JPS62143900A - Classification of whisker - Google Patents

Abstract

PURPOSE:To enable the effective and easy classification of whiskers by fiber length, by dispersing whiskers in a liquid, leaving the suspension at rest for a prescribed period, subjected the suspension to forced filtration and dividing the resultant whisker aggregate into plural portions perpendicular to the direction of filtration. CONSTITUTION:Thoroughly opened whiskers 2 of e.g. SiC, Si3N4, graphite, etc., are uniformly dispersed in a dispersion liquid 3 (e.g. water, alcohol, etc.) in a filtration tank 1 at a concentration of <=5.0wt% under vigorous agitation. The agitation is stopped and the dispersion is left at rest for a prescribed period to effect the successive precipitation of the whiskers to the bottom in the descending order of the fiber length. The dispersion 3 in the tank 1 is forcibly filtered through a filter member 6 by introducing compressed air through an inlet pipe 4 at the top of the filtration tank 1 or by sucking the filtrate outlet pipe 5 at the bottom. An aggregate of whiskers 7 produced by this method has vertically and continuously varying distribution of fiber length. The aggregate 7 is taken out of the tank 1 and cut perpendicular to the direction of filtration in wet state to obtain e.g. three whisker aggregates A-C having different fiber length distributions. If necessary, each aggregate is again dispersed in a liquid and the above procedures are repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for classifying the crystal shape of various whiskers, particularly their fiber length.

[Conventional technology]

Whiskers made of needle-like single crystals of S tc, S L3N4, or graphite can control the crystal shape by selecting thermal and chemical conditions during generation, but there is still a considerable range of fiber length etc. It may give a medium distribution.

Recently, this type of whisker material has been put to practical use as a composite reinforcing material for metals, plastics, ceramics, etc. due to its excellent physical properties such as specific strength, specific modulus, heat resistance, and chemical stability.

However, if there are variations in the crystal shape of the whiskers,
This may cause disadvantageous phenomena such as the inability to impart desired performance to the resulting reinforced composite material or loss of homogeneity of the structure. For this reason, it is necessary to classify the fiber length, which has a particularly large influence, in the distribution.

[Problem that the invention seeks to solve]

Until now, no effective method has been found for classifying fine short fibers having whisker-like aspect characteristics. However, as a means of wet-classifying various fine powders for which sieving paper cannot be used, there is a method in which the target powder is dispersed in a certain type of liquid and classified using the difference in the gravitational settling speed of the particles (
gravity sedimentation method) is known.

The inventors have developed the present invention by applying the principle of the gravity sedimentation method and adding effective process improvements to the method in accordance with the classification of whisker fiber length.

[Means for solving problems]

The structure of the present invention is characterized in that whiskers are dispersed in a liquid, left to stand for a certain period of time, and then forcefully filtered, and the obtained whisker aggregate molded body is divided into a plurality of pieces in a direction perpendicular to one filtration direction. do.

Hereinafter, the process of the present invention will be explained in detail with reference to the explanatory diagram shown in FIG.

(a) Dispersion Whiskers such as SiC, 513N4 or graphite are thoroughly defibrated and then put into a filter tank 1 together with a dispersion liquid, and mechanical stirring is applied to homogeneously disperse whiskers 2 in liquid 3.

As the dispersion liquid, water or an organic solvent such as alcohol, acetone, or ether is used, and if necessary, a dispersant such as sodium hexametaphosphate is used in combination. The dispersed concentration of whiskers needs to be kept within an appropriate range because if the concentration is too high, the whiskers will rapidly aggregate with each other to form a lump. The optimal whisker dispersion concentration is 5.
In the range of 0% by weight or less, if the concentration exceeds this range, there is an increased risk of poor dispersion such as the above-mentioned agglomeration phenomenon occurring.

(a) Stirring in the static sedimentation filtration tank 1 is stopped, and the dispersion is allowed to stand for a certain period of time. At this stage, whiskers with large fiber lengths gradually settle to the bottom, and whiskers with fine fiber lengths stabilize in a suspended state at the top.

(1) Forced filtration The dispersion liquid in the tank is passed through the filter member 6 using means such as forcing compressed air into the inlet pipe 4 of the filtration tank l or suctioning the filtrate outlet pipe 5 at the bottom under reduced pressure. Force filtration.

By this operation, the whiskers are formed by filtration into an aggregate in which the fiber length distribution changes continuously in the vertical direction.

(1) Plural division The obtained whisker aggregate molded body 6 is taken out from the filtration tank 1 and cut in a direction perpendicular to the filtration direction in a wet state to be divided into a plurality of pieces. For example, when divided into three as shown in FIG. 1 (1), A.

Each piece of B and C is classified as a whisker aggregate having a different fiber length distribution. Therefore, the 0 piece located in the lower layer can be classified into a category with a long fiber length, the A piece in the upper layer can be classified into a category with a short fiber length, and the B piece in the middle layer can be classified into a category with a medium fiber length.

The whisker aggregates of each category classified in this way are used as a dried preform or in a fluffy state after drying and defibrated, depending on the purpose of application.

(e) Repetition The wet whiskers of each division divided into multiple parts in (1) above are dispersed in the liquid again, left to stand for a certain period of time, and then forced, and the resulting whisker aggregate molded body is oriented in the filtration direction. Repeat the operation of dividing into multiple parts in the perpendicular direction. Through this processing, the divided sections are further divided into smaller sections, and classification accuracy can be improved.

[For production]

According to the present invention, the processing functions of (a) to (1) above, such as in-liquid dispersion, natural sedimentation, filtration molding, and segmentation, act in a complex manner to effectively control the fiber length distribution of whiskers. Classify. Furthermore, by repeating the operation -(sai), it is possible to further improve the accuracy of classification.

〔Example〕

Example 1゜ Diameter 0.2-0.5μ shoulder, fiber length from 5μ butt to 60μ
β-crystalline SiC whiskers (
The filtrate outlet tube was closed and the defibrated solution was placed in a filtration tank together with pure water. The concentration ratio of SiC whiskers to pure water is
It was bound at 3.5% by weight.

A rotary blade stirrer is installed in the filtration tank and activated, and the Si
The C whiskers were uniformly dispersed. The rotary stirrer was then removed and the dispersion was allowed to stand for 12 hours. After standing still, most of the whiskers had settled to the bottom of the tank, except for a few extremely fine whiskers floating in suspension.

The liquid outlet pipe of the filtration tank was opened, air was forced into the space above the dispersion, and the dispersion was forcibly filtered under a pressure of 6 kg/cm''.

The SiC whisker aggregate formed by filtration had a cylindrical shape with a diameter of 12,511 m and a height of 751 m. Take out this aggregate molded body from the filtration tank, cut it into rings in a direction perpendicular to the filtration direction while keeping it wet, and cut it into rings A, B, and C from above.
It was divided into three equal parts. Each divided whisker aggregate piece was dried and defibrated, and the fiber length distribution of the whiskers belonging to each division was measured. As a result, the fibers were classified into three levels of fiber length distribution (HiH distribution width, average length) as shown in Figure 2.

Example 2 For each of the SiC whisker aggregates A, B, and C obtained by the method of Example 1, the same dispersion, static sedimentation, forced filtration, and three-division treatment as in Example 1 were repeated to obtain the first Figure (o)
It was classified into categories (1) to (5) as shown in .

The relationship between each class classified in this manner and the fiber length distribution (←→distribution width, ■average length) is also shown in FIG. From this result, it was confirmed that the classification accuracy of this example was greatly improved compared to Example 1 (A, B, C).

Among the classified categories, those classified from piece B (2),
The fiber shapes of SiC whiskers belonging to (3) and (4) are shown in Figs. 3 to 5 as 500x magnified micrographs. Figure 3 of (2) shows the fiber length of 15 to 30 μm located in the upper layer divided into 3 parts, and Figure 4 of (3) shows the fiber length of 2 in the middle layer.
(4) with a fiber length in the range of 8 to 45 μs;
The figure shows the lower layer having a fiber length of 40 to 53 μm.

〔Effect of the invention〕

The present invention provides an effective method for classifying whisker fiber length, for which no effective means has been found in the past, and its construction means are extremely simple, so it has great industrial value. It is.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the process of the present invention, and FIG. 2 is a diagram showing the relationship between classification categories and whisker fiber length distribution according to the present invention. Figures 3 to 5 are classification examples (3 categories) of the present invention.
This is a 500x magnified microscopic photograph showing the fiber shape of SiC whiskers in FIG. Patent applicant Tokai Carbon Co., Ltd. Agent Patent attorney Masayasuke Takahata lΣ

Claims (1)

[Claims] 1. The whiskers are dispersed in a liquid, allowed to stand for a certain period of time, and then forcefully filtered, and the obtained whisker aggregate molded body is divided into a plurality of pieces in a direction perpendicular to the filtration direction. How to classify whiskers. 2. Repeat the operation of dispersing the whiskers in each of the multiple divisions into a liquid, allowing it to stand for a certain period of time, then forcefully filtering it, and dividing the obtained whisker aggregate into multiple divisions in a direction perpendicular to the filtration direction. A method for classifying whiskers according to claim 1.