Disk apparatus and filter for disk apparatus

A magnetic disk apparatus includes a casing having a substantially hermetic structure, which houses a magnetic disk, a motor, and a magnetic head. A filter is arranged within the casing. The filter includes an oxidizing agent containing oxidized metal components and serving to oxidize gaseous components, and a trapping agent subjected to the treatment with an alkali, for trapping the acidic gas oxidized by the oxidizing agent.

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention, in which a magnetic disk apparatus of the present invention is applied to an HDD, will now be described in detail with reference to the accompanying drawings. As shown in FIG. 1 , an HDD comprises a casing 11 of a substantially hermetic structure, which includes a case body 10 and a top cover 14 . The case body 10 is formed in the shape of a rectangular box having an upper opening, and the top cover 14 is screwed to the case body 10 with a plurality of screws 12 so as to close the upper opening of the case body 10 . Housed in the case body 10 are two magnetic disks 16 each acting as a magnetic recording medium, a spindle motor 18 for supporting and rotating these magnetic disks 16 , a plurality of magnetic heads 20 for performing read/write of information in and out of the magnetic disks 16 , a carriage assembly 22 supporting these magnetic heads 20 , a voice coil motor 24 (hereinafter referred to as VCM) for rotating and determining the position of the carriage assembly 22 , a substrate unit 26 having a pre-amplifier, etc. Also, a printed circuit board (not shown) for controlling the operations of the spindle motor 18 , the VCM 24 and the magnetic head 20 is screwed to the outer surface of the bottom wall of the case body 10 . The carriage assembly 22 includes a substantially cylindrical bearing assembly 28 fixed to the bottom wall of the case body 10 and four sets of head suspension assemblies rotatably supported by the bearing assembly 28 . Each of these head suspension assemblies includes an arm 30 extending from the bearing assembly 28 toward the magnetic head 16 , and a elongate suspension 32 fixed to the extended end of the arm 30 . Also, the magnetic head 20 is mounted on the distal end portion of the suspension 32 with a slider (not shown) interposed therebetween. The four sets of the head suspension assemblies are arranged such that two magnetic heads 20 are allowed to face each other with the magnetic disk 16 interposed therebetween. It follows that, if the carriage assembly 22 is swung about the bearing assembly 28 , each magnetic head 20 is moved to a desired track of the corresponding magnetic disk 16 . The VCM 24 includes a pair of yokes 34 fixed to the bottom wall of the case body 10 , a permanent magnet (not shown) fixed to the inner surface of one of the paired yokes 34 , and a voice coil (not shown) fixed to the carriage assembly and movable between one of yokes 34 and the permanent magnet. If an electric power is supplied to the voice coil, a magnetic field is generated, with the result that the carriage assembly 22 is swung by the mutual action between the magnetic field generated from the voice coil and the magnetic field generated from the permanent magnet. On the other hand, as shown in FIGS. 1 and 2 , a chemical filter 50 for trapping the gaseous component generated inside and outside the casing, e.g., a hydrogen sulfide gas, is arranged on the bottom wall 12 a of the case body 12 within the casing 11 . The chemical filter 50 is positioned close to the substrate unit 26 . As shown in FIG. 2 , the chemical filter 50 includes a hollow rectangular container 52 formed of, for example, a synthetic resin. The opening on the side of one end of the container 52 forms a first air passage port 54 a , and the opening on the side of the other end of the container 53 forms a second air passage port 54 b . These first and second air communication ports 54 a , 54 b are closed, respectively, by first and second filters 56 a , 56 b each formed of a resin material such as polypropylene or polycarbonate. These first and second filters 56 a , 56 b perform the function of permeable lids and also perform the function of collecting dust. Housed in the container 52 are a first oxidizing section 58 a , a trapping section 60 , and a second oxidizing section 58 b , which are arranged to form a three layer structure. The first oxidizing section 58 a includes an oxidizing agent for oxidizing the gaseous component and is disposed on the first filter 56 a in a manner to close the first air passage port 54 a . The second oxidizing section 58 b includes an oxidizing agent for oxidizing the gaseous component and is disposed on the second filter 56 b in a manner to close the second air passage port 54 b . Also, the trapping section 60 includes a trapping agent for trapping an oxide gas and is sandwiched between the first and second oxidizing sections 58 a and 58 b. Each of the first and second oxidizing sections 58 a , 58 b is formed of 5 mg of, for example, a powdery cobalt oxide (Co 2 O 3 ) used as an oxidizing agent. The oxidizing agent formed of a IVA to IIB group metal promotes the oxidizing reaction of hydrogen sulfide. However, in view of the catalytic function, it is desirable for the oxidizing agent to be formed of any one of the VIIA to VIIIA group metals (Ma, Te, Re, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt) or to be formed of a desired combination of these metals. The trapping section 60 is formed of 15 mg of an activated charcoal treated with an alkali. It is also possible to use as the trapping agent alumina particles, fibrous materials, etc., which are treated with an alkali. On the other hand, an air communication hole 62 for allowing the inner space of the casing 11 to communicate with the outer atmosphere is formed in the bottom wall 12 a of the case body 12 . The chemical filter 50 is fixed on the bottom wall 12 a in a manner to close the air communication hole 62 . In the embodiment shown in the drawing, the chemical filter 50 is arranged such that the air communication hole 62 is surrounded by the container 52 under the state that the first filter 56 a is in contact with the inner surface of the bottom wall 12 a . As a result, the first air passage port 54 a of the chemical filter 50 communicates with the air communication hole 62 through the first filter 56 a , and the second air passage port 54 b communicates with the inner space of the casing 11 through the second filter 56 b . It follows that the air circulated inside and outside the casing 11 through the air communication hole 62 is allowed to pass through the chemical filter 50 . For example, the outer air entering the casing 11 through the air communication hole 62 passes through the first filter 56 a , the first oxidizing section 58 a , the trapping section 60 and the second oxidizing section 58 b so as to flow into the casing 11 through the second filter 56 b . When the outer air passes through the first oxidizing section 58 a , the gaseous component contained in the outer air, e.g., a hydrogen sulfide gas, is oxidized by the oxidizing agent so as to form sulfur dioxide or sulfate ions. When the outer air passes through the trapping section 60 , the sulfur dioxide and sulfate ions thus formed are trapped by the trapping section 60 by the neutralizing (ionic) reaction with the trapping agent subjected to the treatment with an alkali. It follows that the outer air, from which the hydrogen sulfide gas has been removed, flows into the casing 11 through the second oxidizing section 58 b and the second filter 56 b. On the other hand, the air flowing from within the casing 11 into the outside through the air communication hole 62 passes through the second filter 56 b , the second oxidizing section 58 b , the trapping section 60 and the first oxidizing section 58 a so as to flow to the outside of the casing 11 through the air communication hole 62 . When the air passes through the second oxidizing section 58 b , the hydrogen sulfide gas contained in the air is oxidized by the oxidizing agent so as to form sulfur dioxide and sulfate ions. When the air passes through the trapping section 60 , the sulfur dioxide and sulfate ions thus formed are trapped by the trapping section 60 by the neutralizing (ionic) reaction with the trapping agent subjected to the treatment with an alkali. It follows that the air within the casing 11 , from which the hydrogen sulfide gas has been removed, is discharged to the outside of the casing 11 through the first oxidizing section 58 a , the first filter 56 a , and the air communication hole 62 . It is desirable for the first and second oxidizing sections 58 a , 58 b to be arranged in the site where these oxidizing sections 58 a , 58 b are sufficiently brought into contact with the air. It should be noted that the oxidizing agent forming the first and second oxidizing sections 58 a , 58 b is reduced by oxidizing the hydrogen sulfide gas or the like. However, the oxidizing agent is oxidized again by the contact with the air. It follows that the oxidizing power of the oxidizing agent is restored so as to make it possible to use the oxidizing agent substantially permanently. The HDD of the construction described previously was arranged within an exposing apparatus in which the HDD was exposed to the air containing 1 ppm of a hydrogen sulfide gas, and the HDD was operated for every 30 minutes. Under this condition, an air respiration test was conducted 100 times between the inner space of the casing 11 and the outside of the casing 11 through the air communication hole 62 . Then, the HDD was taken out of the exposing apparatus. Further, the chemical filter 50 was taken out of the HDD so as to analyze the sulfur components trapped by the trapping section 60 by using a CS analyzer manufactured by LECO Inc. It has been found that 62 ng of the sulfur components were trapped relative to the theoretical value of 70 ng of the sulfur components. It follows that the chemical filter 50 is capable of trapping not less than about 88% of the oxides of hydrogen sulfide, i.e., sulfur dioxide and sulfate ions. According to the HDD constructed as described above, there is provided the chemical filter 50 . The gaseous component generated inside and outside the casing 11 , e.g., a hydrogen sulfide gas, is oxidized by the first or second oxidizing section 58 a or 58 b , and the formed oxide is trapped by the trapping section 60 by the neutralizing (ionic) reaction with the trapping section 60 arranged in the chemical filter 50 . As a result, the gaseous component adversely affecting the parts within the casing 11 can be removed efficiently so as to make it possible to obtain an HDD with an improved reliability. It should also be noted that the oxidizing sections and the trapping section are arranged to form a laminate structure within the chemical filter 50 , with the result that the air flowing into the chemical filter 50 flows through the oxidizing section into the trapping section. It follows that the gaseous component within the air can be oxidized without fail by the oxidizing agent, and the resultant oxide can be trapped without fail by the trapping agent. The chemical filter 50 of the HDD according to a second embodiment of the present invention will now be described. As shown in FIG. 3 , according to the second embodiment of the present invention, the container 52 of the chemical filter 50 comprises a first partition 64 a between the first oxidizing section 58 a and the trapping section 60 , and a second partition 64 b between the second oxidizing section 58 b and the trapping section 60 . The container 52 also comprises a bottom wall 66 arranged in place of the first filter. The outer surface of the bottom wall 66 is in contact with the bottom wall 12 a of the casing 11 . The first air passage port 54 a is formed in one end portion of the bottom wall 66 of the container 52 so as to communicate with the air communication hole 62 formed in the bottom wall 12 a of the casing 11 . Also, a first air communication port 68 a that permits the first oxidizing section 58 a to communicate with the trapping section 60 is formed in the first partition section 64 a . The first air communication port 68 a is formed in an end portion of the first partition 64 a remote from the first air passage port 54 a . Further, a second air communication port 68 b that permits the second oxidizing section 58 b to communicate with the trapping section 60 is formed in the second partition 64 b . The second air communication port 68 b is formed in the second partition 64 and is positioned remote from the first air communication port 68 a. The second embodiment is equal to the first embodiment in the other parts and, thus, the same portions of the chemical filter 50 are denoted by the same references numerals so as to avoid an overlapping description. According to the second embodiment of the present invention constructed as described above, the outer air flowing into the casing 11 through the air communication hole 62 flows into the first oxidizing section 58 a through the first air passage port 54 a and, then, into the trapping section 60 through the first air communication port 68 a . The outer air flowing into the trapping section 60 further flows into the second oxidizing section 58 b through the second air communication port 68 b and, then, into the casing 11 through the second filter 56 b. When the outer air passes through the first oxidizing section 58 a , the gaseous component contained in the outer air, e.g., a hydrogen sulfide gas, is oxidized by the oxidizing agent into sulfur dioxide and sulfate ions. When the outer air passes through the trapping section 60 , the sulfur dioxide and sulfate ions formed in the first oxidizing section 58 a are trapped by the trapping section 60 by the neutralizing reaction with the trapping agent subjected to the treatment with an alkali. It follows that the outer air, from which the hydrogen sulfide gas has been removed, flows into the casing 11 through the second oxidizing section 58 b and the second filter 56 b. On the other hand, the air flowing from within the casing 11 to the outside through the air communication hole 62 flows into the second oxidizing section 58 b through the second filter 56 b and, then, into the trapping section 60 through the second air communication port 68 b . The air flowing through the trapping section 60 further flows into the first oxidizing section 58 a through the first air communication port 68 a and, then, to the outside of the casing 11 through the first air passage port 54 a and the air communication hole 62 . When the air passes through the second oxidizing section 58 b , the hydrogen sulfide gas contained in the gas is oxidized by the oxidizing agent so as to form sulfur dioxide and sulfate ions. When the air further passes through the trapping section 60 , the sulfur dioxide and sulfate ions formed in the second oxidizing section 58 b are trapped by the trapping section 60 by the neutralizing reaction with the trapping agent. It follows that the air within the casing 11 , from which the hydrogen sulfide gas has been removed, is discharged to the outside of the casing 11 through the first oxidizing section 58 a , the first air passage port 54 a and the air communication hole 62 . As described above, the second embodiment produces the function and effect similar to that produced by the first embodiment described previously. Further, according to the second embodiment of the present invention, the first oxidizing section 58 a and the trapping section 60 are separated from each other by the first partition 64 . Likewise, the second oxidizing section 58 b and the trapping section 60 are separated from each other by the second partition 64 b . What should also be noted is that the first air communication port 68 a formed in the first partition section 64 a is positioned remote from the air communication hole 62 . Similarly, the second air communication port 68 b formed in the second partition section 64 b is positioned remote from the first air communication port 68 a . It follows that the outer air flowing into the first oxidizing section 58 a through the communication port 62 flows over a long distance within the first oxidizing section 58 a . Also, the outer air flowing into the trapping section 60 flows over a long distance within the trapping section 60 and, then, flows into the second oxidizing section 58 a . It follows that the gaseous component contained in the outer air flowing into the chemical filter 50 can be oxidized without fail in the first oxidizing section 58 a , and the formed oxide can be trapped without fail by the trapping section 60 . In the second embodiment of the present invention, it is possible for the container 52 to comprise a ceiling wall formed integral with the container 52 in place of the second filter 56 b and for the second air communication port to be formed in the ceiling wall. In this case, it is desirable for the second air communication port to be formed in the end portion remote from the second air communication port 68 b as in the second embodiment so as to allow the gaseous component contained in the air flowing from within the casing 11 into the chemical filter 50 to be oxidized and trapped without fail. In the chemical filter according to each of the embodiments described above, the oxidizing agent and the trapping agent are housed in the container 52 to form separate layers. Alternatively, it is also possible to house the oxidizing agent and the trapping agent in the container 52 in a manner to form a mixed layer, as shown in FIGS. 4 and 5 . To be more specific, in the chemical filter 50 for the HDD according to a third embodiment of the present invention, the first and second air passage ports 54 a , 54 b are closed by the first and second filters 56 a , 56 b , respectively. Also, the chemical filter 50 is fixed on the bottom wall 12 a in a manner to close the air communication hole 62 of the casing 11 . In this case, the chemical filter 50 is arranged such that the air communication hole 62 is surrounded by the container 52 under the state that the first filter 56 a is in contact with the inner surface of the bottom wall 12 a. Within the container 52 , the oxidizing agent for oxidizing the gaseous component and the trapping agent for trapping the oxidized gas are housed in a mixed state in the clearance between the first and second filters 56 a and 56 b . It is possible to use the oxidizing agent and the trapping agent equal to those described previously in conjunction with the first embodiment. As shown in FIG. 5 , the oxidizing agent 70 and the trapping agent 72 are mixed such that the oxidizing agent particles 70 are dispersed to surround each of the trapping agent particles 72 . Where, for example, a powdery cobalt oxide is used as the oxidizing agent, the cobalt oxide powder has a particle diameter of about 1 nm to 500 nm. Also, where an activated charcoal subjected to the treatment with an alkali is used as the trapping agent, the particle diameter of the trapping agent is about 0.5 &mgr;m to 1.0 &mgr;m. Further, the mixing ratio of the oxidizing agent to the trapping agent is set at about 100:1. The third embodiment is equal to the other embodiments in the other parts and, thus, the same portions of the chemical filter 50 are denoted by the same reference numerals so as to avoid an overlapping description. It is also possible for the third embodiment of the construction described above to oxidize the gaseous component contained in the air flowing within the chemical filter 50 by the oxidizing agent and, then, to trap and remove the formed oxide by the trapping agent. The present invention is not limited to the embodiments described above and can be modified in various fashions within the technical scope of the present invention. For example, the arranging position of the chemical filter 50 can be selected optionally within the casing 11 . In the example shown in FIG. 6 , the chemical filter 50 is arranged in the vicinity of the magnetic disk 16 and in a corner portion of the casing 11 . In this case, it is possible to form the air communication hole 62 communicating with the chemical filter 50 in any of the side wall, the bottom wall and the cover of the casing 11 . Further, the present invention may be applied to another disk apparatus such as an optical disk apparatus. Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the present invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.