BACKGROUND OF THE INVENTION
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1. Field of the invention [0001]
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The present invention relates to a container equipped with packing, that prevents the contamination of a product by moisture, dust, gas, ions and the like, from the surrounding environment, and, for example, to a container and packing that prevents the insertion of a negative pressure in a container used in an environment that produces a difference in air pressure inside and outside the container due to air transportation and the like. [0002]
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2. Description of the Related Art [0003]
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Conventionally, in a container that accommodates products which require protection from the contamination of moisture, dust, gas, ions and the like, from the surrounding environment, a constitution is used at the part where the container main body and the cover body make contact in which a groove is provided in either the container main body or the cover body and packing having rubber elasticity is attached in that gap to maintain airtightness. [0004]
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As an example, a conventional semiconductor wafer housing container (Japanese Patent Laid-Open No. H10-107135) is set forth in FIG. 1, in which a container [0005] main body 1 accommodates a cassette 2; the cassette 2 is provided with a multiplicity of accommodation grooves for accommodating one semiconductor waver w in each groove; and, to the cover body 3 that is joined to the upper surface part of the container main body 1, a pressing means 4 having elasticity, in order to press and hold the semiconductor wafers w from the side of the cover body 3 to the cassette 2 side, is attached; furthermore, in order to make the interior airtight and to maintain a clean state, packing 5 is inserted into the part where the container main body 1 and the cover body 3 are fitted together, here into a ring shaped groove part 1 a on the container main body 1.
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Higher the adhesion of the [0006] packing 5 of the above-mentioned constitution example is, with respect to the container main body 1 and the cover body 3, the area of the gap between the container main body 1 and the cover body 3 becomes smaller, and invasion into the container of moisture, dust, gas, ions and the like by the airborne diffusion can be prevented.
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When the state at the time the container of the above-mentioned constitution is transported by air is explained, as shown in FIG. 2, the container is placed in a low pressure environment in the upper air and a difference in the air pressure inside and outside the container is produced. Here, in the event packing with high adhesion is used, when the adhesive strength of the packing becomes unable to withstand the difference in air pressure inside and outside the container, airtightness breakdown occurs and air is released to the outside from the inside of the container. [0007]
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Due to this, the air pressure inside the container gradually lowers and the difference in the air pressure inside and outside the container becomes smaller, but at the time when the adhesive strength of the packing and the difference in the air pressure inside and outside the container have balanced, the release of air from inside the container stops. As a result, the air pressure inside the container becomes (outside air pressure +adhesive strength of the packing). [0008]
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When an airplane lands, the ambient air pressure now becomes higher than that inside the container and a difference in the air pressure inside and outside the container that is the opposite of the former is produced. At this time also, when the adhesive strength of the packing has become unable to withstand the difference in the air pressure inside and outside of the container, an airtightness breakdown occurs and air flows into the container from the surroundings. Then, at the time when the adhesive strength of the packing and the difference in the air pressure inside and outside of the container are in equilibrium, the flow of air into the container from the surroundings stops. Here the air pressure inside the container after air transportation becomes (one atmospheric pressure—the adhesive strength of the packing). [0009]
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In this way, a negative pressure state has been formed, inside the container, with respect to the outside air, and opening the cover of the container in such a state is extremely difficult, and, depending on the case, the cover must be pried open with a tool. In short, with a conventional packing, a cover becomes hard to open when used in an environment which produces fluctuations of the surrounding air pressure, like air transportation, to the extent that the adhesion strength of the packing is high. When the adhesive strength is restrained so as to make the cover easier to open, preventing the diffusion and invasion of moisture, dust, gas, ions and the like into the container becomes impossible in a normal environment. Consequently, it is very difficult to establish a proper balance. [0010]
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Accordingly, as disclosed in Japanese Patent Laid-open No. H9-139421 (in addition to Japanese Patent Laid-open No. H10-184915 and the like), there is a method of attaching a filter to a container and allowing the entry and exit of air that is not contaminated. However, there are cases in which it is impossible to attach a filter, for example because a container is too small to be provided with a filter that is effective enough to accommodate the speed of the air pressure fluctuations produced in the cargo compartment and the like of an airplane, or because there is no space to attach a filter. Furthermore, there is also the problem that the cost becomes high when a filter is attached. [0011]
SUMMARY OF THE INVENTION
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An object of the present invention is to provide, in a container having packing, a container and packing that prevent the containment of negative pressure inside a container used in an environment which produces a difference in the air pressure inside and outside a container due to air transportation and the like. [0012]
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The inventor, as a result of having completed various studies concerning containers, and particularly concerning packing comprising constitutions in which the containment of a negative pressure in a container does not occur, ascertained that by using packing with superior adhesive strength that is provided with minute uneven forms at one, or more places on the surface of the packing, airtightness is exhibited due to the superior adhesive strength in an environment in which there is no difference in the air pressure inside and outside a container, and at the time of the ambient air pressure fluctuation, for example during the above-mentioned air transportation and the like, the airtightness is slightly vitiated by the minute uneven form part to prevent the containment of a negative pressure in the container, furthermore, that the same kind of effect can be obtained, even if a minute uneven part is provided at one or more places on the surface of the container main body, or cover, which comes into contact with the packing, and perfected the present invention. [0013]
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That is, the present invention provides a container having a container constitution in which packing is interposed between the container main body and a cover so as to establish a seal therebetween, wherein a minute uneven part is provided at one or more places, on the surface of the container main body or of the cover with which the packing comes into contact. [0014]
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Furthermore, the present invention provides a packing for establishing a seal between a container main body and a cover, wherein a minute uneven part is provided at one or more places of the packing that come into contact with the container main body or the cover.[0015]
BRIEF DESCRIPTION OF THE DRAWINGS
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FIG. 1 is an analytic perspective view of a conventional product container with packing attached; [0016]
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FIG. 2 is a graph showing the changes in the altitude of a container and in the air pressure surrounding a container as well as inside a container, when a conventional product container equipped with packing with high airtightness strength is transported by air; [0017]
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FIG. 3A, FIG. 3B and FIG. 3C are perspective views showing the constitutions of the minute uneven parts provided on the surface of the packing; and [0018]
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FIG. 4 is a perspective view showing the constitution of the minute uneven part provided on the container main body to which packing is attached. [0019]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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The constitution of the packing and container, according to the present invention, is explained in detail, based on the drawings. When the [0020] packing 5 in the container of FIG. 1 is explained as an example, the example shown in FIG. 3A provides a shallow narrow groove part 5 a in the inner circumferential surface of the packing 5 that comes into contact with the container main body 1. Furthermore, the example shown in FIG. 3B provides two low narrow parallel ribs 5 b on the inner circumferential surface side of the packing 5.
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When the [0021] packing 5 of the above-mentioned constitution is used in the container of FIG. 1, in an environment in which there is no difference between the inside and outside air pressure, the parts other than the minute uneven part comprising the groove part 5 a or the rib part 5 b of the packing 5 are strongly adhered to the container main body 1 and the cover body 3, and, due to the rubber elastic force, virtually no gap is produced, although the minute uneven part formed in the packing 5 has an adhesiveness lower than that of the other parts. Because of this, the diffusion and invasion of moisture, dust, gas, ions and the like from the surrounding environment into the container can be prevented.
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Next, when this container is transported by air, because the adhesive force of the minute uneven part of the [0022] packing 5 is weak compared with that of the other places, an airtightness breakdown occurs due to an extremely slight pressure difference, whereby air is caused to penetrate very gradually in or out of the container through this groove part 5 a or rib part 5 b and, after some time, the air pressure inside the container becomes virtually equivalent to that outside the container. Then, after the airplane has returned to the ground, the interior of the container finally returns to approximately one atmospheric pressure. Because of this, the containment of a negative pressure inside a container, that will make it difficult to open the cover, is prevented.
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The problem of achieving, at the same time, both the ability to shut off the diffusion and invasion of outside air in an ordinary environment in which there is no air pressure difference, and, the ability to break the airtightness and to eliminate the difference in the air pressure inside and outside of the container, when a difference in the air pressure has arisen, that was difficult in a conventional packing, can be solved easily by impartring as high adhesiveness as possible to the main parts of the [0023] packing 5, while appropriately selecting the shape, size, number and the like of the minute uneven parts provided in the packing 5 so as to adjust the airtightness breakdown property.
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In the present invention it is acceptable for the minute uneven part of the packing to be a small [0024] protruding part 5 c, as shown in FIG. 3C, besides the groove part 5 a or rib part 5 b, shown in FIG. 3A, FIG. 3B. Furthermore, a constitution that lines up a plurality of extremely minute protuberances even smaller than this small protruding part 5 c can also be used. As mentioned above, it is possible to control the airtightness to obtain a desired one by appropriately selecting the shape, size, number as well as the placement locations and the like, of the minute uneven parts, in accordance with the various conditions such as the basic performance of the packing itself, the structure of the container, the atmosphere and environment of use and the like.
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The action and effect of the minute uneven part mentioned above are exactly the same, no matter whether the minute uneven part is provided on the packing itself, or is provided on the required surface of a container [0025] main body 1 to which packing is attached, as shown in FIG. 4, or the cover body 3. That is, in order to obtain fundamentally superior airtightness, packing with superior adhesion is used, and the minute uneven part necessary to cause airtightness breakdown when a difference in the air pressure has been produced acts in the same way, no matter whether it is provided on the side of the packing, or the container, and the shape and dimensions of the minute uneven part are selected, as mentioned above, corresponding to the adhesion of the packing.
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A material of the container and packing can be appropriately selected from various materials including synthetic resin and metal material such as aluminum, corresponding to the use of the container. For example, for containers for semiconductor wafer, polycarbonate, polypropylene, poly(butylene terephthalate), polyester elastomer and the like can be used. Furthermore, silicon rubber, polyolefin elastomer, polyester elastomer and the like can be used in a packing material. [0026]
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In the present invention, although there still remains an apprehension of contamination of products housed in the container due to the inflow of the outside atmosphere at the time of airtightness breakdown, such contamination can be controlled to the minimum by selecting the position of the minute uneven part provided on the packing or the container side so as to minimize the effect on the products housed in the container. Furthermore, if the container itself is packed in a packing case and the like made of plastic which emits little gas and few ions and has few impurities adhering to the inside surface, in a clean room before air transport, the worry about product contamination can be eliminated because the atmosphere outside this container also has no contaminants. [0027]
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When based on the present invention, in a container which accommodates products such as semiconductor wafers required to be protected from contamination by moisture, dust, gas, ions and the like from the surrounding environment, by means of providing a minute uneven part on the surface of the packing or on the main body or the cover body equipped with packing, it is possible to provide a container that shields against an invasion into the container of sources of contamination from the surrounding environment when the container is placed in an environment with no differences in the air pressure, and in case of air transportation and the like which produces differences in the air pressure, it is possible to provide a container that can ensure the necessary inflow and outflow of air, and not bring about the containment of a negative pressure in the container. [0028]
EXAMPLES
Example 1
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As an example of the present invention, for the semiconductor wafer container of FIG. 1, three types of packing were prepared having, respectively, one [0029] groove 5 a oriented at right angles to the circumferential direction of the packing 5, two ribs 5 b juxtaposed in the same direction, and a small protruding part 5 c, on the required surface of the packing 5 that makes contact with the container main body, as shown in FIG. 3. Three types of wafer containers each having these types of packing were prepared.
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Furthermore, on the vertical wall part of the ring shaped [0030] groove part 1 a of the container main body 1 of FIG. 1, a small protruding rib part 1 b arranged at right angles to the circumferential direction was provided as shown in FIG. 4. A wafer container was prepared which employed packing of FIG. 1 that had not been processed at all in the ring shaped groove part 1 a.
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When the conventional container of FIG. 1 and the above four types of wafer containers based on the present invention were actually used and transported by air, in contrast to the conventional container which brought about negative pressure containment after air transportation, the containers of the present invention did not bring about negative pressure containment, and the covers could be easily opened. [0031]
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Furthermore, when a measuring apparatus which could measure and record a relative humidity at set time intervals is installed in each container and left standing for a long time in a high humidity environment, there was a slight increase in humidity both in the four types of containers mentioned above and in the conventional container, and a difference in the speed of that increase was not observed. Accordingly, it was concluded that the containers of the present invention has the ability to prevent the diffusion and invasion of outside air, that is equivalent to that of the conventional containers. [0032]
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Furthermore, by means of the constitution in which a [0033] protruding rib part 1 b was provided on the ring shaped groove part 1 a on the side surface of the cassette 2 of the container main body 1, even when air pressure fluctuations were produced and outside air invaded the container through the protruding rib part 1 b, if the resin of cassette 2 had static electricity, the contaminants of the outside air would be adsorbed by the side surface of the cassette 2 before dust in the outside air reached the product wafer, and adhesion of contaminants to the product wafer could be reduced.
