JPH0694561B2 - Method for producing ultra-thin metal flakes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention is used for strengthening plastics, metals, ceramics, etc., adding design property by imparting a metal melt to paints, imparting corrosion resistance, durability, etc. Aspect ratio of 30 suitable for
The present invention relates to the method for producing the ultra-thin metal flakes.

<Prior art and its problems> In recent years, in order to improve the durability and corrosion resistance of paints, impart metallic luster to paints, and enhance the electromagnetic shielding effect, a high-quality particle size and high aspect ratio are provided. Ultra-thin metal flakes (average major axis / average thickness) are sought.

The ultra-thin metal flakes used for the above purpose have a maximum length of 100 μm or less (more preferably 80 μm or less) and an average thickness of 1 μm or less (more preferably 0.1 to 0.5 μm).
m), average major axis 10 to 90 μm (more preferably 15 to 80 μm)
m) and an aspect ratio of 30 or more (more preferably 100 or more).

This is the maximum length of 10 when using a spray gun for paints, etc.
If it exceeds 0 μm, the nozzle may be clogged, and if the average thickness exceeds 1 μm, the average major axis is less than 10 μm, and the aspect ratio is less than 30, a sufficient specific surface area cannot be obtained, and the labyrinth effect and hiding effect are obtained. In particular, when used for paints, the characteristics of ultrathin metal flakes cannot be exhibited with respect to rust preventive power and the like.

Conventionally, a method for producing flat metal powder includes a method in which a raw material metal is melted, atomized by an atomizing method in which water or an inert gas is ejected from a nozzle, and flattened by a ball mill or the like. However, although it is possible to produce ultrathin metal flakes having a high particle size and thickness and a high aspect ratio, these methods are inefficient and extremely expensive.

In addition, for example, in Japanese Unexamined Patent Publication No. 56-98406, in order to obtain high-quality metal flakes, thin plates and foils of stainless steel are nitrided to increase hardness and easily become fine powder, and after crushing, in a hydrogen stream. We have proposed a method for producing stainless steel flat fine powder for paints by denitrifying by heating, further treating with an aqueous solution of sodium percarbonate, and decarburizing.

Further, JP-A-57-67101 proposes a method of supplying rollable metal powders to a rolling roll without overlapping each other and scraping the rolled flat metal powders from the rolls.

However, it is difficult to efficiently produce an ultrathin metal flake having a high particle size and a uniform thickness and a high aspect ratio at a low cost after the complicated steps as described in the above two prior arts.

<Object of the invention> Therefore, the object of the present invention is suitable for obtaining a high aspect ratio ultra-thin metal flake having a uniform particle size and thickness in a high yield, and it is produced at a very low cost and a high yield by a simple process. The purpose is to provide a possible method.

<Structure of Invention> The above object is achieved by the present invention described below. That is, the present invention was produced by coarsely crushing short fibrous flow-type metal micro-chips having an easily slipping surface in the direction transverse to the longitudinal axis so as to preferentially promote separation miniaturization along the sliding surface. Characterized by further reducing the thickness of a flat metal raw material powder having an aspect ratio of 10 or more by 70% or more by a crushing and spreading means having a large pressing and rubbing action, mainly comprising powders with an aspect ratio of 30 or more The present invention provides a method for producing ultra-thin metal flakes.

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

The metal material used in the present invention is a metal such as steel, brass, aluminum, titanium and stainless, or an alloy of such metals.

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

The flat metal raw material powder produced by the present invention is produced as follows. First, a metal material is processed under the condition that a flow-type microchip having a slip surface that is substantially perpendicular to the cutting or grinding direction is formed. This flow type micro-chip has a small cutting depth and should be 100 μm as far as possible.
Hereinafter, preferably 50 μm or less (set to the cutting condition at the lower right of a broken line a in FIG. 1 described later, and some of the lengths exceeding 300 μm may partially be mixed, but mainly the length 30 to It is desirable to adjust the conditions so that the fibers have a thickness of 300 μm and a thickness of 50 μm or less.

This flow-type microchip has an elongated shape, which is invisible to the naked eye. Since it is a chip produced by cutting and grinding, in reality, it is not a smooth rod-like shape, but it is mostly a slender crescent-shaped one with a large or small curvature.

The chips are so fine that they look like faint dots, and their fine shapes are invisible to the naked eye. However, it is not limited to a strict slice, but it is likely to cause a slip deformation in a direction in which the slice is almost cut, more strictly, in a direction that crosses the curved longitudinal axis at a right angle or at an angle, so that a thin piece is easily formed. Since it has an easy-to-separate easy-sliding surface, it can be easily pulverized into a flat powder like a slice by peeling along the sliding surface by a crushing device such as a ball mill that has a large rubbing action. It Therefore, the short diameter of this flat powder (flat raw material powder of the present invention) substantially corresponds to the thickness of the cutting powder, and the long diameter is equal to it.
The size is slightly increased due to the slanted slices. Some of them also break up and have smaller dimensions. On the other hand, the thickness depends on the crushing time, but as will be seen in Examples described later,
The flattening powder is mainly composed of particles having an aspect ratio of 5 or more, more preferably 10 or more. It is an important feature that thin flat powder can be easily obtained in such a fine size region. This flat raw material powder is further subjected to a simple crushing and spreading process with a crusher having a large pressing and rubbing action, such as a dry stamp mill, a dry ball mill, a wet ball mill, a vibration ball mill, and a bar mill, and powder having an aspect ratio of 10 or more is 70 % Or more flat metal raw material powder. By further reducing the thickness of this flat metal raw material powder, it is possible to produce ultrathin metal flakes with an aspect ratio of 30 or more, which have a uniform particle size and thickness and are suitable for the purpose of use. In the case of raw material powder having an aspect ratio of less than 5, the efficiency is extremely low in order to obtain ultra-thin metal flakes with a high aspect ratio, and flattening such as intermediate annealing occurs as disclosed in Japanese Patent Application No. 59-037480. An extra step is required for this.

The above-mentioned micro chips are too large to exceed 300 μm, especially 500
If the number of particles exceeds μm, coarse crushing is difficult to proceed smoothly, the crushing time is prolonged, and large flat raw material powder and crushed fine particles are mixed, resulting in increased dimensional variation. As a result, when re-grinding into ultra-thin flakes, the efficiency, the ununiformity of the product size, and the yield decrease are likely to occur. Therefore, it is advisable to avoid them except when the dimensional variation tolerance is large.

For the same reason, the major and minor diameters of flat raw material powder are mainly 90 μm.
The average diameter is preferably 50 μm or less, and the average diameter is 10 to 20 μm, which is rather small and good. This size adjustment is mainly performed by adjusting the thickness of the chips.

On the other hand, the finished flat metal powder is preferably 10 μm or less, particularly preferably 5 μm or less, and it is effective to control the crushing means and the crushing treatment time.

Heretofore, it has not been known what kind of raw material powder is suitable for obtaining ultra-thin metal flakes having a high aspect ratio. However, the inventors of the present invention have made various attempts to pulverize cutting chips in order to reuse cutting chips (chips) generated when cutting a metal material or cutting a metal material. If one of the above is selected, flat metal raw material powder having a uniform particle size and thickness and a high aspect ratio is produced by simple pulverization, and further, by treating the flat metal raw material powder with a specific pulverizing means. It has been newly obtained that the ultra-thin metal flakes having an extremely high aspect ratio, that is, the finished flat metal powder can be efficiently obtained, and the yield of the desired size and shape as described above is very high.
The present invention, based on such a new knowledge that has not been known in the past, studies the conditions for reproducing this,
It has been completed.

As the cutting chips in the present invention, as will be exemplified in Examples later, by maintaining the cutting depth at a minute value of, for example, several tens of μm or several μm, a particularly preferable extremely fine short fiber shape You can get As a result, the length is several tens of μm or less, several tens of μm at most, and the diameter is about several μm to several tens of μm. Has a completely different impression and is exactly "powder". It may be more appropriate to call it "microchip". Actually spilling a small amount of it on the paper and shaking the paper lightly,
Like fluttering and scattered ash, the minute spots spread like thin stains. Even with the naked eye, there are rare things that can be recognized as fibers. However, this is 10
When it is magnified about twice, it is apparently in the form of short fibers, and when it is further magnified 1000 times, many parallel lines are present in the direction transverse to the longitudinal axis of the fiber. However, in the case of fibers having different cutting conditions, this type of scoring line is hardly recognized even with slightly larger short fibers. Even if such inappropriate fibers are crushed, the fibers will be lengthened,
Although it may be torn to some extent, it does not produce flattened powder.

In the case of the present invention, the swarf is too small to be discerned by the naked eye, but only in the case of tiny swarf obtained by flow-type cutting (the above-mentioned micro swarf), by a crushing means mainly composed of rubbing, The essence was that it was possible to easily produce flat flakes with minute dimensions that could not be easily obtained by ordinary methods, and that could easily be changed into a finer sliced state. There is. In other words,
It is one of the common crushing techniques that only fine powder (micro chips) that looks like fine dots that can be barely recognized visually as one chip is changed to finer powder (flat raw material powder). It seems to be just an option, but in fact, only with a specific combination of raw material and processing method, it is possible to easily obtain unexpectedly fine and highly flat fine powder. The essential point of the technique of the present invention is that it is possible to produce ultrathin metal flakes having an aspect ratio of 30 or more by further reducing the thickness of the flat metal raw material powder of not less than%.

The flow-type chips used in the present invention are made by cutting or grinding a metal material.
This will be described with reference to FIG. 3, FIG. 3a, FIG. 3b, FIG. 3c and FIG. 3d.

Depending on the cutting conditions, the form of chips generated when cutting a metal material 1 as a work material with a cutting tool 2 such as a cutting tool or a milling cutter is the flow shown in FIGS. 3a, 3b, 3c and 3d. There are four types of chips: micro chips 3, shear chips 31, crack chips 32, and break chips 33. Cutting conditions that affect the morphology of the chips include rake angle 4 (measured clockwise from the normal to the cutting surface at the angle between the normal to the cutting surface and the cutting tool) shown in Figure 3a. Depth 5, cutting speed, and properties of the metal material to be cut.

The flow type micro chips 3 used in the present invention are apt to be generated in the region 1 shown in FIG. 2, that is, in the cutting conditions such as large cutting speed, small cutting depth and large rake angle, and as shown in FIG. 3a. ,
The cutting depth 2 of the metal material 1 to be cut causes shear slip in a direction substantially perpendicular to the cutting direction as the cutting tool 2 advances, and is continuously scraped from the metal material 1. In the flow type micro chips 3, the shear slips that occur in the direction substantially perpendicular to the cutting direction are almost evenly spaced and very narrow.
It appears continuously and the thickness of the chips becomes almost constant. Therefore, the flow-type chips are divided along the shearing slip surface by a simple coarse crushing by a crushing means having a large sliding action such as an attritor mill or a ball mill, and an aspect ratio of 5 or more with a uniform grain size and thickness, In particular, it becomes a flat metal raw material powder of 10 or more.

As shown in Fig. 3b, the shear-type chips 31 that are likely to occur under the cutting conditions such as the small cutting depth and the small rake angle in the area II in Fig. 2 do not have a uniform shear slip, and at regular intervals. Since slip fracture has occurred, it becomes a uniform chip with deep constrictions at regular intervals. Therefore, the raw material powder obtained by coarsely crushing the sheared chips 31 with a Henschel mixer, an attritor mill, a plastic pellet crusher, a ball mill, etc. does not have a uniform particle size and thickness, and contains many metal powders with a small aspect ratio. Therefore, the yield of the "flat metal powder suitable for the purpose of use" is low even if further processed, and it is unsuitable as a flat metal raw material powder.

In addition, region III shown in FIG. 2, that is, a small cutting speed,
Crack chips 32 or fracture chips 33, which are likely to occur under cutting conditions such as critical depth and small rake angle, are brittle cracks that occur instantaneously as shown in Figures 3c and 3d. Since it is generated by, it is not subjected to plastic deformation due to shear slip found in the flow type chips 3 and the shear type chips 31, and it has an agglomerate shape,
Since it is difficult to flatten by coarse pulverization, it is not suitable as a flat metal raw material powder.

In the case of grinding, there are advantages such as not requiring extra steps such as separation of abrasive grains and grinding pieces, and high-speed grinding with a belt grinder or the like containing less abrasive grains,
If the grinding pieces are roughly crushed by a crushing means having a great rubbing action such as an attritor mill or a ball mill, the same as above can be obtained.

As a method for coarsely pulverizing the flow type micro chips used in the present invention, a generally known method can be used. For example, there is a method using an attritor mill and a ball mill. In the present invention, when oily water or the like adheres to the flow type micro chips, a centrifuge or the like was used as a cleaning process for removing the oily water, as long as the chips and the oily water can be well separated. For example, the solvent method and other generally known methods can be used.

Next, the flat metal raw material powder having an aspect ratio of 10 or more and 70% or more thus obtained is further reduced in thickness by a crushing and spreading means having a large pressing and rubbing action, and the aspect ratio of 30 or more is obtained. 80% or more yield of ultra-thin metal flakes,
It is preferably produced at 90% or more.

A horizontal ball mill is preferably used as the crushing and spreading means having a large pressing and rubbing action.

The ultrathin metal flakes obtained should preferably have a crushing time adjusted to a target of an average thickness of 1 μm or less.

In the following, flow type chips were formed according to FIG. 1, and the obtained flow type micro chips were coarsely crushed by means having a strong rubbing action, and contained 70% or more of those having an aspect ratio of 5 or more. Cutting conditions will be described below that, when used as a flat raw material powder, excellent 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, tested them while changing the cutting depth and rake angle of the blade, and I got such a result. In FIG. 1, a
A flat raw material powder containing 70% or more of an aspect ratio of 5 or more can be easily obtained, and the flattened stainless powder having an aspect ratio of 30 or more can be obtained by further crushing and spreading the powder with a means having a strong pressing and rubbing action. This is the boundary line of flow type chips that can be obtained as a product of 90% or more. The curve b can be easily obtained as a flat raw material powder containing 30% or more of aspect ratios of 5 or more, and by further crushing and spreading this with a means having a strong pressing and rubbing action, finished flat stainless steel with an aspect ratio of 30 or more. It is a boundary line at which 60% or more of powder can be obtained as a product, and the c curve is a boundary line between a shear type cutting chip and a crack type cutting chip or a tear type cutting chip.

From this, the conditions (cutting depth,
It has been revealed that cutting with a rake angle gives a flat finished metal powder as described above with a high yield (for example, 90% or more).

The micron chips of the present invention can be obtained even under the conditions between the curves a and b in FIG. 1, but in various aspects such as efficiency, dimensional uniformity, and yield, the following a curves can be obtained. It is not recommended because it is inferior to the conditions.

<Examples> Next, the present invention will be specifically described with reference to Examples.

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

Rake angle: about -20 ° Cutting depth: 10 μm Cutting speed: 1300 m / min The water content adhering to the chips was removed by a centrifuge and coarsely ground by an attritor mill for 2 hours to obtain flat stainless steel raw material powder.

90% or more of those having a major axis of 5 to 30 μm, a minor axis of 2 to 15 μm, a thickness of 1 to 3 μm, and an aspect ratio of 5 or more.
80% or more of them had an aspect ratio of 10 or more. When the obtained raw material powder was further treated with a ball mill for 7 hours, 90% or more of ultrathin flat stainless flakes having a major axis of 5 to 80 μm, a thickness of 0.1 to 0.5 μm and an aspect ratio of 30 or more were obtained.

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

Rake angle approx. -40 ° Depth of cut 3μm Cutting speed 1000m / min The micro chips are centrifuged to separate the oil and water adhered, and crushed with a ball mill for 1 hour to obtain flat titanium raw material powder. .

The major axis was 6 to 30 μm, the minor axis was 2.5 to 16 μm, the thickness was 1 to 2.8 μm, and the aspect ratio of 5 or more was 85% or more, and the aspect ratio of 10 or more was 80% or more. The raw material powder thus obtained was further treated with a ball mill for 6 hours. The major axis was 5 to 80 μm, the thickness was 0.1 to 0.5 μm, and the aspect ratio was
80% or more of ultra-thin flat titanium flake of 30 or more was obtained.

(Example 3) SUS304 stainless steel was ground with a flat belt grinding machine under the following conditions.

Grinding cloth R / R Cross belt # 80 Belt speed 120m / min Grinding speed 10m / min The obtained micro chips have a curled fibrous shape.
It was roughly crushed for half an hour to obtain flat stainless steel raw material powder.

Longest diameter 6-40 μm Short diameter 6-20 μm Thickness 0.9-2.8 μm 95% or more of them have an aspect ratio of 5 or more.
80% or more of them had an aspect ratio of 10 or more. When the obtained raw material powder was further ball-milled for 6 hours and a half, 90% or more of ultra-thin flat stainless flakes having a major axis of 5 to 80 μm, a thickness of 0.1 to 0.5 μm and an aspect ratio of 30 or more were obtained.

(Comparative Example 1) Water atomized powder of SUS304 steel (average particle size 60 μm) was crushed with a ball mill, and the long diameter was 5 to 80 μ after 18 hours of treatment.
55% of the finished ultra-thin metal flakes with m, thickness of 0.1 to 0.5 μm, and aspect ratio of 30 or more.

As described above, even if it took several times as long as that in Example 3, the yield of the finished product of the ultrathin metal flakes was very poor.

Comparative Example 2 Separately, the raw material powder obtained in Example 1 was further treated with a hammer lasher for 6 hours. By this treatment, although the raw material powder was a little dull, the improvement of the aspect ratio was hardly seen, and the ultrathin metal flakes having the aspect ratio of 30 or more reached only 7%. In this case, using a jaw crusher,
Since the micron chips are so fine that they pass through, there is no point in crushing them.

<Effects of the Invention> According to the method of the present invention, when cutting or grinding a metal material, the cutting or grinding conditions such as cutting speed, cutting depth, rake angle, etc. are appropriately selected to achieve cutting or grinding direction. A flat metal raw material powder having an aspect ratio of 5 or more with a uniform particle size and thickness is produced only by coarsely crushing the flow-type micro-shavings that are generated and have shear slip in a direction substantially perpendicular to this direction. It is suitable for the intended use if a flat metal raw material powder with a powder of 10% or more of 70% or more is used and a simple device such as a horizontal ball mill is used to further reduce the thickness by a crushing spreading means with a large pressing and rubbing action. Further, an ultrathin metal flake having an aspect ratio with a uniform particle size and thickness of substantially 30 or more, more preferably 100 or more can be easily produced. According to the present invention, the yield of ultra-thin metal flakes is significantly improved, and the manufacturing cost is significantly reduced.

[Brief description of drawings]

Fig. 1 shows the morphology of cutting chips produced by cutting depth and rake angle when cutting stainless steel, nickel, chromium, titanium and their alloys at a cutting speed of 1200-1500 m / min and the cutting chips produced from the cutting chips. It is a graph which shows the relationship of the flat metal raw material powder made. FIG. 2 is a graph showing the morphology of chips produced by cutting depth and rake angle when mild steel is cut at a constant cutting speed. FIG. 3a, FIG. 3b, FIG. 3c and FIG. 3d are diagrams showing the forms of micro-flow type chips, shear type chips, crack type chips and fracture type chips, respectively. Explanation of symbols I: Area where flow type micro chips can be formed, II: Area where shear type chips can be formed, III ... Region where crack chips or cracks can be formed, 1 ... Metal material to be cut , 2 ... Cutting tool, 3 ... Flow type micro chips, 4 ... Rake angle, 5 ... Cutting depth, 31 ... Shear type chips, 32 ... Crack type chips, 33 ... Fracture type cutting chips, A ... Cutting direction (relative advancing direction of cutting tool), a ... Boundary line of flow type micro chips that can obtain 90% or more of flat stainless powder with an aspect ratio of 30 or more, b ...... Boundary line that can obtain flat stainless steel powder with an aspect ratio of 30 or more by 60% or more, c …… Boundary line with shear type chip and split type chip or split type chip

Claims (1)

[Claims] 1. A short fibrous flow-type metal microchip having an easy slip surface in the direction transverse to the longitudinal axis, which is coarsely crushed so as to preferentially promote separation miniaturization along the slip surface. The aspect ratio is characterized by further reducing the flat metal raw material powder having an aspect ratio of 10 or more by 70% or more by crushing and spreading means having a large pressing and rubbing action.
A method for producing ultra-thin metal flakes mainly consisting of 30 or more powders.