Abrasive tool making process – material – or composition – With inorganic material
Reexamination Certificate
2002-05-06
2004-02-10
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
C051S309000, C423S263000
Reexamination Certificate
active
06689178
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a cerium-based abrasive containing cerium oxide as a main component and excellent in polishing precision and cutting property as well.
BACKGROUND ART
Recently, a cerium-based abrasive containing cerium oxide (CeO
2
) has been used for polishing a variety of glass materials. Especially, a cerium-based abrasive has been employed for polishing from conventional common plate glass materials to glass materials today to be used for electric and electronic apparatuses, for example, glass for magnetic recording media such as hard disks, glass substrates of liquid crystal displays (LCD) and its application field is widened.
The cerium-based abrasive is composed of abrasive particles containing cerium oxide (CeO
2
) particles as a main component. The cerium-based abrasive can widely be classified into a high cerium abrasive and a low cerium abrasive depending on the content of cerium oxide. The high cerium abrasive contains at least 70% by weight of cerium oxide in relation to the whole amount of the rare earth oxides (hereinafter abbreviated as TREO) and is an abrasive containing a comparatively large amount of cerium oxide, whereas the low cerium abrasive is an abrasive containing cerium oxide in the content as relatively low as about 50% by weight in relation to TREO. Although the content of cerium oxide and the raw materials of these cerium-based abrasives are different, the production steps after raw material preparation are not so much different.
FIG. 1
shows the production steps of these cerium-based abrasives. The raw materials to be used for the high cerium abrasive are rare earth chlorides obtained by chemically treating and concentrating a rare earth ore so-called monazite. On the other hand, conventionally usually used as the raw materials of the low cerium abrasive is a bastnasite concentrate obtained by dressing the rare earth ore so-called bastnasite and recently, raw materials mainly used are derived from rare earth oxides or rare earth carbonates synthesized using the bastnasite ore and relatively economical complex ores produced in China. In the steps after raw material preparation, both are produced by chemically treating the raw materials (by the wet treatment), filtering, drying them, and further roasting them and pulverizing and sieving the obtained raw materials. The particle diameter of the abrasive particle constituting an abrasive is 0.2 to 3.0 &mgr;m on the bases of the average particle diameter, although depending on the purposes from the rough finishing to the final finishing, and it is controlled by adjusting the temperature in the foregoing production steps and the roasting step and adjusting the pulverization and the classification steps.
By the way, one reason why a cerium-based abrasive has widely been employed is that a large quantity of glass can be removed by abrasion within a relatively short time to obtain a high polishing value in addition to that a polished face with high precision can be obtained. In this case, regarding the polishing mechanism of the cerium-based abrasive, there are not necessarily any clear established theories, however, it is said that the fluorine component contained in an abrasive takes a significant role. That is, in addition to the mechanical polishing effect by cerium oxide, it is said that also the chemical polishing function is simultaneously caused as follows: the fluorine component contained in the abrasive reacts with the glass face to fluorinate the glass and accelerate corrosion of the glass surface. Therefore, regarding the cerium-based abrasive, it is supposed to be possible to exert the excellent polishing properties when both of the mechanical function and the chemical function are sufficiently performed.
As the first standard to produce an abrasive with excellent polishing properties, first of all, it is required for the abrasive to be free from abnormally grown abrasive particles and to have evenness in the particle diameter distribution. Therefore, in the production steps of the cerium-based abrasive, a variety of countermeasures are performed so as to suppress the abnormal particle growth of the abrasive particles. For example, in the chemical treatment steps, a raw material pulverized with a mineral acid such as hydrochloric acid, sulfuric acid, and the like is treated. That is for dissolving and removing alkali metals, e.g. sodium, and alkaline earth metals contained as impurities in the raw material with mineral acids since these alkali metals and alkaline earth metals cause the abnormal particle growth in the roasting step thereafter.
Further, in addition to the control in these production steps, regarding produced abrasives, product inspection is randomly performed to investigate the average particle diameter and the particle diameter distribution to investigate the existence of coarse particles owing to the abnormal particle growth.
Excellent abrasives have been supplied ever before through the above described control of the particle diameter distribution of abrasive particles in the production steps and the fluorine concentration and product inspection.
However, taking the demands for the cerium-based abrasive in the future into consideration, it is natural to be desired to develop further excellent abrasives. Especially, since further integration to a high density is required in an industrial field of a glass substrate for hard disks, LCD and the like and for that, it is required to obtain an abrasive which not only is capable of forming a polished face with extremely high precision but also has a high cutting property to carry out polishing to a prescribed extent at a high speed.
Hence, the present invention aims to provide a cerium-based abrasive capable of forming a polished face with precision higher than that a conventional method has ever achieved and having an excellent cutting property and a new standard and to provide a production method.
DISCLOSURE OF THE INVENTION
The inventors of the present invention have made investigation in details in polishing properties of conventional cerium-based abrasives and found a problem that scratches are sometimes formed in the polished face even in the case of using a conventional abrasive with a finely miniaturized average particle size and of which the particle diameter distribution is found no problem in a product inspection. Then, a variety of investigations into the causes of the occurrence of such scratches have been performed and consequently, the following two problems are found in the conventional abrasives which are regarded not to have any problem in the particle diameter distribution by the above described inspection method and thus the present invention is achieved.
The first problem in the conventional cerium-based abrasives is the existence of coarse particles in an extremely slight amount, which are inevitably contained by a conventional production method and which are impossible to be detected by a conventional inspection method. In this case, the coarse particles- in the present invention mean particles having a particle diameter several times as large as the average particle diameter of the abrasive particles composing an abrasive and having a particle diameter within a range in which they can not be detected by the particle diameter distribution by a conventional inspection method and within a range of 10 to 50 &mgr;m or more.
The inventors of the present invention have thought it is necessary to clarify the relation between the coarse particle concentration and the polished face even if the amount is extremely slight in order to obtain an abrasive with higher precision ever before. From such a viewpoint, the inventors of the present invention have enthusiastically investigated and consequently found that even if those found having no problem by a conventional inspection method contain coarse particles with a diameter of 10 &mgr;m or larger in 1,500 ppm or more by weight.
The inventors of the present invention have then found as a first invention that an abrasive can be provided corre
Ito Terunori
Mochizuki Naoyoshi
Uchino Yoshitsugu
Yamasaki Hidehiko
Marcheschi Michael
Mitsui Mining & Smelting Co. Ltd.
Rothwell Figg Ernst & Manbeck
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