JPH03150301A - Manufacture of extremely thin metal flake - Google Patents

Abstract

PURPOSE:To manufacture extremely thin metal flake having regular particle diameter and thickness and high aspect ratio by pulverizing, spreading and further reducing the thickness after roughly pulverizing short fibrous flowing shape metal micro chips along shearing slip plane and flaking and making finely of these. CONSTITUTION:Metal or these alloy of steel, brass, aluminum, titanium, stainless steel, etc., is formed into flowing shape metal micro chips having the shearing slip plane to almost circular thin slice direction. This flowing shape micro chip are roughly pulverized by using a ball mill, etc., so as to promote flaking and minuteness in priority along the above shearing slip plane. By this method, the flat metal raw powder having <= about 10mum thickness and >=70% of chip of >=10 aspect ratio is obtd. Successively, thickness reducing treatment is further executed to this flat chip by pressing of drying type stamp mill, etc., and pulverized spreading means having large scrubing action. By this method, the extremely thin metal flake mainly containing chip of >=30 aspect ratio, is obtd. at high yield and a low cost.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is used to strengthen plastics, metals, ceramics, etc., to add design to paints, etc. by imparting metallic luster, and to impart corrosion resistance and durability. The present invention relates to a method for producing ultra-thin metal flakes with an aspect ratio of 30 or more suitable for.

<Prior art and its problems> In recent years, in order to improve the durability and corrosion resistance of paints, etc., give them metallic luster, and enhance the electromagnetic shielding effect, high aspect ratio particles with uniform particle size and thickness have been developed. Ultra-thin metal flakes with the ratio (average major axis/average thickness) are required.

The ultra-thin metal flakes used for the above purpose have a maximum length of lOOμm or less (more preferably 80μm or less) and an average thickness of 1μm or less (more preferably O-l-o
, 5 μm), an average major axis of lO to 90 μm (more preferably 15 to 80 μm), and an aspect ratio of 30 or more (more preferably 100 or more).

When using a spray gun for paint etc., the maximum length is 1
If it exceeds 00um, there is a risk of clogging the nozzle.
If the average thickness exceeds 1 μm, the average major axis is less than 10 μm, and the aspect ratio is less than 30, it will not be possible to have a sufficient specific surface area, and the labyrinth effect and hiding effect will not be obtained. The characteristics of ultra-thin metal flakes cannot be exhibited against rust, etc.

Conventionally, methods for producing flat metal powder include a method in which a raw metal is melted and atomized by an atomization method in which water or inert gas is ejected from a nozzle, and then flattened by a ball mill or the like.
However, although these methods can produce ultrathin metal flakes with a uniform particle size and thickness and a high aspect ratio, they are inefficient and very costly.

In addition, for example, in Japanese Patent Application Laid-Open No. 98406,
In order to obtain high-grade metal flakes, stainless steel thin plates and foils are nitrided to increase their hardness and make them easier to pulverize. After pulverization, they are heated and denitrified in a hydrogen stream, and then treated with an aqueous solution of sodium percarbonate. We are proposing a method for producing stainless steel flat fine powder for paints by decarburizing.

Furthermore, Japanese Patent Application Laid-Open No. 5-67101 proposes a method in which rollable metal powder is supplied to a rolling roll without overlapping each other, and the rolled flat metal powder is scraped off from the roll.

However, it is difficult to efficiently produce ultra-thin metal flakes with a uniform grain size and thickness and a high aspect ratio at a low cost through the complicated processes described in the above two prior art techniques. .

<Objective of the Invention> Therefore, the object of the present invention is to produce ultra-thin metal flakes with a uniform particle size and thickness, a high aspect ratio, and a high yield through a simple process at an extremely low cost and with a high yield. The goal is to provide a method that can be used.

<Configuration of the Invention> The above object is achieved by the following present invention. That is, the present invention is produced by coarsely pulverizing short fibrous flow-shaped metal micro-chips having a shearing sliding surface substantially in the ring cutting direction so as to preferentially promote exfoliation refinement along the shedding sliding surface. A flat metal raw material powder containing 70% or more of powder with an aspect ratio of 1o or more is further reduced in thickness by a crushing and spreading means having a large pressing and rubbing action.
The present invention provides a method for producing ultra-thin metal flakes mainly composed of powder having an aspect ratio of 3o or more.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

The metal materials used in the present invention include metals such as steel, brass, aluminum, titanium, and stainless steel, or alloys of these metals.

In the present invention, the flatness of the fine powder of the metal material is expressed by the aspect ratio defined as the ratio of the average major axis to the average thickness of the fine powder.

The flat metal raw material powder produced according to the present invention is produced as follows: First, a metal material is formed into a flow-shaped micro-chip having a shearing sliding surface in a direction substantially perpendicular to the direction of cutting or grinding. Process under the following conditions. This flow-shaped micro-chip reduces the depth of cut and minimizes lO
0 μm or less, preferably 50 μm or less (partially 30 μm or less by setting the cut condition to the lower right of the broken line a in Fig. 1, which will be described later).
Although some lengths exceeding 0 μm may be mixed in,
It is desirable to adjust the conditions so that the fibers mainly have a length of 3″0 to 300 gm and a thickness of 50 μm or less.

These flow-shaped micro-chips cannot be identified with the naked eye, but since they have the above-mentioned shedding sliding surface in the cutting direction, they can be easily crushed by a crushing method such as a ball mill that has a large rubbing action. It peels off along the sliding surface and is crushed into flat powder that looks like slices. Therefore, the short axis of this flat powder (the flat raw material powder of the present invention) almost corresponds to the thickness of the chips, and the long axis is either the same or slightly larger due to the diagonal cutting. Some of the pieces are crushed and smaller in size. On the other hand, the thickness depends on the crushing time, but as seen in the examples below, the thickness is 10 μm.
Grinding progresses easily to less than m, usually several μm,
The important feature is that thin flat raw powder can be easily obtained in such a fine dimension range, where the main ingredient is flat raw powder having an aspect ratio of 5 or more, more preferably 10 or more. This flat raw material powder is further dry stamp milled,
By adding simple crushing and rolling processing using dry ball mills, wet ball mills, vibrating ball mills, and grinders with large pressing and rubbing effects, the aspect ratio is 30.
If the thickness of this flat metal raw material powder is further reduced, ultra-thin metal flakes with an aspect ratio of 30 or more with uniform particle size and thickness suitable for the purpose of use can be obtained. can be manufactured. If the raw material powder has an aspect ratio of less than 5, the efficiency will be extremely low to make ultra-thin metal flakes with a high aspect ratio.
As disclosed in Japanese Patent No. 480, an extra process for flattening such as intermediate annealing is required.

If the micro-chips mentioned above are too large, exceeding 300 μm, especially exceeding 500 μm, coarse grinding will not progress smoothly ((), the grinding time will be prolonged, and large flat raw material powder and crushed fine As a result, even when re-pulverizing into ultra-thin flakes, it is easy to reduce efficiency, inconsistency in product dimensions, and decrease in yield, so the tolerance for dimensional variation increases. It is wise to avoid it unless it is large.

For the same reason, the major and minor axes of the flat raw material powder are mainly 90 μm.
The average diameter is desirably less than m, particularly less than 50 μm, and the average diameter is preferably slightly smaller, such as 10 to 20 μm.
This dimensional adjustment is mainly performed by adjusting the thickness of the chips.

On the other hand, the finished flat metal powder has a loILm or less, especially 5 μm.
The following is preferable, and it is effective to adjust the crushing means and the crushing treatment time.

Until now, it was unknown what kind of raw material powder was suitable for obtaining ultrathin metal flakes with a high aspect ratio.
However, in order to reuse the cutting waste (chips) generated when cutting or grinding metal materials, the inventors of the present invention have attempted various methods of pulverizing the chips. Once selected, flat metal raw material powder with uniform particle size and thickness and high aspect ratio can be produced by simple crushing, and furthermore, by further processing this flat metal raw material powder with a specific crushing means, New knowledge was obtained that ultrathin metal flakes with an extremely high aspect ratio, that is, finished flat metal powder, can be efficiently obtained, and the yield of desired dimensions and shapes as described above is extremely high.
The present invention was completed based on this new knowledge, which was not previously known, by researching conditions for reproducing it.

As will be exemplified later in Examples, the cutting chips in the present invention are particularly suitable for extremely fine short fibers by maintaining the cutting depth at a minute value of, for example, several tens of micrometers or several micrometers. You can get the following. As a result, the length is several 10 μm or at most several 100 μm,
Since the diameter is about several micrometers to several tens of micrometers, the impression is completely different from the chips that are curled and several centimeters to several tens of centimeters in length, and the impression is completely different from the chips that are used as cutting waste.

It would be more appropriate to call it "micro chips."

When I actually spilled a small amount of it onto a piece of paper and shook the paper, faint, minute dots spread out like thin dirt, like scattered ash, and even when I looked at it with the naked eye, I could tell it was fibers. Recognized things rarely exist. However, when this was observed under 10 times magnification, it was clearly in the form of short fibers, and when further magnified 1000 times,
There are many parallel lines in the direction of cutting the fiber into rings. However, with fibers under different cutting conditions, this type of cut line is hardly observed even in slightly thick staple fibers. Even if such unsuitable fibers are pulverized, the fibers will be elongated and, although they may be slightly torn, no round-shaped flat powder will be produced.

In the case of the present invention, only in the case of minute chips obtained by flow cutting (the above-mentioned micro chips), which are too small to be discerned with the naked eye, a crushing method mainly consisting of rubbing is used to The essence lies in the fact that we have found that it is possible to easily produce flat flakes with minute dimensions that cannot be easily obtained by ordinary methods, and that can be easily transformed into finer round slices. In other words, from the outside, the fine powder (micro chips), which looks like a faint point that can barely be seen with the naked eye, turns into an even finer powder (flat raw material powder). Although it seems to be just one option among the common grinding techniques, in fact, only with a specific combination of raw materials and processing methods, it is possible to easily obtain an unexpectedly fine and highly flattened powder. By further reducing the thickness of the flat metal raw material powder containing 70% or more of the powder with an aspect ratio of 10 or more,
The finding that ultra-thin metal flakes with aspect ratios of 30 or more can be produced is the gist of the technology of the present invention.

The flow-shaped chips used in the present invention are made by cutting or grinding a metal material, and typically, based on the cutting theory, FIGS. 2, 3a, 3b, 3c, and 3d are used. I will explain.

When cutting a metal material 1, which is a work material, with a cutting tool 2 such as a cutting tool or a milling cutter, the shape of chips generated varies depending on the cutting conditions, as shown in Figures 3a, 3b, 3c, and 3d. Shaped micro chips 3. There are four types: shear type chips 31, crack type chips 32, and tear type chips 33. Cutting conditions that affect the morphology of chips include the rake angle 4 shown in Fig. 3a.
(measured clockwise from the normal direction of the cutting surface at the angle formed by the normal direction of the cutting surface and the cutting tool), depth of cut 5, cutting speed, and properties of the metal material to be cut.

The flow-shaped microchip 3 used in the present invention is produced under cutting conditions such as cutting speed, small depth of cut, large rake angle, etc. in the region I shown in Fig. 2, as shown in Fig. 3a. As the cutting tool 2 advances, a portion of the cut depth 5 of the metal material 1 to be cut causes shear slipping in a direction substantially perpendicular to the cutting direction, and is continuously shaved from the metal material 1.
In the flow-type micro cutting 3, the shear slip that occurs in a direction substantially perpendicular to the cutting direction is approximately equally spaced, very narrow, and appears continuous, and the thickness of the cutting is also approximately constant. For this reason, flow-shaped chips can be easily divided along the shear sliding surface by coarse pulverization using a pulverizing means with a large rubbing action, such as an attritor mill or a ball mill, and can be easily divided into grains with a uniform particle size and thickness and an aspect ratio of 5 or more. , especially 1
0 or more flat metal raw material powder.

In the area marked ■ in Fig. 2, that is, under cutting conditions such as a small depth of cut and a small bevel angle, the raw potato shear type chips 31 are
As shown in the figure, the shear slip is not uniform, and slip failure occurs at regular intervals, resulting in uneven chips with deep constrictions at regular intervals. For this reason, the raw material powder obtained by coarsely pulverizing the sheared chips 31 with a Henschel mixer, an attritor mill, a plastic pellet pulverizer, a ball mill, etc. does not have uniform particle size and thickness.
Since it contains a large amount of metal powder with a small aspect ratio, even if it is further processed, the yield of "oblate metal powder suitable for the purpose of use" is low, making it unsuitable as a raw material powder for flat metal.

In addition, the crack-shaped chips 32 or fracture-shaped chips 33 that are likely to occur under cutting conditions such as small cutting speed, large depth of cut, and small bevel angle shown in FIG. 2 are shown in FIG. 3c. and third
As shown in Figure d, it is caused by a brittle crack that occurs instantaneously, so it does not undergo plastic deformation due to shear slip seen in flow type chips 3 and shear type chips 31, and has a granular shape. Since it is difficult to flatten by coarse grinding, it is unsuitable as a flat metal raw material powder.

In the case of grinding, there are advantages such as there is no need for extra processes such as separating the abrasive grains from the grinding pieces, and it is possible to grind at high speed with a belt grinder that contains less abrasive grains.
The same product as above can be obtained by coarsely pulverizing the ground pieces using a grinding means having a large rubbing action such as an attritor mill or a ball mill.

A generally known method can be used for coarsely pulverizing the flow-type microcuts used in the present invention. For example, there are methods using attritor mills, ball mills, and the like. In the present invention, a centrifuge or the like was used as a cleaning treatment to remove oil and moisture etc. attached to the flow-type micro chips, but any device that can effectively separate the chips and oil and moisture etc. For example, a solvent method and other generally known methods can be used.

Next, the thus obtained flat metal raw material powder containing 70% or more of the powder with an aspect ratio of l-0 or more is further reduced in thickness by a crushing and spreading means having a large pressing and rubbing action. Yield of ultra-thin metal flakes of 30 or more is 8
0% or more, preferably 90% or more.

A horizontal ball mill is preferably used as the crushing and spreading means with large pressing and rubbing effects.

Further, it is preferable to adjust the crushing time so that the obtained ultra-thin metal flakes preferably have an average thickness of 1 μm or less.

Below, flow-shaped chips are formed based on Fig. 1, and the obtained flow-shaped micro-chips are coarsely crushed by means of strong rubbing action, and contain 70% or more of particles with an aspect ratio of 5 or more. The cutting conditions will be described so that when used as flat raw material powder, ultrathin metal flakes with an aspect ratio of 30 or more can be obtained with a yield of 90% or more.

The present inventors cut stainless steel, nickel, chromium, titanium, and their alloys at a cutting speed of 1200 to 1500 m/min, and conducted tests while changing the depth of cut and rake angle of the cutter, as shown in Figure 1. I got similar results. In Fig. 1, the a curve shows that flat raw material powder containing 70% or more of particles with an aspect ratio of 5 or more is easily obtained, and by further crushing and spreading it using means with strong pressing and rubbing action, the aspect ratio is 30. This is the boundary line of Nagagata-kiri, which can yield 90% or more of the above flat stainless steel powder as a finished product. Curve b indicates that flat raw material powder containing 30% or more of particles with an aspect ratio of 5 or more can be easily obtained, and by further crushing and rolling it using means with strong pressing and rubbing action, a finished flat stainless steel with an aspect ratio of 30 or more can be obtained. This is the boundary line where 60% or more of the powder can be obtained as a finished product, and C
The curve is the boundary line between sheared chips and cracked chips or fractured chips. - From this, it is clear that when cutting under the conditions (depth of cut, rake angle) below curve a in Figure 1, flat finished metal powder as described above can be obtained at a high yield (for example, 90% or more). It was revealed.

Although it is possible to obtain the micro chips of the present invention even under the conditions between the lines a and b in Figure 1, the efficiency, uniformity of dimensions,
Since it is inferior to the conditions below the a curve in various aspects such as yield,
I cannot recommend it positively.

<Example> Next, the present invention will be specifically explained using examples.

(Example 1) Stainless steel was cut under the following conditions to obtain flow-shaped micro chips.

Rake angle: approximately -20° Depth of cut: 10 am Cutting speed: 1300 m+/win The adhering oil and water content of the chips was removed using a centrifuge, and the chips were roughly pulverized for 2 hours using an attritor mill to obtain flat stainless steel raw material powder.

Long diameter: 5 to 30 μm Short diameter: 2 to 15 μm Thickness: 1 to 3 mm Over 90% of the samples had an aspect ratio of 5 or more.Over 80% of the samples had an aspect ratio of 10 or more. When the raw material powder was further processed in a ball mill for 7 hours, the major diameter was 5-80um and the thickness was 0.1-0.5μ.
90% or more of ultra-thin flat stainless steel flakes with an aspect ratio of 30 or more were obtained.

(Example 2) A titanium plate was cut under the following conditions to obtain flow-shaped micro chips.

(Angle: approx. -40" Depth of cut: 3 μm Cutting speed: 1000 m/sin) The micro chips were centrifuged to separate the oil and moisture attached, and then ground in a ball mill for 1 hour to obtain flat titanium raw material powder. I got it.

Long diameter: 6 to 30 μm Short diameter: 2.5 to 16 μm Thickness: 1 to 2,8 mm Over 85% had an aspect ratio of 5 or more, and over 80% had an aspect ratio of 10 or more. When the obtained raw material powder was further processed in a ball mill for 6 hours, 80% or more of ultra-thin flat titanium flakes having a major axis of 5 to 80 μm, a thickness of O, 1 to 0.5 μm, and an aspect ratio of 30 or more were obtained.

(Example 3) SUS304 stainless steel was ground using a flat belt grinder under the following conditions.

Grinding cloth R/R cross belt #80 belt speed 1
200 m/sin Grinding speed 10 m+/sin The obtained micro-chips exhibit a curled fibrous shape, and the attached oil and moisture are removed using a centrifugal separator.
After coarse grinding for half an hour, flat stainless steel raw material powder was obtained.

Long diameter: 6 to 40 gm Short diameter: 6 to 20 gm Thickness: 0, 9 to 2, 8 mm More than 95% of the pieces had an aspect ratio of 5 or more.

80% or more of the samples had an aspect ratio of 10 or more. When the obtained raw material powder was further subjected to ball milling for 6 and a half hours, the major diameter was 5 to 80 μm and the thickness was 0.1 to 0.5 μm.
90% or more of ultra-thin flat stainless steel flakes with a length of 6 m and an aspect ratio of 30 or more were obtained.

(Comparative Example 1) Water atomized SUS304 steel (average particle size 60 μm)
When the material was pulverized in a ball mill, 55% of the completed ultrathin metal flakes with a long diameter of 5 to 80 μm, a thickness of 0.1 to 0.5 μm, and an aspect ratio of 30 or more were obtained after 18 hours of processing.

As described above, even though it took several times as long as in Example 3, the yield of the finished product of ultra-thin metal flakes was very poor.

(Comparative Example 2) Separately, the raw material powder obtained in Example 1 was further treated with Hammer Rarasha for 6 hours. With this treatment, the raw material powder was slightly improved, but there was hardly any improvement in the aspect ratio. , ultra-thin metal flakes with an aspect ratio of 30 or more reached only 7%. In this case, if a jaw crusher were used, the micro chips would pass through because they were too fine, so there was no point in crushing them.

<Effects of the Invention> According to the method of the present invention, when cutting or grinding a metal material, by appropriately selecting cutting or grinding conditions such as cutting speed, depth of cut, and rake angle, the cutting or grinding direction can be adjusted. Simply by coarsely pulverizing flow-shaped micro-chip powder that has a shear slip in a direction substantially perpendicular to this direction, flat metal raw material powder with a uniform particle size and thickness and an aspect ratio of 5 or more can be produced. 10 or more powder is 70% or more flat metal raw material powder, and if the thickness is further reduced by a crushing and spreading means with large pressing and rubbing action using a simple device such as a horizontal ball mill, it is suitable for the purpose of use. In addition, ultrathin metal flakes with uniform particle size and thickness and substantially an aspect ratio of 30 or more, more preferably 100 or more can be easily produced. According to the present invention, the yield of ultra-thin metal flakes has been greatly improved and the manufacturing cost has been significantly reduced.

[Brief explanation of the drawing]

Figure 1 shows the shape of chips produced by the depth of cut and rake angle when stainless steel, nickel, chromium, titanium, and their alloys are cut at a cutting speed of 1200 to 1500 m/min, and the shapes of chips produced from the chips. It is a graph showing the relationship between flat metal raw material powders. FIG. 2 is a graph showing the form of chips generated depending on the depth of cut and rake angle when mild steel is cut at a constant cutting speed. Figures 3a, 3b, 3c and 3d are diagrams showing the morphology of micro-flow type chips, shear type chips, crack type chips and fracture type chips, respectively. Explanation of symbols ■...A region where flow-shaped micro chips are produced, ■...A region where shear-shaped chips are produced, ■...A region where crack-shaped chips or fracture-shaped chips are produced, l... - Workpiece metal material, 2... Cutting tool, 3... Flow type micro chips, 4... Rake angle, 5... Depth of cut, 31-... Shear type chips, 32. ...Crack-shaped chips, 33...Crack-shaped chips, A...Cutting direction (relative advancing direction of the cutting tool), a-...Flat stainless steel with an aspect ratio of 30 or more 9
Boundary line of flow-shaped microcuts that can be obtained by 0% or more, b...Flat stainless steel with an aspect ratio of 30 or more is 6
Boundary line that can obtain 0% or more, C... Boundary line between shear type cutting and cracked chips or fractured chips Patent applicant Kawatetsu Chikuru Search Co., Ltd. / IGi ■ Rake angle (゜》・IG-2 scoop iji) IG-3a 3), ya4

Claims (1)

[Claims] (1) An aspect ratio produced by coarsely pulverizing a short fibrous flow-shaped metal micro-cut material having a shearing sliding surface that is approximately in the direction of the ring cutting so as to preferentially promote fine exfoliation along the shedding sliding surface. An ultra-thin metal mainly composed of powder with an aspect ratio of 30 or more, which is characterized by further reducing the thickness of a flat metal raw material powder containing 70% or more of powder with an aspect ratio of 10 or more by using a crushing and spreading means with large pressing and rubbing effects. Method of producing flakes.