JPH01254268A - Purification of whisker - Google Patents

Abstract

PURPOSE:To efficiently remove a non-fibrous particle and abnormal whisker aggregate, by continuously supplying a liquid to a dispersion tank filled with a crude whisker and the liquid at a constant speed to form a rising stream having a definite speed toward the upper end of a purifying tower. CONSTITUTION:A dispersion tank 1 is filled with a crude whisker and a liquid as a uniform dispersion and the liquid to be supplied is supplied into the dispersion tank 1 at a constant speed to generate a rising stream having a definite speed from the dispersion tank 1 to the upper end of a purifying tower 6. Since a normal whisker follows said rising stream, the whisker can be efficiently and accurately purified. Since the liquid to be supplied sent in the bottom part of a collection tank 8 is again recirculated to the piping 3 for the liquid to be supplied from reduced pressure suction piping 10, the liquid to be supplied can he economically used. Further, the stagnated non-fibrous particle and abnormal whisker aggregate in the dispersion tank 1 are discharged from the purifying system intermittently or continuously to make long-term continuous operation possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a whisker purification method for separating and removing non-fibrous particles and abnormal whisker aggregates mixed in crude whiskers.

[Conventional technology]

In recent years, whisker-reinforced metals, which use whiskers made of silicon carbide, silicon nitride, graphite, potassium titanate, etc., as reinforcement materials for base materials such as metals, plastics, and ceramics,
Whisker-reinforced plastics, whisker-reinforced ceramics, etc. have been developed and are attracting attention. The whiskers used as the reinforcing material are linear materials in which silicon carbide, silicon nitride, etc. are crystallized in the form of fine whiskers, and have characteristics such as extremely excellent tensile strength and elastic modulus.

The performance of such whiskers as a reinforcing material is determined not only by the shape characteristics (length, diameter, straightness) of the whiskers, but also by the non-fibrous particles (
Substances containing whisker component elements that did not become whisker-like single crystals but were produced as by-products during whisker production, as well as unreacted lumps with particle diameters of several tens of micrometers to several hundred micrometers) and abnormal whisker aggregates (whisker It has a burrow-like form in which fibers are intertwined with each other, and is greatly influenced by the presence or absence of entangled particles (the diameter of which is about the same as that of non-fibrous particles).

This is because the presence of non-fibrous particles and abnormal whisker aggregates may cause the whiskers themselves to be unevenly dispersed in the base material, and the aspect ratio of non-fibrous particles is significantly smaller than that of the whiskers, which contributes to improved strength. This non-fibrous If the above-mentioned materials are composited in a state in which particles and abnormal whisker aggregates are mixed, the strength of the composite material may not be improved or the strength may vary, making it difficult to achieve the initial purpose.

Therefore, various methods have been proposed for separating and removing non-fibrous particles and abnormal whisker aggregates in whiskers, and these proposals have been used to improve the performance of composite materials. As such a proposal, for example, Japanese Patent Application Laid-Open No. 61-146
There are methods disclosed in Japanese Patent Publication No. 798 and Japanese Patent Application Laid-Open No. 61-236700. Of the above, in the former method, silicon carbide whiskers are mixed into a hydrophobic organic liquid with a specific gravity of 2 or more and dispersed uniformly, and then added to the hydrophobic organic liquid with a specific gravity of 80 to 1
Add 50% water by volume and stir to form an emulsion. Then, after adding an appropriate amount of water, the mixture is allowed to stand to separate the hydrophobic organic liquid from the water, and the silicon carbide whiskers are transferred to the water layer side for purification. The latter is
This is a method in which whiskers are dispersed in water or an organic solvent, stirred sufficiently, and then allowed to settle to separate into a bottom layer of concentrated non-fibrous particles and an upper layer of concentrated fiber particles.

[Problem that the invention seeks to solve]

However, the former method uses a special halogenated hydrocarbon such as tetrabromoethane as a hydrophobic organic liquid, and this halogenated hydrocarbon is expensive and requires recovery and regeneration work after its use. The problem is that it is troublesome. Furthermore, these halogenated hydrocarbons are toxic to the human body, and their separation accuracy is also poor.

In the latter method, the non-fibrillated particles migrate to the bottom together with the fibrillated particles during sedation, resulting in a decrease in purification yield, and the non-fibered particles entrap air bubbles, which reduce the sedimentation rate due to their buoyancy. The problem is that the process is delayed and remains in the fiberized particles. Furthermore, since the non-fibrous particles and the fibrous particles are naturally deposited one after another from the bottom, it is difficult to separate the non-fibrous particles and the fibrous particles, resulting in poor purification accuracy.

The present invention was made in view of the above circumstances, and provides a whisker purification method that can economically, efficiently, and precisely separate and remove non-fibrous particles and abnormal whisker aggregates mixed in whiskers. is its purpose.

[Means for solving problems]

In order to achieve the above object, the whisker purification method of the present invention includes a dispersion tank, a purification tower that communicates with the upper part of the dispersion tank and extends upward, and a refining tower that communicates with the upper end of the purification tower through a side overflow port. By filling and uniformly dispersing the crude whiskers and liquid into the dispersion tank of the apparatus equipped with a collection tank, and by continuously supplying the liquid at a constant speed into the dispersion tank, An upward flow is generated at a constant speed toward the upper end of the purification column, and only the whiskers that rise following this upward flow are collected as proper whiskers in the collection tank.

[Effect]

In other words, the inventors came up with the idea that in order for whiskers to exhibit better performance as reinforcing materials, it is necessary to accurately separate and remove non-fiber particles and abnormal whisker aggregates mixed in whiskers. We conducted a series of studies. As a result, we focused on the sedimentation behavior of whiskers in liquid due to gravity, and we filled the bottom of a vertically extending tank with a dispersion liquid in which crude whiskers were evenly dispersed, and the liquid was continuously supplied to the bottom of this tank. It has been found that purification can be carried out efficiently by supplying the liquid directly to the tank and discharging this liquid from the upper side of the tank. That is, by supplying and discharging liquid into and out of the tank, an upward flow at a constant speed is generated from the lower side of the tank toward the upper side. As a result, non-fibrous particles and abnormal whisker aggregates are unable to rise upwards at flow rates below a certain level and remain settled at the bottom.
Only normal whiskers follow the upward flow of the supply liquid and rise to the upper side of the tank. The inventor discovered that it is possible to separate and purify whiskers by applying this phenomenon, and arrived at this invention.

Next, the present invention will be explained in detail.

Purification of whiskers according to the present invention can be carried out using an apparatus as shown in the figure. That is, in the figure,
Reference numeral 1 denotes a cylindrical dispersion tank with a bottom, and the upper side is formed so that the diameter gradually becomes smaller toward the upper end opening. 2 is a stirring device installed at the lower side of the dispersion tank 1, 3 is a supply liquid pipe connected to the side of the dispersion tank l, and by opening the pulp 4, the liquid is supplied from outside the yarn into the dispersion tank 1. It is supposed to be done. At the upper opening of the dispersion tank 1, there is a refining tower 6 in the form of a cylinder with a ceiling, which is formed so that its lower side gradually becomes smaller in diameter toward the lower end opening, with its opening aligned with the opening of the dispersion tank 1. and are connected by the flange portion 5. A pipe 7 extends slightly downward from the side surface of the upper end of the purification tower 6, and is arranged at the other end 7b to carry the liquid in the purification tower 6 sent from the side overflow lower a on the purification tower 6 side. The water is sent to the collecting tank 8. 9 is a filter plate provided in the collection tank 8, and 10 is a vacuum suction pipe connected to the bottom side of the collection tank 8. The other end of the vacuum suction pipe 10 is connected to the supply liquid pipe 3, so that the supply liquid sent to the collection tank 8 can be circulated to the dispersion tank 1 side.

In this configuration, first, crude silicon carbide, silicon nitride,
Whiskers made of graphite, potassium titanate, etc. are uniformly dispersed in the liquid, and this dispersion liquid is filled into the dispersion tank 1 and the stirring and dispersion is continued with the stirring device 2 to achieve secondary aggregation (
- Prevent the once-dispersed whiskers from agglomerating again. Then, the valve 4 is opened and the liquid is supplied from the supply liquid pipe 3 into the dispersion tank 1 at a constant speed (linear speed, the same applies hereinafter).

As a result, the dispersion liquid in the dispersion tank I is diluted and rises in the purification tower 6 at a constant speed together with the feed liquid, and the whiskers also rise in the purification tower 6 following this upward flow. It is fed into the collection tank 8 from the overflow lower a on the upper end side of the tank 6 via the pipe 7. However, among the crude whiskers in the dispersion, non-fibrous particles and abnormal whisker aggregates with particle diameters larger than normal whiskers have a faster settling speed in the liquid than the whiskers, so they cannot resist the upward flow. It settles and stays in the dispersion tank 1. Therefore, only normal whiskers can be purified and sent into the collection tank 8 while the non-fibrous particles and abnormal whisker aggregates in the crude whiskers remain in the dispersion tank 1. The purified whiskers placed in the collection tank 8 are separated from the feed liquid by a filter plate 9 in the collection tank 8, collected, dried, and crushed to form a bulk reinforcing material. Further, the supply liquid is sent out of the system from the reduced pressure suction piping 10, and is again supplied into the dispersion tank 1 via the supply liquid piping 3.

In the above method, the most important point is that the purification column 6
The rate of rise of the feed liquid within the feedstock is preferably within the range of 0.2 to 5 cm/min. When the above speed exceeds 5 CID/min, the settling speed of non-fibrous particles with a larger particle size than whiskers and abnormal whisker aggregates becomes slower than the rising speed of the feed liquid, and they rise together with normal whiskers. This makes separation and purification difficult. In addition, when the above speed is lower than 0.2 cm/min, the settling speed of some of the whiskers becomes faster than the rising speed of the feed liquid, and the whiskers are dispersed together with non-fibrous particles and abnormal whisker aggregates. Remains in tank 1, reducing purification efficiency. Therefore, in order to improve whisker purification efficiency, it is preferable that the rate of rise of the feed liquid be within the above range.

Next, what is important is the concentration of the dispersion liquid in which the crude whiskers are dispersed.In order to uniformly disperse the whiskers in the liquid, it is necessary to keep the concentration of the dispersion liquid below 5% by volume. In order to prevent the secondary coagulation of whiskers and perform efficient purification within the purification system consisting of the dispersion tank 1 and the purification tower 6, it is necessary to (Concentration when the dispersion reaches the top)
It is preferable to keep it at 2% by volume or less. If the concentration of the dispersion liquid when dispersing the crude whiskers in the liquid exceeds 5% by volume, the whiskers cannot be dispersed, or even if they are dispersed, secondary aggregation is likely to occur immediately, leading to a decrease in purification efficiency and precision. In addition, if the concentration of the dispersion exceeds 2% by volume in the above purification system, the degree of contact between whiskers, between whiskers and non-fibrous particles, and between abnormal whisker aggregates increases, making it easy to cause secondary aggregation. as well as lead to a decrease in purification efficiency and precision. For this reason, the concentration of the crude whisker dispersion should be 5% by volume or less to ensure sufficient dispersion of the crude whiskers, and the initial concentration of the dispersion in the purification system should be 2% by volume or less to prevent secondary aggregation. is preferred.

Any method may be used to disperse the crude whisker dispersion, including ultrasonic stirring or other mechanical stirring (as long as the whiskers have particularly good separability, Instead of preparing a dispersion liquid in advance by stirring the whiskers and the liquid, they may be placed separately in the dispersion tank 1 and then stirred and dispersed. In addition, an organic solvent such as alcohol can be used, and as long as the whiskers have poor dispersibility, a dispersion liquid may be added for smooth dispersion, if necessary.

In the method of the present invention, crude whiskers and liquid are filled into a dispersion tank 1 as a uniform dispersion liquid, and the dispersion tank 1
By supplying the feed liquid at a constant rate into the dispersion tank 1.
From this, an upward flow at a constant speed is generated at the upper end of the purification tower 6, and by causing only normal whiskers to follow this upward flow, efficient and accurate purification can be performed. There is. According to this method, after the dispersion tank 1 is filled with the dispersion liquid and the pulp 4 is opened, continuous processing can be carried out unattended. Further, according to the illustrated device, the supply liquid sent to the bottom side of the collection tank 8 is
Since the supply liquid is circulated from the reduced pressure suction pipe 10 to the supply liquid pipe 3 again, the supply liquid can be used economically. Furthermore, long-term continuous operation is also possible by intermittently or continuously discharging the non-fibrous particles and abnormal whisker aggregates that remain in the dispersion tank 1 from the refining system. in this way,
According to this method, it is possible to purify whiskers that have extremely high industrial utility value.

Moreover, the method of this invention is not only applicable to the purification of whiskers (
, it can also be used to classify purified whiskers. In other words, when classifying the fiber length and diameter of whiskers according to certain values, the rate of rise of the feed liquid in the purification system is set to 0.
．． The speed is changed stepwise within the range of 2 to 5 cm/min.

For example, the speed may be low at first, and the speed may be gradually increased at regular intervals. As a result, initially only small-sized whiskers are refined, then slightly larger-sized whiskers, and gradually larger whiskers. Therefore, they can be classified by collecting them separately.

〔Effect of the invention〕

Since the present invention purifies whiskers as described above, it is possible to separate and purify whiskers from non-fibrous particles and abnormal whisker aggregates in an extremely simple manner, efficiently, accurately, and economically. In addition, the whiskers purified in this way do not contain non-fibrous particles or abnormal whisker aggregates, so when they are composited into a base material such as plastic, metal, or ceramic, they are dispersed extremely uniformly in the base material. As a result, the strength of the composite material can be significantly improved, and a highly reliable composite material with no variation in strength can be obtained, which has high industrial utility value.

Next, examples will be described.

[Example 1] 100 g of silicon nitride whiskers (fiber diameter 0.5 to I μn
+, fiber length 20 to 100 μra) was mixed with 800 d of water (silicon nitride dispersion concentration 3.9% by volume) and sufficiently dispersed using a Juicer mixer to prepare a uniform dispersion. This dispersion liquid is filled into the illustrated dispersion tank (inner volume 1, 1,500 ml), the valve 4 is opened, and the upward flow of liquid in the cylindrical portion of the dispersion tank 1 and the purification tower 6 is introduced into the dispersion tank 1. Water was continuously supplied at a speed of 2 cm/min.

While diluting the dispersion of silicon nitride whiskers, this feed liquid is added to the purification tower (the inner diameter of the cylindrical part is 50 mm) together with this dispersion.
mm, length 400 on) 6 and overflowed into piping 7 from lower a. In this case, the initial concentration of the dispersion was 1
．． It was set to 5% by volume. The dispersion liquid overflowing into pipe 7 is collected in a collection tank (
While recovering the water using a filter (inner diameter 100 mm, filtration height 200 M) 8, the above-mentioned water supply was continued until there were no whiskers rising in the purification tower 6 and the feed liquid in the purification tower 6 became transparent. At this time, an aspirator (not shown) is connected to the reduced pressure suction piping 10 of the collection tank 8, and by reducing the pressure on the lower side of the collection tank 8, the liquid portion is sucked into the reduced pressure suction piping 10,
Whiskers were collected on the filter plate 9. The purified whiskers collected on the filter plate 9 were examined using an optical microscope (x200x).
As a result of observation, no non-fibrous particles or abnormal whisker aggregates were observed in this purified whisker, and only normal whiskers were observed. Furthermore, when the residue that remained in the dispersion tank 1 was collected by filtration, 14.3 g of residue was obtained, and when this was observed in the same manner as above, it was found that most of it was non-fibrous particles and abnormal whisker aggregates. Therefore, the purification yield based on the charged weight in this example was 85%.

[Example 2] 100 g of silicon carbide whiskers (fiber diameter 0.3 to 1 μm
, fiber length 30 to 150 μm (11) was mixed with 1,000 μm of water (silicon carbide dispersion concentration: 3.1% by volume) and sufficiently dispersed using an ultrasonic disperser to prepare a uniform dispersion. This dispersion liquid was filled into the dispersion tank 1, and while stirring and dispersing it with the stirring device 2, the valve 4 was opened and water was supplied into the dispersion tank 1 at various speeds shown in Table 1 below. Thereafter, the same treatment as in Example 1 was performed to obtain the results shown in Table 1.

(Margin) [Example 3] 100 g of silicon carbide whiskers (fiber diameter 0.3 to 1 u
"*Fiber length 30-150μ11) was mixed with 1ooo* of water (silicon carbide dispersion concentration 361% by volume) and sufficiently dispersed using an ultrasonic disperser to prepare a uniform dispersion. This dispersion was dispersed as shown in the figure. Fill the tank (inner volume 1500ml!l) 1, open the valve 4 while stirring with the stirring device 2,
Water was continuously supplied into the dispersion tank 1 so that the rate of liquid upward flow in the cylindrical portions of the dispersion tank 1 and the purification tower 6 was 1.5 cm/min. At this time, the purification tower 6 was changed to one with a different internal volume so that the initial concentration of the dispersion liquid was 1 and 2.3% by volume, respectively, and the same treatment as in Examples 1 and 2 above was carried out. The results shown in Table 2 below were obtained.

(Margin below)

[Brief explanation of the drawing]

The figure is a longitudinal sectional view of an apparatus used in the method of the present invention. 1...Dispersion tank 6...Refining tower 7a...Side overflow port
8... Collection tank

Claims (3)

[Claims] (1) In the dispersion tank of an apparatus equipped with a dispersion tank, a purification tower that communicates with the upper part of the dispersion tank and extends upward, and a collection tank that communicates with the upper end of the purification tower through a side overflow port. , by filling and uniformly dispersing the crude whiskers and liquid, and by continuously supplying the liquid at a constant speed into this dispersion tank, a constant speed increase is achieved from this dispersion tank toward the upper end of the purification tower. A method for purifying whiskers, characterized in that a flow is generated, and only whiskers that rise following the upward flow are collected as suitable whiskers in the collection tank. (2) The speed of the upward flow in the purification column is 0.2 to 5 cm/mi
The whisker purification method according to claim 1, wherein n. (3) The method for purifying whiskers according to claim 1 or 2, wherein the initial concentration of the crude whisker dispersion is 2% by volume or less.