JP2003213248A - Cerium abrasive and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powdery cerium abrasive easily providing an abrasive slurry remaining no scratch on a polished surface obtained by polishing with the slurry, and to provide a method for producing the abrasive. <P>SOLUTION: The method for producing the cerium abrasive has a step drying an abrasive slurry, wherein the abrasive slurry is dried by spray drying. For instance, the slurry is sprayed into a chamber with a spraying device such as a nozzle to contact the sprayed foggy slurry with a heating gas and is dried. The foggy abrasive slurry is dried in the heating gas within a short time. By the spray drying, abrasive particles in the slurry are instantaneously separated each other and dried. Thereby, coagulation in drying is suppressed and coarse agglomerate-arising is prevented. As the coarse agglomerate amount is suppressed, an abrasive slurry having low coarse agglomerate content can be prepared only by slurrying the abrasive. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cerium-based abrasive and a method for producing the same.

[0002]

2. Description of the Related Art Cerium-based abrasives (hereinafter also simply referred to as abrasives) are used, for example, for polishing glass lenses. In actual polishing, usually, a cerium-based abrasive powder is dispersed in a dispersion medium such as water to give a solid content of 1%, for example.
An abrasive slurry of about 0% by weight is prepared, and polishing is performed using the prepared abrasive slurry. However, when an abrasive slurry prepared by simply mixing cerium-based abrasive powder and a dispersion medium into a slurry is used, scratches are often formed on the surface to be polished.

As a method for obtaining a dry abrasive powder capable of preventing the occurrence of such scratches, there are the following methods. When this method is used, wet crushing is used as crushing (crushing) performed at the final stage of the abrasive manufacturing process. Then, when the abrasive slurry is obtained by this wet pulverization, first, the pH of the abrasive slurry is adjusted to a predetermined range. Next, ammonium hydrogencarbonate or the like is added to this slurry to form flocs, which are then dried (see Japanese Patent Laid-Open No. 64-54090). The abrasive powder thus obtained has coarse particles (hereinafter, referred to as
It is considered to be an abrasive that contains almost no coarse particles) and is less likely to cause scratches.

However, when polishing was carried out using an abrasive slurry obtained by mixing the abrasive powder with a dispersion medium such as water, the surface obtained by the polishing was carefully observed.
It was found that quite a few fine scratches were generated.

The fine scratches have hardly caused any problems in the conventional glass polishing, but in recent years, for example, finish polishing of a glass substrate for a hard disk or an LCD, a higher precision polishing is required. It turned out to be a problem in such cases.

[0006]

The cause of such fine scratches is caused by the coarse particles (for example, particle size 1) in the abrasive slurry.
Particles of 0 μm or more). Therefore, until now, before performing polishing, the abrasive slurry used for polishing is subjected to ultrasonic waves, or the abrasive slurry is passed through a sieve to reduce the content of coarse particles. There is. However, in order to surely prevent the generation of fine scratches by performing such a treatment, a high level of technology is required and it takes time and effort. And it may be difficult for some users to perform such processing.

Further, it is possible to prevent the generation of fine polishing scratches by providing an abrasive slurry prepared so as not to contain coarse particles. This is because it becomes unnecessary for the user to prepare an abrasive slurry or to subject it to ultrasonic waves before polishing. However, since the abrasive slurry contains a large amount of water, the abrasive slurry is heavier than the abrasive powder and is easily deteriorated, which requires transportation and storage costs. Further, there is a problem that some of the abrasive particles in the slurry settle out during transportation and storage, which takes another trouble of redispersing.

The present invention has been made under the above background, and a powdery cerium-based abrasive capable of easily preparing an abrasive slurry having no scratch on the surface obtained after polishing and a method for producing the same. The challenge is to provide.

[0009]

In order to solve such problems, the invention and the like examined the process for producing a cerium-based abrasive. The manufacturing process of the abrasive is roughly as follows. First, the prepared raw material is pulverized to an appropriate size, and the pulverized raw material is subjected to a mineral acid treatment or a fluorination treatment as needed. Then, the raw material is dried and roasted, and the raw material after roasting is pulverized (crushed) again. In this pulverization, for example, when wet pulverization is used, the pulverized product is further dried. The thus obtained material is pulverized and classified as necessary. Then, an abrasive is obtained.

As a result of the examination, whether or not the obtained abrasive is likely to be scratched when the raw material after roasting is wet-milled is determined by the drying step performed after the wet-milling after roasting and It was found that it is greatly influenced by the conditions of the subsequent steps (crushing step and classification step). And it turned out that the drying process is considered to be particularly important. Therefore, the inventors have particularly examined the drying method. As a result, the inventors have come up with the following invention.

The present invention is characterized in that in the method for producing a cerium-based abrasive having a step of drying the abrasive slurry, a drying step by spraying the abrasive slurry is used.

[0012] Drying by spraying (hereinafter, also referred to as spray drying) means, for example, a slurry to be dried is sprayed into a drying chamber (chamber) by a rotating disk type or nozzle type spraying means and is atomized into a mist. The abrasive slurry thus obtained is brought into contact with heated gas to be dried. The atomized abrasive slurry is dried in a very short time when it is released into the heated gas, whereby an abrasive powder is obtained.

In such spray drying, the abrasive particles in the slurry are instantly separated from other particles and dried. As a result, it is considered that the agglomeration during drying is suppressed and the generation of coarse agglomerated particles is prevented. If the amount of coarse particles in the abrasive is suppressed, the abrasive slurry with a low content of coarse particles can be prepared by simply mixing the abrasive with a dispersion medium such as water to form a slurry. Therefore, when the abrasive slurry is prepared, it is not necessary to perform ultrasonic treatment or sieving in order to improve dispersibility, so that the preparation work is simple. Since the abrasive slurry thus prepared has a low content of coarse particles, a fine surface without fine scratches can be obtained by polishing with the abrasive slurry. Incidentally, the abrasive slurry referred to herein is a slurry prepared by mixing the manufactured abrasive with a dispersion medium such as water, and the abrasive raw material powder that has undergone the roasting step in the abrasive manufacturing process as a dispersion medium. And a slurry prepared by mixing with.

By the way, as can be understood from the above description, spray drying can dry the abrasive slurry without filtering. Conventionally, filtration, which is performed as one step of drying,
In order to prevent a decrease in the recovery rate of the solid content (abrasive material) due to so-called filtration leakage, a coagulant was added to aggregate the solid content to some extent, and then the solid content was filtered. However, in this way, the content rate of the agglomerated particles is significantly increased after drying. And, the obtained abrasive tends to be easily scratched. If the solid content obtained by filtration is squeezed by a filter press or the like to dehydrate the liquid portion for rapid drying, the content rate of aggregated particles is further increased.
In this respect, spray drying does not use a filtration step, and therefore it is possible to prevent an increase in agglomerated particles due to filtration, and is suitable for producing an abrasive having a low agglomerated particle content and excellent dispersibility.

The abrasive slurry sprayed during spray drying preferably has a solid content of 1% by weight to 50% by weight.
In order to atomize (form fine droplets) by spraying, basically, the smaller the solid content in the abrasive slurry, the better. However, if the solid content is less than 1% by weight, there is a limit to increase the drying efficiency. In order to maintain or improve the drying efficiency, there arises a problem that, for example, the size of the device needs to be increased. On the other hand, if the solid content exceeds 50% by weight, it is difficult to form a mist. Considering both the drying efficiency and the droplet size, the solid content of the slurry to be sprayed is more preferably 10% by weight to 40% by weight.

The abrasive slurry spraying means (or spraying means), that is, means for making the slurry into droplets (fog), is of the rotating disk type, two-fluid nozzle type or pressure nozzle type. Any thing can be used. Of these, the rotary disc type and the two-fluid nozzle type are preferable. This is because the abrasive slurry is easily atomized by spraying, and dry agglomeration is reliably prevented. The resulting abrasive powder has a lower content of coarse agglomerated particles. Therefore, when the abrasive slurry is prepared again, the content of coarse agglomerated particles lower than before can be obtained.

When a rotating disk type spray is used among the above spraying means, the peripheral speed of the outer peripheral edge of the disk is generally 10
Although it is about 200 m / sec, finer droplets are obtained as the peripheral speed is higher, and generation of coarse aggregated particles during drying is suppressed. Therefore, in drying the abrasive slurry, the peripheral speed is preferably 50 m / sec or more, and 10
It is more preferably 0 m / sec or more. When using the two-fluid nozzle type spray, the slurry supply pressure (discharge pressure of the supply pump) is preferably 0.29 MPa to 0.98 MPa, and the spray pressure (pressure of gas (usually air)) is
0.29 MPa to 0.98 MPa is suitable. This is because if either pressure is less than the lower limit pressure, the particles obtained are too large due to insufficient dispersion during spraying. If the upper limit pressure is exceeded, the spray becomes non-uniform and both fine particles and coarse particles increase, which is also undesirable. For the same reason, when the pressure nozzle spray is used, the spray pressure is preferably 0.98 MPa to 29.4 MPa.

When the nozzle type spraying means is used, the nozzle diameter is preferably 0.1 mm or more. This is because if the abrasive slurry is dried below this amount, the spray amount will be extremely small and the productivity will be poor. Further, since the abrasive slurry to be sprayed contains abrasive particles, the problem that the slurry is likely to be clogged during spraying easily occurs. On the other hand, the nozzle diameter is preferably 2.0 mm or less. This is because if the diameter is larger than this, the droplets generated are too large for the abrasive slurry to be dried, and the abrasive particles tend to agglomerate during drying. When comprehensively considering productivity, clogging, droplet size, etc., the nozzle diameter is 0.1 mm.
~ 1 mm is more preferable.

Further, the maximum temperature of the atmosphere for drying the droplets of the abrasive slurry formed by spraying, that is, the maximum temperature in the drying chamber (chamber) of the spray dryer (spray dryer) is 120 ° C. to 300 ° C. preferable. 300
This is because if the temperature is higher than 0 ° C, coarse particles are likely to be formed due to dry aggregation. From this point of view, 200 ° C. or lower is more preferable, and the maximum temperature of the atmosphere is further preferably 150 ° C. or lower in order to more reliably prevent the formation of coarse aggregated particles. However, if the maximum temperature of the atmosphere becomes too low, the time required for drying becomes long. Therefore, the maximum temperature of the atmosphere is preferably 120 ° C. or higher from the viewpoint of lowering work efficiency and rapid drying. The spray dryer includes a co-current type, a counter-current type, a co-current type (mixed type), etc., depending on the direction of spraying and the direction of flow of hot air, and any type can be used. The maximum temperature of the dry atmosphere is, for example, the inlet set temperature in the parallel flow type, and the outlet set temperature in the counterflow type.

By the way, the easiness of preparation of the abrasive into a slurry of the abrasive was examined in relation to the dry state of the abrasive before preparation. As a result, when the conditions of the drying process are changed, the water content (humidity) of the manufactured abrasive material changes, and when the abrasive material slurry is prepared later, the dispersion state of the abrasive material in the slurry may differ. I understand. For example, it has been found that in the case of an abrasive that has a low water content and is completely dried, it is difficult to disperse even if mixed with a dispersion medium such as water. On the contrary, when the water content became high, the abrasives sometimes adhered to each other before the preparation, and it was found that the dispersion at the time of preparation did not proceed due to this. Therefore, in consideration of such points,
The preferred moisture content of the abrasive in the dry state was investigated.
Here, based on the ratio of the weight difference (weight reduction) before and after drying, which is measured by heating and drying the powdery abrasive material placed at room temperature after manufacturing for 2 hours (at 105 ° C.), The degree of dryness of the abrasive was judged. As a result of examination, it was found that a preferable abrasive, that is, an abrasive that can be easily prepared into an abrasive slurry is an abrasive having a loss on drying of 0.1% to 5.0%.

Then, the relationship between the weight loss of the abrasive and the drying condition in the manufacturing process was examined. As a result, it is preferable to set the outlet temperature of the atmosphere (drying chamber) at the time of spray drying to be low in order to reduce the loss on drying to the above preferable range,
From this point, it was found that the spray dryer type is preferably a co-current type in which the spray port is located on the upstream side of the hot air.

Further, as a result of examining spray drying conditions for the co-current type, it was found that the outlet temperature is preferably 30 ° C to 100 ° C. Dried products such as abrasives and raw materials that have reached the vicinity of the outlet are almost dry, and if the dried product in such a state is exposed to an atmosphere at a temperature higher than 100 ° C, dry agglomeration of the dried product will proceed. is there. On the other hand, the outlet temperature is 3
This is because if the temperature is lower than 0 ° C, there is a high possibility that the drying will be insufficiently completed.

Further, the inventors have come up with the following two inventions from a study on the drying process at the time of manufacturing the abrasive material.

First, in the method for producing a cerium-based abrasive having a step of drying the abrasive slurry, a drying step of heating the abrasive slurry while vibrating the abrasive slurry is used. It is characterized by that.

Drying under vibration (hereinafter also referred to as vibration drying) means, for example, putting an abrasive slurry to be dried into a drying container installed so that it can vibrate, and vibrating the drying container. The drying is performed by moving the slurry in the drying container. There is also a means of supplying the abrasive slurry onto a fluidized bed using a perforated plate and drying the fluidized bed while vibrating the fluidized bed. However, the former drying method is preferable because handling of the apparatus is easier. It is considered that when the abrasive slurry is vibrated during the drying, the abrasive particles are prevented from agglomerating, so that it is possible to produce an abrasive that is less likely to cause scratches.

The frequency of vibration drying is generally
The frequency is 15 Hz to 35 Hz, but in the case of drying the cerium-based abrasive slurry, 20 Hz or higher, particularly 25 Hz or higher is preferable. This is because a higher effect can be obtained with respect to the suppression of dry aggregation. The solid content of the abrasive slurry at the start of vibration drying is preferably 5% by weight to 50% by weight. This is because if the concentration of the solid content is less than 5% by weight, rapid drying is difficult and the drying cost becomes too high. Further, in order to obtain a slurry of more than 50% by weight, a separate concentrating step such as heating and evaporation is required, and the drying step becomes rather complicated. The drying time varies depending on the slurry concentration, the drying temperature, the pressure of the atmosphere during drying, etc., but is preferably 1 hour to 24 hours. When vibration is applied to the drying container to dry it, the abrasive slurry may be made of, for example, alumina or M.
A medium such as a ball made of C nylon may be mixed. When such balls are mixed, the effect of flowing the abrasive slurry by vibration is improved, and the agglomeration of the abrasive raw material particles during drying is more reliably prevented.

The other is a method for producing a cerium-based abrasive, which has a step of drying the abrasive slurry, characterized in that the atmosphere of the abrasive slurry in the drying step is a vacuum atmosphere. . In a vacuum atmosphere, that is, in an atmosphere whose pressure is lower than atmospheric pressure,
It is considered that the environment is such that evaporation of the solvent is easily promoted, and therefore rapid drying is possible, and dry aggregation is unlikely to occur.

Further, as a result of the examination, with the drying method used in these two manufacturing methods, it is possible to carry out the drying in which the dry agglomeration is sufficiently suppressed even if the abrasive slurry to be dried is dried while being heated. It has been found that it is possible to produce an abrasive powder which is capable of producing polishing scratches with less scratches.

The heat source for drying while heating is not particularly limited, and for example, hot water, steam, hot air or hot air can be used. The ambient temperature of the abrasive slurry during drying is preferably 200 ° C or lower. If it is higher than this, dry aggregation is likely to occur.
However, the ambient temperature is preferably 30 ° C. or higher. This is because if it is lower than this, the time required for drying becomes long and the working efficiency is lowered.

By the way, as a result of studying a method for further suppressing dry aggregation, it was found that it is more preferable to add an organic solvent to the abrasive slurry to be dried. This is because dry aggregation is further suppressed. However, if the temperature of the abrasive slurry exceeds the boiling point of the organic solvent, all the organic solvent in the abrasive slurry evaporates, and there is a high possibility that dry agglomeration easily occurs. Therefore, when the organic solvent is added, the ambient temperature of the abrasive slurry in the drying step is preferably lower than the boiling point temperature of the contained organic solvent. It has been found that generally, 30 ° C to 100 ° C is preferable.

The organic solvent is not particularly limited as long as it has a solubility in the solution of 1% or more. For example, when water or a solution containing water as a main component (aqueous solvent) is used as the dispersion medium, the solubility in water is 1
% Or more of the organic solvent is preferable. When the solubility is less than 1%, the affinity with water is too low and the sufficient effect of suppressing dry aggregation may not be obtained. In this respect, it has been found that many organic solvents having high solubility are more preferable. In addition, as a preferable organic solvent, for example, methanol, ethanol, 1-propanol (n-propyl alcohol), 2-propanol (isopropyl alcohol), 2-methyl-1-propanol (isobutyl alcohol), 2-methyl-2-propanol. (Tert−
Butyl alcohol), 1-butanol (n-butyl alcohol), 2-butanol (sec-butyl alcohol)
Alcohols such as 1,2-ethanediol (ethylene glycol), 1,2-propanediol (propylene glycol), 1,3-propanediol (trimethylene glycol), 1,2,3-propanetriol (glycerin), etc. Examples of the polyhydric alcohol, acetone, ketones such as 2-butanone (methyl ethyl ketone), tetrahydrofuran, N, N-dimethylformamide, dimethyl sulfoxide, and 1,4-dioxane.

The concentration of the organic solvent in the solvent of the abrasive slurry at the start of drying is 0.1% by weight to 30% by weight.
Is preferred. The concentration of the organic solvent in the solvent is 0.1
This is because if the content is less than wt%, the effect of preventing the aggregation of the abrasive particles may not be sufficiently obtained. And 30
This is because even if the organic solvent is contained in an amount of more than 100% by weight, the effect of preventing aggregation hardly changes and the cost increases unless 100% by weight of the organic solvent from which water is completely removed is used.

The drying method in which the atmosphere of the abrasive slurry is a vacuum atmosphere and the drying method in which the abrasive slurry to be dried contains an organic solvent are used not only in the case of vibration drying but also in the case of spray drying. be able to. That is,
This means that the abrasive slurry in which the organic solvent is added to the liquid component may be sprayed, or the inside of the chamber, which is the spray destination, may be depressurized.

The particle size before and after the drying step is 10
The ratio of the amount of particles of μm or more (after drying / before drying) is preferably 1 or more and 5 or less.

Generally, particles having a particle size of 10 μm or more (hereinafter also referred to as coarse particles) in the abrasive raw material during the production process of the abrasive.
It is considered that the higher the content ratio of (3), the higher the risk of finally obtaining an abrasive that is more likely to be scratched when used for polishing. As a result of studying this point, it was found that if the amount of coarse particles increased more than 5 times before and after drying, the quality (particularly for scratches) deteriorated excessively, which was not preferable. On the other hand, in order to make the content of coarse particles less than 1 time before and after drying (that is, to reduce the content rate compared to before drying), it is necessary to sufficiently perform time such as dry pulverization and dry classification after drying. However, it takes a lot of labor and production cost. From the above, it was found that the above range is considered to be preferable for the rate of increase of coarse particles.

If the increase of coarse particles in the drying step is suppressed, the content ratio of coarse particles in the produced abrasive can be suppressed low. If the content of coarse particles in the abrasive is low,
It is possible to manufacture an abrasive that can easily prepare an abrasive slurry that is not easily scratched. More specifically, it is possible to prepare an abrasive slurry which is not easily scratched simply by mixing the obtained abrasive with a dispersion medium.

The content of the particles having a particle size of 10 μm or more in the abrasive slurry before drying is preferably 500 ppm or less. When the material to be dried is such an abrasive slurry, the amount of coarse particles contained in the abrasive raw material or the abrasive obtained after drying can be more reliably suppressed. further,
As the abrasive slurry to be dried, it is more preferable that the content of coarse particles is 100 ppm or less. This is because the content of coarse particles after drying can be suppressed more reliably.
The content of the coarse particles here is a value indicated based on the weight of the dry powdery abrasive raw material or the abrasive even when the measurement target is the slurry abrasive raw material or the abrasive.

The method of measuring the content of particles having a particle size of 10 μm or more is an electro-sieving method,
A measurement method in which ultrasonic dispersion treatment is not performed as the pretreatment is preferable. This is because if ultrasonic treatment is performed, even if coarse particles are contained in the abrasive, they will be dispersed to some extent by this treatment and cannot be detected. On the contrary, if the ultrasonic treatment is not performed, the object to be measured comes closer to the abrasive slurry used for actual polishing. That is, the measuring method described here is a method capable of measuring the actual state of the abrasive material. Therefore, the abrasive having good results obtained by this measuring method is unlikely to be scratched when used for actual polishing.

The powder of the cerium-based abrasive obtained by the method for producing the cerium-based abrasive described above is more dried than the powder of the cerium-based abrasive produced by the conventional production method using the same raw material. The aggregation of is suppressed. Therefore, an abrasive slurry having a lower content rate of coarse particles can be prepared by simply mixing it with a dispersion medium such as water to form a slurry. Further, by using the prepared abrasive slurry, scratches on the surface obtained by polishing can be suppressed more reliably.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below.

A cerium-based rare earth oxide (made in China) was prepared as a raw material. The raw material TREO is 99%, Ce
O ₂ / TREO was 60%. 25 kg of this raw material,
25 kg of pure water and 140 kg of grinding medium were put into a grinding container of a wet ball mill to carry out grinding. The grinding medium is a zirconia (YTZ) ball having a diameter of 5 mm,
The crushing container had a capacity of 100 L (liter). The crushing time was 8 hours. After crushing, filtration by a filter press method is performed, and the filtered abrasive material raw material is put in a PTFE pad at 120 ° C. for 2
It was left to stand and dry for 4 hours. After statically drying, the obtained abrasive raw material was dry pulverized with a roll crusher. Then, the abrasive raw material obtained by dry pulverization was placed on a quartz dish and baked in an electric furnace at 900 ° C. for 12 hours. After roasting, dry milling was performed with a sample mill (manufactured by Fuji Paudal Co., Ltd.) for one pass (one time).

A slurry prepared by mixing 18 kg of the abrasive raw material obtained after the dry pulverization and 72 kg of pure water was pulverized (crushed) for 3 hours using a mill. The mill used is "Mitsui Mining Co., Ltd., Kao: SC22.
0/70 type ", 0.8 mm diameter as a grinding medium
2.7 kg of the zirconia ball was used. The rotation speed of the rotor installed in the mill was 1500 rpm. In addition, this mill supplies the slurry in the holding tank to the crushing container of the mill, and returns the slurry crushed in the crushing container to the holding tank again for crushing while circulating. The volume was 15 l / min.

Through these steps, an abrasive slurry having a solid content of 20% by weight (hereinafter, also simply referred to as slurry)
Got In each embodiment and comparative example described below,
Except for Comparative Example 3, all the same slurries are targeted for drying. As a result of measuring the particle size of the abrasive particles in this slurry, the content of the abrasive particles having a diameter of 10 μm or more was 40 ppm, and the average particle size (D ₅₀ ) was 0.7.
The particle size was 6 μm and the maximum particle size was 3.06 μm. The methods described below were used to measure these values. The slurry used in Comparative Example 3 is described separately.

First Embodiment : The slurry to be dried thus obtained was sprayed and dried to obtain a cerium-based abrasive powder. For spray drying, a so-called co-current type spray dryer (L-8 type manufactured by Okawara Kakohki Co., Ltd.) was used. The co-current type device sprays the slurry into a drying chamber (drying chamber), and blows hot air (drying air) in parallel with it to dry the slurry. Then, in the present embodiment, a rotating disk type is used as the spraying means. Other spraying conditions are as follows: rotating disc (atomizer) diameter 50 mm, disc rotation speed 35000.
rpm (peripheral speed 92 m / sec), jet amount 30 mL (milliliter) / min, chamber inlet temperature of hot air (rotating disc position temperature) 150 ° C., outlet temperature was 50 ° C.

Second Embodiment : The hot air inlet temperature is different from that of the first embodiment. In this embodiment, the hot air inlet temperature was 250 ° C and the outlet temperature was 85 ° C. The other conditions are the same as those in the first embodiment, and the description thereof will be omitted.

Third Embodiment : This is an embodiment in which the slurry to be dried is not dried by spraying, but is dried while being vibrated. Specifically, the slurry to be dried was dried using a vibration dryer (VU type manufactured by Chuo Kakoki Co., Ltd.). This dryer is provided with a vibrating means for vibrating the container into which the slurry to be dried is put, and the slurry in the container can be dried while vibrating. Further, the container of this dryer has a so-called jacket structure, and the material forming the container has a gap inside which a liquid (heat source) such as hot water can be circulated. Therefore, the inside of the container can be heated by circulating the heat medium in the jacket. In this embodiment, the container is vibrated by the vibrating means, and hot water is circulated in the jacket to heat the container to dry the slurry. In addition,
The drying conditions were that the frequency of the container was 30 Hz, the container temperature during drying was 60 ° C., and the internal pressure in the container was 0.0067 MPa.
The conditions were the same as those in the first embodiment except that the drying method was different.

Fourth Embodiment : Part of the drying conditions is different from that of the third embodiment. The conditions in this embodiment were that the heat medium to be circulated in the jacket was water vapor, the container temperature was 130 ° C., and the container internal pressure was 0.10 MPa. The other conditions were the same as in the third embodiment.

Fifth Embodiment : Different from each of the above embodiments, an organic solvent (additive) is added to the slurry to be dried to dry the slurry. Specifically, the abrasive slurry was dried using a vacuum mixing dryer (Dalton Co., Ltd .: AMV type). This dryer includes a container having a jacket structure into which the slurry is charged and a means for stirring the charged slurry. In addition, this dryer is equipped with a vacuum pump, and the inside of the container can be sealed and decompressed (vacuum is applied) to dry the slurry if necessary.

In the present embodiment, first, 10 kg of the abrasive slurry to be dried (of which 8 kg of the dispersion medium) is set aside,
To this, 0.42 kg of ethanol (organic solvent) was added to prepare an abrasive slurry having an ethanol content of about 5.0% in the dispersion medium. This slurry was put into a container of a dryer and dried. As the drying conditions, the water temperature of the water flowing through the gap between the containers was 50 ° C., and the internal pressure of the container was 0.0067 MPa. Also, the container is rotated at 230 rpm and revolved at 159 rpm.
The slurry was agitated by spinning at. It was the same as the first embodiment except that the drying method was different.

Comparative Example 1 : Abrasive slurry to be dried was
After being dried through a filtration step, it was pulverized by dry crushing to obtain a cerium-based abrasive powder. First, in 10 kg of slurry to be dried (dispersion medium is 8 kg), a polymer flocculant having a concentration of 2 g / L (manufactured by Toagosei Co., Ltd., trade name: AMFLOCK)
Was added to form so-called floc. afterwards,
The abrasive was filtered off by filtration with a filter press method, and the obtained cake of the abrasive was placed in a PTFE pad and allowed to stand and dry. The ambient temperature during drying is 12
The drying time was 12 hours at 0 ° C. Then, the abrasive material obtained by drying was subjected to 1 pass using a roll crusher (manufactured by Dalton Co., Ltd .: MRCA type), followed by further 5 passes using a sample mill, all of which were dry-crushed to cerium-based polishing. Material powder was obtained. The two-step pulverization was carried out in this manner because the abrasive obtained by drying is solidified, and it is considered that the two-stage pulverization is necessary for forming the powder. It was the same as the first embodiment except that the drying method was different.

Comparative Example 2 : A coagulant different from that of Comparative Example 1 was used. In this example, first, 0.1 mol / L sulfuric acid aqueous solution was added to the abrasive slurry to be dried to adjust the pH to 7.0, and then the concentration of the aggregating agent was added to the slurry. 50 g / L ammonium hydrogen carbonate aqueous solution was added with stirring for 1 L to form a floc of abrasive. Then, the slurry was sprayed and dried to obtain a cerium-based abrasive powder. Note that p
The conditions were the same as in the first embodiment except that H was adjusted and a flocculant was added.

Comparative Example 3 : Different from the first embodiment, 5 kg of the abrasive material raw material obtained by roasting and dry pulverizing in the same procedure as described in the first embodiment was dry pulverized. Then, an abrasive was obtained. More specifically, it means that further 2-pass crushing (crushing) was performed under the same conditions (sample mill) as the dry crushing performed after roasting. The abrasive raw material obtained by this pulverization was subjected to dry pulverization using a turbo classifier (manufactured by Nisshin Engineering Co., Ltd., TC-15N) with a classification point set to 5 μm to obtain a cerium-based abrasive powder. .

Evaluation : With respect to the abrasives obtained in the respective embodiments and comparative examples, the coarse particle concentration, the average particle diameter and the maximum particle diameter were measured. Based on the measurement results, the dispersion performance of the abrasive particles in the abrasive slurry was measured. evaluated. In addition, an abrasive test was conducted with an abrasive slurry prepared using each abrasive, and the abrasive performance of each abrasive powder was evaluated.

Measurement of coarse particle concentration : First, abrasive powder 20
0 g and 800 g of pure water were mixed to prepare an abrasive slurry to be measured. After that, the abrasive slurry and
1 kg of 18% sodium hexametaphosphate aqueous solution was mixed and stirred for 2 minutes. The slurry after stirring was filtered through a micro sieve (electron sieve) having an opening of 10 μm, and the residue on the sieve was collected. The collected residue was dispersed in a 0.1% sodium hexametaphosphate aqueous solution to form a slurry. In addition, the ultrasonic agitation that is usually performed was not performed. Then, this slurry was filtered through a micro sieve having an opening of 10 μm to collect the residue. After that, the recovered residue is reslurried and filtered twice to obtain coarse particles (particle size 10 μm).
particles larger than m) were collected. The coarse particles were sufficiently dried and weighed, and the coarse particle concentration was determined from the weight of the coarse particles.

Measurement of average particle size and maximum particle size : Laser diffraction / scattering particle size distribution measuring device (manufactured by Shimadzu Corporation: S
ALD-2000A) was used to measure the particle size distribution, and the average particle size (D ₅₀ : particle size at the cumulative volume of 50% from the small particle size side) was determined. The measurement target in this measurement method is
It is a dispersed particle group consisting of a large number of particles in a dispersed state that exist in an emulsion or the like. In this measurement method, the light intensity distribution pattern of the diffracted / scattered light generated when the dispersed particle group is irradiated with a laser beam is detected and analyzed to determine the particle size distribution, and the maximum particle size is calculated based on the obtained distribution. (Dmax) can be obtained. Thus, the maximum particle size (Dmax)
Is a value measured by a measuring method completely different from the coarse particle concentration described above and cannot be simply compared, but it is reference data and is shown in Table 1 together with the average particle diameter (D ₅₀ ). It was

Polishing test : A test for polishing a glass surface using an abrasive slurry in which abrasive powder is slurried,
The polishing value was measured and the surface to be polished was evaluated (evaluation of scratches). In the polishing test, a high-speed polishing tester was used and 65 mmφ
The surface (surface to be polished) of the flat panel glass of (1) was polished using a polishing pad made of polyurethane. The concentration of solids in the abrasive slurry used was 10% by weight. Polishing was performed while supplying this at a rate of 5 liters / minute. The pressure of the polishing pad against the polishing surface was 1.54 MPa (15.7 MPa).
kg / cm ² ). Further, the rotation speed of the polishing tester was set to 1000 rpm. After the polishing, the glass material was washed with pure water and dried without dust.

Evaluation of polishing value : The weight of glass before and after polishing was measured to determine the reduction amount of glass weight due to polishing, and the polishing value was determined based on this value. Here, the polishing value when polishing was performed using the abrasive slurry before drying, which was obtained by wet disintegration after roasting, was used as the standard (100).

Evaluation of scratches : The state of the glass surface (surface to be polished) obtained by polishing was evaluated. The scratches were evaluated based on the presence or absence of scratches on the glass surface. Specifically, the surface of the glass after polishing was irradiated with a halogen lamp of 300,000 lux, and the glass surface was observed by a reflection method, and the number of large scratches and fine scratches was scored. Evaluation points were set by the deduction system. In the evaluation, the precision required for the finish polishing of the glass substrate for hard disk or LCD was used as a criterion.

Evaluation of Washability: A washability test was conducted on the surface to be polished, which was polished using the cerium-based abrasives obtained in the respective embodiments and comparative examples. First, a glass preparation for optical microscope observation was prepared, washed by ultrasonic cleaning and dried. Next, the cerium-based abrasive powder was dispersed in water to prepare an abrasive slurry with a concentration of 10% by weight. A dried preparation was immersed in this abrasive slurry, then pulled up and sufficiently dried with a drier, and the abrasive was attached to the surface of the preparation to obtain a test piece for a detergency test. The temperature of the preparation atmosphere during drying is 50 ° C.
And Ultrasonic cleaning was performed for 5 minutes while the obtained test piece was immersed in pure water in a beaker. After washing, the preparation was taken out of the beaker and washed with running pure water. Then, the surface of the preparation after washing with running water was observed with an optical microscope to evaluate the remaining amount of the abrasive particles remaining on the surface.

[0060]

[Table 1]

The coarse particle concentrations shown in Table 1 are obtained by simply mixing the cerium-based abrasive powder of each embodiment and comparative example with pure water,
It is the coarse particle concentration in the abrasive slurry prepared by stirring. It was found that by using the abrasive of the embodiment, an abrasive slurry having a low coarse particle concentration can be prepared by simply mixing and stirring the abrasive and water. Then, it was found that when polishing was performed using this, a good surface with few fine scratches was obtained. In contrast, the abrasive powder of Comparative Example had a high coarse particle concentration. Then, when it was used for polishing, not only fine scratches but also large scratches were generated, and a good surface could not be obtained.

Further, in the case of the cerium-based abrasive powder of the embodiment, the maximum particle size, the average particle size and the abrasive value of the abrasive are almost the same as those of the "abrasive slurry before drying" shown in the beginning of Table 1. There was no difference. As a result, if the abrasive powder of the present embodiment is used, it is possible to obtain a polished surface of the same quality as when polishing is performed by using the slurry as it is without drying the abrasive slurry obtained after wet crushing. I understand. In contrast,
In each of the abrasives of Comparative Examples, the maximum particle size was slightly larger. From this, it is considered that many scratches occur. The average particle size of Comparative Example 1 was almost the same as that of the embodiment, but it is considered that this is because the pulverization was repeated. Further, the average particle size of Comparative Example 2 was large. It is considered that this is because it was not crushed after drying.

It was found that the abrasives of the first, third and fifth embodiments have extremely low coarse particle concentrations and are particularly excellent abrasives. Further, regarding the coarse particle concentration and the scratch evaluation, from the result comparison between each embodiment and the comparative example, if the coarse particle concentration is 500 ppm or less, it is a practical abrasive, and if it is 100 ppm or less, it is an excellent abrasive. It turned out that It has been found that the quality can be sufficiently ensured under the manufacturing conditions of each embodiment.

Further, from the measurement results of the coarse particle concentration, when the abrasive powder to be finally prepared in which the coarse particle concentration of the abrasive slurry is 500 ppm or less is produced by using the production method according to the present invention, a wet method is used. It became clear to what extent the coarse particle concentration should be kept low in the crushing. For example,
When the manufacturing methods of the first, third and fifth embodiments are used, the coarse particle concentration is 400 ppm in the wet crushing.
It turns out that the following should be done. Then, it was found that the production method of the second embodiment should be 120 ppm or less, and the production method of the fourth embodiment should be 150 ppm or less. Further, if the coarse particle concentration in the state of the abrasive powder is 500 ppm or less, the coarse particle concentration tends to decrease during slurry formation, so that the abrasive slurry in which fine scratches are prevented is surely adjusted. It was found that it was possible and preferable.

[0065]

As described above, according to the present invention, a powdery cerium-based abrasive capable of preparing an abrasive slurry which hardly scratches the surface to be polished can be prepared by simply mixing it with a dispersion medium to form a slurry. The material can be manufactured.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuya Ushiyama             1-11-1 Osaki, Shinagawa-ku, Tokyo Mitsui Kin             Rare Meta, Functional Materials Business Group, Genus Mining Co., Ltd.             Within the business unit (72) Inventor Yuki Nakajima             1-11-1 Osaki, Shinagawa-ku, Tokyo Mitsui Kin             Rare Meta, Functional Materials Business Group, Genus Mining Co., Ltd.             Within the business unit F term (reference) 3C058 AA07 CB02 DA02

Claims (10)

[Claims] 1. A method for producing a cerium-based abrasive, which comprises a step of drying the abrasive slurry, wherein a drying step by spraying the abrasive slurry is used. . 2. The maximum temperature of the atmosphere for drying the droplets of the abrasive slurry formed by spraying is 120 ° C. to 300 ° C.
The method for producing a cerium-based abrasive according to claim 1, which is at a temperature of ℃. 3. A method for producing a cerium-based abrasive having a step of drying the abrasive slurry, wherein a drying step of heating the abrasive slurry in a state where vibration is applied to the abrasive slurry is used. A method for producing a cerium-based abrasive characterized by the above. 4. A method for producing a cerium-based abrasive, which comprises a step of drying the abrasive slurry, wherein the atmosphere of the abrasive slurry in the step of drying is a vacuum atmosphere. 5. The atmosphere temperature of the abrasive slurry is 30 ° C.
The method for producing a cerium-based abrasive according to claim 3 or 4, which has a temperature of about 200 ° C. 6. The method for producing a cerium-based abrasive as claimed in claim 1, wherein the abrasive slurry contains an organic solvent. 7. The method for producing a cerium-based abrasive according to claim 6, wherein the concentration of the organic solvent in the solvent of the abrasive slurry at the start of drying is 0.1% by weight to 30% by weight. 8. A particle size of 10 μm before and after the drying step.
The ratio of the amount of the above particles (after drying / before drying) is 1 or more and 5
The method for producing a cerium-based abrasive according to any one of claims 1 to 7, which is as follows. 9. The abrasive slurry before drying has a particle size of 10 μm.
The method for producing a cerium-based abrasive according to claim 8, wherein the content of particles of m or more is 500 ppm or less. 10. A cerium-based abrasive obtained by the manufacturing method according to claim 1.