Abrasive tool making process – material – or composition – With inorganic material
Reexamination Certificate
2000-03-09
2002-05-07
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
C051S308000, C051S309000, C106S003000, C106S008000
Reexamination Certificate
active
06383239
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a free abrasive slurry composition containing free abrasive particles which is advantageously used in uniform grinding or processing of a composite material composed of a plurality of materials having different hardness from each other, without causing difference in the grinding amount between soft materials and rigid materials, i.e. selective grinding, during lapping and polishing processes of the composite material.
PRIOR ART
Recently, higher performance and higher function have been more and more demanded for optical parts, electronic parts, precision machine parts or the like, and wide range of materials have been used for such parts, such as metallic crystalline materials, ceramics, glass, plastics and so forth.
As one of the manufacturing processes of such parts, grinding or polishing of a composite material composed of a plurality of materials having different hardness from each other is frequently introduced. Recited as examples of grinding processing of composite materials are: in the field of electronics, texturing of Ni—P plating of a hard disk substrate, uniform working of wiring metal layers and insulation films between the layers in multiple layer wiring process of LSI; and in the field of optics, grinding of the connector end faces of optical fibers consisting of a composite material composed of zirconia ceramics (so called “ferrule”), quartz glass (so called “core” of fiber) and fluoroplastics (so called “clad”).
With respect to a hard disk drive (i.e. a recording medium of computer), the packing density has been increased year by year. As means to attain a higher packing density, the gap or spacing between the hard disk and a magnetic head has been reduced. In other words, reduction of the spacing of the raised head has been attempted. A magnetic head mounted on a hard disk drive is generally of a thin film type magnetic head type, and examples of this type are of an inductive type, an MR-inductive complex type wherein MR (magnet resistance) is used as a recording/reproducing element, and a type using GMR (Giant MR).
These thin film type type magnetic heads are composed of a composite material comprised of a substrate such as Altic (Al
2
O
3
—TiC), a ceramic protective/insulation film such as alumina (Al
2
O
3
), a metallic film which is a magnetic material such as permalloy (Fe—Ni) and Sendust (Fe—Al—Si) and the like.
For example, a thin-film type magnetic head
12
′ shown in
FIGS. 1 and 2
comprises an Altic substrate
1
, an alumina insulation film
2
, a bottom shield film
3
(Sendust: Fe—Al—Si, permalloy: Fe—Ni or the like), an alumina film
4
, an MR element
5
, an alumina film
6
, a head shield film
7
(permalloy or the like), an alumina film
8
, a write pole tip
9
(permalloy or the like), an alumina protective film
10
, and a coil conductor
11
.
When a conventional free abrasive slurry is used for grinding of ABS (Air Bearing Surface) of a thin film type magnetic head, in most cases, stepped (as indicated by “STEP” in
FIG. 1
) or rough surface results due to selective grinding or abrasion of a metallic film made of soft materials such as permalloy and Sendust, due to difference in hardness between the materials. As a result, there is a problem in that the metallic film (such as magnetic pole portion) is recessed from ABS composed of ceramics, which is called PTR (Pole Tip Recession), increasing the magnetic spacing to a recording medium (as shown in FIG.
1
), thereby leading to substantial increase in raised or floating distance of the head.
In general, lubricants have been used for grinding a composite material composed of a plurality of materials having different hardness from each other, and such lubricants are classified mainly into three categories based on mechanisms of lubrication on the materials to be ground: 1) oily agent which is fatty acid such as stearic acid and oleic acid, 2) anti-abrasion agent such as phosphoric ester and Zn-DTP, and 3) organic Mo compound.
Among them, the anti-abrasion agent lowers friction even in a severe grinding condition where the oily agent loses its lubrication action. It is known that an anti-abrasion agent forms a lubricating film as the result of a tribochemical reaction with the frictional surface in a low load condition to a a high load condition at higher temperature (Seichiro Hironaka, Action mechanism of lubricant additive, Plastic Processing Symposium, 33-43,1994; R. J. Hartley et al., Anti-abrasion agent and high-pressure agent, Tribologist, 326-331, 1995).
Among such anti-abrasion agents, those compounds containing sulfur atom in its molecular chain are decomposed by frictional heat generated on the frictional surface and form an inorganic film containing sulfide between the grinding surface and the substance to be ground, thereby maintaining a lubricating property.
In the same manner, anti-abrasion agents containing a phosphorus atom in its molecular chain are decomposed by frictional heat generated on the frictional surface and form an inorganic film consisting of phosphide or phosphate between the grinding surface and the substance to be ground. It is believed that phosphite ester compound from among such compounds containing phosphorus is hydrolyzed by frictional heat to form an inorganic film. (Toshihide Omori et al., “Adsorption and reaction on the iron surface of phosphorus high-pressure additives (second report)”, Tribologist, 188-194, 1990).
It is known that compounds containing both sulfur and phosphorus atoms also exhibit the same effect as that of the compound comprising a sulfur atom alone or a phosphorus atom alone. (Masafumi Mashiko, “Chemistry and physics of lubricant”, Fundamentals and applications in tribology, 15-34, 1996).
Since these inorganic films are chemisorbed to a substance to be ground, the adsorption force is stronger than that of physical adsorption of organic molecules and the film is stable up to temperatures. A large amount of energy is required in order to remove the inorganic film, and thus it is known that the lubrication effect of the film on the substance to be ground is maintained, so long as the grinding condition is not so severe that the inorganic film is removed (Toshio Sakurai, “Chemistry of lubrication and grinding”, Lubrication, 635-642, 1982).
As an anti-abrasion agent, sulfur-containing organic molybdenum is also studied (P. C. H. Mitchell “Oil Soluble Mo—S Compounds as Lubricant Additive” Wear 100 (1984) 281-300; edited by Hehachiro Okabe, “Development and the Latest Technology of Additives for Petroleum Products” CMC (1988) p99-106; and so forth), and the possibility is studied for sulfur-containing organic molybdenum to be used as a lubricant for the grinding of a composite material composed of materials of various hardness (Japanese Patent Application No.10-255022).
As mentioned above, although the effects of anti-abrasion agents have been widely known, those anti-abrasion agents have been conventionally used for lowering the friction of the sliding surface of machine parts, such as the surface of a gear or a turbine. On the other hand, the load applied on a conventional composite material, such as a thin film type magnetic head composed of a plurality of materials of various hardness, during grinding is much lower than that on the sliding surface such as the surface of a gear and, therefore, it is quite possible to process a composite material without using an anti-abrasion agent. However, a uniform working have not been attained. Accordingly, no one has tried to add the anti-abrasion agent to a free abrasive slurry composition as an anti-selective grinding agent for the purpose of preventing selective grinding of a composite material composed of materials of various hardness as in the present invention.
Japanese Patent Application Nos. 10-113327 and 10-255022 propose the use of free abrasive slurry containing an anti-selective grinding agent which can achieve a sliding surface with high precision, thereby avoiding such selective grinding or damage.
In Japanese Patent Applic
Fujita Yasutoshi
Kaku Tomohiro
Orii Kazuya
Saito Isao
Sasaki Masahiro
Drinker Biddle & Reath LLP
Marcheschi Michael
Tokyo Magnetic Printing Co. Ltd.
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