1. Field of the Invention
The present invention relates in general to an abrasive film, and more particularly to such an abrasive film which is advantageously used to polish a magnetic disk, an end face of an optical fiber or other object or workpiece with high precision.
2. Discussion of the Related Art
There is known an abrasive film which is used to polish a magnetic disk, an end face of an optical fiber or other object or workpiece, with application of a polishing fluid to the abrasive film and/or the workpiece. Such an abrasive film includes (a) a substrate, (b) a binder and (c) a multiplicity of abrasive grains which are fixed to a surface of the substrate by the binder, and is commonly formed to take a roll, sheet or disk shape. In a polishing operation with the abrasive film, the abrasive film and the workpiece are moved relative to each other while being forced to each other, with the application of the polishing fluid, so that the workpiece is polished by the abrasive film. As one example of such an abrasive film, JP-A-2000-354944 (publication of unexamined Japanese Patent Application laid open in 2000) discloses an abrasive film which is used to polish end faces of an optical fiber and a ferrule that is a component of a connector connecting the optical fiber with another optical fiber. In general, the size of the abrasive grains of the abrasive film is reduced with an increase in a required degree of surface smoothness of the workpiece to be polished. For polishing the end face of the ferrule which is commonly required to have a so-called xe2x80x9cmirror-finished surfacexe2x80x9d, for example, fine grains having an average size of not larger than 10 xcexcm are used as the abrasive grains of the abrasive films.
However, the applied polishing fluid is more likely to be repelled by a polishing surface of the abrasive film, as a degree of surface smoothness of the polishing surface is increased as a result of the reduction in the size of the abrasive grains. This means that the applied polishing fluid is less likely to be held between the polishing surface of the abrasive film and a surface of the workpiece that is to be polished during the polishing operation, whereby a frictional heat generating between the abrasive film and the workpiece is undesirably increased, thereby causing the resin binder to be fused and stuck onto the surface of the workpiece, causing the polishing surface to be glazed and/or causing the surface of the workpiece to be burnt. The sticking of the fused binder on the surface of the workpiece inevitably reduces the polishing performance, leading to a problematic reduction in a reliability of the polished workpiece as a product. For example, if the end face of the ferrule is polished in such a condition of the reduced polishing performance, there will be caused a considerable loss in an optical transmission between the optical fibers through the connector which is provided by the polished ferrule.
It might be possible to form pits and projections in the polishing surface of the abrasive film, for example, by roughening a surface of the substrate of the abrasive film, in the interest of facilitating the polishing fluid to be held between the abrasive film and the workpiece during the polishing operation. However, the roughened surface of the substrate is smoothed as the abrasive film is repeatedly used for the polishing operation. The polishing fluid can not be sufficiently held between the abrasive film and the workpiece, once the surface of the substrate of the abrasive film is smoothed. That is, the formation of the pits and projections in the polishing surface of the abrasive film does not provide a fundamental solution to the above-described problem.
It is therefore a first object of the present invention to provide an abrasive film which includes fine abrasive grains and which is capable of reliably exhibiting an excellent polishing performance without causing a binder to be fused to be stuck onto a polished surface of a workpiece and without causing the polished surface of the workpiece to be burnt, owing to provision for facilitating a polishing fluid to be held between the abrasive film and the polished workpiece in spite of the fineness of the abrasive grains. It is a second object to the invention to provide a polishing method by using the abrasive film having the above technical advantage. The first object may be achieved according to any one of first through tenth aspects of the invention which are described below. The second object may be achieved according to any one of eleventh through fourteenth aspects of the invention which are also described below.
The first aspect of this invention provides an abrasive film for grinding or polishing an object or workpiece, comprising: (a) a substrate; (b) a binder; (c) a multiplicity of abrasive grains which are fixed to a surface of the substrate by the binder; and (d) a water-soluble inorganic compound which is added to the binder.
According to the second aspect of the invention, in the abrasive film defined in the first aspect of the invention, the abrasive grains have an average size of not smaller than 0.01 xcexcm and not larger than 10 xcexcm.
According to the third aspect of the invention, in the abrasive film defined in the first or second aspect of the invention, the water-soluble inorganic compound is added in an amount of 1-15 parts by weight per 100 parts by weight of the binder.
According to the fourth aspect of the invention, in the abrasive film defined in any one of the first through third aspects of the invention, the water-soluble inorganic compound consists of a weak-alkali metal salt which is formed of a combination of an alkali metal and a weak acid.
According to the fifth aspect of the invention, in the abrasive film defined in any one of the first through third aspects of the invention, the water-soluble inorganic compound consists of a weak-acid metal salt which is formed of a combination of a metal and a strong acid.
The sixth aspect of the invention provides an abrasive film for grinding or polishing an object or workpiece, comprising: (a) a substrate; (b) a binder; (c) a multiplicity of abrasive grains which are fixed to a surface of the substrate by the binder; and (d) a water-soluble organic acid alkali metal salt which is added to the binder; wherein the water-soluble organic acid alkali metal salt is a solid at an ordinary temperature.
According to the seventh aspect of the invention, in the abrasive film defined in the sixth aspect of the invention, the abrasive grains have an average size of not smaller than 0.05 xcexcm and not larger than 10 xcexcm.
According to the eighth aspect of the invention, in the abrasive film defined in the sixth or seventh aspect of the invention, the water-soluble organic acid alkali metal salt is added in an amount of 1-10 parts by weight per 100 parts by weight of the binder.
According to the ninth aspect of the invention, in the abrasive film defined in any one of the sixth through eighth aspects of the invention, the water-soluble organic acid alkali metal salt consists of an anionic surface-active agent.
According to the tenth aspect of the invention, in the abrasive film defined in any one of the sixth through eighth aspects of the invention, the water-soluble organic acid alkali metal salt consists of a carboxylic acid alkali metal salt.
The eleventh aspect of this invention provides a method of grinding or polishing an object or workpiece, by using the abrasive film defined in any one of the first through fifth aspects of the invention. The method comprises steps of moving the workpiece and the abrasive film relative to each other, while forcing the workpiece and the abrasive film against each other; and applying a polishing fluid or liquid including a water, to at least one of the workpiece and the abrasive film.
According to the twelfth aspect of the invention, in the method defined in the eleventh aspect of the invention, the abrasive grains have an average size of not smaller than 0.05 xcexcm and not larger than 10 xcexcm.
The thirteenth aspect of this invention provides a method of grinding or polishing an object or workpiece, by using the abrasive film defined in any one of the sixth through tenth aspects of the invention. The method comprises steps of moving the workpiece and the abrasive film relative to each other, while forcing the workpiece and the abrasive film against each other; and applying a polishing fluid or liquid including a water, to at least one of the workpiece and the abrasive film.
According to the fourteenth aspect of the invention, in the method defined in the thirteenth aspect of the invention, the abrasive grains have an average size of not smaller than 0.05 xcexcm and not larger than 10 xcexcm.
In a wet polishing operation with the abrasive film defined in the first aspect of the invention, the water-soluble inorganic compound contained in the binder is dissolved into a water component of the polishing fluid, so that a degree of wettability of a polishing surface of the abrasive film with respect to the polishing fluid is increased whereby a sufficient amount of the polishing fluid is held between the abrasive film and the workpiece. The presence of the sufficient amount of the polishing fluid between the abrasive film and the workpiece makes it possible to minimize a temperature rise due to a frictional heat and to accordingly prevent fusion of the binder, glazing of the polishing surface and burning of the polished surface of the workpiece, thereby advantageously assuring an excellent polishing performance with a high stability.
As described above in the BACKGROUND OF THE INVENTION, the applied polishing fluid is less likely to be held between the abrasive film and the workpiece, particularly, where the average size of the abrasive grains is so small as in the abrasive film defined in the second aspect of the invention. However, also in a wet polishing operation with the abrasive film defined in the second aspect of the invention, a sufficient amount of the polishing fluid is held between the abrasive film and the workpiece, owing to the water-soluble inorganic compound contained in the binder, whereby the fusion of the binder, the glazing of the polishing surface and the burning of the polished surface of the workpiece are prevented.
In the abrasive film defined in the third aspect of the invention in which the water-soluble inorganic compound is added in the amount of 1-15 parts by weight per 100 parts by weight of the binder, a sufficient amount of the polishing fluid is held between the abrasive film and the workpiece, and the fusion of the binder is accordingly prevented, without deteriorating the function of the binder, i.e., the function of holding the abrasive grains.
In the abrasive film defined in the fourth aspect of the invention, the water-soluble inorganic compound consists of the weak-alkali metal salt which is formed of the combination of an alkali metal and a weak acid. In the abrasive film defined in the fifth aspect of the invention, the water-soluble inorganic compound consists of the weak-acid metal salt which is formed of the combination of a metal and a strong acid. In either of the abrasive films defined in the respective fourth and fifth aspects-of the invention, the water-soluble inorganic compound contained in the binder is dissolved into the water component of the polishing fluid, so that the degree of wettability of the polishing surface of the abrasive film with respect to the polishing fluid is increased whereby a sufficient amount of the polishing fluid is held between the abrasive film and the workpiece.
The principle of the invention is advantageously applied to, particularly, an abrasive film which includes abrasive grains whose average size is not larger than 10 xcexcm, or not larger than 5 xcexcm, or not larger than 3 xcexcm, and which is used for polishing a magnetic disk or an end face of an optical fiber ferrule in a wet polishing operation with high precision. The ferrule consists of a tubular cylindrical sleeve which is formed of, for example, zirconium oxide or ceramics and which accommodates an optical fiber fixed in a hole of the sleeve. The ferrule is mirror-finished by the abrasive film such that a distal end face of the ferrule is provided by a smoothed, brightened, semi-spherical face. The polishing fluid may consist only of a water, or alternatively, may include a liquid component other than the water and also a solid component such as abrasive particles. It should be noted that the invention may be applied also to an abrasive film which includes abrasive grains whose average size is larger than 10 xcexcm, and to an abrasive film which is used for polishing workpieces other than the magnetic disk and the optical fiber ferrule.
The abrasive grains of the abrasive film are preferably provided by diamond abrasive grains, but may be provided by also silicon carbide abrasive grains, alumina abrasive grains or other known abrasive grains. The binder of the abrasive film is preferably provided by a resin binder which is formed of modified vinyl chloride resin or other resin having a high degree of water resistance. An abrasive structure or layer in which the abrasive grains are held together by the binder has a thickness which may be determined depending upon, for example, the size of the abrasive grains.
The substrate of the abrasive film is preferably provided by a thin plate, sheet or film which is formed of polyethylene terephthalate or other resin material which has a predetermined degree of mechanical strength and high degrees of water resistance and oil resistance.
If the amount in which the inorganic compound is added to the binder is smaller than 1 part by weight per 100 parts by weight of the binder, the polishing fluid would not be held necessarily in a sufficient amount between the abrasive film and the workpiece that is to be polished. If the amount in which the inorganic compound is added to the binder is larger than 15 parts by weight per 100 parts by weight of the binder, on the other hand, the function of the binder might be reduced due to possible reduction in holding strength with which the binder holds the abrasive grains, or due to possible deterioration of the binder as a result of deliquescence of the inorganic compound. Therefore, the amount in which the inorganic compound is added to the binder is preferably 1-15 parts, more preferably 3-10 parts by weight per 100 parts by weight of the binder, and is suitably determined depending upon the kind of added inorganic compound and the material of the binder such that the amount is held within the preferable range or more preferable range. However, it should be noted that the amount of the inorganic compound does not have to be necessarily held within the preferable range or more preferable range. That is, there are cases where it is possible to achieve the above-described object of the invention even if the amount of the inorganic compound is not held within the preferable range. It is also noted that other additives such as pigment, dispersing agent and antistatic agent may be also added as needed to the binder.
The inorganic compound may be a substance which takes the form of particles dispersed substantially evenly over the entirety of the binder, or alternatively may be a substance which is dissolved in the binder. In either of these cases, the content of the added inorganic compound can be measured or confirmed by a metal-ion analyzing device or other measuring device. Where the inorganic compound takes the form of particles in the binder, it is preferable that the size of each particle of the inorganic compound is smaller than the size of each of the abrasive grains, so that pits or recesses are not formed in the polishing surface of the abrasive film even when the inorganic compound is dissolved in the binder. This is because the formation of the pits or recess in the polishing surface of the abrasive film would lead to deterioration in the polishing performance of the abrasive film.
The inorganic compound preferably consists of the weak-alkali metal salt which is formed of a combination of an alkali metal and a weak acid, as in the abrasive film of the fourth aspect of the invention. The alkali metal may be, for example, sodium or potassium. The weak acid may be, for example, phosphoric acid, boric acid, carbonic acid or silicic acid. The weak-alkali metal salt may be, for example, potassium tertiary phosphate, sodium borate or sodium silicate, each of which can be formed of the corresponding combination of the alkali metal and the weak acid.
Alternatively, the inorganic compound preferably consists of the weak-acid metal salt which is formed of a combination of a metal and a strong acid, as in the abrasive film of the fifth aspect of the invention. The metal may be aluminum, copper, silver, nickel, cobalt, iron, silicon, zinc or other stable metallic element. The strong acid may be, for example, hydrochloric acid, sulfuric acid or nitric acid. The weak-acid metallic may be, for example, an inorganic iron compound such as ferrous chloride, ferric chloride, ferric nitrate, ferrous sulfate and ferric sulfate, or alternatively, copper sulfate or copper nitrate, each of which can be formed of the corresponding combination of the metal and the strong acid.
In a wet polishing operation with the abrasive film defined in the sixth aspect of the invention, the water-soluble organic acid alkali metal salt contained in the binder is dissolved into a water component of the polishing fluid, so that a degree of wettability of a polishing surface of the abrasive film with respect to the polishing fluid is increased whereby a sufficient amount of the polishing fluid is held between the abrasive film and the workpiece. The presence of the sufficient amount of the polishing fluid between the abrasive film and the workpiece makes it possible to minimize a temperature rise due to a frictional heat and to accordingly prevent fusion of the binder, glazing of the polishing surface and burning of the polished surface of the workpiece, thereby advantageously assuring an excellent polishing performance with a high stability. Further, the abrasive film defined in the sixth aspect of the invention can be easily formed since the water-soluble organic acid alkali metal salt is a solid at an ordinary temperature. That is, it is possible to brake or crush the organic acid alkali metal salt into small particles, so as to directly add the organic acid alkali metal salt to the binder. If the additives take the form of a liquid rather than a solid, the additives would have to be added to the binder via a medium which is impregnated with the additives.
As described above in the BACKGROUND OF THE INVENTION, the applied polishing fluid is less likely to be held between the abrasive film and the workpiece, particularly, where the average size of the abrasive grains is so small as in the abrasive film defined in the seventh aspect of the invention. However, also in a wet polishing operation with the abrasive film defined in the seventh aspect of the invention, a sufficient amount of the polishing fluid is held between the abrasive film and the workpiece, owing to the water-soluble organic acid alkali metal salt contained in the binder, whereby the fusion of the binder, the glazing of the polishing surface and the burning of the polished surface of the workpiece are prevented.
In the abrasive film defined in the eighth aspect of the invention in which the water-soluble organic acid alkali metal salt is added in the amount of 1-10 parts, preferably 3-5 parts by weight per 100 parts by weight of the binder, a sufficient amount of the polishing fluid is held between the abrasive film and the workpiece, so that the fusion of the binder is accordingly prevented, without deteriorating the function of the binder, i.e., the function of holding the abrasive grains.
The organic acid alkali metal salt preferably consists of an anionic surface-active agent, as in the abrasive film of the ninth aspect of the invention. The anionic surface-active agent may be, for example, fatty acid sodium, alpha olefin sulfonic acid sodium, lauryl sodium sulfate, or sodium stearate. The anionic surface-active agent is easily mixable into the resin binder and is not likely to be separated from the binder once the anionic surface-active agent is mixed into the binder. Further, the anionic surface-active agent has a high stability even at a high temperature, so that the anionic surface-active agent is not likely to chemically react with the binder even where the anionic surface-active agent is heated. Accordingly, in a wet polishing operation with the abrasive film of the ninth aspect of the invention, the anionic surface-active agent contained in the binder is dissolved into a water component of the polishing fluid, so that a degree of wettability of the polishing surface of the abrasive film with respect to the polishing fluid is increased whereby a sufficient amount of the polishing fluid is held between the abrasive film and the workpiece. The presence of the sufficient amount of the polishing fluid between the abrasive film and the workpiece makes it possible to prevent fusion of the binder, glazing of the polishing surface and burning of the polished surface of the workpiece.
Alternatively, the organic acid alkali metal salt preferably consists of a carboxylic acid alkali metal salt, as in the abrasive film of the tenth aspect of the invention. The carboxylic acid alkali metal salt may be, for example, sodium oxalate, sodium acetate, sodium succinate, sodium citrate, polyacrylic acid sodium, sodium benzoate, potassium oxalate, potassium acetate, potassium succinate, potassium citrate, polyacrylic acid potassium, or potassium benzoate. The carboxylic acid alkali metal salt is easily mixable into the resin binder and is not likely to be separated from the binder once the carboxylic acid alkali metal salt is mixed into the binder. Further, the carboxylic acid alkali metal salt has a high stability even at a high temperature, so that the carboxylic acid alkali metal salt is not likely to chemically react with the binder even where the carboxylic acid alkali metal salt is heated. Accordingly, in a wet polishing operation with the abrasive film of the tenth aspect of the invention, the carboxylic acid alkali metal salt contained in the binder is dissolved into a water component of the polishing fluid, so that a degree of wettability of the polishing surface of the abrasive film with respect to the polishing fluid is increased whereby a sufficient amount of the polishing fluid is held between the abrasive film and the workpiece. The presence of the sufficient amount of the polishing fluid between the abrasive film and the workpiece makes it possible to prevent fusion of the binder, glazing of the polishing surface and burning of the polished surface of the workpiece.