PRODUCING METHOD FOR CERIUM-BASED GLASS POLISHING MATERIAL AND METHOD FOR USING THE SAME

Technical Field The present invention relates to a cerium-based polishing material, a method of producing the same and a method of using the same to polish glass and, more particularly, to a high-dispersion slurry type cerium-based polishing material having a low scratch incidence rate, a high polishing rate and an excellent polishing characteristic, a method of economically producing the same in large quantities and a method of using the same to polish glass.

Background Art A powder type cerium-based polishing material, using cerium oxide (CeO ₂ ) as a major component, is chiefly used when polishing glass . Particularly, the powder type cerium- based polishing material has been recently used for polishing glass for electric and electronic apparatuses, such as glass for a magnetic recording medium, for example, a hard disc, or a glass substrate for a Liquid Crystal Display (LCD) , as well as in conventionally polishing flat glass, therefore the application field thereof is gradually increasing. The reason why the cerium-based polishing

material is being widely used in polishing glass is that high precision polished surfaces can be obtained, and glass can be polished in large quantities due to the high removal performance . The powder type cerium-based polishing material is classified as a high-cerium polishing material or a low- cerium polishing material according to the content of cerium. The high-cerium polishing material is a polishing material having a relatively high cerium content, in which the weight percentage of cerium oxide to Total Rare Earth Oxides (hereinafter 'TREO') is 70 weight% or more, and the low-cerium polishing material is a polishing material having a relatively low cerium content, in which the weight percentage of cerium oxide to TREO is about 50 weight% . These cerium-based polishing materials have different contents and raw materials, but the methods of producing the materials after the preparation of raw materials are not very different.

Generally, the cerium-based polishing material is produced through steps of: 1) calcining a raw material; 2) wet pulverizing the calcined raw material, if necessary, treating it using a mineral acid, and then chemical treating it using a fluoric acid or ammonium fluoride; 3) filtering, drying and calcining an obtained slurry; and 4) pulverizing and classifying the obtained powder.

However, in the conventional production method, there

have been problems in that the diameter of the powder itself as well as that of particles thereof increases during polishing because the calcining process is performed two times, thereby the size of primary particles increases, and many scratches are generated due to the aggregation of particles occurring in the drying process. Furthermore, there has been another problem in that the production steps are complicated, and thus the production time is long, with the result that the economic efficiency thereof is low. Further, since the conventional cerium-based polishing material, produced through the above method, generally has a powder form, the polishing material and water are mixed in a polishing tank at a ratio of 1:9 at the time of use, and then polishing is performed while the mixture is injected into a polishing machine. However, since the powder type polishing material has low dispersibility (Zeta potential: -10 mV or less), it is deposited in the polishing tank, and then the particle size thereof increases, thus scratches occur when the polishing material having large-size particles is injected into the polishing machine to be then used for polishing, thereby decreasing the production yield of precision LCD glass to 75% or less . Accordingly, a secondary polishing process must be performed, with the result that there are problems in that the overall processing time and production cost increase .

Disclosure Technical Problem

Accordingly, an object of the present invention is to provide a high-dispersion and high-precision slurry type polishing material, which is capable of replacing a dry powder type polishing material used for polishing a glass substrate for a display, particularly, a glass substrate for an LCD, having a low scratch incidence rate, a high polishing rate and an excellent polishing characteristic, a method of economically producing the same, and a method of polishing glass, which is capable of decreasing polishing processing time and polishing time.

Technical Solution

As a result of continuously studying the technology for polishing material in order to accomplish the above object, the present inventors developed a method of producing a material for polishing glass using only extremely simple processes, found that the high-dispersion and high-precision slurry type polishing material produced using the method has a low scratch incidence rate, a high polishing rate and an excellent polishing characteristic, and further found that the polishing rate can be increased by using the polishing material, so that the entire polishing processing time and polishing cost can be

decreased, thereby finishing the present invention.

In order to accomplish the above object, the present invention provides a method of using a cerium-based polishing composition to polish glass for a display, wherein the cerium-based polishing composition is produced using a method comprising the steps of calcining trivalent cerium salt, thereby converting the trivalent cerium salt into tetravalent cerium oxide having a particle size of 10 to 100 nm; and mixing 1 to 90 weight% of the tetravalent cerium oxide with 9 to 98 weight% of water and 0.1 to 20 weight% of dispersant into a mixture, and then pulverizing the mixture without drying, thereby producing a slurry type cerium-based polishing composition having a particle size of 0.3 to 3 μm. Further, the present invention provides a method of producing a cerium-based polishing composition to polish glass for a display, comprising the steps of calcining trivalent cerium salt, thereby converting the trivalent cerium salt into tetravalent cerium oxide having a particle size of 10 to 100 nm; and mixing 1 to 90 weight% of the tetravalent cerium oxide with 9 to 98 weight% of water and 0.1 to 20 weight% of dispersant into a mixture, and then pulverizing the mixture without drying, thereby producing a slurry type cerium-based polishing composition having a particle size ranging from 0.3 to 3 β\\\.

Hereinafter, the present invention will be described

in detail .

First, the method of producing a polishing material according to the present invention includes the step of calcining trivalent cerium salt, thereby converting the trivalent cerium salt into tetravalent cerium oxide having a particle size ranging from 10 to 100 nm. It is preferable that the trivalent cerium salt used as a raw material be at least one selected from the group consisting of cerium chloride, cerium nitrate, cerium carbonate, cerium hydroxide, cerium ammonium nitrate and cerium oxalate. The procedure for converting cerium nitrate, which is trivalent cerium salt, into tetra cerium oxide is represented by the following reaction formula

[reaction formula 1] Ce(NO3)3 + 3H2O → Ce (OH) 3 + 3HNO3

CeO2 + 3HNO3 + 2H2O → Ce(OH) (NO3)3 ^• 3H2O

2Ce (OH) 3 + 302 → CeO2 + 3H2O T

It is preferable that the step of calcining trivalent cerium salt be performed for 10 minutes to 5 hours at a temperature ranging from 400 to 1100 ^° C . If the temperature is below 400 ^° C, the strength of the particles is decreased, and thus the particles are easily differentiated and the polishing rate is decreased. If the temperature is above

1100 ^° C, the strength of the particles is increased, and thus the scratch incidence rate is increased.

In the present invention, there is a characteristic

in that the size of the primary particles is adjusted to a size of 10 to 100 nm by calcining the trivalent cerium salt under the above conditions. Therefore, if the size of primary particles is adjusted, there is an advantage in that the rate of incidence of scratches in the polished material is decreased.

It is preferable that the weight ratio (CeO2/TREO) of cerium oxide to TREO be in the range from 40 to 99.99 weight%. Generally, in the conventional polishing material, the ratio of cerium oxide to TREO is relatively low. However, in the present invention, the weight ratio of cerium oxide is high, with the result that polishing material having an excellent polishing characteristic can be produced. Meanwhile, the method of producing a polishing material according to the present invention includes the step of mixing 1 to 90 weight% of the tetravalent cerium oxide, obtained through the step of calcining trivalent cerium salt, with 9.9 to 98.9 weight% of water and 0.1 to 20 weight% of dispersant into a mixture, and then directly pulverizing the mixture without drying.

If the content of the dispersant is below 0.1 weight%, the polishing material cannot be easily used when injected into a polishing machine because dispersibility is decreased and cerium oxide particles precipitate. If the content of the dispersant is above 20 weight%, uniform

polishing cannot be performed because bubbles are generated when slurry is stirred, and the conglomeration of particle occurs due to the excessive amount of additives . Accordingly, it is preferable that the dispersant be added in an amount within the above content range.

It is preferable that the dispersant be selected from the group consisting of a water-soluble anionic dispersant, a water-soluble nonionic dispersant, a water-soluble cationic dispersant, a water-soluble zwitterionic dispersant and a polymer dispersant.

The water-soluble anionic dispersant includes triethanolamine lauryl sulfate, ammonium lauryl sulfate or triethalolamine polyoxyethylenealkylether sulfate.

The water-soluble nonionic dispersant includes polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxymethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene higher alcohol ether, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, polyoxyalkylenealkyl ether, polyoxyethylene derivatives, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tetraoleate, polyethyleneglycol monolaurate, polyethyleneglycol monostearate, polyethyleneglycol

distearate, polyethyleneglycol monooleate, polyoxyethylenealkyl amine, polyoxyethylene hydrogenated castor oil or alkylalkanol amide .

The water-soluble cationic dispersant includes coconut amine acetate or stearyl amine acetate .

The water-soluble zwitterionic dispersant includes lauryl betaine, stearyl betaine, lauryldimethyl amine oxide or 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolium betaine . Further, a polymer compound such as polyvinylacetal , polyvinylformal, polyvinylbutyral, polyvinylpyrrolidone, polyvinylpyrrolidone iodine complex, poly (vinyl 5-methyl- 2-pyrrolidinone) , poly (vinyl 2-piperidinone) , poly (vinyl 3,3, 5-trimethyl-2-pyrrolidinone) , poly (N-vinylcarbazole) , poly (N-alkyl-2-vinylcarbazole) , poly (N-alkyl-3- vinylcarbazole) , poly(N-alkyl-4-vinylcarbazole) , poly (N- vinyl-3, 6-dibromocarb azole) , polyvinylphenylketone, polyvinylacetophenone, poly (4-vinylpyridine) , poly (4- β- hydroxyethylpyridine) , poly (2-vinylpyridine) , poly (2- β - vinylpyridine), poly (4-hydroxyethylpyridine) , poly (4- vinylpyridinium salt), poly ( α-methylstyrene-co-4- vinylpyridinium hydrochloride), poly (1- (3-sulfonyl) -2- vinylpyridiniumbetaine-co- p -styrenesulfonic acid potassium), poly (N-vinylimidazole) , poly (N-vinylimidazole) , poly (4-vinylimidazole) , poly (5-vinylimidazole) , poly(l- vinyl-4-methyloxazolidinone) , polyvinylacetamide,

polyvinylmethylacetamide, polyvinylethylacetamide, polyvinylphenylacetamide, polyvinylmethylpropionamide, polyvinylethylpropionamide, polyvinylmethylisobutylamide, polyvinylbenzylamide, poly (meth) acrylic acid, poly (meth) acrylic acid derivatives, poly (meth) acrylic acid ammonium salts, polyvinyl alcohol, polyvinyl alcohol derivatives, polyacrylein, polyacrylonitrile, polyvinyl acetate, poly (vinylacetate-co-methylmethacrylate) , poly(vinylacetate-co-pyrrolidine) , poly (vinylacetate-co- acetonitrile) , poly (vinylacetate-co-vinylacrylate) , poly(vinylacetate-co-pyrrolidine) , poly (vinylacetate-co- acetonitrile) , polylvinylacetate-co-diarylcyanide) , poly(vinylacetate-co-N,N-diarylamine) or poly (vinylacetate- co-ethylene) can be used as the dispersant. As such, after the steps of calcining and pulverizing are performed, slurry is formed, and this slurry type mixture may additionally pass through the step of filtering. The production method according to the present invention has a characteristic in that it includes only the steps of calcining and pulverizing, and decreases the scratch incidence rate because the agglomeration phenomenon of raw material, which can occur during a drying process in a conventional method of producing a powder type polishing material, can be prevented. As described above, the polishing material, produced by the method of producing a polishing material according

to the present invention, has advantages in that a weight ratio (Ce02/TRE0) of cerium oxide to TREO is 40 to 99.99 weight%, the particle size is 0.3 to 3 μm, the form thereof is a slurry form, the scratch incidence rate is low, and the polishing rate is high.

Since the conventional polishing material is a dry powder type polishing material, it was used by directly mixing a polishing material with water at a constant ratio of 1:9. In this case, since the dry powder type polishing material is accumulated in a tank due to the decrease of dispersibility (Zeta potential: -10 mV or less) and the accumulated powder increases the scratch incidence rate, the polishing rate is decreased, thereby secondary polishing is performed. However, since the polishing material of the present invention, compared to the conventional dry powder type polishing material, is a slurry type polishing material, it has advantages in that the polishing material cannot be accumulated in a tank due to high dispersibility (Zeta potential: -40 mV or more), the proportion of inferior goods produced is greatly decreased, and a polishing machine is easily maintained and controlled. Further, the conventional polishing material has a problem in that large particles can be formed due to moisture in air when storage conditions (for example, humidity) of polishing material are not suitable, however, the polishing material of the present invention has an

advantage in that such a phenomenon does not occur because it is a slurry type polishing material .

Meanwhile, a process of polishing display glass, particularly LCD glass, using the conventional dry powder type polishing material includes the step of primarily polishing the glass using a polishing machine and the step of secondarily polishing the primary polished glass using a polytex pad (manufactured by Rohm & Hass corporation) so as to remove generated minute scratches. However, when the slurry type polishing material, which is produced using the method according to the present invention, is used, a high polishing rate and good polished products can be obtained, unlike those in the conventional process, thereby decreasing polishing processing time and cost. Further, in the case in which a glass substrate for a high-precision display is required, if polishing is performed the same as the existing secondary polishing after primary polishing, there is an advantage in that a significantly precise glass substrate for a display, particularly a glass substrate for a LCD, can be produced, compared to that obtained through the existing process.

Advantageous Effects

As described above, since the method of producing a polishing material according to the present invention includes only calcining and pulverizing steps, polishing

materials can be produced in large quantities in a short time using only simple processes, therefore the method is extremely economical. Furthermore, a high-dispersion slurry type polishing material, produced using the method according to the present invention, has a low scratch incidence rate, a high polishing rate and excellent polishing characteristics because it has a small maximum particle size. When glass is polished using the slurry type polishing material instead of powder type material, many scratches due to the accumulation in a polishing tank and a pipe is prevented, so the yield of glass increases . Accordingly, the high-dispersion slurry type polishing material is used to polish glass in the fields requiring high precision glasses such as optical lens glass, glass for a displays, glass for magnetic recording discs and liquid crystal glass. Moreover, due to the improvement of the polishing process based on the above advantages, yield increases, and polishing time and cost decrease.

Description of Drawings FIG. 1 is a graph showing the distributions of particle sizes of the polishing materials based on example 1 of the present invention and comparative examples 1 and 2;

FIG. 2 is a photograph comparing the extent of scratch generation based on the polishing material produced

according to example 1 of the present invention and comparative example 1;

FIG. 3 is a graph showing the polishing rates of the polishing materials based on example 1 of the present invention and comparative example 1;

-•- : example 1 -H- : comparative example 1

FIG. 4 is a photograph showing the results of polishing an LCD glass substrate using the polishing material produced through the conventional method;

FIG. 5 is a photograph showing the results of polishing an LCD glass substrate using the polishing material produced through the conventional method and then secondarily polishing the same; FIG. 6 is a photograph showing the results of polishing an LCD glass substrate using the polishing material produced through the method of example 1 of the present invention; and

FIG. 7 is a photograph showing the results of polishing an LCD glass substrate using the polishing material produced through the method of example 1 of the present invention and then performing secondary polishing.

Mode for Invention

Hereinafter, the present invention will be described

in detail through the following examples. However, the following examples illustrate the present invention, therefore the present invention is not limited to the following examples . [Example 1] Production of polishing material

A trivalent cerium salt (95 weight% of cerium oxide of TREO) was heat-treated in a calcining furnace at a temperature of 1000 ^° C, thus being converted into tetravalent cerium oxide. 90 weight% of the tetravalent cerium oxide, 9 weight% of water and 1 weight% of triethanolamine lauryl sulfate as the dispersant were mixed and stirred using a stirrer, and particle size was then adjusted to 0.3 to 3 μm using a wet pulverizer (manufactured by Union corporation) .

[Example 2] Analysis of characteristics of polishing material

2-1. Measurement of particle diameter 10 g of powder of the polishing material, which was produced by the method in Example 1, was added to 0.1 weight% of an aqueous sodium hexametaphosphate solution or 100 ml of distilled water, and dispersed for 2 to 3 minutes . Part of the obtained dispersion solution was adopted, the particle size distribution was measured using LS-230 (Coulter Counter corporation) , and the results thereof are shown in FIG. 1. Although generally, the particle diameter of powder is measured using ultrasonic waves, it was measured without using the ultrasonic waves

in this case because the conditions for measuring the particle diameter must be identical to the conditions for polishing glass.

As shown in FIG. 1, it was found that the polishing material produced in the present invention, compared to the polishing materials (comparative examples 1 and 2) produced using the conventional method, had a small average particle size, and a notably small maximum particle size. Further, it was found that the polishing material of the present invention had uniform polishing characteristics because the degree of concentration of particle size distribution was high.

2-2. Evaluation of scratch

Glass was polished using the polishing material which was produced by the method in Example 1 under the polishing conditions described below, and the glass was then cleaned. The surface of the glass was measured using a polarization microscope (Olympus STM6) , and the results are shown in FIG. 2. As shown in FIG. 2, it was found that the polishing material (Comparative Example 1) produced by the present invention, compared to the polishing material produced by the conventional method, generates almost no scratches . <Polishing condition>

1) Machine: Oscar type single polisher, plate 1400mm 2) Workpiece : lOOOpcs, soda lime glass

3) Platen Rotation Speed (rpm) : 55

4) Pressure (psi) : lOOg/cin ²

5) Pad: Rohm & Hass MH14B

6) Solid content in Slurry (wt%) : 10 7) Slurry Flow Rate ( I /min) : 40 i /min 8) Polishing Time (min) : 4pcs/6min

2-3. Evaluation of polishing rate

Glass was polished using the polishing material which was produced by the method in example under the same polishing conditions as that of 2-2, and the glass was then cleaned. The polishing rate was measured using a thickness measuring instrument (Woritech WT-5890) , and the results are shown in FIG. 3. As shown in FIG. 3, the polishing material (-#-) produced by the present invention, compared to the polishing material (-H-) produced by the conventional method, has a high average polishing rate, and particularly has a high polishing rate after the glass has been polished 30 times.

[Example 3] Comparative test of polishing LCD glass substrates were polished using the polishing material which was produced by the method in

Example 1 and the polishing material produced by the conventional method, respectively, and the results are shown in FIGs . 4 to 7. The polishing process was performed

using a MHC14B Cerium pad manufactured by Rohm & Hass Corporation.

FIG. 4 shows the results of polishing an LCD glass substrate using the polishing material produced by the conventional method. In FIG. 4, a large number of scratches were generated even after the polishing was performed. Accordingly, subsequently, secondary polishing was performed using Polytex products again. FIG. 5 is a photograph showing the surface state of an LCD glass substrate after the LCD glass substrate is merely secondarily polished. as can be seen in FIG. 5, it was confirmed that the scratches could not be completely removed even after the secondary polishing was performed.

In contrast, FIG. 6 shows the results of polishing an LCD glass substrate using the polishing material produced by the method of Example 1 of the present invention. In FIG. 6, it was confirmed that almost no scratches were generated, even after primary polishing was performed. The surface state of the LCD glass substrate in FIG. 6 was the same as that of the LCD glass substrate in FIG. 5. That is, when the polishing process was performed using the polishing material of the present invention, it was found that the same state as the state after the secondary polishing in the conventional polishing process could be

obtained through only the primary polishing. FIG. 7 is shows the results of polishing an LCD glass substrate using the polishing material. Here, an LCD glass substrate, from which scratches were completely removed, could be produced. Accordingly, when the polishing process was performed using the polishing material of the present invention, it was found that the polishing time and cost could be decreased because the polishing rate could be increased.