Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
1998-04-23
2001-06-05
Hendrickson, Stuart (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
Reexamination Certificate
active
06241956
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a glassy carbon and a process for producing it.
BACKGROUND ART
Glassy carbon has properties of carbon material, such as heat resistance, corrosion resistance and electrical conductivity; toughness, non-permeability to gases and very low dust-generating property, derived from the dense amorphous structure characteristic of glassy carbon; and a low specific gravity as compared with metal materials. Therefore, glassy carbon is in use, for example, as a substrate for magnetic recording medium or as a member of apparatus for semiconductor fabrication used in electronics industry.
As the substrate for magnetic recording medium, a substrate having less defects and higher accuracy has come to be required as the magnetic density of magnetic recording medium has become increasingly higher. With respect to the member of apparatus for semiconductor fabrication, generation of fine dust therefrom (which has not been a problem heretofore) has come to be taken up as a problem as the semiconductor integrated circuit has come to possess a higher density in recent years, that is, the linewidth has become finer; with respect to, in particular, the electrode plate used in plasma etching of semiconductor, an electrode plate has become necessary which generates dust in a smaller amount and in a finer size during etching.
Conventional glassy carbon used as a substrate for magnetic recording medium or as a member of apparatus for semiconductor fabrication, although having a dense amorphous structure and a very low dust-generating property, microscopically has, on the surface or inside, fine pores or low-density non-homogeneous portions (defects); as a result, a gas tends to remain inside the glassy carbon and, when a magnetic recording layer is formed on the glassy carbon, the above surface defects or the gas remaining inside has made the magnetic recording layer nonuniform locally. Also, when such glassy carbon is used as an electrode plate for plasma etching, the surface or inside defects have caused structural destruction owing to the abnormal discharging during etching and have become a source of fine dust generation.
The present invention has been completed with an aim of providing a glassy carbon which has no defects on the surface or inside and consequently contains no gas inside and which, when used particularly as a substrate for magnetic recording medium or as an electrode plate for plasma etching, does not make the magnetic recording layer non-uniform or does not substantially generate any fine dust; and a process for producing such a glassy carbon.
DISCLOSURE OF THE INVENTION
The glassy carbon employed in the present invention in order to achieve the above aim, is obtained by heat-curing a phenolic resin and firing the cured-phenolic resin in a non-oxidizing atmosphere, wherein the phenolic resin has a number-average molecular weight of 300-500 and is used in the form of a hydrophilic organic solvent solution containing 40-80% by weight of the phenolic resin. Also, the process for producing a glassy carbon, employed in the present invention in order to achieve the above aim, comprises heat-curing a phenolic resin and firing the cured-phenolic resin in a non-oxidizing atmosphere, wherein the phenolic resin has a number-average molecular weight of 300-500 and is used in the form of a hydrophilic organic solvent solution containing 40-80% by weight of the phenolic resin.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is hereinafter described in detail.
As mentioned above, the glassy carbon of the present invention is obtained by heat-curing a phenolic resin and firing the cured-phenolic resin in a non-oxidizing atmosphere. As the phenolic resin used in the present invention, there can be used a phenolic resin soluble in a hydrophilic organic solvent. Specific examples thereof are a resol type phenolic resin and a novolac type phenolic resin. A resol type phenolic resin is preferred because of the high compatibility with a hydrophilic organic solvent, and a liquid resol type phenolic resin is most preferred.
The phenolic resin has a number-average molecular weight of preferably 300-500. When the number-average molecular weight is smaller than 300, the phenolic resin produces a large amount of water per unit weight during the curing, which tends to generate bubbles of water in the cured resin. When the number-average molecular weight is larger than 500, the phenolic resin gives a high viscosity when made into a phenolic resin solution as described later; the air taken into the phenolic resin solution when the solution is cast into a mold, is difficult to remove; as a result, the resulting glassy carbon tends to have defects.
The glassy carbon of the present invention is obtained from a solution of the phenolic resin. The solvent used in the phenolic resin solution is a hydrophilic organic solvent in order to uniformly disperse therein the water formed during the heat-curing of the phenolic resin.
The hydrophilic organic solvent can be exemplified by ethers such as tetrahydrofuran (THF), dioxane and the like; acid derivatives such as dimethylformamide (DMF), N,N-dimethylacetamide and the like; ketones such as acetone, methyl ethyl ketone and the like; nitriles such as acetonitrile, propionitrile and the like; alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, isobutyl alcohol, isopentyl alcohol, benzyl alcohol and the like; and phenols. Of these, preferred are those having a boiling point of 100° C. or less, because they are easily removed during the curing of the resin. Particularly preferred are lower alcohols having 1 to 5 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol and the like, because these solvents can give a resin solution of relatively low viscosity and yet high resin concentration. These hydrophilic organic solvents can be used in admixture of two or more kinds.
The resin concentration in the phenolic resin solution must be in the range of 40 to 80% by weight.
The phenolic resin solution has a viscosity at 25° C. of preferably 200-300 cp, more preferably 200-250 cp for easy handling during the curing of the phenolic resin and easy removal of the air bubbles taken into the solution. The phenolic resin solution can have a viscosity of the above range when produced by dissolving a phenolic resin having a number-average molecular weight of 300-500, in, for example, the above-mentioned alcohol at a concentration of 40-80% by weight.
However, for example, when the concentration of the phenolic resin is lower than 40% by weight, the amount of the solvent to be removed during the curing of the resin is large, making long the time for resin curing and inviting poor economy. When the resin concentration is higher than 80% by weight, the resulting phenolic resin solution has a viscosity of 300 cp or higher; the air incoming when the phenolic resin solution is cast into a mold, is not easily removed; as a result, the resulting glassy carbon tends to have defects.
The phenolic resin solution has a gelation time as measured at 150° C. by the hot plate method, of preferably 80-150 seconds, more preferably 100-130 seconds. When the gelation time is too short, the air incoming when the phenolic resin solution is cast into a mold, is not easily removed. When the gelation time is too long, the curing of the phenolic resin takes a long time, which is not economical.
It is not necessary to add a curing agent to the phenolic resin solution. Rather, addition of a curing agent or a curing accelerator is not preferred because the molecular structure of the cured resin tends to become nonuniform microscopically and the glassy carbon after firing has grain boundaries.
The glassy carbon of the present invention is produced from the above-mentioned phenolic resin solution as follows according to the production process of the present invention. First, the phenolic resin solution is as necessary filtered to remove the impurities contained there
Ishimatsu Takeshi
Saito Kazuo
Hendrickson Stuart
Kubovcik & Kubovcik
Nisshinbo Industries Inc.
LandOfFree
Glassy carbon and process for production thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Glassy carbon and process for production thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Glassy carbon and process for production thereof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2541346