, it is difficult to uniformly disperse the fiberized sintering aid in the molded body, and if a material in which the sintering aid is dispersed non-uniformly is sintered, the strength of the obtained ceramics is reduced. Further, when the sintering aid is used in the form of fibers, it is necessary to add a little more sintering aid in order to improve the sintering, but generally, when the amount of the sintering aid is large, the high temperature strength of the obtained ceramic is high. descend.

In order to solve the above-mentioned problems, the present applicant has previously filed a patent application for a ceramic molded body containing a ceramic fiber obtained by pyrolyzing polysilazane fiber (Japanese Patent Application No. 3-13799). ). As described above, if a ceramic fiber obtained by thermally decomposing polysilazane fiber is blended into the molded body, instead of blending a sintering aid such as Al ₂ O ₃ in a fibrous state, it is sufficient for the ceramic molded body. It can provide mechanical strength and crack resistance to prevent its breakage and cracking. Further, since it is not necessary to increase the amount of sintering aid, the high temperature strength of the ceramic obtained by firing is also improved.

Not limited to the above examples (when introducing ceramic fibers obtained by pyrolyzing polysilazane fibers into a silicon nitride ceramic molded body), it is conceivable to use polysilazane as a preceramic polymer for various purposes. However, in any case, the magnitude of the ceramic yield of polysilazane is an important factor for producing a ceramic product having good physical properties.

By the way, polysilazane fibers are generally
A product obtained by reacting cyclosilazane and halosilane is reacted with ammonia, and then polysilazane obtained by heat treatment is melt-spun.

In the above production method, it is generally known that polysilazane which gives a high ceramic yield can be obtained by sufficiently advancing the reaction between cyclosilazane and halosilane and increasing the degree of polymerization (increasing the molecular weight). However, polysilazane having a large molecular weight has a high softening point, which makes it difficult to form fibers (deterioration of moldability).

Accordingly, it is an object of the present invention to provide a polysilazane fiber having a high ceramic yield, a method capable of easily producing such a polysilazane fiber, and a ceramic fiber obtained from the polysilazane fiber.

[0011]

Means for Solving the Problems As a result of intensive research to achieve the above object, the present inventors have found that when polysilazane is produced from cyclosilazane and halosilane as starting materials,
By adjusting the reaction time between cyclosilazane and halosilane, the ratio M _W / M _n between the weight average molecular weight and the number average molecular weight of the polysilazane produced is set to a specific value or more (the molecular weight of polysilazane is relatively small. , And that the molecular weight distribution of the polysilazane is relatively wide), the moldability of the polysilazane becomes good and it can be easily melt-spun, and the polysilazane fiber obtained therefrom has a high ceramic yield, The present invention was conceived.

That is, the polysilazane fiber of the present invention is
After carrying out ammonolysis to the product obtained by reacting cyclosilazane and halosilane for a predetermined time, the polysilazane obtained by heat treatment is melt-spun, and the weight average molecular weight of the polysilazane after the heat treatment is obtained. And the number average molecular weight ratio M _W / M _n is 7 or more.

Hexamethylcyclosilazane and trichloromethylsilane are reacted to form a chlorosilazane oligomer, ammonolysis is performed on the chlorosilazane oligomer, and then heat treatment is performed to form polysilazane, and the polysilazane is melted. The method of the present invention for producing a polysilazane fiber by spinning is to adjust the reaction time of the hexamethylcyclosilazane and trichloromethylsilane to give a ratio M of the weight average molecular weight to the number average molecular weight of the polysilazane after the heat treatment. _W /
It is characterized in that M _n is 7 or more.

Further, the ceramic fiber of the present invention is characterized in that the above polysilazane fiber is heated to 800 ° C. or higher in a vacuum or in an inert gas atmosphere and thermally decomposed.

The present invention is described in detail below. The polysilazane fiber of the present invention is produced from cyclosilazane and halosilane.

Cyclosilazane is (R ₂ SiNR) ₂ ,
(R ₂ SiNR) ₃ and (R ₂ SiNR) ₄ (wherein R represents H or an alkyl group). Cyclosilazanes include (Me ₂ SiNH) ₂ , (MeHSiNH) ₂ , (H
₂ SiNH) ₂ , (Me ₂ SiNH) ₃ , (MeHSiNH) ₃ , (H ₂
SiNH) ₃ , (Me ₂ SiNH) ₄ , (MeHSiNH) ₄ , (H ₂ Si
NH) _{4 and the} like, but preferably hexamethylcyclosilazane (Me ₂ SiNH) ₃ is used.

As the halosilane, chlorosilane (R _n SiCl _4-n , where n = 0, 1, 2, 3, R or H) is used.
Is preferably an alkyl group). Among them, it is particularly preferable to use trichloromethylsilane.

A method for producing a polysilazane fiber will be described below by taking an example of using hexamethylcyclosilazane and trichloromethylsilane as cyclosilazane and halosilane, respectively.

First, hexamethylcyclosilazane and trichloromethylsilane are mixed. The mixing ratio is preferably 1: 1 to 1: 5 of hexamethylcyclosilazane to trichloromethylsilane in terms of molar ratio. More preferably, this mixing ratio is about 1: 3.

Next, the above-mentioned mixture of hexamethylcyclosilazane and trichloromethylsilane is heated under reflux at about 190 to 200 ° C. As a result, hexamethylcyclosilazane is ring-opened and a chlorosilazane oligomer is produced.

In the present invention, the heating reflux time of the mixture of hexamethylcyclosilazane and trichloromethylsilane is adjusted to control the molecular weight (distribution) of the resulting chlorosilazane oligomer. The molecular weight (distribution) of the chlorosilazane oligomer can be adjusted to a desired value by changing the heating / refluxing time. However, by adjusting the molecular weight of the chlorosilazane oligomer, ammonolysis and heat treatment (ammonolysis and The molecular weight distribution of the polymer (polysilazane) obtained by performing heat treatment will be described later. Details will be described later, in the present invention, the ratio M _W between the chloro silazane ammonolysis and weight average molecular weight M _W to the number average molecular weight M _n of the polysilazane obtained by performing heat treatment on the oligomer
The heating / refluxing time is set so that / M _n is 7 or more. When the ratio M _w / M _n of the weight average molecular weight to the number average molecular weight of the polysilazane is less than 7, the softening point of the polysilazane becomes high and the moldability in spinning or the like becomes poor, or when the polysilazane is thermally decomposed. The ceramic yield of is decreased.

The specific heating / refluxing time is about 3 to 24 hours, although it depends on the kind and amount of the starting materials.

Next, ammonia gas is blown into the solution of the above-mentioned chlorosilazane oligomer to carry out ammonolysis. Amount of ammonia gas blown is 70 liters /
It is good to do it for about 3 to 4 hours depending on the time. After this ammonolysis, the by-produced ammonium chloride is removed.

The polymer obtained above is subjected to a deammonification step in an inert gas such as nitrogen gas while being heated to about 250 to 400 ° C. to obtain a colorless solid polysilazane having thermoplasticity. The heating time is preferably 30 to 60 minutes.
As described above, M _W / M _n of the polysilazane at the End of deammoniation step by heating (heat treatment) is 7 or more.

Next, the obtained polysilazane is kept at a temperature equal to or higher than the softening point, melted and spun. At this time, the winding speed should be about 25 to 400 m / min.
Polysilazane fibers having a diameter of -30 μm can be obtained.

The obtained polysilazane fiber is vacuumed or in an inert gas such as nitrogen gas at 800 ° C. or higher, preferably 8
When fired at 00 to 1400 ° C. for about 1 to 4 hours, a silicon nitride ceramic fiber is obtained. The diameter of the finally obtained ceramic fiber is about 1 to 20 μm.

In the present invention, as described above, the molecular weight distribution of polysilazane immediately before spinning (after the above-mentioned heat treatment) is controlled within a predetermined range, that is, by weight, by adjusting the reaction time between hexamethylcyclosilazane and trichloromethylsilane. The ratio M _W / M _n of the average molecular weight to the number average molecular weight is 7
That is all. The relatively large M _W / M _n of 7 or more means that the polysilazane has a wide molecular weight distribution. Since such polysilazane has a low softening point, it has good moldability and can be easily made into fibers. The number average molecular weight M _n of the polysilazane after heat treatment was 10
It will be 00 or more.

In the above-mentioned polysilazane fiber production process, the molecular weight of the polymer (polysilazane) after ammonolysis and before heat treatment is smaller than that after heat treatment, and the number average molecular weight M _n is 1000 or less. This is because deammonification has not progressed before the heat treatment and aminosilazane having a relatively small molecular weight exists. When the M _W / M _n of the polymer before the heat treatment is 2 or more, the M _W / M of the polysilazane after the heat treatment under the above conditions is performed.
_n becomes 7 or more. According to the research conducted by the present inventors, the molecular weight distribution state set before the heat treatment can be maintained even after the heat treatment, so that the polysilazane to be fibrillated (polysilazane after the heat treatment) has M _W / M _n of 7 or more. The reaction time of hexamethylcyclosilazane and trichloromethylsilane may be set so that M _W / M _n before heat treatment is 2 or more.

According to the study by the present inventors, when the number average molecular weight M _n is 1000 or more, the yield of ceramics increases as M _W / M _n increases. Therefore, when the ratio M _W / M _{n of} the weight average molecular weight to the number average molecular weight is 7 or more,
If polysilazane having a number average molecular weight M _n of 1000 or more is used, it can be easily made into a fiber, and the obtained polysilazane fiber gives a high ceramic yield.

The molecular weight of the polysilazane used in the present invention is determined by gel permeation chromatography (GP
It is the value obtained by polystyrene conversion using method C).

[0031]

In the present invention, polysilazane having a relatively small molecular weight and a wide molecular weight distribution is produced by adjusting the reaction time of hexamethylcyclosilazane and trichloromethylsilane. When the molecular weight distribution is wide, the softening point is low, and the moldability in fiberization is good.

By increasing the molecular weight distribution (M _W / M _n is 7 or more), the ceramic yield of polysilazane is also improved. The reason for this is not necessarily clear, but it is considered that the crosslinking reaction is likely to proceed or the proportion of the high molecular weight component is increased.

[0033]

The present invention will be described in more detail by the following examples.

Examples 1 and 2 and Comparative Example 1 Hexamethylcyclosilazane and trichloromethylsilane were placed in a 500 ml eggplant type flask equipped with a cooling tower and a condenser so that the molar ratio was 1: 3, and 190 to 200 The mixture was heated to reflux for 6 hours (Example 1), 12 hours (Example 2), or 3 hours (Comparative Example 1) while being kept at 0 ° C., cooled to room temperature, and then ammonium chloride produced as a by-product was filtered, A chlorosilazane oligomer was obtained.

The obtained chlorosilazane oligomer was placed in a 2 liter three-necked flask equipped with a stirrer, about 1 liter of cyclohexane was added, and ammonia gas was blown at a rate of about 70 liter / hour for 3 hours while stirring to carry out ammonolysis. went. Then, ammonium chloride produced as a by-product was filtered to obtain a colorless liquid (polysilazane). The molecular weight of this liquid was determined by the gel permeation chromatography (GPC) method. Also, the ceramic yield was determined by thermogravimetric analysis. The results are shown in Table 1.

The polysilazane obtained above was subjected to a heat treatment at 350 ° C. for 30 minutes in a nitrogen gas atmosphere to obtain a colorless solid polysilazane exhibiting thermoplasticity.

The molecular weight of the polysilazane after the heat treatment was determined by gel permeation chromatography (GPC) method. Also, the ceramic yield was determined by thermogravimetric analysis. Further, the softening point was measured by a penetration method with a load of 1 g. The results are shown in Table 1. Further, FIG. 1 shows the relationship between each of the ceramic yield and the softening point and M _W / M _n . Further, it is shown with M _W / M _n in the polysilazane before the heat treatment, the relationship between M _W / M _n after heat treatment in Figure 2.

Table 1 M _n M _W M _W / M _n Yield ⁽¹⁾ Before softening point heat treatment Example 1 900 5590 6.21 27.9 ─ Example 2 530 1120 2.11 19.2 ─ Comparative example 1 560 880 1.57 12.9 ─ After heat treatment Example 1 1440 21600 15.0 58.1 86 Example 2 1100 8560 7.71 54.5 96 Comparative Example 1 1000 6120 6.12 51.1 95 Table 1 Note: Ceramic yield, which was determined from the weight loss rate by thermogravimetric analysis.

[0039] As can be seen from Table 1 and Figure 1, when M _W / M _n of the polysilazane after heat treatment is 7 or more,
A high ceramic yield is obtained and the softening point is low. Further, it can be seen from FIG. 2 that the molecular weight distribution state set before the heat treatment is maintained even after the heat treatment.

[0040]

As described above, in the method of the present invention, the softening point of polysilazane is lowered by setting the molecular weight distribution (M _W / M _n value) of polysilazane before molding (before spinning) to a specific range. Therefore, good moldability is obtained,
Can be easily made into fibers. It also becomes a polysilazane that gives a high ceramic yield.

The method of the present invention can be applied not only to the production of polysilazane fiber but also to the production of polysilazane having other shapes.

When the polysilazane fiber of the present invention is heated to 800 ° C. or higher in a vacuum or an inert gas atmosphere and pyrolyzed, a ceramic fiber can be obtained. This ceramic fiber is a reinforcing material for a silicon nitride ceramic molded body. Can be used as The ceramic fiber is not limited to this, and can be used for various ceramic products.

[Brief description of drawings]

FIG. 1 shows M _W of polysilazane in Examples and Comparative Examples.
3 is a graph showing the relationship between the / M _n value and the softening point, and the M _W / M _n value and the ceramic yield.

[Figure 2] and M _W / M _n values of the polysilazane before the heat treatment is a graph showing the relationship between the M _W / M _n after the heat treatment.

Claims (5)

[Claims] 1. A polysilazane fiber obtained by subjecting a product obtained by reacting cyclosilazane and halosilane for a predetermined time to ammonolysis and then melt-spinning the polysilazane obtained by heat treatment. The polysilazane fiber has a ratio M _w / M _n of the weight average molecular weight to the number average molecular weight of the polysilazane of 7 or more. 2. The polysilazane fiber according to claim 1, wherein the cyclosilazane is hexamethylcyclosilazane. 3. The polysilazane fiber according to claim 1 or 2, wherein the halosilane is trichloromethylsilane. 4. Hexamethylcyclosilazane and trichloromethylsilane are reacted to produce a chlorosilazane oligomer, ammonolysis is performed on the chlorosilazane oligomer, and heat treatment is further performed to produce polysilazane, and the polysilazane is melted. In the method for producing a polysilazane fiber by spinning, by adjusting the reaction time of the hexamethylcyclosilazane and trichloromethylsilane, the ratio M _W / M of the weight average molecular weight and the number average molecular weight of the polysilazane after the heat treatment is adjusted. _A method for producing a polysilazane fiber, wherein _n is 7 or more. 5. The polysilazane fiber according to claim 1, which is used in a vacuum or in an inert gas atmosphere.
Ceramic fiber characterized by being heated to 0 ° C. or higher and thermally decomposed.