JP4404668B2 - Method for stirring fine particles and surface modification method for abrasive grains using the same - Google Patents

Description

  The present invention relates to a method for stirring fine particles and a surface modification method for abrasive grains using the same. Here, the fine particles referred to in the present specification are particles having a small particle diameter such that when the particles are stirred in a container, the particles aggregate to form secondary particles. Hereinafter, as an example of such fine particles, fine abrasive grains used for electroforming tools or electrodeposition tools for precision grinding will be described.

  In electroforming tools or electrodeposition tools using diamond abrasive grains, cBN abrasive grains, etc., it is important that the abrasive grains formed on the base material or the substrate are uniformly arranged with a predetermined density. Various measures for this have been proposed. In general, an electroforming tool or an electrodeposition tool is used to form an abrasive layer on a base material by stirring and dispersing the abrasive grains in a plating solution to allow the abrasive grains to settle on the base material or the substrate and by performing electroplating. Alternatively, it is produced by a method of obtaining a sheet-like abrasive layer by peeling off the abrasive layer deposited on the substrate. In this manufacturing process, diamond grains, cBN abrasive grains, etc., and Ni plating liquid or Ni-P plating liquid, which are usually used as plating liquids, are close in pH range. Agglomeration tends to occur, and the abrasive grain distribution of the abrasive grain layer deposited on the base material or the substrate tends to be inhomogeneous.

Therefore, by applying a specific surface modification treatment to the abrasive grains, the isoelectric point of the abrasive grain surface is changed, thereby making a difference between the pH of the plating solution and the isoelectric point of the abrasive grain surface and plating the fine abrasive grains. A method for uniformly dispersing in a liquid has been proposed (see Patent Document 1). In Patent Document 1, a method of coating a metal oxide such as Al ₂ O ₃ is proposed as a surface modification treatment of abrasive grains.

FIG. 4 is a diagram showing a configuration of an apparatus described in Patent Document 1 for coating diamond abrasive grains with Al ₂ O ₃ by a high frequency sputtering method. In this apparatus, argon gas is used as a process gas and oxygen gas is used as an assist gas to coat Al ₂ O ₃ on the abrasive grains 52 from the target 51. Since the target 51 is not conductive, the target 51 is connected to a high-frequency power source 53, and ionization efficiency is increased by a tunnel-like magnetic field parallel to the surface of the target 51. Furthermore, the spiral ion magnetic field generated by the cathode coil 54 accelerates the plasma ions to accelerate the increase in coverage. The cylindrical container 55 is rotated by the stepping motor 56, and the abrasive grains 52 spread in the container 55 are agitated by the stainless steel wire 57. The container 55 is made of stainless steel, and a bias potential 58 is applied to activate the surface of the abrasive grains 52 by argon bombardment.
JP 2000-254866 A

  By the way, the sputtering apparatus for the abrasive grain surface modification described in Patent Document 1 has a structure in which a cylindrical container that contains abrasive grains is installed in an inclined state. For this reason, it is difficult to increase the size of the apparatus, and it is not suitable for surface modification treatment for a large amount of abrasive grains. In addition, since the distance between the target is changed between the upper side and the lower side of the inclined container, the film formation rate is different, and it is difficult to perform surface modification while maintaining a constant film thickness.

  Further, since the abrasive grains are fine particles having a particle diameter of about 50 μm or less, when the abrasive grains are stirred in a rotating container, the abrasive grains aggregate to form secondary particles. Growing further increases the particle size. Abrasive grains mixed with secondary particles are non-uniformly dispersed and settled in the plating solution in the subsequent electroforming process or electrodeposition process, and the abrasive distribution of the abrasive layer deposited on the base material or substrate is not uniform. Become homogeneous. It should be noted that such agglomeration of fine particles and growth of secondary particles at the time of stirring are not limited to the case of abrasive grains, but are problems common to other fine particles in general.

  An object of the present invention is to provide a stirring method that increases the stirring efficiency of fine particles and suppresses the growth of secondary particles when stirring the fine particles in a rotating container, and this stirring method is an abrasive by sputtering. The present invention provides a method for suppressing the growth of secondary particles of abrasive grains and further increasing the efficiency of coating formation of abrasive grains.

The fine particle agitation method of the present invention is a method for agitating fine particles contained in a rotating container, wherein the rotation axis of the container is set to the vertical direction and the rotation direction is repeatedly switched between forward and reverse directions to rotate the container. And stirring the fine particles by entering a stirring plate that can move up and down with respect to the fine particle layer in the container, and at least the fine particle layer entering portion of the stirring plate is inclined with respect to the rotation direction of the container, and the rotation in response to the direction of switching, and wherein the Rukoto switching a function of crushing the secondary particles of the fine particles formed during agitation and effect of stirring fine particles scooped by the inclination portion of the stirring plate.

  In the fine particle agitation method of the present invention, the rotation direction of the container is switched between forward and reverse directions, and the agitation plate is introduced into the fine particle layer in the container to agitate the fine particles, thereby increasing the agitation efficiency of the fine particles. be able to. Furthermore, in accordance with the switching of the rotation direction of the container, a stirring method that switches between the action of scooping up the fine particles by the inclined portion of the stirring plate and the action of crushing the secondary particles of the fine particles formed during the stirring. Therefore, it is possible to suppress the growth of secondary particles generated during stirring.

  In the abrasive grain surface modification method of the present invention, the film forming process in a state where the rotation of the container installed so that the rotation axis is in the vertical direction is stopped, and the rotation direction of the container is switched between the forward and reverse directions. A stirring process of rotating and rotating the abrasive plate in the container to stir the abrasive grains, and a cleaning process of cleaning the exposed surface of the abrasive grains in the container with the rotation of the container stopped By repeating this sequence a plurality of times, it is possible to improve the stirring efficiency of the abrasive grains and completely modify the surface of the abrasive grains by forming a film. Furthermore, in response to switching of the rotation direction of the container, an agitation method for switching between the action of scooping up the abrasive grains by the inclined portion of the agitation plate and the action of crushing the secondary particles of the abrasive grains formed during the agitation By doing so, the growth of secondary particles generated during stirring can be suppressed, and the dispersion of the abrasive grains in the plating solution in the subsequent electroforming process or electrodeposition process can be made uniform.

  The fine particles referred to in the present invention refer to particles having a small particle diameter such that when the particles are stirred in a container, the particles aggregate to form secondary particles. Such fine particles include various types such as grain powder, powder resin, mineral powder, metal powder, etc. Here, fine particles (particle size of about 50 μm or less) used for electroforming tools for precision grinding or electrodeposition tools. Taking abrasive grains as an example, an embodiment of a method for stirring the abrasive grains and a method for modifying the surface of the abrasive grains using the stirring method will be described.

  In surface modification in which a metal or metal oxide thin film is coated on the surface of the abrasive grains by a sputtering method, stirring of the abrasive grains is essential. The stirring of the abrasive grains is generally carried out by storing the abrasive grains in a container and stirring the abrasive grains in the container by rotating the container. The particles are aggregated to form secondary particles, and the secondary particles further grow to increase the particle size. Abrasive grains mixed with secondary particles are non-uniformly dispersed and settled in the plating solution in the subsequent electroforming process or electrodeposition process, and the abrasive distribution of the abrasive layer deposited on the base material or substrate is not uniform. Become homogeneous.

  Therefore, in the present invention, the abrasive grains are accommodated in a container installed so that the rotation axis is in the vertical direction, and the rotational direction of the container is switched between the forward and reverse directions to rotate, and the abrasive grains in the container are rotated. The stirring plate is entered to stir the abrasive grains. Thereby, the stirring efficiency of an abrasive grain can be improved. More preferably, at least the abrasive layer entry portion of the stirring plate is inclined with respect to the rotation direction of the container, and the abrasive particles are scooped up by the inclined portion of the stirring plate in response to switching of the rotation direction of the container. The stirring method switches between the stirring action and the action of crushing the secondary particles of the abrasive grains formed during stirring. By such a stirring method, the growth of secondary particles generated during stirring is suppressed, so that secondary particles having a large particle size are not mixed, and dispersion and sedimentation in the plating solution in the subsequent process become uniform. .

  Now, even if the above stirring method is incorporated into the surface modification of the abrasive grains by the sputtering method, the method of continuously forming the film by sputtering while stirring the abrasive grains in the container as in the past, Depending on the individual abrasive grains, a film may not be formed or only an incomplete film may be formed.

Therefore, in the present invention, the film forming process in a state where the rotation of the container is stopped, the stirring process for stirring the abrasive grains while rotating the container by rotating the rotation direction of the container to the normal direction, and the state where the rotation of the container is stopped The cleaning process for cleaning the exposed surface of the abrasive grains in the container is repeated a plurality of times in this order. By setting it as such a process, a perfect film can be formed with respect to all the abrasive grains in a container, and the dispersion | distribution in a plating liquid and the uniformity of sedimentation in a post process are improved further. Here, the rotation speed of the container is about 2 to 6 min ⁻¹ during forward rotation and reverse rotation, and the number of repetitions of forward / reverse rotation is preferably about 2 times, and the number of repetitions of a series of steps is about 300 times or more. It is desirable to do.

  FIG. 1 is a diagram showing a configuration of a high-frequency magnetron sputtering apparatus in an embodiment of the present invention. The apparatus of the present embodiment is an apparatus for forming a metal or metal oxide film on the surface of the abrasive grains to modify the surface of the abrasive grains. In this apparatus, argon gas is used as a process gas, and oxygen gas is used as an assist gas when a metal oxide is used as a target. The target 1 is connected to a high frequency power source 3 and increases ionization efficiency by a tunnel magnetic field parallel to the target 1. Furthermore, the spiral magnetic field generated by the cathode coil 4 accelerates the plasma ions and improves the coating efficiency. Thereby, the thin film of a metal or a metal oxide can be coat | covered on the surface of the abrasive grain 2. FIG.

  The cylindrical container 5 containing the abrasive grains 2 is installed in a reduced pressure atmosphere so that the axis of rotation is in the vertical direction, and is rotated by the motor 6 while switching the rotation direction between forward and reverse directions. While the container 5 is rotating, the motor 7 also rotates, the shaft 10 is moved up and down by the action of the eccentric cam 8 and the push spring 9 provided on the rotating shaft, and the stirring plate 11 attached to the shaft 10 is moved up and down. As a result, the stirring plate 11 stirs the abrasive grains 2 when the stirring plate 11 enters the abrasive grain layer that is moved by the rotation of the container 5. The container 5, the eccentric cam 8, the push spring 9, the shaft 10, the stirring plate 11 and other mechanical parts are all made of stainless steel, and the surface of the sliding member is covered with a molybdenum disulfide film. Further, the upper portion of the shaft 10 that comes into contact with the eccentric cam 8 is made of a resin containing a reinforcing material having excellent wear resistance.

  FIG. 2 is a diagram schematically showing the shape seen from the side of the stirring plate 11 and the mode during stirring of the abrasive grains. The stirring plate 11 has a cross-sectional shape as viewed from the side, in which a portion of the abrasive layer entering the lower portion of the stirring plate 11 is inclined with respect to the rotation direction of the container 5. As shown in FIG. 2A, when the rotation direction of the container 5 is the forward rotation direction (indicated by a rightward arrow Da), the inclined portion 11 a of the stirring plate 11 scoops up the abrasive grains 2 in the container 5. However, stirring of the abrasive grains 2 proceeds. The abrasive grains 2 are temporarily deposited on the upper surface of the inclined portion 11a of the stirring plate 11, but are pushed back to the inclined portion 11a, and are rolled and aggregated again on the front surface of the inclined portion 11a to form secondary particles 2a. However, the secondary particles 2a are crushed so as not to interfere with the subsequent electrodeposition process when the container 5 is reversed. That is, as shown in FIG. 5B, when the rotation direction of the container 5 is the reverse direction (indicated by the left-pointing arrow Db), the secondary particles 2a are crushed by the lower surface of the inclined portion 11a of the stirring plate 11. Finely sheared and crushed, and the secondary particles 2a almost disappear. By repeating forward and reverse rotations of the container 5 in this way, the abrasive grains 2 can be sufficiently stirred while suppressing the secondary particles 2a from remaining and growing.

  The surface modification of the abrasive grains 2 is performed with a sputtering apparatus equipped with such a stirring mechanism. A series of surface modification operations include a film forming process for forming a film on the abrasive grains 2 while the rotation of the container 5 is stopped, and a stirring process for stirring the abrasive grains 2 while repeating normal rotation and reverse rotation of the container 5. Each process of the cleaning process for cleaning the exposed surface of the abrasive grains 2 in the container 5 in a state where the rotation of the container 5 is stopped is repeated a plurality of times in this order. In the film forming step, a film is formed on the surface of the abrasive grains 2 by a sputtering method while the rotation of the container 5 containing the abrasive grains 2 is stopped. In the agitation step, the container 5 is rotated by repeatedly switching the rotation direction of the container 5 in the forward and reverse directions, the agitation plate 11 enters the abrasive grain layer in the container 5, and the secondary particles 2 a of the abrasive grains 2. The abrasive grains 2 are stirred while suppressing the growth of. In the cleaning step, the bias potential 12 is applied to the container 5 while the rotation of the container 5 is stopped, and the exposed surface of the abrasive grains 2 in the container 5 is cleaned and activated by argon gas bombardment. By repeating these series of steps many times, the surface modification of the abrasive grains 2 is completely performed.

FIG. 3 is a diagram showing an experimental result of evaluating the dispersion state of the abrasive grains in the plating solution in the electroforming process or the electrodeposition process using the abrasive grains whose surface has been modified by the above method. In the experiment method, an acrylic cylindrical container is filled with Ni-P plating solution (pH 1.2), and the abrasive grains whose surface is modified so that the abrasive concentration in the plating solution is 2.5% are added and stirred. Then, the thickness at which the abrasive grains settle and spontaneously accumulate over time was measured. It is known that if the dispersion of the abrasive grains in the plating solution is uniform, the sedimentation rate is slow, and if the dispersion is not uniform, the sedimentation rate is fast. Can be judged. Here, it was estimated that the effect of uniform dispersion was influenced by the number of repetitions of a series of steps of the film-forming step, the stirring step, and the cleaning step of the surface modification operation. Surface modification was performed in increments of units. The abrasive grains used in the experiment were diamond abrasive grains having an average grain size of 5 μm, the rotation speed of the container containing the abrasive grains was 3 min ⁻¹ , and the forward / reverse rotation was repeated twice, and the average film thickness in one film forming step. Is about 20 nm.

  In FIG. 3, the curve (A) is when there is no surface modification, the curve (B) is when the surface modification process is repeated 300 times, the curve (C) is when the surface modification process is repeated 400 times, and the curve (D) is In the case of repeating the surface modification process 500 times, the curve (e) shows the deposition thickness in the case of repeating the surface modification process 600 times. As can be seen from the figure, in the case of no surface modification, rapid deposition occurred in the initial stage, whereas the surface-modified abrasive grains confirmed a decrease in sedimentation rate after 300 repetitions. This tendency increases as the number of repetitions of the surface modification process increases, and the effect of the surface modification appears remarkably. This indicates that the degree of surface modification of the abrasive grains can be controlled by increasing or decreasing the number of repetitions of the surface modification process.

  The present invention has been described above by taking the surface modification of abrasive grains as an example, but this stirring method can be applied to the stirring of various fine particles other than abrasive grains. Further, the surface modification of the abrasive grains by the sputtering method has been taken up as an application technique of this stirring method, but it can also be applied to fine particles other than the abrasive grains and surface modification other than the sputtering method.

It is a figure which shows the structure of the high frequency magnetron sputtering apparatus in the Example of this invention. It is a figure which shows typically the shape seen from the side surface of the stirring plate of the apparatus of FIG. 1, and the aspect at the time of abrasive grain stirring. It is a figure which shows the experimental result which performed surface modification by the method of this invention. It is a figure which shows the structure of the conventional high frequency sputtering device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Target 2 Abrasive grain 2a Secondary particle 3 High frequency power supply 4 Cathode coil 5 Container 6,7 Motor 8 Eccentric cam 9 Push spring 10 Shaft 11 Stirring plate 11a Inclined part 12 Bias potential Da, Db Rotation direction

Claims (1)

  A method for stirring fine particles contained in a rotating container, wherein the rotation axis of the container is set to a vertical direction and the rotation direction is repeatedly switched between forward and reverse directions, and the container is rotated several times to rotate the fine particle layer in the container. Then, the stirring plate capable of moving up and down is entered to stir the fine particles, and at least the fine particle layer entering portion of the stirring plate has a shape inclined with respect to the rotation direction of the container, corresponding to the switching of the rotation direction, A method of stirring fine particles, which switches between an action of scooping up and stirring fine particles by an inclined portion of a stirring plate and an action of crushing secondary particles of fine particles formed during stirring.

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