JP2013188811A - Abrasive grain and method of manufacturing the same - Google Patents

Abstract

An inexpensive alternative abrasive having polishing performance equivalent to that of an abrasive using cerium oxide as a raw material is provided.
Two kinds of calcia-stabilized zirconia having different mixing ratios and particle sizes of calcia are mixed at a predetermined mixing ratio to provide abrasive grains. That is, an abrasive comprising a mixture of first calcia-stabilized zirconia and second calcia-stabilized zirconia in which the amount of calcia added is increased from that of the first calcia-stabilized zirconia, and the first calcia-stabilized Zirconia is electrofused zirconia, and the second calcia-stabilized zirconia is the coexistence of electrofused zirconia and calcium zirconate, and the particle size of the first calcia-stabilized zirconia is second calcia It is set larger than the particle size of zirconia.
[Selection] Figure 1

Description

  The present invention relates to abrasive grains and a method for producing the same, and more particularly to a dedicated abrasive grain for lapping machines and polishing machines and a method for producing the same.

  As this kind of conventional abrasive grains used in the final process for polishing glass or the like, diamond, cerium oxide, colloidal celica, alumina-based particles, zirconium oxide particles, magnesium oxide particles and silicon carbide are mainly used. (See Patent Document 1 below). Of these, many use cerium oxide as a raw material from the viewpoint of polishing performance (see Patent Document 2 below). In other words, in polishing of glass including optical lenses and prisms, a polishing material that finally uses cerium oxide as an abrasive material through a plurality of processes is often used. This is a surface required in the finishing process of glass and the like. This is related to the fact that diamonds are difficult to produce “mirror surfaces” and are too expensive to achieve accuracy. A so-called liquid abrasive in which abrasive grains are mixed in a liquid or the like is often used when a surface having a high surface accuracy is required over a certain area, as can be seen from a lapping polishing process. Unlike the fixed abrasive grains, these polishing mechanisms can reduce the depth of the abrasive material itself to be cut into the workpiece. This is a point that differs greatly from fixed abrasive grains in which the polishing itself cannot be performed unless the bond is always cut (if the self-generated blade does not occur). Clogging with chips, spilling, and crushing are not a problem with loose abrasives (although the grindability of the abrasive needs to be seen), but with very soft felt pads and low pressure If conditions are applied, it is possible to achieve polishing in a state where only a small amount of fine abrasive grains are cut. This is why it is said to be suitable for finishing. Glass is widely used for hard disk substrates and photomask substrates. It can be said that it is one of the production materials indispensable for optical lenses and prisms. Cerium oxide has a crushing fist that is different from alumina and silicon carbide, and the shape and dimensions of the abrasive grains are often designed for finishing. There are also cases where multiple processes with different grain sizes are required for lapping and polishing. Even in such a case, it can be said that a wide range of required accuracy can be met by changing the granularity.

JP 2011-241109 A (Claim 14) JP2012-11526A (paragraph 0003)

  In addition to the above-mentioned usage, there are grindstones in which cerium oxide is mixed into resin-based bonds, and cerium oxide itself is hardened like a compound and used as fixed abrasive grains. In the final finishing of glass, cerium oxide, which is also used as loose abrasive grains, is most often used. However, this cerium oxide relies on China for most of its raw materials, and the price may fluctuate depending on international issues and speculative movements. In particular, with the recent rise in the price of rare earths, cerium is increasingly difficult to obtain, and abrasive manufacturers are looking for alternative materials for cerium. In the case of using a large amount, the processing cost is directly affected by these effects, and therefore, some alternatives are being studied. Specifically, research on using zirconium oxide (zirconia) or the like as an alternative to cerium oxide has been published.

  However, the present situation is that zirconium oxide alone has not been adopted as abrasive grains. This seems to be due to problems in polishing power and surface roughness. Tests by the applicant have shown that abrasive grains using commercially available zirconium oxide are significantly inferior to abrasive grains using cerium oxide. In the polishing operation, many users use tens of laps for production. In other words, it is usually operated with 4 to 5 units / person, and variations in quality by workers are regarded as a problem. Therefore, the abrasive grains that provide improved workability with less catching are attractive to the user. However, an alternative raw material having a polishing performance equivalent to that of abrasive grains using cerium oxide as a raw material has not been proposed so far.

  The present invention provides an abrasive grain that has few defects using zirconium oxide, can obtain polishing performance equivalent to that of a conventional abrasive grain using cerium oxide, and can improve workability, and a method for producing the same. The purpose is to provide.

  In order to achieve the above goal, in the present invention, two kinds of calcia-stabilized zirconia having different calcia mixing ratios and particle sizes are mixed at a predetermined mixing ratio to provide abrasive grains. That is, according to the present invention, there is provided an abrasive comprising a mixture of first calcia-stabilized zirconia and second calcia-stabilized zirconia in which the amount of calcia added is increased from that of the first calcia-stabilized zirconia, The first calcia-stabilized zirconia is electrofused zirconia, and the second calcia-stabilized zirconia is a mixture of electrofused zirconia and calcium zirconate, and the first calcia-stabilized zirconia Abrasive grains having a grain size greater than that of the second calcia stabilized zirconia are provided.

According to the present invention, the first calcia-stabilized zirconia raw material is pulverized and classified to obtain a predetermined particle size distribution, and the second calcia-stabilized zirconia raw material is pulverized and classified to obtain the predetermined particle size distribution. Obtaining a particle size distribution with a center particle size smaller than the center particle size;
Mixing the pulverized and classified first calcia-stabilized zirconia and the pulverized and classified second calcia-stabilized zirconia at a predetermined ratio;
A method for producing abrasive grains is provided.

  In the abrasive grains and the method for producing the same according to the present invention, the calcia addition amount of the first calcia-stabilized zirconia is several weight percent, and the calcia addition amount of the second calcia-stabilized zirconia is several tens weight percent. This is a preferred embodiment of the present invention.

  Moreover, it is a preferable aspect of the present invention that the second calcia-stabilized zirconia is mixed at 10 to 90% by weight with respect to the first calcia-stabilized zirconia.

  Similarly, it is a preferred embodiment of the present invention that the particle size difference index of the first calcia-stabilized zirconia is 1.0 or less in comparison with the particle size of the second calcia-stabilized zirconia.

  Similarly, it is a preferred embodiment of the present invention that cerium oxide having a particle size larger than that of the first calcia-stabilized zirconia is added in several weight percent.

  According to the present invention, it is possible to provide abrasive grains having polishing performance equivalent to that of conventional abrasive grains made of cerium oxide without using expensive cerium oxide or using only a small amount of cerium oxide.

It is process drawing which shows the process of manufacturing the abrasive grain which concerns on preferable embodiment of this invention. It is a graph which shows the particle size distribution of each component of the abrasive grain concerning the 2nd Embodiment of this invention. It is a graph which shows the performance of the abrasive grain concerning this invention compared with a conventional product.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing a manufacturing process of abrasive grains according to a preferred embodiment of the present invention, and shows both a first embodiment and a second embodiment to be described later. The abrasive grains of the present invention are manufactured by obtaining or obtaining first calcia-stabilized zirconia and second calcia-stabilized zirconia in a predetermined method in advance, and mixing them at a predetermined ratio to obtain a final product. is there. “Calcia” is a common name for “calcium oxide (CaO)”, but this common name is used in the present application. “Zirconia” is a common name for “zirconium oxide (ZrO ₂ )”, but this common name is used in the present application. The first calcia-stabilized zirconia and the second calcia-stabilized zirconia are both known zirconium oxide mixed with calcia (hereinafter sometimes simply referred to as CaO). In particular, the first calcia-stabilized zirconia is sold by IDU under the trade name “FSD”, and the second calcia-stabilized zirconia is also available under the trade name “FSD-26C” by IDU Corporation. Is sold by Hereinafter, these will be described.

The first calcia-stabilized zirconia has a calcia addition amount of about 3 to 4 wt% and is also called partially stabilized zirconia. The first calcia-stabilized zirconia is a trade name “FSD” used as a refractory material, and is used as an abrasive in the present invention. Compared with monoclinic-ZrO ₂ which is a general zirconium oxide, it becomes cubic-ZrO ₂ which is an electro-fused zirconia, so that it is considered that improvement in crystallinity, hardness and toughness can be obtained. Zirconia has excellent characteristics when used as a refractory, but ZrO ₂ alone undergoes a phase transition in which the crystal structure changes with temperature. Since this phase transition is accompanied by a volume change, when the temperature rise and fall are repeated, the sintered body is repeatedly expanded and contracted, and the sintered body is damaged. Therefore, it is common to add calcia as a stabilizer so as not to cause a volume change. In the preferred embodiment, the amount of calcia added in the first calcia-stabilized zirconia is 3 to 4 wt%, but is not limited thereto.

The second calcia-stabilized zirconia has a calcia addition amount of 20 to 28 wt%, and cubic-ZrO ₂ and CaZrO ₃ (calcium zirconate) coexist. The calcia addition amount in the second calcia stabilized zirconia is not limited to 20 to 28 wt%, and can be 10 wt% to several tens wt%.

  In the present invention, the second calcia-stabilized zirconia is not used as a refractory but is used as an abrasive. Increasing the CaO addition amount leads to lowering the abrasive hardness of zirconia. As a result, soft polishing can be performed, and improvement in surface roughness can be expected. In addition, the present inventors have found that calcium zirconate is hardly soluble in water, but when the particle size is 10 μm or less, slight alkali dissolution occurs, and the pH can be shifted to alkali. As the pH became alkaline, the slurry characteristics of zirconia were changed, and an improvement in dispersibility was confirmed visually. In the present invention, the first calcia-stabilized zirconia has a calcia content of several weights (wt)%, and the second calcia-stabilized zirconia has a calcia content of several tens of weights (wt)%. The specific amount of calcia to be added can be arbitrarily changed depending on the use of the abrasive grains.

  As shown in FIG. 1, the first calcia-stabilized zirconia raw material and the second calcia-stabilized zirconia raw material are pulverized (steps S1 and S11) and classified (steps S2 and S12). For crushing and classification, a crusher / ball mill and a sieve screen are used. Thereafter, the first calcia-stabilized zirconia and the second calcia-stabilized zirconia are mixed through fine pulverization (steps S3 and S13) and fine powder classification (steps S4 and S14), respectively (step S16). In addition, at the time of mixing in step S16, an additive is added as needed (step S15). When the mixing in step S16 is completed, the abrasive grains of the present invention are completed, packed (step S17), and shipped.

  Next, the particle sizes of the first calcia-stabilized zirconia and the second calcia-stabilized zirconia will be described. Here, the particle size refers to the particle size (average particle size) at the center of the particle size distribution. In a preferred embodiment of the invention, the particle size of the first calcia stabilized zirconia is 1.5 μm and the particle size of the second calcia stabilized zirconia is 1.0 μm. Note that the particle size distribution is measured by an electrical resistance method.

  In the preferred embodiment, the particle size difference Δd between the first and second calcia stabilized zirconia is Δd = 0.5 μm. The second calcia-stabilized zirconia is not expected as a polishing force because the abrasive hardness is small due to the addition of CaO more than the first calcia-stabilized zirconia. Therefore, by increasing the particle size of the first calcia-stabilized zirconia having polishing power, the second calcia-stabilized zirconia improves surface roughness and brings about pH action while maintaining the polishing performance of the zirconia. It becomes possible. Accordingly, when the relationship between the particle sizes of the first and second calcia-stabilized zirconia is the same or reversed, the polishing power is significantly reduced. Further, when the particle size of the second calcia-stabilized zirconia is extremely small (for example, d50 = 0.1 μm), the work effect as an abrasive is not exhibited at all, and only the effect of pH characteristics is obtained.

  Table 1 below shows examples of preferred particle size combinations of the first calcia stabilized zirconia and the second calcia stabilized zirconia.

  Next, the first calcia-stabilized zirconia and the second calcia-stabilized zirconia are both pulverized by a fine powder pulverizer and then each finely classified by a fine powder classifier. The particle sizes are in the range of 1 to 3 μm so as to be related. Thereafter, both are mixed. This mixing is performed for 30 minutes to 120 minutes using, for example, a V blender mixer. Here, the mixing ratio is 10 to 90 wt% for the first calcia stabilized zirconia and 90 to 10 wt% for the second calcia stabilized zirconia. In addition, when both mixing ratio exists in the said range, it is confirmed that the predetermined effect is exhibited. Here, the predetermined effects are polishing performance (processing rate, surface roughness), workability, and the like, and therefore, the mixing ratio can be changed depending on which one is important depending on the object to be polished and the purpose of use. . Specifically, since the first calcia-stabilized zirconia contributes to the improvement of the processing rate, when importance is attached to the improvement of the processing rate, the ratio of the first calcia-stabilized zirconia is increased. On the other hand, the second calcia-stabilized zirconia contributes to improvement in surface roughness and workability. Therefore, when importance is attached to these, the ratio of the second calcia-stabilized zirconia is increased. As a result of various tests by the present inventors, it has been confirmed that a general-purpose abrasive can be provided when the second calcia-stabilized zirconia is mixed with 10 to 40 wt% with respect to the first calcia-stabilized zirconia.

  In the mixing step of the first calcia-stabilized zirconia and the second calcia-stabilized zirconia, an additive can be added as necessary. Hereinafter, a case where cerium oxide is added as an additive will be described as a second preferred embodiment.

  Zirconia is generally used as an abrasive for glass, but depending on the type of glass, the polishing performance may be extremely poor when compared with cerium oxide. In general, materials such as quartz and quartz having a high hardness (low wear) fall on them. On the other hand, water glass, borosilicate glass, fluorite, etc. are said to be relatively soft glass. Therefore, the amount of decrease can be compensated for by adding a minimum amount of cerium oxide to a hard material.

  The blending ratio in the second embodiment is shown below.

  In the same way as explained in the first embodiment, the cerium oxide particle size is made larger than the first and second calcia-stabilized zirconia, thereby reducing the polishing performance by cerium oxide. It is possible to demonstrate. FIG. 2 is a graph showing the particle size distribution of cerium oxide, first calcia-stabilized zirconia, and second calcia-stabilized zirconia in the second embodiment. It has been confirmed that when cerium oxide having an extremely coarse particle size is added in order to improve the polishing performance, the balance between the polishing force and the surface roughness is unbalanced and the overall performance is reduced.

  FIG. 3 includes a table and a graph showing evaluation results showing the results of comparing the abrasive grains of the present invention with other abrasive grains. The evaluation result list in FIG. 3 shows three abrasive grains. “Domestic product ceria A” is an abrasive using cerium oxide, “foreign product zirconia B” is an abrasive using general zirconium oxide, and “invention product” is an abrasive according to the present invention. From this table, it can be seen that the abrasive grains according to the present invention have almost the same abrasive grain distribution as the other abrasive grains, and the average grain size (dv50) of the abrasive grains is almost the same as that of the other abrasive grains. Furthermore, it can be seen that the processing rate (polishing amount per unit time) of the abrasive grains according to the present invention is almost the same as that of cerium oxide, which is far superior to that of general zirconium oxide. The processing rate comparison graph in FIG. 3 is a graph of the processing rates shown in the evaluation result list. The polishing conditions are as described in FIG.

  As described above, in the present invention, since the raw materials are produced independently, it is also a great feature that the mixing ratio can be changed according to the required conditions as described above. If you look at the composition table, it is possible to adjust the formulation from the beginning and produce the raw material of the same composition with a single molten raw material, but in that case the raw material of calcia stabilized zirconia, the polishing performance of the present invention, There is no improvement in workability. That is, the effect is exhibited by mixing each raw material after melting.

  According to the abrasive grains of the present invention and the method for producing the same, the conventional cerium oxide is used as the main raw material without using cerium oxide or by using only a very small amount of the conventional abrasive grains even when cerium oxide is used. Therefore, the present invention can provide abrasive grains as an alternative to expensive cerium oxide, and therefore, the abrasive grains as an abrasive are manufactured. It is useful not only in the industrial sector, but also in various industries for polishing glass products including optical lenses and others.

S1, S11 Grinding step S2, S12 Classification step S3, S13 Fine grinding step S4, S14 Fine powder classification step S15 Additive mixing step S16 First calcia-stabilized zirconia and second calcia-stabilized zirconia step S17 Packing step

Claims (8)

  An abrasive comprising a mixture of first calcia-stabilized zirconia and second calcia-stabilized zirconia in which the amount of calcia added is increased from that of the first calcia-stabilized zirconia, the first calcia-stabilized Zirconia is electrofused zirconia, the second calcia-stabilized zirconia is a coexistence of electrofused zirconia and calcium zirconate, and the particle size of the first calcia-stabilized zirconia is the second Abrasive grain larger than that of calcia stabilized zirconia.   The abrasive according to claim 1, wherein the calcia addition amount of the first calcia-stabilized zirconia is several weight percent, and the calcia addition amount of the second calcia-stabilized zirconia is several tens weight percent.   The abrasive according to claim 1 or 2, wherein the second calcia-stabilized zirconia is mixed in an amount of 10 to 90% by weight with respect to the first calcia-stabilized zirconia.   The abrasive grain according to any one of claims 1 to 3, wherein a particle size difference index of the first calcia-stabilized zirconia is 1.0 or less in comparison with a particle size of the second calcia-stabilized zirconia. .   The abrasive according to any one of claims 1 to 4, wherein cerium oxide having a particle size larger than that of the first calcia-stabilized zirconia is added by several weight percent. Crushing and classifying the first calcia-stabilized zirconia raw material to obtain a predetermined particle size distribution; crushing and classifying the second calcia-stabilized zirconia raw material; Obtaining a particle size distribution;
Mixing the pulverized and classified first calcia-stabilized zirconia and the pulverized and classified second calcia-stabilized zirconia at a predetermined ratio;
The manufacturing method of the abrasive grain which has.   The step of pulverizing and classifying the first calcia-stabilized zirconia and the step of pulverizing and classifying the second calcia-stabilized zirconia have a particle size of the first calcia-stabilized zirconia, respectively. The manufacturing method of the abrasive grain of Claim 6 performed so that it may become 1.0 or less by a particle size difference index compared with the particle size of a zirconia. The method for producing abrasive grains according to claim 6 or 7, further comprising a step of adding several weight percent of cerium oxide in the mixing step or before and after the mixing step.

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