Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
  • B29C45/17—Component parts, details or accessories; Auxiliary operations
  • B29C45/46—Means for plasticising or homogenising the moulding material or forcing it into the mould
  • B29C45/47—Means for plasticising or homogenising the moulding material or forcing it into the mould using screws
  • B29C45/50—Axially movable screw
  • B29C45/52—Non-return devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
  • B29C45/17—Component parts, details or accessories; Auxiliary operations
  • B29C45/20—Injection nozzles
  • B29C45/24—Cleaning equipment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
  • B29C45/17—Component parts, details or accessories; Auxiliary operations
  • B29C45/46—Means for plasticising or homogenising the moulding material or forcing it into the mould
  • B29C45/47—Means for plasticising or homogenising the moulding material or forcing it into the mould using screws
  • B29C45/50—Axially movable screw
  • B29C45/52—Non-return devices
  • B29C2045/528—Mixing means forming part of or in close proximity to the non-return valve

Definitions

• the present invention relates to a process and apparatus for materials improved to provide effective melt filtration and mixing.
• the filtering device comprises a tubular member having a plurality of round 0 or elongated perforations formed therethrough in a parallel and spaced relation.
• the perforated tubular member is disposed in or connected to the nozzle so that the perforations communicate with the nozzle.
• such a melt 5 filtering device or means is provided with a means for purging the impurities accumulated upstream of, but in the vicinity of, the perforations, as needed.
• a purging operation for example, is performed with the melt including the accumulated impurities discharged out of an outlet of the nozzle without passing through the perforations. This requires detachment of the nozzle with the barrel from a mold arrangement defining the mold cavity, and thus requires a relatively long period of time to reset up the injection molding machine for a normal injection molding operation.
• the conventional melt filtering device has an inherent problem in that it is subjected to a high pressure loss or exhibits a high pressure resistance against a hot plasticized material, the so called "melt", in the process of injection.
• a high pressure loss due to the filtration is increased as filtration performance is increased and also as an injection rate or speed is increased.
• the filtration performance relies on a size of the perforations.
• an injection molding apparatus comprising a mold arrangement, including a cavity mold and a hot runner mold and/or a manifold, and an injection machine having the nozzle, is required to be subjected to a high fluid pressure loss or exert an injection pressure, for
• melt filtering means is likely to operate with an injection rate lower (for example, 60 to 65 g/sec) than that (for example, 70 g/sec) of the same apparatus but with melt filtering nozzle means provided.
• an injection rate lower for example, 60 to 65 g/sec
• melt filtering nozzle means provided.
• a first object of the present invention is to provide a process and apparatus for injection molding of plastic material with improved melt filtration for removing possible impurities contained in a plasticized material, which melt filtration is effected with no substantial increase in driving power for injection relative to a case where no melt filtration is effected.
• a second object of the present invention is to provide a process and apparatus for injection molding of plastic material with improved melt filtering means which facilitates purging of accumulated impurities out of the machine system, and also removing impurities clogging the filtering means therefrom, resulting in increased long run productivity due to a decreased period of time during which temporary stopping of the operational run is effected for the purging and/or the removing and then for resetting the apparatus for normal injection molding operation. Both the purging and removing processes can be performed without substantially disassembling any part of the apparatus.
• a third object of the present invention is to provide a means for admixing a variety of materials incorporated in an injection machine with a screw plunger before injection of the materials toward a mold cavity to thereby provide a molded product with a distribution of the materials therein mixed well with each other.
• a process of injection molding with melt filtration using an injection machine having a body provided there with means for plasticizing, metering and injecting plastic material and a hollow extension, comprising a nozzle, therefrom forming a nozzle passage, and a mold arrangement defining a cavity, the mold arrangement incorporated with the machine to communicate between the interior of the machine body and the mold cavity via the nozzle passage.
• the process comprises the steps of: having a plastic material, in every shot cycle, plasticized and metered while being heated within the machine body; having the hot plasticized material injected under pressure for the mold cavity through the nozzle passage; and having the hot injected material held at least partially within the entire mold cavity under pressure while the mold arrangement is being cooled to thereby provide and freeze a molded article therein.
• the process is characterized in that the plasticizing and metering step is carried out such that the plasticized material is subjected to the melt filtration during the metering, and the injecting step is carried out with the filtered and metered material.
• the melt is subjected to the filtration not by passing the melt through a filter disposed in or connected to the nozzle but by passing a filter connected to the metering means through the melt as the metering means is withdrawn in the metering stage.
• EP 0204133A1 GB patent No. 888,448 and the like, wherein: a piston-cylinder is used in association with the nozzle passage so that a closed space variable in volume according to a piston stroke is defined by a combination of the mold cavity and the nozzle passage, or the combination with the piston-cylinder, with the nozzle passage interruption; and in the pressure-holding step the injected material compacted in the closed variable space is subjected to an external holding pressure by the piston-cylinder upon the nozzle passage interruption.
• Figs. 10A, 10B and IOC are cross-sectional views of an injection molding apparatus according to the present invention, showing another embodied melt filtering means incorporated with a screw plunger and a barrel.
• Fig. 10A showing plasticiging, filtering and metering processes
• Fig. 10B showing an injection process
• Fig. IOC showing an impurity discharging process
• Fig. 11 is an exploded perspective view of parts forming the filter as shown in Figs. 10A to IOC;
• Fig. 12 shows another embodiment of an injection molding machine according to the present invention with a filter modified from that of Figs. 11A for enhancing a stirring ability of the melt filter.
• FIGs . 1 and 3 show first and second embodiments of apparatuses according to the present invention.
• each apparatus for injection molding of plastic material has a conventional single barrel type injection machine 1 and a mold arrangement 10 incorporated therewith.
• the machine 1 is axially movable for a suck-back operation and for injection, plasticizing and metering operations, and comprises a body forming a cylindrical barrel 2 having a screw plunger 3 therein, a hydraulic piston-cylinder (not shown) with a piston connected to the plunger 3, and a cylindrical hollow extension 20 extending forwardly from the barrel 2.
• the apparatus further comprises a hot runner mold 13 incorporated with a manifold.
• the cylindrical hollow extension 20, which provides an exit passage, is divided into three parts, that is, a forward part 21 connected to the hot runner mold 13, an intermediate piston part 22 axially disposed in the forward part, and a rear part 23.
• the rear part 23 forms a head portion of the barrel 2, and the intermediate piston part 22 forms a so called “nozzle” detachably connected to the head barrel portion 23.
• the cylindrical extension 20 is designed so that its hollow space has an enlarged diameter portion
• the valve means 40 comprises a driving means, for example, a pulse motor (not shown) mounted on the rear cylindrical part 23, and a circular valve rod 42 extending vertically from the motor.
• the rear part 23 has a vertically circular hole 30 crossing the nozzle passage Y.
• the valve rod 42 is rotatably disposed in the vertical hole 30, and has a horizontal through-hole 42a.
• the valve hole 42a forms a portion of the nozzle passage Y when the valve means 40 or the valve rod 42 is in an opened position.
• the valve rod 42 effects a nozzle passage interruption or a chamber closing against communication of the barrel 2 with the cavity 20a, when it is in a closed position.
• the universal non-pressure-holding chamber system where an external pressure-holding is performed by an injection machine per se using a screw plunger for use in the plasticizing and metering and the injection, is substantially equivalent to the external pressure- holding chamber system in that the pressure-holding relies on an external hydraulic driving source such as the injection machine (in the non-pressure-holding chamber system) or the additional piston-cylinder device (in the external pressure-holding system), and thus the external driving source is likely to cause the weight of a molded product to be varied due to an inevitable pressure variation in the external holding pressure.
• the internal pressure-holding chamber system is advantageous relative to both the above systems in that such a pressure variation as the above does not occur during the internal pressure- holding operation, and thus variation in the weight of a molded product is considerably decreased.
• the internal pressure-holding chamber system can be used effectively in production of precision molded products with high productivity.
• the second valve means 50 When the first valve means 40 is in the closed position and if the melt pressure is over the predetermined valve, the second valve means 50 is forced by the melt pressure to be in the opened position against the force of the coil spring 53c to thereby allow an excess part of the melt in the space Z to be discharged out of the machine system through the above mentioned passage route until the remaining part of the melt in the space Z is balanced with or reduced to the predetermined pressure exerted by the coil spring 53c.
• the melt compacted in the space Z upon the nozzle passage interruption which is effected by the first valve means 40 immediately after injection, is regulated to a predetermined pressure or metered to a predetermined amount (mass) with a possible excess part of the melt being discharged out of the system.
• the check valve 70 comprises a valve chamber defined by the barrel 2, the tip head portion 3a, a rod portion of the intermediate plunger portion 3c and a valve seat member 61 of a disk form connected to the plunger rod 3b'and a valve body member 71 of an annular form axially slidable in the valve chamber.
• the melt filtering means 60 comprises the valve seat member 61, which has circumferentially arranged perforations P of a round cross-sectional shape, and is slidably fitted to an inner surface of the barrel 2 so that the melt is allowed to flow forwardly through only the perforations P.
• the annular valve body member 71 is also slidably fitted to the barrel inner surface with an annular space gap between the valve body member 71 and the plunger rod portion, which space gap forms a valve passage. The valve passage is closed when the valve body member 71 closes the filtering perforations P of the valve seat member 61 with the valve body member 71 abutting against the valve seat member 61.
• the check valve 70 is provided to be opened for allowing a plasticized material or melt to flow forwardly therethrough, while a plasticizing and metering step is carried out with the screw plunger 3 being forced to rotate and move rearwardly against a back pressure by an increasing part of the melt which has passed through the check valve 70 and accumulated in the forward spacial portion 2a, a so called “metering chamber” .
• the metering chamber 2a is variable in volume, and is defined by the tip head portion 3a, the check valve 70, the valve rod 42 of the first valve means 40 within both the nozzle passage and the interior of the barrel 2. That is, the metering chamber 2a is increased in volume during the so called “metering", which is carried out over a predetermined rearward stroke of the rotating and axially withdrawing screw plunger.
• the screw plunger is forced to rotate, while it is axially fixed, to thereby have non-filtered or residual impurities or foreign materials accumulated on the rear face of the disk member discharged out of the machine system through the purging hole 63.
• This purging operation is performed intermittently during a long run operation, as needed.
• the perforated disk member 61 it is pref ⁇ erable to have a peripheral portion 61a extending radially from a level of a periphery of the plunger rod 3'b, which peripheral portion 61a has a conical face as the rear face, converging in a rearward direction as shown in Fig.
• the perforations P may be designed to be as small in size as 0.7mm or less and as low in number as 36 or less.
• the internal pressure-holding system is advantageous in that it can perform an injection molding with high productivity in not only a short run but also in a long run where the impurity purging is effected intermittently, compared with the universal non-chamber system incorporating the conventional filtering device.
• the filtering means of the present invention mounted to the screw plunger is advantageous in the following aspects.
• the electric energy required to operate the injection molding apparatus is substantially the same as that required to operate a conventional apparatus involving a filtering means mounted to not the screw plunger but a nozzle located downstream of the metering chamber.
• an injecting power required to attain the same high injection rate (for example, 70 g/sec) is equivalent to that required in a non-filtering apparatus, whereas a filtering apparatus having a nozzle incorporated with a filtering device requires a greater injecting power to attain the same high injecting rate.
• the valve means 40 is intentionally closed so that the nozzle passage interruption is effected and during the intentional nozzle passage interruption a quasi-metering operation is performed to some extent and then is intentionally changed to a quasi-injecting operation with the effect that a metered melt in the metering chamber limited by the valve means 40 at one side thereof exerts a high pressure instantaneously against the impurities clogging the perforations P of the disk member 61 to remove the impurities rearwardly out of the perforations.
• the above impurity removing process may be repeated to complete the removal of the impurities as needed.
• the impurities accumulated in a local zone facing the rear face of the perforated disk member 61 can be purged with some part of the melt in the plasticizing space in the barrel 2 through the purging hole 63 as needed.
• the purging is effected by rotating the screw plunger 3 at the most forward axial position thereof, while the purging hole 63 is opened. It is preferable to carry out the above-mentioned impurity removing process and the purging process in this order.
• the purging process can be carried out in a considerably short period of time without disassembling any part of the apparatus except for the plug 64 being removed from the purging hole 63. In this connection, reduction of the working ratio or productivity in a long molding run due to the purging process being repeated as needed is suppressed or considerably improved in comparison with that in the case of the conventional melt filtration occurring at the nozzle during the injection step.
• the disk member 61' is fixed to the screw plunger and defines an annular space gap between the barrel and its periphery.
• the valve body 71' has an annular groove 72 axially extending in a rearward direction from a forward surface of the valve body, and many axial perforations P for melt filtration open to both the annular groove 72 and a rear surface of the valve body forming an abutting face against the valve seat.
• the disk member 61' has a forwardly extending circumferential projection 61' A which provides the valve seat of a circumferential form and defines an annular recess about the screw plunger.
• the valve seat or circumferential projection 61' A is positioned so that it can abut against a peripheral or outer portion of the rear valve body surface and the annular recess can cover all of the perforations 61' with a local space zone 74, when the check valve 70' is in a closed position, to thereby have the valve body perforations 61'interrupted from communicating with a plasticizing space defined between the barrel 2 and a main screw portion of the screw plunger.
• This design of the annular valve seat projection 61' A relative to the valve body perforations P is intended not to have the filtering perforations P closed directly by the annular projection 61' A.
• a tip head portion 3a of the screw plunger 3 forms a stopper for stopping a forward axial movement of the valve body 71'.
• This stopper and notched grooves formed in a peripheral surface of the valve body at a forward end thereof define several outlet openings 73' of the check valve 70'. In an opened position, the check valve 70' allows the melt to flow forwardly from the plasticizing space to a metering chamber through the perforations P and the outlet openings 73'.
• the difference between the apparatuses shown in Fig. 4 and Fig. 1 or 3 resides in that the former apparatus incorporates the check valve 70' which is designed to have the perforated valve body member 71' exert a melt filtering function, whereas the latter apparatus is designed to have the perforated valve seat member 61 exert the same melt filtering function.
• the apparatus having the filtering check valve 70' as show in Fig. 4 has the same advantages as those of Figs. 1 and 3, but is more advantageous in comparison with an apparatus as shown in Fig. 1 or 3 as well as with a conventional injection molding apparatus provided with no filtering check valve in that the perforated filtering valve body 71' of Fig.
• the apparatus with the check valve 70' incorporated therein as shown in Fig. 4 has a purging hole 63 and a plug 64 corresponding to those of the apparatus shown in Fig. 1 or 3.
• the corresponding purging hole 63 is axially positioned so that it opens to the local space zone 73 in the vicinity of the rear surface of the perforated valve body 71' between the valve body and the non-perforated valve seat member 61', when the screw plunger is in the most forward position with the check valve being.in the opened position.
• the melt with impurities accumulated on the rear perforated surface of the valve body 71' can be discharged out of the machine system through the purging hole 63 by rotating the screw plunger at the most forward position thereof.
• the melt filtering means comprises a perforated member 80 and a purging hole 63 formed in the barrel 2 for discharging the accumulated abnormalities with the melt.
• a check valve 70' of a back-flow ring type comprises front valve abutment members 80 and a rear valve seat member 61' of an annular form and a valve body member 71' of an annular form located therebetween and slidably fitted to an inner surface of the barrel 2.
• the front valve abutment member 80 is mounted to a rod portion of the crew plunger 3, and located upstream of and adjacent to a tip heat portion 3a of the screw plunger 3, and forms the above mentioned perforated member, which gas circumferentially arranged perforations P for the filtration and metering.
• a check valve .70' of a back-flow ring type is the same as that of Fig. 4 in that a tip head portion 3a of the screw plunger 2 forms a front valve seat member, but is different from that of Fig. 4 in that a valve body member 71' has through-holes P defining not perforations for the filtration but inlets of the check valve.
• the melt filtering means comprises a perforated member 81 and a purging hole 63 formed in the barrel 2 for discharging the accumulated impurities with the melt.
• the perforated member 81 is of an annular form mounted to a forward end of the main screw plunger portion and is located adjacent to and upstream of a rear valve seat member 61'.
• the perforated member 81 is slidably fitted to an inner surface of the barrel 2 and has circumferentially arranged perforations P for the filtration, the filtered melt is flown into the check valve for the metering.
• a check valve 70' is of a ball check type, and comprises a front valve abutment member, a rear valve seat member 61", and a valve body member forming a ball 71".
• the front valve abutment member provides a tip head portion 3a of the screw plunger 3.
• the front valve abutment member and rear valve seat member in combination form a valve chamber 84 with inlet and outlet passages 85, 86 communicating therewith.
• the ball 71" is designed so as to have a diameter smaller than that of the valve chamber 84 so that there is a substantial radial space gap between the ball and the valve chamber.
• the ball 71" is disposed in the valve chamber 84, and it is allowed to rotate and be slidebly movable with the radial space gap between both the inlet and outlet passages so that it closes the inlet passages 86 in a closed position of the check valve, whereas it opens both the inlet and outlet passages in an opened position of the check valve.
• the melt filtering means comprises a perforated member 81 corresponding to that of Fig. 6 and a purging hole 63 formed in the barrel 2 for discharging the accumulated impurities with the melt.
• the filtered melt is forced to flow toward the check valve fox the metering.
• the purging hole opens to a local zone LZ of a plasticizing space in the vicinity of a rear face of the perforated member when the screw plunge 3 is in the most forward position in the barrel 2.
• the screw plunge 3 is forced to rotate, while it is axially fixed, to hereby have non-filtered or residual impurities or foreign materials accumulated on the rear face of the perforated member discharged out of the machine system through the purging hole 63.
• the cylindrical barrel 2 is connected by an exit passage 87 provided with a valve 88 to a second cylindrical barrel 89.
• the barrel 89 is connected by passage 90 to the valve means 40.
• valve 88 shut plastic material is plasticized, metered and filtered in barrel 2 as described with reference to Fig. 1.
• Valve 88 is then opened and the plasticized material is transferred through passage 87 into the barrel 89.
• Valve 88 is then closed and the plastic material is injected by forward movement of the plunger 91 through open valve 40 into the mold arrangement 10. Back-flushing and purging of the filtering means 60 is carried out. when necessary as described with reference to Fig.
• valve 88 can be closed when removing impurities clogging the filter.
• Figs. 1 to 9 all indicate screw plugs 64 as means for closing and opening the purging holes 63, these plugs may, of course, be replaced by conventional shut-off valves or the like.
• Fig. 10A to IOC show another embodiment of the injection machine effecting melt filtration during metering of a plasticized material or melt.
• a filter 100 of this embodiment is mounted to a screw plunger 3 at a position between a cone tip head 3a of a screw plunger 3 and a check valve 70, that is the filter 100 is not incorporated in the check valve 70.
• the machine is further different from that of Fig. 1 in that no discharging hole is formed in a wall of a barrel 2, but an annular recess or groove 110 is formed at an inner surface of the barrel 2.
• a nozzle 22 is intentionally detached from another part 21 of a hollow extension forming a nozzle passage with a valve 40, and also the valve 40 is opened as shown in Fig. 10C, while the screw plunger 3 is intentionally shifted in the most forward position.
• the screw plunger 3 is intentionally rotated with the result that the melt with the accumulated impurities is discharged from the nozzle 22 through the by-pass passage provided at the recess 120.
• the purging means of this embodiment is disadvantageous in comparison with that of Fig. 1 in that the purging operation requires detachment of the nozzle 22, from the counterpart 21, but is advantageous in the following respect .
• the purging hole 60 of Fig. 1 has a weak point in that it is likely to be damaged at its inner edge due to rotation of the screw plunger. Therefore, it is required to reinforce the hole at the inner edge thereof by a special treatment, for example a titanum coating treatment, whereas no such damage as the above occurs in the case of Fig. 11A.
• a stirring ability A may be represented as follows:
• V is an injection rate of the melt (volume/second);
• ' is a linear velocity of melt streams flowing out of perforations of the conventional filter having a cross-sectional area S' in total;
• vl is a linear velocity of the melt at an outlet of the nozzle having a cross-sectional area Si;
• the stirring ability as defined above may be considered analogically to be stirring bars inserted axially into the accumulated static melt.
• A S j S j ⁇ + 1
• A' S /S - 1, since S 2 is much larger than SA, even if S, is assumed to be the same as
• the stirring ability is naturally enhanced due to an increase in the member of the filter perforations. Further, the stirring ability is enhanced, in the metering filtration, due to impingement of the filtered melt streams against the valve 40 provided for the pressure-holding, whereas such an impingement as above does not occur in the injecting filtration using the nozzle filter with no valve provided downstream of the nozzle.
• stirring ability is enhanced in the metering filtration due to rotation of the filtered melt streams about the screw plunger 3, whereas such a rotation as above does not occur in the injection filtration.
• a screw plunger 3 is provided with a filter 100' forming a rear section of a tip head 3a of a cone shape downstream of a check valve 70 with perforations P' designed so as to originate along the slope of the cone tip head 3a.
• the filtered melt streams as indicated by F are forced to flow so as to intersect the axis of the barrel 2 or the metering chamber with the effect that a turbulent flow of the accumulated melt in the chamber occurs at an inner part of the melt.
• a recess 110' corresponding to the recess 110 of Fig. 11A for purging the accumulated impurities is formed at a forward portion of the interior of the barrel having the same inner diameter over the length, so that the filter can be covered by the recess 110' at the most forward position of the screw plunger 3.
• the filter of the present invention may comprise two parts.
• One of the parts is an inner disk 120 having a bore 120A.
• the other part is an outer ring 130, having an inner diameter small enough to be in tight contact with the disk 120 at a periphery thereof and an outer diameter large enough to be silidably fitted to an inner surface of a uniform diameter section of the barrel 2 upstream of the recess 110.
• the disk 120 has a plurality of grooves 120B formed at its periphery and extending axially to provide openings between its opposite surfaces.
• the grooves 120B have the same size with a basically rectangular cross section, which has a peripheral width and a radial depth. Preferably the radial depth is longer than the width.
• the grooves 120B are equally spaced around the periphery of the disk 120.
• the disk 120 is combined with the outer ring 130 to form the filter 100 with the grooves 120B and the ring 130 in combination defining the perforations P for filtration
• the ring 130 may be fixed to the disk 120 by a heat treatment.
• the filter 100 is fixed to the screw plunger 3 such that it is sandwitched by a forward section of the screw plunger 3 having a threaded bolt extension 140 and a rear section of the screw plunger forming a threaded nut portion 150 with the bolt extension 140 passing through the bore 120A of the filter and screwed into the nut portion 150.
• the filter according to the present invention may be used as not only a means for melt filtration but also a melt mixer.
• the claimed scope of the present invention covers not only an injection molding apparatus with the filter intended for melt filtration but also that intended for melt stirring or mixing, although the claims recite “melt filtration” .

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Injection Moulding Of Plastics Or The Like (AREA)

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Cited By (4)

Citations (7)

• 1991
  • 1991-01-28 JP JP3503160A patent/JPH06506405A/ja active Pending
  • 1991-01-28 WO PCT/JP1991/000089 patent/WO1992005940A1/en active IP Right Grant

Patent Citations (7)

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