Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-06-08
2003-04-08
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S545000, C524S570000, C524S592000, C524S593000, C524S601000, C524S609000, C428S412000, C428S421000, C428S480000, C428S500000, C428S524000, C428S692100, C428S690000, C428S690000
Reexamination Certificate
active
06545081
ABSTRACT:
TECHNICAL FIELD
The present invention relates to synthetic resin compositions, and more particularly to synthetic resin compositions in which the volume resistivity is in a moderately conductive region, can be strictly controlled to a desired value within this region, can be developed in the moderately conductive region with good reproducibility and is scarcely varied by melt forming or molding.
The present invention also relates to formed or molded products obtained by forming or molding such a synthetic resin composition. The synthetic resin compositions and formed or molded products according to the present invention can be suitably applied to a wide variety of fields of which control of static electricity, prevention of electrification, electromagnetic interference shielding, prevention of dust collection, etc. are required.
The present invention further relates to synthetic resin compositions in which the surface resistivity can be strictly controlled at a specific value within a moderately conductive region, a scatter of the surface resistivity with the locality is narrow, and the mechanical properties are excellent. The synthetic resin compositions according to the present invention can be formed into formed or molded products which have a surface resistivity of 10
5
to 10
12
&OHgr; (=&OHgr;/□), are excellent in mechanical properties and extremely small in exudation of impurities, and so it is suitable for use as a molding material for carriers such as a carrier box which is a container for shipping or storing wafers.
BACKGROUND ART
Resin materials having a volume resistivity ranging from 10
5
to 10
13
&OHgr;·cm are generally referred to as moderately conductive resin materials (moderately conductive plastics) because the volume resistivity is situated between an insulator and a metallic conductor. Such moderately conductive resin materials are applied to a wide variety of fields as, for example, films for packaging electronic parts, sheathing materials for OA apparatus, etc. making good use of their antistatic property, anti-dust-collecting property, electromagnetic interference shielding ability and the like. The moderately conductive resin materials are used in field of which control of static electricity is required, as, for example, resin materials for charging rolls, charging belts, static charge eliminating belts, etc. in image forming apparatus such as electrophotographic copying machines and electrostatic recording apparatus.
Although the moderately conductive resin materials include those that the synthetic resin itself is moderately conductive, most thereof are synthetic resin compositions obtained by blending a conductive filler such as conductive carbon black, metallic powder, metal fiber or carbon fiber into a synthetic resin, which is an insulator, to impart moderately conductivity to the resin. However, the volume resistivity of a synthetic resin composition obtained by blending a conductive filler into a synthetic resin depends on the dispersed state and content of the filler in the synthetic resin. Therefore, there have been encountered problems that (1) the volume resistivity greatly varies even when the blending proportion of the conductive filler is changed to a slight extent, (2) the distribution of the volume resistivity is uneven, and the volume resistivity greatly varies with the locality, (3) the volume resistivity greatly varies when the synthetic resin composition is melt formed or molded, and (4) the loaded amount of the conductive filler must be increased in order to attain a volume resistivity within the moderately conductive region, and consequently the molding and processing ability and mechanical strength of the resulting synthetic resin composite material are lowered, or its hardness becomes too high. Accordingly, it has been extremely difficult to provide a synthetic resin composition having a desired volume resistivity with good reproducibility.
More specifically, in the case where a synthetic resin and a conductive filler are blended to prepare a synthetic resin composition, the volume resistivity of the resulting synthetic resin composition is liable to rapidly change according to a change in the content of the conductive filler, since a difference in volume resistivity between both components is great, and the development of conductivity (lowering of the volume resistivity) depends on the dispersed state and content of the conductive filler. The change in the volume resistivity of the synthetic resin to the change in the content of the conductive filler is rapid when the volume resistivity of the synthetic resin composition falls within the moderately conductive region of 10
5
to 10
13
&OHgr;·cm in particular. In addition, when the conductive filler is not evenly dispersed, a scatter of volume resistivity with the locality becomes wide. Accordingly, it has been very difficult to stably produce a synthetic resin composition having a volume resistivity within the range of 10
5
to 10
13
&OHgr;·cm with good reproducibility.
In synthetic resin compositions obtained by incorporating conductive carbon black having a high DBP oil absorption or a certain kind of graphite into a synthetic resin, a synthetic resin composition having a desired volume resistivity within a range of 10
3
-10
13
&OHgr;·cm can be provided with a certain probability by strictly controlling raw materials used and processing conditions.
However, this synthetic resin composition has involved problems that the reproducibility of volume resistivity is insufficient and that the volume resistivity greatly varies when the synthetic resin composition is formed into a molded product by a melt molding process such as injection molding. Further, molded products obtained from this synthetic resin composition have involved a problem that the volume resistivity varies during their use by wearing.
Carriers of various forms such as carrier boxes are used for shipping or storing wafers, semiconductor devices (IC, LSI, etc.), electronic parts (semiconductor devices, circuit parts, functional parts, etc.), information recording media (magnetic disks, optical disks, etc.) and the like. The carriers are generally formed with a synthetic resin material. Such a carrier is required to have a moderate surface resistivity, not to contaminate wafers and the like by exudation of impurities, emission of gases, or the like and to be also excellent in mechanical strength. In many cases, the carrier is required to have excellent water resistance, heat resistance, chemical resistance, etc.
More specifically, when silicon wafers or magnetic disks are subjected to a processing treatment, a carrier is used for shipping or storing them. For example, the wafers are subjected to treatments such as oxidation, thin-film formation by CVD, ion implantation and photo processing (resist treatment, exposure, development, washing, dry etching, sputtering, etc.) in a wafer treatment process to provide them as semiconductor devices. The semiconductor devices are mounted on a wiring board in an assembly process to foam electronic parts. In the wafer treatment process, the carrier for shipping wafers is immersed in hot water and/or a chemical agent and dried. When a carrier having a surface resistivity higher than 10
12
&OHgr; is used, the carrier is charged to high voltage to damage semiconductor devices or the like. The carrier having a high surface resistivity tends to charge and thus collects dust and the like suspended in the air, thereby contaminating the semiconductor devices or the like.
When a carrier having a surface resistivity lower than 10
5
&OHgr; is used on the other hand, rapid discharging occurs when an electronic part electrified, short-circuited or charged is brought into contact with the carrier, thereby easily damaging semiconductor devices or the like. As described above, it is necessary to strictly control the surface resistivity of the carrier within a range of 10
5
to 10
12
&OHgr; in order to protect the wafers, semiconductor devices, electronic parts, information rec
Nishihata Naomitsu
Ohuchi Kiyomi
Tada Masahito
Dinsmore & Shohl LLP
Kureha Kagaku Kogyo K.K.
Sanders Kriellion A.
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